Accessible Requires Authentication Published by De Gruyter November 7, 2013

The Effects of Processing Parameters on the Residual Wall Thickness Distribution at the Sharp Angle Corner of Water Assisted Injection Molded Parts

T. Pudpong, P. Buahom, S. Areerat, W. Rungseesantivanon, I. Satoh and T. Saito

Abstract

Water-assisted injection molding (WAIM) has been widely used for tubular plastic parts due to its advantages of relatively low cost and fast cycling time. However, the non-uniform distribution of the wall thickness, especially at the sharp corner, is still a basic problem in the WAIM process. This work presents the effects of sharp corner angles on wall thickness distribution in sections near corners for various processing conditions of the WAIM process, including melt temperature, mold temperature, water delay time, water holding time, and holding pressure. Three grades of polypropylene (PP) resins with different melt flow indices were studied using seven mold geometries that varied the angle of the sharp corner section. The wall thickness distribution at the corner sections were characterized in terms of inner and outer residual wall thicknesses, hollow core ratio, and the percentage of difference between the inner and outer wall thicknesses. In addition, computational fluid dynamic simulations with Moldflow Plastics Insight version 4.1 were performed for each sharp corner angle. It was found that the wall thickness distribution of the straight tube was more uniform than those of the curve tubes. Water injection delay time and water pressure were the major parameters that had a significant impact on the hollowed core ratios, while the percent difference between inner and outer wall thicknesses was mainly influenced by melt temperature.


Mail address: Surat Areerat, School of Chemical Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand, E-mail:

References

Knights, M., “Water Injection Molding Makes Hollow Parts Faster”, Plast. Tech., 48, 4247 (2002) Search in Google Scholar

Liu, S.J., Chen, Y.S., “Water Assisted Injection Molding of Thermoplastic Material: Effect of Processing Parameter”, Polym. Eng. Sci., 43, 18061817 (2003) 10.1002/pen.10153 Search in Google Scholar

Liu, S. J., Chen, W. K., “Experimental Investigation and Numerical Simulation of the Cooling Process in Water Assisted Injection Molded Parts”, Plast. Rubber Comp., 33, 260266 (2004) 10.1179/174328904X4882 Search in Google Scholar

Liu, S. J., Hsieh, M. H., “Residual Wall Thickness Distribution at Transition and Curve Section of Water-Assisted Injection Molded Tubes”, Int. Polym. Proc., 22, 8289 (2007) Search in Google Scholar

Liu, S. J., Lin, S. P., “An Experimental Study of Water-assisted Injection Molding of Plastic Tubes with Dimensional Transitions”, J. Reinf. Plast. Compos., 26, 14411453 (2007) 10.1177/0731684407079756 Search in Google Scholar

Liu, S. J., Wu, Y. C., “Dynamic Visualization of Cavity Filling Process in Fluid-assisted Injection Molding-Gas vs. Water”, Polym. Test., 26, 232242 (2007) 10.1016/j.polymertesting.2006.10.008 Search in Google Scholar

Michaeli, W., Juntgen, T. and Brunswick, A., “WIT-En Route to Series Production: First Industrial Application of the Water Injection Technique”, Kunststoffe Plast. Eur., 91, 3738 (2001) Search in Google Scholar

Received: 2013-3-26
Accepted: 2013-8-19
Published Online: 2013-11-07
Published in Print: 2013-11-01

© 2013, Carl Hanser Verlag, Munich