Performance Of Coated Cutting Tools In Turning A Malleable Cast Iron

The malleable cast iron with graphite tempered is used usually for thin wall castings such as front and rear wheel shells of automobile and tractor,camshafts,steering knuckle shells and redactor shells etc.It is difficult to cut the malleable cast iron because its high strength,high toughness and elongation results in the serious cutting tool wear.The coated tools are much widely used for machining malleable cast irons,as the brittleness of the ceramic cutting tools and the expensive price of the PCBN cutting tools limit their practical application,Despite the numbers of work on machining cast irons by coated inserts,there was few report involving on cutting the malleable cast irons.As an important cast iron material,research on developing the suitable coatings and cutting parameters for it would bring us a great of benefits,such as lower processing cost and higher processing efficiency and machining quality,at same time it also shed a light on the fabrication and application of coated cutting tools.To fill in the gap,the Al2O3/Ti(C,N),TiN/TiAIN with two thickness coatings and nc-TiAlSiN coated cemented carbide tools and TiAlSiNceramic tools were tested in turning the malleable cast iron under different experiment parameter in this paper.The performance of coated cutting tools in turning a malleable cast iron was explained and illustrated based on the analysis and investments of cutting force,cutting temperature,workpiece surface roughness,chip morphology and tools wearthrough single factor,orthogonal and wear experiments.The main research conclusions are as follows:1.Chips morphology and forms of chips mainly becomes chippings for gray cast iron,however,under this study conditions,different coated cemented carbide tools presented similar chips morphology and forms of chips mainly become continuous chips,such as arc,short tubular,long tubular C-shaped and fragment chips depending on this study,Malleable cast iron with graphite tempered has not performed the brittle characteristics as grey cast iron,but has performed great toughness and plasticity.2.The maximum cutting forces and temperatures were measured in coated TiAlSiN ceramic inserts used in turning malleable cast iron under all cutting parameters,and cutting forces and temperatures for CVD Al2O3/Ti(C,N)inserts were second biggest,however the minimum were measured for PVD TiN/TiAIN coating tools.From the perspective of surface roughness,the good machined workpiece surface roughness can gained in turning malleable cast iron with nc-TiAlSiN inserts under all experiment conditions.The experiment results show that CVD Al2O3/Ti(C,N)coating tools is the first choice for the cutting parameters of low-cutting speed,medium-feed rate and large-depth of cut,and PVD TiAlSiN coated ceramic tools is the first choice for the cutting parameters of high-cutting speed,fast-feed rate.3.From the point of cutting forces,the order from large to small that the influence of various cutting parametersand coating on cutting component forces and resultant forces based on the range and variance analysis is depth of cut ap>feed rate f>tool coatings>cutting speed V.If the minimum cutting force is regarded as the optimization goal,namely the optimal combination is250 m/min,0.3 mm,0.05 r/min and PVD TiN/TiAlN coated tools.Cutting forces models of five coated tools were respectively set up,and cutting forces models of both CVD Al2O3/Ti(C,N)and PVD TiN/TiAlN with thicker coating are highly significant.4.From the view of tool life,PVD TiAlSiN coated ceramic toolperformed the worst too life with the shortest tool life,while PVD TiN/TiAlN thicker coating and nc-TiAlSiN coated inserts performed the longest tool life.The maximum cutting forces and temperatures for PVD TiAlSiN coated tools resulted in its wear curve to resemble a line,meanwhile the flank face wear increased with an increase in cutting length,but the wear curves of other four tools contained initial wear,normal wear and severe wear three stages.5.From the perspective of wear mechanism,the primary wear mechanism of CVD Al2O3/Ti(C,N)coated inserts in turning malleable were chipping of cutting edge and abrasive wear,peel of coatings attributed to the low affinity Al2O3 coating to iron,while PVD TiN/TiAlN coated inserts,PVD nc-TiAlSiN inserts and PVD TiAlSiN inserts mainly occured abrasive and adhesion wear.PVD TiAlSiN ceramic tool performed the shortest tool life due to serious adhesion wear,PVD TiN/TiAIN coated inserts also occurred oxidative wear.6.It is found that the effect of graphite morphology on wear mechanism is obvious,the graphite in cast irons can be regarded as a void and small cavity,when cutting cast irons,the graphite cutting is equivalent to empty cutting,while matrix cutting belongs to the continuous metal cutting.Because the graphite is widely distributed in cast irons,it are repetitively loaded by stress concentration when cutting tool cuts into and out graphite,so that the cutting tools is inclined to occur chipping of cutting edge.Compared with gray cast iron,chipping of cutting tools is not so serious as gray cast iron when cutting malleable cast iron Compared to other cast iron,such as,alloy cast iron,compacted cast iron,cast iron and wear-resistance cast iron,alloy elements in the malleable iron are less,so chipping of cutting tools is also not so serious as other cast irons,the graphite distributed in the malleable iron is close to spheroidal graphite in ductile cast iron,so it is similar for the wear mechanisms of cutting tools used cutting the two cast irons and mainly occurs adhesive wear and abrasive wear.