Once deviations are identified, it’s essential to clearly identify the affected parts and their scope, so as to prevent problematic products from continuing to be used in production. Clear labeling and isolation measures can help preserve factual information for future analysis.

Control the scope first, then analyze the causes

Once nonconformities are identified, it’s important to identify other products that may also be affected under the same conditions, processes, or circumstances. On-site personnel should temporarily halt the flow of products and record the status of the products, preserving evidence for further investigation. This prevents hasty decisions when information is incomplete.

Use facts to test assumptions about causes

dimensional deviations may be related to procedures, clamping methods, tools, materials, or measurement techniques. During analysis, possible causes should be listed, and each cause should be verified using records and rechecks. Simply attributing the problem to human error often fails to explain why existing control measures failed to detect the issue.

Cause analysis should distinguish between phenomena and causes, and verify this by reviewing records, physical samples, and on-site conditions. Treatment plans must undergo appropriate review, and acceptance criteria should not be changed based solely on experience.

Do not confuse handling with improvement

Rework or repair addresses the current product, while corrective actions address the mechanisms that caused the problem. Both should be documented separately. For issues involving design requirements, it’s also necessary to obtain appropriate review conclusions. Changing records alone won’t make the product appear to meet the requirements.

Check the effectiveness of measures before closing the issue

After implementing training or updating documents, it’s important to observe whether subsequent batches are followed according to the new requirements, and whether the original problems reappear. Verification of results can be done by combining process records with actual inspections. Only when evidence supports the effectiveness of the measures can the problem be considered properly resolved.

Process example: Why is it necessary to investigate the reasons after rework?

Assume that a batch of parts exhibits deviations in their positions in the same direction. Rework is performed to bring the dimensions back within acceptable limits, but the issue with clamping and positioning remains unresolved. In the next batch, if the same conditions are applied, similar deviations may occur again. When dealing with this situation, it’s necessary to separate the handling of individual parts from the correction of the underlying causes, and document both clearly. Only by verifying the effectiveness of corrective measures through targeted inspections in subsequent batches can we ensure that the problem has truly been resolved through process improvement rather than temporary fixes.

Common questions: Is a large-scale investigation required for every exception?

The depth of investigation should be appropriate to the risks and recurrence patterns. The focus should be on generating evidence that supports judgments, rather than using complex procedures or simply categorizing issues as random occurrences.

Key points for verification during implementation

• The scope has been controlled
• There is evidence for the causes
• Handling has been reviewed
• The effects have been verified

Before closing a problem, it’s essential to confirm that measures have been implemented and their effectiveness has been verified. Incorporating effective measures into relevant documents helps reduce the likelihood of similar problems occurring again.