Laser rapid prototyping (LRP) is a new manufacturing technology that integrates advanced technologies such as CAD, CAM, CNC, laser, precision servo drive and new materials. Compared with the traditional manufacturing method, it has the replication and high interchangeability of the prototype; the manufacturing process has nothing to do with the geometry of the prototype; the processing cycle is short and the cost is low, the general manufacturing cost is reduced by 50%, and the processing cycle is shortened by 70%. Above; highly technical integration to achieve design and manufacturing integration.

Recent developments in LPR include: stereo light modeling (SLA) technology; selective laser sintering (SLS) technology; fuse stack forming (FDM) technology; laser cladding forming (LCF) technology; laser near-shape (LENS) technology; Laser sheet laminate manufacturing (LOM) technology; laser induced thermal stress forming (LF) technology and three-dimensional printing technology.

First, three-dimensional light shaping (SLA) technology

SLA technology is also called photo-curing rapid prototyping technology. The principle is that the computer-controlled laser beam scans the surface of the photosensitive resin as a raw material point by point, and the thin layer of resin (about a few tenths of a millimeter) of the scanned area is photopolymerized and solidified. Form a thin layer of the part. The workbench is moved down a layer of thickness so that the surface of the cured resin is coated with a new layer of liquid resin, and the next layer is scanned and repeated until the entire prototype is manufactured. Since photopolymerization is based on the action of light rather than on the action of heat, only a lower power laser source is required for operation. In addition, because there is no thermal diffusion, and the chain reaction can be well controlled, it can ensure that the polymerization reaction does not occur outside the laser spot, so the processing precision is high, the surface quality is good, the utilization rate of raw materials is close to 100%, and the shape can be manufactured. Complex, sophisticated parts with high efficiency. For larger parts, it can be made by first forming and then bonding.

The United States, Japan, Germany, Belgium, etc. have invested a lot of manpower and material resources to study this technology, and new products are constantly coming out. Xi'an Jiaotong University in China has also successfully developed the stereo light molding machine LPS600a. Currently, there are more than 10 factories around the world that produce this product.

The application of SLA technology in the manufacture of automobile body can produce the required proportion of precision casting molds, thereby casting a certain proportion of the body metal model, and using this metal model to conduct tests such as wind tunnels and collisions, thereby completing the final evaluation of the vehicle body. To determine whether the design is reasonable. Chrysler Corporation of the United States has used SLA technology to make a body model, and placed it in a high-speed wind tunnel for aerodynamic test analysis, which has achieved satisfactory results and greatly reduced the test cost.

Used for automotive engine intake pipe test. The shape of the inner cavity of the intake pipe is composed of a very complicated free-form surface, which has a very important influence on improving the intake efficiency and the combustion process. In the design process, airway test is required for different intake pipe schemes. The traditional method is to manually process the tracheal wood mold or plaster mold described by dozens of sections, and then use the sand mold to cast the intake pipe. Wood molders' understanding of drawings and their own technical level often lead to deviations between parts and design intent, and sometimes the impact of such errors is significant. Although CNC machining can better reflect the design intent, it has a long preparation time, especially when the geometry is complex. The British rover company used rapid prototyping technology to produce the outer and inner cavity molds of the intake pipe, and achieved satisfactory results.

Second, selective laser sintering (SLS) technology

The SLS technology is very similar to the SLA technology in that it replaces the liquid photopolymer with a powdered material and acts on the powder material at a certain scanning speed and energy. The technology has the advantages of wide selection of raw materials, easy cleaning of excess materials, and wide application range, and is suitable for the manufacture of prototypes and functional parts. During the forming process, the laser working parameters as well as the characteristics of the powder and the sintering atmosphere are important parameters that affect the quality of the sintering.

Used in the manufacture of automotive molds. The SLS technology researched by Texas State University has been commercialized by the US company dtm. At present, the company has developed the third generation of SLS2000 series. The system can sinter various materials such as wax, polycarbonate, nylon, and metal. The steel-copper alloy injection mold made by the system can inject 50,000 pieces of workpiece. In recent years, mold manufacturing technology based on RPM technology has evolved from initial prototype manufacturing to rapid tooling manufacturing, which has become the focus of applied research and development at home and abroad. RPM-based mold manufacturing methods can be divided into direct molding and indirect molding.

The direct molding method is to directly use the RPM technology to make the mold, and the SLS method can directly produce the metal mold in the RPM technology methods. The steel copper alloy injection mold manufactured by this method has a service life of more than 50,000 pieces. However, this method has a large shrinkage of the material during the sintering process, and the precision is difficult to control.

Indirect molding can be divided into:

1. Production of soft simple molds. The prototype is accurately copied into a mold by using silicone rubber, metal powder epoxy powder and low melting point alloy, or the surface of the prototype is surface-treated, and a lower melting alloy is plated by metal spraying or physical evaporation deposition to make a mold. . These simple molds have a lifespan of 50 to 5,000 pieces. Due to their low manufacturing cost and short cycle, they are especially suitable for small batch production in the product trial stage.

2. Production of steel molds. The combination of RPM technology and precision casting technology enables rapid manufacturing of metal molds. Or directly to produce EDM electrodes with high complex precision for the processing of steel mold cavities such as injection molds, forging dies and die casting. A medium-sized, relatively complex electrode can be completed in 4~8h, and the complex accuracy fully meets the engineering requirements. Ford Motor Company has achieved satisfactory results with this technology for the manufacture of automotive molds. Shanghai Jiaotong University has also produced more than 80 pairs of imported substitute molds for the automotive and automobile tire industries through the combination of rp and precision casting. Compared with the traditional machining method, the production cost and cycle of rapid mold manufacturing are greatly reduced. China needs to import more than 800 million US dollars of molds each year, mainly complex molds and precision molds. Therefore, the application prospects of SLS technology in the future automotive mold manufacturing industry are very broad.