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Materials

2008;():1-6. doi:10.1115/MSEC_ICMP2008-72061.

Delamination between sub-micron thick films is initiated at an interface edge due to creep deformation, and leads to the malfunction of microelectronic devices. In this study, the cohesive zone model approach with a cohesive law based on damage mechanics was developed to simulate crack initiation process at an interface edge between film layers under creep. Delamination experiments using a micro-cantilever bend specimen with a Sn/Si interface were conducted. The parameters charactering the cohesive law were calibrated by fitting displacement-time curves obtained by experiments and simulations. In addition, the order of the stress singularity, which increases with time and has a significant jump in its value at the crack initiation, was investigated.

Commentary by Dr. Valentin Fuster
2008;():7-14. doi:10.1115/MSEC_ICMP2008-72309.

Despite the superior tribological and mechanical properties, the advantages of diamond coated tools have been largely compromised by the insufficient adhesion. Interface characteristics play a vital role in the failure and performance of diamond coated tools. Thus, quantitative modeling of the coating-substrate interface is important to the design and usage of diamond coating tools. In this study, a cohesive zone model was incorporated to investigate the diamond coating on a tungsten carbide substrate. The cohesive zone model is based on the traction-separation law, and is represented by four parameters, determined from the tungsten-carbide fracture properties. The cohesive zone model was implemented in finite element codes to simulate the indentation process, using a spherical diamond indenter. The model was applied to examine the interface effects during indentation and the coating property effects on different coating failure modes. The simulation results are summarized as follows. (1) Normal mode delamination is the dominant mechanism of interface failure and takes place during unloading if the substrate yielding occurs during the loading stage. (2) The cohesive zone interface does not affect the critical load for coating surface tensile cracking, but affects the plastic strain during loading. In addition, for thin coatings, the maximum stress location changes between the perfect interface and cohesive zone interface cases. (3) Elasticity has a complex effect on coating failure. As the coating elasticity increases, the critical load for coating cracking decreases, but the critical load for substrate yielding increases slightly. Moreover, the interface delamination size will decrease with increasing coating elasticity.

Commentary by Dr. Valentin Fuster
2008;():15-21. doi:10.1115/MSEC_ICMP2008-72034.

Disassembly planning and costing is a major task in the achievement of sustainable manufacturing. This paper presents a systematic approach to identify the feasible ways to disassemble a product then to select the most economical one using reliable time data gathered from experimental and practice-oriented sources. The disassembly process is modeled after the Petri Net approach, a technique that has proven to be fairly popular with the research community in the last few decades. The result of our systematic approach is a reliable derivation for a time-effective disassembly plan.

Commentary by Dr. Valentin Fuster
2008;():23-31. doi:10.1115/MSEC_ICMP2008-72130.

Preventive maintenance has been a mainstream strategy to keep equipment and machinery going. In this paper a Markov model is used to characterize the performance of a continuously operating device that is subject to random failure as well as failure generated by deterioration. The optimum preventive maintenance of this device is based not only on its maximum availability but also on the consideration of the total cost of operation and maintenance against a backdrop of replacement cost. The economic model proposed in this paper provides a more complete decision process to determine when to replace it even while the device is maintained optimally.

Topics: Maintenance
Commentary by Dr. Valentin Fuster
2008;():33-40. doi:10.1115/MSEC_ICMP2008-72490.

Remanufacturing is a process that restores old products to perform like new, while saving energy, reducing consumption of natural resources, and lowering environmental emissions. By extending the product life cycle, remanufacturing approaches enable closed loop material cycles that are ultimately necessary for a sustainable society. This paper provides some description of the current automotive remanufacturing enterprise, with a particular emphasis on key vehicle components that are currently remanufactured. The analysis yields two major conclusions. First, market price of a remanufactured component in the automotive sector is surprisingly uncorrelated with the number of companies engaged in remanufacturing that component — at least for companies registered with the Automotive Parts Remanufacturing Association (ARPA). Second, and less surprisingly, we find that remanufacturing reduces environmental burden significantly over new production. This improvement, for the case of the alternator used as a case study, can easily exceed one order of magnitude in the categories of material use, energy consumption, and greenhouse gas (GHG) emissions that are considered here.

Commentary by Dr. Valentin Fuster
2008;():41-47. doi:10.1115/MSEC_ICMP2008-72046.

Fracturing in a tight radius during stretch bending has become one of the major manufacturing issues in stamping advanced high strength steels (AHSS), particularly for those AHSS with a tensile strength of 780 MPa or higher. Computer simulations often fail to predict this type of fracture, since the predicted strains are usually below the conventional forming limit curve. In this study, a laboratory stretch-forming simulator (SFS) is used to simulate the stretch bending of AHSS in stamping to develop a possible failure criterion for use in computer simulations. The SFS simulates the stamping process when sheet metal is drawn over a die radius with tension applied. Various sizes of die radius are used during the experiment, and the shear fracture phenomenon can be recreated using this test for a given material and gauge. It is found that shear fracture depends not only on the radius-to-thickness ratio but also on the tension/stretch level applied to the sheet. The experimental data show that a critical radius-to-thickness ratio for shear fracture exists for any given material and gauge, but this ratio is not unique and it depends upon the amount of tension imposed during the bending.

Commentary by Dr. Valentin Fuster
2008;():49-57. doi:10.1115/MSEC_ICMP2008-72091.

Manufacturing engineering has had to undergo drastic changes in the approach to material selection in order to meet new design challenges. In the automotive industry, researchers in their effort to reduce emissions and satisfy environmental regulations, have shifted their focus to new emerging materials such as high-strength aluminium alloys, metal matrix composites, plastics, polymers and of late, Austempered Ductile Iron (ADI). ADI is a good choice for design where the criterion is high performance at reduced weight and cost. The unique, ausferrite microstructure gives the material desirable material properties and an edge over other materials. A comparative study of ADI in terms of materials properties and machining characteristics with other materials is desirable to highlight the potential of the material. This paper focuses on a comparative assessment of material and machining characteristics of ADI for different applications. The properties under consideration are machinability, weight and cost savings and versatility. ADI has a higher strength-to-weight ratio than aluminium making it a ready alternative for material selection. In terms of machinability, there are some problems associated with machining of ADI due to its work hardening nature. This paper attempts to identify the possible potential applications of ADI, by critically reviewing specific applications such as machinability, overall economics and service.

Commentary by Dr. Valentin Fuster
2008;():59-65. doi:10.1115/MSEC_ICMP2008-72238.

Hydraulic bulge testing is a material characterization method used as an alternative to tensile testing with the premise of accurately representing the material behavior to higher strain levels (∼70% as appeared to ∼30% in tensile test) in a biaxial stress mode. However, there are some major assumptions (such as continuous hemispherical bulge shape, thinnest point at apex) in hydraulic bulge analyses that lead to uncertainties in the resulting flow stress curves. In this paper, the effect of these assumptions on the accuracy and reliability of flow stress curves is investigated. The goal of this study is to determine the most accurate method for analyzing the data obtained from the bulge testing when continuous and in-line thickness measurement techniques are not available. Specifically, in this study the stress-strain relationships of two different materials (SS201 and Al5754) are obtained based on hydraulic bulge test data using various analysis methods for bulge radius and thickness predictions (e.g., Hill’s, Chakrabarty’s, Panknin’s theories, etc.). The flow stress curves are calculated using pressure and dome height measurements and compared to the actual 3-D strain measurement from a stereo optical and non-contact measurement system ARAMIS. In addition, the flow stress curves obtained from stepwise experiments are compared with the ones from above methods. Our findings indicate that Enikeev’s approach for thickness prediction and Panknin’s approach for bulge radius calculation result in the best agreement with both stepwise experiment results and 3D optical measurement results.

Topics: Testing
Commentary by Dr. Valentin Fuster
2008;():67-72. doi:10.1115/MSEC_ICMP2008-72329.

The paper presents the results of an experimental investigation on the machinability of fabricated Aluminum metal matrix composite (A356/SiC/10p) during continuous turning of composite rods using medium grade Polycrystalline Diamond (PCD 1500) inserts. Metal Matrix Composites (MMC’s) are very difficult to machine and PCD tools are considered by far, the best choice for the machining of these materials. Experiments were conducted at LMW-CNC-LAL-2 production lathe using PCD 1500 grade insert at various cutting conditions and parameters such as surface roughness and specific powers consumed were measured. The present results reaffirm the suitability of PCD for machining MMCs. Though BUE formation was observed at low cutting speeds, at high cutting speeds very good surface finish and low specific power consumption could be achieved. An Artificial Neural Network (ANN) model has been developed for prediction of machinability parameters of MMC using feed forward back propagation algorithm. The various stages in the development of ANN models VIZ. selection of network type, input and output of the network, arriving at a suitable network configuration, training of the network, validation of the resulting network has been taken up. A 2-9-9-2 feed forward neural network has been successfully trained and validated to act as a model for predicting the machining parameters of Al-SiC (10p) -MMC. The ANN models after successful training are able to predict the surface quality; and specific power consumption for a given set of input values of cutting speed and machining time.

Commentary by Dr. Valentin Fuster
2008;():73-78. doi:10.1115/MSEC_ICMP2008-72415.

The sandwich sheet is a novel laminated sheet material with advanced vibration damping advantages, and the sheet is composed with 2 outer thick metal layers and 1 thin polymer layer in between. In order to investigate its drawing characteristics, an improved cohesive model between the skin sheets was developed using a contact/interface approach. Based on the proposed model, a cup drawing process was numerically simulated using commercial FEM code ABAQUS. Numerical simulation shows that the thickness strain distribution and thinning phenomenon have similar modes on the top layer and bottom layer except at the cup bottom corner, and cohesive strength does not have severe effect to the drawing force. The drawing experiments were conducted on a hydrauic press in order to compare the whole sheet and two skin sheets thickness distribution of sandwich sheet metal cup drawing, FEM simulation result fits well with the experiment.

Topics: Sheet metal
Commentary by Dr. Valentin Fuster
2008;():79-83. doi:10.1115/MSEC_ICMP2008-72049.

