Michael Bräunig

Thermal deformations of cutting tools: measurement and numerical simulation

Challenges for machining include greater and greater material removal rates coupled with an increase in the use of difficult to machine materials, as well as environmental-friendly dry or minimum quantity lubrication machining, small manufacturing batches and frequently changed manufacturing orders. These trends are accompanied by high temperatures in the machining process and large, variable heat flows causing thermo-elastic displacements of the tool, the workpiece and the clamping devices. Although the displacements are small, in the range of a few micrometers, they have assumed more and more importance because of growing requirements for manufacturing accuracy. Thermo-elastic displacements of the tool due to heat flow during machining are investigated and analysed in this paper. Temperatures and displacements are measured on a test bed equipped with measuring instruments. The identification of the thermal boundary and contact conditions is supported by finite element models. Knowledge of the heat flows resulting from the machining process is a prerequisite for control of and compensation for displacements. Since these heat flows either cannot be measured or can only be measured with enormous effort, heat flows are determined by means of numerical simulation of the machining process itself. This strategy has been previously used as a systematic approach for turning in orthogonal cutting conditions. However, further investigations are needed for oblique turning conditions, milling and drilling operations.

Untersuchungen zur thermisch bedingten Werkstückverformung

Kurzfassung Die Wärmequelle aus dem Zerspanungsprozess erzeugt Wärmeströme und resultierende thermo-elastische Verformungen auf Seiten des Werkstücks und dessen Spannvorrichtung. Diese Wärmeströme und Verformungen werden in einem Versuchsstand in Kombination mit numerischer Simulation untersucht und bewertet. Die Identifikation der thermischen Rand- und Kontaktbedingungen wird durch Finite-Elemente-Modelle unterstützt. Die Thematik ordnet sich in einen Sonderforschungsbereich der DFG ein, in dem die thermo-energetische Gestaltung von Werkzeugmaschinen untersucht wird.

Industrial consideration of thermal issues in machine tools

Regarding the undisputed relevance of thermal errors, the question arises in which way the consideration of several activities will lead to an improvement of the thermal behavior of machine tools. The answer comes from 75 small to very large machine tool manufacturers and mainly larger production companies from Europe and Asia. Therefore, the entire process chain is considered, from design, assembly to the installation conditions and procedures in daily operations of the machine tool. The companies describe the expenditure regarding the design and the organization to increase the thermoelastic manufacturing accuracy. There are the following remarkable facts. The use of mineral castings is highly dependent on the region. In addition to the thermo-symmetric design, heat removal is an alternative design solution. There are only a few alternatives for tempering. Corrective methods can be very diverse. The consideration of the installation conditions strongly depends on the company size. In addition, the necessary measures in the operation are described by the users, for which purpose they often remain in contact with the manufacturers. Finally, the paper discusses the difficulties regarding the control of thermal behavior from an industrial perspective, deriving future research areas and establishing work priorities.

Berührungslose Werkzeugerwärmung: Induktionsspule und Steuerung zur Parameteridentifikation mit definiertem Wärmeeintrag

Kurzfassung Zur experimentellen Untersuchung des thermischen Verhaltens rotierender Werkzeuge ist eine berührungslose Erwärmung erforderlich. Der Beitrag beschreibt den Entwurf einer Induktionsspule und die Entwicklung einer Steuerung, um einen homogenen und steuerbaren Wärmeeintrag zu ermöglichen. Dabei wird die Steuerung so konzipiert, dass sowohl die Frequenz des generierten Wechselstroms als auch Strom und Spannung einstellbar und somit genau definiert sind. Erste Untersuchungen demonstrieren die Funktionalität des Induktors zur definierten und reproduzierbaren Werkzeugerwärmung.

Model-Based Representation of Thermo-energetic Effects in Cutting Tools and Part Clamping Devices

In the representation of the machine tool’s manufacturing accuracy, involving thermo-elastic deformations in the tool and its chuck in the considerations is unavoidable, since a portion of the process heat is transmitted into the tool. Capture and estimation of the resultant thermo-elastic deformations is of significant importance for their compensation and correction. This paper presents the investigation and evaluation of thermo-elastic displacements in the tool-chuck system resulting from the heat flows from machining. The temperature and displacement measurements were conducted on a test bed with measuring equipment. In the first series of experiments, the transient heat conduction in the stationary tool and the chucking system, decoupled from the motor spindle, was captured. The chucks were compared in terms of their working principle. The identification of the thermal boundary and contact conditions was assisted by Finite Element models. The paper describes the experimental setups, the methods of measurement and the numerical models. An additional section discusses the determination of realistic heat sources generated in the machining process. Since measurement of these heat flows is either impossible or expensive and time-consuming, they are determined by numerical simulation of the machining process itself. This way, it can be determined to what extent the heat flows generated in the experiments by means of heating cartridge or induction correspond to those generated by the actual machining heat sources.