Mistake Proofing

Error: Is the cause of a defect
Defect: Is the result of an error

Source of Defects – Errors
1. Processing omissions
2. Processing errors
3. Errors in set up
4. Missing parts
5. Wrong parts used
6. Operation errors
7. Adjustment or measurement error
8. Error in equipment maintenance

Human error
Many defects occur because of a human error.
8 areas of human error

Error ExamplePossible Solutions
1. Forgetfulness Forgetting to do something due to a lack of concentration Alert operators of mistake or perform regular checks
2. Misunderstanding
Jumping to conclusions due to a lack of familiarization Training & standardization
3. Misidentification Misjudgments due to viewing something too quickly or from too far away or due to lack of attention Training, easier methodof identification and attentiveness
4. Insufficient Experience
Mistakes made due to a lack of experience in any particular operation Training & standardization
5. Willful Errors Ignoring of rules or proper procedures & methods Education and discipline
6. Change in Pace / Product Changes in process could result in loss of pattern and disorientation, resulting in mistakes Standardization &attentiveness
7. Lack of Standards
Mistakes made due to a lack of suitable instructions or visual samples Boundary samples work instructions and procedures
8. Surprise Errors
Errors can occur when equipment runs differently than expected Total productive maintenance and standardization

Product Description Defect Cost / Consequence Where Detected Where Made Elapsed Time
What product isaffected? What is defect? Did the defect result in rework/scrap? What % or cost? Where was the defect found in the process or at the customer Where did the defect occur in the process? How much time passed? Or how many operations did not detect the defect?


Red flag conditions
As noted previously, errors in any of the 5 areas of the process can result in defects. During the APQP process, someconcerns may arise where there is a high possibility of error in processing and the potential for a resultant defect. These conditions are termed “red flag conditions”.


1. Adjustments
Adjustments are required when a piece of equipment, fixture or tool must be brought into correct position or alignment, with respect to the product, in order to manufacture a part to specifications. A microadjustment suggests we make small adjustments.
Red flag: oftentimes, adjustments are made by what looks of feels right according to experience, opinion or intuition. This can result in errors or adjustments and a resultant defect. The tendency to make numerous errors increases with the number of adjustments that must be performed.

2. Tooling changes
Tooling changes are required when a part of themachine, fixture or tool needs replacement, or where a different specification or product is required
Red flag: broken or worn tooling can result in defects being produced. Likewise the subsequent changing of tooling may require adjustment or setting that can be done improperly and could result in defective parts.

3. Precise dimensions or critical conditions
At times, precise dimensions ormeasurements are required to establish the correct location of features on the product. Likewise, critical condition settings like correct temperature, pressure, speed, etc may be required to produce a part to specification.
Red flag: precise dimensions / conditions leave little room for deviations or error. Errors often result due to the level of operator skill, machine or material characteristicsand operating conditions.

4. Many parts / mixed parts
Where an assembly requires many parts be installed or where parts may be mixed when presented at the work cell.
Red flag: where a work cell contains many different parts it is important to select the right part in the right quantity. This can be difficult if the parts are similar in size, shape and color. The higher the complexity of a...