# Correction of Thermal Errors in Machine Tools by a Hybrid Model Approach
## 3 Experimental Characteristic Generation  
At first, a reference characteristic of the DMU80 machine tool was created by extensive thermal experiment studies that were, in addition, the basis for the validation of the created simulation models. The experiments were carried out on the demonstrator machine during operation in different load situations, where, at the same time, the physical variables of temperatures, displacements, motor currents, and axis speeds were recorded. To do so, a structured experimental plan was drawn up in order to provide meaningful load cases for the validation of the simulation calculations. This plan outlines the number, duration, and type of experiments, as well as an estimated workload for the measurements. Based on this, the measurement set-up with the corresponding sensors was practically built and the measurement data acquisition system was set up. When carrying out the experiments, care was taken to eliminate as many disturbance variables as possible and to ensure that the target variable could be sufficiently resolved so that a clear distinction could be made from measurement noise at all times. The measurements were carried out on the DMU 80 evo in a stationary climate chamber (Figure 2), which allows the ambient and ground temperatures to be controlled. In addition, the climate chamber offers a wide range of options for the climate control, which was used for the experiments:  
* Setting of a fixed ambient temperature in the range of 10-40 \({}^{\circ}\)C;
* Regulation of the air humidity to a stable value of 50%;
* Control of the floor temperature in the range of 15-30 \({}^{\circ}\)C;
* Variation of the ambient temperature in a day-night cycle (sine wave). A cooling lubricant module with a capacity of up to 900 L was available for the test machine, which was equipped with a cooling unit with a capacity of up to 6 kW. The temperature of the cooling lubricant was recorded at all times. Figure 1: Architecture of the hybrid model approach. Further operational parameters of the machine are the type of coolant supply (external coolant supply through side nozzles, coolant supply through tool, and bed flushing) and the internal and external heat sources. The internal heat sources arise from the power loss of moving machine components (bearings and motors) due to friction and winding losses in electric motors. These are mainly caused by the rotary motion of the table, the motor spindle, and the rotation of the swivel axis. External heat sources include chips during the machining process and heating pads, which are used in experiments to introduce heat in a specified manner. For experiments without machining (air cuts), the external heat sources are omitted. In the experimental design, the heat sources within the machine and the environmental influences due to cooling lubricant and global ambient temperature were considered and investigated in a decoupled manner, Table 1.  
The basic experimental plan was divided into three main blocks. In the first main block, the influence of the cooling lubricant on an unmoved machine was investigated at a previously defined and stable ambient temperature. The parameters temperature, volume flow, and type of supply were varied. In the second main block, the temperature of the cooling lubricant was controlled as stably as possible, whereby the parameters of the ambient temperature and machine load (internal heat sources), expressed as the percentage of the maximum travel speed of the machine, were considered separately, Table 1. In the third and last main block, practical load cases were examined and considered in order to verify the correction approaches developed in the project. Hereby, the change in ambient temperature, room-temperature-controlled cooling lubricant temperature, but also machining processes were included. These investigations can also be carried out outside a climate chamber and are intended to prove the newly developed simulation approaches for practical use.