Friction stir processing is an advanced manufacturing process in which a specially designed rotating pin is first inserted into the adjoining edges of the materials to be processed with a proper tool tilt angle and then move all along the adjoining edges. The pin produces frictional and plastic deformation heating in the processing zone. As the tool pin moves, materials are forced to flow around the pin. Material flows to the back of the pin, where it is extruded and forged behind the tool, consolidated and cooled under hydrostatic pressure conditions. The primary research about friction stir processing has been focused on aluminum alloys. In recent years many researchers have been trying to apply this technology for processing other alloys and materials including stainless steels, magnesium, titanium, and copper. In addition, this technology has been used to modify the microstructure of reinforced metal matrix composite materials. However, friction stir processing polymeric based materials are much less studied. Friction stir processing has the advantage of reducing distortion and defects in materials. It has potential to be used in manufacturing nanoparticle-reinforced polymeric composite materials. In this work, modeling the flow pattern and the distribution of nanoparticles in friction stir processed polymeric composite materials was performed. The internal pressure in friction stir processed composite materials was also derived, which may be used to predict the residual stress state in the nanocomposite material joint. It is found that the pressure in the joint is a function of radial position from the tool pin. The magnitude of the pressure is related to the tool geometry and the welding conditions such as tool rotating speed etc.

Commentary by Dr. Valentin Fuster
2008;():85-93. doi:10.1115/MSEC_ICMP2008-72196.

The research presented in this paper involves numerical and experimental efforts to investigate the relative thin-wall injection molding process in order to obtain high dimensional quality complex parts. To better understand the effects of various processing parameters (the filling time, injection pressure, the melting temperature, the mold temperature) on the injection molding of a thin-wall complex part, the molding experiments are regenerated into the computer model using the Moldflow Plastics Insight (MPI) 6.1 software. The computer visualization of the filling phase allows accurate prediction of the location of the flow front, welding lines and air traps. Furthermore, in order to optimize the injection molding process, the effects of the geometry of the runner system on the filling and packing phases are also investigated. It is shown that computational modeling could be used to help the process and mold designer to produce accurate parts.

Commentary by Dr. Valentin Fuster
2008;():95-101. doi:10.1115/MSEC_ICMP2008-72382.

Composite textile reinforcement draping simulations aid in determining the processing conditions for a quality part and in finding the positions of the fibers after forming. This last point is essential for the structural computations of the composite part and for resin injection analyses in the case of LCM processes. Because the textile composite reinforcements are multiscale materials, continuous (macro) approaches and discrete (meso) approaches that model the yarns have been developed. The finite element that is proposed in this paper for textile fabric forming is composed of woven unit cells. The mechanical behaviour of these is analyzed by 3D computations at the mesoscale. The warp and weft directions of the woven fabric can be in an arbitrary direction with respect to the direction of the element side. This is very important in the case of multi-ply deep drawing and when using remeshing. The element is efficient because it is close to the physics of the woven cell while avoiding the very large number of unknowns in the discrete approach. A set of validation tests and forming simulations on single-ply and multi-ply fabrics is presented and shows the efficiency of the approach.

Commentary by Dr. Valentin Fuster
2008;():103-109. doi:10.1115/MSEC_ICMP2008-72466.

Polymethylmethacrylate (PMMA) based polymers are commonly used in orthopedic implant applications, and have been a successful cement for many decades. Recent implant designs use PMMA as a structural material, and additional applications are envisioned, but only if improvements in the PMMA mechanical properties, especially fatigue performance, can be attained. This paper presents a number of strategies for improving the performance of PMMA as an orthopedic structural polymer, including modification of the polymer chemistry, incorporation of acrylic reinforcement and the use of metal braids as reinforcement of a specimen exterior. Experimentally measured properties of the material are presented. Results include up to 100% increase in cycles to failure compared to commercially available medical grade PMMA through chemistry modifications, up to 800% increases due to fiber reinforcement, and further significant improvements due to metal braid reinforcement.

Topics: Orthopedics
Commentary by Dr. Valentin Fuster

Processing

2008;():111-116. doi:10.1115/MSEC_ICMP2008-72322.

Zirconia (Y2 O3 )-alumina ceramic nanocomposites were fabricated by spark plasma sintering (SPS). A commercially available nanocomposite powder TZP-3Y20A was used as starting powder, the other from conventionally mechanical mixed powder 3YSZ-20A used for comparison. The effect of sintering temperature on the densification, sintering behavior, mechanical properties, and microstructure of the composites were investigated. The results show that the density increase with increasing of sintering temperature, and thus mechanical properties were strengthened with enhancing of densification. The nanocomposite powder TZP-3Y20A was easily sintered and good mechanical properties were achieved, compared with the powder from conventionally mechanical mixed, where the maximum strength and toughness of composites are 967 MPa and 5.27 MPam1/2 , respectively.

Commentary by Dr. Valentin Fuster
2008;():117-122. doi:10.1115/MSEC_ICMP2008-72368.

A powder mixture of ZrO2 +WO3 and ZrO2 powder were stacked, co-compacted and co-sintered in the processing steps commonly used to fabricate multi-layer materials. However, the observation of the cross-sectional microstructures as well as the measurement of the radial thermal expansion provided the evidence that the sintered samples are continuous Functionally Graded Materials (FGMs) made of ZrW2 O8 and ZrO2 , Because of the discrepancy in the sintering potentials between two materials, the sintered samples do not retain the original cylindrical shapes of the green compacts. This problem has been resolved by choosing the appropriate powder mixture for each layer of the compacts. The formation of the continuous FGM structure is due to three factors: 1) the diffusion of WO3 , 2) the sublimation of WO3 and 3) the reaction between ZrO2 and WO3 . The continuous variation in the radial coefficient of thermal expansion can be utilized to reduce the thermal stress induced from a thermal gradient loading within a material system. This study shows that the processing steps typically used in processing stepwise FGMs can also be used to create continuous FGMs for some special powder mixtures.

Commentary by Dr. Valentin Fuster
2008;():123-128. doi:10.1115/MSEC_ICMP2008-72071.

The development of manufacturing processes for joining and assembling of lightweight aluminum vehicles requires detailed process capability studies as well as dimensional variation analysis studies to ensure process controls are in place. These manufacturing processes not only have to provide cycle time viability but also need to maintain or surpass product safety and quality. T-Nodes joint designs are an integral of aluminum architectures based on hybrid designs, i.e those fabricated from mixed aluminum products consisting of castings, stampings and extrusions. The purpose of this study was to find optimum parameters for minimum distortion for the gas metal arc welding (GMAW) of 6063-T52 T-Nodes. The welding factors considered were locators (4-way and 2-way pins verses net surfaces), the welding equiment process factors (power input, pulse frequency, gas flow rate, torch angle and arc intensity), the use of simultaneous welding, and welding sequence order. A partial factorial design of experiment (DOE) was conducted to understand the effects of these factors on T-node joint distortions. A total of 14 points were considered for dimensional distortion measurements. Results showed power (heat) input is the only statiscally significant factor on joint distortion. Locators type as well as welding sequence and simultaneous welding also had a measurable affect on part deviation during welding.

Commentary by Dr. Valentin Fuster
2008;():129-132. doi:10.1115/MSEC_ICMP2008-72110.

The mechanical properties of welding material is correlative with the chemical composition Artificial neural network (ANN) program to predict mechanical properties — yield strength, tensile strength, elongation and average Charpy impact toughness — of welding material is established by Visual C + + 6.0 based on improved BP arithmetic with momentum factor, in which one input layer with 13 nodes, one hidden layer with 23 nodes, one output layer with 4 nodes, and Sigmoid activation function are included. The 20 samples are from the experimental data of semi-automatic welding material of X70. The average maximum relative error of the 4 mechanical properties is less than 0.5%. Based on the program, the influence of the chemical composition, such as C, S, P, Si, Mn, Cr, Ni and Al on the mechanical properties is analyzed. The results show that the different element has different influence on the mechanical properties. For non-metallic elements, the mechanical properties are becoming worse with the increase of composition, in which the influence of C is primary, then P and then S. For metallic elements, the influence is greater and more complex than that of non-metallic ones.

Commentary by Dr. Valentin Fuster
2008;():133-136. doi:10.1115/MSEC_ICMP2008-72127.

The purpose of the study was to understand effects of weld travel speed and wire feed rate in metal inert gas (MIG) welding on the aluminum materials joint strength. Initial experiments indicated a noticeable positive effect of travel speed on weld strength with an over 95% statistical significance. Nonetheless further experimentation at a significantly lower wire feed rate proved the opposite with similar statistical significance. A negative effect of welding travel speed on joint strength was measured at lower wire feed rates. In order to understand the weld travel and wire feed rate on the joint strength, a Design of Experiment (DOE) was conducted. For this experiment, weld system process factors were set constant (wave control, gas flow rate, torch angle, trim and wave type) except for travel speed and wire feed rate. A two-factor two-level full factorial design of experiment (DOE) was conducted in order to understand the effects of these two factors on weld strength. Additional welding at higher wire feed rates were conducted in order to confirmed the trend found. Results showed travel speed effects on joint strength as a result of its direct interaction with wire feed rate. This occurrence can have significant economic implications if proven to be repeatable and will be the subject of this and future MIG welding studies as they relate to aluminum structures.

Topics: Metals , Aluminum , Welding , Wire
Commentary by Dr. Valentin Fuster
2008;():137-142. doi:10.1115/MSEC_ICMP2008-72207.

This paper describes efforts to develop a web-based E-Design tool for the Friction Stir Welding (FSW) technique. The input parameters to the E-Design tool are the joint specifications. The output parameters of the E-Design tool are process parameters such as tool geometry details, tool rpm, and plunge depth. The heart of the E-Design tool is the FSW database. The FSW database contains mappings of various input parameters and output parameters that are captured by referring to various experimental studies cited in the literature. The proposed E-Design tool deals with lap joints and butt joints between similar aluminum alloys.

Topics: Friction , Welding , Design
Commentary by Dr. Valentin Fuster
2008;():143-146. doi:10.1115/MSEC_ICMP2008-72224.

