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Rapid prototyping
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       Laser rapid prototyping technology is a high-tech developed in the 1980s. It is a multidisciplinary integrated technology that uses laser technology, CAX technology, automatic control technology, new material technology, direct modeling, and rapid manufacturing of product models. Laser rapid prototyping technology has changed the traditional processing "removal" molding process, and the "stacking" molding process has an epoch-making significance in the field of processing. At present, laser rapid prototyping technology is mainly used in aerospace, automotive, toy manufacturing and other industries. .
 
       1. The basic principle of laser rapid prototyping
 
       The principle of laser rapid prototyping technology is to use CAD to generate 3D solid model, layered by layered software, 2D data of each thin layer section is used to drive and control laser beam, sweep liquid, powder or sheet material, and process the required shape. The thin layer accumulates layer by layer to form a solid model. Most of the traditional industrial forming techniques follow the method of material removal, such as turning, milling, drilling, grinding, and planing; others are formed by molds, such as casting and stamping. Laser rapid prototyping uses a new forming principle – layering and superposition. The rapid prototyping of laser models or prototypes can be directly used for new product design verification, functional verification, engineering analysis, market ordering, decision-making, etc., shortening new product development cycles, reducing R&D costs, and improving corporate competition. force. Laser rapid prototyping is divided into the following categories:
 
       (1) SL-Stereolithography (or SLA) A computer-controlled UV laser scans a liquid photosensitive resin point by point according to the contour of each layered section of a predetermined part, and a photopolymerization reaction is performed on the scanned resin layer. Curing forms a section of the part, which is then applied with a new layer of liquid resin for scanning, and so on until the entire prototype is manufactured. This method is characterized by high precision, good surface quality, and the ability to manufacture parts with complex shapes and special fineness. The lack of equipment and materials is expensive, and design support is required in the manufacturing process.
 
       (2) Layered entity manufacturing (LOM—Laminated Object Manufacturing)
 
       The LOM process uses a laser to cut the thin material according to the contour information obtained by layering the parts, and the obtained layer is bonded to the undercut layer by a hot pressing device, and then a new layer of paper is superimposed thereon, and sequentially bonded into 3D solids. The main features of LOM are lower equipment and material prices, better workpiece strength and higher precision. Helisys has developed a variety of molding materials for LOM processes that can be used to make molded parts made from sheet metal. The company also develops a LOM process based on ceramic composites.
 
       (3) Selective laser sintering (SLS - Se1ected Laser Sintering)
 
       SLS is a part in which a solid powder is selectively layered by a laser and the solidified layer of the sintered layer is superposed to form a desired shape. The entire process includes the establishment of CAD models and data processing, powdering, sintering and post-processing. The most outstanding advantage of SLS is that it uses a wide range of molding materials. Theoretically, any powder material capable of forming an interatomic bond after heating can be used as a molding material. At present, the materials that can be successfully processed by SLS are paraffin, polymer, metal, ceramic powder and their composite powder materials. Due to the variety of SLS molding materials, material savings, extensive distribution of molded parts, suitable for a variety of applications, and SLS, there is no need to design and manufacture complex support systems, so its application is more and more extensive. However, SLS uses a mixture of a metal material and another low melting point material (which may be a low melting point metal or an organic bonding material). During processing, the low melting point material melts or partially melts, but the metal with a higher melting point The material does not melt, but is coated and bonded together by a melted or partially melted low-melting material. The three-dimensional solid is a powder metallurgy-sintered blank with a certain proportion of pores in the solid, which cannot reach 100% density, mechanical properties. It is also poor, and it often needs to be post-treated by high temperature remelting or metal infiltration to fill the pores.
 
       (4) Laser Cladding Forming
 
       LCF refers to pre-set or synchronously feeding the selected cladding material on the surface of the base alloy in different ways, and then simultaneously irradiating it with the surface layer of the substrate by laser irradiation, and rapidly solidifying into a low dilution and metallurgy with the substrate material. The combined surface layer, thereby significantly changing the wear resistance, corrosion resistance, heat resistance and electrical properties of the surface layer of the substrate material. LCF is a surface modification method in which a laser is used as a heat source to coat a surface of a substrate to form an alloy layer having completely different compositions and properties from the substrate. LCF has many excellent features: low requirements for the working environment; intelligent and automated processing through computer control; the appearance of the cladding layer is flat, the workpiece deformation is small, and the workpiece can be directly used without processing after processing; suitable for key local areas Processing; because the laser has a rapid heating process of approximately adiabatic, the laser cladding has less thermal influence on the substrate, and the induced deformation is also small; controlling the input energy of the laser can control the dilution of the substrate material to the cladding material at a low level. To the extent that the metallurgical bond between the cladding layer and the substrate is ensured, the excellent properties of the original selected cladding material are maintained; the scope of application is wide, and in theory almost all metal or ceramic materials can be laser-clad to any alloy. Therefore, laser cladding has broad application prospects in various fields such as aviation, automobile, chemical industry, machinery, etc. It is being paid more and more attention by research institutions and enterprises, and its research is becoming more and more extensive. But cracks are the most difficult problem in large-area laser cladding technology, and scientists at home and abroad are working hard.