Statistical Quality Control Method for Manufacturing Parts
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Solution Overview
Problem
Current quality control methods in manufacturing, particularly in the aeronautical industry, face challenges in balancing increased throughput with stringent quality requirements, often resulting in overly restrictive controls that impede production due to high tolerance for parts in non-conformity, such as 2700 ppm, which can be excessively conservative.
Innovation Solution
A method that calculates the mathematical expectation of parts in non-conformity based on statistical indicators like the capability index Cpk, allowing for more precise and reliable control reduction by comparing this expectation to a threshold value, thereby optimizing production parameters to meet quality specifications while reducing unnecessary restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If statistical controls are performed on all parts manufactured, then quality assurance is improved, but manufacturing throughput is considerably impaired
Solution Approach 1:
The patent divides the manufacturing population into sampled parts and non-sampled parts, performing detailed statistical analysis only on the sampled portion while using statistical inference to assess the entire population, thereby reducing control costs while maintaining quality assurance
Solution Approach 2:
The patent extracts a representative sample from the manufacturing population to perform quality control analysis, separating the control function from the entire production flow and applying it only to a subset, which reduces the burden on overall manufacturing throughput
2Reliability
If production is stopped completely when excessive quality defects are detected, then quality control is improved, but production efficiency deteriorates
Solution Approach 1:
The patent implements dynamic control by continuously monitoring statistical indicators and adjusting production status accordingly, allowing production to continue when quality metrics are acceptable and stopping only when necessary, rather than using static stop-go approaches
Solution Approach 2:
The patent establishes a feedback mechanism where statistical indicators from sampled parts are used to monitor and regulate the manufacturing flow in real-time, enabling continuous quality improvement without complete production stoppages
3Manufacturing precision
If a high capability index threshold (e.g., Cpk=1.22) is required for batch acceptance, then quality specification compliance is improved, but the number of required controls increases
Solution Approach 1:
The patent changes the control parameter from requiring a high capability index threshold (Cpk≥1.22) to using a mathematical expectation of non-conformity proportion (Eppm), which provides equivalent quality assurance with reduced control requirements
Solution Approach 2:
The patent discards the overly conservative Cpk threshold approach and recovers quality assurance through a more efficient statistical metric (Eppm) that directly measures the expected proportion of non-conforming parts, eliminating unnecessary controls
Data Source
AI summary
The invention pertains to a method of manufacturing a population of parts produced with a manufacturing device, based on the analysis of at least one statistical indicator representative of a characteristic dimension of the parts, according to which: a) a sample comprising a number n of parts is collected from among the parts produced with the manufacturing device; b) the characteristic dimension of each part of the sample is measured, and a measured value of the statistical indicator is calculated for the sample; c) a mathematical expectation of the proportion of parts which are noncompliant with respect to a specification regarding the characteristic dimension is calculated, said calculation being performed on the basis of the measured value of the statistical indicator for the sample collected and of the number n of parts of the sample; d) the mathematical expectation of the proportion of parts that are noncompliant calculated is compared with a threshold value of proportion of noncompliant parts; e) the manufacture of the parts is steered as a function of the results of the comparison of step d).