tailieunhanh - Machinability and Surface Integrity Part 3

Tham khảo tài liệu 'machinability and surface integrity part 3', 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 289 Fig. 153a-c . The influence of this irregular harmonic rotational belt-driven rotation can be gained from the schematic representation shown in Fig. 153d where a repeating-series of tumbling three-lobed harmonic geometric shapes are reproduced on the workpiece. The irregular but periodic nature of the rotational action of the belt-driven headstock is reproduced on the workpiece by a series of kinematic combinations of headstock rotation and linear motion supplied by the longitudinal feed of the cutting tool along the part Fig. 153d . If a direct-drive headstock configuration is utilised Fig. 153e then there is virtually no harmonic influence associated from the machine so more consistent turned components result. Returning to Fig. 152 the overall machine-toolworkpiece system can be isolated to consider the simple effect of a cantilevered cutting tool that is inadequately supported or the unlikely occurrence of too small a cross-sectional area - making it somewhat under-strength . The main cutting force in turning operations is the tangential force . see Fig. 19 it results from several factors such as Resistance to rotation - caused by the workpiece material s inherent shear strength Undeformed chip thickness - resulting from the radial DOC selected Orientation of cutter rake angle geometry - this being a combination of either a positive neutral or negative rakes plus to a lesser degree the effect of shape and size of the tool nose radius Feedrate - in combination with DOC will heavily influence the size of the effective chip thickness and play a dominant role in the resulting surface texture. In the upper diagram in Fig. 152 the tangential force is simplistically shown contacting the cutting insert at the point. The application of the cutting force here causes a large bending moment to occur at the pivot point - as shown. The resultant dynamic action of this effect is depicted in the lower diagram of Fig. 152 where the .