G. Barrow

An experimental study of burr formation in square shoulder face milling

Abstract Previous research on burr formation in face milling operations has usually been limited to the study of the rollover burr in the cutting direction and/or to a few machining parameters. This paper presents the results of an experimental study on the influence of the main cutting parameters on the formation of the more important burrs produced in face milling operations, namely exit burr in the cutting direction, exit burr in the feed direction and the burr formed at the top edge in a square shoulder face milling operation. Feed per tooth ( Sz ), cutting velocity ( V ), axial depth of cut ( a ) and exit angle ( EXA ) were the cutting parameters investigated. The effects of mode of milling, tool nose geometry and tool coating were also investigated to a lesser extent. The results show that exit angle and depth of cut are the cutting parameters which have a major influence on the exit burr in the cutting direction, whereas the exit burr in the feed direction is mainly affected by depth of cut. The top burr is very small and only slightly influenced by cutting conditions. It is also shown that down-milling can effectively eliminate the formation of burrs in some cases, whereas an unfavourable tool nose geometry can double the size of buns.

Automatic tool selection for rough turning operations

Abstract A method of automatically selecting cutting tools for rough turning operations on a CNC lathe is presented. While the selection procedure can deal with various economic objectives, only the minimum cost per component is considered in this paper. Selection is made from an appropriate tool library and in order to reduce the search time a heuristic method is employed. The cost of machining with a given tool is estimated following the determination of the cutting conditions consistent with the constraints acting on the process. From a detailed examination of the constraints it is possible to ascertain whether the next tool in the library will give improved cutting conditions and the possibility of a lower cost. This procedure eliminates the need for an exhaustive search of the library and results in a very fast and efficient algorithm. The results of ten tool selections are presented. In all cases the computation time for the heuristic approach was less than 5% of that for the exhaustive search. In eight out of ten cases the heuristic method selected the same tool as the exhaustive search; in the two cases where the tools selected were different, those selected by the heuristic method produced only a marginal increase in the operation cost.

Determination of the radial width of cut and cutting modes in milling

Abstract This paper describes a method to calculate the variation in the radial width of cut which occurs when the centre of a milling cutter follows the toolpath segments generated by a postprocessor. This variation is approximated by a stepped curve, thus enabling the toolpath segment to be divided into subsections, the radial width remaining constant over each subsection. The method also enables the cutting modes to be determined. The variation in the width of cut is obtained by performing a 2-D Boolean union between the area swept by the cutter when traversing the current segment and the area already machined. As an example, the actual widths of cut are calculated for the toolpaths for machining a pocket. The example clearly demonstrates that the actual widths of cut vary over a wide range and are very different from the value used to calculate the toolpaths. In fact, for the example considered, slotting occurs over 40% of the distance travelled, and only 10% of the actual widths of cut are approximately equal to the original value used for toolpath generation.

Determination of optimum cutter diameter for machining 2-O pockets

Abstract Tool paths in milling are calculated using user-defined values of the radial width of cut (b) and the cutter diameter (D). When calculating the other cutting parameters, most researchers and practising engineers assume that the ratio of the radial width of cut to the cutter diameter i.e. b/D remains constant over the entire tool path length. However, in practice, when machining pockets and many other features with window-frame type toolpaths, b/D does not remain constant. In this paper, the optimum cutter diameter is chosen following a consideration of the variation of b/D throughout the cutter path. It is shown that while a smaller cutter diameter gives a more favourable variation, it leads to a longer toolpath. Hence the final optimum cutter diameter is a compromise between the increased costs of a larger diameter with a shorter toolpath and the lower costs of a smaller diameter with a longer toolpath.

Prediction of the radial force in turning using feed force data

Abstract This paper addresses the problem of calculating the radial force in turning, when the feed force is known. The empirical equations presented are used to predict the chip flow direction for tools with a nose radius that may also have a cutting edge inclined to the direction of primary motion. The predicted chip flow direction, measured feed force, known tool geometry and cutting conditions are then used to predict the radial force component. A comparison between the predicted and experimentally measured forces, for tools with a range of chipbreaker geometries, shows good agreement.