Stephan Bäumler

Energy Efficient Cooling Systems for Machine Tools

Cooling systems are used in machine tools e.g. for the cooling of the spindle, the drives, the cooling lubricant, the control cabinet and the hydraulic system. Cooling systems are one of the main consumers of energy of machine tools. This paper analyses and compares different decentral cooling systems with regard to their power consumption for an exemplary machining centre. To achieve this, the power consumption of the exemplary machining centre is analysed for different operating conditions. On the one hand a cooling system is analysed that from the perspective of energy efficiency represents state-of-the-art technology. And on the other hand a unit is examined whose energy consumption has been optimized. Besides power, displacement of tool centre point and further values as pressure, flow rate and temperature are monitored for the different machining conditions and cooling systems.

Measurement of structure dynamics using a tracking-interferometer

Measurement of structural dynamics can be used for dynamic characterization, diagnostics, condition monitoring, analyzing sources of vibration problems, design optimization and, finally, as comparison data to improve computation results. Mainly for open surfaces in automotive and aerospace industries the modal testing is often performed using laser vibrometers. In the case of partially closed structures as machine tools, modal analyses comprises the three dimensional vibration measurements at up to several hundred points of the structure and is classically conducted using accelerometers. This paper presents a novel approach to perform modal analyses using a tracking-interferometer. The modal analysis is shortly introduced along with the two mentioned methods. Further, the functionality of tracking-interferometers is discussed as well as the basics for their application in dynamic measurement. One-dimensional measurements using a tracking interferometer are conducted and benchmarked against other devices. Three-dimensional measurements are presented including the necessary coordinate transformation. A small modal analysis is demonstrated. Finally, a measurement strategy for fast modal testing is suggested and additional functionalities required for the tracking interferometer are discussed.

Prediction of Dynamics of Modified Machine Tool by Experimental Substructuring

Until now the methods of experimental substructuring are rarely adopted in the machine tool sector, except for receptance coupling of tools and tool holders. In this paper, the methods are adopted to predict a general modification of a machine tool structure by coupling experimental and numerical models. This approach seems appropriate, since most design changes of machine tools affect only some part of the structure. Additionally, single components of a machine tool are easier to simulate than the complete machine tool, since they include less joints, which are usually difficult to parameterize. This contribution evaluates the proposed method, when it is applied to a single axis test bench. The slide is taken as the modified component—thus its dynamics are modeled analytically—and the remaining assembly is modeled experimentally. Particular emphasis is put on the modeling of the interfaces of the linear guides connecting the slide to the frame. Both a fixed connection between slide and frame and a linear spring-damper joint are adopted. Moreover, the dynamics of the assembly are predicted, for different positions of the slide. As a reference, the dynamics of the test bench are measured, when the slide is mounted.

Calculation of Kinematics and Friction of a Spindle Bearing Using a Local EHL Friction Model

A new calculation method was developed to determine the kinematics and friction in high-speed angular contact ball bearings (spindle bearings) under steady-state conditions. The basic idea of this model is to determine the exact ball kinematics by taking the resulting local friction forces on the ball into account. For this purpose, a simple elastohydrodynamic lubrication (EHL) friction model derived from measurement data of a two-disk test rig considering local relative motions, sum velocities, and contact pressures over the area of the Hertzian contact ellipse is proposed. Depending on the assumed bearing kinematics (pitch and yaw angle and ball and cage speed), the resulting forces and torques on the ball vary. By alteration of the ball kinematics, equilibrium in forces and torques can be achieved in order to predict the actual operation conditions. Experiments indicate that this approach allows for a good approximation of the resulting bearing friction torques and the actual pitch angles. The model is applicable for standard angular contact ball bearings as well as for multipoint contact ball bearings.

Hybrid Production Systems

While virtual product development allows great freedom in terms of design, actual development processes are rather restricted. Those boundary conditions are at best hardly possible to exert influence on. Therefore, future research has to focus both on the realisation of the concept of one-piece-flow while simultaneously increasing flexibility and productivity and on the technological advancement. Hence, hybridisation of manufacturing processes is a promising approach, which often allows tapping potentials in all the aforementioned dimensions.

Design of a Highly Dynamic Hydraulic Actuator?for Active Damping Systems in Machine Tools

The positioning accuracy of conventional servo hydraulic cylinders is limited by oil compressibility, leak oil, nonlinearities, hysteresis effects, etc. This affects the control quality of the actuator, which is essential for a use in high dynamic positioning tasks, such as applications in active damping systems for machine tools. The presented hydraulic actuator design is a new approach to extend those limitations by using membrane based piston guidance and casing of pressure chambers. The actuator design is based on a linear mathematical model and FE-Simulations. The developed linear actuator model is integrated into a coupled multi body simulation of an existing active damping system. As the results of the coupled multi body simulation were promising, the actuator was manufactured and put into operation. A first insight into the behavior of the actuator and the verification of the linear actuator model is provided.

Identification method for damping parameters of roller linear guides

A virtual prototype can save cost and time during the design phase of today’s machine tools. Beside the calculation of the static behavior the prediction of the dynamic behavior gets more and more important, but the calculation results are often not satisfactory. Basically this is caused by a lack of knowledge about damping properties of machine tool components and their modeling. Within a project of the German Research Foundation (DFG) the damping of roller linear guides is investigated. The measuring method used to identify the components’ damping utilizes a simulation model to separate the damping of the machine component from the damping of the test bench itself and is state of the art. This article illustrates an extended version of this measuring method which isolates the components’ damping more precisely. Furthermore a first set of results for three types of roller linear guides with different preload classes is presented.

Design of Energy Efficient Hydraulic Units for Machine Tools

Within the research project EWOTeK—Enhancing the efficiency of machine tools by optimising the technologies for operating components—that is funded by the German Federal Ministry of Education and Research (BMBF) amongst others energy efficient hydraulic ancillary units for machine tools are designed. Hydraulic is used in machine tools e. g. for the clamping of the tool in the spindle, for the change of tools, for the clamping of the workpiece, for the change of palettes that serve for the allocation of workpieces, for hydrostatic guidings or for the hydraulic weight compensation of vertical axes. This paper compares different hydraulic ancillary units of machine tools with regard to their energy consumption for an exemplary machining centre.

Virtual Production Systems

The use of simulation systems is of significant importance for companies in high-wage countries as the requirements of product- and process quality are generally higher than in low-wage countries due to conditions of the market. Since the implementation of simulation tools is not value-adding in the first place, the performance of virtual product development chain must therefore be continuously increased in terms of greater planning efficiency. Research in the field of virtual production systems therefore addresses the following issue.

Modal Testing Using Tracking-Interferometers

Modal testing is performed for the characterization of structure dynamics, diagnostics, and condition monitoring. Modal analysis is also used for the detection of sources of vibrations, design optimizations and as comparison data to improve computation results. For open surfaces in the automotive and aerospace industries, the modal testing is often performed using scanning laser vibrometers. In the case of partially closed structures such as machine tools, vibration measurement is typically conducted using three-axial accelerometers. This paper presents a novel approach to performing modal analyses using a single laser tracking-interferometer. First, tracking-interferometers are introduced – followed by an explanation of the modal testing using this device. A holistic measurement method for modal testing is introduced and the individual functionalities are explained as follows. The principle for three-dimensional dynamic measurement is discussed and the performance of the tracking-interferometer measurements in beam direction and in lateral directions are benchmarked against alternative measurement methods. Three-dimensional measurements are presented, including the coordinate transformation and modal analysis results of a machining center. Dynamic measurements and tracking-interferometer-aided geometric model design are presented along with the multiangulation-based position detection for the interferometer head.