Klaus Weinert

Online sculpting and visualization of multi-dexel volumes

The idea of multi-dexel volumes is to use more than one dexel volume for representation of a solid. In this manner the difficulty of unequal sampling densities dependent on the slope of the surface relative to the direction of the dexels is overcome. We present algorithms for orthogonal 3-dexel volumes, which concern on-line sculpting by erasing and generating tools and direct rendering. The algorithms achieve computation times better than real time for simulation of milling processes in mechanical engineering.

Turning and Drilling of NiTi Shape Memory Alloys

Abstract Shape memory alloys based on NiTi have a high potential for a large variety of applications. This functional material is very difficult to machine because of its high ductility, its different shape memory properties in dependence on temperature and the strong work hardening when this material is deformed. This paper presents the process design for producing a pipe coupling from NiTiNb. The design is based on experiments regarding turning and drilling of the intermetallic compound NiTi. The influence of the cutting tool material on the machining process was evaluated. As a result of the experiments, the metal removal rate was increased significantly and the tool life could be extended while at the same time ensuring a high work piece quality.

On Stability and Dynamics of Milling at Small Radial Immersion

Stability and dynamics of milling at small radial immersion are investigated. Stability charts are predicted by the Semi Discretization method. Two types of instability are predicted corresponding to quasiperiodic and periodic chatter. The quasiperiodic chatter lobes are open and distributed along the spindle speed axis only, while the periodic chatter lobes are closed curves distributed in the plane of spindle speed and depth of cut. Experiments confirm the stability predictions, revealing the two principal types of chatter, the bounded periodic chatter lobes, and some special chatter cases. The recorded tool deflections in these cutting regimes are studied. The experiments also show that the modal properties of a slender tool may depend on spindle speed.

Milling Simulation for Process Optimization in the Field of Die and Mould Manufacturing

Abstract When milling sculptured surfaces the major problems are the limited precision due to milling-cutter deflections caused by the cutting force and a unsatisfactory process reliability. One method for improving surface quality while maintaining high process reliability is the computer-based engagement analysis and feed-rate adaptation. The aim of the feed-rate adaptation is to avoid intolerably high tool loads as they occur while semi-finishing sculptured surfaces. The method developed uses an efficient, volume model to simulate the cutting process. The calculation of the optimal feed-rate takes the main technological aspects of 3-axis milling into account. The efficiency of the approach developed is demonstrated with a practical example.

On stability prediction for low radial immersion milling

ABSTRACT Stability boundaries for milling are predicted by the zeroth-order approximation (ZOA) and the semi-discretization (SD) methods. For high radial immersions, the methods predict similar stability boundaries. As radial immersion is decreased, the disagreement between the predictions of the two methods grows considerably. The most prominent difference is an additional type of instability predicted only by the SD method. The experiments confirm the predictions of the SD method. Three different types of tool motion are observed: periodic chatter-free, quasiperiodic chatter, and periodic chatter motion. Tool displacements recorded during each of the three motion types are analyzed.

Model-based optimization revisited: Towards real-world processes

The application of empirically determined surrogate models provides a standard solution to expensive optimization problems. Over the last decades several variants based on DACE (design and analysis of computer experiments) have provided excellent optimization results in cases where only a few evaluations could be made. In this paper these approaches are revisited with respect to their applicability in the optimization of production processes, which are in general multiobjective and allow no exact evaluations. The comparison to standard methods of experimental design shows significant improvements with respect to prediction quality and accuracy in detecting the optimum even if the experimental outcomes are highly distorted by noise. The universally assumed sensitivity of DACE models to nondeterministic data can therefore be refuted. Additionally, a practical example points out the potential of applying EC-methods to production processes by means of these models.

Modeling regenerative workpiece vibrations in five-axis milling

During milling—especially of thin-walled components—the dynamic behavior of the workpiece-tool-machine-system influences the milling process and particularly the quality of the resulting workpiece surface. This article focuses on the presentation of a simulation concept for predicting regenerative workpiece vibrations, which combines a finite element model for analyzing the dynamic behavior of the workpiece with a time domain simulation for the five-axis milling process. Both concepts, their linking, and the experimental setup for verifying the simulation will be described. A comparison of the simulation results with the data measured in experiments with regard to the vibration frequencies as well as the surface quality will be given.

On the Influence of Drilling Depth Dependent Modal Damping on Chatter Vibration in BTA Deep Hole Drilling

BTA (Boring and Trepanning Association) deep hole drilling is applied for machining bore holes with a high length to diameter ratio. The slender tools involved make BTA processes highly susceptible to chatter vibration. Chatter-free states and states with chatter vibration corresponding to one of the first three torsional eigenfrequencies can be observed to alternate during processes with constant cutting parameters. A detailed FEA model of the significant BTA tool components involved was developed. This takes into account the drilling depth variant boundary conditions. Using this model, the state transitions can be attributed to drilling depth dependent modal damping of the involved torsional vibration modes.

New Solutions for Surface Reconstruction from Discrete Point Data by Means of Computational Intelligence

Surface reconstruction by means of triangulation of digitized point data leads to computational complex optimization problems. Here, deterministic algorithms often result in insu cient solutions or very long computation times. In this article, alternative methods of computational intelligence are discussed. A comparative analysis of two evolutionary algorithms applied to four di erent smoothness criteria for the triangulation of sparse point data sets is presented. Optimally triangulated surfaces are the basis for many practical applications. The results presented here cover the e cient implementation and the in uence of di erent triangulations for an adequate touch probe radius compensation (TPRC).

Improved NC path validation and manipulation with augmented reality methods

Five-axis milling offers many advantages over the conventional three-axis milling process. However, because of the potentially complex motions, it is difficult for the machine tool operator to anticipate the actual movement based on the NC program. In this paper a software system for the NC path validation and manipulation during the milling process is introduced. This system is meant to expand the information given to the machine tool operator by enriching the view with data of a concurrently running milling simulation. The simulation is synchronized with the real-world machine tool movement by detecting the position of a marker that is mounted on the head stock. With this combination of real-world view and computer-generated data, which is called Augmented Reality, the machine tool operator is able to detect critical situations—like collisions between tool holder and workpiece or excessive forces—and may adjust the NC program accordingly.