Galvanized steels have been widely used in the different industries such as automotive, aerospace and marine industry, due to their high corrosion resistance and excellent mechanical properties. However, the zinc coating on the metal sheet offers a big challenge to the welding operation, specifically in the high-power laser welding process of the lap joint if the metal sheets are installed in a gap-free configuration. Spatters, one of the critical problems for the weld quality, is readily generated by the high-pressurized zinc vapor developed at the interface of two metal sheets. It takes extra procedures to clean the weld surface or repair the blowholes generated by the spatters. The on-line process monitoring is critical to assure the achievement of the high quality welds. Therefore, it is necessary to develop an on-line efficient monitoring system for the welding of galvanized steels. In the past few years, acoustic emission (AE) technique has been applied to monitor different manufacturing processes. This paper will highlight its application in the laser welding of galvanized steels. An AE signal acquisition system is used to real-time monitor the welding process. The results of the investigation show that the amplitude of AE signals varies with the welding process status. When the welding process is stable, the amplitudes of AE signals are almost constant and with the low intensity compared to the AE emission signals when the weld defects are presented. When the spatter is formed, a sharp spike with the high amplitude is shown in the collected acoustic emission signal. In order to extract the features of the AE signals in frequency domain, the acquired signal in time domain is further processed using Short-time Fourier Transformation (STFT). The STFT processed results indicated that the spatter-induced AE signals cover a wide range of frequencies and the background noise is mainly presented in the range below 100 Hz.

Commentary by Dr. Valentin Fuster
2008;():147-153. doi:10.1115/MSEC_ICMP2008-72502.

The effects of metal matrix composite (MMC) on the joint strength of Spot Friction Welded (SFW) specimens made of Al 1100 and Al 6111 alloys are studied. The MMC-SFW joints were created by sandwiching metal reinforcing powder (<75μm mesh) between the upper (1.3mm thick) and lower (1.5mm thick) Al coupons, at the center of the SFW joint. To maximize the heat input into the specimen, a Zirconium (ZrO2 ) ceramic anvil was used. Depth of penetration of the tool played an important role in determining the distribution of the reinforcing material within the MMC during plastic mixing in the SFW joint, and hence its influence on the joint strength. At a lower depth of penetration, 2.1 mm, the results showed that the MMC-SFW reinforced with Ancorsteel 1000, copper or Al12Si powders did not increase the joint strength since they did not spread uniformly in the stir zone. However, at a higher depth of penetration, 2.5 mm, the MMC-SFW joint reinforced with Ancorsteel 1000, copper, or Al12Si did increase the joint strength compared to that of the base SFW specimens. Using steel powder as the reinforcement material, the MMC showed the maximum increase in the lap shear joint strength. For example, at 2.5 mm depth of penetration, the SFW joint strength increased by 19% and 24% compared to that of the base SFW specimen made of Al 1100 and Al 6111 alloys respectively.

Topics: Friction , Metals
Commentary by Dr. Valentin Fuster
2008;():155-161. doi:10.1115/MSEC_ICMP2008-72145.

Silicon carbide (SiC) is one of the advanced engineered ceramics materials designed to operate in extreme environments. One of the main reasons for the choice of this material is due to its excellent electrical, mechanical and optical properties that benefit the semiconductor, MEMS and optoelectronic industry respectively. Manufacture of this material is extremely challenging due to its high hardness, brittle characteristics and poor machinability. Severe fracture can result when trying to machine SiC due to its low fracture toughness. However, from past experience it has been proven that ductile regime machining of silicon carbide is possible. The main goal of the subject research is to improve the surface quality of a chemically vapor deposited (CVD) polycrystalline SiC material to be used in an optics device such as a mirror. Besides improving the surface roughness of the material, the research also emphasized increasing the material removal rate (MRR) and minimizing the diamond tool wear. The surface quality was improved using a Single Point Diamond Turning (SPDT) machining operation from 1158nm to 88nm (Ra) and from 8.49μm to 0.53μm (Rz; peak-to-valley).

Commentary by Dr. Valentin Fuster
2008;():163-168. doi:10.1115/MSEC_ICMP2008-72234.

End milling titanium Ti-6Al-4V has wide applications in aerospace, biomedical, and chemical industries. However, milling induced surface integrity has received little attention. In this study, a series of end milling experiment were conducted to comprehensively characterize surface integrity at various milling conditions. The experimental results have shown that the milled surface shows the anisotropic nature with a surface roughness range in 0.6 μm–1.2 μm. Surface roughness increases with feed and radial depth-of-cut (DoC), but varies with the cutting speed range. Compressive residual normal stress occurs in both cutting and feed directions, while the influences of cutting speed and feed on residual stress trend are quit different. The microstructure analysis shows that β phase becomes much smaller and severely deformed in the very near surface with the cutting speed. The milled surfaces are at least 60% harder than the bulk material in the subsurface.

Commentary by Dr. Valentin Fuster
2008;():169-174. doi:10.1115/MSEC_ICMP2008-72441.

PVD technique incorporating CrN coating was applied to the titanium alloy (Ti-6Al-4V) and its effects on the fatigue life and fatigue strength were studied in this paper to explore the fatigue behavior of Ti-6Al-4V specimens. A CrN film deposited by arc ion plating (AIP) improved the mechanical properties; specially hardness and fatigue life of Ti-6Al-4V specimens. The properties were studied using XRD, hardness and fatigue testers. The fatigue life of CrN-coated Ti-6Al-4V specimens was improved significantly compared to those of uncoated specimens. The enhanced fatigue life can be attributed to the improved hardness of CrN film due to change of bias voltage during the film deposition. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the substrate surface. It has been determined that the fatigue fracture of the substrate-coating composite is dominated by the fracture of the CrN film since fatigue cracks have been observed to form first at the surface of the film and subsequently to propagate towards the substrate. It has also been concluded that the increase in fatigue properties of the coated substrate is associated mainly with the changing of bias voltage during the coating observed in most of the maximum alternating stress range explored in this work.

Commentary by Dr. Valentin Fuster
2008;():175-182. doi:10.1115/MSEC_ICMP2008-72078.

This study investigates the effect of tool wear on the rolling contact fatigue performance of superfinish hard machined surfaces. Specimens were machined at two different cutting tool conditions: new and worn tools. The condition of a new tool is defined as the state of an unused tool, while that of a worn tool is defined as the state of a tool after being used for machining 150 identical specimens at the same machining conditions. It is noted that tool wear induces less compressive residual stresses for the specimens machined by square tools, while tool wear induces more compressive residual stresses in a deeper region for the specimens machined by round tools, which have a relatively large tool nose radius. In the micro-hardness distribution, the specimen machined by a worn tool typically shows a more softened layer than the specimen machined by a new tool. The rolling contact fatigue test results indicate that the rolling contact fatigue life of the specimen machined by a new tool is generally longer than that of the specimen machined by a worn tool.

Commentary by Dr. Valentin Fuster
2008;():183-190. doi:10.1115/MSEC_ICMP2008-72083.

Compacted graphite iron (CGI) has been viewed as the next generation casting material for diesel engines to further the automotive energy efficiency because of its better mechanical strength for lighter engine designs as compared to gray cast iron. The machinability of CGI is analyzed and tested in honing, a standard engine manufacturing process for cylinder bores. Its comparable stock removal rate and tool life to cast iron honing lessen the concern of the machinability problems normally seen in other machining operations on CGI parts.

Commentary by Dr. Valentin Fuster
2008;():191-195. doi:10.1115/MSEC_ICMP2008-72111.

A new method called submersed gas-jetting EDM was proposed, in which the high-pressure gas working as the dielectric medium, is blown throughout the inner hole of a tubular electrode, and machining liquid around the gas plays significant roles of helping cooling and debris evacuation but doesn’t involve in the discharge directly. Experiments were conducted to investigate the influence of polarity, pulse duration, peak current, gas pressure and different gas/machining liquid combination. The comparison of submersed gas-jetting EDM and dry EDM indicated that this new method revealed higher material removal rate (MRR), better surface quality and equivalently minute electrode wear.

Commentary by Dr. Valentin Fuster
2008;():197-204. doi:10.1115/MSEC_ICMP2008-72258.

Final polishing operation for die and mould manufacturing represents up to 30% of the total manufacturing cost and it is a high added value operation carried out manually by qualified personnel. The work presented in this paper proposes an automated solution for this task by the process known as Laser Polishing. This process is based on the application of a laser beam melting a microscopic layer of material, which lately solidifies filling the gaps, and smoothing the overall topography. Several Laser Polishing tests have been done with CO2 and High Power Diode Lasers (HPDL) on two different materials commonly used in die and mould industry: a DIN 1,2379 Tool Steel tempered up to 62HRC, used for injection moulds inserts, and a spheroidal graphite Cast Iron DIN GGG70L used typically on large stamping dies manufacturing. By means of the tests and Design of Experiments (DoE) technique, the operation parameters for the Laser Polishing process as well as its degree of influence in the melted surface have been defined. Starting off from an initial surface obtained by means of High Speed Milling operation, it has been possible to obtain satisfactory results with final roughness reductions higher than 80% with respect to the initial values, and mean roughness values below 0.8μm Ra.

Commentary by Dr. Valentin Fuster
2008;():205-209. doi:10.1115/MSEC_ICMP2008-72274.

A new understanding of the expulsion mechanism in electrical discharge machining (EDM) is discussed in this investigation. The shifting secondary discharge inside a cathodic root is revealed as the major driving force for metal expulsion in EDM. A typical electrode couple of steel for cathode and copper for anode is used in all the experiments and discussions. Micro graphs of discharge craters are taken from the complex surface directly after a continual discharging process while either normal or reversed polarity is applied. The apparent difference in crater morphologies on anode and cathode indicates the unique expulsion mechanism, namely secondary discharges, which only take place inside the cathodic root. The compliance of secondary discharges with long-disputed phenomena, such as the discrepancy between energy distribution and metal removal, is demonstrated through the applications of the mechanism to the phenomena. The applied methods and results are more realistic since single pulse discharge among other process changes is prohibited. Such a more reliable understanding can correlate the complex metal removal mechanisms to better future process developments.

Commentary by Dr. Valentin Fuster
2008;():211-218. doi:10.1115/MSEC_ICMP2008-72501.

