Water-Assisted Injection Moulding

KATHOLIEKE HOGESCHOOL LIMBURG
Departement Industriële Wetenschappen en Technologie

Water Assisted Injection Moulding: A Study on the Influence of Melt and Process Parameters on the Residual Wall Thickness and the Occurrence of Part Defects for PA6.

Gielen Bjorn, Heynickx Lien, Van den Brink Dominique, Vandersteegen Jochen

Water Assisted Injection Moulding: A Study on the Influence of Melt and Process Parameters on the Residual Wall Thickness and the Occurrence of Part Defects for PA6.

Gielen Bjorn, Heynickx Lien, Van den Brink Dominique, Vandersteegen Jochen

Received 7 March 2011
Abstract
Although water assisted injection moulding is a relatively new and advanced technique to produce hollow parts, several problems which reduce the product quality can occur. Namely, water inclusions in the wall, severe fingering and double wall defects reduce the product part stiffness. This study investigated the effect of the process parameters water volume flow rate, water injection delay time and melt temperature on the part defects to obtain a better understanding of the formation of these part defects. The effect on the residual wall thickness and the weight of the products was also investigated. Three materials were used: two polyamides and one polypropylene as a reference. The experiments were carried out on an injection moulding machine equipped with a water-injection unit to produce hollow handles. The parts were weighed before and after drying, their wall thickness was measured and their percentage of defects was calculated in order to determine the influence of the processing parameters. IR images and pressure profiles ware also used to investigate possible detection methods for part defects. It was found that all the investigated parameters have a significant influence on the residual wall thickness and part defects. Their ‘ideal’ settings depend on the material and the desired properties since small wall thicknesses and few part defects do not always

References: [1] Knights, M. (2002). Water Injection Molding Makes Hollow Parts Faster, Lighter [2] Liu, S.-J., & Lin, M.-J., & Wu, Y.-C. (2007). An experimental study of the water-assisted Composites Science and Technology, pp. 1415- 1424. [3] Liu, S.-J., & Hsieh, M.-H. (2007). Residual Wall Thickness Distribution at the Transition Polymer Engineering and Science, pp. 1806- 1817. [5] Liu, S.-J., & Wu, Y.-C. (2007). Dynamic visualization of cavity-filling process in fluid- [6] Liu, S.-J. (2009). Water Assisted Injection Molding: A Review [8] Chavarria, F., & Paul, D.R. (2004). Comparison of nanocomposites based on nylon 6 and nylon 66. Polymer 45, pp. 8501-8515. [9] Li, D., Liu, Q., Yu, L., Li, X., & Zhang, Z. (2009) Surface Science 255 pp. 7871-7877. [10] Sannen, S. (2010). Polyamides. Intern presentation of Catholic University Leuven. [11] Su, K., Lin, J., & Lin, C. (2007). Influence of Reprocessing on the Mechanical Properties [12] Fornes, T., Yoon, P., Keskkula, H., & Paul, D. (2001) matrix molecular weight. Polymer, pp. 9923- 940. 6 Clay Nanocomposites. Polymer 44, pp. 2441-2446 [14] Steeman, P. & Nijenhuis, A. (2010). The Effect of Random Branching on the Balance [16] Meng, Y. Z. & Tjong, S. C. (1996). Rheology and morphology of compatibilized polyamide [17] Acierna, S., & Van Puyvelde, P. (2005). Rheological Behavior of Polyamide 11 with [18] Chow, W., Bakar, A., & Ishak, Z. (2005). Water Absorption and Hygrothermal Aging [19] Liu, S.-J., & Lin, S.-P. (2005,april). Study of ‘Fingering’ in Water-assisted Injection [20] Lin, K.-Y., & Liu, S.-J. (2009). The Influence of Processing Parameters on Fingering [21] Walter Michaeli, E.H. (2010). ‘Perspective Kunststofftechnik berichte 2010’ IKV- [23] Huang, H-X., & Zhou, R-H. (2009). Preliminary investigation on morphology in [24] Liu, S.-J., & Wu, Y.-C. (2006). A Novel High