Shoot from the Hip

JRI Orthopedics Ltd (London, UK) has been an innovator in its field since 1970 and is renowned for its Furlong® Hydroxyapatite Ceramic (H-A.C) Coated Total Hip Replacement (THR). A world first, this coating enables new bone to grow primarily on and directly into the ceramic surface, ensuring even distribution of forces transmitted through the prosthesis to the host bone.

At its Sheffield facility that encompasses manufacturing, research and development, marketing, warehousing and distribution, the company introduced an advanced manufacturing cell for the production of bespoke femoral stem prostheses using machine tools from DMG MORI UK Ltd (Coventry, UK). Starting with a NMV 3000 DCG universal machining center in 2012, it added a NTX 2000 turn-mill center at the end of 2013.

Ian Chambers, the principal process engineer, says, “Our objective is to produce bespoke solutions for each patient, developed from a CT scan which determines where the bone is located and, from that, a solid model enabling the implant to be designed around the cavity. Previously we were limited to standard designs and this would require two or three machines to complete the process.”

http://youtu.be/Uymm8voUpsA
A demonstration of the NTX 2000 turn-mill center.

Not only did JRI Orthopedics want to produce bespoke implants, but it also wanted to reduce the number of operations to achieve one hit machining all in an automated lights out environment.

Starting with the NMV 3000 DCG, the shop began producing rasps that are used to form the cavity in the bone to suit the implant. Programming is done on the Esprit system supplied with the machine tool. The rasps are size critical and need to be burr-free. Attention to detail within the process by using chamfer and radius cutters ensures the parts come off the machine in a finished state.

Chambers says, “DMG MORI was extremely helpful in getting the machine running and in developing the machining methods for the part. As a precaution, we check everything with Vericut because every part is unique and high value. We can now seamlessly produce programs for bespoke parts from scratch, relying absolutely on the postprocessed data. The NMV 3000 DCG is better than anything else we have got.”

The shop was sold on these machines and service after installing the NMV3000 DCG so, when it was looking to expand the advanced manufacturing cell with turn-mill capability, the NTX 2000 was the obvious choice. Chambers adds, “We looked at other turn-mill machines, however, the workholding on the NTX 2000 was significantly better, enabling us to make full use of the tools.

Additionally, the advantages of the build quality, machine rigidity and service, which we had experienced with the NMV 3000 DCG, convinced us we were making the right decision.”

The NTX 2000 has opened up new possibilities for parts that previously required at least two operations. Rasp handles, which are currently being subcontracted, will be some of the first components to be loaded onto the new machine. Work is currently being undertaken on bespoke shoulder implants.

Tight tolerances of ±2.5 minutes on tapered holes, 6µ straightness and 10µ roundness have been easy to achieve. Starting with titanium bar, milling operations are completed on the main turret, using a standardized tool setup, before the part is transferred to the second turret, which is fitted with special jaws, for boring operations, enabling the part to come off complete in the part catcher. Savings of 20 percent to 30 percent in cycle time are anticipated.

To successfully produce bespoke implants in a lights out environment, the whole process has to be examined from design and programming to automated machining processes and tooling. JRI Orthopedics works with tooling distributor Helix which offers a range of suppliers’ tools including Iscar, OSG and SGS in a line side vending system.

Additionally, the company controls the CNC programs using DMG MORI-Server software that allows programs to be remotely managed on both the NMV3000 DCG and the NTX 2000, essential for a rapidly changing workload. Chambers says, “We are continually working to push the boundaries of what is possible, carrying out cutting trials to test the best solutions. For lights out machining we need to develop robust and reliable methods for cutting our titanium, high end stainless and cobalt chrome products.”

JRI Orthopedics Ltd-Sheffield, 18 Churchill Way, 35A Business Park, Chapeltown, Sheffield, S35 2PY, UK, www.jri-ltd.co.uk.

DMG MORI UK, 4030 Siskin Parkway East, Middlemarch Business Park, Coventry CV4 4PE UK, 44-2476-516137, www.dmgmori.com.