Beyond Swiss Precision

This medical-industry job shop has staked its reputation on superior process expertise with multi-axis--and multifunction--CNC Swiss-style turning centers. The ability to cut small and complex parts completely in a single setup provides huge benefits to the shop and its customers.

Article From: 9/1/1995 Modern Machine Shop, ,

When Jim and Joe Davis started their job shop in 1987, they thought they had a good shot at making it big in the medical industry. They were already half-way there. Rather than starting from scratch, the two brothers bought out the precision Swiss lathe department from the downsizing medical-industry company for which they both worked. And thus Micro Med Machining, Inc. (Miami Lakes, Florida) was born.

The young men had a lot going for them. They had more or less grown up in their father's machine shop. Both were degreed manufacturing engineers, and they had gone through their former employer's manufacturing management intern program. So the two were hands-on familiar with metalworking processes in general and with Swiss turning for the medical industry in particular--with a good understanding both of the industry's quality requirements and its regulatory environment. Moreover, they knew from their own experience how hard it was to find machined parts suppliers who could consistently live up to industry standards. Surely there was a niche to be filled.

For the first five months Micro Med's only work was making parts for their former owner's catheters and implantable pacemakers. But thereafter, the shop's prospects busted wide open. Indeed, they started with 19 people and today have more than a hundred, while their sales volume has grown by a larger proportion.

That growth has stemmed in no small way from their correct assumption about the medical industry's need for dependable suppliers. Equally important, though, is how the shop has applied technology. They started mostly with automatic Swiss lathes and Hardinge chuckers, as well as a battery of secondary equipment. Today they do the vast majority of the work on multi-axis CNC turn/mill centers. The shop has 30 of these sophisticated machines in various configurations.

While the technology is surely more expensive than the old automatics, it provides the ability to machine most of the shop's very complicated parts completely in a single setup. Essentially they are displacing the costs of multiple setups with more capable equipment--which is a lower cost solution overall--and delivering the quality levels their customers demand, batch after batch. But Micro Med's technical formula requires much more than put-ting good machines on the shop floor. They have a huge amount of process expertise with these machines, which is what truly separates this shop from run-of-the-mill competition.

While we can't disclose the most critical elements of the shop's process knowledge here, we can provide a peek at what makes this remarkable shop click. Here's how they do it at Micro Med.

The Parts And The Machines

To understand demands on the processes, it helps to begin by looking at some of the parts. They are complicated, precise--and small. Indeed, Micro Med's display of sample parts looks more like something from a jewelry store than a machine shop. The typical fare includes bone screws; tiny tubes, fittings and valves; components for miniature surgical instruments; and dental posts. Precision screws, for instance, go as small as 1 mm long, and 1 mm in diameter with 1-mm cancellous thread. Cosmetics are critical, and virtually all parts are finished and visually inspected under a microscope at 20x magnification. Burrs of any sort are flatly unacceptable.

Compounding the difficulty of machining these small parts are the tough materials from which they are made. Some 65 percent of the parts are cut from titanium, another 30 percent from the toughest stainless steels, and the rest from precious metals such as gold and platinum. More than 60 percent of the pieces require some sort of milling or drilling operation. Drilled cross holes are common, some as small as 0.005 inch in diameter (smaller holes are EDMed). Many of these small holes must be both precise and deep. For instance, one tubular part requires a 0.04-inch diameter center hole drilled 1.5 inches deep . . . with only a 0.007-inch wall thickness . . . in titanium. And the parts aren't just round. Quite a few essentially prismatic parts are produced on the CNC Swiss machines thanks to their milling capabilities and the inherent workholding advantages of producing these delicate parts from bar stock.

All of the multi-axis machines are Citizens (Marubeni Citizen-Cincom, Allendale, New Jersey). Some of the machines are comparatively simple three-axis designs with the characteristic Swiss-style sliding headstock and guide bushing (Z), single-axis tool turret (X), and rotary positioning of the main spindle (C). Both stationary and powered tools are mounted on the turret for turning or on-center drilling and milling operations.

Micro Med's other machines are considerably more complex. The E-Series models are six-axis designs, which add a second two-axis turret and a subspindle for back-working operations. The twin turrets allow pinch turning--that is, turning with two tools at once--which is efficient and, equally important, counteracts the inclination of thin workpieces to deflect from a single tool. And the second turret allows a wider range of operations to be executed on parts held either in the primary or secondary spindle. Moreover, turning or milling operations can be executed on both spindles simultaneously.

