Automated manufacture of laminated hip prosthesis coverings
Aesculap AG‘s headquarters are situated in Tuttlingen, the hidden global capital, in the Mecca of German medical technologies. Aesculap is part of the B. Braun group, one of the world-wide leading manufacturers of medical technologies and pharmaceutical products and services with more than 64,000 employees in 64 countries worldwide. Founded in 1867 as a small workshop for surgical instruments, Aesculap is now one of the most well-known manufacturers of medical products and technologies. In order to hold on to and further develop this market position, the demands on production are remarkably high. Aesculap produces tools of extremely dissimilar dimensions. The range spans from a composite tool 2.5 meters in length with a weight of up to three tons down to micro-production with tiniest tools, for example for holding micro-needles of a hair‘s breadth, approximately 70 μm (micrometers). But not only are the size differences of the products stunning – their immensely wide product range is, too. The current count is 28,000 different products included in the company‘s portfolio.
Aesculap and GROB – a long history of collaboration
As is fitting for its wide and diverse product range, Aesculap‘s tool and prototype manufacture machinery is designed accordingly. Universal machining centers from GROB have also already been included in this machinery since 2010. This makes Aesculap one of our oldest customers that use GROB universal machining centers. „After interesting initial talks, we came up with a model for the applications engineers at GROB to build,“ Hans Keller, Head of Tool and Prototype Manufacture at Aesculap AG, recalls. „The model was a hip impactor, a relatively large piece of equipment for hip operations. This was a problematic piece for us then, having an extremely long machining time of more than three hours.“ The problem was clearly defined: Despite its tough, hard-to-machine material – the impactor is fashioned from 17-4PH, a chromium-nickel stainless steel – the machining time had to be reduced as much as possible. We ended up actually managing to reduce the machining time for the hip impactor by more than half due to the high speeds GROB universal machining centers could be operated at without vibrations, meeting the requirements for automated machining in large quantities in mostly unmanned shifts.
Impressive GROB engineering for medical technologies
Nevertheless, despite excellent results from the manufactured prototype, it was a long road to overcome all of Aesculap‘s concerns about the GROB machine. The reason for this was simple: „My machining engineers in Tool Manufacture were only familiar with vertical machining,“ Keller recollects. „Horizontal machining was unknown to them at that time. The spindle from the rear, the different programming and clamping for the machine. These processes were new to them.” This could only be solved by a visit in Mindelheim and a successful machining test in GROB‘s Technology and Applications Center.
The Tool Manufacture colleagues quickly realized the extremely high productivity GROB universal machining centers could achieve by utilization of strong spindles and the stable machine design. This is a design that is very well-suited for machining solid blocks of material, which is often the case for medical instruments. This presents a very interesting situation for medical technologies, as the high diversity for variants often only allows for very small batch sizes.
They also saw that the slender spindle design and the specific arrangement of the axes on GROB universal machining centers permits the use of short tools, reducing tool costs. Aside from that, it quickly became clear that the innovative 5-axis cycles facilitated by the two torque drives on the A-B-axis ensured optimal tool use with significantly better service life. But not only our GROB technologies had impressed Hans Keller. He also quickly saw why GROB is one of the most important partners in the automotive industry during the tour of our facilities that followed.
Tool Manufacture – driver of applied technologies at Aesculap
Under the leadership of Hans Keller and with his approximately 70 employees, the Tool Manufacture division represents the ‚think tank‘ of the company. If Hans Keller is impressed by new machining technology, it is first used for the manufacture of tools and is tested exhaustively before being granted approval for production. „Since we know precisely what is required for application in production despite the extensive range of several thousand different products, this process has proven itself thoroughly over the years.“
So, after successful test machining of a hip impactor in the GROB Technology and Applications Center, a GROB G350 - Generation 2 was procured for Tool Manufacture. This machine is equipped with a Heidenhain TNC640 control system, an air-lubricated spindle with 16,000 rpm, a torque of 220 Nm and a double disk-type tool magazine for an HSK-A63 with 117 tool pockets. „For an automation system, we decided on a LANG Robotrex system with two automation trolleys and 30 5-axis clamping fixtures each. This is equipped with a mechanical clamping mechanism with no rotary transmission in the machine table and needs no separate pallets,“ explains Keller. This automation system is completed by a FANUC articulated robot with a vise-type gripper. However, the original problem with this was that the LANG automation system had been designed together with Heidenhain so that only one product could be machined at one time. Regardless, according to requirements, each vise of the 60 units would have had to be able to machine different products as well. A customized modification to the controls was finally implemented for this in a collaboration between GROB, Heidenhain and LANG. In the Heidenhain control system, each vise was assigned its own designation via the Batch Process Manager. This allows Aesculap to manufacture different components, as each vise can hold a different product. In principle, the system now works like a large palletizing system.
„Not only the production setup at GROB fascinated me. I also really liked family atmosphere. The way the employees reacted to Mr. Grob and vice versa, that was impressive for such a large company. It was comparable to our group at Aesculap.“
Hans Keller - Head of Tool and Prototype Manufacture
Coverings devices for hip prostheses that will later be grafted into the femur are currently being manufactured on the G350. The material used is 1.4301. The covers are made from flat material in one clamping sequence. After this, a small amount of manual work is required to remove a small connection. The run times vary from between 20 and 85 minutes depending on the cover size. If the two automation trolleys are equipped with the maximum number of 60 5-axis clamps, this means that continuous production can run for between 20 and 85 hours without machine maintenance, depending on the variant produced. The machine runs seven days a week with the least man hours possible. „We have around 200 different hip prostheses, small, large and medium,“ explains Applications Engineer Thilo Hagen. „The run times vary depending on the size of the part. The longest run time is one hour and 25 minutes.“ He adds: „We‘ve had this machine for four years now and never had a problem with it. With the extensive GROB service package, complete maintenance is carried out on the machine once per year, which is important for us, as we can total up to 6,000 spindle hours per year.“