Since the advent of 3D printing technology, it has been gradually applied to the manufacture of actual products. Among them, the development of 3D printing technology for metal materials is particularly rapid. In the field of national defense, developed countries in Europe and the United States attach great importance to the development of metal 3D printing and invest huge sums of money in research. 3D printing metal parts has always been the focus of research and application. Not only can it print molds and bicycles, it can also print unprecedented new weapons, and it can even print large equipment such as cars and airplanes. As a new type of intelligent manufacturing technology, metal 3D printing has shown a very broad application prospect, and has shown a strong development momentum in more fields such as equipment design and manufacturing, equipment support, and aerospace.
Metal 3D printing features
1) High precision. At present, the accuracy of metal 3D printing equipment can basically be controlled below 0.05mm.
2) The cycle is short. Metal 3D printing does not require the production process of molds, which greatly shortens the production time of the model. Generally, a model can be printed in a few hours or even tens of minutes.
3) It can be personalized. Metal 3D printing has no limit to the number of printed models, no matter one or more can be produced at the same cost.
4) Diversity of materials. A metal 3D printing system can often realize the printing of different materials, and the diversity of this material can meet the needs of different fields.
5) The cost is relatively low. Although metal 3D printing systems and metal materials for 3D printing are relatively expensive now, if they are used to make personalized products, the production cost is relatively low.
Metal 3D printing technology
As the most cutting-edge and most potential technology in the entire 3D printing system, 3D printing technology of metal parts is an important development direction of advanced manufacturing technology. With the development of science and technology and the needs of popularization and application, the direct manufacture of metal functional parts by rapid prototyping has become the main development direction of rapid prototyping. At present, the rapid prototyping methods that can be used to directly manufacture metal functional parts mainly include: Selective Laser Melting (SLM), Electron Beam Selective Melting (EBSM), Laser Engineered Net Shaping (LENS) )wait.
Selective Laser Melting (SLM)
SLM is an important part of the field of metal 3D printing. Its development process has gone through stages such as sintering of low melting point non-metallic powder, sintering of low melting point coated high melting point powder, and direct melting of high melting point powder. The University of Texas at Austin first applied for a patent in 1986, and successfully developed the first SLM equipment in 1988. It uses a finely focused spot to quickly melt into a preset powder material of 30-51 μm, and can almost directly obtain any shape. As well as functional parts with complete metallurgical bonding. The density can reach nearly 100%, the dimensional accuracy can reach 20-50 μm, and the surface roughness can reach 20-30 μm. It is a rapid prototyping technology with great development prospects.
SLM molding materials are mostly single-component metal powders, including austenitic stainless steel, nickel-based alloys, titanium-based alloys, cobalt-chromium alloys and precious metals. The laser beam quickly melts the metal powder and obtains a continuous melting channel, which can directly obtain nearly dense metal parts with almost any shape, complete metallurgical bonding, and high precision. It is a 3D printing technology for metal parts with great development prospects. Its application range has been extended to aerospace, microelectronics, medical treatment, jewelry and other industries.
There are more than 50 influencing factors in the SLM process, and there are six categories that have an important impact on the molding effect: material properties, laser and optical path systems, scanning features, molding atmosphere, molding geometric features, and equipment factors. At present, researchers at home and abroad mainly conduct process research and application research on the above factors, with the purpose of solving defects in the molding process and improving the quality of molded parts. In terms of process research, the important process parameters in the SLM forming process include laser power, scanning speed, powder layer thickness, scanning distance and scanning strategy, etc. By combining different process parameters, the forming quality can be optimized.
The main defects in the SLM molding process are spheroidization and warping deformation. Spheroidization is the insufficient melting of the upper and lower layers during the molding process. Due to the effect of surface tension, the molten droplets will quickly roll into a spherical shape, resulting in spheroidization. In order to avoid spheroidization, the input energy should be increased appropriately. Warpage deformation is caused by the thermal stress in the SLM forming process exceeding the strength of the material, resulting in plastic deformation. Due to the difficulty in measuring the residual stress, the current research on warpage deformation of the SLM process is mainly carried out using the finite element method, and then The reliability of the simulation results is verified by experiments. The basic principle of SLM technology is: first use Pro/e, UG, CATIA and other 3D modeling software to design the 3D solid model of the part on the computer, and then slice and layer the 3D model through the slicing software to obtain the contour data of each section , the filling scanning path is generated from the contour data, and the equipment will control the laser beam to selectively melt the metal powder materials of each layer according to these filling scanning lines, and gradually stack them into three-dimensional metal parts.