Precision through thermostability

The two machine series are designed for machining workpieces in the automotive, e-mobility, agricultural and construction machinery, aerospace and water and fuel cell technology sectors and are geared towards high productivity. While design principles such as the monoblock and the box-in-box three-axis unit optimize machine rigidity with the lowest mass used and thus machining accuracy, the swivelling fixture carrier for loading and unloading during machining reduces unproductive downtimes. For example, series parts made of aluminum alloys for transmissions, wheel suspension and steering, brakes or battery housings, as well as implants for medical technology, can be produced with maximum precision and efficiency.

In order to further increase positioning accuracy, the company is working on improving thermal stability via the existing precision cooling circuit. "We see thermal accuracy as an important competitive advantage in precision machining," explains SW Head of Development Marcus Mixner. "After initial tests and optimizations with the Z-slide, which moves into the work area, we are now concentrating on the temperature control of the guide in the vertical main axis, which carries the X and Z slides."

Direct heat dissipation in the guide rail

The decisive solution with which SW achieves the desired positioning accuracy economically and in a space-neutral manner comes from linear technology partner Bosch Rexroth. Their patented Thermo Compensating Rail System TCRS works according to a principle that is as simple as it is effective: the temperature control function is integrated as an optional feature into the roller or ball rail guide selected by the customer. For this purpose, Bosch Rexroth equips the underside with grooves for inserting commercially available pipes that are connected to the machine's cooling circuit.

The integrated cooling lines dissipate the energy loss caused by friction and motors from the two roller rail guides installed in the main axis, thus ensuring a stable temperature level. At SW, the integrated cooling lines primarily have to dissipate the waste heat absorbed by the linear drives. "An efficient heat management system is so important for us because the weight-optimized three-axis unit in box-in-box design with thin-walled welded constructions can only absorb a small amount of heat," explains Marcus Mixner. "Without temperature control, the dynamic power output of the linear motors would quickly lead to thermal deformation."

The integrated TCRS temperature control option enables thermally stable precision machining. The space-neutral solution can be ordered via the Rexroth online configurator for guide rails. © Bosch Rexroth

To illustrate this, Mixner calculates that the 3 meter high monoblock expands by almost 0.05 mm with a temperature increase of just 1 Kelvin. In comparison, the BA W06 and BA W08 machining centers with integrated temperature control from Bosch Rexroth achieve a positioning accuracy A (X/Y/Z) of less than 0.006 mm in the main axes and a repeatability R according to ISO 230-2 of less than 0.004 mm. Temperature control further reduces dimensional fluctuations in the process and minimizes the reject rate.

Without the installation space-neutral temperature control option, the design and assembly would have been significantly more complex, as additional components such as cooling fins would have been required for the cooling function. "In other machine series, we had already achieved thermal improvements with our own solution by attaching specially manufactured aluminum profiles next to the axes," explains Sascha Röder, who is responsible for mechanics in the development department and was involved in the introduction of the temperature-controlled guide rails. "The integrated solution from Bosch Rexroth saves us this effort, as it requires no additional components or work on the machine bed apart from the piping. This allows us to implement thermal compensation with minimal construction and operating costs." According to Röder, the TCRS guide rail can be installed just as quickly and easily as the standard guide with identical dimensions. The tried-and-tested clip-on cover strip saves even more time.

Fast and stable production

Head of Development Mixner also sees a major customer benefit in the faster production of good parts: "The market is increasingly demanding machines for smaller batch sizes. We are therefore required to keep the time constants as short as possible." After intensive research, SW succeeded in "cooling away" the high power losses that occur at high speeds in order to minimize rejects as soon as possible after start-up. "Based on measurement data collected over two years, we developed a complex cooling water temperature control system," says Mixner. The result is impressive. Since the market launch of the BA W06, the feedback from the field has been consistently positive.

The flexible temperature control option also offers great potential for the future. "We are already working on further applications," reveals Mixner. In addition to guiding and temperature control, the possibility of integrating measurement as a third function into the guide in a space-neutral manner, which Bosch Rexroth can also map with the integrated measuring system IMS, is interesting.

Klaus Mandau, Sales Linear Technology Europe Central, Bosch Rexroth / as

EMO, Hall 6, Stand H12