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Dr. Mark Curtis, after working as a manufacturing engineer at Eaton and elsewhere, has spent decades in education teaching dimensional measurement. He also is co-author of the Handbook of Dimensional Measurement, now in its fourth edition.
This month, Fabricating & Metalworking talks with Dr. Curtis about how lean manufacturing has changed the fundamentals of quality and dimensional measurement.
F&M: Describe the "traditional" path from art to part, and how quality fit into the mix, and compare this with the lean approach.
Curtis: When a part was designed in the 1960s, the concept was proven out in advanced engineering, and prototype models would prove that the product worked. Then, the design would make its way over to engineers who would make it "manufacturable." There was a fair amount of demarcation between design and manufacturing. We were occasionally asked for input, when designers would come to us and ask us to cost it out based on the tolerances, dimensions and material. Manufacturing engineering would find the machines and tools, set up the job and run some samples based on real-world conditions. Sometimes tolerances were too tight or other particulars didn't work out, so compromises had to be made. Note that only at this point did discussion of meeting tolerances on the shop floor occur. It was linear, compartmentalized and took a fair amount of time.
Today, everything is on a compressed time scale. Simultaneous engineering ensues, with collaboration between design, manufacturing and quality. Certain manufacturability parameters are set early—machine-tool capabilities, dies jigs and fixtures, etc.
The reasoning follows simple logic: Why design it if you can't manufacture it?
This planted the seed for a sea change in quality circles, including a name change. It used to be called quality control. That name implied the company would make bad parts, and it would need people to identify them and pull them out of production. Now, they are called quality assurance, implying those who "assure" no bad parts (or at least a minimal amount) are made in the first place.
For this, quality assurance has a seat at the table from the beginning. We now ask, "How do we minimize and simplify the amount of inspection needed?"
Consider gear manufacturing. Once, raw material came in as forged blanks, which would be machined, hobbed, ground and so on, and each process had to be carefully monitored and checked, all the way through the production line. Today, precision forging has allowed gears to be warm-forged with the teeth already on them, minimizing the number of subsequent machining operations required—and, hence, the amount of inspection needed.
There's now significant interaction between all departments. Job descriptions are blurred; machine operators as well as CMM technicians perform quality checks. "Gauge it where you make it" practices have become the norm within many organizations. And quality now has more than just a seat at the table; in modern manufacturing, it has a very prominent presence.
F&M: Many talk about the lack of skilled labor. How does this affect a company's QA operation?
Curtis: The danger today is that the fundamentals seem to be going by the wayside. Consider geometric dimensioning and tolerancing. The 14 symbols that form its foundation have a lot of meaning. (Editor's Note: See "The Symbology of GD&T" in the March 2007 issue, archived at www.fandmmag.com.)
And here we are more than three decades after GD&T became a national standard designed to eliminate confusion, and confusion still persists. For instance, in the feature control frame, we may have the position symbol alongside the controlling location of a hole pattern in a flange. Reading the control frame properly, it says we should hold holes to within a diameter plus or minus 0.010 inch at MMC, or maximum material condition. Here, things can fall apart if workers don't have a clear understanding of MMC. They see "maximum" and think "big," inferring "maximum hole diameter." Of course, MMC in a hole means the maximum material amount; the more material you have, the smaller the hole will be.
The company may have a clean room and have the best computerized dimensional-measurement equipment on the market. But if they miss those fundamentals, all that technology investment won't do any good.
Editor's Note: Dr. Mark Curtis is vice president for instruction at Alpena Community College, Alpena, Mich. Formerly, he was a professor in Purdue University's College of Technology and director of the South Bend, Ind., location. Before that he was dean of the College of Technology and Applied Sciences and professor of industrial technologies at Northern Michigan University. Curtis also consults on various related topics through LC Studio and Consulting, LLC.