CEMEC Intelligente Mechanik (CEMEC), located in Spalt, near Nuremberg, Germany, develops and manufactures high-end, high-precision products for customers in various industries, a key one of these being aerospace. Martin Schwab, founder and MD of CEMEC, and his seven employees can look up into the sky and feel a great sense of pride knowing that their components are out there, deep in space, helping to make a real difference.
The Kern Micro HD 5-axis machining centre at CEMEC Intelligente Mechanik (CEMEC).
Schwab has made it his mission to invest in the machines required to deliver optimal solutions for his customers and allow for the manufacture of products that might otherwise be considered unmanufacturable. In 2019, for example, he acquired a Kern Micro HD five-axis machining centre from the German machine manufacturer Kern Microtechnik (Kern). This has allowed CEMEC to mill some of the most difficult materials and achieve new levels of precision and reproducibility for large as well as small series production. The company had previously only been able to accept small series projects.
Schwab started his own business, known as Schwab Feinwerktechnik, in Munich in 1986, straight after obtaining a degree in precision engineering. The realisation soon grew that development and production are more closely interdependent than is reflected in many companies and projects. Schwab elaborated: “Especially in the case of high-precision requirements, experts in these two areas have to constantly exchange information in order to reach the desired result.” He therefore decided to set about creating his own processes and bringing the two fields together.
Schwab renamed his company CEMEC Intelligente Mechanik in 1999 and moved it to the current location in Spalt in 2001. Here, thanks to a larger workshop, he was able to focus on further perfecting the aforementioned principle and established a reputation for being a problem solver for the seemingly impossible. Today, it is often the case at CEMEC that tolerances of a few micrometres or a few hundred nanometres must be achieved in a reproducible manner.
Martin Schwab, founder and managing director of CEMEC.
The Kern Micro HD makes an optical telescope possible
Tesat-Spacecom recently commissioned CEMEC to serially produce parts of an optical telescope for satellite communication, a project that has been made possible thanks to the Kern Micro HD. CEMEC produced the telescope mount, tube, screw-in rings to fix the lenses and ring to compensate for thermal expansion. The telescope tube is inconspicuous, measuring just 66 mm long by 20 mm diameter. Housed inside the communication unit of the satellite, it incorporates a laser and two lenses to give the laser beam an accuracy to target of 10 mm after travelling 100,000 km (62,000 miles). The laser beam must have a diameter of less than 5 mm in a temperature window of -40 to +60°C. In addition, the lenses, which are part of a larger system, must withstand the enormous loads during rocket launch and not lose any of their precision.
The aluminum alloy used for the telescope tube, selected by CEMEC and Tesat-Spacecom on account of its homogeneity and special thermal conductivity, is a challenging material. It consists of 40 percent silicon, so is extremely brittle and difficult to machine. “I hadn't worked on such a difficult material for a long time,” said Schwab. “But it wasn’t a problem because with the Kern Micro HD, we can still mill the finest threads with micrometre accuracy.”
Furthermore, the parallelism of the two lens seats must be better than 2 µm and because a ring is installed in between to compensate for thermal expansion, the individual parts must be machined with an accuracy of less than 1 µm. “Before the Kern Micro HD, I would have had to turn down such a request, and I don't think anyone else could have done it either,” continued Schwab. “Here we have a new product that was made possible with this high-precision milling machine and our knowledge. With the Kern Micro HD, we achieve an evenness of less than 800 nm and can rework micrometres if necessary.”
The telescope tube is a typical turning part. However, it is not possible to achieve the necessary accuracy using a drilling lathe. Therefore, CEMEC manufactured it completely in one setting on the Kern Micro HD. Processing took 40 minutes on one side and around two hours on the other.
The tool changer of the Kern Micro HD. CEMEC often uses all 210 spaces for complex machining tasks.
Key Kern Micro HD developments
The Kern Micro HD features developments necessary for achieving the required high precision and reproducibility required for the aforementioned and other such projects. In particular, the micro-gap hydrostatics, linear direct drive and temperature management provide significant advantages. All three of these developments are closely interlinked so that a coherent overall system is created.
Micro-gap hydrostatics
Micro-gap hydrostatics is a patent pending further development of the hydrostatic drives that have featured on the Kern Pyramid Nano machining centre for some time. The big advantage of micro-gap hydrostatics is that the hydrostatic guides and drives are not subject to mechanical wear. In addition, micro-gap hydrostatics allows for high accelerations and excellent vibration damping as well as significantly gentler and jerk-free movement of the tools, thus increasing their service life.
The Kern Micro HD’s micro-gap hydrostatics, as well as its smart design and linear direct drive, mean it is more robust and requires around 80 percent less energy than conventional hydrostatic systems. At the same time, the micro-gap hydrostatics improves the rigidity and vibration damping properties of the system, ensuring exceptional accuracy and surface quality of the part. If required, Ra values of 0.05 μm can be achieved in serial production, eliminating the need for a finishing process.
Linear direct drive
Linear motors are a popular drive system for machines, offering advantages over ball screw drives in terms of dynamics and control accuracy. However, they have been of limited suitability for high-precision machines due to their enormous heat input. According to many studies, temperature is responsible for around 70 percent of all accuracy errors in the high-precision range.
The Kern Micro HD’s linear motors are large and actively temperature controlled to help minimise heat input and thus improve drive of the axes. The successful integration of the three developments depended heavily on being able to control the heat generated by the linear motor.
Temperature management
Temperature management has been taken to a new level for the Kern Micro HD. The coolant is regulated very precisely and sent at a volume flow rate of up to 200 l/min through the machine frame, rotary/swivel axes, linear axes and spindles. The result of this development is shown in a thermal stress test. Barbara Bergmann, sales manager at Kern, explained: “The control accuracy of the central temperature management is +/- 0.05 Kelvin and therefore provides the perfect basis for extremely precise machining.”
Half of the aluminium alloy optical telescope tube produced by CEMEC for its client Tesat-Spacecom. CEMEC milled this part and other parts such as the ring to compensate for thermal expansion on the Kern Micro HD with an accuracy of less than 1 µm in serial production.
A trusted supplier and partner for the long term
The micro-gap hydrostatics and temperature management are the main reasons for CEMEC’s deciding to invest in the Kern Micro HD. The telescope, for example, could not have been produced on a machine suffering from influences caused by heat. “When machining with coarse cutting and high torque, with fast cutting steps, the machine inevitably warms up,” said Schwab. “If temperature is not actively managed, the thermal expansion often causes such large deviations during final processing that the required precision cannot be met.”
Furthermore, the Kern Micro HD provides the guarantee that the precision will be achieved over the long term. “Knowing that the machine will still work as precisely as it does today in 15 years' time is very important for me,” added Schwab.
Not only does Schwab regard the Micro HD as “an essential component” in meeting CEMEC’s exceptionally high-quality standards but he cannot fault the support received from Kern technicians. “If we have a problem, we contact Kern and get all the support we can think of,” he said. “I have never experienced this with any other supplier.”
Prior to the arrival of the Kern Micro HD, CEMEC mostly produced prototypes and small series of 5 to 2,000 pieces. Today, the company has the means to produce larger series with the same precision. However, Schwab has no intention of stopping here and anticipates further expanding CEMEC’s capabilities in the not-too-distant future, a future that is guaranteed to involve Kern. “My plan is to work with at least two or three more Kern machines,” he concluded.
CEMEC Intelligente Mechanik
Kern Microtechnik