COMBINING EXPERTISE FOR THE MEDICAL INDUSTRY

Using new and modern manufacturing processes, a few prominent medical industry players together have tackled the challenges for economical machining of implants with multifunctional as well as non-round bionic designs. The focus was on the three manufacturing processes of eccentric turning, polygon turning, and high-speed whirl milling (turn whirl milling).

Modern medical implants for orthopedics, traumatology, and dental technology are characterized by rigorous demands on strength, biocompatibility, and bionic-optimized geometry. The geometry of an implant is adapted to the bone and tissue. In the process, the functional surfaces of the implants are given an increasingly sophisticated design to facilitate their attachment to the body and make them less invasive for the patient. The new designs of implants drive up manufacturing costs because the surfaces are no longer circular or square. They have more curved surfaces and functional elements with continuous transitions in a very small space. In particular, the need for several manufacturing steps on different machines causes costs to rise significantly. For example, precise handling for the exact reclamping of a workpiece represents a considerable cost factor. Therefore, despite the high level of functional integration, an efficient process route is needed for economical production.

Novel processes

ZykloMed, a joint project funded by the Federal Ministry of Education and Research (BMBF), has the participating partners INDEX, Paul Horn GmbH, Beutter Präzisions-Komponenten GmbH, and the wbk Institute for Production Engineering at the Karlsruhe Institute of Technology (KIT) demonstrate their expertise in the medical industry.

Using new and modern manufacturing processes, the partners have tackled the challenges for economical machining of implants with multifunctional as well as non-round bionic designs. The focus was on the three manufacturing processes of eccentric turning, polygon turning, and high-speed whirl milling (turn whirl milling).

The novel manufacturing processes of eccentric turning, polygon turning, and high-speed whirl milling (turn whirl milling) are all based on the same kinematic principle of multiple synchronized rotating axes. While this principle is well known, its application to non-circular and curved shapes is highly demanding. At the same time, the practical implementation must meet the high-quality requirements of the Medical industry.

R-L: The project participants at the final presentation of the BMBF joint project. Dr-Ing Volker Sellmeier, INDEX-Werke GmbH & Co KG Hahn & Tessky; Andreas Kanz, Paul Horn GmbH; Dr-Ing Wolf-Dieter Kiessling, BEUTTER Präzisions-Komponenten GmbH & Co.KG and Tassilo Arndt, Institute for Production Engineering at the Karlsruhe Institute of Technology (KIT).

The project partners researched and developed novel manufacturing procedures along the entire process and supply chain, from the machines and control technology to the tool design to prototype and pre-series production. The manufacturing processes were simulated and designed based on known methods with the same mathematical principles in order to determine the requirements for the tool and machine. The tests were divided into equivalence tests under laboratory conditions as well as pre-series tests in laboratory and near-application environments. The engineers focused on both machine and tool technology for the development and design of the individual processes.

Eccentric turning enables highly productive production of non-round external contours.

Polygon turning offers the possibility of producing non-round contours on lathes.

High-speed whirl milling (turn whirl milling) is a highly productive process for manufacturing bone screw threads.

In eccentric turning, a rotating non-circular tool is guided along a rotating workpiece under positional coupling. The speeds are brought into a certain ratio to each other. The out-of-round shape is thus reproduced on the component within certain limits. The process offers highly productive production of eccentric outer contours. The rotation of the tool reduces the thermal load at the cutting edge, which ensures long tool life. The process also enables the production of tapered profiles.

In addition to the production of new component geometries, the processes also offer optimization potential for the economic production of existing implants, as well as possible applications beyond the Medical industry.

Polygon turning is a process for producing non-circular external and internal contours with the shape of a hypotrochoid. Like rotary eccentric turning, the process offers the possibility of producing non-circular contours on lathes. In the process, the parallel axes of the workpiece and the tool are offset from each other by an axial distance and are brought into a specific speed ratio under positional coupling. The axial distance, the speed ratio of the workpiece to the tool, and the cutting diameter of the inserts define the dimension of the contour. A tool system for polygon turning is individually adapted to the contour of the workpiece to be produced.

High-speed whirl milling (turn whirl milling) is a highly productive process for producing threads for bone screws. One or two circular milling cutters are set at a certain angle to the workpiece. The directions of rotation of the cutters and the workpiece can be the same or opposite. The speed ratio of the workpiece to the two cutters depends on the number of threads and the number of cutter inserts. For the first time, high-speed whirl milling (turn whirl milling) can also be used to economically produce threads with a true variable pitch by dynamically changing the thread profile.

Tests close to series production successful

With successful tests in a near-series production environment, the partners of the ZykloMed project have come a big step closer to the goal of the research project, the economic production of implants of multifunctional and non-round bionic design. The engineers proved that the synchronized manufacturing processes enable the economic production of modern implants. In addition to the production of new component geometries, the processes also offer optimization potential for the economic production of existing implants, as well as possible applications beyond the Medical industry.