An emphasis on revision prosthetics

Based in Germany, Peter Brehm GmbH, develops, manufacturers, and sells medical implants for primary and revision joint supply. The strength of the company is in the area of revision prosthetics for large joints such as hip, knee, and spinal column. Here, a carbon fibre workholding solution from Hainbuch, available from Tamworth-based workholding specialist, Leader Chuck Systems, addressed exacting production demands.

Every year in Germany around 400,000 people receive artificial hip and knee joints. The main endoprosthesis (an artificial device to replace a missing bodily part that is placed inside the body) operations can be defined as 210,000 hip joints and 165,000 knee joints. If, after a number of years, the prostheses requires replacement the primary joints fitted often cannot be re-implanted due to physiological changes of the patient. In these cases, revision joints are necessary. The modular character of these joints offers more variation possibilities in the structure to create different bone grip situations or size variations.

Located in Weisendorf, Germany, Peter Brehm is a full-service provider and one of the company’s core strengths is revision prosthetics for large joints for hip, knee, and the spinal column. So, hip endoprosthesis or spine fixators are important products in its portfolio. The product line also includes special implants that are used if the patient’s bone defects are so extensive that they can no longer be covered with standard implants. Supporting the industry fully the company also manufactures the instruments necessary for the implantation.

Customers for all of these products are clinics – particularly those clinics that specialise in the difficult revision operations. With few exceptions, all university hospitals in Germany belong to the customer base of the company. The company also supplies many international customers, with around 40 per cent of its production being exported.

Peter Brehm only uses high-quality materials, such as titanium, cobalt-base alloy, and ceramics that are particularly bio-compatible, strong, and low-wearing to manufacture the implants and instruments. All semi-finished materials are forged so that the possibility of imperfections and fatigue failures are almost completely excluded. “The titanium material we frequently work with is the alloy TiAl6V4 that has established itself in the field of medical technology,” explains Production Manager, Gerd Kirsch. “For example, we use pure, grade 1 titanium for hip sockets, and cobalt-base alloys in the knee area due to the excellent polish ability and high strength.”

For implants the batch sizes extend from five to a hundred parts, depending upon the product. “The trend is downward,” admits Gerd Kirsch. “This development also applies for smaller parts, like screws, which we formerly manufactured in either lots of 500 or 1,000. Today it is 200 or 300 pieces.” However, the instrument sets the company produces in five to twenty-fold types can include 3,000 individual parts. So the quantity is low and the variation is high.

Machining of the implants and instruments is carried out in the prefabrication department. Here the emphasis is on turning and milling with the objective of increasingly complete machining is consistently pursued. “Fixed and sliding headstock lathes can cover everything that is customary in the turning area”, emphasizes Gerd Kirsch. “Now we are prepared and set-up for every application in the field of medical technology. We invested in four C30 machines that are configured for simultaneous 5-axis machining. We have automated one so we can manufacture unmanned with even shorter cycle times.”

Milling Technician, Walter Kloha, adds: “We decided on pallet automation so we can manufacture either batches or just a single part in any sequence, unmanned. We have integrated a pallet changer that has more than 24 pallet positions, and that can handle pallet weights up to 60 kg.”

The automated C30 is currently operated by Marco Horny and Stephan Stahl, who alternately program the machine and run the parts, in order to handle the high volume of work. They clamp round material with nine manual Manok CFK stationary chucks from Hainbuch purchased to meet very exacting requirements.

Chucks from a competitor, used prior to automating, did not have a construction height sufficient to move the loading station into the machine. The company was also dissatisfied with the shape of these clamping devices and the resulting swarf ingress. In the subsequent search for an alternative, these and other criteria, for example, the new stationary clamping device should also be able to accommodate bars that are as long as possible; have a low construction height to avoid waste material, and should be easily accessible, were the crucial factors.

“With these requirements we sought out different manufacturers and selected Hainbuch,” explains Gerd Kirsch. “Preliminary discussions with Hainbuch had shown that our idea of obtaining a steel clamping device with as smooth a surface for diameters to 65 mm were achievable. We decided on the Manok that is made from carbon fibre.”

The carbon version is as much as 70 per cent lighter and at the same time is extremely rigid because they are equipped with hexagon Toplus clamping heads that offer a positive locking of the clamping head and clamping device. Unlike the round clamping heads, the hexagon model prevents radial displacements to the taper of the clamping device. Therefore, the chips cannot penetrate into the Manok. This is particularly important when milling as chips often fall over and into the clamping device.

Currently, a wide range of parts are milled from solid material using the CKF Manok system. The clamping devices have repeatedly proven their capability for lot sizes of 30, 50 or 150 pieces. Stephan Stahl highlights an example: “We had a situation that required the machining of residual material, and we only had 6 mm to clamp. So we tried it, and it was rock solid. Compared with a conventional three-jaw chuck that needs at least 2O mm, of course there is significantly less material scrap with the Manok.”

The high holding forces and the high rigidity also have positive effects on the surface quality of the manufactured implants and instruments. “ln addition to functionality, the appearance of our components also plays a very important role,” Walter Kloha comments.

“Previously, we could produce parts with the same quality. However, the effort was significantly higher. We simply had more rework. Moreover, we were by no means able to run the cutting parameters that we are running today. Formerly, two stagess were required. Today it is often just one step.”

“However, the advantages of the Manok system also include user friendly set-up, built-in vibration dampening, and lower weight. These Manoks also combine to reduce the formation of chatter marks, and it is also very easy to quickly change something in the machine,” reports Marco Horny.

The components are machined using coolant on the Hermle C30 so a wash program is applied after milling. This removes all the chips from the parts as well as the clamping heads. “With open chucks, the chips fall through in the middle and stay at the bottom on the zero position clamping system,” is how Walter Kloha describes his experiences. “Then if the pallets are changed automatically at night, eventually they will be placed on the chips. This cannot happen with the Manoks System.”

Posted in Gripping News, Hainbuch.