SLM selective laser melting: irreplaceable metal 3D printing technology
As the most cutting-edge and most promising technology in the entire 3D printing system, metal 3D printing is an important development direction of advanced manufacturing technology. With the development of technology and the demand for popularization and application, the rapid development of rapid prototyping has become the main development direction of rapid prototyping. SLM metal 3D printing technology is currently the most advanced and highest precision metal laser 3D printing forming technology in the world.
How SLM works
Selective Laser Melting, SLM technology was first proposed by the German Froounholfer Research Institute in 1995, and its working principle is similar to SLS. SLM converts the energy of the laser into heat to shape the metal powder. The main difference is that in the manufacturing process of SLS, the metal powder is not completely melted, while in the manufacturing process of SLM, the metal powder is heated to complete melting and then formed.
The SLM workflow is that the printer controls the laser to selectively irradiate the powder above the laid powder, and the metal powder is heated to be completely melted and shaped. Then the piston lowers the table by one unit height, a new layer of powder is spread on top of the current layer that has been formed, the device transfers the data of the new layer section to laser melting, and bonds with the previous layer section, this process Cycle through the layers until the entire object is formed. The entire process of SLM is carried out in an inert gas-protected processing room to avoid metal oxidation at high temperatures.
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The difference between SLM and SLS
SLS is laser sintering. The metal material used is a mixed powder of processed and low-melting metal or polymer material. During processing, the low-melting material melts but the high-melting metal powder does not melt. First, the lamp is heated or the heat radiation of the metal plate is used to heat the powder beyond the crystallization temperature, about 170 degrees Celsius. The melted material is used to achieve bonding molding, so the body has pores and poor mechanical properties. If some parts are to be used, they need to be remelted at high temperature.
SLM is selective laser melting. As the name implies, the laser is used to completely melt the powder during processing. No binder is needed. The molding accuracy and mechanical properties are better than SLS. However, because SLM does not have a thermal field, it needs to heat the metal from a normal temperature of 20 degrees Celsius to a melting point of thousands of degrees. This process requires a lot of energy.
SLM main advantages
The metal parts formed by SLM have high density, which can reach more than 90%;
Tensile strength and other mechanical performance indicators are better than castings, and can even reach the level of forgings. Micro Vickers hardness can be higher than forgings;
Because it is completely melted during printing, the dimensional accuracy is high;
Compared with traditional subtractive manufacturing, it can save a lot of materials.
SLM material
The powder materials that can be used in SLM technology are mainly divided into three categories, namely mixed powder, pre-alloyed powder, and elemental metal powder.
1. Mix the powder. The mixed powder is made by mixing a certain proportion of different powders. Existing research shows that the mechanical properties of components molded by SLM are affected by the density and the uniformity of the molding, and the density of the current mixed powder needs to be improved;
2. Pre-alloyed powder. Depending on the composition, the pre-alloyed powder can be divided into nickel-based, cobalt-based, titanium-based, iron-based, tungsten-based, copper-based, etc. Studies have shown that the density of components made of pre-alloyed powder materials can exceed 95%;
3. Elemental metal powder. Generally, the elemental metal powder is mainly metallic titanium, and its formability is good, and the density can reach 98%.
Metal powder for 3D printing
At present, SLM technology is mainly applied in the industrial field, and has outstanding technical advantages in the fields of complex molds, personalized medical parts, aerospace and automobiles.