MIM Process Equipment

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Metal Powder Injection Molding (MIM for short) is a near-net-shape forming technology formed by introducing modern plastic injection molding technology into the field of powder metallurgy. The basic process of MIM is shown in the figure: firstly, the solid powder and organic binder are uniformly mixed and made into granular injection materials, which are injected into the mold cavity by an injection molding machine under heating to condense and form, and then chemically dissolved or The method of thermal decomposition removes the binder in the formed blank, and finally obtains the final product through sintering and densification. MIM can directly manufacture parts with the final shape, and the product has high precision, uniform structure, excellent performance and low production cost, so it has won attention and attention. This technology is known as “the hottest part forming technology today”.

Mixing equipment

The mixing process is an important process of the MIM process. Due to the special requirements of the MIM process for the injection material, the mixing equipment should be able to meet the MIM uniformity, no agglomeration, no change in chemical composition, and no defects that cannot be eliminated by subsequent processes. Currently widely used such as double planetary mixer, single screw extruder, piston extruder, twin screw extruder, double eccentric wheel mixer, Z-type impeller mixer.

The twin-screw extruder is composed of two conical screws that mesh with each other and rotate in opposite directions. It is heated by a high-pressure oil pump at a constant temperature, so that the mixture can be formed into a uniform and thin cylindrical product along the heated extrusion tube. The shear rate is high, the mixture is uniform and isotropic, and it is the most commonly used mixer in the laboratory, but the design and manufacturing cost is high.

The double planetary mixer is composed of two rotors that are mutually perpendicular to each other for planetary motion, and the heating is uniform, fast and accurate. The filling volume can be expanded proportionally, and the cleaning is convenient. In actual production, it is often used for the initial high-precision mixing of binders and metal powders. It is optimized for cost, throughput and mix quality and is widely used in MIM industrial production.

For sub-micron fine powders, it is difficult to obtain a uniform mixture with a double planetary mixer. The Z-blade mixer is a horizontal structure, composed of a pair of Z-blade, mainly composed of a mixing cylinder, a mixing paddle, and a heating rod. The stirring paddle is heated by the heating rod immersed in the heat-conducting oil in the jacket, which has high thermal efficiency and corrosion resistance, and can ensure the chemical properties of the raw materials.

Internal mixer is suitable for internal mixing of metal powder and binder. The rotational speed of the output shaft can be adjusted smoothly, with high efficiency, which can meet the requirements of different materials and formulas, and obtain better tissue uniformity, higher productivity and good working environment.

Injection molding equipment

The biggest similarity between MIM technology and plastic injection molding technology is the injection molding process and its equipment. That is, MIM technology can be used for injection molding of metal powders and binder injection materials by borrowing injection molding machines or by technically transforming them. The metal injection molding process is a mixture of metal powder and a thermoplastic material (such as polystyrene), which is injected into a mold under a certain temperature and pressure. The injection molding machine was originally a plunger type. Since then, new injection processes and corresponding injection equipment have continued to emerge, such as dual-loop injection molding machines, dual-template injection machines, tie-barless injection machines, automatic injection machines, and electromagnetic dynamic injection molding machines. Among them, the double-template injection machine separates plasticization and injection, and the plasticization is stabilized by the extruder. The plunger injection machine is stable and uniform, and the measurement is accurate. The dual-platen, tie-bar-less injection machine greatly simplifies the clamping system of the injection machine. The all-electric injection machine replaces the hydraulic power transmission system with an electromechanical drive structure, and the torque is increased, and the transmission speed and stroke control are accurate. In actual production, because the pressure from the plunger to the nozzle of the screw injection machine is almost the same, the injection parameters can be accurately controlled, so it is widely used.

Dewaxing equipment

Dewaxing is the most difficult and time-consuming process in the production process of MIM. Therefore, the development of MIM industry is inseparable from advanced and rapid dewaxing technology. , the removed binder will be cooled centrally to facilitate the rapid cleaning of the furnace body, thereby shortening the dewaxing time. At the same time, environmental protection also requires that the dewaxing furnace can effectively treat the dewaxed products, so as to avoid the pollution of the dewaxed products to the environment. For paraffin-based binders, vacuum thermal dewaxing is most suitable, and solvent dewaxing can be used in combination with thermal dewaxing. Catalytic dewaxing has the fastest dewaxing time, good formability and shape retention, and can realize batch and continuous production, which is the current development trend of dewaxing equipment.

