Summary of 3D printing metal powder technology molding process methods (Tech Center of Shanghai HY Industry Co., Ltd)
3D printing metal powder refers to a group of metal particles smaller than 1mm in size. Including single metal powder, alloy powder and some refractory compound powder with metallic properties.
3D printing metal powder materials include cobalt-chromium alloys, stainless steel, industrial steel, bronze alloys, titanium alloys, and nickel-aluminum alloys. However, in addition to good plasticity, 3D printing metal powder must also meet the requirements of fine powder particle size, narrow particle size distribution, high sphericity, good fluidity and high bulk density. Due to different application and subsequent molding process requirements, the preparation methods of metal powders are also different. According to the preparation process, there are two main methods: physical and chemical methods and mechanical methods.
In the powder metallurgy industry, preparation techniques such as electrolysis, reduction, and atomization are widely used. However, it should be noted that both electrolysis and reduction have certain limitations and are not suitable for the preparation of alloy powders. At present, metal powders for additive manufacturing are mainly concentrated in materials such as titanium alloys, high-temperature alloys, cobalt-chromium alloys, high-strength steels and die steels. In order to meet the requirements of additive manufacturing equipment and technology, metal powder must have the characteristics of low oxygen and nitrogen content, good sphericity, narrow particle size distribution range and high loose density. Plasma rotating electrode method (PREP), plasma atomization method (PA), gas atomization method (GA) and plasma spheroidization method (PS) are the main methods for preparing metal powders for additive manufacturing, all of which can be used to prepare spherical shapes Or nearly spherical metal powder.
Plasma rotating electrode method
Plasma rotating electrode method is to process metal or alloy into rods and use plasma to heat the rod end. At the same time, the rods are rotated at a high speed, relying on centrifugal force to refine the molten droplets, solidify in an inert gas environment and ball under the action of surface tension. The powder is transformed into powder; the powder of different particle size is classified by sieving, and the final powder product is obtained after electrostatic removal of inclusions (for high-temperature alloys only).
Plasma atomization method uses an ion torch installed symmetrically at the top of the melting chamber to form a high-temperature plasma focus, the temperature can even be as high as 10,000 K. A special feeding device feeds the metal wire into the plasma focus, and the raw materials are quickly melted or vaporized. The high-speed impact of the plasma is dispersively atomized into ultra-fine droplets or gas mist. During the flying deposition process in the atomization tower, it exchanges heat with the cooled argon gas introduced into the atomization tower to cool and solidify into ultra-fine powder.
At present, the common technologies for gas atomization preparation of metal powder materials for additive manufacturing include crucible vacuum induction melting atomization and crucible-free electrode induction melting gas atomization. The VIGA method uses a crucible to smelt alloy materials. The alloy liquid flows to the atomization nozzle through the tube at the bottom of the tundish, and is impacted and broken by supersonic gas. The method is mainly suitable for the production and preparation of powders such as iron-based alloys, nickel-based alloys, cobalt-based alloys, aluminum-based alloys, and copper-based alloys.
Radio frequency plasma has the characteristics of high energy density, high heating intensity, and large plasma arc volume. Since there is no electrode, it will not pollute the product due to the evaporation of the electrode. The principle of RF plasma powder spheroidization technology is that under the action of high-frequency power, inert gas (such as argon) is ionized to form a stable high-temperature inert gas plasma; irregularly shaped raw material powders are transported by carrier gas (nitrogen) The powder is sprayed into the plasma torch. The powder particles absorb a large amount of heat in the high-temperature plasma, and the surface melts quickly; and enters the reactor at a very high speed, and cools rapidly under an inert atmosphere. Under the action of surface tension, it cools and solidifies It becomes spherical powder and then enters the receiving chamber for collection.