Showing papers in "International Journal of Machine Tool Design and Research in 1962"

Shear angle solutions in orthogonal machining

Abstract: After briefly considering the more important shear angle solutions a new analysis is presented which is based on recent observations at slow cutting speeds and which takes into account the variable flow stress property of the work material. It is shown that the effective shear angle will be smaller at slow speeds, for given values of tool rake angle and tool-chip interface friction, than at high speed sowing to the increase in width of the deforming zone with decrease in cutting speed. The limiting case where this zone degenerates to a plane is also considered and the resulting equations are shown to give reasonable agreement with experiment.

Some recent research on the wear behaviour of carbide cutting tools

Abstract: Metallographic investigations have shown that a ferrite-austenite transformation occurs in the flow layer at the back of the chip when steel is machined with carbide tools. These transformation phenomena affect the wear reactions between the carbide tools and the steel. The alpha-gamma transformation starts at relatively low cutting speeds according to the selected cutting conditions. This results in a reduction of the formation of the built-up edge until, after complete transformation at higher cutting speeds no built-up edges occur. The flank wear varies in accordance with the size of the built-up edge. Within the range of high cutting speeds, considerable influence of the alpha-gamma transformation upon the crater wear can be observed. The carbon content of the resulting austenite phase depends upon the progress of the ferrite-austenite transformation. This influences the diffusion reactions between carbide and steel, and therefore quite considerably the strength of the resulting diffusion layers. It was possible to observe that in order to obtain good machinability, the most favourable structural states are those which result in an austenite phase with little carbon at the back of the chip. In this connection it should be stated that from the point of view of low crater wear, it is not the average carbon content which is important, but the lowest possible proportion of dissolved carbon in the individual austenite crystals. For practical purposes, these experiments show that the most favourable cutting conditions, from the point of view of wear, occur only if no built-up edge exists. The formation of the built-up edge is unfavourable, not only from the point of view of wear, but also from the point of view of the quality of the machined surface.

Dynamic acceptance tests for machine tools

Abstract: It is proposed that the dynamic quality of machine tools, in particular of radial drilling machines, be measured by the coefficient of merit. This coefficient is a product of the static stiffness between tool and workpiece, in the direction of the cutting thrust, and a non-dimensional ratio determined from the harmonic response locus of the machine structure. The determination of the coefficient of merit in the case of radial drilling machines is discussed in details and its relationship with the stability chart of the drilling process is elucidated. It is shown that the coefficient of merit is proportional to the maximum drill diameter which is stable at all speeds and that its increase signifies a contraction of the speed ranges over which the machine chatters.

Vibration in horizontal milling

Abstract: This paper sets out to distinguish between forced vibration and chatter during horizontal milling, comparing their causes and effects. The influence of changes in machining conditions on both types of vibration are assessed, and their relative importance discussed. It is shown that chatter is the primary limitation when machining ferrous materials, but forced vibration can be the more significant for light alloys.

Experiments in the piercing of soft metals

Abstract: Experiments on annealed and work-hardened tellurium lead, and cast tin using flat headed and conical tipped punches with and without lands are described. Principally the results presented show: (i) How the parameter, p / Y varies with reduction for a given shape punch; p is the steady state punch pressure and Y the saturation compressive yield stress of the material; these experimental values are compared with theoretical values. (ii) The variation with reduction of certain critical depths and thicknesses at which the steady state and the post-steady state commence. (iii) Photographs of both the metal deformation ahead of the punch, and of cavitation.

The mechanics of cutting strip with knife-edge and flat-face dies

Abstract: The cutting of strip using a pair of wedge-shaped dies which approach each other along a common centre line is similar to the cutting action of a pair of pliers The process is analysed in detail using some slip line field theory and the results of many experiments are given

Finish on surface ground steel

Abstract: The argument between production and inspection or supplier and purchaser regarding surface finishes on machined parts often is not very easily resolved Surface finishes will vary from one spot to another even if taken in the same direction relative to machining marks A change in direction of the stylus of the measuring instruments in relation to tool marks on the surface will give different readings and, within limits, could cover almost any particular surface finish requirements that the specifications may demand This paper treats several important factors involved and presents an analysis of differences in surface finish, as encountered on a flat ground surface and measured with two types of surface finish measuring instruments A series of surface grinding tests were carried out under fixed machining conditions in order to determine the relationship between surface finish and table feed for two kinds of steel Results are given in the form of diagrams with profilometer readings plotted against table feed The existence of maximum and minimum surface finish reading directions at any point of the testpiece surface is pointed out, as well as the orientation of these preferential directions, assuming as a reference the local direction of the tangent to the wheel marks A short mathematical analysis confirms these assumptions

A continuous path machine tool control system using coarse optical gratings

Abstract: The paper describes a new continuous path control system using a specially developed coarse optical grating measuring system, which provides linear interpolation within the pitch of the gratings Details of the measuring system are given The control system on the machine tool uses magnetic tape as the input medium The method of operation of this system is described

Widening the applications of diffraction gratings for measurement and control

Abstract: The paper describes the construction of radial gratings having between 90 and 32,400 lines photographed on to plate glass disks of 12 in. dia. or less. Errors less than ±3 seconds of arc are obtained. Applications of radial and linear gratings to various machine tools are described. In a gear hobbing machine errors have been reduced to 1/20 for worm/table rotation and 1 4 in actual cut gears of 20 in. dia. Circuits for phasemeters for servo and for measuring purposes are contrasted, and new techniques for using batching counters with gratings described; typical applications to gear measurement and a gearboxless lathe are mentioned.

Measurement of the mean friction coefficient in sheet drawing

Abstract: The effects of cross-sectional shape and size of draw bead on the induced additional tension in a two-dimensional bending test were studied. Beads of rectangular cross-section were found to have a greater range of effectiveness for controlling the tension than those of circular section. Moreover, the rectangular beads of small height sufficed to produce the desired tension. The tension under rigid blank holding conditions was more sensitive to changes in shape and size of bead than when under constant-pressure blank holding.

Studies of friction and lubrication of machine tool slideways

Abstract: MACHINE too1 slideways are now facing demands for higher accuracies under more severe operating conditions; their limitations are affecting also the application of automatic control in both positioning and smooth movement of slideway components. In this context of demands for higher slideway performance, new materials and new beating systems are being examined in order to give a range of alternatives to the designer faced with providing slideways to suit various applications. Many aspects of three basically different slideway systems have been or are being investigated at PERA. These are: conventional cast iron on cast iron slideways lubricated by mineral oils [1, 2]; a P.T.F.E. impregnated bronze sliding on cast iron [3]; and hydrostatic slideway bearings. Instead of describing in general terms the full range of the investigations conducted, detailed consideration of parts of this work has been chosen as a better method of illustrating the research. Only one aspect of each of the investigations mentioned above will be discussed; each aspect, in fact, forms a separate subject of investigation, and each is capable of yielding practical conclusions as a guide to machine tool design. These aspects are, with their corresponding slideway arrangements: