It was a vision at first: a proton accelerator for cancer treatment was to be developed as a commercial product. Meanwhile, the project has advanced so far that manufacturing has already started, tests are being carried out and series production is planned for next year - provided everything is found to be functioning properly. The system of such a proton accelerator with an overall length of 24 meters comprises 20 modules, in each of which 64 copper plates are installed. These copper plates confronted all responsible parties with numerous challenges. All of the component tolerances are restricted to within 10 µm. As to the surfaces, RA 0.2 are required.  We are talking about an accuracy which is particularly difficult to achieve in series production. Thus, the main question for Peter van der Elzen, Quality & Operation Manager at VDL ETG Projects, at the beginning of the project four years ago was: can this accuracy be achieved at all. „VDL is known for the fact that we are able to machine with such accuracy without any problem. In this particular case, however, the problem was that these plates are of different design in terms of shape, thickness of the cutouts etc. On the other hand, it was the series which we intended to machine in unmanned operation for economic reasons. While other machine tool manufacturers saw themselves unable to achieve the requested accuracy, we heard a "We can try" from Fehlmann.  In other words, in principal Fehlmann said "Yes", using the VERSA 825. Still, for this task, a certain "tuning" was necessary, even for the already highly precise VERSA.    As Roland Sandmeier, Sales Manager Germany at Fehlmann, puts it: „Even the standard version of the VERSA is considered a high-precision machining center due to its geometrical precision and thermal stability. For machining the copper plates for VDL ETG Projects, however, we have changed fine details, such as swiveling cycles or also the zero point shift, by two µm, as the contours are finely milled line-by-line. However, the findings from this project have then also been incorporated into the production of our standard machines.“

Temperature fluctuations controllable, all production-related prerequisites fulfilled
Now, this task did not only involved the machine, but also the topic of unmanned production. The target was to control automation using the Soflex software - based on the positive experiences.  The choice concerning hardware or robots and pallet magazines, therefore, fell to Messrs. Gibas in Nijkerk, The Netherlands (Fehlmann agent in The Netherlands with their own automation department). All the more, since Gibas was in the position to integrate this software without difficulty.

Numerous examples in Eindhoven demonstrate how sensible such ultra precision is in series production, as machining is often done to the limits of possibility. For instance, the machine was opened after a machining time of two hours. The influx of the air conditioned air of the room immediately had such a negative impact on the component that it became unusable. Changing the spindle proved to be just as fatal. When replacing a warm spindle, extended in length, with a cold one, the responsible people were downright shocked. Which means that temperature fluctuations in machine and room invariably affect each other, although the responsible people at Fehlmann positively assure that temperatures are under control without fail. On the one hand, the machine is designed in a way that no coolant emulsion may drop on the cast construction. On the other hand, the motors are cooled automatically and the coolant is kept at a constant temperature of 20°C. The high importance of controlling the temperature in this way is shown by the fact that the machining time of just one copper plate is to six hours. Taken all together, this adds up to 30,000 milling hours for a system totaling 20 modules.

These six hours of machining time, however, could only be realized in close consultation as VDL ETG Projects intended to use a spindle frequency of 80,000 min-1 for economic reasons. To this end, numerous tests were executed at Fehlmann in Switzerland.
In the meantime, the end phase of the tests in question has started in Eindhoven and people there are convinced that all fundamental prerequisites can be fulfilled from a manufacturing point of view. Having made the apparently impossible possible can certainly be put down to the joint intensive development work and close cooperation. This is impressively proven by the fact that the entire project finally took four years, but then only two months passed from placing the order up to start of production.

To sum it up, there are also numerous aspects which finally led to the successful completion of the project according to Peter van der Elzen: „To realize such accuracy in series production, one needs competent partners and appropriate technical equipment. On the other hand, one must not forget that one has to have employees who have everything under control and are one with the machine. Independently of the height of the investment - when tackling such a project one has to have faith that it is going to function. And that faith I have had right from the beginning.“

VDL-Groep at a glance
As 100 % family-owned business, the company deals with development, production and sale of semi-finished products, busses and the assembly of passenger cars (currently BMW Group with the MINI Cooper). Taken together, 87 subsidiary manufacturing companies in 19 countries with approx. 10,500 employees belong to the Group. VDL ETG Projects in Eindhoven develops, produces, assembles and installs production equipment all over the world - among other things for industrial sectors like food and medical technology up to solar and semiconductor technology.

Interesting side note
Messrs. VDL ETG Projects is continuously searching for extremely precise machine tools. For instance, they also employ air-bearing precision machines which, however, are not suited for series production.

By the way ...
After the tests have proven to be entirely positive this year, VDL ETG Projects presumes that the series production of the proton accelerator can be started in 2017.

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