Friction, electrical losses, cooling systems and ambient conditions influence the thermal field of machine tools and cause a significant amount of positioning inaccuracies and production errors. Compensation strategies aim to reduce the thermal error in machine tools. The global urgency for energy-efficient production also affects the selection of specific compensation strategies, especially since some of them consume significant amounts of energy while others are potential energy savers. As of today, there is no method to select the optimal compensation strategy for thermal errors in machine tools. The main reasons are that the quality of any compensation strategy depends heavily on the examined machine tool and its intended usage. Besides this, there are several, often conflicting assessment criteria.This paper provides an overview of existing compensation strategies and presents an evaluation of their effect on the energy consumption. The investigated strategies comprise methods for reducing the heat losses, for decreasing the sensitivity of the tool center point to thermal influences, cooling strategies for removing heat from the machine tool, air conditioning and methods for controllable heat transfer and also various computational methods aimed at predicting and correcting the existing thermal positioning error in the machine tool control.As an addition to previous research, the rating of thermal error compensation strategies was extended by their effect on energy efficiency. The authors demonstrate that accuracy and energy efficiency must be considered jointly for each individual machine tool and manufacturing task.

The Collaborative Research Centre (CRC) “Transregio 96” focuses on the thermo-elastic behaviour of machine tools and the development of solutions, that aim at reducing thermally induced manufacturing errors. Various compensation and correction solutions were developed. To verify the efficiency of those solutions, a measuring technique involving a test work piece (TWP) and defined load cases were developed. The load cases are given in the form of NC-programs to create thermal loads on a machine tool by moving its feed axes on a pre-defined route, rotating the main spindle at pre-defined speeds or letting the machine tool rest for a pre-defined period of time. The TWP was used to capture the resulting thermally induced displacements of the tool center point (TCP).In this publication the TWP and the two load cases are described. And the test procedure itself, as well as experimental data to validate the results are presented. The described approach has the potential to be a cost effective way for measuring thermally induced errors of machine tools. It allows for a simple and time saving experimental setup and is easy to apply on, and compare the results between multiple machine tools. Furthermore, the presented method of determining thermally induced displacements of a machine tool’s TCP will be compared to other commonly used direct or indirect measurement techniques, showing its benefits, drawbacks and limitations.

Conventional approaches to counteract thermal issues in machine tools often require a significant amount of electrical energy input, such as in active cooling systems. An energy-efficient way for reducing thermal errors is to use passive components that redistribute heat introduced by feed drives and other internal heat sources. On the one hand, latent heat storage units can be integrated into the machine to enhance the thermal stability within the phase transition temperature range of the underlying phase change material. By using latent heat storage units, the impact of highly time-varying heat flows on the thermal displacement of the tool center point can be reduced. On the other hand, passive heat-transfer devices such as heat pipes allow for an increased heat exchange within the machine tool or between the machine tool and the environment. Heat pipes exhibit a very high effective thermal heat conductivity and can be used to transfer heat from machine-internal heat sources to additionally integrated heat sinks. A compensation system is presented combining latent heat storage units and heat pipe systems. To evaluate the effect of the corresponding components on thermally induced displacements, experimental investigations of the system within a machine tool are conducted. By means of temperature and displacement measurements it is demonstrated that the proposed compensation approach allows for partial compensation of the thermal error of the machine tool.

Thermally-induced displacements cause large parts of residual machining errors on modern machine tools. Their transient behavior makes it difficult to manufacture with high accuracy. To still increase machining accuracy and to meet the demands of the industry, research offers various solution methods to minimize this error.Within the Collaborative Research Centre Transregio 96 (CRC/TR96), various solutions have been developed that either try to compensate the heat flow in the machine so that large temperature gradients and resulting displacements are avoided or aim to predict the amount and direction of the thermally induced deviation at the TCP.In order to make these solutions comparable, they were first consistently classified and analyzed in terms of their implementation effort and risks. Potential benefits were proved by measurements. The benefits and efforts identified in this way were evaluated with the help of a multi-criteria decision analysis method so that the feasibility and implementation effort of the various solutions can be estimated for manufacturers and users of machine tools.A software-based tool was developed to help interested industrial users to select a suitable process for their individual production scenario from the available processes via an input mask. The tool thus fulfills two aspects. On the one hand, it facilitates the transfer of the developed solutions into industrial applications. On the other hand, it documents the research status of the various solutions, shows potential for improvement, and new methods can be uniformly documented in the future and thus, made comparable.