Powder metallurgy vacuum sintering process

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304 stainless steel powder metallurgy vacuum sintering process.

The first is mixing: for the convenience of injection, metal powder and binder are generally mixed to form a feed with certain fluidity. An important function of the binder is to drive the powder into the mold cavity, and at the same time wet the surface of the metal powder to facilitate mixing and injection. Therefore, the binder will affect all aspects of injection molding and various properties of materials. An ideal binder should be able to wet the powder surface well, reduce the viscosity of the feed, meet the rheological requirements of the metal, and increase the loading capacity of the solid powder. First put the paraffin wax (PW) in a self-made mixer to heat and melt at a temperature of 80°C; then add low-density polyethylene (LDPE) and stearic acid (SA) for blending at a temperature of 150°C for 30 minutes; finally add Powder, mixed for 2.5h.

At the injection temperature, the large change in viscosity with temperature will increase the difficulty of process control, and it is also the cause of various defects. Paraffin wax has a lower molecular weight and higher volatility, which is beneficial to degreasing; thermoplastic polymers will soften when heated and decompose at high temperatures; some surfactants (stearic acid) are added to the binder to facilitate Reduce tool wear and facilitate injection, and can increase the viscosity of the mixture, which is conducive to injection.

The mixing of metal powder injection molding feedstock is completed under the combined action of shear force and thermal effect. In this process, the uniformity changes exponentially with time and is constant, which is related to the mixing method, powder characteristics, powder agglomeration and powder surface condition. Through the calculation and process experiment data, the process parameters are continuously optimized, and the binder formula and corresponding mixing parameters suitable for injection molding copper-based anti-friction materials are studied.

The second is injection: the metal feed is heated to a sufficient temperature to melt it, injected into the mold cavity under a certain pressure, and then cooled to obtain an injection part. Due to the better ductility of copper, lower heating temperature (150°C) and lower injection pressure (90Pa) can be used. Compared with plastic injection molding, the cooling time should be extended appropriately.

The third is degreasing and vacuum sintering: it is a delicate and complicated process to remove the binder and maintain the shape of the product. It is necessary to prevent the deformation of the product and remove the adhesive. Solvent degreasing + thermal degreasing two-step degreasing method is adopted. Before thermal degreasing, the injection body is immersed in a solvent to remove part of the soluble binder and open part of the pores. The solvent used is n-heptane + ethanol + acetone; the solvent degreasing temperature is 30-50°C, and the degreasing time is 0-36h. After a certain period of solvent degreasing, the specimens were removed, dried for six hours, and then thermally degreased. Vacuum sintering is the last step in metal powder injection molding. Sintering is carried out in a vacuum sintering furnace to reduce the pores between powder particles, so that the metal powder injection molding products can achieve full densification or close to full densification. Due to the use of binders in metal powder injection molding technology, the shrinkage is very large during degreasing and vacuum sintering, generally up to 13%, so there is a problem of deformation control and dimensional accuracy control. Especially because most of the metal powder injection molding products are special-shaped parts with complex shapes, this problem is even more prominent. The control of dimensional accuracy is a complex issue involving raw materials, mixing materials, injection molding, degreasing, and vacuum sintering. Therefore, the control of dimensional accuracy actually reflects the advantages and disadvantages of various metal powder injection molding technologies.

SIMUWU vacuum thermal degreasing furnace, vacuum sintering furnace, equipped with rapid cooling system, improve product quality, shorten production cycle and improve production efficiency. Special degreasing sealed furnace and grease catcher to reduce the pollution of the inner furnace wall, heat shield and heating body, degreasing and fat collection are more effective, and the special sealed furnace is beneficial to improve the uniformity of furnace temperature. Directional airflow degreasing enhances degreasing effect and makes degreasing more thorough.

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