Laser hardening is a laser assisted process devoted to the surface hardening of the mechanical components. This process is highly suitable for medium carbon steels with carbon content comprised between 0.2 – 0.6% or for low alloy steels which are usually surface hardened during their manufacturing process. Laser hardening technology is gaining a great industrial interest in the last years in fact, the possibility of integrating the heating source directly on the production line, together with the absence of the quenching medium, meets the production needs of modern industries. Laser hardening optimization could be complex especially when tempering due to multiple passes effects must be considered. Many research studies have been proposed in the last years aimed at predicting the optimal laser process parameters such as beam power density, beam velocity and scanning strategies. Many Authors agree with the assumption that the whole austenite resulting from the heating is transformed into martensite during the quenching. This is a valid approximation for single pass but could be a rough hypothesis in multiple-passes when the cooling rate could be not so high. Moreover hysteresis phenomena, due to the severe heat cycle occurring in laser hardening, should be taken into account for pearlite to austenite and martensite to austenite transformations during heating and for martensite tempering during multiple passes. In this paper the crucial problems to be faced regarding laser surface hardening modeling are discussed with respect to current literature. In particular, partial austenitization of the pearlite is suggested as a solution of the hardness prediction of the profile depth. Then three transformation parameters are proposed in order to take into account the hysteresis phenomena in martensite and pearlite transformations into austenite and in martensite tempering. Finally several experimental examples are proposed in order to validate the mentioned assumptions.

Commentary by Dr. Valentin Fuster
2008;():219-226. doi:10.1115/MSEC_ICMP2008-72604.

In this paper the effects of machining parameters on the surface roughness (Ra) in cylindrical wire electro discharge machining (CWEDM) are investigated. CWEDM is a new technology in which a rotary axis is added to a usual Wire EDM machine. In this process, a new machining parameter, such as rotational speed, is introduced, which changes the normal machining conditions in conventional wire electrical discharge machining (WEDM). Current paper investigates the effects of main parameters of CWEDM including power, voltage, pulse-off time, rotation speed of rotary axis and form factor (cone angle) on the surface roughness in CWEDM. This has been done by means of the technique of design of experiments (DOE); the three levels fractional factorial method (3k−p ) was used for studying the selected factors which allows us to carry out the above-mentioned analysis performing a relatively small number of experiments. Analysis of Variance (ANOVA) has been used to determine significant factors; also an equation based on data regression has been presented. Results from ANOVA show that power is a significant variable to surface roughness of cylindrical wire-EDMed AISI D3 cold worked steel parts. The surface roughness of test specimen increased as power and voltage increased and pulse off time and rotation speed decreased. Surfaces of the cylindrical WEDM parts were examined using Scanning Electron Microscopy (SEM) to identify the macro-ridges and craters on the surface. Cross-sections of the EDM parts are examined using the SEM to quantify the sub-surface recast layers and heat-affected zones under various process parameters and to determine their relation with surface roughness of parts.

Commentary by Dr. Valentin Fuster
2008;():227-236. doi:10.1115/MSEC_ICMP2008-72210.

Non-linear absorption of femtosecond laser pulses enables the induction of structural changes in the interior of bulk transparent materials without affecting their surface. This property can be exploited for the transmission welding of transparent dielectrics, three dimensional optical data storages and waveguides. In the present study, femtosecond laser pulses were tightly focused within the interior of bulk fused silica specimen. Localized plasma was formed, initiating rearrangement of the network structure. The change in material properties were studied through employment of spatially resolved Raman spectroscopy, atomic force microscopy and optical microscopy. The nature of the physical mechanisms responsible for the alteration of material properties as a function of process parameters is discussed.

Commentary by Dr. Valentin Fuster
2008;():237-244. doi:10.1115/MSEC_ICMP2008-72231.

Laser shock peening (LSP) is an innovative surface treatment developed to improve surface integrity. This study explores the feasibility using LSP to direct-write surface micro dents for lubricant retention. Since LSP is a highly transient process with a pulse duration of 10 – 100 ns, a real time in-situ measurement of laser/material interaction such as transient stresses/strains is challenging. Therefore, a 3D finite element simulation of micro-scale laser shock peening was developed to determine the effect of laser pulse duration and peak pressure on the transient material behaviors of titanium Ti-6Al-4V. The simulated dent geometry is similar to the measured dent geometry in terms of morphology. The results suggested there is an optimal peening time that produces the deepest dent. The maximum transient stress in peening direction occurred at a certain laser pulse time. However, the stress along the depth and radius were drastically affected by the peak pressures.

Commentary by Dr. Valentin Fuster
2008;():245-254. doi:10.1115/MSEC_ICMP2008-72259.

Laser shock peening (LSP) under the water confinement regime (WCR) involves several complicated physical phenomena. Among these phenomena, the interaction between laser and coating material during LSP is very important to the laser induced residual stress, which has an important effect on the fatigue and corrosion properties of the substrate material. To gain a better understanding of this interaction, a series of experiments, including single shot, single track overlapping, and multi-track overlapping LSP, have been carried out on 4140 steel with black paint coating. A 3-D finite element model has also been developed to simulate the LSP process. Combining this with a previously developed confined plasma model, which has been verified by the experimental data from literature, the 3-D finite element model is used to predict the residual stresses induced in the substrate material as well as the indentation profile on the substrate surface. The model prediction of indentation profiles are compared with the experimental data and good agreements are obtained. The effect of process parameters on the residual stress has also been investigated both experimentally and theoretically.

Commentary by Dr. Valentin Fuster
2008;():255-261. doi:10.1115/MSEC_ICMP2008-72293.

Tuning the plasma field in reactive ion etching generates different etching profile of nanoparticles. For nanoparticles in an isotropic plasma field, there will be uniform shrinkage of the particle sizes due to the isotropic etching, with the curvature of the particles unchanged after the etching. An anisotropic etching, on the other hand, provides rich opportunities to modify the shape of the particles with reduced dimensions. For a monolayer of silica nanoparticles on a flat substrate in a unidirectional plasma field, the reactive ion etching changed the shape of silica nanoparticles from spherical to spheroid-like geometry. The mathematical description of the final spheroid-like geometry was discussed and matched well with the experimental results. The surface curvature of the particles after etching remained the same for both the top and the bottom surfaces, while the overall shape transformed to spheroid-like geometry. Varying the etching time resulted in particles with different height to width ratios. The unique geometry of these non-spherical particles will impact fundament properties of such particles, such as packing and assembly. In the case of spheroid-like particles, packing of such particles into ordered structures will involve an orientational order, which is different from spherical nanoparticles that have no orientational order.

Commentary by Dr. Valentin Fuster
2008;():263-273. doi:10.1115/MSEC_ICMP2008-72426.

Traditional numerical study of the temperature field of laser thermal processing is based on two assumptions: 1. heat source is a surface heat flux, and 2. uniform material properties. This method is not accurate when it comes to the laser sintering of nanoparticle integrated bioceramics coating with certain porosity. In this paper, Heat transfer (HT) model and electromagnetic (EM) model is coupled to investigate the temperature field of bioceramics nanoparticles. The heat source calculated from EM field is simultaneously input into the HT model to calculate the temperature field of the nanoparticle assembly. The interaction between the nanoparticles in the EM field is analyzed and its influence to the optical penetration depth of laser is discussed. The effects of laser parameter, including wavelength, pulse energy, pulse width, and mixing ratio of nanoparticles are also investigated.

Commentary by Dr. Valentin Fuster
2008;():275-282. doi:10.1115/MSEC_ICMP2008-72463.

This paper discusses the operating temperature in laser assisted milling (LAMill) of silicon nitride ceramics. Experimental investigation shows that the laser parameters including laser power, laser beam diameter, laser translating speed and preheat time affect the temperatures at the cutting zone. Especially, laser intensity plays an important role in the heat absorption of silicon nitride ceramics. In LAM, high laser intensity is desired. In addition, laser interaction mechanism with silicon nitride shows that high operating temperature may cause the material at the thin top layer of the workpiece to oxidize and thereby forming silica bubbles. With high operating temperature the machined surface of the workpiece has good finish and less edge chipping.

Commentary by Dr. Valentin Fuster
2008;():283-292. doi:10.1115/MSEC_ICMP2008-72512.

Previous studies have shown that the presence of a pulsed electrical current, applied during the deformation process of an aluminum specimen, can significantly improve the formability of the aluminum without heating the metal above its maximum operating temperature range. The research herein extends these findings by examining the effect of electrical pulsing on 5052 and 5083 Aluminum Alloys. Two different parameter sets were used while pulsing three different heat treatments (As Is, 398°C, and 510°C) for each of the two aluminum alloys. For this research, the electrical pulsing is applied to the aluminum while the specimens are deformed, without halting the deformation process. The analysis focuses on establishing the effect the electrical pulsing has on the aluminum alloy’s various heat treatments by examining the displacement of the material throughout the testing region of dogbone shaped specimens. The results from this research show that pulsing significantly increases the maximum achievable elongation of the aluminum (when compared to baseline tests conducted without electrical pulsing). Significantly reducing the engineering flow stress within the material is another beneficial effect produced by electric pulsing. The electrical pulses also cause the aluminum to deform non-uniformly, such that the material exhibits a diffuse neck where the minimum deformation occurs near the ends of the specimen (near the clamps) and the maximum deformation occurs near the center of the specimen (where fracture ultimately occurs). This diffuse necking effect is similar to what can be experienced during superplastic deformation. However, when comparing the presence of a diffuse neck in this research, electrical pulsing does not create as significant of a diffuse neck as superplastic deformation. Electrical pulsing has the potential to be more efficient than traditional methods of incremental forming since the deformation process is never interrupted. Overall, with the greater elongation and lower stress, the aluminum can be deformed quicker, easier, and to a greater extent than is currently possible.

Topics: Heat , Aluminum alloys
Commentary by Dr. Valentin Fuster
2008;():293-302. doi:10.1115/MSEC_ICMP2008-72514.

As the laser spot size in micro-scale laser shock peening is in the order of magnitude of several microns, the anisotropic response of grains will have a dominant influence on its mechanical behavior of the target material. Furthermore, conventional plasticity theory employed in previous studies needs to be reexamined due to the length scale effect. In the present work, the length scale effects in microscale laser shock peening have been investigated. The crystal lattice rotation underneath the shocked surface was determined via Electron Backscatter Diffraction (EBSD). From these measurements, the geometrically necessary dislocations (GND) density that the material contains has been estimated. The yield strength increment was then calculated from the GND distribution by using Taylor model and integrated into each material point of the FEM simulation. Finite element simulations, based on single crystal plasticity, were performed of the process for both with and without considering the GND hardening and the comparison has been conducted.

