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Best discusses the factors that affect the additive manufacturing process

time:2020-06-02Views:370 Author:Best Seiko

At present, additive manufacturing technology has become a technology that has received much attention. It has been vigorously developed in aerospace, automotive, biomedicine and other industries, and has become an important force to promote the transformation and upgrading of traditional manufacturing industries. China's additive manufacturing technology has developed rapidly in recent years, and various application service markets are gradually taking shape. Although it has achieved certain results in some fields, compared with foreign countries, the entire industry has insufficient technical reserves. The core technologies and patents related to additive manufacturing are all Foreign companies dominate. At present, metal materials are still widely used in industrial production. Additive manufacturing technology is used to replace traditional process methods. Manufacturing metal parts that are difficult to be processed by various traditional processing methods is an important development direction of current additive manufacturing technology. Different from traditional process methods, additive manufacturing technology puts forward higher requirements on the performance and applicability of materials, but metal powder materials as an industrial foundation have become an important factor restricting my country's rapid development of additive manufacturing industry. Although there are many technical methods to achieve additive manufacturing, the processing mechanism is basically the same, that is, the material melts quickly under the action of a high-energy heat source. Due to the short action time, the molten metal rapidly solidifies under the cooling effect of the substrate, thereby achieving The specific scanning area is formed. The energy of additive manufacturing products is determined by the amount of heat source properties, material characteristics and process parameters, and the type of heat source and powder feeding method are the fundamental factors that distinguish various additive manufacturing technologies. Now, the editor of Guangdong Dahong New Materials will analyze the influencing factors of the additive manufacturing process in detail:   1, heat source  In the field of metal additive manufacturing, lasers and high-energy electron beams are very mature heat sources. The working principle of the electron beam and the laser is different. The heating method of the electron beam is that the high-energy electrons pass through the surface of the target to a certain depth from the surface, and then transmit the energy of the target atom, so that the vibration of the target atom is intensified and the electron The kinetic energy is converted into heat energy; the heating method of the laser is that the surface of the target absorbs the photon energy, and the laser does not pass through the surface of the target. In the process of material manufacturing and processing, the power and scanning speed of the heat source are generally constant, that is, the energy density acting on the material is constant, and the effect of the heat source is directly determined by the material's ability to absorb the heat source. The absorption of heat energy by a material is determined by factors such as the mechanism of action of the two and the surface state of the material. For a very commonly used laser heat source, the absorption of laser light energy is related to the wavelength, the reflectivity of the illuminated material, and the energy density. During the molding process, the surface state and size of the material have obvious constraints on the laser. Due to the different mechanism of action, the electron beam shows better adaptability than the laser in the additive manufacturing process.   2. Materials    Powder materials are currently commonly used materials for metal additive manufacturing. Metal powder, as an important part of the metal parts additive manufacturing industry chain, is also of great value. Metal powder materials are generally used in the powder metallurgy industry. Powder metallurgy molding is to shape the powder using high pressure and high temperature conditions after preforming. During the entire process, the physical metallurgical changes of the material occur relatively slowly, and the material has more time to fuse and diffuse. ,reaction. Due to the limitation of temperature and pressure during powder metallurgy processing, in order to ensure the compactness of the workpiece, the powder material used is required to fill the molding cavity as much as possible. In view of the technical characteristics of the powder metallurgy process, a set of more complete powder evaluation methods and standards have been developed. There are relatively complete indicators that can be used for the performance of constant powder materials, such as particle size, specific surface area, particle size distribution, powder Density, flow rate, bulk density, porosity, etc. For powder metallurgy, powder fluidity, tap density and other indicators are important indicators for measuring powder materials for powder metallurgy.  3. Process   When the powder filling method adopts the powder spreading method, the heat source preferentially acts on the powder. To ensure that the powder is fully metallurgically combined with the formed area, it is necessary to ensure that the depth and size of the molten pool during processing are within a reasonable range. When the synchronous powder feeding method is adopted, whether it is coaxial powder feeding or lateral powder feeding, the effect of the heat source on the material is divided into two parts, which act on the formed area and act on the powder material. After the powder is heated to a certain temperature by a heat source during the movement, it is driven into the molded area under the action of its own kinetic energy. The entire molding process is equivalent to the process of bombarding the fusion area with relatively high-energy powder materials. This method is more beneficial than the powder spreading method. Improve the density of products. The additive manufacturing process is significantly different from the powder metallurgy process. The metallurgical change of the powder material under the action of the heat source is very fast. During the molding process, the powder material directly interacts with the heat source. The powder material has no mold constraints and external durability The role of pressure. It is generally believed that powder materials with a diameter of less than 1 mm are suitable for additive manufacturing, and powder materials with a particle size of about 50 μm have good moldability. Compared with the powder metallurgy industry, there is currently no mature evaluation method or standard to determine the applicability of powder materials and additive manufacturing processes. The related evaluation methods and indicators of powders for additive manufacturing require further in-depth research and thinking.

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