Research On Cutting Performance And Tool Reliability During Milling Of Compacted Graphite Iron By Coated Cemented Carbide Tool

Compacted graphite iron has excellent mechanical and thermal properties,and it is considered to be an ideal material for manufacturing new high-performance engines.However,the cutting performance of compacted graphite iron is poor,the cutting temperature is high,the cutting force is large,the integrity of the machined surface is poor,and the tool life is low.This is an important reason for restricting the wide spread of compacted graphite iron engine.In this paper,the compacted graphite iron GJV450 material used in the manufacture of diesel engine cylinder body was selected as the research object.The cutting performance of coated cemented carbide tool in milling compacted graphite iron is studied by means of heat conduction,cutting theory analysis,cutting experiment and microscopic observation.The main research contents of this paper are as follows,the influence of cutting parameters on chip morphology and chip geometric size,and the forming mechanism of serrated chip.Considering the influence of flank wear,the temperature field model and temperature gradient model of coated tool were constructed to study the tool temperature and temperature gradient of coated cemented carbide tool in milling of compacted graphite iron.The impacts of cutting parameters on workpiece material removal volume,cutting force,tool wear mechanism and machined surface quality was investigated.The reliability of coated cemented carbide tool in milling of compacted graphite iron was studied.The research in this paper can be used to improve the production efficiency and reduce the production cost of compacted graphite iron engine production line by providing guidance for the optimization of cutting parameters during the machining of compacted graphite iron.The single-factor cutting experiment was designed to analyze the influence of cutting speed and feed per tooth on chip morphology and geometric size in machining compacted graphite iron.It is found in the experiment that the chip in machining compacted graphite iron is serrated chip or needle chip.With an increase of cutting speed or feed per tooth,the adjacent serrated chip units separated gradually,and the morphology of cutting chip changes from serraed chip to needle chip.Either decrease in cutting speed or increase in feed per tooth will lead to the increase in the thickness and pitch of the serrated chip unit.The bottom angle of serrated chip unit decreased with an increase in cutting speed,which increases the shear angle and is beneficial to cutting.The formation frequency of serrated chip unit increases linearly with the increase of cutting speed,and decreases gradually with the increase of feed per tooth.Through the microscopic analysis of the chip surface morphology and the metallographic structure of the chip cross section,the geometric forming model of serrated chip was proposed,and the model was verified by the analysis of the cutting root specimen which was prefabricated grid.It is found that plastic deforrnation occurs at the bottom of serrated chip,and the prefabricated grid line here bends to the bottom of trapezoidal tooth section,and the plastic deformation area is triangular.Based on the one-dimensional heat conduction model of coated tool,the heat flux actually conducted into the tool substrate due to the thermal barrier effect of the coating is obtained,and the influence of coating structure on the coating thermal barrier effect is analyzed.It is found that the coating thermal barrier effect is obvious in a short time when the heat source is loaded,so the coated tool is more suitable for intermittent cutting.The changes in the thickness of Al2O3 layer and the total thickness of the composite coating have great influence on the thermal barrier effect of the coating.The thermal barrier effect of the coating is more obvious when either the thickness of Al2O3 layer or the total thickness of the composite coating are larger.The temperature field model and temperature gradient model of coated tool considering the influence of flank wear are established considering the influence of rake face heat source and flank face heat source on tool temperature rise.The tool temperature and temperature gradient distribution along the main cutting edge,rake face and flank face of coated cemented carbide tool during milling of compacted graphite iron is analyzed,and the influence of cutting parameters on the maximum tool temperature and maximum tool temperature gradient value is analyzed.It is found that the tool temperature increases when the flank wear occurs.Due to the thermal barrier effect,tool temperature is slightly affected by the increase of cutting speed.Increasing the feed per tooth and workpiece width will significantly improve the tool temperature.The tool temperature gradient increases significantly when the flank wear occurs.The increase of cutting speed slightly affects