Abstract: In this paper, an innovative approach for contact zone analysis of skive hobbing is presented. This process is characterised by varying tool engagements and very small chip thicknesses. The paper describes the process-modelling and the analysis of the workpiece-tool contact. For efficient modelling, a novel dexel-based method for the description of a gear segment with discretized stock allowance is presented. Characteristic for the method is an analytical description of the target workpiece contour which allows to describe points of the surface by Cartesian coordinates on the winding off. On this workpiece contour, dexel are modelled in surface-orthogonal direction. The initial lengths of these dexel describe the stock allowance. By cutting these dexel with a tool, a time-and position-dependent prediction of material removal values, like width of undeformed chip, undeformed chip thickness or cutting directions can be obtained. Selected results are presented and interpreted.
Abstract: For the process design of a cutting process, the knowledge of the cutting force is of fundamental importance. The cutting force influences the dimensioning of machine components and process parameters . A precise interpretation of those process elements enables for high manufacturing and component accuracy. Due to the complexity of the chip geometries, the cutting force in gear hobbing is calculated by using a penetration calculation. The applied cutting force models have been developed by BOUZAKIS  and GUTMANN  in the 1980s. These models are based on data from longitudinal turning processes. Advancements in machine tool technology of the past decades have led to more efficient processes. The use of new cutting materials allows for higher speeds and feeds. This led to larger chip thicknesses. The bases of the models by GUTMANN and BOUZAKIS covers today's usual hobbing parameters not extensive enough. The influence of tempered levels on the cutting force is not included in the models. Therefore, the aim is to create a cutting force model and adjust the calculation base after GUTMANN. A radial turning process with interrupted cutting is used as analogy process. The influence of the heat treatment at 42CrMo4 is to be examined for the cutting force. This will be compensated in three different tensile strengths. The investigated process parameters are extended beyond the current state of the art.
Abstract: High mechanical impact loads in interrupted or inhomogeneous machining processes frequently lead to spontaneous fracture of the cutting edge. Even modern cutting materials cannot provide a combination of high enough hardness and toughness that is capable of preventing this sort of tool failure. Such machining conditions therefore remain difficult and further investigations, aiming to reduce the impact load of the cutting tool in order to enhance tool-life, are necessary. A simulation model of the impact situation, that serves to optimize a force conducting structure with regard to elasticity, damping properties and resulting force peaks, was developed and is presented in this paper. Furthermore measurement devices were composed that are needed for high-resolution recording of impact forces without repercussions and for verification of the elaborated simulation model. It could be shown that mechanical damping of the cutting tool can lead to reduced impact forces on the cutting edge, which in turn should lead to longer tool life.
Abstract: Granulators are widely used to reduce reinforced and unreinforced plastic strands in small pieces. The tools implemented in this machining process are mainly made of high-speed steel. This work investigates diverse PVD hard thin coatings with the aim of improving tool life and efficiency in granulation technology. A test facility reproducing the main features of a real granulator has been designed and assembled. The machined strand materials are ABS plastic and fibreglass-reinforced polyamide 6, while the tested PVD films are CrN, TiCN, TiAlN and two different diamond-like carbon coatings. The wear evaluation of all coated tools has been done via structured light projection, together with a scanning electron microscopy-based analysis, before and after their implementation on the test facility. Furthermore, a suitable 2D finite element modelling of the machining process has been realized.
Abstract: Sawing with bandsaws is a fast and efficient process for cutting semi-finished parts out of bar stock in the metalworking industry. However, the produced surface quality on the workpiece is low due to the unguided length of the saw blade during the engagement in the workpiece. The kinematic correlation between the thin, unstable structure of the saw blade, only pre-stressed in the cutting direction, and the distance of the two saw blade guides according to the workpiece dimensions leads to an indefinite behaviour of the saw blade in the kerf. Apart from the surface quality, this cutting behaviour also causes a great wear of the tool. With increasing wear of the tool, the process becomes more and more unstable and the cutting loss increases. For an optimization of the sawing process, the influences on the stability of the process are investigated by experiment on a test bandsaw equipped with extensive measurement equipment. This paper examines how the saw blade tension influences the stability of sawing processes subject to tool wear. For this purpose, the saw blade tension is varied in a wide range and the stability of the process is assessed. The results obtained show a great influence of the saw blade tension on the sawing process and form the basis for developing a stand-alone stability control system to automatically adjust the sawing parameters.
