Good quality means controlling the important factors!

statistical process control

To improve quality, it is important to consider all factors that can be significant for product quality. Start with process mapping to identify variables that can affect product quality.

All processes are subject to variation, which may be classified as random / noise (common cause) or assignable cause variation (special cause). 

Common cause variation is found in all processes and exhibits random yet stable variation that is predictable within calculated process control limits. Common cause variation is synonymous with natural variation, expected variation, or random variation.

Special cause variation, on the other hand, is unpredictable, sporadic, or unstable variation. It is the result of a specific assignable cause, for example Machine (Equipment), Man (Operator), Material, Method, Milieu (environment) & Measurement (referred to as 6M in a Fishbone).

Humidity is an example of specific assignable cause (Milieu) that can be controlled. The challenge of quality assurance is to identify the critical factors and control that the variation of them are within allowed tolerances. 

Six Sigma involves statistical tool to understand variation and identify critical factors. It is important to know the critical factors of your processes to avoid spending time controlling non-important factors and failing to launch new products. Lean Tech has experienced both scenario's. In the last scenario, the variation of product quality was unacceptable for the customer. If critical factors are unknown it's hard to reduce variation. 

What are the critical factors of your processes? Regression analysis, Component of Variation - CoV & Design of Experiment can help you decide the critical variables.

How do you control the variation of critical factors? Critical factors can be monitored using Statistical process control - SPC. Lean Tech has made a video about SPC application. Here is an example of implementation of online statistical process control - SPC (Norwegian article) at Axis-Shield. 

References

  • value stream mapping"I was very impressed with Sissel's Lean Six Sigma knowledge. She makes it easy to identify improvements and create results"
    - Daryl Powell, Lean Manager, Kongsberg Maritime SubseaValue stream mapping
  • Lean engineering"Sissel has worked as part of Cambis project team for two of our projects. Her main focus has been on process design, engineering and procurement. Sissel has proven herself as a competent and committed employee. She has been an important contributor to make good progress in the projects she has worked with. At the same time she is accurate and has good quality of the work she performs."
    - Eivind Willoch, Project Manager, Cambi AS lean engineering
  • benchmarking"We are very happy with the work carried out. We was not very clear what the order was, but with your background and expertise the outcome was what we were looking for and a document we will benefit from in the future"
    - Roger Søråsdekkan, Site Leader at Allnex, Norwaybenchmarking
  • monitoring program"We hired Lean Tech to develop monitoring program for air emission. The monitoring program should satisfy requirements from the Norwegian Environment Agency including sampling frequency to ensure representative samples, uncertainty estimates, calculations and preparation of reporting templates, etc. The assignment was delivered with the correct content at the right time. Recommended." monitoring program
    - Kjell Even Misfjord, SHE manager at Allnex, Norway  
  • monitoring program"Sissels ability to quickly understand the issue, as well as her commitment and expertise is impressive. Her analytical and thorough contribution to our monitoring program has been precise and targeted, and very educational. " monitoring program
    - Thomas Løvik, HSEQ advisor at TWMA, Norway