Food for Thought "If you have the right people, with good, basic values and good work ethic, you can have a tremendous journey."

Buy Now
Food for Thought 2 "The follow-up in my Food for Thought series, with more focus on my experiences with Six Sigma and Kaizen."

Buy Now: Paper Back
Buy Now: E-Book

January 28, 2013

Six Sigma: Get Back to the Basics

Filed under: Food for thought for friends,Services,Six Sigma — Alec @ 12:39 pm

Time to get back to basics. Making money and streamlining processes are such important steps in becoming or staying profitable. So here’s a little Six Sigma story to help illustrate my point.

One of the easiest, I mean strangest Green Belt projects I worked on involved solving a 1/8″ diameter pin quality issue. We started by doing all the normal things in the DMAIC process: picked a cross discipline team, defined the problem and went to the floor to observe. I tend to be suspicious of the gauges being accurate, so when we found out they were 100% gauging parts and scrapping 25%, I suspected the gauge right away. My first question was, “Why are we 100% gauging?” And the answer was, “We have a 0.8 Cp (process capability).”

We ran a quick Reliability and Repeatability (R & R) test to assess the gauges. We gathered the 3 inspectors, 3 gauges and 20 parts at random from the last lot of 100 and ran our gauge R & R. While this was running we completed our Value Stream Map and investigated the upstream and downstream. We collected a lot of data and analysis of every step within the Swiss Screw Machine (lathe) that was running the parts including the tools that machined the dimension in question.

The results of the gauge R & R showed that our gauges were using more than 100% of the process. We quickly began to seek a better gauge. This was the fun step…the part was round and symmetrical. So when it was gauged, the inspector could measure either end or any cross section.

We rewrote the inspection procedure to be more specific. The new process included always measuring on the cutoff end and marking the area cross-section that was measured. We re-ran the gauge R & R and this time the gauge R & R with the same gauge dropped to 35%.

Having an accurate gauge as well as re-doing the gauge R & R we realized that the part had both taper and out-of-round condition. Our next step was to improve the process. While observing the process someone noticed that the cut-off tool was 1/2″ from the collet. This was necessary because we were using the standard left-hand cut-off tool holder and it was not cutting on center perfectly enough for this small diameter part.

We made a few process changes, at very little cost, to solve all the problems:

1. We moved the tool to be on center. This reduced tool forces and eliminated the cut-off nipple. The lower tool forces significantly reduced taper and run out.

2. We changed to a right-hand cut-off tool. This further reduced taper. Now we are making excellent quality parts, our Cpk (centered process) was over 1.7 (which eliminated the need for 100% inspection), and cutting on-center eliminated the secondary operation of removing the nipple.

Success! Good parts, no inspection required, eliminated the secondary process.

What is funny, or ironic about this all, is that from the beginning the part was designed and dimensioned wrong so it probably did not require all this effort. The part was pressed fit at assembly to hold 3 parts together and welded at both ends. The part in the middle was a clearance hole.

Conclusion? Always do a gauge R & R. Always go observe. Always look upstream and downstream of the process. This way you can ALWAYS improve.

No Comments

No comments yet.

RSS feed for comments on this post. TrackBack URL

Sorry, the comment form is closed at this time.

Powered by WordPress