The top priority of any joint implant is to restore mobility and ensure longevity. Ralf Merz, a specialist for precision parts, relies on the vertical 5-axis machining center VM-2 from Haas to meet this demand.
Specialization in medical components and joint prostheses
Based in Sankt Ingbert, Germany, engineer Ralph Merz’s business specializes in developing and manufacturing high-quality medical components and prosthetic joints for some of the best-known names in the medical device and implant sector. Clients such as the British company Corin Group Plc. employ Herr Merz to improve their products and to redesign parts for easier, quicker and more cost-effective manufacturing.
Biotechnology growth market
The bioengineering market is growing fast. People are living longer but their joints are wearing out and every year, surgeons all over Europe perform hundreds of thousands of joint replacements to treat degenerative arthritis, congenital abnormalities and other disorders that affect specific joint functions.
The importance of surface quality
“Each joint implant is designed to restore mobility and help relieve pain,” says Merz, “so the surface finish is vitally important. For instance, with replacement ankle joints the main titan body surface has to be sufficiently good to accept in addition a titanium coating.
Joint replacements come in for a lot of wear and tear: they need to last as long as possible to avoid revision.”
Haas CNC machine creates freeform surfaces on ankle joints
The freeform surfaces of ankle joints made by Mr. Merz are machined using simultaneous motion on a five-axis Haas VM-2 vertical machining center. For the program generation, the ESPRIT CAM System from DP Technology is used. “We chose the VM-2 because it is equipped with everything we need to make our parts,” he says. “We also ordered the high-speed option, the TR160 trunnion table, a Renishaw spindle probe, and a tool-setting probe.”
Mr. Merz worked with Haas CNC machine tools at his previous company and for a while, he gave programming lessons at the local Haas Factory Outlet (HFO), a division of Katzenmeier, – an activity he continues to this day. When it came to selecting a suitable CNC machine tool for his business, there was only one name on the list.
Price-performance ratio prevails against the competition
“Apart from first-class support and service, there are several advantages to using Haas,” he explains. “Above all, the price-performance ratio is very good compared with competitor machines – resulting in lower hourly rates/operating costs. We could have bought much more expensive machines, but we wouldn’t have used all their functionality and the cost of our parts would have increased.”
Herr Merz’s DIN 9001 certified company also specializes in making titan surgical implant kits for knee replacements. “Surgeons take these kits into theatre so that they have everything they need to complete a knee replacement operation,” he says. “Of course, people come in different sizes, so the kits have to contain different sized tools.”
Armed with what is known as an AMC guiding block pattern (or ‘Schnittblock’ in German) it is possible to prepare the geometry of the bone ready for knee surgery. The pattern Merz has designed integrates four surgical instruments in a single block measuring approximately 75 x 25 x 60mm.
Machined from a solid billet of 1.4542 stainless steel (20% chrome content), the blocks are finished in a single set-up on the five-axis Haas VM-2. Spindle speeds up to 4000 rpm are deployed along with 2.5m/min feed rates and 3mm depths of cut. Solid carbide coated milling cutters as small as 1.0mm in diameter and drills of 0.8mm in diameter are used to create specific features to tolerances as small as 0.005mm. These features were once created using an EDM machine, but are now made using the Haas VM-2 as well as a Haas Super MiniMill. “In order to use such small tools, the run-out of the spindle must be very precise otherwise cutters will break.”
A busy and growing workshop with only two CNC machine tools needs to know those machines can be relied upon.
“The Haas machines run Monday to Saturday from 06:00 to 20:00,” says Merz. “Depending on the order intake they also run overnight and on Sundays, but they are very reliable machines and the excellent support from HFO Katzenmeier means we never have to worry about missing delivery deadlines. ”
