Integration of Industrial and Manufacturing Systems Engineering Using a Microprocessor Controlled Injection Molding Machine: Applications of Statistical Process Control

An independent study project was developed to apply the principles of statistical process control (SPC) to polymer processing using a new microprocessor controlled injection molding machine, purchased through a 1994 Instrumentation and Laboratory Improvement (ILI) award from the National Science Foundation. The project began with a machine capability study and an investigation of the SPC package on the machine. An investigation of the repeatability of specimens produced included mass, length and thickness measurements. Following this, a simulation designed to vary the viscosity of the material being processed was undertaken, and the SPC methods and measurements previously defined were applied in order to determine which machine monitors were capable of detecting slight changes in viscosity typical of material contamination. The hydraulic pressure applied when the machine switched from filling to packing the mold cavity proved to be excellent in detecting changes in material viscosity within only a few machine cycles. Use of this SPC technique can therefore halt production of polymer parts leading to poor quality soon after material contamination - or any other process variation leading to a change in material viscosity - occurs.