Friedrich Kuster

Microstructure and Mechanical Performance of Cu-Sn-Ti-Based Active Braze Alloy Containing In Situ Formed Nano-Sized TiC Particles

A Cu-Sn-Ti-based active brazing filler alloy was in situ reinforced with nanosized TiC particles by adding different amounts of a cellulose nitride-based binder. The TiC particles emanate from a reaction of the Ti within the filler alloy with the carbon from the binder that does not decompose completely during heating. The correlation between the microstructure and mechanical performance was studied. In addition, the effect of different binder amounts on the shear strength and cutting performance of brazed diamond grains was studied in shear tests and single grain cutting tests. The results clearly show that the mechanical performance of the brazed diamond grains can be improved by the formation of TiC particles. This is attributed to particle strengthening of the filler alloy matrix as well as to the decreasing grain size and more homogeneous distribution of the (Cu,Sn)3Ti5 phase with increasing amount of binder.

Modelling of Hard Broaching

Hard broaching is a finishing process to correct geometrical deviations of internal profiles on hardened workpieces, typically using a hardened steel body overlaid with a single layer of metal-bonded diamond grits. The tool essentially has the opposite contour as the workpiece. The process is characterized by an oscillating movement of the broaching tool, while the tool is pushed sequentially deeper into the workpiece. During the retraction phase the chips are removed from the chip spaces. The tool consists of a roughing part and a finishing part to increase the surface quality and reduce the tolerances. For gaining a deeper understanding of the process and for its optimization a stochastic tool model is introduced, which takes into account the differing shape, size, orientation and position of the single grains. Specifications about the tool geometry and the diamond coating as well as process parameters are used as input. The model is capable to predict the active grains, the respective cutting areas, cutting forces and surface roughness of such a virtual image of the broaching tool, which is thus capable to be used to layout and optimize the shape, layer and process strategy of hard broaching. It further allows analyzing the effects of the feed per stroke on the process in dependence of different process and tool parameters. By the modeling a strategy for process optimization is derived. The influences of the optimization strategy on the process are presented and discussed.© 2008 ASME

Analysis and optimisation of the hard broaching process with diamond tools

Hard broaching is a finishing process to correct geometrical deviations of inner profiles on hardened work pieces, using a hardened steel body overlaid with a single layer of metal-bonded diamond grits. The process is characterised by a pendulum movement of the broaching tool. The tool consists of a conical roughing and a cylindrical finishing part. The finishing part increases the surface quality and reduces the tolerances. To get a deeper understanding of the process, and also for its optimisation, a stochastic model of the broaching tool was developed. The model-based analysis showed several suggestions for the improvement and optimisation of the hard broaching process, which have been experimentally verified in this work. With a modified pendulum strategy a relevant process time reduction of about 60% can be achieved.

The Behaviour of Graphitized Steels in Machining Processes

Graphitized steels are claimed to perform excellent in machining processes. They therefore can be considered as environmental friendly alternatives to the widely used Pb-alloyed steels. Due to liquid metal embrittlement and in-situ lubrication Pb improves machinability in a narrow tool-chip interface temperature window corresponding to low machining speeds. Although graphite inclusions are also supposed to generate in-situ lubrication, the mechanism and the corresponding optimum working zone is not very clear. The present work applies a new test methodology (including in-situ tribology, analysis of material flow and chip formation, optimum working zone analysis) to investigate the effects of graphite inclusions on turning and drilling operations. A Pb-alloyed low carbon free-cutting steel and Pb-alloyed case hardening steel were used as reference steels.