Design Simulation And Experimental Research Of Powder Metallurgy Piston Mold For Automobile Shock Absorber

Die is an indispensable tool for developing and realizing material forming.The direct contact between powder metallurgy forming die and powder has an important influence on the strength,hardness and surface accuracy of piston compact.In order to obtain compacts with good surface quality and high dimensional accuracy,it is of great practical significance and economic value to study the design,verffication and long life use of dies.In this paper,the design,numerical simulation and wear resistance of powder metallurgy piston die are studied.A new precision forming die for piston of powder metallurgy automobile shock absorber was designed.According to the specific parameters of mould,mandrel and die punching in piston product design,the structure scheme,pressing mode,demoulding mode and structure form of die base are determined,the powder loading height,axial dimension and radial dimension are calculated,and the mould,mandrel and die which meet the requirements of piston dimension and geometric tolerance design are produced according to the design parameters.Die stamping,the forming die is assembled and installed on the die base for productionBased on AN SYS software,the key parts of the die and the whole die base are analyzed by finite element method.Using ANSYS Workbench module,the static characteristics of the die assembly and the upper and lower die assembly are analyzed separately,and the stress and displacement nephograms of the die assembly and the die assembly under the static analysis of the single constraint are obtained.The strength and stiffness of the die assembly and the die assembly are analyzed and checked respectively according to the requirements of the working conditions.Static analysis is carried out,considering the constraints of actual working conditions.Hex Dominant mesh generation is carried out for the die and die punch in direct contact with powder.Tetrahedrons are used for the rest parts to obtain the maximum equivalent stress and displacement,and modal analysis is carried out for the whole die frame.The first ten modal modes of the die holder verify the rationality of the die design.The metallographic structure and micro-structure of the die after vacuum quenching were studied,and the mechanical properties and tensile properties were tested.The low temperature tempering structure of Cr12MoV cold working die steel is observed.The structure is composed of tempered martensite+retained austenite+white carbide.The content of C and C r elements is high,and a large number of carbides with high hardness are easily formed,which greatly improves the wear resistance of the steel.At the same time,the addition of Mo and V can refine the grain size and further improve the wear resistance of steel The average hardness of the sample is 52.7 HRC,which meets the hardness requirements of the die.The tensile strength of the vacuum oil quenched die is 826 MPa,the elongation after breaking is 28%,and the impact energy is 9.5J,which meet the production requirements.The wear resistance of the die was studied by using MMW-1A universal friction and wear tester controlled by computer.The friction coefficient and wear amount under different loads,rotational speeds and temperatures were analyzed.The three-dimensional wear morphology of the sample was observed by using a three-dimensional morphology instrument,and the causes of wear scar morphology were analyzed.With the increase of load,the friction coefficient of the specimen increases first and then decreases,and the fluctuation range of friction coefficient is larger;with the increase of rotational speed,the friction coefficient of the specimen increases first and then decreases,the fluctuation range of friction coefficient is small,and the wear amount increases;under low load,the wear mode of the specimen is abrasive wear,with the increase of load.The wear mode changes to a mixture of abrasive wear and adhesive wear.At low speed,the wear mode of the specimen is abrasive wear.With the increase of rotational speed,the wear mode of the specimen changes to delamination wear caused by continuous formation and peeling of oxide film on the friction interface.At different temperatures,the friction coefficient of the specimens is stable at a high level between 0.48 and 0.52.The wear rate of all specimens increases first and then decreases,and the wear rate increases slowly.Using FY80 powder forming press,according to the design parameters,the powder metallurgy piston blank was prepared by using the designed die equipment.A batch of piston parts were prepared.24 of them were randomly.selected and divided into three groups.Dimension measurement was carried out by Mitutoyo profilometer.Profit and position tolerance were measured by coordinate measuring instrument.Roughness of parts is measured by surface roughness meter,flatness is measured by Polytec white light meter,and all parameters of zero samples are measured by image measuring instrument.The results show that 24 parts meet the production requirements.