Vacuum dewaxing furnace is suitable for dewaxing and pre-sintering of metal and ceramic powder products before sintering. The rated working furnace temperature is 950℃, the highest test furnace temperature is 1100℃, the rated working pressure can reach 1Pa, and the inflation pressure (absolute pressure) is 0.15MPa. It is composed of furnace body, capture system, vacuum system, gas charging system, external circulation cooling system, electrical control system and other parts. The vacuum system consists of a rotary vane vacuum pump, a multi-stage filter, and a roots pump vacuum pump, which can meet the performance requirements of the vacuum equipment to obtain the required materials or products.

Sintering equipment

Sintering is heating at high temperature under vacuum or atmosphere to achieve final densification of the formed debonded body. According to the sintering pressure, it can be divided into normal pressure sintering and pressure sintering. According to the working mode, it can be divided into two types: intermittent (the furnace must be stopped for each loading and unloading) and continuous (the loading and unloading can be carried out without cooling down). According to the heating method, it can be roughly divided into resistance heating electric furnace and induction heating electric furnace, which can be divided into two forms: direct electric heating and indirect electric heating of the sintered body; according to different sintering temperatures, sintering equipment can be divided into medium temperature sintering furnace 900 ~ 950 ℃) and high temperature sintering furnace (1100 ~ 1700 ℃); according to the different protective atmosphere, it can be divided into air sintering furnace, hydrogen sintering furnace (such as molybdenum wire furnace, stainless steel tube hydrogen furnace), vacuum sintering furnace, etc.

Vacuum sintering furnace

In industrial applications, the working temperature of the vacuum furnace is generally 600 ~ 2200 ℃, and the vacuum degree is 1 ~ 0.0001Pa. The advantage of heating or sintering parts in vacuum is that the parts are easy to degas, desulfurize, deoxidize, and vaporize and separate harmful impurities to avoid oxidation of the parts. Vacuum sintering can use protective atmosphere gas with suitable purity as low pressure permeable gas to promote sintering and avoid reaction with gas. It is widely used in various metals, alloys, ceramics, cemented carbides, permanent magnet alloys and other high melting point metals and their carbides. , borides and other intermetallic compounds and oxides in the sintering. In recent years, vacuum furnaces have become more and more widely used in powder metallurgy industry and even in metal injection molding process. Different from the protective atmosphere gas furnace in terms of equipment, the vacuum system, furnace body, etc. must maintain good air tightness against the external gas.

Post-processing equipment

In the production process of metal injection molding products, some products require subsequent processing after sintering to further improve product performance and quality. Commonly used are: grinding, sandblasting, surface treatment (steam treatment, carburizing, carbonitriding), oil immersion and heat treatment. Grinding can remove surface burrs, and sandblasting can clean the surface of sintered or heat-treated MIM parts with rough skin and oxide skin. Steam treatment, also known as bluing treatment, is mostly used in iron-based MIM and powder metallurgy products to improve density and rust resistance. Heat treatment can trim the oxidized surface of MIM parts after high temperature sintering, further eliminating voids and sintering stress. The heat treatment equipment used for MIM products is slightly different from the steel heat treatment equipment, such as annealing, tempering, and normalizing heat treatment can be carried out in a vacuum sintering furnace.

Equipment Selection

The RVS series MIM sintering furnace and MIM degreasing furnace produced by SIMUWU are high-quality products that can meet related processes. The degreasing furnace can quickly and steadily remove the binder from the parts, and collect them in a special container for environmental protection and safe disposal. The high temperature uniformity and high temperature control accuracy of the sintering furnace determine the excellent sintering quality, and can also undertake a certain heat treatment function. Good after-sales service can meet various needs of customers, and are exported to overseas developed countries and Southeast Asian countries, with convenient production, high quality and low price.