Abstract:
Based on the current setting of Polypropylene injection process in selected
factory, there are 5,500 pieces of incomplete shape per month which is cost about baht
110,000 or it is about 9.5 percent per production lot size. Based on the analysis, the
factors influenced on the incomplete shape are plastic melt temperature before the
injection, holding pressure, cooling time, injection speed, and proportion between
recycle polypropylene (RPP) and new polypropylene (NPP). The 25 factorial
experimental design with 2 replicates at significant level of 0.05 is then conducted in
order to determine the optimal setting for these factors. The result shows that the
minimum number of incomplete shapes are obtained at 220°C of plastic melt
temperature before the injection, 10 MPa of holding pressure, 15 seconds of cooling
time, 30 mm/s of injection speed, and 90:10 of proportion between RPP and NPP (old
ratio; 80:20). Based on this setting, the number of incomplete shapes can be reduced to
only 3.58 percent and the selected factory can also reduce the NPP by 10 percent which
leads to cost saving about 67,950 baht per month.