Additive manufacturing process

Additive manufacturing technology includes a number of modern processes. With the continuous development of various technologies, the application effect of additive manufacturing technology continues to improve. According to the classification of energy types, it can be divided into “laser forming” and “non laser forming”; According to the shape classification of molding materials, they can be divided into five categories: “metal powder”, “thin material”, “silk material”, “liquid” and “non-metallic powder”. At present, the five kinds of additive manufacturing technologies with high application frequency are: selective laser sintering technology, light curing molding technology, melt deposition manufacturing technology, three-dimensional printing technology and layered solid manufacturing technology.

1. Selective laser sintering technology

The selective laser sintering technology uses the laser beam as the energy source. Firstly, the printing materials shall be evenly laid on the printing platform, and then the laser beam shall be used to scan in the designated area according to the contour and path derived from the computer software, and the powder materials shall be melted at the same time. After sintering, the powder material forms a sintering layer. After layer by layer sintering treatment, it can form a whole part. There are many printing materials that can be used in this technology, such as paraffin, ceramic powder, metal powder and polymer materials, and the required energy source is laser beam. However, various printing materials can take on different forms. For example, photosensitive resin is in liquid state, and most metal and non-metal materials are in powder state.

2. UV curing technology

UV curing technology is also called stereolithography technology. Using this technology, the photosensitive resin is used as the raw material, controlled by computer software, and the ultraviolet laser beam is used as the energy source to scan point by point for different section shape trajectories. The scanned photosensitive resin layer can appear photopolymerization reaction and gradually cure, and then a thin section can be formed on the part. After each layer is formed, the printing platform can move downward by the thickness of one layer, and then continue to lay photosensitive resin on the surface of the formed photosensitive resin, and then continue the above operations. After the new layer of photosensitive resin and the previous layer of photosensitive resin are completely cured and bonded, the one-time molding operation is completed. Repeat this, and the parts can be printed step by step. At present, the UV curing molding technology is basically in a mature state, with relatively high dimensional accuracy. The thickness of each layer is usually 0.05 mm ~ 0.15 mm. It can efficiently process complex parts that are difficult to be effectively processed in the traditional processing form, but it also has some limitations. For example, it is necessary to add a certain degree of support in it, and because the material is resin, there may be looseness.

3. Melt deposition manufacturing technology

Melt deposition manufacturing technology, also known as volume extrusion technology, requires the use of thermoplastic materials such as nylon or paraffin as printing materials. First, heat it until the material is in the state of solid-liquid mixing. Then, through computer control, print the solid-liquid mixed thin layers layer by layer on the printing platform. Through the stacking of thin layers layer by layer, the complete parts can be gradually formed. In the process of printing products, each layer of sheet needs to be supported by its upper layer of sheet. For hollowed out positions, another supporting part needs to be added. The biggest advantage of applying this technology is that there is no need to apply laser beam, and the equipment cost is relatively low. Especially, if wax is selected as the printing material, the formed parts can also be directly applied to the mold manufacturing.

4. 3D printing technology

The principle of 3D printing technology is similar to that of inkjet printer. Firstly, the powder material shall be laid on the printing platform, and then the liquid adhesive shall be sprayed by the nozzle according to the path established by the computer software. After spraying, the powder material shall be laid on the adhesive again, and the above steps shall be repeated until the printing of the parts is completed. After the adhesive is cured, the excess powder can be removed. In the process of applying this technology, the printing material is usually polymer material or other types of pastes. After the printing work is completed, the parts shall be placed in the printing forming box for thermal insulation treatment, or placed in the heating furnace for reasonable heating, so as to further improve the curing effect of the adhesive and improve the strength of the parts. From a practical point of view, the advantages of this technology mainly lie in the convenient operation process, high cleanliness of the operation process, more types of printing materials that can be applied, no support, and the recycling of excess materials; The disadvantage lies in the lack of surface roughness and accuracy, which is not suitable for processing thin-walled parts with more details and complex structure.

5. Layered solid manufacturing technology

The main energy sources of layered solid manufacturing technology are heating rollers and lasers. The printing materials that can be used in layered solid manufacturing technology mainly include metal strips, plastic bags and paper coated with hot melt adhesive on one side. The forming principle is as follows: according to the two-dimensional model that has been layered and sliced, the internal and external contours that need to be printed can be confirmed, and then the laser is used to cut and process the strip material. At the same time, the heating roller is used to heat the hot-melt adhesive paper, so that the cut sheet can effectively bond with the previous sheet, and the above steps are repeated several times until the printing of parts is completed. The advantage of using layered solid manufacturing technology is that the manufacturing accuracy is high. After a small amount of binder in raw materials is converted from solid state to molten state, the paper material is still in its original state, and the formed parts have strong machining performance and high strength. At the same time, the forming speed is fast, and there is no need to add support; The disadvantage is that plastic parts cannot be directly formed, and parts with complex structure cannot be formed, and the elasticity and tensile strength of parts are insufficient.

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