No book, website or article explicitly explains when and how to implement poka-yokes in your production process. On this page we want to give our advice based on practical experience how to manage a poka-yoke project.
When to implement?
A quote from Praveen Gupta covers the answer: “One error is human, two errors are a warning and 3 errors shout for poka-yoke implementation”.
For each error caused by human intervention, a poka-yoke can be installed. Of course it needs to be judged based on severity and occurrence if the poka-yoke is worth implementing or not.
Poka-yoke is only relevant when your process is stable and when you are producing in one-piece flow. If you produce in batch, you could potentially need to scrap a large lot of material.
How to implement?
We recommend using the DMAIC (Define, Measure, Analyse, Improve, Control) method which is often used in Six Sigma projects for improving processes.
- Identify the product and process in scope
- Analyse customer requirements
- Select a cross-divisional team (operator, team leader, quality inspector, process and product engineer, maintenance engineer, …)
- Define the defect/error
Depending on the stage of the product life cycle, the problem can be identified during development stage or during serial production stage.
- Brainstorm on possible mistakes/errors. Quantity is more important than quality of the ideas. Do not critisize.
- Make DFMEA and PFMEA studies and define Risk Priority (RPN).
- Collect lessons learnt from previous projects.
- Serial Production
- Analyse internal and external PPM (Parts Per Million).
- Analyse customer claims.
- Brainstorm on other possible mistakes/errors.
- Define the Current State
- Make a process flow and think where human errors can occur
- Define the Control Plan
- Define the capability results
- Define internal and external scrap results
- Create awareness on the problem
- Ensure management support. This is often overseen but a mandatory requirement to ensure implementation and maintenance of the poka-yoke system. Management must free up time and resources for dedicated work teams to analyse problems and create solutions. Kaizen teams and incentive-based suggestion systems can support to encourage operators to solve the problems that result in defects.
- Prevent finger pointing at operators. It is normal that defects can occur. Make this clear from the beginning.
- Where to begin?
- Focus on operator intensive work areas which are susceptible to stress and interruption.
- Focus on processes with high product mix ratio.
- Focus on processes with similar set up, tools, configurations, components.
- Focus on processes with similar start but different finishing.
- Focus on processes where orientation and positioning are key for defect prevention.
- Confirm stability and capability of the process.
- Measure PPM
- Measure defect ratio (internal and external)
- Measure customer claims
- Prioritize defects based on Pareto results
- Prioritize defects based on RPN values
- Analyse by means of histograms, scatter plots, run charts, control charts
Perform a root-cause analysis on the most critical defect.
- 5-Why and Ishikawa: the link between cause and effect must be clear.
- Consider elimination of the process step and non-value adding activities.
- Brainstorm on potential poka-yoke devices. A poka-yoke should not be perfect. If it improves a portion of the defect occurrence, it is already worth implementing. Do not criticize other people ideas. It could form the base of the final poka-yoke device. Focus on idea generation, not on judgement.
- Keep it simple.
- Select the most effective and efficient poka-yoke device.
- Think of ways to make the mistake impossible to take place
- replacement of the operation
- elimination of the operation
- facilitate the action (make the operation simpler, more easy than making the mistake itself)
- Think of loop-holes in the poka-yoke. If you can by-pass the poka-yoke, you did not choose properly. e.g. using a system that forces 2 hands on 2 buttons, ensure they cannot just be taped or covered with something else.
- Prioritize on prevention. If the error cannot be prevented, consider detection systems to minimize the impact.
- Setting method
- control method
- fixed-number method
- sequence method
- Regulative action
- control action
- shutdown action
- warning action
- Inspection method
- judgement inspection
- informative inspection
- point-of-origin inspection
- Setting method
- Make an action plan to implement the poka-yoke device
- Follow up on the implementation progress by means of a follow-up list that contains action description, responsible, due and status.
- Implement the poka-yoke. Install the device and validate it. Update work instructions and control plan accordingly. Train members to the new way of working.
- Try to implement poka-yokes early in the development phase. It will improve effectiveness and will result in lower costs due to no need for later modifications. If you implement it only at Start of Production of the project, the implementation costs will be a lot higher.
- Test with quick feedback methods.Use red rabbits (defects created on purpose) to validate of the poka-yoke prevents or detects the defect.
- Evaluate the effectiveness by monitoring your key performance indicators.
- Recognize people efforts.
- Initiate continuous improvement. There is no need for 100% success ratio from the beginning.
- Continue until requirements are met. After, consider challenging the requirements.
- Maintain the poka-yoke. Ensure usage of the poka-yoke. Do not allow exceptions. Go and check on different occasions, different shifts, diffferent days, …
Resistance for implementation
Barriers for implementation of poka-yoke will be abundant. Most often, poka-yokes are not installed due to resistance to change from management or operators. Also the investment necessary might form a blocking point.
To overcome these burdens, a well executed Define Stage is mandatory.
Practical Case Study
A case study will be provided in the future.
Note: Multiple sources were used for summarizing the content on this page. You can find these sources on the following page: References.