Six Sigma SPC - Statistical Process Control

Waste-Free Industrialized Systems
DFSS - Design for Six Sigma

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These articles are from the Six Sigma SPC Newsletter and other publications. All articles written by Jim Winings

How Can Product/Process Designs Be A
Factor To A Waste-Free Industrialized System?


100% functional purchased parts
and materials is the objective


Basic Principles of Design for Assembly/Formation


A. Design for assembly/formation

  • Minimize the number of parts.

  • Minimize assembly surfaces.

  • Design for z-axis assembly.

  • Improve assembly access.

  • Maximize part conformity.

  • Maximize part regularity.

  • Optimize part handling/placement.

  • Keep away from separate fasteners whenever possible.

  • Supply parts with basic "self-locking" features.

  • Push toward modular design.

  • Avoid mixtures of procedure/ process technologies.

  • Specialized piece part packaging is well-matched with the process's material handling and automation schemes.


B. Design for simplest flow (minimum parts, kits, subassemblies, test, paper work, etc.)

Why should testing be minimized? Testing is used to detect the presence of failures, (sometimes cause by external failures), induced by the industrialized process. Testing is


C. Design for minimum uniqueness/distinctiveness (common parts, processes, workflow, etc.)

How much does it cost in time and dollars to add a part?

Initial Cost

  • Drafting/changing the print
  • Securing/updating the print number
  • Changing the Bill Of Material
  • Print reviews by Development, Process, and Quality Engineering as well as the Purchasing department
  • Releasing of the new Print
  • Making and distributing the new print
  • Purchasing Quote cycle. Finding suppliers, etc.
  • Supplier survey
  • Possible tooling costs
  • Possible test equipment expenses
  • Qualification costs

On Going Cost

  • Inspection costs (training, etc.)
  • Stock costs (inventory, etc.)
  • Getting part to the assembly line
  • Storage for part on the assembly line
  • Added tracking and ordering for the production
  • Added purchasing tracking
  • Carrying cost (inventory turns)

You MUST work with you suppliers and become their partners in order to achieve 100% useable, (no waste in time or parts), incoming purchased materials. Designing the assembly for simplicity and minimum uniqueness helps in the removal of defects. This includes NOT having duplicate parts with different part numbers. This is a really large waste of resources based on the above information.


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Last Updated: Saturday, 15-Apr-06 19:47:36 PDT