Andreas Schiffler

Analyzing Energy Consumption of Machine Tool Spindle Units and Identification of Potential for Improvements of Efficiency

This paper describes the results of the analyses of a representative machine tool spindle unit and the thereof identified potentials for increasing the energy efficiency. This is done within the project “EnergieMSP”, whose aim it is to develop an energy optimized spindle unit with an adapted electric drive train. The holistic analysis of the system is done in a machine tool to determine the consumption of pressurized air, the energy demand for the tool change and hydraulic stand-by losses. The frictional losses in the bearings and rotary union and the electrical drive train where separately investigated at test benches.

Development and design of an active work piece holder driven by piezo actuators

The use of piezo actuators in machine tools is a current topic. There are many research works which show the advantages of this kind of actuators in various fields around machining. In this paper an active work piece holder is presented, which is designed for reducing the dynamic displacement between the tool and the work piece relatively. The paper shows the design process for the fixture, the finite element analysis of the mechanical parts and the actuators. Also a specially designed power amplifier is presented which fits best to the needs of voltage and frequency range of the active work piece holder. First experimental results are shown.

System identification during milling via active magnetic bearing

One of the main focuses of recent machine tool development is to increase the machining performance. But the enhancement of the metal removal rate (MRR) is often limited by the stability of the milling process. To prevent unintentional chatter vibrations and to observe changes in the system’s behavior, there is a need to observe the state of the milling process during machining. Beside others, one approach is the development of an adaptronic motor spindle using active magnetic bearings (AMB) combined with conventional roller bearings in a so called “hybrid approach”. The AMB acts as a contact less sensor and actuator, in order to estimate the frequency response function (FRF) of the spindle-tool system during the milling process. The two major dependencies on the FRF are the spindle speed and the cross-sectional area of the chip. Also the closed loop damping can be observed to estimate the stability margin. This paper presents the identification of the varying eigenvalues during the machining.

Analysis of cutting force during milling with regards to the dependency on the penetration angle

In recent years the modeling of dynamic processes in milling has become increasingly important especially in the determination of process stability. In the future the importance of these models will increase in order to establish a virtual machine tool technology. In literature several mathematical models are used for the prediction of cutting forces assuming simplified dynamic (chatter free) conditions. These models are based on different parameters which are identified in various ways. The aim of this paper is to improve the identification process for the coefficients of a basic state of the art cutting model by using a numerical optimization method. Based on this optimized model, which reflects the measured cutting force chart more precisely, dependencies of the cutting force parameters on the penetration angle are proven.

Method for chatter detection with standard PLC systems

The aim of growing productivity together with increasing quality demands in machining leads to milling processes that are near their stability limits. The remaining stability reserves become smaller and the risk of unstable processing conditions like chatter increases. Unstable processes cause unwanted vibrations with high amplitudes in bearing loads. As a result, the lifetime of the bearings of the main spindle is reduced. Besides this, the surfaces of unstable processed work-pieces have unwanted chatter marks and do not fulfill the quality demands. To basically avoid unstable processing,a continuous monitoring of the process state is necessary. In this paper, a method for monitoring cutting processes using a standard programmable logic controller which is integrated in the drive controller of the machine tool spindle unit is presented. The method is real time-capable and based on the hypothesis that unstable process conditions result in a modulation of the amplitudes of the cutting forces. To detect this, an order tracking method is implemented, which uses a recursive parameter estimation algorithm together with inherently given signals of the drive controller. It is shown that the characteristic property of the used estimation algorithm and allowed aliasing lead to a reliable chatter detection even at sub-sampling. Finally some results of the first experimental investigation of the method are given.

Digitally controlled output filters for improvement of temperature behavior of machine tool main spindle drives

Variable speed main spindle drives of machine tools are usually fed by three-phase two-level inverters. Because of the switching operating mode of these inverters, the motor voltages and currents contain harmonics which do not contribute to torque formation but solely to an undesirable warming of motor spindle elements. This warming results in thermal elongation of the spindle shaft and therefore to a deviation in dimensional accuracy. The increased wear of the spindle bearings through high temperature differences between the inner and outer rings of the bearings is another drawback. This paper proposes a novel high-performance control system of an interior permanent magnet synchronous motor (IPMSM) using an inverter with an LC output filter. The combination of inverter and filter reduces the motor losses by compensating the switching ripples and therefore leads to an evident improvement of the temperature behavior of the main spindle drive.

Herstellung multifunktionaler Strukturen: Mittels Integration des Zerspanprozesses in Walzprofilieranlagen

Kurzfassung Die Integration des Zerspanprozesses in einer Walzprofilieranlage im Zusammenspiel mit Spaltbiege- und Spaltprofilierprozessen ermöglicht die Herstellung von neuartigen Produkten. Sie zeichnen sich durch besondere Eigenschaften wie Leichtbau, Funktionsintegration und hohe Festigkeit aus. Die spanende Bearbeitung von laufendem Blech in der Walzprofilieranlage stellt hohe Anforderungen an die Eigenschaften des Zerspanmoduls. Eine besondere Herausforderung ist dabei das Synchronfräsen am fließenden Band.