Automated manufacture around the clock

08.09.2015

Even if the place of application is special, the requirements placed on the production of medical devices are similar to those for products from other industries – automated, high-precision and efficient. Consequently, Stryker-Leibinger in Mühlheim-Stetten on the Danube relies on production measurement technology from Blum-Novotest for its machining centres for medical instruments and implants, not only does the system guarantee reliable unmanned operation, but also consistently high quality.

"The production of instruments uses several milling machines from DMG Mori, particularly the DMU 50 and DMU 60 models. Three of these systems are equipped with LaserControl Micro Compact NT laser measuring systems and TC52 touch probes from Blum-Novotest," says Simon Heyse, Milling team leader and responsible for machinery procurement and equipment. "The measuring systems enable unmanned production as it is organised at Stryker: Machine operators work on the milling machines during the early and later shifts, while the night shift is unmanned." On weekends, work is unmanned around the clock, to this end the machines are equipped with workpiece storage units and handling systems, which remove and insert workpieces during unmanned hours.

In order to ensure the smoothest possible unmanned operation the machining must be monitored, if a tool breaks there is no one there to press the emergency stop button. Therefore, each tool – from the 0.5 mm ball nose cutter to the 63 mm saw blade – is measured using the laser measuring system after each machining process and prior to replacement in the tool magazine. Should the measuring system determine that the tool is broken, it is clear that the machining step was not properly completed. The workpiece is rejected and the broken tool is replaced in the next machining step by a new tool. This ensures that only one component is lost and that machining continues to run smoothly even in the event of a broken tool.

"The touch probe, which is mounted in a tool holder and stored in the tool magazine, is used by the machine, for example, to register zero points or to check actual dimensions after machining. This enables worn cutters to be identified amongst other things," explains Simon Heyse.

"With particular forceps, it may be that the blank is not correctly inserted. Then the milling cutter does not run laterally over the handle to create gripping grooves, but slams into the blank and breaks." These special profile milling cutters can have a delivery time of up to nine weeks, which is why the Mühlhofen company would like to avoid breakages. Therefore, it has inserted a short measurement sequence at the beginning of the NC program, during which the touch probe touches the forceps handle and ensures that it is correctly clamped. Since then, it has lost no more milling cutters to breakage.

The BLUM laser measuring systems were included with the DMG Mori milling machines. However, at that time, touch probes from another manufacturer were still being used for workpiece measurement. But when the Stryker NC specialists saw the BLUM TC52 at AMB 2012, they also switched to Blum products here and were surprised that it was possible to touch so quickly. The BLUM probes can be pre-positioned at 40 m/min, while the maximum speed of the old probes was 3 to 5 metres per minute. Naturally, the actual touch movement must be slower, but even here, at 2 m/min, the BLUM probe is able to touch a lot quicker than its predecessor. The high positioning speed and the rapid touching shorten the measurement processes considerably. On the one hand, the machining time is significantly reduced, on the other hand an additional measurement cycle, which is inserted to make the process more reliable, does not require as much time as before. The frequency at which the measurement occurs is, in part, a balance between longer machining time and increased reliability. However, the less time the measuring costs, the more measuring processes the Mühlheim company can 'afford'.

The latest machine, a DMU 60 Linear was equipped with BLUM systems from the outset, and it is already clear that future purchases will feature the measuring systems from the company based in Grünkraut, Upper Swabia. For a long time, the NC specialists at Stryker did not fully utilise the potential of the laser control systems. The reason for this was that they were simply not aware of all the possible uses, as at that time the systems were purchased with the machines. When they learnt from a service engineer that BLUM also offers training, they immediately arranged a meeting. The training took just one day and was carried out at Stryker's premises. Since then, they know how to utilise the full range of cycle functionality and are inspired by the many opportunities.

"We no longer only use the laser measuring systems for breakage control, but also measure the cutting of shaft and T-slot cutters, drills or gear cutting tools for wear and chipping. The concentric runout of the tools and the complete form of cutters are also measured by laser," explains manufacturing engineer Jörg Hermann. "Our pre-setting device is now very rarely used, since we calibrate the tools directly in the machine. It is quick and easy and has the crucial advantage that the tools are measured under rated speed and in the real clamping situation. This enables us to offset any influences from the machine, making our machining even more precise."

If all tools are still OK after machining and the program has completed without any error messages, the workpiece must be OK – thanks to the measurements, the Stryker manufacturing experts can be certain of this during the process. Nevertheless, a milling machine is no measuring machine, so the first, middle and last part of each production order are verified on the coordinate measuring machine. The NC specialists have not had any losses for a long time, just 100 percent good parts from the outset – except for when a tool breaks.

The production measurement technology from Blum-Novotest has completely proven itself in Mühlhofen-Stetten. For Stryker, it is also a great advantage to have only one supplier for its laser measuring technology and the touch probes. Thanks to the high speeds possible with the BLUM touch probes, the measuring processes are 50-70 percent shorter. "Without the BLUM laser measuring system, the reliability of the unmanned operation that we have here would be unthinkable. Details such as special blowing nozzles demonstrate how comprehensively BLUM analyses the entire process within which the products work. The next systems will certainly be equipped with BLUM measuring technology," says Jörg Hermann positively. "And it should not be forgotten that the services associated with the products – from service via advice to support – are first-class."

The manufacturing experts have nothing but good things to say about the service and advice from Blum-Novotest. Not only do the service engineers take care of the machine for which they were called, but they also look at the other machining centres, provide tips and really get involved when something does not function properly. So much commitment is rarely seen at Stryker. The telephone hotline operators have also always provided quick and expert help.

One great example of the expertise demonstrated by the BLUM developers is the blowing nozzles developed in-house that we have already mentioned. These are attached to the carrier of the laser measuring system and are used to clean any coolant and chips off the tool during the measurement. A unidirectional valve is integrated in the nozzles developed by BLUM, which prevents the ingress of coolant. Simple nozzles without this valve easily fill with coolant during machining. "If the tool is then cleaned, a surge of liquid and chips will first pour out over the tool. BLUM blowing nozzles do not fill up and prevent the tool being contaminated," summarises Simon Heyse. "In addition, a great deal of development work has been invested in the form of the jet, resulting in perfect tool cleaning. Since we have been using these nozzles, the measurements are much quicker and more precise."


Stryker Leibinger GmbH & Co. KG

Tuttlingen and its surroundings in the Swabian Alb region is an industrial hub for medical devices and instruments. One of the many companies located in this area is Stryker Leibinger GmbH & Co. KG in Mühlhofen-Stetten. Founded by Oswald Leibinger in 1951, the company has been owned since 1998 by the Stryker Corporation, a global medical technology group with more than 25,000 employees.

In Mühlheim, as well as instruments, Stryker also manufactures implants, for example, for stiffening wrists or to fix a broken jaw. Within the Stryker Group, the site is the centre of excellence for instruments. In addition to manufacturing the constituent parts of more than 1,800 components that are produced in Mühlheim, the process stages also include assembly and surface treatment. These are undertaken by the around 120 employees working at the site. www.stryker.de

 


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