Paper ID #7829 A Study of Process Variability of the Injection Molding of Plastics Parts Us- ing Statistical Process Control (SPC)

Process variability in the manufacturing of products is a serious concern, which, if left unchecked, could lead to product wastes, low productivity, and poor quality products 1. To prevent these unwanted effects from happening, statistical process control (SPC), a statistical tool, is used to monitor and control process variability. SPC assumes that manufactured products have measureable attributes such as mass, dimensions of the products, mechanical properties, and visual appearance to name a few. These attributes are affected by natural and assignable causes. Natural causes are inherent to the process and may include variables such as ambient temperature, machine vibration, and relative humidity- variables that are often very difficult to control. Unlike natural causes, assignable causes are controllable and may include items such as bad or worn-out machine components that should be replaced. By monitoring a process, an assignable cause is detected when process variability exceeds the expected range caused by natural causes. The primary advantage of SPC is that it detects a faulty process, which if corrected, prevents the manufacturing of defective products. This is unlike traditional qualit