EFFECT OF TOOL VIBRATIONS ON SURFACE-ROUGHNESS DURING LATHE DRY TURNING PROCESS

Choice of optimized cutting parameters is very important to control th e required surface quality. In fact, the difference between the real a nd theoretical surface roughness can be attributed to the influence of physical and dynamic phenomena such as: built-up edge, friction of cu t surface against tool point and vibrations. The focus of this study i s the collection and analysis of surface roughness and tool vibration data generated by lathe dry turning of mild carbon steel samples at di fferent levels of speed, feed, depth of cut, tool nose radius, tool le ngth and work piece length. A full factorial experimental design (288 experiments) that allows to consider the three-level interactions betw een the independant variables has been conducted. Vibration analysis h as revealed that the dynamic force, related to the chip-thickness vari ation acting on the tool, is related to the amplitude of tool vibratio n at resonance and to the variation of the tool's natural frequency wh ile cutting. The analogy of the effect of cutting parameters between t ool dynamic forces and surface roughness is also investigated. The res ults show that second order interactions between cutting speed and too l nose radius, along with third-order interaction between feed rate, c utting speed and depth of cut are the factors with the greatest influe nce on surface roughness and tool dynamic forces in this type of opera tion and parameter levels studied. The analysis of variance revealed t hat the best surface roughness condition is achieved at a low feed rat e (less than 0.35 mm/rev), a large tool nose radius (1.59 mm) and a hi gh cutting speed (265 m/min and above). The results also show that the depth of cut has not a significant effect on surface roughness, excep t when operating within the built-up edge range. It is shown that a co rrelation between surface roughness and tool dynamic force exist only when operating in the built-up edge range. In these cases, built-up ed ge formation deteriorates surface roughness and increases dynamic forc es acting on the tool. The effect of built-up edge formation on surfac e roughness can be minimized by increasing depth of cut and increasing tool vibration.