Dirk Biermann

Burr Minimization Strategies in Machining Operations

Reducing burr formation in machining operations is of vital importance as they can decrease the functionality of components and can cause injuries. Nowadays, additional processes for deburring are often necessary. To avoid deburring, the modification of machining processes is a promising approach. Here, different parameters have a significant influence on burr formation. For example, the use of alternative machining processes or the reduction of the workpiece temperature near the edge of the workpiece shows high potential for burr reduction. This temperature reduction causes a change in material properties which decreases burr formation. In this paper, methods for burr minimization in various cutting processes are presented. Burr reduction strategies for turning, drilling and milling of different materials are presented.

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.

Analysis and simulation of size effects in micromilling

In this paper the influence of a downscaling of the tool diameter and of the machining parameters on the milling process is analyzed. Starting with an analysis of the cutting edge radius of the tools, the influence of the downscaling on the process is determined by analyzing the surface quality and the cutting forces. The simulation system NCChip, which has been developed at the ISF, is used to simulate the cutting forces when using small tool diameters. This simulation is also used to predict the cutting forces for more complex engagement conditions, like increasing radial immersion or milling of a slot pocket. Additionally, the effects of a downscaling on the tool deflection are analyzed, and strategies to reduce these effects are investigated.

Modelling, simulation and experimental investigation of chip formation in internal traverse grinding

We present recent developments in modelling and simulation of internal traverse grinding, a high speed machining process which enables both a large material removal rate and high surface quality. We invoke a hybrid modelling framework, including a process scale model, simulations on a mesoscale capturing the proximity of a single cBN grain and an analysis framework to investigate the grinding wheel topography. Moreover, we perform experiments to verify our simulations. Focus in this context is the influence of the cutting speed variation on the grain specific heat generation.

Empirical modeling of hard turning of AISI 6150 steel using design and analysis of computer experiments

In the present paper an experimental study to investigate the turning of hardened AISI 6150 heat treatable steel using polycrystalline boron nitride (PCBN) tools is presented. Design and analysis of computer experiments (DACE) was used to generate a comprehensive empirical description of the process characteristics. More specific, the effects of the parameters cutting speed, feed and depth of cut on the objectives tool wear, tool life, tool life volume, surface finish and process forces were modeled. A total of 157 experiments was carried out with 15 different parameter-value sets to obtain the training data for modeling the progression of the objectives versus cutting path length and width of flank wear land. Pseudo-3D surface plots are generated to visualize the effects and interactions. Unexpected effects of depth of cut on tool life were found and the validity of conclusions about the effect of cutting speed on tool wear and tool life are discussed. Moreover, qualitative explanations for some of the observed effects are presented.

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.

Model-Based Multi-objective Optimization: Taxonomy, Multi-Point Proposal, Toolbox and Benchmark

Within the last 10 years, many model-based multi-objective optimization algorithms have been proposed. In this paper, a taxonomy of these algorithms is derived. It is shown which contributions were made to which phase of the MBMO process. A special attention is given to the proposal of a set of points for parallel evaluation within a batch. Proposals for four different MBMO algorithms are presented and compared to their sequential variants within a comprehensive benchmark. In particular for the classic ParEGO algorithm, significant improvements are obtained. The implementations of all algorithm variants are organized according to the taxonomy and are shared in the open-source R package mlrMBO.

Manufacturing of dies from hardened tool steels by 3-axis micromilling

In this paper the results of an experimental investigation to analyze the machinability of a hardened, carbide-rich cold-work tool steel 1.2379 (approx. 62 HRC) with coated micro end-milling cutters are discussed. Fundamental experiments were performed to determine a cutting-parameter set, which enables an economic manufacturing of dies by 3-axis micromilling with commercially available cemented-carbide tools. The evaluation of the applicability of different tool types is conducted by analyzing the process forces, the tool wear, the surface quality, the material removal rate, and the entire chip volume. Design of experiments was used to significantly reduce the number of experiments and to model the active and passive forces. Concerning the design of tools for the micromilling of such difficult-to-machine materials, it is shown that cemented-carbide tools with robust cutting edges are applicable for this kind of machining. Furthermore, test microstructures were manufactured with the intention of validating the determined cutting-parameter set in combination with the selected tool types. In addition, the dimension and shape accuracy of the microstructures are analyzed.

SIMULATION CONCEPT FOR PREDICTING WORKPIECE VIBRATIONS IN FIVE-AXIS MILLING

The characteristic discontinuous cut of the milling process influences the whole machining process by an increased susceptibility to vibrations of the machine-tool-workpiece system. This can result in undesirable effects on the workpiece surface or in a shorter lifetime of the tool and the spindle. Especially with regard to the machining of thin-walled components, such as turbine blades and thin profiles, the dynamic behavior of the workpiece is of particular interest. In this paper a simulation concept for predicting regenerative workpiece vibrations during the five-axis milling process is presented. This concept combines an accurate and fast simulation of the five-axis machining process including material removal and force calculation with an implemented finite element model for computing workpiece displacements. The simulation results are compared with data from experiments, which were conducted using a milling tool with high stiffness in order to minimize the influence of the milling tool dynamics.