The shop's eight-axis M-20 models go a few steps further. Rather than a second turret, the machines have an eight-station gang plate, capable of holding up to five stationary and three rotating tools. Gang tooling is extremely efficient in turning operations because it eliminates the time turrets require to index from tool to tool. These machines also have Y-axis capability for the gang plate tooling, meaning off-center milling and drilling operations can be performed with the powered stations. An eighth swivel-axis accommodates in-process workpiece or tool gaging, or robotic workpiece manipulation.

The point of all these machines is that they permit Micro Med to machine even very complicated parts in a single setup. The advantages of this capability are many. Perhaps most obvious, it saves the time, labor and the work-in-process costs of routing jobs across a progression of single-purpose machines. It also allows the shop to be much more responsive to customers' increasingly demanding delivery requirements. Knocking out a rush order is far simpler when the job need only be routed over a single machine, rather than three or four.

Just as important are the qualitative advantages. Each time a part is released from a workholder and then regripped, a new element of dimensional variability is added to the process. With Micro Med's work, 0.001-inch tolerances are typical, but they often have to hold to a "tenth"--0.0001 inch--and do it consistently. Considering how difficult it can be to fixture these small parts for secondary operations, it doesn't take a very high stack of workholding tolerances to drive the total machining process out of acceptable bounds. It's far better to keep a single grip on the part for the whole process and eliminate that issue altogether.

Maintaining constant physical control of the workpiece also brings a scientific credibility to the shop's command of its processes, which is a central concern to Micro Med's quality-conscious customers. Says Joe Davis, "People today are looking at your Cpk values. They want to know that you have your process under control." And for their most sophisticated customers, Micro Med is in a position to provide statistically reliable manufacturing feasibility studies. That goes a long way to getting new business into the shop.

Still, competition returns cost to a prime consideration--and for the quality levels the shop is geared to deliver, eliminating setups has a huge beneficial impact. A good example is a medical connector that another supplier was producing in six setups on a succession of single-purpose chuckers and milling machines. At volumes of 4500 a month, the customer was paying $8 per piece. Micro Med took a look at the part, suggested a few simple changes for the sake of machinability and put it on one of the six-axis machines. "We got the cost down to four dollars and change," says Mr. Davis. Was the former supplier charging an excessive rate? "Not really," he says, "that was probably pretty much in line with his costs. He just didn't have the best process to do the job."

Better Processes

Anyone can go out and buy equipment, but making the best use of it is quite another matter, and this is where Micro Med excels. Process creativity is extremely important--for the sake of efficiency and quality--and that can only come with people who are thoroughly familiar with the machines. Also critical is knowing what can and can't be done with standard tooling, and how tooling can be modified or specially built. This expertise allows the shop to do things with their machines that astonish even the machine developers. "Not using these machines to their full potential is like driving a racing car 50 miles an hour," says Mr. Davis. At Micro Med, they like to drive fast.

But that is speaking only figuratively, as achieving fast metal removal rates is clearly not what this shop is about. A critical concern to the medical industry is how the part is finished--burr free and cosmetically flawless--but the efficiency and quality of that final operation has very much to do with how the metal was removed in the first place. Finishing is a hand operation, and like any other precision metalworking shop, something they like to keep to a minimum. "We'll gladly trade primary machine time for finishing time," says Mr. Davis, but they can only reap the payoff of that trade through careful construction of the machining routine.

Burrs are probably the greatest single concern. The best way to deal with burrs is to prevent them, and if they are unavoidable, to manage the process in such a way that they'll be readily removable in a reasonably efficient secondary process. That means they must be concerned with the direction of the burr, its size and what it's going to take to break it off. These considerations can have a major impact on cycle times. In this case, however, speed is not as important as the condition of the part as it comes off the machine.

Managing part deflection is another factor that can add some very noticeable time to machining cycles, and perhaps the area of the shop's finest trade secrets. Consider that Micro Med is maintaining precise dimensional integrity on a range of very slender parts made from extremely tough-to-machine materials, and often cut with delicate tools that are even more inclined to deflect than the workpiece. They must understand to an extraordinarily fine degree the speeds, feeds and cut depths appropriate for these conditions. For instance, a thread that seems like it should take eight passes may in fact take 18. They've also discovered ways to thread in sections and flawlessly blend them all together. It's frequently a slow and painstaking process, but worthwhile because process predictability is the shop's overriding concern.

