Research On Powder Injection Molding Of Ultrafine Cemented Carbide

High strength and high hardness were marked on ultrafine cemented carbide and the application of hard alloy was extended by using metal injection molding technology.This thesis was separated into two parts: Research on process of ultrafine cemented carbide powder injection molding; Trail-manufature of straight spur gear and milling blade. Ultrafine cemented carbide was successfully manufactured; the composition of materials were: 10%Co, 89.28%WC, 0.27%VC, 0.45%Cr3C2; grain size of alloy is 0.465μm; the level of carbide is C06; density is 13.99g/cm3; hardness is 90.1HRA and bending strength is 250 MPa.The process of powder injection molding include praperation of binder, injection molding, debinding, sintering.(1) Ball milling of powder, determing binder formulation and powder loading were included in praperation of feedstock. Single factor comparison was applied to obtaining optimized parameters, that is liquid-solid ratio: 0.7/1, ball material ratio: 10/1, ball milling speed: 300 r/min, ball milling time:12h. The amended formulation of binder was determined by considerring powder propertity which was 70%PW, 21%EVA, 4%HDPE, 5%SA; The powder loading of55% was determined by torque method.(2) Orthogonal test was applied to injection molding experiment, and analysis of variance were applied to analyze the experimental result, which finally obtained the optimal parameters were injection temperature is 160 ℃, injection pressure is 110 MPa, injection speed is 60% and the holding pressure is 90 MPa.(3) Thermal and solvent method were applied to debinding. The parameters of thermal and solvent debinding were selected by judging defect on sample’s surface. Thermal debinding temperature were selected through TGA of feedstock. Selected solvent debinding temperature were 30℃ and time for 2h.(4) Vacuum sintering were applied to process. Parameters of vacuum sintering were selected by analyzing the mechanical property and microscopic structure of sintered samples that are: sintering temperature for 1440℃ and sintering time for 60 min.Mold design, shrinkage of sample’s dimension and friction performance test were included in trail-manufacture of gear and blade. Pro/E5.0 was applied to mold design. The straight spur gear and milling blade have been shaped using designed mold and optimized process. The contraction ratio of ultrfine cemented carbide feedstock has been ascertained at 21.47% by measuring principle dimensions of gearand milling blade. Testing results of friction performance shows that friction coefficient declined with the rising loading and the fluctuation of coefficient decreased first then increased when 50 N reached the minimum. The friction coefficient decreased first then increased with the rotate speed increasing when600r/min reached the minimum. The fluctuation of friction coefficient decreasing with the increasing rotate speed.