A system for quick change

Modern Machine Shop, May, 1995 by Tom Beard

The company name hardly gives a clue to what this aerospace job shop is all about. Danville Metal Stamping (Danville, Illinois) has 350 people in three locations, and does well over $20 million in a slow year. Virtually all the sophisticated parts they make go into jet engines or stationary turbines. They do a wide variety of metalworking - machining, laser cutting and welding, conventional welding and brazing, and a variety of forming and bending operations. They even have their own heat treat facility. And many of the complicated assembled parts they make require just about all of those operations.

Moreover, the materials they routinely use are some of the toughest to machine: titanium, Inconel, Hastelloy, stainless steel. Nothing comes easy.

So it comes as little surprise that the shop historically focused more on metal removal than setup. They had their hands full getting lengthy cycle times down, yet still maintaining the stringent quality standards their customers demand.

Over time that priority began to change, as long setups simply became too expensive. According to Andy Minnick, who oversees the machine shop, the company first saw it coming some 14 years ago when they decided to cut their eight-hour setups to an hour and a half. He smiles about that now since, by today's standards of ten-minute set-ups, that was not such a lofty goal as it seemed.

But back then, Danville Metal didn't have the setup reduction tools either, tools which they've aggressively acquired and applied since. And we're not just talking quick-change cutting tools here, though that's the focus of this story. A tool presetter, quick-change fixture mounting systems for machining centers, quick-change vise and chuck jaws all play a role. For to truly to achieve the highest performance, Mr. Minnick believes, you have to rethink how you handle setup throughout the shop, and create a system that supports that objective.

The Concept

Danville Metal's investments in quick-change tooling are profit driven. Back when setups took a whole shift, an order of 500 pieces might be typical, but so too were releases as low as 50. So they maintained a lot of finished goods inventory. In more recent years, both the order and release quantities have been driven lower, and that combined with the company's desire for inventory cost reductions has placed a clear financial priority on reducing setup.

Output was an issue as well. When lot sizes fell to as few as five pieces, they simply had to figure out how to get more jobs across their machines. Now they do as many setups in a day as they did in a week only a few years ago.

The initial thrust on setup reduction focused on education and information. Operators were trained in new procedures, and engineers began producing setup sheets for each job. Gradually they added simple but important physical reference points - locators on fixtures, counterbores on chucks, and so on - so that initial location of critical surfaces could be established faster. In time they added highly repeatable quick change fixture mounting systems to machining centers, and quick-change chucks to lathes. The idea was not only to change workholders quickly, but also to have workpiece position become a constant, and thus eliminate the time-consuming process of re-establishing fixture location with every changeover.

This very same thinking was applied to cutting tools. And that required building a system to support quick change both on and off the machine. It's a system that's roughly one third hardware, one third information and one third discipline.

The quick-change tooling is the KM system from Kennametal, Inc. (Latrobe, Pennsylvania). The system consists essentially of a short-shank, tapered toolholder and a mating receiver that is mounted on the turret of a lathe, or even in a standard tapered toolholder for a machining center. In the initial KM design, a wedge-and-ball locking mechanism allows the connection to be loosened or locked with three turns of a hex wrench; newer cam-lock models are actuated with a half turn. Danville Metal has some of both designs, but in any case, they count on the quick-change connection allowing operators to load a new tool in just a few seconds. However, by Mr. Minnick's reckoning, obtaining the benefits of quick-change tooling is not just something that happens at the machine tool. How the crib is managed is of critical importance, and equally so, how tooling information is integrated with other important process documentation.

His basic tool management concept is this: Kit tools for every job before the setup begins and pre-measure each tool so that initial offset values can be established off the machine. Apply a similar process for locating the workpiece. And then move immediately into production without taking any trial cuts. Of course, a good concept is one thing, making it work is quite another. But with more than a modest amount of planning, research and attention to detail, the shop is in many cases applying that ideal.