Tool life is another important factor, not so much for the cost of the tooling itself as for, again, maintaining qualitative control of the process. Operators must remain constantly vigilant to remove wearing tools from a process before they drive it out of control. And they must weed substandard tools out of the process altogether. Tool quality is critical even with some seemingly soft materials such as platinum--indeed especially with platinum, which is a highly abrasive material, and obviously of such a value that scrap is a costly proposition. Or as Mr. Davis more succinctly puts it, "When you are drilling a 0.012-inch diameter hole, tool quality is pretty damn critical, and you can't assume that any off-the-shelf tool will do the job."

Because average runs are 1500 to 2,000 pieces, and multi-axis turn/mill centers are rather expensive assets to sit idle, operators have to be very good at getting jobs on and off the machines. One way they do this is by presetting the tools. On some machines, for example, they have purchased extra turrets. This way tools are set up and qualified off-line "within a couple `tenths.'" Then once those turrets are mounted, it only takes a few setup parts to get the process up and running. That's not to say that they are approaching single-digit changeover times; these machines are too complex. But they are getting jobs running in an hour versus the six it might take to individually load and dial in all the tools on the machine.

And there are many other things to know. Programming is important, but the machine controls offer a good deal of help in this regard. Individual turning or milling operations can be programmed independently, and then the CNC automatically compiles them into a single, efficient routine. Workholding is also critical, particularly for picking up machined parts in the subspindle, and sometimes special collets are made. It's a lot to know. But the shop's mastery of this critical process information has, by their own reckoning, been the crucial difference between Micro Med and its competition.

Pushing The Envelope

Micro Med has reaped some of this knowledge by doing the expected things on a daily basis and paying close attention to the results. They use SPC to qualify each new process, for example, and thereafter chart the process for the sake of production control. But the larger measure of the shop's most potent competitive advantage has come from their persistent inclination to push the process envelope, constantly seeking new efficiencies that don't undermine their quality standards.

No doubt, the Davis brothers take considerable pride in their "process adventurousness"--their inclination to try new ideas and to work out the difficult problems. But it is not simply bravura that drives them; they believe that continuing experimentation with processes provides the learning experiences the shop needs to maintain its competitive edge. That's a big part of the reason why this production shop is willing to do prototyping--simultaneously working out part and process on production equipment--for the knowledge it provides. Quite literally, they seek to marry the outermost reaches of their very capable production equipment with the unusual requirements of the industry they serve. Because the shop's key people are from the medical industry, they have a significant advantage in this regard. They carry a great deal of knowledge of appropriate processes within the constraints of the field, and they can even go a long way to helping customers develop designs--improving manufactur-ability without sacrificing functionality or running into common regulatory constraints. For these reasons, the shop's managers are determined to keep the business very focused. Micro Med is best at multi-axis Swiss-type turning to very high quality standards, and that's what they'll continue to do. Interestingly, this strong and consistent sense of focus helps the shop's employees adjust their own personal quality standards to an appropriate level for the kinds of customers Micro Med serves, which in turn helps the shop achieve the right balance of quality and efficiency. That's a touchy issue in the medical industry, which is growing increasingly cost-conscious, yet where parts still have to look perfect. "You want to instill a desire for perfection," says Mr. Davis, "but at the same time, you don't want them wasting time achieving a level that's beyond the practical requirements of the job." It's a delicate balance, and one he feels will not lend itself to bringing more commodity-type machining into the mix. Either the shop would have excessive costs for such parts or, worse, they would introduce a destructive ambiguity into the shop as to what "good enough" means.

So Micro Med will continue to focus on difficult parts. Mr. Davis believes there's far more of them out there, and he's more than willing to take his chances on their shop's ability to continue to successfully compete for that work. MMS

Editor's note: Two weeks after our visit with Micro Med, the company announced that it had been sold to Uniform Tubes, a manufacturer of custom tubular components. Uniform Tubes will give Micro Med increased engineering and sales support. According to Joe Davis, company management and mission will remain intact.

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