Metal 3D printing material breakthrough is the basis for development
Metal 3D printing materials are an important material basis for the development of metal 3D printing technology. To some extent, the development of materials determines whether 3D printing can be more widely used. At present, metal 3D printing materials mainly include engineering plastics, photosensitive resins, rubber materials, metal materials, and ceramic materials. field has been applied. These raw materials used in metal 3D printing are specially developed for metal 3D printing equipment and processes, which are different from ordinary plastics, gypsum, resins, etc., and their forms are generally powdery, filamentous, lamellar, and liquid. wait. Usually, depending on the type of printing equipment and operating conditions, the particle size of the powdered metal 3D printing materials used ranges from 1 to 100 μm, and in order to maintain good fluidity of the powder, the powder is generally required to have a high degree of sphericity. .
The research and development and breakthrough of metal 3D printing materials are the basis for the promotion and application of metal 3D printing technology, and also the fundamental guarantee for satisfying printing. One is to strengthen the research and development of materials and form a complete printing material system. In recent years, metal 3D printing materials have developed rapidly. In 2013, metal material printing increased by 28%, and in 2014 it reached more than 30%, accounting for about 12% of metal 3D printing materials. Metal materials are mainly titanium, aluminum, steel and nickel. Titanium alloys, high-temperature alloys, stainless steel, die steel, high-strength steel, alloy steel and aluminum alloys can be used as printing materials, and have been widely used in equipment manufacturing and repair and remanufacturing. However, there is currently no metal 3D printing material system, and the existing materials are far from meeting the needs of metal 3D printing.
The materials used for laser stereoforming are mainly metal inert materials, and the next step is to try other active metal printing materials. Metal powders traditionally used in powder metallurgy cannot fully meet the requirements of 3D printing, and currently there are few types of metal materials that can be used for printing, and the price is relatively high. There have been a few foreign companies specializing in metal powder for 3D printing, such as Sulzer Metco in the United States and Sandvik in Sweden, but they can only provide a few conventional metal powders. Domestic material research and development is relatively lagging behind, and printing powder is too expensive. Because the material research and development cycle is long and the research and development is more difficult than that of equipment, enterprises are reluctant to conduct material research and development out of the maximization of interests. Huanghe Cyclone Co., Ltd. is one of the few domestic enterprises engaged in the production of diamond micropowder and CBN micropowder. University research is also keen on 3D printing equipment and software, so printing materials largely restrict the development and application of metal 3D printing technology.
Metal powders
Metal powders used in 3D printing generally require high purity, good sphericity, narrow particle size distribution, and low oxygen content. At present, the metal powder materials used in 3D printing mainly include titanium alloys, cobalt-chromium alloys, stainless steel and aluminum alloy materials, in addition to gold, silver and other precious metal powder materials used for printing jewelry. 3D printing metal powder, as the most important link in the 3D printing industry chain of metal parts, is also where the greatest value lies.
At the "2013 World 3D Printing Technology Industry Conference", authoritative experts in the world's 3D printing industry gave a clear definition of 3D printing metal powder, which refers to the group of metal particles whose size is less than 1mm. Including single metal powder, alloy powder and some refractory compound powder with metallic properties. At present, 3D printing metal powder materials include cobalt chromium alloy, stainless steel, industrial steel, bronze alloy, titanium alloy and nickel aluminum alloy, etc. 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.
Titanium Alloy 3D Printing
Titanium alloy has the advantages of high temperature resistance, high corrosion resistance, high strength, low density and biocompatibility, and has been widely used in aerospace, chemical industry, nuclear industry, sports equipment and medical equipment and other fields. Titanium alloy parts prepared by traditional forging and casting techniques have been widely used in high-tech fields. The amount of titanium used in a Boeing 747 aircraft reaches 42.7t. However, the production of large titanium alloy parts by traditional forging and casting methods has hindered its wider application due to unfavorable factors such as high product cost, complicated process, low material utilization rate and difficult subsequent processing. Metal 3D printing technology can fundamentally solve these problems, so this technology has become a new technology for directly manufacturing titanium alloy parts in recent years. The development of new titanium-based alloys is the main direction of the application research of titanium alloy SLM. Due to the low strain hardening index of titanium and titanium alloys (approximately 0.15), the resistance to plastic shear deformation and wear resistance are poor, which limits the use of its parts under high temperature and corrosive wear conditions.
