Tobias Surmann

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.

Micromilling of NiTi Shape-Memory Alloys with Ball Nose Cutters

Micromilling of NiTi shape-memory alloys (SMA) places high demands on tools and machining processes. NiTi is classified as a difficult-to-cut material due to its special properties. A new approach to machine NiTi with higher process flexibility is the application of ball nose cutters in micromilling processes. The article presents the latest results of the simulation-based analysis of five-axis micromilling processes of NiTi SMA. The emphasis is placed on the influence of different tool inclinations, the range of applicable cutting speeds, and a comparison of different machining properties of martensitic and austenitic NiTi alloys. Furthermore, this simulation-based approach helps in exploring new possibilities to optimize the NC-code programming of milling.

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.

The effect of runout on the milling tool vibration and surface quality

When milling with tools of a high length to diameter ratio, there is often a non negligible runout. Since those tools tend towards chatter because of their low stiffness, the effect of runout on the dynamic behavior of the tool must be considered. Runout adds an additional dynamic component to the tool vibration and thus to the dynamicly changing cutting forces. Furthermore runout affects the surface quality even in stable machining. This paper analyzes the effect of runout by simulation of the dynamic milling process and compares the results to experimental data. One aspect is the difference of the vibration patterns with and without runout. Furthermore, a method for the analysis of timeseries is presented in order to distinguish between chatter and runout. Another topic is the expected surface quality resulting from stable processes with runout. This surface is modeled, examined and compared to the one produced by a process without runout.

Simulation of the Temperature Distribution in NC-Milled Workpieces

In most cases the simulation of temperature distributions in machined workpieces is carried out by moving a heat source along a predefined workpiece model within a commercial FEM-system. For performance reasons, the material removal is often neglected or performed by removing small predefined parts of the workpiece. Furthermore, the heat source often has a constant heat flux and therefore it is not dependent on the current tool engagement. In this paper we present a voxel-based finite difference method for the thermal behavior of the process-state dependent workpiece, which is integrated into the milling simulation system NCChip, developed at the ISF. This simulation is capable of modeling the cutting forces along any arbitrary NC-path. Since the tool rotation and the cutting edges in this time domain simulation are divided into discrete angle steps and cutting wedges respectively, the thermal energy that is applied to the workpiece at each time step and at each cutting wedge can be computed as a fraction of the corresponding cutting work. In this way, the correct heat is introduced to the workpiece exactly at the current contact zone of the tool.

Evolutionary surface reconstruction using CSG-NURBS-hybrids

This work presents a surface reconstruction system which combines the concepts of GP and ES in one main algorithm as well as the concepts of CSG (Constructive Solid Geometry) and NURBS (NonUniform Rational B-Splines) to represent arbitrarily sculptured surfaces.

Non-rigid isometric ICP: A practical registration method for the analysis and compensation of form errors in production engineering

The unprecedented success of the iterative closest point (ICP) method for registration in geometry processing and related fields can be attributed to its efficiency, robustness, and wide spectrum of applications. Its use is however quite limited as soon as the objects to be registered arise from each other by a transformation significantly different from a Euclidean motion. We present a novel variant of ICP, tailored for the specific needs of production engineering, which registers a triangle mesh with a second surface model of arbitrary digital representation. Our method inherits most of ICPs practical advantages but is capable of detecting medium-strength bendings i.e. isometric deformations. Initially, the algorithm assigns to all vertices in the source their closest point on the target mesh and then iteratively establishes isometry, a process which, very similar to ICP, requires intermediate re-projections. A NURBS-based technique for applying the resulting deformation to arbitrary instances of the source geometry, other than the very mesh used for correspondence estimation, is described before we present numerical results on synthetic and real data to underline the viability of our approach in comparison with others.

Direct free-form deformation of NC programs for surface reconstruction and form-error compensation

In this paper a new approach for manufacturing modified workpieces by milling is presented. In course of product development, several optimization iterations are often required, in which the shape of the workpiece is modified. Conventional method for manufacturing modified workpieces includes a time-consuming and error-prone step of reverse engineering, where the new CAD/CAM data is generated with respect to the measurement data of the manufactured workpiece. The new approach generates a continuous deformation function in order to approximate the discrete displacement vectors between the initial and the modified shapes, and applies this function on the original NC programs of the workpiece. Hence, it is possible to directly manufacture the modified shape. The process of reverse engineering can be eliminated so that manufacturing costs and the time from workpiece design to the production decrease significantly.

Design of Evolutionary Algorithms and Applications in Surface Reconstruction

Evolutionary algorithms are a class of direct search methods. They can be used whenever classical optimization methods do not yield satisfactory results. In the following we discuss the design of problem-specific evolutionary algorithms. We present a technique for the systematic integration of domain knowledge. Surface reconstruction by means of evolutionary algorithms serves as a practical example. For this problem the integration of domain knowledge is essential for a successful application of evolutionary algorithms.

Parallel Surface Reconstruction

The task of surface reconstruction is to find a mathematical representation of a surface which is given only by a set of discrete sampling points. The mathematical description in the computer allows to save or transfer the geometric data via internet, to manipulate (e.g. for aerodynamic or design specific reasons) or to optimize the machining of the work pieces. The reconstruction of the shape of an object is a difficult mathematical and computational problem. For this reason a GP/ES-hybrid algorithm has been used. Due to the high complexity of the problem and in order to speed up the reconstruction process, the algorithm has been enhanced to work as a multipopulation GP/ES that runs in parallel on a network of standard PCs.