Metal Sintering 3D Printing

3D  printing technology is rapidly changing the traditional mode of  production and lifestyle. In just 30 years, 3D printing technology has  gained rapid development and received extensive attention from countries  around the world. With the continuous improvement of the maturity and  performance of 3D printing technology, the materials used in 3D printing  are becoming more and more extensive, especially metal materials. We  know that SLM technology and SLS technology are the mainstream metal  part printing technology, so what is the difference between them?

In  1989, the United States of America, the University of Texas C. Deckard  proposed laser selective sintering (SLS) technology, later set up the  DTM company. 1995, the German Fraunhofer Institute for Laser Research  put forward the laser selective melting (SLM) technology, with which can  be molded directly out of the metal parts close to completely dense.  SLM and SLS with the same powder printing technology, in the printing  process is basically the same. Printing before the start of the powder  by the powder laying car to the powder material spread to the printing  platform, and then by the laser for sintering or melting, to achieve a  layer of printing, each layer, molding platform will drop a layer of  height, and then laying the powder car will be re-laying the powder, and  then by the laser thermal role of the molding, layer by layer stacked  until the formation of a three-dimensional parts, in order to prevent  the oxidation of the metal, the whole process needs to be carried out in  the environment of inert gas.

 SLM molding schematic 

 SLS Molding Schematic 

Although  the principle of both technologies is to utilize the thermal action of  the laser beam, SLM and SLS lasers use different lasers due to their  different targets.SLM technology, in order to better melt the metal,  needs to use a laser beam with a higher absorption rate of the metal, so  it generally uses a shorter wavelength laser beam, such as a Nd-YAG  laser (1.064 µm) and a fiber laser (1.09 µm).SLS technology generally  applies a CO2 laser with a longer wavelength (9.2-10.8 µm). Shorter  wavelength laser beams are used for SLS technology, which generally uses  CO2 lasers with longer wavelengths (9.2-10.8 microns).

SLM technology for printing metals 

SLM  technology through the laser on the metal powder direct thermal action,  so that it is completely melted and then after cooling molding.SLM is a  very promising metal parts 3D printing technology, SLM molding  materials are mostly single-component metal powder, including austenitic  stainless steel, nickel-based alloys, titanium-based alloys,  cobalt-chromium alloys and precious metals. The laser beam rapidly melts  the metal powder and obtains a continuous melt channel, which can  directly obtain almost any shape, with complete metallurgical bonding,  high precision and nearly dense metal parts.

 Metal parts printed using SLM technology 

 SLS technology for printing metals 

 Single metal powder sintering 

Sintering  of single metal powders: For example, iron powder is preheated to a  certain temperature, then scanned and sintered with a laser beam. The  sintered parts are subjected to hot isostatic pressing, which results in  a relative density of 99.9% for the final part.

 Mixed metal powder sintering 

Sintering  of mixed metal powders: mainly mixed powders of two metals, where one  powder has a lower melting point and the other has a higher melting  point. For example, a mixture of bronze powder and nickel powder. First  the metal mixture of powder preheating to a certain temperature. Then  scanning with a laser beam, so that the low melting point of the metal  powder melting (such as bronze powder), so that the refractory nickel  powder bonded together. The sintered parts are then post-treated by  liquid-phase sintering, which results in a relative density of 82% for  the final part.

 Blend of metal powder and organic binder powder 

 Metal parts printed using SLS technology 

In  addition, the laser sintering process is first heated with a lamp or  metal plate heat radiation, the powder material is heated to more than  the crystallization temperature, about 170 degrees Celsius, the use of  melted material to achieve bonding molding, so the entity exists  porosity, poor mechanical properties, some parts to be used if you have  to go through high-temperature remelting.SLM is a laser selective  melting, as the name implies, that is, in the processing of the process  with the Laser to make the powder completely melted, without the need  for bonding agent, 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 20 ℃ room temperature to the melting point of  thousands of degrees, this process requires the consumption of huge  amounts of energy.

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