the temperature gradient of sharp tool,but it will significantly increase the temperature gradient of the worn tool.Increasing the feed per tooth will significantly improve the temperature gradient of the tool.The orthogonal experiment with three factors and four levels was designed,and the influences of the cutting speed,feed per tooth and exit angle on the workpiece material removal volume was analyzed.It is found that the feed per tooth has the greatest impact on the material removal of the workpiece,followed by the exit angle,and the impact of cutting speed is the smallest.In order to obtain the maximum workpiece material removal volume,the cutting speed is 600 m/min,the feed per tooth is 0.25 mm/tooth,and the exit angle is 30°.At the same time,considering the improvement of machining efficiency and the workpiece material removal volume,the cutting speed is 800 m/min,the feed per tooth is 0.25 mm/tooth,and the exit angle angle is 30°;The tool failure mechanism was analyzed.Adhesive wear,diffusion wear and oxidation wear are found to be the main wear mechanisms.An important reason for the uneven wear of the tool is due to the thermal crack.The mechanical impact crack parallel to the main cutting edge is an important cause of tool damage under the condition of large cutting speed and feed per tooth.The single factor cutting experiment was designed,and the influence of cutting speed on cutting force was analyzed.The experimental results show that the cutting force decreases with the increase of cutting speed under the condition of low cutting speed,while the cutting speed does not significantly affect the cutting force under the condition of high cutting speed.In order to reduce the cutting force during the milling of compacted graphite iron by coated cemented carbide tool,the cutting speed should be selected in the range of 600-1000 m/min;The orthogonal experiment with three factors and four levels was designed to analyze the influence of cutting parameters on cutting burrs.It was found in the experiment that the cutting burr on the entrane side was curled burr,and the cutting burr on the exit side was curled burr and secondary burr.The influence of feed per tooth,exit angle and cutting speed on the cutting burr height on the entrance side is in decending order.The influence of cutting speed,feed per tooth and exit angle on the cutting burr height on the exit side is in decending order.Based on the above research,the cutting parameters of coated cemented carbide tools for milling of compacted graphite iron were optimized.It is found that the cutting speed of 800 m/min,the feed per tooth of 0.25 mm/tooth and the exit angle of 60° are suitable to chose considering the material removal volume,cutting efficiency and machining surface quality.The repeated life experiment of coated cemented carbide milling cutter surface milling of compacted graphite iron was designed and implemented.The wear life distribution and damage life distribution of single blade milling cutter were analyzed.The failure life reliability model of single blade milling cutter was established based on the principle of series failure system.The relationship between tool failure reliability and wear reliability and fatigue damage reliability of single blade milling cutter was analyzed.It is found that the tool wear life of single blade milling cutter obeys lognormal distribution and the tool fatigue life obeys Weibull distribution.In low-speed cutting,the failure reliability of single-blade milling cutter mainly depends on its fatigue damage reliability.In high-speed cutting,the failure reliability of single blade milling cutter is affected by its fatigue damage reliability and wear reliability.The failure life reliability model of multi-blade milling cutter is established on the basis of the principle of series failure system,and the reliability of single blade and multi-blade milling cutter are compared.It is found that the multi-blade milling cutter is more reliable in high-speed cutting than in low-speed cutting.At the same cutting length,multi-blade milling cutter is more reliable than single-blade milling cutter.Compared with low-speed cutting,the tool life reliability of multi-blade milling cutter is significantly improved than that of single-blade milling cutter in high-speed cutting.From the perspective of improving tool reliability,the cutting speed of 800 m/min should be adopted when using coated cemented carbide tools to mill compacted graphite iron.The influence of the number of blades mounted on the cutterhead on the reliability of multi-blade milling cutters is analyzed.It is found that the reliability of multi-blade milling cutter is gradually improved with an increase of the number of blades,and it is more obvious in high-speed cutting process.From the perspective of improving tool reliability,the milling cutter with a large number of clamping blades on the cutterhead should be used when using coated cemented carbide tools to mill compacted graphite iron.