Commentary by Dr. Valentin Fuster
2008;():303-309. doi:10.1115/MSEC_ICMP2008-72541.

The long cycles of modern economy is driven by technology innovations. New methodologies are needed to increase the efficiency of technology innovations. Intelligent Energy Field Manufacturing is one of such methodologies. The evolution and the fundamentals of Intelligent Energy Field Manufacturing (EFM) are reviewed in this paper. One issue in technology innovation is that the importance of manufacturing process innovations is underestimated. The other issue is how and why shall manufacturing Go Green to increase long-term sustainability. These should be the important topics in the research of Intelligent EFM.

Commentary by Dr. Valentin Fuster
2008;():311-318. doi:10.1115/MSEC_ICMP2008-72029.

Engineering designers consider many aspects surrounding a product’s life in order to meet safety, reliability, quality, manufacturing, and cost requirements. Most of the time this is done in an excellent way and the resulting products offers broad functionality with high quality and reasonable price. However serious considerations of integration of environmental requirements are often missed in the product development process. All products contribute to a range of environmental problems. These problems arise through the entire life cycle of products from the creation to the disposal of products. Design for environment (DfE) is the systematic consideration of design performance with respect to environmental, health, and safety objectives over the full product and process life-cycle. It takes place early in a product’s design or upgrade phase to ensure that the environmental consequences of a product’s life cycle are considered. The key issue to success is how to select the most appropriate and effective strategy for a particular product to reduce environmental impacts without disregarding the business strategies in the decision making process. In this paper, a general framework is proposed to integrate the life cycle assessment and decision analysis for prioritizing the design for environment strategy by considering uncertainty issues exist in the decision making process. A case study is illustrated focusing in the product upgrade phase. The ultimate goal is to provide a design advisory tool for product designers in the hopes of facilitating their complex decision making processes by considering the environmental issues in mind.

Commentary by Dr. Valentin Fuster
2008;():319-326. doi:10.1115/MSEC_ICMP2008-72129.

In response to the global trend towards implementing sustainable manufacturing practices, we put forth an exploratory approach that uses energy monitoring as a means to introduce sustainability criteria early into manufacturing process planning. Typically cost, quality and time are the indices for manufacturability assessment in generating manufacturing process plans. In this paper, we propose the idea of introducing sustainability to complement cost, quality and time to arrive at alternative sustainable plans in identified manufacturing processes. To be sustainable, it is pertinent that manufacturing firms understand the energy consumption of different manufacturing equipment used to produce products. This will enable industry to implement energy reduction processes in a more effective manner and pave the way for improved and alternate manufacturing solutions. The paper presents the potential utility of energy usage readings in the interest of continuing dialogue and collaboration.

Commentary by Dr. Valentin Fuster
2008;():327-335. doi:10.1115/MSEC_ICMP2008-72223.

A sustainable manufacturing strategy requires metrics for decision making at all levels of the enterprise. In this paper, a methodology is developed for designing sustainable manufacturing metrics given the specific concerns to be addressed. A top-down approach is suggested that follows the framework of goal and scope definition: (1) goal - what are the concerns addressed and what is the appropriate metric type to achieve the goal (2) scope - what is the appropriate geographic and manufacturing extent. In this methodology a distinction is made between environmental cost metrics and sustainability metrics. Utilizing this methodology, metrics focused on energy use, global climate change, non-renewable resource consumption, and water consumption are developed.

Commentary by Dr. Valentin Fuster
2008;():337-341. doi:10.1115/MSEC_ICMP2008-72456.

The paper deals with machining of High C–High Cr die steel with Ti N, TiAlN Coated end mill cutter, using solid lubricant and obtaining a generalised relationship of surface roughness dependent on input parameters, based on response surface methodology. The hardness ratio of the tool and the workpiece, as one of the important parameters, having significant influence under near-dry machining condition, was studied under minimum quantity of oil using solid-lubricant (MOS2 ) mixed with base oil SAE-20 in different proportion.

Commentary by Dr. Valentin Fuster
2008;():343-350. doi:10.1115/MSEC_ICMP2008-72082.

Even though many models for machining exist, most of them are for low-speed machining, where momentum is negligible and material behavior is well approximated by quasi-static plastic constitutive laws. In machining at high speeds, momentum can be important and the strain rate can be exceedingly high. For these reasons, a fluid mechanics approach to understanding high-speed, very high-speed, and ultra-high-speed machining is attempted here. Namely, a potential flow solution is used to model the behavior of the material around a sharp tool tip during machining at high speeds. It is carefully argued that the potential flow solution is relevant and can be used as a first approximation to model the behavior of a metal during high-speed, very high-speed, or ultra-high-speed machining events; and at a minimum, the potential flow solution is qualitatively useful in understanding mechanics of machining at high speeds and above. Interestingly, the flow solution predicts that there is a stagnation point on the rake face, not at the tool tip as is usually assumed. Because the stagnation point is not at the tool tip, the flow solution predicts a significant amount of deformation in the workpiece resulting in large residual strains that may lead to a temperature rise on the finished surface.

Commentary by Dr. Valentin Fuster
2008;():351-358. doi:10.1115/MSEC_ICMP2008-72131.

The drive for ever increasing productivity puts continuously increasing demands on cutting tool performance. With the cost of a single prototype tool design near $10,000, the benefits of virtual development are clear. Computer simulation can provide accurate information on chip form, cutting force, temperature, workpiece surface integrity and other vital performance information. Recent advances in simulation technology, combined with ever increasing available of computational power at low cost, have vastly expanded the range of machining applications which can be studied in practical times. This paper examines finite element solver technology, recent research and test results enabling virtual development and prototyping of cutting tools.

Commentary by Dr. Valentin Fuster
2008;():359-368. doi:10.1115/MSEC_ICMP2008-72200.

The main drawback of the high speed milling of monolithic parts for the aerospace industry is the high buy-to-fly ratio that leads to a huge material waste. This problem is caused by the need to stiffen the part during the machining in order to avoid chatter, excessive vibration and residual stresses. The present work proposes a methodology for the milling of compliant parts based on the selection of cutting conditions free of chatter. First, the modal parameters of the part in the most problematic stages of the machining are calculated by means of the finite elements method. Secondly, a three-dimensional stability model is used in each stage to calculate a three-dimensional stability lobes diagram dependent on the tool position along the whole tool path. Given the fact that the depth of cut is defined by the bulk of material, the three-dimensional stability diagram can be reduced to a two-dimensional one, which relates tool position during the machining and spindle speed, and indicates how to change the spindle speed in order to avoid the unstable areas. What is more, the proposed methodology can also be used to dimension the bulk of material, select the proper tool or improve the fixturing of the part. Finally, the methodology is validated experimentally on a test part.

Commentary by Dr. Valentin Fuster
2008;():369-375. doi:10.1115/MSEC_ICMP2008-72204.

Diamond-coated cutting tools are attractive alternatives to polycrystalline diamond tools for machining lightweight, high-strength components made of advanced materials such as composites. However, residual stresses induced by the diamond deposition process, due to thermal mismatch between diamond and the substrate, significantly impact the coating-substrate adhesion, and thus, the tool performance in machining. Moreover, the tool geometry, particularly at the very tip, complicates the stress fields because of the sharp geometry changes. The objective of this research is to investigate the effects of critical tool geometry parameters on the residual stress augmentations in diamond coated cutting tools. In this study, computer-aided design (CAD) software was used to create the solid model of various tool geometries. It was used to create an accurate model of the tool, which emulates each aspect of the tool geometry, e.g., as small as 5-micron edge radius on a 12.7-mm tool. The solid model was then exported to finite element analysis (FEA) software for 3D simulations of residual stresses generated in the tool with given deposition conditions. The obtained stress data was transformed to evaluate the interface stress profiles around the tool edges. To systematically investigate the tool geometry effects, a test matrix, determined using the design of experiments approach, includes 4 factors (edge radius, relief angle, corner radius, and corner angle) and 2 levels with a full factorial design. Analysis of variance was performed to quantitatively reveal the significant factors and interactions between the factors that dominate the stress concentrations. Results are summarized as follows. (1) The cutting edge radius is the most significant factor to the interface stresses. (2) For a 5 μm edge radius, the radial normal stress (σΓ ) increases from 0 at the top uniform surface to about 1.5 GPa in tension, and the circumferential normal stress (σθ ) increases from around 3.0 GPa in compression to over 3.7 GPa. (3) The corner radius is of secondary importance to σΓ , and the relief angle is of secondary importance to σθ .

Commentary by Dr. Valentin Fuster
2008;():377-386. doi:10.1115/MSEC_ICMP2008-72209.

This paper investigates a thread making process called thrilling, which performs both drilling and thread milling with one tool. A chip thickness and mechanistic cutting force model has been developed for a thread milling operation with a thrilling tool. The model considers the complex geometry of a thrilling tool and the unique tool paths associated with the thread milling operation. Calibration experiments have been conducted to estimate the cutting coefficients associated with specific cutting energies. Experiments have been conducted to validate the developed model. Comparison of the average torque and forces between experiment and simulation results shows that the model predicts the experimental results within 12% error. The model has also been used to analyze the effects of helix angle and number of engaged threads on the cutting forces.

Commentary by Dr. Valentin Fuster
2008;():387-396. doi:10.1115/MSEC_ICMP2008-72230.

Hard turning and grinding are competitive processes in many cases for manufacturing various mechanical products. Product performance is highly dependent on the process induced residual stresses. However, there exist some inconsistence regarding the true residual stress profiles generated by hard turning and grinding with and without the presence of a white layer. This study aims to clarify the pressing issues via an extensive residual stress measurement for five surface types: hard turned fresh (HTF), hard turned with a white layer (HTWL), ground fresh (GF), ground with a white layer (GWL), and as heat treated. The x-ray diffraction data revealed distinct differences in the residual stress profiles between the turned and ground surfaces. Specifically, the key findings are: (i) HTF surfaces generate a “hook” shaped residual stress profile characterized by surface compressive residual stress and maximum compressive residual stress in the subsurface, while GF surfaces only generate maximum compressive residual stress at the surface; (ii) HTWL surfaces generate a high tensile stress in the white layer, but has highly compressive residual stress in the deeper subsurface than the HTF surface; (iii) GWL surfaces only shift the residual stress to more tensile but does not affect the basic shape of the profile; (iv) Tensile residual stress in the HTWL surface is higher than that for the GWL one. However, the residual stress for the ground white layer does not become compressive and remains tensile in the subsurface; (v) Elliptical curve fitting is necessary for measuring residual stress for the HTWL surface due to the presence of shear stress induced severe Ψ splitting; (vi) Residual stresses by grinding show more scattering than those by hard turning; and (vii) Machining is the deterministic factor for the resulting residual stress magnitudes and profiles compared with the minor influence of initial residual stress by heat treatment.

