Work Instructions for Mistake Proofing

1. Use cross-functional teams (CFT) approach to mistake proofing.

2. Selection of process for mistake proofing.

During the third phase of advanced product quality planning (APQP), the CFT shall identify the processes, where, due to avoidable human errors, the rating of “occurrence” and/or “detection” have increased thereby increasing the risk priority number (RPN) for the process. Poka-yoke techniques of mistake proofing are applied to these processes in order to lower the ratings of occurrence and/or detection.

Analysis of customer complaints also reveals activities which are in need of mistake proofing, in order to achieve a zero defect level of working. CFT will undertake application of poka-yoke techniques to these processes.

3. The selected mistake proofing technique should qualify the following criteria:

  • Inexpensive
  • Based upon common sense, preferably of the operator or the first line employee
  • It MUST eliminate occurrence/detection of the problem at the source itself

4. Occurrence oriented poka-yoke should follow the procedure as below:

First classify the source of occurrence as follows:

  • Required action is NOT performed or is performed incorrectly.
  • Undesired action is exercised.
  • Information essential for performing the action is mis-interpreted.
  • Mistake occurs due to complexity.

After having classified the source, apply one of the following techniques, as appropriate, to prevent the occurrence:

  • Use of 100 percent prevention devices such as fouling pins; contoured locators or templates; proximity or photo-electric sensors; limit- or micro-switches; warning lights or buzzers; or pressure transducers.
  • Design to modify to ensure that in assembly the parts shall not join if aligned wrongly. The machine will not run if operators’ hands or feet are not outside, or if the job and tooling are not in right position.
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These techniques should be integral part of the process. The devices are placed sufficiently close to where the mistakes occur, providing fast feedback to the operator, of mistakes occurring.

5. Detection oriented poka-yoke should use one of the following techniques for ensuring 100 percent detection of the mistake:

  • It should be autonomous inspection occurring without intervention.
  • It should be 100 percent inspection which occurs without intervention.
  • It should determine before-the-fact whether the conditions for 100 percent quality exist or not.
  • It should make the error visible to the operator.
  • Consider supply of exactly made kits of components to the assembler, so that any balance part will signal error in assembly.
  • Consider use of electronic sensors to activate warning lights or buzzers.
  • Use color coded parts or graphics.
  • Make use of contact devices (e.g., fixtures, limit switches, probes or non-contact devices such as LEDs and pressure transducers).

6. Effectiveness of the applied poka-yoke technique should be judged after observing the performance, for a period on minimum one month.

Comments 3

  1. Rob Tahamtan

    Some useful hints when developing a Poke Yoke process:

    1. Start with a list of lessons learned or root-cause analysis. If neither is available, start with a list of issues

    2. When approaching a problem, develop a process map such that there is only one factor or motion is involved. (i.e: Steps involve in mating 2 connectors: direction of motion, alignment, angle of approach, self alignment features, line of sight, number of opportunities for mating (presence of insertion key), self locking, etc.

    3. Use FMEA (Failure Mode Effect Analysis) to quantify and prioritize risk for each of process step

    4. Ensure balance between defect cost vs. defect cost avoidance. This is one area that at times, a $1 is spent in design corrections to save a dime in manufacturing process.

  2. hui

    I searched and saw that CFT actually means cross functional teams.

    So does it mean the members of the team should brain storm ideas on mistake proofing ?

    Anyone has a structured approach on getting the cross functional teams to work , esp in a warehouse ?

  3. Raimo

    Great article, but … (re: “It MUST eliminate occurrence/detection of the problem at the source itself”)

    I would add:
    ‘ The solution must be validated to be effective on all possible alternative routes.’

    Now you say “It MUST eliminate … detection of the problem at the source itself”. … oops, you missed to include devil’s advocate to the team :-P


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