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Strength Enhancement of Styrene Acrylonitrile Co-Polymer via Delay Pack Injection Molding

[+] Author Affiliations
David C. Angstadt

Clemson University

John P. Coulter, Ryan Hydro

Lehigh University

Paper No. IMECE2005-81615, pp. 707-715; 9 pages
  • ASME 2005 International Mechanical Engineering Congress and Exposition
  • Manufacturing Engineering and Materials Handling, Parts A and B
  • Orlando, Florida, USA, November 5 – 11, 2005
  • Conference Sponsors: Manufacturing Engineering Division and Materials Handling Division
  • ISBN: 0-7918-4223-1 | eISBN: 0-7918-3769-6
  • Copyright © 2005 by ASME


This study investigates the effects of processing of styrene acrylonitrile (SAN) by injection molding using a delayed packing stage. The concept of Delay Pack Injection Molding (DPIM) evolved from an in-situ study of vibration-assisted injection molding (VAIM) which indicated that the beneficial effects of VAIM came not from the vibration itself, but rather from the delay in the onset of packing resulting from the application of the vibration. Conceptually, DPIM involves normal filling of the mold immediately followed by a slight retraction of the injection screw for a specified time period before the final packing pressure is applied. Application of DPIM results in increased birefringence in the molded parts and increases in the ultimate tensile strength of molded parts very similar to the effects seen using VAIM. A parametric study using a design of experiments framework was carried out to determine the delay pack parameters affecting SAN and resulted in a maximum increase in UTS of 11.6%. Observation of birefringence patterns in Delay Pack processed samples shows a significant impact on molecular orientation while observation of failed specimens and their fracture surfaces shows distinctly different modes of crack growth and failure. Growth of craze cracks resulting from tensile loading appeared to be arrested by oriented areas surrounding the part core allowing the specimen to sustain higher loads relative to conventionally molded parts. All of the above observations are consistent with the observed effects of vibration-assisted injection molding.

Copyright © 2005 by ASME



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