Topics: Stress
Commentary by Dr. Valentin Fuster
2008;():397-405. doi:10.1115/MSEC_ICMP2008-72307.

This paper presents implementation results of the multirate estimation scheme, proposed by Lee (Lee, C.W., 2007, “Multirate Estimation for the Machining Process under Multirate Noise,” Proceedings of the 2007 ASME IMECE, November 11–15, 2007, Seattle, WA), on the cylindrical plunge grinding process. The multirate scheme is an efficient tool for integrating real-time sensor signals with postprocess inspection data for estimating the immeasurable variables. In order to accomplish this goal, process models for grinding power, surface roughness and wheel wear are developed using experimental data. Case studies are performed on simultaneous state-parameter estimation for actual grinding batches after the multirate observers are built based on the process models. Results from case studies validate the applicability of the proposed scheme to challenging estimation tasks in the manufacturing industry that cannot be undertaken by traditional approaches.

Topics: Grinding
Commentary by Dr. Valentin Fuster
2008;():407-415. doi:10.1115/MSEC_ICMP2008-72366.

The objective of this study is to examine the relationship between microstructure and material content at critical locations of used WC-Co ball-end mills. The performance of three similar tools was tested at identical cutting conditions. From each tool, three samples were cut from the same positions on the WC-Co ball-end mills at key locations. Scanning Electron Microscopy (SEM) was used for observation of the microstructure of material and three methods were used to determine the chemical compositions of each tool. The first method used to examine the chemical composition was Energy Dispersive Spectrometry (EDS). Higher accuracy chemical analysis using Wave Dispersive Spectrometry (Microprobe) techniques and Slice-Averaged Wet Chemistry (ICP) results were also completed to verify trends and chemical contents. The results of this study showed that the microstructure is closely related to the cobalt content. Moreover, cobalt losses resulting from the machining process as well as phenomena resulting in microstructure defects in the manufacturing stage of the carbide were evident in worse performing tools. Furthermore, differing grain-growth inhibitor contents of each tool might have led to additional performance differences.

Commentary by Dr. Valentin Fuster
2008;():417-425. doi:10.1115/MSEC_ICMP2008-72369.

This study examines the performance of a new class of wear-resistant but economical cutting tools produced by varying the binder composition of standard cemented carbide composites. By replacing some or all of the cobalt binder with rhenium and nickel-based superalloy, a stronger composite tool results, potentially capable of machining heat-resistant superalloys at significantly higher cutting speeds. Sample tools with alternative binder were produced and compared to standard tools bound with cobalt only. Turning experiments on Inconel 718 were run to evaluate wear resistance and tool life for several grades. The experimentation also examined the effects of varying the relative proportions of each binder constituent as well as the overall binder percentage in the composite. Results show a clear advantage of the alternative binder tools as evidenced by a 150% increase in tool life or the equivalent of an 18% increase in cutting speed. Although increasing amounts of rhenium in the binder show a positive effect on performance, the effects of superalloy and overall binder % are inconclusive.

Commentary by Dr. Valentin Fuster
2008;():427-436. doi:10.1115/MSEC_ICMP2008-72388.

Since recent studies have demonstrated the benefits of hard turning over other abrasive machining processes as a finishing process in terms of surface integrity, a strong need has existed to improve the performance of chucking. It is because the poor repeatability and accuracy in the positioning of chucked workpieces became the major bottleneck in the implementation of finish hard turning for precision mechanical components. However, the understanding of chucking has not been adequate, nor has any systematic method been reported for improving chucking accuracy. In this paper, all the major factors that affect the positioning accuracy and repeatability of a chucked workpiece have been identified by error budgeting and systematic measurements. In addition, the characteristics of these factors, as well as their effect on chucking accuracy, were investigated. From the results, a chucking error map that summarizes the relations between these factors and the positioning error of a chucked workpiece was developed. Then, a series of experiments were carried out, based on the results of the earlier works to test the effectiveness of the error budget. The results demonstrated that the knowledge on these factors was accurate and it could be effectively used to improve the positioning accuracy and repeatability of a range of cylindrical workpieces chucked for machining. It was also shown that hard turning alone, without any extra machining process, could satisfy the same level of concentricity which is currently achieved by finish grinding in the machining of different types of cylindrical workpieces. Even if this study was originally intended for the implementation of finish hard turning that can replace finish grinding, the methods developed can be used to improve the final form accuracy of cylindrical workpieces in other finishing processes including grinding if any workholding devices similar to chucks are used to hold the workpieces. The methodology and the procedures for improving chucking accuracy are covered in a pending patent by the authors.

Commentary by Dr. Valentin Fuster
2008;():437-445. doi:10.1115/MSEC_ICMP2008-72402.

The crater topography of wear patterns on a series of multi-layer coated tools after machining for a series of machining times has been measured using Confocal Laser Scanning Microscopy and Stylus Profilometry in order to study the crater wear patterns and their evolution. The crater profile and raw patterns were processed using multi-resolution 1D and 2D wavelet analysis to eliminate noise, spike/pits and then to decouple the large/short scale wear features in order to examine the development and history of crater wear accurately. The wavelet method proved to be very powerful to extract the meso-scale crater wear pattern free of noise/artifacts without losing the general crater pattern. Microscale details were successfully identified which indicates a great potential for the local analysis of wear mechanisms.

Commentary by Dr. Valentin Fuster
2008;():447-455. doi:10.1115/MSEC_ICMP2008-72469.

This paper reviews the literature on dry machining with VT cooling (using vortex-tube generated cold air as coolant). It presents reported experimental results on effects of VT cooling on cutting force, cutting temperature, tool wear, surface roughness, and residual stress. It also points out areas where VT cooling applications have not been reported and potential directions for future research.

Commentary by Dr. Valentin Fuster
2008;():457-464. doi:10.1115/MSEC_ICMP2008-72489.

KDP (potassium di-hydrogen phosphate) crystal is used to fabricate important electro-optic parts. It is a typical hard-to-machine material because it is soft, brittle, and anisotropic. Parts made of KDP usually have extremely high requirements for machining quality. Reported machining methods so far for KDP crystal include single point diamond turning, grinding, magnetorheological finishing, and polishing. This paper presents an experimental investigation on diamond drilling of KDP. Data of several output parameters (including grinding force and torque, surface roughness, and edge chipping) were collected and analyzed. Ultrasonic vibration was superimposed to the rotation of the tool to study its effects.

Commentary by Dr. Valentin Fuster
2008;():465-474. doi:10.1115/MSEC_ICMP2008-72492.

A low cost, wireless vibration sensor system has been developed for noninvasive integration into commercial end milling tool holders. Electret based accelerometers are used as the sensors and a Bluetooth compatible digital transmitter is used as the sensor interface. The use of mass market consumer electronic components is low cost and plug and play with modern PC hardware. Two prototypes were built and, in both cases, were able to collect good quality data at high sampling rates. The objective of the research is to enable accurate observation of NC metal cutting system dynamics. Initial results indicate the system can be used to estimate tool runout and detect the onset of regenerative chatter, prior to workpiece damage.

Topics: Sensors , Vibration , Milling
Commentary by Dr. Valentin Fuster
2008;():475-484. doi:10.1115/MSEC_ICMP2008-72513.

Traditional piezoelectric accelerometers used for machine condition monitoring are expensive and represent a capital risk when placed in the harsh environment of a cutting process. Additionally, these components require signal conditioning hardware and are sampled on a PC via an independent data acquisition interface (DAQ card). The goal of the research discussed herein is to test an industrial-friendly electret-based accelerometer that can perform tasks similar to a traditional piezoelectric accelerometer. The sensor will be adapted to utilize Bluetooth wireless data capabilities, further enhancing the sensors industrial practicality. The output of this electret-based sensor will be compared to the output of a traditional piezoelectric accelerometer and accompanying DAQ. More specifically, the study will focus on the effects of elevated temperature on the sensor. To achieve this, a comparison of both the electret and piezoelectric accelerometer response spectra will be observed over a range of 21°C to 77°C. To further validate the sensor, turning data is collected wirelessly from the sensor and compared to the output of the traditional piezoelectric sensor. Finally, the performance of the sensor for monitoring a tool’s condition during turning is evaluated and presented. The generated trend is contrasted to the comparable trend developed from the piezoelectric-based accelerometer.

Topics: Accelerometers
Commentary by Dr. Valentin Fuster
2008;():485-494. doi:10.1115/MSEC_ICMP2008-72212.

This paper presents a novel dynamic optimization framework for the grinding process in batch production. The grinding process exhibits time-varying characteristics due to the progressive wear of the grinding wheel. Nevertheless, many existing frameworks for the grinding process can optimize only one cycle at a time, thereby generating suboptimal solutions. Moreover, a dynamic scheduling of dressing operations in response to process feedback would require significant human intervention with existing methods. We propose a unique dynamic programming - evolution strategy (DP-ES) framework to optimize a series of grinding cycles depending on the wheel condition and batch size. In the proposed framework, a dynamic programming module dynamically determines the frequency and parameter of wheel dressing while the evolution strategy (ES) locates the optimal operating parameters of each cycle subject to the constraints on the operating ranges and part quality. A case study based on experimental data is conducted to demonstrate the advantages of the proposed method over conventional approaches.

Commentary by Dr. Valentin Fuster
2008;():495-502. doi:10.1115/MSEC_ICMP2008-72218.

