Bernhard Karpuschewski

Grinding Chatter – Origin and Suppression

Abstract Grinding chatter is one of the most critical errors in grinding operations and one that has a strong impact on the ultimate geometrical workpiece accuracy. In the paper the origin of chatter that is particularly due to regenerative effects during inner and outer diameter as well as surface grinding is explained. After the discussion on its influence on surface quality, the possibilities related to process monitoring for the detection of chatter during grinding are presented. Special attention is paid to the suppression of chatter e.g. by employing active or passive damping methods. Furthermore, information on a suitable procedure to conduct a stability assessment for grinding machines is provided.

A classification scheme for quantitative analysis of micro‐grip principles

This paper proposes a classification scheme for the quantified analysis of micro‐grip principles. Micro‐part gripping has received quite some attention in micro‐assembly research. However, there is a lack of quantified data on the characteristics and applicability of micro‐grip principles. The micro‐grip principle is the physical principle that produces the necessary forces to get and maintain a part in a position with respect to the gripper. The classification scheme defines criteria that are essential in the evaluation and selection of a micro‐grip principle for gripping a given part. The criteria are defined on the basis of characteristics of the parts to be gripped, demands on the grip operation to be performed and characteristics of the environment in which the grip operation takes place. The classification scheme is evaluated using examples from literature.

Modelling of high velocity, loose abrasive machining processes

In the recent years the interest in loose abrasive machining processes as efficient, flexible processes is rising. This paper describes the development of a ‘coherent set of models’ for a category of these processes, namely those which use high velocity of the particles to obtain the necessary energy to machine a workpiece surface. The usability of this ‘coherent set of models’ will be explained with its application in the field of high-pressure abrasive waterjet cutting. At the end of this paper a forecast to the application of this modelling technique to other loose abrasive machining processes as Micro-Abrasive Air Jet Machining is given.

High Performance Cutting with Abrasive Waterjets beyond 400 MPa

Abrasive waterjet (AWJ) cutting has been widely accepted by the industry after the successful introduction of 400 MPa cutting systems. This paper describes the cutting with AWJ beyond the current industrial pressure limit. Firstly, the factors that limit the water pressure are discussed. Secondly, the jet formation is considered by addressing the effects of the geometry of the upstream tube and the orifice. Finally, the AWJ cutting process is described in terms of energy transfer efficiency. There is an optimum abrasive load ratio over which the cutting ability of the jet decreases due to the less efficient power transfer from waterjet to the abrasives.

Simulation and Improvement of the Micro Abrasive Blasting Process

Abstract Micro abrasive blasting (MAB) is becoming an important machining technique for the fabrication of Micro Electro Mechanical systems. The process is based on the erosion of a mask-protected brittle substrate by an abrasive-laden air jet. Currently available blasting machines are relatively simple. However, to exploit this technique for applications of industrial interest a more efficient and controllable process is required. In this paper abrasive blasting is analysed by means of a set of models containing different sub-models for the particle beam, the material removal mechanism and the resulting blasting profile. A new line-shaped Laval nozzle has been developed, which is able to increase the particle velocity by 40% compared to a conventional round nozzle. The blasting-profile of this line-shaped nozzle is more uniform and the material removal rate is significantly higher compared to conventional nozzles, which in turn leads to higher achievable aspect ratios of the three-dimensional microstructures.

CoCr Is Not the Same: CoCr-Blanks for Dental Machining

Modern computer-aided technologies for manufacturing of individual prostheses are gaining popularity in the dental technology. The CAD/CAM technology promises a material-oriented processing of the manufactured material blanks. Especially with the cast processing of metals to master the process is essential. The control of the casting process directly affects the material quality and thus the clinical chances of success. Possible errors in the casting process, such as gas cavities, scabs, bubbles and cast stresses lead to a significant deterioration in the quality of the material. With the industrial production of material in blank form and their industrial machining this problem should be avoided. But it was the machining of difficult to machine materials such as cobalt-chromium alloys which presents new challenges.

Monitoring Systems for Grinding Processes

This chapter is dedicated to the description of monitoring systems for grinding processes. Grinding is by far the most important abrasive process with geometrically non-defined cutting edges and plays a prominent role to generate the final surface quality of machined parts. The monitoring systems will be discussed in terms of their ability to measure process quantities during manufacturing, or on the grinding wheel or the workpiece. Monitoring of peripheral units like dressing systems will also be discussed. After the description of different technical solutions an outline of adaptive control and intelligent grinding systems is provided.

Advances in high performance micro abrasive blasting

Micro abrasive blasting (MAB) has been successfully improved by the introduction of a rectangular Laval nozzle concept. In this paper the earlier presented set of models has been extended to predict the performance of such nozzles. The results of the sub-model for the jet show that its energy intensity is more evenly distributed and at a substantial higher level compared to conventional nozzle concepts. The results of the material removal sub-model show that it is more beneficial to increase particle velocity rather than particle size to increase the blasting efficiency. The developed sub-model for the contour generation predicts the shape and the roughness of the blasting profile. A scanning strategy has been developed which enables a significant reduction of the processing time. The developed models have been experimentally proved and verified. The knowledge gained in this investigation opens the possibility to derive new rules for the design of microstructures.

First investigations on force mechanisms in liquid solidification micro-gripping

The paper reports on ongoing research on liquid solidification based micro-gripping. First, micro-grip technology and the features of liquid solidification gripping are introduced. Next, the physical mechanisms of adhesion in terms of the role they play in solidification gripping are described. A research prototype design and first experimental results, focused on the grip force that can be generated, are then reported on. It is shown that the main parameters which influence the grip force are the surface roughness of the part, the material combinations and freezing temperature. Forces are measured in the range of 0.6 up to 5.3 N with a contact area of about 1 to 2 mm2

Energiebedarf für die Hartmetallherstellung

Kurzfassung Durch steigende Energiepreise und das wachsende Umweltbewusstsein rückt die Thematik Energieeffizienz von Bearbeitungsprozessen immer weiter in den Fokus der Industrie und der Prozessgestaltung. Der folgende Aufsatz befasst sich mit dem Energiebedarf bei der Werkzeugherstellung, da dieser bei der Prozessoptimierung hinsichtlich des Energiebedarfs von Bearbeitungsprozessen berücksichtigt werden muss. Gegenstand dieses Aufsatzes ist die Herstellung des Hartmetallstabs, welcher als Rohling zur Fertigung eines Vollhartmetall-Spiralbohrers dient.