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Machinability and Surface Integrity Part 7

Tham khảo tài liệu 'machinability and surface integrity part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Machinability and Surface Integrity 329 LARGE FACE MILL CUTTING-DRY AND CONVERTING SIGNIFICANT HEAT INTO THE RESULTANT CHIPS ICourtesy of Sandvik Coromant Figure 172. Typical temperature distributions isotherms during machining illustrated across the chip insert and workpiece at relatively low cutting speed 330 Chapter 7 secondary deformation zone tends to be linear in nature from ỹint - at the interface - zero - at the boundary of the triangular secondary zone. The frictional stress along the tool chip interface can be assumed to be constant along the first half of the contact region then linearly decreasing to zero at its end. The frictional heat source distribution at this interface can be obtained from stress and velocity distributions at this location. In Fig. 173a the basic FEM mesh is shown with typical temperature distributions obtained from this being illustrated in Fig. 173b. The accuracy of this particular example for the Tay-model for the total sum of all heat sources was within 2.6 of actual measured power consumption FcU . Moreover the values of 0 calculated from the temperature distributions closely-agreed to those obtained some years earlier by Boothroyd 1963 . The FEM approach to machining data capture and analysis covers these and other related parameters and clearly indicates the power of simulation - more will be mentioned on this subject later in the chapter. 7.7 Tool Wear and Life Introduction The working environment for most machining processes is extremely harsh with pressures exerted onto a minute area of tool tip being of the order of 1600 MPa with localised temperatures reaching over 750 C creating a sterile surface at the tool chip interface making this an ideal state for a pressure-welding condition. In attempting to minimise this affinity between the work-hardened chip - often this plastic deformation making the chip 5 times harder than that of the parent workpiece material means that there are several ways of relieving this tool chip