New vision technologies provide an opportunity for fast detection and diagnosis of quality problems compared with traditional dimensional measurement techniques. This paper proposes a new use of image processing to detect quality faults using images traditionally obtained to guide manufacturing processes. The proposed method utilizes face recognition tools to eliminate the need of specific feature detection on determining out-of-specification parts. The algorithm is trained with previously classified images. New images are then classified into two groups, healthy and unhealthy. This paper proposes a method that combines Discrete Cosine Transform (DCT) with either Principal Component Analysis (PCA) or Linear Discriminant Analysis (LDA) to detect faults, such as cracks, directly from sheet metal parts.

Commentary by Dr. Valentin Fuster
2008;():503-512. doi:10.1115/MSEC_ICMP2008-72219.

Dimensional variation propagation and accumulation in multistage manufacturing processes are among the most important issues that affect quality. Although robust design and statistical process quality control help to reduce the effects of these problems, neither of these two methods can be used for instant variation reduction during assembly operations. This paper introduces a complete methodology for error compensation in compliant sheet metal assembly processes. The proposed methodology can be divided in two steps: (1) an off-line error control-learning module using virtual assembly models, and (2), an in-line control implementation using a feedforward control strategy. The off-line learning method focuses on determining the optimal control actions or corrections to a set of predefined deviations. Specifically, it utilizes a newly developed iterative sampling method based on Kriging fitting to efficiently determine an optimal control action. The in-line feedforward control uses measurements of incoming assembly components to select an appropriate pre-learned control action. Two case studies are presented; first, a mathematical case study is used as the empirical proof for the feasibility of the iterative sampling and fitting algorithm. Second, a simulation-based case study is used to illustrate the effectiveness of the proposed methodology to improve dimensional quality in assembly operations of compliant sheet metal parts.

Commentary by Dr. Valentin Fuster
2008;():513-521. doi:10.1115/MSEC_ICMP2008-72222.

This paper presents an innovative real time 2-dimensional position feedback method, which processes visual input data from a target image on an actively-controlled planar pixel matrix. The objective is to demonstrate the ability to position an X-Y stage with high resolution, using direct position sensing of a dynamically controlled image. In order to achieve high spatial resolution using a pixel array as a target, an algorithm that processes both the geometric shape and the grayscale intensities of the image is implemented. The test platform consists of an X-Y stage carrying a Liquid Crystal Display (LCD) screen that is imaged by a stationary digital camera. The pixel intensities on the LCD screen are modified dynamically to provide 2-dimensional position command inputs that translate to the desired stage motion. The digital images acquired by the camera are used to provide position error feedback to the controller. Experimental results show that direct position sensing is possible to a certain degree of accuracy. However, in order to match today’s CNC machines’ accuracy levels further processing of the digital images is required. A noise reduction algorithm to filter the fluctuations of the measurements in the digital images is proposed as future work, as well as other considerations.

Commentary by Dr. Valentin Fuster
2008;():523-532. doi:10.1115/MSEC_ICMP2008-72310.

Software configuration and engineering costs have limited the application of model predictive control (MPC) for small but fast dynamic systems. This work illustrates the benefits of using a graphical programming framework for the configuration and implementation of MPC controllers. Graphical programming facilitates the understanding and configuration of advanced applications so that engineers in industry can be responsible for the installation and maintenance of advanced controllers. Costs reduction and minimal specialized labor opens the possibilities of applying MPC to small systems with fast dynamics. Fast MPC execution is achieved by including the optimization constraints as penalty terms in the cost function. An air-heater pilot system is successfully used to demonstrate the advantages of a graphical framework for process modeling, design, and real-time implementation of MPC controllers in systems with fast dynamics.

Topics: Dynamic systems
Commentary by Dr. Valentin Fuster
2008;():533-540. doi:10.1115/MSEC_ICMP2008-72468.

Past work at UNC Charlotte has demonstrated that the use of oscillating CNC toolpaths provides a reliable chip breaking alternative to conventional methods such as the use of cutting inserts with special geometries and/or adjusting machining parameters. The specific toolpath geometry and the selection of the oscillating parameters is an important step to reliably and constantly create broken chips using this new method. This paper builds on the past work and discusses the proper selection of oscillation amplitude and its effect on the ability to break chips and to achieve desired chip lengths.

Commentary by Dr. Valentin Fuster
2008;():541-549. doi:10.1115/MSEC_ICMP2008-72542.

ERP (Enterprise Resource Planning) and Lean manufacturing are two production control methodologies. ERP systems were once considered as hindrance to Lean manufacturing efforts. The explosive growth of e-business is forcing many companies to revisit where they stand in relation to these two methodologies. Vendors of ERP systems begin to recognize the power and advantages of Lean manufacturing and then explore ways to build Lean-related features into their ERP systems. The main objective of this paper is to answer the question “Can ERP and Lean co-exist?” To accomplish this, the paper first discusses the misconception about ERP and Lean and then summarizes the differences between the two methodologies that led to the misconception. The paper discusses the importance of linking ERP and Lean methods and summarizes some of the key Lean toolsets that are offered in some ERP systems. From a list of ERP vendors offering Lean enabled modules three vendors are discussed in details. They are Oracle, TTW WinMan and Pelion systems.

Topics: Manufacturing
Commentary by Dr. Valentin Fuster
2008;():551-560. doi:10.1115/MSEC_ICMP2008-72548.

A lumped parameter dynamical model is developed to describe the metal transfer for gas metal arc welding (GMAW) in the globular mode. The oscillations of molten drop are modeled using a mass-spring-damper system with variable mass and spring coefficient. An analytical solution is developed for the variable coefficient system to better understand the effect of various model parameters on the drop oscillations. The effect of welding drop motion on the observed current and voltage signals is investigated and the model agrees well with the experimental results. Furthermore, the effect of wire feeding rate (or welding current) on the metal transfer cycle time is studied and the model successfully estimates the cycle times for different wire feeding rates.

Commentary by Dr. Valentin Fuster
2008;():561-570. doi:10.1115/MSEC_ICMP2008-72133.

A novel sheet metal forming technology based on aspects of both warm forming and superplastic forming has recently been developed. The new forming process, referred to as hot draw mechanical preforming (HDMP), uses two sequential steps to form a panel within a single tool at elevated temperature. In the first step, the cushion system acts on a binder and upper die to draw the blank over a punch which serves to draw in metal from the perimeter of the blank. In the second step gas pressure is applied to finish the panel details. This two step process of drawing in metal followed by gas forming can result in a significant expansion of the forming envelope for conventional AA5xxx series aluminum sheet alloys commonly used within the automotive industry. Similar to SPF, the HDMP process is performed within a single forming press equipped with heated platens and using gas pressure to shape the component during elevated temperature forming. However, the HDMP process utilizes a blankholder to control the flow of material into the forming cavity during the drawing stage and therefore requires the addition of an integrated cushion system in the bed of the press. HDMP dies are of interest in automotive applications because they maintain the low-investment attributes of SPF tooling while also significantly reducing the forming time as compared to conventional SPF. This work details the CAE based design of an HDMP die to form a one-piece aluminum door inner that can not be formed with conventionally forming processes. Critical aspects addressed in the development of the die include manufacturing targets, part design for manufacturing, and die design for operation at elevated temperature.

Topics: Doors
Commentary by Dr. Valentin Fuster
2008;():571-576. doi:10.1115/MSEC_ICMP2008-72136.

Tearing failure in sheet metal forming has traditionally been predicted based on the strain state of the material. However, a concern with this failure prediction method is that the strain based forming limit curve exhibits significant strain path dependence. A stress based failure criterion has been proposed and shown to be less sensitive to the strain path through numerical simulations and by analytically converting strain based data to stress space. However, a means to predict this stress based failure criterion without prior knowledge of the strain based forming limit curve for sheet metal is required. In this paper, an analytical prediction of the stress based forming limit curve is derived and compared to experimental and numerical results. The effects of model parameters are also investigated.

Topics: Sheet metal , Stress , Failure
Commentary by Dr. Valentin Fuster
2008;():577-581. doi:10.1115/MSEC_ICMP2008-72137.

During the past two decades, bio-physicists have had an increasing interest in finding out what happens when two bio-material solutions are mixed under high pressure. Compared to temperature, pressure makes more contributions to our fundamental understanding of the structure-function relationship of biological systems, because pressure produces only volume changes under isothermal conditions, and pressure results can then be interpreted in a more straightforward manner. Window-type High Pressure Optical Cell (HPOC) such as the one designed by Paladini and Weber have provided biophysicists with a powerful tool to understanding the structure-function relationships of biological molecules. However, the conventional HPOC is only good for single solution testing and does not allow for quick mixing and stirring of additional components while the specimen is under pressure. This research is to thoroughly study the feasibility of Shape Memory Alloy (SMA) as an actuator to perform mixing and agitation functions; and five types of SMA actuators were designed, simulated and tested for unplugging and mixing purposes. To conduct this research, SMA helical springs were fabricated in house according to the design requirements. With different combinations of SMA tensile springs, SMA compressive spring and biasing spring, significant ranges of vibration were developed. To further improving mixing process, a unique hybrid design of SMA as an actuator to unplug the stopper and micromotor as a stir device to agitate the solutions was developed. Rapid mixing of 95% of total solution in 10 seconds was achieved under 300 bars. A new HPOC was designed according to the new cuvette with its new unplug and mixing mechanism. Our industrial partner, ISS, further modified our design for easy manufacturing reason and fabricated the HPOC which made SMA actuator mixing test under pressure possible. A complete testing of the new HPOC system to observe bio-reagent mixing and reaction under high pressure was conducted and the results were satisfactory.

Commentary by Dr. Valentin Fuster
2008;():583-590. doi:10.1115/MSEC_ICMP2008-72139.

While welded forging preforms offer potential benefits for producing forged parts, work to date has mainly been concentrated on assessing static mechanical properties. As dynamic properties are an important consideration, the objective in the current study was to assess the high cycle fatigue properties of 6061-T6 aluminum forging performs which were prepared using friction welding. Monolithic and friction welded specimens were prepared and hot worked using a laboratory press. Fatigue data was then generated using a rotating beam test machine and a metallurgical evaluation of the weld zone performed. The results showed that, in general, forged preforms demonstrated superior fatigue life when compared to as-friction welded preforms in the same temper condition. Fatigue performance was also found to be comparable to that obtained from monolithic forging preforms which had an identical processing history.

