Research On The Machinability In High Speed Machining Of Powder Metallurgy Material

High-speed and high-efficiency machining are the way of main cutting methods of modern manufacturing industry, have been widely used in the field of high-speed machining(HSM) of steel, aluminum and other materials maturely. However, for the application and research on HSM technology of powder metallurgy (PM) materials are rarely. The cutting performance of HSM powder metallurgy automobile engine parts were studied by theoretical analysis, numerical calculation and experimental method, research on chip deformation process, cutting force and cutting temperature, tool wear morphology and failure mechanisms, blunt standard of tools, surface roughness and the tool reliability issues in automated production. Provide a theoretical basis and technical support for more efficient machining of this type of material.Through a lot of cutting tests proved that PCBN cutting tools with negative chamfer structure were the best tools in HSM powder metallurgy valve seat (PMVS). By means of Oxley shear zone model,chipping deformation mechanism was studied in high-speed cutting process with chamfered tools; and pointed out that in the case of tool-chip contact length smaller than the chamfered width, PCBN tools were in the state of negative-chamfered-cutting, on this basis negative chamfer cutting model has been proposed. In the cutting model of negative chamfered tools, surface friction coefficient and friction angle formula were established through stress analysis on the negative chamfered surface; and the calculation method of the shear angle was obtained based on Merchant model. By comparing the domestic and foreign common tool-chip contact length of the empirical formula, a suitable empirical formula has been found to approximate calculation the tool-chip contact length. For PM materials, the chip formation and chip morphology were analyzed by observing a large number of chips, and the mechanism of the process of lamellar type chip was interpreted.Through orthogonal cutting tests, regression analysis were used when establishing the empirical formula of cutting force on two most commonly used PMVS, looking for the general law of cutting force in HSM. By single-factor test method to study the influence on the cutting forces with cutting parameters, workpiece material, negative angle of chamfered tool and corner radius. When high-speed cutting powder metallurgy valve seat, cutting speed vc=200-240m/min, cutting depth αp= 0.1-0.2mm, feed ratef=0.1-0.15mm/r were the best cutting parameters. Corner radius have a significant impact on the cutting force, should choose between 0.4mm-0.8mm. With increase of corner radius cutting resistance increased significantly, but the head strength and wear resistance have been significantly improvedInfrared temperature measurement method had been used to obtain the average cutting temperature of cutting zone. By orthogonal test, the empirical formulas of cutting temperature had been established with cutting parameters under different negative angle. The relationship of cutting temperature with feed rate, cutting speed, depth of cut and negative angle of chamfered tool were analyzed. In addition, empirical formulas were established about cutting parameters, nose radius and surface roughness of three kinds of PMVS commonly used. Studies have shown that when the corner radius equal to 0.8mm, cutting surface quality was the best..Through a large number of tool wear test, tool wear morphology and failure mechanism of PCBN tools were studied during HSM powder metallurgy valve seat. Main forms of tool wear performance were rake face wear, flank wear and breakage. Main mechanisms of tool wear were abrasive wear, adhesive wear, oxidation wear, diffusion wear, micro-cracking and breakage. Main forms of tool breakage were chipping, flaking, cracked, brittle fracture, cracks. According to the breakage feature of PCBN tools, blunt standard of tools should be based on surface roughness value Rα=1.6μm in actual production. For ease of operation and statistics, it is recommended to use the number of parts N as tool life which can be processed by a single blade.After the data collection and statistical analysis during tool life test, Weibull distribution model of tool life was established in high speed cutting PMVS with PCBN tools. Based on this model, tool life can be rational plan based on the tool reliability on production site through this model. Research shows:when the tools were reground only once, the tool reliability R=0.68 and the tools life Nr= 8247, highest productivity and the costs of each blade down 29% can be obtained.