Abstract: Deep hole drilling is a process for the production of cylindrical bore holes with a large length to diameter ratio. The variation of parameters is limited to those ones of the conventional drilling process such as rotation and feed motion. A special deep hole drilling process, named “chamber-boring”, was developed for the production of contoured bore holes in axial direction . For specific applications not only a contouring in axial direction is required but also a radial contouring is necessary. In the course of a ZIM – project (Central Innovation Programme for SMEs), supported by the Federal Ministry for Economic Affairs and Energy (BMWi) and in close collaboration with the BGTB GmbH and the Institute of Machining Technology (ISF), a new “chamber boring system” which allows contouring of boreholes in axial and radial directions was developed. Based on this machining system, the manufacturing of pipes with a wavelike cross section in radial direction is possible.
Abstract: The modelling of machining operations aiming at the compensation of thermal effects regarding workpiece distortion requires detailed knowledge of the thermal impact of the examined process. The objective of this paper is therefore to form an empirical basis for the modelling of the heat flux into the workpiece in drilling of steel. In order to achieve this goal the temperature matching technique in combination with two dimensional thermographic measurements was utilised. The moving heat source was characterised as a primary heat source with a constant heat flux density near the cutting zone and a secondary declining heat source on the bore hole wall. With an iterative approach it was possible to match the simulated temperature fields very closely to the measured temperature fields. The evaluation of the thermal impact of the drilling process with varying machine parameters yielded additional insight into the generation and distribution of thermal energy in drilling. The lowest overall heat partition to the workpiece was observed at the higher feed rate in combination with the lower cutting speed where the heat partition in the cutting zone as well as heat transfer to the bore hole wall are minimal.
Abstract: The occurrence of chatter vibrations in milling processes often results in bad surface qualities and in an increased tool wear. When using special fixture systems for structural parts in the aerospace industry, the vibrations of the workpiece and the fixture can become critical due to their limited stiffness. For the process design, a prediction of the appearance of these kind of vibrations using specialised simulation approaches is very helpful. In this article, a simulation system is presented, which is able to simulate chatter vibrations of the workpiece in spindle direction, taking the dynamic behaviour of the thin-walled bottom of the workpiece and the fixture into account. Experiments were conducted to demonstrate the basic effect and to validate the simulation system. Furthermore, the machining and the simulation of a pocket of a structural component for aerospace applications is analysed.
Abstract: The chip formation mechanisms during grinding are not yet fully understood. The abrupt interruption of the grinding process with a quick stop device is a suitable method to analyze the chip formation mechanisms during grinding. However, there is no device available that enables a reproducible interruption at cutting speeds above vc = 5 m/s. Therefore a new method for the interruption of face grinding processes in order to analyze the chip formation mechanisms is presented in this paper. A quick stop device is designed and constructed based on the advantages and disadvantages of former approaches of other researchers. Grinding experiments with different rotational speeds confirm the potential of this new device. Interruptions of the grinding process at cutting speeds of vc = 5 m/s, 15 m/s, 25 m/s and 35 m/s are successfully accomplished. A detailed analysis of the contact zone with the help of SEM pictures impressively shows the interaction of hundreds of cutting edges along the contact zone.
Abstract: One research objective for generating gear grinding is to increase economic efficiency and productivity of the process. Furthermore, the gear quality must be equal or higher compared to the non optimised process. In addition to the grinding process and the grinding tools, the dressing process can be suitable to lead to an increase of efficiency of generating gear grinding. Due to the variety of dressing tool specifications process users have the problem of selecting the best fitting dressing tool for their demands. Therefore, it is necessary to know the interactions of dressing tool specification and dressing tool wear. But the influence of the dressing tool specification onto dressing tool wear has yet not been sufficiently investigated for generating gear grinding.