Researchers at the Columbia University in New York demonstrated an experimental lab additive system using selective laser sintering (SLS) technology that can print multiple materials simultaneously.
The experimental system differs from usual SLS 3D printers in the location of the laser emitter. The scientists borrowed the solution from some stereolithographic systems and applied an "inverted" scheme with a laser under the working area. A layer of powder is pressed between the glass bottom and the substrate, then the laser sinters the model layer, after which the substrate is lifted, a fresh layer of powder is applied, and the process is repeated again and again until the finished model is obtained.
Why such difficulties? Firstly, this approach allows for the use of several materials in a single workflow: the substrate with already applied layers can simply be transferred from one container to another and the next layer or part of the last one can be printed with another material. The illustration above shows an example that is half nylon and half polyurethane. In conventional SLS 3D printers, multi-material printing is difficult due to the mixing of powders, although the Belgian company Aerosint is trying to solve this problem with a system of raster application of two or more materials in two directions at once — using polymer and metal powders.
Secondly, the usual SLS 3D printing does not allow for tracking the product condition directly during printing, as the workpiece is buried in the residual powder. Here, a flaw can be detected as soon as it appears. Scientists are experimenting with both metal powders and other polymers.
“This technology could find applications in 3D printing of embedded electronic circuits, electromechanical components, and even robot elements. It is possible to manufacture machine parts from various alloys with a gradient structure: for example, turbine blades with cores from one material and coatings from another. We believe that with the ability to manufacture complex parts from multiple materials without the need for assembly, this technology will expand the range of applications for laser sintering across industries. In other words, this could be the key to moving the additive industry from 3D printing only passive homogeneous parts to printing active integrated systems,” commented Hod Lipson, professor of mechanical engineering and data analytics, one of the authors of the study.
