Dr. Marlene Smith
University of Colorado Denver
Objective
Explore the effectiveness of different sampling plans in detecting changes in the occurrence of manufacturing defects.
Background
Defect sampling is used in industrial settings to determine the types and amounts of defects in manufactured items. Items at various stages of production are removed from the process and inspected for defects. Sustained testing allows operations managers to discover whether some part of the manufacturing process is failing to meet performance criteria and product standards. To minimize manufacturing defects, early detection and problem resolution are critical.
ACME Manufacturing produces electronic components used in the assembly of industrial robotic equipment. The components are technologically sophisticated, and quality must be rigorously monitored to ensure that specifications are met. Of course, inspection can be a time consuming and costly activity. ACME production managers must determine how much sampling and testing is needed to minimize costs and maximize yields.
In the current sampling plan, one component from the production line is randomly selected every 15 minutes. Each component is inspected and tested for major and minor defects. Major defects, which affect component performance, must be addressed immediately. Fortunately, major defects are rare and are generally contained and corrected early in the process. Minor defects, such as nicks and scratches, are those that affect the appearance of a component but not its functionality. Monitoring minor defects to ensure the rate doesn’t increase is of particular concern to ACME management.
The Task
ACME currently inspects one part every 15 minutes during an eight hour shift. Production managers have complained this sampling rate is too high, which has driven up costs and decreased output. They suggest implementing sampling plans involving fewer parts.
In this case, we explore the effectiveness of the current defect sampling plan, and several alternative plans, in detecting changes in the occurrence of minor defects.