The Experimental Research On The Cutting Performance Of High Strength And Hardness Steel Hard Cutting

Since the1980s, hard turning is gradually replacing grinding and becomes animportant processing technology of semi-finishing and finishing in aerospace, defenseindustry, automobile and aircraft manufacturing industries. In the process of hard turning,the cutting tool is exposed to a very severe environment. Much high stress and temperatureexist in the interface of tool-chip and tool-workpiece due to the high hardness of themachined steels and the small contact area between the tool and the workpiece. For acutting tool to perform successfully under these severe conditions, factors such as thecutting tool edge geometry (chamfer angle and hone radius), feed rate, and cutting speedneedto be carefully selected.Moreover, it is well known that the surface quality andintegrity of hard machined parts are influenced by many factors such as process variables,tool wear and cutting edge preparation. Although a high surface quality can be achievedusing hard turning, there are many unknown factorsinfluencing the surface integrity. Whenhardened steel is machined, the machined surface may undergo phase transformation due tothe heat generated. Furthermore, large plastic deformation and shear occur during chipformation. Therefore, a complex residual stress pattern is generated in the machinedsurface.This paper presents the following research work:(1) In the aspect of chip formation, eight groups of typical morphology of chip fromcontinuous chip to unit chip were obtained through single factor experiment in largespeed range. Then, the change law of chip formation are systematically analyzed. Whenvc=20m/min, apophysis appearred on the free surface of chip. Serrated chip could befound at cutting speed of60m/min. With the increase of cutting speed, serrated chip wasincreasingly apparent. When vc=180m/min, obvious cracks began to appear at the root ofserrated chip. The continuity of chip was interrupted, and unit chip appears.(2) In the aspect of cutting force, a simplified calculation method of serrated chipequivalent chip thickness was proposed and then it was used to calculate the equivalentchip deformation coefficient. In addition, a cutting force model is derived based on theenergy division. It was verified by corresponding cutting tests which proved that themodel had good prediction capacity. The most significant factor was cutting depth among the three main cutting parameters, followed by feed rate and cutting speed. Withthe increase of tool wear, cutting force increased which can be attributed to thecombining influence of a variety of positive and negative effect factors.(3) In terms of cutting temperature, the influence law of cutting parameters and tool wearon cutting temperature were studied. And found that the influence of different factors onthe cutting temperature were differences. The ranking of the cutting parametersaccording to the impact degree is as follows: cutting speed, feed rate and cutting depth.When cutting speed changed, the cutting tool temperature trend of PCBN(Polycrystalline Cubic Boron Nitride) and carbide tools changedat120m/min and260m/min, respectively, after that, the increasing trend of the cutting temperature sloweddown, while the pattern of cutting tool temperature of the ceramic tools remainedunchanged. Cutting temperature increased with the increased tool wear and when thetool wear reached a certain level, the degree of interaction between the temperature andcutting tool wear enhanced and cutting temperature experience a accelerating rise.(4) In terms of tool wear, wear mechanism of coated cemented carbide tool was mainlyadhesion, diffusion, oxidation, brittle damage and plastic damage. The wear mechanismof ceramic tool was mainly abrasive, adhesive, chemicaland brittle damage.The mainwear mechanism of PCBN tool was abrasive, diffusion, oxidationand brittle damage.(5) In terms of surface integrity, the law of the changing of surface intergrity evaluationindexes with their influence factors was studied. The factor of cutting parameters whichhad the most significant effect on surface roughness is feed rate, followed by cuttingspeed.Cutting depth had no direct effect on surface roughness. Surface roughnessincreased with feed rate increasing, and decreased with the increase of cutting speed.The residual compressive stress of machined surfacewas translated into tensile stresswith the increase of cutting speed and feed rate.The maximum value of residualcompressive stress under surface was decreased with increase of cutting speed and offeed rate. The action depth decreased with the increase of cutting speed and increasedwith the increase of feed rate.Surface residualstress and action depth did not changeobviously with the increase of cutting depth. Surface microhardness and the action depthreduced with the increase of cutting speed, and increasedwith increase of feed rate.Surface microhardness and the action depth increased slightly with the increase of cutting depth.