Optimization of Injection Moulding Process Parameters in the Moulding of Low Density Polyethylene (LDPE)

Injection moulding is one of the most popular polymer processing methods due to its high production rate as well as its ability to produce very intricate geometries at very cheaper cost and within few seconds. There are several flaws which occur while producing plastic parts by Injection moulding, like warpage, shrinkage, flash, sink marks etc. Shrinkage is one of the most critical problems which causes dimensional changes in the parts during the moulding process. Shrinkage can be minimized by setting optimal process parameters on injection moulding machine. In this study, optimal injection moulding conditions for minimum shrinkage during moulding are found by DOE technique (Taguchi method). Different observations were taken for a material namely Low Density Polyethylene (LDPE). Taguchi method is used to investigate the effects of melting temperature, injection pressure, refilling pressure and cooling time on the shrinkage of LDPE. Taguchi method has two main instruments, which are signal-to-noise (S/N) ratio and orthogonal arrays. S/N ratios were used for determining the optimum combinations of the process conditions for shrinkage. The S/N ratio takes both the average and the variability of the quality characteristics into consideration. The results showed that the cooling time was the most effective factor for LDPE followed by refilling pressure and injection pressure was found to be the least effective factor.