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A study on the effects of polymer core gate sizes on thickness shrinkage rate  

Choi, Han-Sol (Dept. of Mechanical Engineering, Dankook University)
Jeong, Eui-Chul (Dept. of Mechanical Engineering, Dankook University)
Park, Jun-Soo (Molds and Dies Technology Group, Korea Institute of Industrial Technology)
Kim, Mi-Ae (Molds and Dies Technology Group, Korea Institute of Industrial Technology)
Chae, Bo-Hye (Molds and Dies Technology Group, Korea Institute of Industrial Technology)
Kim, Sang-Yun (Molds and Dies Technology Group, Korea Institute of Industrial Technology)
Kim, Yong-Dae (Molds and Dies Technology Group, Korea Institute of Industrial Technology)
Yoon, Kyung-Hwan (Dept. of Mechanical Engineering, Dankook University)
Lee, Sung-Hee (Molds and Dies Technology Group, Korea Institute of Industrial Technology)
Publication Information
Design & Manufacturing / v.14, no.1, 2020 , pp. 1-7 More about this Journal
Abstract
In this study, the variation of the shrinkage in the thickness direction of the molded parts according to the gate size of the polymer core fabricated through the 3D printer using the SLS method was studied. The polymer cores are laser sintered and the powder material is nylon base PA2200. The polymer cores have lower heat transfer rate and rigidity than the metal core due to the characteristics of the material. Therefore, the injection molding test conditions are set to minimize the deformation of the core during the injection process. The resin used in the injection molding test is a PP material. The packing condition was set to 80, 90 and 100% of the maximum injection pressure for each gate size. The runner diameter used was ∅3mm, and the gates were fabricated in semicircle shapes with cross sections 1, 2, and 3 ㎟, respectively. Thickness measurement was performed for 10 points at 2.5 mm intervals from the point 2.5 mm away from the gate, and the shrinkage to thickness was measured for each point. The shrinkage rate according to the gate size tends to decrease as the cross-sectional area decreases as the maximum injection pressure increases. The average thickness shrinkage rate was close to 0% when the packing pressure was 90% for the gate area of 1mm2. When the holding pressure was set to 100%, the shrinkage was found to decrease by 3% from the standard dimension due to the over-packing phenomenon. Therefore, the smaller the gate, the more closely the molded dimensions can be molded due to the high pressure generation. It was confirmed that precise packing process control is necessary because over-packing phenomenon may occur.
Keywords
3D printing Nylon powder; Gate size; Injection molding; Packing pressure; Polymer core; SLS;
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  • Reference
1 Zonder, L. L., Nadav, S., "Precision prototyping: The Role of 3D Printed Molds in the injection Molding Industry", White Paper by Stratasys Inc, 2013
2 Kovacs, J. G. "Thermal simulations and measurements for rapid tool inserts in injection molding applications," Applied Thermal Engineering, Vol. 85, pp. 44-51, 2015.   DOI
3 Hassan, H., Rehnier, N., Arquis, C. E. and Defaye, G., "Moldling the dffect of cooling system on the shrinkage and temperature of the polymer by injection molding," Applied Thermal Engineering, Vol. 30, pp. 1547-1557, 2010.   DOI
4 Marin, F., Miranda, J. R. and Souza, A. F., "Study of the design of cooling channels for polymers injection molds," Polymer Engineering and Science, Vol. 58, pp. 552-559, 2017.
5 Hassan, H., Rehnier, N., Le Bot, C. Pujos, C. and Defaye, G., "3D study of cooling system effect on the heat transfer during polymer injection molding," Int. J. Therm, Vol. 49, pp. 161-169, 2010.   DOI
6 Cho, S. W., Kim, J. S. Yoon, K. W. and Kim, J. D., "An experimental study of injection molding for multi-beam sensing lens using the change of gate geometry," Transactions of Materials Processing, Vol. 20, pp. 333-338, 2011.   DOI
7 Lyu, M. Y., Mo, J. H., Chung, W. J., "Shrinkage in injection molded part for operational conditions and resins", Elastomers and Composites, Vol. 38, pp. 295-302, 2003.