Quality Scan: Flexible Gaging Can Help Maximize Quality
By Frank Powell
Auburn Hills, MI
Web site: www.marposs.com
In a globally decentralized manufacturing environment, where parts from Indonesia and China are assembled in Mexico and shipped to Canada for installation in a product that will be sold in Kentucky, those responsible for "quality control" face some very interesting challenges.
First of all, the parts have to fit and they have to work. That’s a quality issue.
But, they also have to be produced efficiently in ever-smaller batches, because the plant is supplying many different customers around the world with JIT deliveries. That’s an economic issue that directly impacts manufacturing ROI.
From a systems point of view, the solution to efficiently producing smaller batches is flexibility. That usually means one machine is used to perform multiple operations on a workpiece, and that machine can accommodate a range of parts within a given size envelope.
Systems built on the flexible model are nearly always cellular and nonsynchronous. As a result, they require different approaches to both production monitoring and process control than do traditional in-line synchronous manufacturing systems.
Flexible systems need flexible gages and process controls to deliver an acceptable ROI while meeting both "first-part-good-part" and "no-bad-parts-ever" quality goals. Moreover, the gages and process controls need to be integrated with each other and also the manufacturing process, not just added on.
It’s true that traditional "inspection" of in-process or finished parts will help meet the "no-bad-parts-ever" goal by weeding out "bad" parts, but it’s certainly not the most effective way to do it. The most cost-effective way to keep bad parts from leaving a plant is to avoid making them in the first place.
That is best done by linking the gages and controls into a system that actively manages the process in real-time. To make that approach practical, the gages need to be physically close to the production processes they are controlling, to keep the feedback loop as short as possible. Ideally, they should be engineered into the system from the very beginning by including the gaging supplier as an integral part of the design team.
Moving the gages near or, preferably, directly into the manufacturing process creates its own set of challenges. Factors like cycle time, changeover frequency, production volume, and part tolerances all impact the selection of an appropriate gaging technology.
For example, an optical gage provides almost infinite flexibility, but only on clean parts. A reconfigurable pneumatic or contact gage probably can handle as-machined parts with no difficulty, but it’s not nearly as flexible.
The optical system might well be the best choice for a high-volume, automated, flexible CNC camshaft grinding cell. But the contact gage is more likely to be the right choice for a cell producing turned or milled parts.
The temptation to include "bleeding edge" technology for its own sake should be avoided. The goal is to install just enough capability to optimize and control the process, and no more. Often all that is needed is a simple electronic gage or even a machine-mounted touch probe that feeds data to a processor with enough intelligence to make the appropriate process-control decisions.
While flexible systems need flexible gages and process controls to deliver an acceptable ROI, flexibility is not free. The gaging system needs to include flexibility only to the degree necessary to accomplish required tasks. For example, if a family of parts can be accommodated by moving or changing a few gage details, and the machine operator can make those changes inside the cycle time, then flexibility achieved through gage automation probably isn’t a wise investment.
There are no "one-size-fits-all" flexible gaging solutions and infallible guidelines. Every gaging decision involves trade-offs between flexibility, cost, and operational compatibility, and the best way to achieve an efficient solution is to include the gaging supplier in the design team from the very beginning.
Flexibility is clearly going to become increasingly important as globally decentralized manufacturing continues to grow. The success stories of the next decade will be written by a new breed of flexible manufacturing systems that close the loop on quality, while maximizing ROI with tightly integrated process monitoring and control. ME
This article was first published in the May 2011 edition of Manufacturing Engineering magazine. Click here for PDF.