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contributor.authorChawla, B S-
contributor.authorDas, N S (Guide)-
contributor.authorBiswas, C K (Guide)-
identifier.citationAn Analysis of Strain in Chip Breaking Using Slipline Field Theory with Adhesion Friction at Chip/Tool Interface, Doctoral Thesis, June 2005, P 222en
descriptionCopyright for this thesis belongs to National Institute of Technology, Rourkela, Indiaen
description.abstractDespite rapid growth in the applications of metal machining in manufacturing, a comprehensive analysis of the problem of chip control has always been a di±cult task. This is because of the complex mechanism of the chip formation process and a lack of knowledge of the factors that in°uence chip form/chip breakability under a given set of input machining conditions such as work material properties, tool geometry, chip breakers and cutting conditions. Consequently, the solution to the problem has been approached empirically with a limited degree of success. In the present investigation, an attempt has been made to examine chip breaking by a step-type chip breaker using the rigid-plastic slip-line ¯eld theory. Orthogonal machining is assumed and the deformation mode is analysed using the solutions pro- posed earlier by Kudo and Dewhurst. The rake face friction is represented by the adhesion friction law suggested by Maekawa et al. The ¯elds are constructed and analysed by the matrix operational procedure developed by Dewhurst and Collins. Limit of validity of the ¯elds has been determined from the consideration of overstress- ing of the rigid vertices at the chip and the workpiece and also from the consideration that friction angle along the tool face nowhere becomes negative. The extent of `ma- terial damage' is assessed by computing the cumulative shear strain su®ered by the material in passing through the primary shear line and secondary deformation zones, by a method due to Atkins et al. Variation of total strain, breaking strain and the chip curl radius as a function of the chip breaker height and its distance from the cutting edge is studied. The variation of strain across the chip thickness is estimated. The accuracy of prediction of the degree of chip breaking by some of the breakability criterion is examined in the light of rigid-perfectly plastic slip-line ¯eld theory. It is found that as the chip breaker moves away from the cutting edge the radius of chip curvature (Rchip=t0), tool-chip contact length (ln=t0), speci¯c cutting energy (Fc=t0), cutting ratio ³ and total strain ²t in the chip increase while the breaking strain and the secondary strain decrease. This observation is found to be in°uenced both by uncut chip thickness t0 and tool rake angle °. The cutting force increases as WTR increases and rake angle ° decreases, however, the reverse trend is exhibited by chip breaker force Fb. The amount of shear strain in the secondary deformation zone is found to be about 10 to 15 % of total strain. The trend of variation of total strain ²t, speci¯c cutting energy (Fc=t0) and the breaking strain ²b with chip breaker position supports the view that chip breaking is governed mainly by the breaking strain and not by \material damage" or by speci¯c cutting energy consumed during machining. Experimental investigation has been carried out to validate the theoretical ob- servations. Orthogonal machining tests were carried out on mild steel tubes using HSS tools with 10 % cobalt. Chip breaking was accomplished using a step-type chip breaker. Chip thickness and chip curl radius were measured using an image analyser. For the chips, the shift in the position of the neutral axis from the centre was cal- culated using the theory of bending of curved beams. The chip curl radius before breaking was determined taking into account the elastic recovery of the chips. Break- ing strain was calculated from a simpli¯ed formula, ²b = tchip=(2 Rchip) and this was correlated with the degree of chip breaking. A procedure for chip breaker design to achieve e®ective breaking is also suggested. It is seen that chip breakability criteria based on t0, tchip and Rchip predict the e®ectiveness of chip breaking more accurately than those based on speci¯c cutting energy and material damage.en
format.extent3466622 bytes-
publisherNational Institute of Technology, Rourkela, Indiaen
titleAn Analysis of Strain in Chip Breaking Using Slipline Field Theory with Adhesion Friction at Chip/Tool Interfaceen
Appears in Collections:Thesis (Doctor of Philosophy)

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