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Heat Transfer Handbook part 126. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | MACHINING PROCESSES METAL CUTTING 1247 Figure 17.9 Chip formation during orthogonal metal cutting. From DeVries 1992. is assumed to be continuous at least in the vicinity of the cutting tool characteristic of a duGine workpeece such as brass tow-carbon seed or an alummum altoy. Plastic shear is the principal mechanism of chip formation. Three ss a finhe volume to the shear zone however at common cutting speeds the angle between the planes which defines the deformation zone collapses so that the deformation appears to occur in a single plane. For this reason an infinitely thin zone of deformation is assumed in most models. Figure 17.9 shows the force components between the cutting tool and the workpiece that are needed to characterize the cutting process including the heat generation and temperature distributions. DeVries 1992 has described the relationships among these forces and the geometrical features of chip formation all based on the classical literature. Several theories are available to determine the shear plane angle o. One that minimizes the cutting power is o 4 - 0.5 0 - y0 17.21 where 0 is the friction angle defined by tan-1 i and jl is the coefficient of friction between the chip and the tool Ff Fn. The resultant force at the shear plane must equal the resultant force at the tool-chip interface. R Fc Fs - R Ff Fn 17.22 1248 HEAT TRANSFER IN MANUFACTURING AND MATERIALS PROCESSING The shear force is then given by Fs lsb rs Ts ba sin q 17.23 where Ts is the plastic flow stress of the material ls the length of the sher zone a the depth of cup and b the width of cut. Combining his informatinn nee may obiain results for the force components Fc and Fn as I1 cos K - Yq sin Q - Yq F c F s . COs Q YQ fl sin Q Y0 1 Fn Fs-------------------- ----------- COs Q YQ fl sin Q Y0 17.24a 17.24b The x component of the resuhant force Fpi is also easily obtained. 17.4.2 Thermal Analysis Typically the heat sources in orthogonal cutting can Oe regarded as being localized in .
