The idea of 3D printing originated in the United States in 1892 and was developed and popularized in the 1980s. From the first 3D printer produced by 3D systems in 1987 to the first 3D printing car “urbee” in 2011, 3D printing technology, as an important symbol of “the third industrial revolution”, has been developing rapidly due to its fast, environmental protection and other advantages.
Automobile industry is the pillar industry of China’s national economy. Automobile mold plays a very important role in automobile design, research and development, manufacturing and other aspects. The application of 3D printing technology in the field of automobile mold can not only shorten the R & D and production cycle, reduce various costs, but also make use of its super complex construction ability to achieve technological breakthroughs that cannot be achieved in the traditional way.
When talking about the process types of 3D printing technology, people usually think of 3D powder bonding technology (3DP), filament material selective cladding technology (FDM), photosensitive resin selective curing technology (SLA), powder material selective sintering technology (SLS), etc. However, due to the rapid development of 3D printing technology in recent years, some new technologies have emerged in the market, such as selective area light transmittance resin curing process (LCD), projection 3D printing process (DLP), etc.
The automobile mould has a high demand for the process parameters of rapid prototyping, so this paper introduces three kinds of molding processes which are most widely used in the field of automobile mould, and briefly describes its working principle and technical characteristics.
1. Selective curing process of photosensitive resin
The selective curing process of photosensitive resin (SLA) is the first 3D printing equipment in the world. As shown in Figure 1, the working principle of the process is: the laser beam is scanned on the X-Y plane according to the specified path according to the preset slicing program, and the photosensitive resin in the resin tank is cured after being irradiated by the laser. Then the z-axis lifting table moves to carry out the scanning and curing process of the next layer, which circulates and finally forms the solid workpiece. According to the experience of using SLA process equipment in the past, after the solid workpiece is printed, it is necessary to carry out secondary light curing to ensure the strength of the workpiece.
The advantages of the process are: the forming speed is very fast; the surface finish of the formed object is high; the forming accuracy is high. However, the disadvantages of this process are: secondary curing is required; the resin is brittle and easy to break after curing, and it is not easy to carry out secondary processing; the chemical properties of the workpiece after forming are poor, and the requirements for the working environment are high [5]. Therefore, the process is suitable for manufacturing medium and large-scale, high-precision parts with low requirements for mechanical properties.
2. Selective sintering process of powder materials
Selective sintering (SLS) is commonly used in the rapid prototyping of powder materials such as plastic powder, wax powder, metal powder and ceramic powder. As shown in Fig. 2, its working principle is: before starting processing, it is necessary to raise the temperature of the worktable to the melting point temperature of the powder, and then carry out laser sintering of the powder material layer by layer according to the profile of the cross section to make the solid powder melt and then coagulate, forming a predetermined workpiece. According to the experience of using SLS process equipment in the past, after the workpiece is formed, it needs to be cooled for one to two hours to ensure the strength and integrity of the workpiece.
The advantages of the process are: rapid molding speed; high material utilization; more kinds of raw materials available for powder. The disadvantages of this process are: poor surface quality and low strength of the formed parts; low forming accuracy; complex post-processing of the formed parts, secondary processing is easy to lead to workpiece deformation.
Therefore, the process is suitable for manufacturing casting parts and samples needed in the process of design and development of metal parts.
3. Three dimensional powder bonding process
3D powder bonding process (3DP for short) is the most suitable molding process for 3D printing literal meaning. As shown in Figure 3, its working principle is: first lay a layer of powder material on the working plane, and then spray the adhesive to the area to be formed through the nozzle, so that the powder material in the area to be formed can be bonded together to form the required cross-section shape. This process is repeated, and the final product is obtained. The powder material can be metal powder, ceramic powder, plastic powder, etc.
The advantages of this process are: it can be used to manufacture parts with heterogeneous materials; raw materials can be powder materials; it can be used to manufacture parts with extremely complex shape and structure with fast forming speed. The disadvantages of this process are: in the forming process, there are many variable parameters, low yield and high process cost.
Therefore, the process is suitable for manufacturing high-precision, small and medium-sized parts.
