Planning inspection strategies in assembly manufacturing processes by modeling defect generation

The increasing complexity of manufacturing processes requires even more accurate quality inspections to check whether specifications and functional requirements are satisfied, and to identify defects and/or anomalies. In literature, many studies focus on the identification of factors which may cause defects (e.g., improper design, defective part, variance in assembly system, and operator error). For each produced workpiece, different types of defects may be identified: randomly distributed, systematically distributed, or a combination of both. This paper presents an attempt to define models of defect generation in assembly manufacturing processes, in order to get reliable estimates of the probability of occurrence of defects at each production step. These models are useful in the design of quality inspection strategies for short-run productions for which traditional approaches, such as statistical sampling, may not be performed. The proposed models are applied to a case study concerning the assembly of hardness testing machines.