Part Lot Grading Using CTQ Event Scores for Inspection Triage
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Solution Overview
Problem
Existing methods for determining the acceptance or rejection of part lots in high-volume production environments are costly due to the need for extensive manual inspection and sampling, which is inefficient and resource-intensive.
Innovation Solution
A system and method for post-production part lot grading that involves sampling parts during processing, identifying critical to lot quality (CTQ) events, assigning weighted values, calculating a part lot score, and making acceptance or rejection decisions based on these scores, thereby reducing the need for full inspection of all parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sampling plans are used to determine part lot acceptance, then inspection resources are reduced, but the risk of accepting defective lots increases
Solution Approach 1:
The system performs preliminary grading of part lots during production by capturing process data and CTQ events before final inspection. This preliminary action assigns grades (A, B, C, D) based on process capability and critical events, allowing downstream processes to pre-screen lots and focus detailed inspection only on graded D lots or those failing minimum thresholds, thus reducing inspection resources while maintaining quality assurance
Solution Approach 2:
The system implements feedback by continuously monitoring process data and CTQ events during production, using this information to dynamically grade part lots. The grade assignment provides feedback about lot quality that informs downstream inspection and processing decisions, enabling a closed-loop quality system that reduces waste while maintaining reliability
2Reliability
If manual inspection of all parts is performed, then quality control is improved, but cost of quality increases significantly
Solution Approach 1:
The system applies local quality by differentiating inspection intensity based on part lot grade. Graded A, B, and C lots receive minimal or no detailed inspection, while graded D lots receive full inspection. This localized approach to quality control ensures thorough inspection only where necessary, reducing overall inspection costs while maintaining quality control for problematic lots
Solution Approach 2:
The system uses partial action by inspecting only a portion of part lots (specifically, graded D lots and those below minimum thresholds) rather than all parts. This partial inspection approach is sufficient to catch defective lots while significantly reducing inspection costs compared to 100% inspection of all parts
3Reliability
If higher frequency and volume of part lots are inspected, then quality assurance is improved, but cost of quality increases
Solution Approach 1:
The system performs preliminary grading of part lots during production based on process data and CTQ events, assigning grades before downstream processes receive the lots. This preliminary action enables downstream processes to quickly identify and prioritize inspection of only those lots that require it (graded D or below minimum threshold), dramatically reducing the volume of parts requiring detailed inspection while maintaining quality assurance for high-risk lots
Solution Approach 2:
The system implements feedback by using process data and CTQ events to grade part lots, creating a quality signal that flows downstream. This feedback mechanism allows the system to adapt inspection volume dynamically - inspecting more when process conditions indicate higher risk and less when conditions are stable - thereby reducing overall inspection volume while maintaining quality assurance
Data Source
AI summary
A method, system and computer-usable medium are disclosed for determining acceptance or rejection of part lots after production. A part lot of parts is processed/machined. Parts are sampled in particular size and frequency during production. Critical to lot quality (CTQ) events that occur during sampling of parts are determined and monitored. Weighted values are assigned if CTQ events occurred for all the sampled parts. A production lot score is calculated based on the weighted values of the CTQ events. Acceptance or rejection of the part lot is based on the calculated lot score.