Steffen Ihlenfeldt

An extended procedure for convective boundary conditions on transient thermal simulations of machine tools

The need of reliable structural properties of machine tools in the development phase are becoming increasingly important due to mounting accuracy demands and shrinking development periods. The finite element method is the most established tool applied in this context. Currently, calculating thermal properties and compensation of thermally caused shifts are mainly the focus of simulation studies due to high performance and the usage of dry processing. The accuracy with which thermal properties can be mapped today is measurably lower than current static and dynamic properties. The reason is due to strong interaction of the specific physical effects and the complexity of pertinent constraints. With constrained parameters the impact caused is defining the convective heat transmission. The heat transmission coefficient can be calculated analytically or numerically. This article is presenting a method that allows permanent adaptation of this coefficient to make it possible to better apply convective heat transmission to time-variable thermal simulations especially for mechanical based finite element models.

Method for the Optimization of Kinematic and Dynamic Properties of Parallel Kinematic Machines

The following paper introduces an approach, which allows the consideration of the kinematic as well as the dynamic properties of parallel kinematic machines. Based on the results of a preceding kinematic optimization, a FEM-model with arbitrary input parameters is designed. The full kinematic functionality of struts and joints used is ensured. By coupling the FEM-model to the GNU Octave numerical program system, a variety of movements including machining forces can be simulated. A Broyden-Fletcher-Goldfarb-Shanno optimization algorithm, using GNU Octave, was written and coupled to the FEM-system. Now, this algorithm is able to influence the models arbitrary input parameters during the optimization process. Thus, the model is optimized automatically for a certain machining process and/or dynamic behavior. This procedure is demonstrated using the example of a delta robot structure originally designed by Raymond Clavel [7].

A frequency-based substructuring approach to efficiently model position-dependent dynamics in machine tools:

Structural deformations of machine tool components that translate and/or rotate relative to each other to realize tool motion results in tool point dynamics varying along the tool path. These changing dynamics interact with the cutting process and the control loop of the drives to limit machine performance, making it necessary to virtually characterize these interactions such as to guide design decisions. To facilitate rapid evaluation of these varying dynamics, this paper describes a generalized frequency-based substructuring approach that combines the position-invariant component level receptances at the contacting interfaces between substructures to obtain the position-dependent tool point response. Receptances at the contacting interfaces are approximated by projecting them to a point to facilitate a multiple point receptance coupling formulation. Complete machine behavior is represented by just a few sets of receptances, making the model computationally more efficient than full-order finite element models and other dynamic substructuring methods. Position-dependent dynamic behavior for a representative three axis milling machine is simulated and numerically verified. Rapid investigations of the varying dynamics assist in virtually characterizing machine performance before eventual prototyping.

Dämpfung in verspannten Fugen

Kurzfassung Im Rahmen der Analyse und Bewertung des dynamischen Verformungsverhaltens und der Prozessstabilität von Werkzeugmaschinen kommt der modellgestützten Ermittlung vonNachgiebigkeitsfrequenzgängen eine zentrale Bedeutung zu. Die Aussagekraft dieser Frequenzgänge wird dabei wesentlich von der treffenden Berücksichtigung der Dämpfung – in Ansatz und Parametrik – bestimmt. Einen wesentlichen Anteil an der Systemdämpfung leistet dabei die lokale Fugendämpfung in verschraubten Flanschverbindungen, deren Wirkung von der Vorspannung und der Beanspruchung in den verschiedenen Schwingungsformen abhängt. Der vorliegende Beitrag stellt aktuelle Ergebnisse zur experimentellen Ermittlung dieser Dämpfung und zur Ableitung geeigneter Modellparameter vor.

Increasing the Performance of Processing Machines by Executing Output Rate Dependent Motion Profiles

From the economic point of view, rising the output rate of processing machines is a key requirement. Thereby, particular demands are to be met, i.e., product quality, process stability, energy consumption, impact of surroundings, or safety at work. Rising the output rate is limited, if only one of these demands can not longer be met. In this paper, a novel control approach is presented that allows to change the executed motion profile due to the actual output rate. Increasing the machine’s performance is evaluated on experimental results. Unused potentials of servo drives are opened up to generate highly dynamic multi-axis motions in processing machines.

