Faster is Not Always Better

That old “Overhead” article reminded me of what a shock it was when we first moved into cellular manufacturing. After years of investigating ways to reduce cycle times to a minimum, a completely new approach was needed with “cells.” For those of you unfamiliar with this terminology, a manufacturing “cell” is a group of machine tools arranged and tooled to produce a particular part number or family of parts. Usually staffed by a single operator, the cell eliminates many indirect expenses normally associated with part manufacture.

While there is a reduction in transportation expense and less time is spend counting and recounting “work-in-process”, the actual number of “minutes” associated with making chips sometimes increases. The concept requires slavish devotion to the wonders of “single piece flow” and ignores the long held assignment of “cost per minute” to the operator.

When you group all the operations needed to produce a part you quickly see that they are not equal. Reducing hobbing time by 24 percent is not a “savings” unless hobbing is the longest operation cycle in the cell, for example. You also have to be careful that your operator has the skills and the time to attend to all the machines.

There is no “savings” if hobbing only takes half the time of turning side one. As a result the engineer has to look at reducing the time on the longest process while conserving tooling wear on the others. It is a challenge that requires sharp thinking and a willingness to experiment.

Remember when I said “a good engineer works for free?” Some of the brightest people I have worked with figured out that slowing things down sometimes SAVES money. A prime example was a cell for making large internal gears. No matter what tooling was employed it took 125 minutes to turn the first side. Gashing took only 87 minutes. Once we determined there was no way to get that turning time down, my genius teammates started playing with SLOWING the gasher. To achieve minimum gashing time required changing corners on the custom insert every second piece and replacing about 25 percent of the insert on each part. Inserts were “only” $12 each but there were over 50 of them in the cutter.

Dialing back the feeds and speeds at the gasher made it possible to gash three parts without changing a corner and reduced overall insert use by half. When you did the math it was a “no brainer” but real brilliance was needed to see it as a possibility. Sometimes you have to let the smart folks play outside the box.

About Charles D. Schultz 678 Articles
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.