The researchers measure the thermal expansion of machine and workpiece. This enables them to compensate for the error during the production process. As a result, the machine maintains its exactness independently of the ambient temperature, leading to significant savings in operating costs and reduced cooling efforts.
In large workpieces and large machines, up to 75 % of all manufacturing defects are associated to temperature variations. Large machines and workpieces are affected particularly hard because thermal expansion is most perceivable over long distances. The typical solution, cooling the machine to achieve equal temperature distribution, has a drawback: It only achieves satisfying results if the cooling system as well as the machine is active around the clock since it can take very long time to reach the steady state. Plus, the thermal stabiliser system consumes much energy.
In the EPSIS research project, Fraunhofer researchers along with tool machine manufacturer SHW Werkzeugmaschinen GmbH are exploring ways to achieve thermal stability without complex temperature control. Instead, the researchers rely on sensors and algorithms: A large number of integrated sensors constantly measures the deformation. In addition, they created a mathematical model that describes and predicts the thermal deformation in relation to the type of processing step and material used. Once the deformation is known, the machine can compensate for it by taking the expansion into account. The thermal deformation is monitored pre-computed continuously, enabling the machine to achieve the original precision even without any thermal control. With this method, tool machine operators can reduce their operating costs considerably.
Within the scope of the project, the research partners installed a measurement system at SHW Werkzeugmaschinen that directly registers the thermal expansion of a machine bed with a size of 20 metres. The system indicates how the machine bed works at different temperatures. While the exactness of the measurements is comparable to a laser interferometer, the costs of the system are much lower. Initial measurement series under typical conditions for the production of large parts have shown that external factors such as vibrations or oil mist have no negative effect on the results, proving that the system is robust enough for industrial deployment.
In a next step, the researchers plan to determine at detail how the data acquired can be used to correct the positioning errors of the machine axis. Their goal: They want to automatically compensate for the manufacturing errors caused by deformations of the machine components. In addition, they plan to install additional sensor systems to gain a more detailed and comprehensive image of the machine.