Dämpfung in Konstruktionswerkstoffen

Kurzfassung Im Rahmen der Analyse und Bewertung des dynamischen Verformungsverhaltens und der Prozessstabilität von Werkzeugmaschinen kommt der modellgestützten Ermittlung von Nachgiebigkeitsfrequenzgängen eine zentrale Bedeutung zu. Die Aussagekraft dieser Frequenzgänge wird dabei wesentlich von der treffenden Berücksichtigung der Dämpfung – in Ansatz und Parametrik – bestimmt. Einen betragsmäßig meist sehr kleinen jedoch für die Systembetrachtung wesentlichen Anteil an der Dämpfungswirkung leistet dabei die Werkstoff- bzw. die Bauteildämpfung. Der vorliegende Beitrag stellt aktuelle Ergebnisse zur effizienten experimentellen Ermittlung dieser Dämpfung und zur Ableitung geeigneter Modellparameter vor. Dabei wird auch auf die Besonderheiten bei extrem schwacher Dämpfung eingegangen.

Towards the identification of heat induction in chip removing processes via an optimal control approach

AbstractThis paper presents a linear-quadratic regulator (LQR) approach for solving inverse heat conduction problems (IHCPs) arising in production processes like chip removing or drilling. The inaccessibility of the processed area does not allow the measuring of the induced temperature. Hence the reconstruction of the heat source based on given measurements at accessible regions becomes necessary. Therefore, a short insight into the standard treatment of an IHCP and the related LQR design is provided. The main challenge in applying LQR control to the IHCP is to solve the differential Riccati equation. Here, a model order reduction approach is used in order to reduce the system dimension. The numerical results will show the accuracy of the approach for a problem based on data given by practical measurements.

Commissioning new applications on processing machines: Part I - process modelling:

The subject of this splitted article is the commissioning of a new application that may be part of a processing machine. Considering the example of the intermittent transport of small-sized goods, for example, chocolate bars, ideas for increasing the maximum performance are discussed. Starting from an analysis, disadvantages of a conventional motion approach are discussed, and thus, a new motion approach is presented. For realising this new motion approach, a virtual process model has to be built, which is the subject of this article. Therefore, the real process has to be abstracted, so only the main elements take attention in the modelling process. Following, important model parameters are determined and verified using virtual experiments. This finally leads to the possibility to calculate useful operating speed–dependent trajectories using the process model.

Dämpfung in verspannten Fugen: Teil 2: Modellierung von Dämpfung in Pressverbindungen

Kurzfassung Im Rahmen der Analyse und Bewertung des dynamischen Verformungsverhaltens und der Prozessstabilität von Werkzeugmaschinen kommt der modellgestützten Ermittlung von Nachgiebigkeitsfrequenzgängen eine zentrale Bedeutung zu. Die Aussagekraft dieser Frequenzgänge wird dabei wesentlich von der treffenden Berücksichtigung der Dämpfung – in Ansatz und Parametrik – bestimmt. Einen wesentlichen Anteil an der Systemdämpfung leistet dabei die lokale Fugendämpfung in Pressverbindungen, deren Wirkung wiederum von der Flächenpressung und der Beanspruchung in den verschiedenen Schwingungsformen abhängt. Der vorliegende Beitrag stellt aktuelle Ergebnisse zur effizienten experimentellen Ermittlung dieser Dämpfung und zur Ableitung geeigneter Modellparameter vor.

Intuitivere Produkt-FMEA mittels Virtual Reality

Kurzfassung Dieser Beitrag beschreibt die Nutzung der Virtual Reality (VR)-Technologie zur Optimierung von Qualitätsmanagement-Methoden am Beispiel der FMEA. VR fungiert hierbei nicht nur als unterstützendes Visualisierungswerkzeug, sondern bildet das Kernstück zur Interaktion und Darstellung aller relevanten Informationen. Die VR-Technologie ist durch die realitätsnahe 3D-Darstellung in Kombination mit der Interaktion in sechs Freiheitsgraden besonders geeignet, komplexe mechanische Zusammenhänge zu veranschaulichen.