The Solutions for Reducing the Plastic Flow Hesitation and Its Application for Solving the Defect of Auto Parts


  • Supachart Thunyakasemsan Mechanics, Materials and Engineering Design Research Group, Rajamangala University of Technology Lanna
  • Niwat Moonpa Mechanics, Materials and Engineering Design Research Group, Rajamangala University of Technology Lanna
  • Jen-An Chang R&D Center for Smart Manufacturing (SMC), Chung Yuan Christian University
  • Belinda Changkajonsakdi Mold Technology Center, Thai-Taiwan (BDI) Technological College



flow hesitation, injection molding simulation, flow position difference, various part thickness design


The hesitation phenomena occur while the molten plastic flows into a cavity with variable thickness. When the molten plastic entering a cavity is filling a thin section and a thick section, the flow velocity of the molten plastic in each area is different, resulting in the flow position difference (FPD). When the flow hesitation happens, defects will occur on the part surface, such as weld line, air trap and short shot, etc. Therefore, the objective of this study was to present solutions for reducing the occurrence of hesitation phenomena by using various thickness design with difference thickness ratio (THK ratio) and injection speed to control the flow hesitation phenomena. Seven basic testing models with different THK ratio (1.2, 1.4, 1.6, 1.8, 2.0, 2.2 and 2.4) combine with different injection speeds were used for simulating. Through the simulation, different flow hesitation level (Flow Position Difference, FPD) could be computed. The engineering plastic material ABS was applied for the simulation testing to build up the database and produce the design guidelines. Eventually, the results of this study were used to solve the weld line issue caused by flow hesitation on the actual molding part. The study result showed that the THK ratio design was the main effect for the final FPD. The injection speed was a key parameter to reduce the FPD with different THK ratio. In the max THK ratio 2.4 design case, the FPD could be reduced by 70% (from 156.23 mm to 46.56 mm) by speed control. For the actual molding case of the motorcycle part, the serious weld line defect could be reduced about 69% by speed control solutions


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How to Cite

Thunyakasemsan, S., Moonpa, N., Chang, J.-A., & Changkajonsakdi, B. (2019). The Solutions for Reducing the Plastic Flow Hesitation and Its Application for Solving the Defect of Auto Parts. วารสารวิศวกรรมศาสตร์ มหาวิทยาลัยเทคโนโลยีราชมงคลล้านนา, 4(2), 1–6.