tailieunhanh - Machinability and Surface Integrity Part 4

Tham khảo tài liệu 'machinability and surface integrity part 4', 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 299 either entirely eliminating it or at the very least minimising its affect on the overall machining process. Chatter during machining can result from a range of multifarious and often linked-factors they include Depth of cut DOC - can be considered as the principal cause and for the prospective control of chatter. The DOC delineates the chip width acting as the feed-back gain31 within the closed-loop cutting process NB The machining processes stability limit - being the threshold between stable cutting and chatter - can be determined from trial-and-error by simply incrementally increasing the DOC until the commencement of chatter then backing-off at this level. The prediction of chatter s onset can be found analytically this value being based upon thorough knowledge of material stiffness and cutting system dynamics. Rotational speed - is probably the simplest parameter to modify thereby altering chatter and its associated amplitude NB The peripheral speed of either the rotating tool or workpiece affects the phase-shift between overlapping surfaces and its associated vibration regeneration. Feed - for milling operations the feed per tooth defines the average uncut chip thickness t influencing the magnitude of the cutting process. Chatter is not unduly affected by the feedrate selected but feed does have an effect on the predictable severity of vibration during machining NB As no cutting force exists if the vibration occurs in the Y direction - resulting in loss of contact between the tool and workpiece - the maximum amplitude of chatter vibration will be limited by its feed. 31 Gain can be practically defined in the following way The ratio of the magnitude of the output of a system with respect to that of the input - the conditions of operation and measurements must be specified Smith 1993 et al. . Cutting stiffness Ks - is a material property connected to shear flow stress hardness as well as work-hardening characteristics of