304L stainless steel powder metallurgy vacuum sintering process

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SIMUWU’s long-term partners are engaged in the process of metal powder injection molding products. The control of dimensional accuracy involves complex issues in all aspects of raw materials, mixing, injection molding, debinding, and sintering. Therefore, the control of dimensional accuracy actually reflects each The pros and cons of this kind of metal powder injection molding technology.

The first step is mixing: In order to facilitate injection, the metal powder and the binder are generally mixed to form a feed with a certain fluidity. An important function of the binder is to drive the powder to flow into the mold cavity, while also wetting the surface of the metal powder to facilitate mixing and injection. Therefore, the binder will affect all aspects of injection molding and the properties of the material. The ideal binder should be able to wet the powder surface well, reduce the viscosity of the feed, meet the requirements of metal rheological properties, and increase the loading of solid powder. First put the paraffin wax (PW) in a self-made blender and heat it to 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, mix for 2.5h.

The second step 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. This experiment uses a horizontal injection machine. Due to the better ductility of copper, a lower heating temperature (150°C) and a small injection pressure (90Pa) can be used. Compared with plastic injection molding, the cooling time should be extended appropriately.

The third step is degreasing and sintering: removing the binder and maintaining the shape of the product is a delicate and complicated process. It is necessary to prevent the deformation of the product, but also to remove the binder. Determine the sintering process by studying the relationship between dimensional changes and time and temperature, gradually study the linear shrinkage rate of the product, and continuously optimize the process to improve its dimensional accuracy.

The reference process for vacuum sintering 304L stainless steel powder is as follows:
1. Debinding/dewaxing stage (two times)
First debinding/dewaxing: 0.625°C/min, heating to 220°C, holding for 2h (remove most of the binder)
Second degreasing/dewaxing: 1°C/min, heating to 500°C, holding for 2h (removal of residual binder)
Remarks: Argon gas protection should be filled during debinding/dewaxing.

2. Pre-sintering stage
Heating rate: 2°C/min, heating to 900°C/min, heat holding for 1h (to ensure that all binders are completely removed and become a porous structure composed of powder particles and pores), and the shrinkage rate is about 0.5%

3. Sintering stage
Heating rate: 5℃/min, sintering temperature 1360℃, heat holding 1h.

4. Cooling stage
Determined according to product size and loading capacity.

Learn More : Powder Metallurgy Vacuum Sintering Furnace