The cobalt content in the taps provides additional hardness while the vanadium provides additional wear resistance. OSG reports that its VC-10 taps are for tapping some of the popular stainless steels, such as 17-4 precipitation hardenable and 15-5 PH. The medical field uses various types of stainless steel, mostly for medical instruments. If the tap breaks and can’t be removed from the part, the part ends up being scrapped. Because tapping is often one of the final operations, a shop already has a lot of time and money invested in the part. If the titanium does clamp around the tap and it is not able to rotate, the tap may break. It may make the tap a little weaker, but it eliminates the issues involved because of the ‘springiness’ of titanium.” Adding back taper does not influence the cutting properties of the tap. “The chamfer on the front of the tap is what is cutting or forming the thread. “With that back taper on the tool, the collapsed titanium does not actually make contact with the back of the tool,” he continued. This provides the clearance necessary to successfully tap titanium,” Goodman explained. “A tap designed for titanium is going to have extra back taper, taper from the chamfer or the cutting edge to the back of the thread section. This is a unique characteristic of titanium.”Īn implant for the ankle made of titanium. “This causes the material to collapse around the trailing threads of a tap. “Titanium has a low modulus of elasticity,” Goodman said. When tapping, the material closes tightly, or “shrinks,” around the tap, increasing cutting edge wear. One characteristic that makes titanium difficult to tap is its high elastic memory. “Its characteristics of being both strong and lightweight make it a very attractive alloy for use in the medical industry,” said Ray Moring, technical sales marketing specialist for Greenfield Industries Inc., Evans, Ga. “When you talk about medical parts, some made from titanium might require a totally different tap than those made from stainless steels,” Goodman said.Ī large percentage of medical implants are made of titanium alloys. Most tap manufacturers have a product line specifically designed for each material. Key medical part materials include medical-grade stainless steels, titanium and cobalt chrome. “Typically, there are few medical parts that are going to need a tap over ½", and most of them need a tap under ¼",” said Ed Goodman, application specialist for OSG Tap & Die Inc., Glendale Heights, Ill. Medical parts that are tapped include implants, such as hip and knee replacements, and surgical instruments.Īgain, small is one of the operative words. Small is for the tiny size of many medical parts, and challenging is for the difficult-to-machine materials from which the parts are often made.ĭeveloping strategies for tapping medical parts, then, typically involves many factors, including the cutting tool geometry, machine capability, toolholder, metalworking fluid and the parts themselves. When tapping medical parts, two words come up repeatedly: small and challenging. OSG’s Exo-Carb VX carbide taps can thread cobalt chrome. Tapping medical parts requires unique considerations not required in general-purpose machining.
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