The materials used for replacement parts are often made of polymer, titanium or a cobalt-chrome alloy, materials where PCBN is usually not recommended. Polymers are machined with either PCD or carbide, and titanium and cobalt-chrome are normally machined with carbide.
The components are often asymmetrical, and the majority of the applications are with round tools, with little need for turning tools. One exception is finishing of joints for hips, elbows etc. The component is a spherical ball, called a femoral head, with a diameter of between 25 and 50 mm, and with a hole on one side. After forging, the components are rough and finish turned, and then polished to final dimensions, with very tight requirements on the tolerances.
Cobalt-Chrome is an alloy with about 60% cobalt and 40% chrome. The hardness is only about 30 HRC, but the material is very abrasive. Turning has traditionally been done with carbide, but in finish turning of the sphere, tool life is very low due to the abrasiveness of the material, and the high tolerances required.
Seco UK has been successful in turning of these components, using CP500 for roughing and CBN200 for finishing. We have now used this information to implement the solution at one company in China, with large improvements in productivity and component quality. An additional benefit in finishing is the much longer tool life with PCBN, from a few components with carbide to over 100 with PCBN. We are now working with this at a second company with potential for further growth.
Three conclusions drawn from this:
- The application area for PCBN is growing, as new materials are being developed and used in the market.
- We have a very good solution to offer our medical customers.
- The importance of sharing success stories cannot be underestimated. If we have good results on a specific component, this should be spread to colleagues domestically as well as internationally, in order to avoid “inventing the wheel again”, or even “never inventing the wheel at all”.
Product Specialist SECOMAX PCBN/PCD/CERAMIC
SECO TOOLS Shanghai CO., Ltd. Level 2, Building 8, 456 HongCao Rd., Shanghai 200233, China
Office: +86 21 5426 5849
Mobile: +86 186 167 90063