Investigation of the secondary shear zone in metal cutting
01 Mar 1971-International Journal of Machine Tool Design and Research (Pergamon)-Vol. 11, Iss: 1, pp 75-83
TL;DR: In this article, the secondary shear zone has been investigated with mild steel with H.S. tool having 5 per cent cobalt and metallurgical behavior of the work material in the extreme conditions of strain and temperature in the SZ has been discussed.
Abstract: Earlier investigations of secondary shear zone have been carried out mostly with the use of carbide tools. In this work investigation has been carried out with machining mild steel with H.S.S. tool having 5 per cent cobalt. The emphasis is made on the metallurgical behaviour of the work material in the extreme conditions of strain and temperature in the secondary shear zone as it is an important factor in machinability. Changes in structural features in different types of built-up-edge and the secondary shear zone are discussed.
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TL;DR: In this paper, an experimental analysis was performed to evaluate the width of the secondary deformation zone and the mean coefficient of friction during the machining of 5083-H34 aluminum alloy.
Abstract: An experimental analysis was performed to evaluate the width of the secondary deformation zone and the mean coefficient of friction during the machining of 5083-H34 aluminum alloy. Dry orthogonal cutting tests using high speed steel and sintered carbide tools of different rake angles were carried out at a wide range of feed rates at constant cutting speed for tubular workpieces. The width of the secondary deformation zone and the mean coefficient of friction were found to be direct functions of the parameters involved in the cutting process. The results were analyzed in terms of the variation in the mean tool-chip contact temperature and its influence on the specific tangential load and specific normal pressure on the tool face.
11 citations
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TL;DR: In this paper, the influence of microstructural directionality on machining behavior was examined for two commercial steel plates with respect to both ferrite-pearlite banding and inclusions, using orthogonal cutting tests.
Abstract: The influence of microstructural directionality on machining behaviour is examined for two commercial steel plates with respect to both ferrite-pearlite banding and inclusions, using orthogonal cutting tests. In relation to machining forces, chip morphology, and surface finish, one steel exhibited marked anisotropy, and comparisons with a non-banded steel indicated that the anisotropy was primarily due to the presence of ferrite-pearlite banding. Reasons for the anisotropy are briefly discussed in terms affracture energy, and the difficulties of machining in certain directions and relevance of the results to practical machining operations are also highlighted.
7 citations
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TL;DR: In this article, the authors proposed a methodology to determine the value of minimum chip thickness by analysing acoustic emission (AE) signals generated in orthogonal machining experiments conducted in micro milling.
Abstract: The determination of minimum chip thickness is important for establishing the lower limit of the feasible process window in micro mechanical machining for a given tool and workpiece material. The minimum chip thickness is encountered in micro milling operations owing to the variation in chip load as predicted by the chip density function. This study proposes a methodology to determine the value of minimum chip thickness by analysing acoustic emission (AE) signals generated in orthogonal machining experiments conducted in micro milling. Cutting trials were performed on a near balanced ferrite/pearlite microstructure (AISI 1045 steel) with a range of undeformed chip thicknesses spanning across the tool edge radius. The characteristics of AE r.m.s signals were studied for conditions when the tool was rubbing the workpiece. This base signal signature was used to study and contrast AE signals to other machining parameters. This study enabled the identification of threshold conditions for occurrence of minimum chip thickness. The value of minimum chip thickness predicted by this new approach compares reasonably well with that existing in published literature.
5 citations
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TL;DR: In this paper, the machinability of AISI-1045 steel in a magnetically assisted environment was discussed, and the changes were manifested through an enhancement in steel plasticity, resulting in a widened slip band area within the primary shear zone (PSZ) and improved plastic flow at tool-steel interfaces along the SZ.
Abstract: This work discusses the machinability of AISI–1045 steel in a magnetically assisted environment. Physically, magnetization causes suppression of Bloch walls in ferromagnetics, which enhances the dislocation paths within the Weiss domains of the matrix material. From a material point of view, the changes were manifested through an enhancement in steel plasticity, resulting in (i) a widened slip band area within the primary shear zone (PSZ) and (ii) improved plastic flow at tool-steel interfaces along the secondary shear zone (SSZ). From a mechanical point of view, the modifications can be summarized as a neat drop of the thrust force component due to the magnetic action generated by the external source, i.e., the current coil. The changes observed in the local diagram of forces cause alterations in the tribological properties at the tool-material interfaces. These alterations act to accelerate formation of the chip and lead to save energy because of the decrease in the cutting period, which should signific...
2 citations
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01 Jan 1973
TL;DR: In this paper, an attempt has been made to fit the X-ray intensity profiles by Fourier series and transforms, and the result is discussed, where the similarity in structure of the negative wedge built-up-edge and the secondary shear zone is also analyzed.
Abstract: The study of recrystallisation in metal cutting is of significant importance since it influences tool wear and surface finish. The formation of recrystallised crystallites in the secondary shear zone (flow layer) when machining mild steel with HSS tools and the determination of size of such crystallites by X-ray diffraction techniques were reported by the author in earlier papers. In this paper an attempt has been made to fit the X-ray intensity profiles by Fourier series and transforms. Computer programmes have been developed for solving Fourier series and the result is discussed. The similarity in structure of the negative wedge built-up-edge, and the secondary shear zone is also analysed. The changes in X-ray diffraction patterns give a vivid picture of metallurgical changes in the flow layer. Fourier analysis lends sophistication to the analytical approach to the X-ray diffraction technique.
References
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TL;DR: In this paper, it was shown that the most favorable cutting conditions, from the point of view of wear, occur only if no built-up edge exists, and 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.
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.
27 citations