Fine Form: Medical Manufacturing

Courtesy of Deringer-Ney

Cold-formed electrical contacts made from silver alloys and silver-plated copper.

Cold forming is a fast, chipless way to make parts.

Clack-tick-clack-tick-clack-tick-clack-tick. That’s the sound of a six-die, cold forming machine spitting out parts at rates up to 200 pieces per minute. In addition to being quick, the process imparts a fine surface finish, meets tight tolerance requirements and produces parts that are often ready to ship. And there’s no wasted material because cold forming doesn’t produce chips.

Courtesy of Bigelow

Examples of cold-headed parts.

Cold-formed parts are common. A visit to a hardware store’s fastener section reveals numerous examples, including screws, nuts, bolts, rivets and nails. But far more than just fasteners are cold-formed. The process is pushing the manufacturing envelope for creating parts that are impractical or nearly impossible to make by other methods.

Round Stock

Cold forming involves feeding wire or round stock, typically from a spool, into a high-speed, single- or multiple-station, automated reciprocating machine. The machine shears off a small portion of the raw material to create a blank with the same volume as the finished part. Then, via a set of feed fingers, a pick-and-place attachment or a die, the machine feeds the blank into a series of horizontal punch and die sets, which progressively “spank” it—at a rate of one hit per station—into the correct shape.

This multistep process can involve numerous operations, such as coining, piercing, extruding, shearing, trimming, threading and knurling. With a few exceptions, any operation that can be performed on a lathe or mill can be cold-formed.

Similar to squeezing toothpaste from a tube, cold forming forces brass, copper, steel and even difficult-to-machine materials such as Inconel, tantalum and molybdenum into each successive die cavity. At each step, the material takes the mirror shape of the station’s die before moving to the next station.

Because virtually no material is wasted, cold forming is especially beneficial when manufacturing parts from precious metals. Your scrap man might not be happy, but because there are no chips, it’s easier to find microparts on a cold former than in a lathe’s chip pan.

Another advantage is that cold-formed parts are stronger and more durable than machined parts, because there’s no interruption of the material grain flow as there is with traditional machining processes like milling and turning. This makes it possible to create complex shapes while holding close tolerances. For example, one manufacturer of cold-formed parts holds tolerances of ±0.0005 ” on a 0.010 “-dia. part.

However, despite the benefits, cold forming does have limitations. It’s challenging, for example, to cold-form parts with long length-to-diameter ratios, undercuts or “choke” diameters, and complex parts with multiple features.

Want to Cold-Form?

If you’re looking to purchase a cold-forming machine, your options range from breaking open your kid’s piggy bank to buy an old, used machine for as little as $500 to groveling for a bank loan to buy a new machine with all the bells and whistles, which can cost upwards of $500,000.

The reality for most shops is probably somewhere in between. Cold-forming machine builders offer various versions. For instance, Tiffin, Ohio-based National Machinery LLC’s offerings range from its new Microformer machine with a wire diameter capacity of 3mm to a six-die monster capable of processing 34mm-dia. stock with forming pressures up to 600 metric tons. National equips its machines with features such as quick-change tooling, CNCs, zero-clearance slide mechanisms and linear feeds.

Needless to say, effective cold forming requires more than just buying a machine. Cold forming is an art. Be prepared to develop your own tooling, processes and possibly your own equipment.

That’s what leading medical-component manufacturer Deringer-Ney Inc. does. The 200-year-old company, headquartered in Vernon Hills., Ill., performs stamping, machining and insert molding, and develops custom precious-metal alloys.

Microforming, however, is the company’s sweet spot. “A 5mm part is huge for us,” said Tom Schieber, product development engineer. ” ‘Micro’ to us means anything under 0.5mm.”

Courtesy of Deringer-Ney

A cold-formed dental screw.

At its Marshall, N.C., plant, Deringer-Ney specializes in forming microparts, including antenna leads; actuator pins; medical-grade, implantable, radiopaque markers; and miniature screws for medical and electronic devices. It forms standard and high-value work materials, including gold, platinum and tantalum.

Deringer-Ney regularly cold forms parts with dimensions down to 0.25mm—only three times the width of a human hair.

“The rules change when you move into the microworld,” said Garth Boyd, the company’s vice president of marketing. “For example, during a normal cold-forming operation, a stock diameter reduction of up to 75 percent might be possible. But when you’re below 0.5mm, that size reduction might be limited to only 55 percent due to constraints, such as material ductility, tooling accuracy and workpiece grain structure.”