Production processes

Bernhard Fischbacher, Tobias Telser, and Paul Heilmann, the managing directors of DHF Precision Mechanics GmbH, were visiting a fair to catch up on laser marking systems. While visiting the Rofin-Baasel exhibit, they were invited to take a seat in front of the manual laser welding system to weld some parts by themselves, an experience that caused the three DHF managers to re-think their investment agenda.

Today, two years later, DHF uses laser material processing to manufacture Brainlab's DASH, among others. It is an intra-surgical navigation system for knee endoprothesis, which relies on an iPod touch for analysis, planning, and exact positioning of cutting tools.

Headquartered in Ostermünchen near Munich (Fig. 1), DHF Precision Mechanics counts among its customers well-known medical device, electronics, and aerospace engineering companies. The company specializes in high-precision CNC-milled parts and assemblies. After 15 years of virtually continuous growth, the company now operates 18 CNC machining centers and offers a service portfolio ranging from prototype manufacturing to bulk production of several 10,000 parts/year.

DHF has established a very good reputation in the market with utmost precision and fast and flexible reaction to customer requirements. When needed, DHF pushes the technical limits of CNC milling, like series production of parts for electrical motors, which must be produced with tolerances down to some microns on a lathe. The parts feature bearing seats where ball bearings have to be glued in place.

With quick reaction to customer requirements as a major objective, DHF established high in-house production depth. From CAD/CAM construction to preparing wrought material (various steel and aluminum alloys and titanium), to CNC-milling, to surface finishing, assembly and quality assurance.

Production processes at DHF frequently comprise welding, engraving and marking. Techniques for marking and joining on high-precision workpieces call for the laser. Welded parts have to feature perfect, pore and crack-free weld seams, especially in medical device manufacture, which has to provide sterile hardware and calls for immaculate surface quality to eliminate any chance of bacterial colonization. The same goes for all deep engravings and markings; contours have to be free from burrs and ditches. The marking process must not induce any material changes that might promote surface corrosive action.

Until 2012, DHF had been outsourcing laser material processing jobs completely. However, outsourcing significantly reduced production flexibility and speed for certain parts and increased complexity of logistics. More than that, the annual outsourcing business volume had been reaching the six-digit range; reason enough to think about establishing an in-house laser material processing center. Being laser rookies, Fischbacher, Telser, and Heilmann initially focused on laser marking because they expected laser welding to be much more difficult to control, at least before they had their first personal laser welding experience.

The complete solution
The DHF managers decided to incorporate a laser welding system in their investment planning. That meant sending samples to various laser manufacturers and asking them for a live presentation of the laser welding process. This was not an easy task, considering the required acuteness and surface quality, namely for medical devices. Andreas Sch?llhorn (Rofin-Baasel Lasertech Starnberg) knows about the importance of an optimum presentation in the application lab. He also knows that's just the beginning: "Medium-sized companies expect way more from us than just selling suitable laser systems. We take care of the employee's training, help setting up the first applications and our application support provides unbureaucratic assist during the first months. If required, we even design the production room according to laser safety standards, like we did for DHF."

Establishing an in-house laser processing center
Six months after Rofin and DHF's first contact at the fair, a Rofin laser processing center was installed at DHF GmbH, comprised of the integrated CNC and manual laser welding system and the CombiLine Advanced marking system (Fig. 2). The laser welding workstation seamlessly integrates manual or joystick-controlled deposition welding with CNC operation (Fig. 3). It offers a cross table for workpieces of up to 500 kg weight and an additional rotary axis. The Integral was chosen because of its large working chamber, which is spacious enough to freely rotate parts of up to 400 mm in diameter.

Even today when looking back, Paul Heilmann still expresses his surprise. "We had been planning to ramp up things slowly and to backsource the laser jobs one by one. In fact external laser processing was gone within a few weeks. Today we have ready-to-use setups for some 100 marking and welding applications right at our hands."

Laser processing for high-tech medical devices
A lengthy cooperation with Brainlab, a worldwide market leader for image-guided surgery and radiotherapy, benefitted from laser technology as well. Fischbacher says, "Frequently, we are cooperating in early product design stages. It is a big advantage to know exactly not only the possibilities of CNC milling but also of joining technology and marking, not to mention the faster manufacturing of prototypes."

For Brainlab's DASH (Fig. 6), DHF Precision Mechanics GmbH manufactures and assembles the iPod holder with all fixed or detachable 3D position markers and cutting devices. All pieces have to meet the sophisticated quality standards for medical devices. The entire parts set comprises 14 weld joints of precision milled parts, even of different stainless steel alloys. The mostly circular weld seams feature a width of only some 100 μm and must not show any pores or micro cracks (Fig. 7).

DHF deep-engraves the plastic iPod holder with the laser to form cavities which will be filled with a special paint. Thus, the marking is still visible when the paint slowly vanishes after numerous sterilizations.

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