Replicated Defects in Stamping A Multidimensional Approach with Motivation Theory and Signal Detection

Due to the nature of automated machinery, a fault in the stamping presses results in a replicated defect where each consecutive part is produced defective. A stamping company in Illinois, possessing six stamping machines is the focus of this intervention. This company produces stamped parts used in consumer vehicles. One such stamped part is a friction shoe similar to that present in multiple Toyota vehicles. These friction shoes are used in applying force between a pad and the traveling portion of the pedal assembly to cause friction. This part is made of a type of spring steel within the SAE 1XXX series of carbon steels. Due to a replicated defect of the friction shoe, the accelerator pedal of the affected vehicles became stuck when depressed. The defective friction shoe lead to the deaths of multiple vehicle owners and ultimately resulted in over 2 million vehicles being recalled and cost Toyota over 1 billion dollars. While this part is not produced at the focus company, similar parts are produced at the facility. The company has on average 21 uncontrolled replicated defects annually, resulting in about 2.3% of all parts produced to be defective due to replicated defects. The number of uncontrolled replicated defects must be reduced. As the level of the worker’s attention increases, the number of undetected replicated defects decreases. Employees monitoring presses are the main factor in replicated defect detection. Signal detection theory describes the effectiveness of operators detecting defects, dictated by the worker’s level of attention. The state of attention was determined by work sampling. 79% of the time, workers are in a low attention state. Low attention is due to low worker motivation. From McGregor’s motivation theory X and Y, it was observed theory X was in place. Managers employing theory X assume that employees dislike work and are incompetent. As a result, workers dislike their work and will avoid responsibility. By contrast, managers employing theory Y assume that employees take pride in their work and are willing to take initiative and perform difficult tasks if they are involved in decision-making. To increase worker motivation, McGregor’s theory Y was utilized. The intervention involved the replacement of the previous quality manager with a new manager. The operators were involved in decision-making and treated as competent. Following the intervention, now only 37% of the time the workers were unable to detect defects. Only one uncontrolled replicated defect occurred in the following quarter, reducing the expected annual impact to about $3,000, a 93% improvement. Implementing theory Y improved worker morale which lead to an increase in operator attention. The number of undetected replicated defects was reduced.