Study On Performances Of Cermet Cutting Tools In Machining Austempered Ductile Iron

Cermet cutting tools have excellent superiority in machining accuracy, efficiency and tool lives because of their great hardness, high wear resistance and super chemical stability. However, the cutting performances of Ti(C,N)-based cermet cutting tools are directly influenced by the proportion of C and N in content. It is generally agreed that Ti(C,N)-based cermet cutting tools with a higher N content have smaller grains and higher toughness, but lower hardness. Austempered ductile iron is a kind of difficult-to-machine material due to its high hardness and strength and work hardening. Thus, it is required that the cutting tools used to machine it also need to be superior in hardness and toughness, which are just virtues of Ti(C,N)-based cermet cutting tools. In order to have a better understanding of cutting properties of Ti(C,N)-based cermet cutting tools, a series of comparison experiments with the austempered ductile iron workpiece were carried out, using four types of inserts home and abroad, and the machining properties of ADI were also analysed.Firstly, the effects of cutting parameters on cutting forces were studied, and the friction coefficients of the rake face of these inserts were compared. The results indicated that cutting forces of these four kinds of inserts all declined with the increasing of cutting speed. Due to the larger amount of N in NX2525 than that in YNG151, the former cermet inserts had lower friction coefficients. In condition of high-speed turning, the coats on PV30 and YBC251 could reduce friction significantly.Secondly, tool lives and abrasions of the four types of inserts, as well as their wear mechanism, were analyzed. Conclusions were drawn as following: 1) YNG151 inserts which had lower N contains enjoyed a much longer cutting life than NX2525; 2) Due to their different substrates, coated cermets inserts PV30 had a longer life than coated cemented carbide YBC251; 3) The high temperature produced by high cutting speed in the contacting area, accelerated the adhesion of cermets inserts, which was the mainest wear-out mechanism of cermet inserts at high speed, and resultantly led to a shorter tool life. So cutting speed was the most significant factor for tool lives. "Halve the cutting speed and double the cutting depth" was an effective way to get a balance between machining efficiency and tool life.Thirdly and lastly, the influence of cutting parameters on the deformation rate of chips was also analyzed. It was revealed that, the cutting speed and feed rate had a higher impact on the deformation rate of chips and cutting depth had a less impact. In the cutting process, the length of the chips reduced as the tools became dull. Subsequently, according to the orthogonal experiment of cutting Austempered ductile iron, the influence of cutting parameters on surface roughness of the workpiece was analyzed. The results showed that the feeding rate was the most remarkable factor and the effect of insert type, cutting speed and cutting depth declined in succession.