Commentary by Dr. Valentin Fuster
2008;():591-600. doi:10.1115/MSEC_ICMP2008-72250.

Common part failures in tube hydroforming include wrinkling, premature fracture, and unacceptable part surface quality. Some of these failures are attributed to the inability to optimize tribological conditions. There has been an increasing demand for the development of effective lubricants for tube hydroforming, due to widespread application of this process. This paper presents an analytical model of the guiding zone tribotest commonly used to evaluate lubricant performance for tube hydroforming. Through a mechanistic approach, a closed-form solution for the field variables contact pressure, effective stress/strain, longitudinal stress/strain, and hoop stress can be computed. The analytical model was validated by the finite element method. In addition to determining friction coefficient, the expression for local state of stress and strain on the tube provides an opportunity for in-depth study of the behavior of lubricant and associated lubrication mechanisms. The model can aid as a quick tool for iterating geometric variables in the design of a guiding zone, which is an integral part of tube hydroforming tooling.

Commentary by Dr. Valentin Fuster
2008;():601-607. doi:10.1115/MSEC_ICMP2008-72279.

This paper presents a new configuration for sheet metal incremental forming using DSIF (Double Sided Incremental Forming) to overcome the limitation of single point incremental forming (SPIF). The new process can produce geometrical features on either side of the initial plane of the sheet without changing setup. A component having such challenging features is selected to demonstrate the capabilities of the proposed method and a contour tool path is generated using UniGraphics (UG) surface machining module and formed by mounting the new setup on a CNC milling machine. The final formed shape was scanned and compared to the designed profile. In addition, two more components having cylindrical and spherical geometries are formed to study the effect of geometry on the accuracy of the component that can be produced by using the proposed method. A simple analysis model has been developed to explain the effect of squeezing and stretching to the part elongation during the DSIF process.

Commentary by Dr. Valentin Fuster
2008;():609-616. doi:10.1115/MSEC_ICMP2008-72439.

In pyramid type three-roller bending process, it is difficult to deform the plate perfectly to the required circular shape and it mainly depends on the skill of the operator. Presented work shows the finite element (FE) simulations of three-roller plate bending process to study the influence of different parameters, such as roller position, rolling speed, plate material, plate length and friction (at roller plate interfaces) on the bending quality of the deformed plate. FE simulations were performed based on the elastic–plastic explicit dynamic finite element method under the Hyperform LS-DYNA environment. FE simulation results were verified with the experimental results. Parametric studies were carried out to investigate the effect of various parameters on the quality of the final shape. Reported work will be helpful to process engineers in predicting the final radius of curvature and deviation of plate prior to manufacturing. This will reduce the trail and error in achieving the final geometry.

Commentary by Dr. Valentin Fuster
2008;():617-625. doi:10.1115/MSEC_ICMP2008-72454.

Continuous three roller bending process is widely used in practice to bend the plates into cylinders. Bending load for plate material under bending is affected by plate thickness, width and shell diameter combinations. Maximum top roller load is encountered during the edge pre-bending stage as top roller is set at an offset distance from its mid position. Shell diameter, thickness and material for cylindrical structural element to be produced are fixed by design. Width of the plate for roller bending decides number of cylindrical segments required to achieve the designed shell length. Maximum pre-bending width depends on maximum top roller load imparting capacity. Looking to the above considerations, maximum width which can be pre-bend at limiting top roller load (for designed shell diameter, thickness and material combinations) specifies the capacity. Presented work aims at developing the mathematical model of top roller load for pre-bending. Top roller offset for pre-bending were calculated based on practical top roller pre-bending load data, for different grades of C-Mn steel plates (as per ASME sec II part-A). Based on these top roller offsets, finite element analysis (FEA) of pre-bending stage were performed using Hyperform LS-DYNA. Effect of co-efficient of friction at roller plate interfaces was analyzed. FE simulation of pre-bending of cladded plate (54 mm thick C-Mn steel plate of material grade SA-387Gr11Cl2 having 3 mm thick layer of stain less steel material grade SS-308) was performed. FEA load results were found in good agreement with the practical load results and can be used for capacity assessment and analysis of roller bending machines.

Commentary by Dr. Valentin Fuster
2008;():627-637. doi:10.1115/MSEC_ICMP2008-72530.

Many different modes of chatter and their possible causes have been identified after years of research, yet no clear and definite theory of their mechanics has been established. One of the most important reasons for this can be attributed to the fact that only oversimplified models with a single input and a single output were historically used to formulate chatter in rolling. Such a situation has hindered a complete analysis of the underlying mechanisms. In this paper, a state-space representation of single- and multi-stand chatter models will be proposed in a rigorous and comprehensive mathematical form for stability analysis of the various chatter mechanisms. First, a dynamic model of the rolling process that utilizes homogeneous deformation theory will be established that includes the material strain-hardening and work roll flattening effects. By coupling this dynamic rolling process model with a structural model for mill stands, a single-stand chatter model in a state-space representation will be proposed. Based on the single-stand chatter model, a multi-stand chatter model will be formulated by incorporating the inter-stand tension variations and the time delay effect of the strip transportation. A simulation program will also be presented for the study of the dynamic rolling process in the time domain and for verifying the results from stability analysis.

Commentary by Dr. Valentin Fuster
2008;():639-643. doi:10.1115/MSEC_ICMP2008-72544.

A computer aided blank design method based on the potential theory and boundary element methods is presented. The potential theory approximately describes the material flow involved in deep drawing processes. Using the CAD model of an irregular shaped component, a specific number of cross sections at different heights can be generated. In order to obtain the blank shape, the outermost contour is determined by developing these sections gradually. This blank design procedure is like an imaginary reverse material flow governed by the potential theory. In addition, the boundary element method provides a good computational efficiency. This computer aided design method has been found effective by a manufacturer and the proposed approach can be used for a wide variety of complicated deep drawing components.

Commentary by Dr. Valentin Fuster
2008;():645-654. doi:10.1115/MSEC_ICMP2008-72545.

The failure strain level in a single point incremental forming (SPIF) process is found to be much higher than that in the traditional stamping process. Based on the assumption that forming limits in SPIF are dominated by fracture failure, the Oyane ductile fracture criterion is introduced in this paper to predict the fracture initiation site, and hence the forming limit, given the stress and strain values obtained from finite element simulations. The predicted results compare well with those obtained from the SPIF experiments. Furthermore, this fracture criterion is used to study the size effects in SPIF. Analytical equations are derived to comprehensively consider the effects of design and process parameters on sheet formability including sheet thickness, tool diameter, and incremental depth. Previously published experimental data is used to verify the feasibility of the proposed size effect equation.

Topics: Size effect
Commentary by Dr. Valentin Fuster
2008;():655-660. doi:10.1115/MSEC_ICMP2008-72547.

This paper presents a generic methodology for tool path generation for an arbitrary component that can be formed by single point incremental forming (SPIF) to obtain required geometrical accuracy. Adaptive slicing concepts used in layered manufacturing have been modified and used for generating tool path for SPIF. Experiments and FEA have been carried out to study the effectiveness of the proposed methodology. Results indicate that the proposed methodology enhances the accuracy achievable in SPIF.

Commentary by Dr. Valentin Fuster
2008;():661-667. doi:10.1115/MSEC_ICMP2008-72555.

The Forming Limit Diagram (FLD) as developed by Keeler etc. has been widely used to assess sheet metal failure during a variety of forming operations. Its theoretical and empirical foundation is based on localized necking under biaxial loading for the sheet metal. While the in-plane deformation is generally the dominant mode for most forming operations, sheet metal bending is inevitably coupled to the deformation process, and the traditional Forming Limit Diagram has to be modified to take into account the bending effect, especially when the bending radius becomes smaller. This paper presents a theoretical formulation for the Bending-Enhanced Forming Limit model. The deformation theory of plasticity is employed for the instability analysis, and the bending is assumed only in the direction along one principal loading. The obtained results show that the forming limit is enhanced by the bending effect, consistent with experimental observations.

Commentary by Dr. Valentin Fuster
2008;():669-676. doi:10.1115/MSEC_ICMP2008-72059.

As an important branch of materials, soft and brittle functional crystals (SBFC) are widely used in the field of modern technology. However, the softness, brittleness, deliquescence, and strongly anisotropic natures of these materials present a challenge for their ultra-precision machining. The definition of SBFC is firstly given and their applications in many fields are also presented. For the ultra-precision machining technologies to satisfy the applied requirements, many methods such as single diamond turning, ultra-precision grinding, magnetorheological Finishing and so on, are successfully applied in SBFC materials, the challenges and difficulties occurred during machining these SBFC materials, such as KH2 PO4 , CdZnTe and CaF2 , etc., are reviewed and the limits are also analyzed in detail. Moreover, many novel machining methods are suggested to achieve better surface quality and enhance machining efficiency.

Commentary by Dr. Valentin Fuster
2008;():677-680. doi:10.1115/MSEC_ICMP2008-72171.

We have investigated polishing non-cubic crystal wafers using a unique dry polishing process. The wafers tested were GaN and SiC. Wafers of both GaN and SiC have surfaces terminated by different materials. Each of these surfaces will react differently when polished. For GaN the Ga (000–1) surface has a higher degree of chemical inertness than the nitrogen terminated surface (0001). To compensate for this difference in chemical inertness complex slurries and long polish times are used in chemo-mechanical polishing (CMP). Dry polishing equaled the surface finish and removal of subsurface damage of CMP in significantly reduced polishing times.

Commentary by Dr. Valentin Fuster
2008;():681-688. doi:10.1115/MSEC_ICMP2008-72253.

Free abrasive machining (FAM) processes, such as slicing using slurry wiresaws, lapping, and polishing, are very important manufacturing processes in wafer production for microelectronics fabrication. Since the materials in semiconductor industry are usually brittle, such as silicon, gallium arsenide, ... etc., the FAM processed can provide more gentle machining than the bonded abrasive machining process. Various machining theories and models have been developed to understand those processes. In this paper, the free abrasive machining processes in wafer manufacturing will be discussed in conjunction with the brittle material cracking theory. The modern slurry wire-saw slicing process and lapping process in wafer production will be presented with comparison to abrasive grits, manufacturing process models, characterization of manufacturing mechanisms, and properties of processes.

Commentary by Dr. Valentin Fuster

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