Dr.-Ing. Bernd Mittmann

Dr.-Ing. Bernd Mittmann holds a Ph.D. in Engineering and a Diploma in Mathematics, both of University of Technology Berlin. Since June 2013 he is Engineer for Continuous Improvement at TRW Braking in Koblenz/Germany where he is leading Technical Problem Solving activities and related People Development. Prior to joining TRW he spent most of his career at Delphi Automotive Systems in Innovations and Continuous Methodology. He is certified Shainin Red X® Master, Six Sigma Black Belt and DFSS Black Belt.

 

 

 

 

Abstract

How the Human Factor Impacts the Technical Problem Solving Strategy

A problem solving investigation will be presented where different strategies have been successfully applied to reduce scrap and risk for the customer. The strategies and main results will be described. The strategies will then be compared regarding resources required to gain results. Also, the human factor will be highlighted: risk of misinterpretation of data and easiness of getting team consensus is different for the strategies applied here.

A new production line had been established in China adding capacity to an existing line in a plant in Europe. This new line produced parts that did not pass leak test the first time; the European line ran with almost 100% First Time Quality. An additional hurdle in this case was instability of leaking parts; they wouldn’t show leak all the time they were tested and leak rate varied drastically.

Swapping components of pairs of extreme parts allowed the team to quickly identify the components valve body, key and control unit contributing to high values of the product performance index, i.e. leak rate. Because of the instability it was difficult to quantify the level of contribution for each of these three components.

Considering the line to line contrast, a series of studies was performed importing valve bodies, keys and control units from Europe and assembling these with the remaining components from Chinese suppliers on the production line in China. Tracking the line performance index, i.e. First Time Quality demonstrated that the valve body had the strongest effect on failure rate.

With this focus, measurements of dimensions critical for the sealing function were taken on valve bodies from Chinese and European supplier. A dimension had been identified that was out of the desired range for the Chinese supplier. Finally, a confirmation test was conducted and passed, giving 95% statistical confidence that the anticipated tool change to correct the critical dimension would yield the desired improvement of First Time Quality. The tool had then been modified and this failure mode was eliminated.

This case demonstrates that working with the product performance index leak rate only few parts were needed and results were available within few days. This index hit the individual part behavior directly, quickly and with high resolution. Time and money needed were minimal. But this type of index is technically more complex, and with the significant variation of data due to part’s instability communication wasn’t always easy. No matter what the standard of communicated material is, there is always room for misinterpretation. People of different functions have different background and interests, again leading to dispute about the validity of the results.

Results of the study using the line performance index First Time Quality were much more easily understood and all team members agreed without dispute to the conclusions. But this strategy consumed much more time and money shipping parts around the world.

For future root cause analysis studies it is recommended to select the appropriate strategy not only based on aspects like resources needed but also on the criticality of communication of results.

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