Stainless steel 3D printing
Stainless steel has the characteristics of chemical corrosion resistance, high temperature resistance and good mechanical properties. Due to its good powder formability, simple preparation process and low cost, it is the earliest material used in 3D metal printing. For example, Huazhong University of Science and Technology, Nanjing University of Aeronautics and Astronautics, Northeastern University and other institutions have conducted in-depth research on metal 3D printing. The current research is mainly focused on reducing porosity, increasing strength, and the spheroidizing mechanism of metal powder in the melting process. Li Ruidi et al. used different process parameters to conduct SLM forming tests on 304L stainless steel powder, obtained an empirical formula for the density of 304L stainless steel, and summarized the grain growth mechanism.
3D printing of superalloys
Superalloys refer to a class of metal materials based on iron, nickel, and cobalt that can work for a long time at high temperatures above 600°C and under certain stress environments. It has high high temperature strength, good thermal corrosion and oxidation resistance, and good plasticity and toughness. At present, according to the type of alloy matrix, it can be roughly divided into three types: iron-based, nickel-based and cobalt-based alloys. High-temperature alloys are mainly used in high-performance engines. In modern advanced aero-engines, the amount of high-temperature alloy materials accounts for 40% to 60% of the total mass of the engine. The development of modern high-performance aero-engines has higher and higher requirements on the service temperature and performance of superalloys. The traditional ingot metallurgical process has a slow cooling rate, severe segregation of certain elements and second phases in the ingot, poor hot workability, uneven structure, and unstable performance. Metal 3D printing technology has become a new method to solve the technical bottleneck in the forming of superalloys. NASA claimed that in the high-temperature ignition test conducted on August 22, 2014, the rocket engine nozzle manufactured by metal 3D printing technology produced a record 9t thrust.
Aluminum alloy 3D printing
As the lightest structural alloy, aluminum alloy has the possibility to replace steel and aluminum alloy in many application fields due to its special high strength and damping properties. For example, the lightweight application of aluminum alloys in automobile and aircraft components can reduce fuel consumption and exhaust emissions. Aluminum alloy has in-situ degradability, low Young's modulus, strength close to human bone, excellent biocompatibility, and has more application prospects than traditional alloys in surgical implantation.
Since the emergence of metal 3D printing technology in the 1990s, the printing of polymer materials has gradually focused on the printing of metal powders, and a large number of new technologies, new equipment and new materials have been developed and applied. At present, the pace of information technology innovation continues to advance, and industrial production is entering a new stage of intelligence and digitalization. In 2014, Germany proposed the "Industry 4.0" development plan, which is bound to cause disruptive changes and innovations in the industrial field, and 3D printing technology will be a powerful thrust for the development of industrial intelligence. Metal powder 3D printing technology has achieved certain results, but the material bottleneck will inevitably affect the promotion of 3D printing technology, and 3D printing technology puts forward higher requirements for materials. There are many types of metal materials suitable for industrial 3D printing, but only special powder materials can meet the requirements of industrial production.
The future development direction of 3D printing metal materials mainly has three aspects:
One is how to strengthen the research on the relationship between material structure and properties on the basis of existing materials, further optimize process parameters according to the properties of materials, increase printing speed, reduce porosity and oxygen content, and improve surface quality;
The second is to develop new materials to make them suitable for metal 3D printing, such as developing new materials with excellent corrosion resistance, high temperature resistance and comprehensive mechanical properties;
The third is to revise and improve the technical standard system of 3D printing metal powder materials to realize the institutionalization and normalization of metal material printing technical standards.