tailieunhanh - Metal Machining - Theory and Applications Episode 1 Part 4

Tham khảo tài liệu 'metal machining - theory and applications episode 1 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chip formation mechanics 53 No better relationship has ever been found for machining with plane-faced tools. The reason for this is easy to understand. Qualitatively a curled chip may be regarded as shorter more compressed at its inner radius than at its outer radius. Only rarely are chips so tightly curled that r t 5 even then the variation in compression from the chip centreline to its inner and outer radii is only . t 2r . Average chip equivalent strains equation b are typically greater than 1. Thus the modifications to flow associated with curvature are secondary relative to the magnitude of the flow itself. The sort of factors that could affect chip radius are variations of friction along the chip tool contact length and the roundness of the cutting edge and also the work hardening behaviour and variations of work hardening behaviour through the thickness of the chip most chips are formed from surfaces which themselves have previously been strained by machining . Shear plane angle prediction The previous section gives data that show that chip thickness and hence shear plane angle depends on tool rake angle friction and work hardening and it records how forces and tool stresses can be estimated if shear plane angle rake angle and friction angle are known. In this section early attempts by Merchant 1945 and Lee and Shaffer 1951 to predict the shear plane angle are introduced. Both attempted to relate shear plane angle to rake angle and friction angle and ignored any effects of work hardening. Merchant suggested that chip thickness may take up a value to minimize the energy of cutting. For a given cutting velocity this is the same as minimizing the cutting force equation b with respect to f. The well-known equation results f p 4 - 1 - a 2 Lee and Shaffer proposed a simple slip line field to describe the flow see Appendix 1 and Chapter 6 for slip line field theory . For force equilibrium of the free chip it requires that the pressure on .