Metal 3D printing technology: the simple difference between SLM and SLS

3D printing technology is rapidly changing the traditional way of production and life. In just 30 years, 3D printing technology has been developed rapidly and has been widely concerned by all countries in the world. With the continuous improvement of the maturity and performance of 3D printing technology, more and more materials, especially metal materials, are used in 3D printing. We know that SLM technology and SLS technology are the mainstream metal part printing technology, so how are they different?

 

In 1989, C. Deckard of Texas university put forward Selective Laser Sintering (SLS) technology and later formed the DTM company. In 1995, Selective Laser Melting (SLM) technology was proposed by Fraunhofer Laser Research Institute in Germany. It can be used to directly from nearly completely dense metal parts. SLM and SLS are both powder printing technologies, and they are the same in the printing process. Before printing, the powder material is spread to the printing platform by the powder spreading car and then sintered or melted by the laser to realize the printing of one layer. After each layer is completed, the forming platform will drop a layer thickness height, and then the powder spreading car will be spread the powder, and then formed by the laser thermal effect, stacking layer by layer until forming a three-dimensional part. To prevent metal oxidation, the whole process needs to be lazy It is carried out in a sexual gas environment.

 

 

SLM forming schematic diagram

 

SLS forming schematic diagram

 

Although the principle of the two technologies is to use the thermal effect of the laser beam, the laser used by SLM and SLS is different due to the different objects of action. To melt metal better, SLM technology needs to use a laser beam with high absorptivity of metal, so the laser beam with short wavelengths such as Nd YAG laser (1.064 μm) and fiber laser (1.09 μm) is generally used. SLS technology is generally applied to CO2 laser with long-wavelength (9.2-10.8 μm).

 

 

SLM technology printing metal

SLM technology uses the laser to directly heat metal powder so that it can be completely melted and then cooled. SLM is a promising 3D printing technology for metal parts. Most SLM molding materials are single-component metal powders, including austenitic stainless steel, nickel base alloy, titanium base alloy, cobalt-chromium alloy and precious metals. The laser beam can melt the metal powder quickly and obtain the continuous melting path, which can directly obtain almost any shape, completely metallurgical combination, high precision, and nearly dense metal parts.

 

Metal parts printed by SLM Technology

 

SLS technology printing metal

SLS technology irradiates the material powder by laser, melts the special added material to achieve the function of binder, to combine the metal powder to form and realize metal printing. There are three kinds of metal powder used in SLS sintering: single metal powder, metal mixed powder, and metal powder plus organic powder.

 

Metal parts printed by SLS Technology

 

Also, in the process of laser sintering, the powder material is first heated to over crystallization temperature (about 170 ℃) through lamp heating or metal plate thermal radiation, and the melted material is used to realize bonding forming. Therefore, the entity has pores and poor mechanical properties. Some parts need to be remelted at high temperature if they are to be used. SLM is laser selective melting. As the name implies, in the process of processing, the powder is completely melted by a laser, without binder, and the forming accuracy and mechanical properties are better than SLS. However, because SLM has no heat field, it needs to heat the metal from 20 ℃ to thousands of degrees of melting point, which requires huge energy consumption.