Forming Equipment Design And Forming Basic Theory Research For Warm Flow Compaction Of Metal Powder

As a new technology based on warm compaction technology and combined with the advantages of metal powder injection molding, warm flow compaction technology of powder not only overcomes the shortcomings of traditional powder metallurgy in forming complex geometric shape parts, but also avoids the high cost of metal powder injection molding. Therefore, this technology has wide potential application prospects.In the present dissertation, theoretical analysis is combined with experimental investigation to study basic problems of forming process of domestic atomized and carbonyl iron powders. Based on design of manufacturing facility and testing set dedicated to warm flow compaction, by means of experimental investigation of warm flow compaction, and numerical simulation study on accumulation process of powder particles and forming process of warm flow compaction, densification mechanism was revealed and forming process was improved during warm flow compaction of iron powders. This provides theoretical and technical guides for manufacturing powder metallurgy parts with high performance.As a first step, through comprehensive analysis of technical features of main powder presses and multilayer die-sets documented so far, and thorough comparison of the merits and demerits of various powder heating patterns such as microwave heating, thermal oil heating and resistance heating, the mechanical structure testing platforms of frame type press system, and multilayer die-set system and agitated powder heating system for the warm flow compaction system, were designed in detail by using design theory of production and experiment. The three-dimensional entity models of the press and formwork system were established; press deformation process and stress distribution were simulated and calculated by the finite element analysis software in order to optimize structure design of the press and die-set. The results shows that the structure design of the press and die-set meets the strength and rigidity requirements of production system, realizing rapid heating, continuous powder feeding as well as sufficiency of powder feeding for parts forming.One special test set is designed and developed to measure directly, continuously and dynamically the variation of different forces in compacting process of typical crisscross part during warm flow compaction. In this test set, the horizontal position distance of green compact can be adjusted conveniently, and the variation of the average side pressure can be measured directly, which can satisfy the test requirements of warm flow compaction of metal powder.Subsequently, on the basis of the material characteristics research on the mixed powders of domestic atomized iron powder and fine carbonyl powder with polyethylene glycol as binder or lubricant, the warm flow compaction process of metal powder is discussed through experimental investigation of side pressure, friction factor, green density distribution, green strength of green compact and elastic aftereffect in various working conditions by using the special test set for warm flow compaction. The influence of press parameters on powder filling capacity and compact quality was analyzed through studies on the variation of lateral pressures in different positions of the transverse direction of the crisscross part caused by the factors such as different compaction pressures, velocities, temperatures and adhesive contents, which reveals the densification mechanism of warm flow compaction of metal powder.The data program structure of particles packing was established based on the analysis of force condition of movement and crash of powder particles as well as interaction force model of powder particles. Also, the ParticleSim system platform for numerical simulation of powder particles pile-up process was developed based on a grid calculation platform. By numerical simulation of the pile-up process of single diameter particles and the relative packing density of the binary particle mixtures of the ten times diameter particles with different number ratios, the rules of particle pile-up process and density distribution were obtained. By comparison analysis of the rules with experimental results, the validity of numerical simulation model and practicability of the platform are corroborated.The powder material characteristics, such as poison ratio, elastic modulus and initial yield strength, were investigated on the basis of analyzing the fundamental equation of elastic-plastic mechanics problem and spheroidicity yield criteria followed during warm flow compaction. The applicability of different flow stress models to warm flow compaction was discussed. The flow stress assumption of typical spheroidicity yield criteria and warm flow compaction process of the typical crisscross test specimen were simulated. By comparison analysis between the variation of green density distribution in compacting process obtained from numerical simulation and the experimental results, the validity of the model for warm flow compaction was confirmed, which provides theoretical guides for production and experiment.