Analysis of laser rapid prototyping technology

Knowledge sharing by Guangdong Shunde Teamwork Model Technology Co., Ltd, whom with over 20 years rapid prototyping experience.

Email: ken@gdtwmx.com

Website: www.gdtwmx.com

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.

Application in the manufacture of automotive lighting. Most of the shapes of automobile lamps are irregular, the surface is complicated, and the mold manufacturing is very difficult. Through rapid prototyping technology, accurate product samples can be obtained quickly, providing a favorable reference for mold design CAD and CAM. At the same time, it is also possible to manufacture the lamp mold quickly and accurately by the rapid casting technique and the investment casting method.

Figure 1 shows a cylinder head of a 250-type twin-cylinder motorcycle made by a motorcycle factory. This is a newly designed engine that requires 10 samples for engine simulation experiments. The part has a complex internal structure that cannot be machined by conventional machining and can only be cast. The whole process needs to go through the processes of mold opening, core making, group mold, casting, sand blasting and machine adding, which is the same as the actual production process. It takes only three months to open the mold alone. This is unacceptable both in terms of time and cost for small batch production. Using selective laser sintering technology, the casting material was used as the molding material. On the AFS molding machine, 10 casting molds of the part were processed in only 5 days, and then the investment casting process was carried out. After 10 days, the casting blank was obtained. . After the necessary machining, the prototype of this engine was completed in 30 days.

Third, fuse stack forming (FDM) technology

FDM materials are generally thermoplastic materials such as waxes, ABS, nylon, etc., which are fed in the form of filaments. The material is heated and melted in the spray head, and the spray head moves along the cross-sectional profile and fill path of the part while extruding the molten material, the material solidifies quickly and adheres to the surrounding material.

1. The FDM process does not use laser, so it is easy to use and maintain, and the cost is low.

2. Prototypes of parts formed with wax can be directly used for lost wax casting.

3. The prototype made with ABS is widely used in product design, testing and evaluation due to its high strength.

4. Since the deposition of molten material represented by the FDM process has some significant advantages, the process is extremely rapid.

  Fourth, laser cladding molding (lcf) technology

　　 The working principle of lcf technology is basically the same as that of other rapid prototyping technologies. It is also through the numerical control of the worktable to realize the scanning and cladding of the powder by the laser beam, and finally the parts with the required shape are formed. The results show that the factors such as part slicing method, laser cladding layer thickness, laser output power, spot size, light intensity distribution, scanning speed, scanning interval, scanning mode, powder feeding device, powder feeding amount and powder particle size are all correct. The accuracy and strength of the formed part has an effect.

The difference from other rapid prototyping technologies is that laser cladding can be made into very dense metal parts with strengths that exceed or exceed those produced by conventional casting or forging methods, and thus have good application prospects.

Five, laser near shape (LENS) technology

　　 LENS technology combines SLS technology with LCF technology and maintains the advantages of both technologies. The metal powder chosen has three forms:

1. Single metal;

2. Metal plus low melting point metal binder;

3. Metal plus organic binder. Since the powder coating method is employed, the metal after laser sintering has a low density, a high porosity, and a low strength regardless of the type of powder used. To increase the strength of the sintered part, post-treatment, such as impregnating the resin, low-melting metal, or hot isostatic pressing, must be performed. But these post-processing will change the accuracy of the metal parts.

Sixth, laser sheet laminate manufacturing (LOM) technology

　　 LOM technology is a new type of rapid prototyping technology commonly used to make molds. The principle is to first cut the metal foil with a high-power laser beam, then superimpose the multi-layered sheet, and gradually change its shape to finally obtain the solid geometry of the desired prototype.

The LOM technology produces a die, which costs about 1/2 less than the conventional method, and the production cycle is greatly shortened. It is used to make composite molds, thin material molds, progressive molds, etc., and the economic benefits are also very significant. This technology has been widely used abroad.

Seven, laser induced thermal stress forming (LF) technology

　　 The principle of LF technology is based on the characteristics of thermal expansion and contraction of metal, that is, uneven heating of the material to produce predetermined plastic deformation. This technology has the following characteristics:

1. No mold forming: short production cycle and high flexibility, especially suitable for the production of single-piece small batch or large workpieces;

2, no external force molding: the root of material deformation lies in its internal thermal stress;

3, non-contact molding: high molding precision, no tool wear, can be used for the manufacture of precision parts;

4. Thermal cumulative molding: It can form difficult-to-deform materials or high-hardening index metals at normal temperature, and can produce self-cooling hardening effect, which can improve the structure and properties of materials in the deformation zone.

German scholars m.geiger and f.vollertsen have done a lot of research on the composite processing of laser forming and other processing methods. At present, this technology has been applied to the flexible leveling of automobile covers and the molding of other shaped parts.