1.Direct casting method
An important feature of the direct casting method is the one-step molding. There is no need to weld or otherwise splicing in the middle. Metal parts are typically obtained by metal casting. In this process, since the metal parts do not require other shape changes, they are called direct casting methods. However, this method is basically used for relatively simple part casting. The direct casting method includes two modes.
First, direct shell casting. This casting method is to sinter the reactive resin-coated ceramic powder by laser, in which the laser has a certain selectivity in the sintering process, so that the one-time casting of the shell-shaped object can be realized. To implement this method, first convert the part model into a shell shape in the auxiliary design software, and then set up the casting system. The thickness of the shell can usually be chosen between 5 and 10 mm. When laser sintering is used, the non-part material is selectively sintered while the parts are still in a powder state. When the sintering is completed, the remaining portion is cured to obtain a shell shape. Then, by pouring into this shell-shaped object, metal parts can be obtained. This method obviously saves a lot of traditional processing, such as mold design and manufacturing, so it can effectively improve the processing speed of parts. However, there are some drawbacks in this process, that is, the parts constructed by this casting method have a high surface roughness. Therefore, the key point of this technical method is the choice of shell thickness, curing process and optimization of surface roughness.
Second, the direct molding method. This method is not selective sintering, but is achieved by selective bonding by an adhesive. The specific method is to convert the parts into a form by an auxiliary design software, and then use the method of investment casting to process the parts. Investment casting is undoubtedly the most important part of this process, and the process is environmentally friendly and flexible, and can be precisely manufactured for any complex part shape and internal structure. It is also possible to directly select the sand for manufacturing by using this process, thereby obtaining a sand type model, and then obtaining a metal part by pouring. This method is currently mainly used for casting of large and complex parts.
2. Secondary conversion method
The core of this method is to first construct the prototype mold by rapid prototyping technology. It can choose soft materials such as wax, silicone rubber and epoxy resin, and then soft mold and investment casting, ceramic casting machine coating transfer method and other precision. The casting process combines to obtain high precision metal parts. Since this process requires two or more conversions, it is called a secondary conversion method. This method usually allows casting of batch parts. The core of technology lies in the processing of dimensional progress and surface roughness.