Innovative upside-down approach enables multi-materials 3D printing

Over the past decade, 3D printing has experienced staggering growth. One of the most widely used manufacturing processes is selective laser sintering (SLS) which is limited to printing with a single material at a time. Researchers have recently invented a new technique that enables multi-materials 3D Printing.

SLS prints parts by using laser to heat micron-scale material powders to the point where they fuse together to form a solid mass. The limitations of printing in only one material have been blocking the expansion of 3D printing and preventing it from reaching its full potential. 

Led by Prof. Hod Lipson, researchers at New York's Columbia University have developed a new approach to overcome the SLS limitations.

By inverting the laser so that it points upwards, they invented a way to enable SLS to use multiple materials at the same time. Their working prototype, along with a print sample that contained two different materials in the same layer, was recently published online by journal Additive Manufacturing.

Laser beam transmitting upwards through glass.

SLS traditionally has involved fusing together material particles using a laser pointing downward into a heated print bed. A solid object is built from the bottom up, with the printer repeatedly deposits and fuses uniform layer of powders until the part is completed.

This process works well if there is just one material used in the printing process. But using multiple materials in a single print has been very challenging, because once the powder layer is deposited onto the bed, it cannot be unplaced, or replaced with a different powder.

The researchers decided to find a way to eliminate the need for a powder bed entirely. They set up multiple transparent glass plates, each coated with a thin layer of a different plastic powder. They lowered a print platform onto the upper surface of one of the powders, and directed a laser beam up from below the plate and through the plate’s bottom.

This process selectively sinters some powder onto the print platform in a pre-programmed pattern according to a virtual blueprint. The platform is then raised with the fused material, and moved to another plate, coated with a different powder, where the process is repeated. This allows multiple materials to either be incorporated into a single layer, or stacked. Meanwhile, the old, used-up plate is replenished.

Dual thermoplastic SLS print sample.

Multi-layer, single material print sample.

The researchers demonstrated their working prototype by generating a 50 layer thick, 2.18mm sample out of thermoplastic polyurethane (TPU) powder with an average layer height of 43.6 microns and a multi-material nylon and TPU print with an average layer height of 71 microns.

“This technology has the potential to print embedded circuits, electromechanical components, and even robot components,” Lipson notes. “We think this will expand laser sintering towards a wider variety of industries by enabling the fabrication of complex multi-material parts without assembly. In other words, this could be key to moving the additive manufacturing industry from printing only passive uniform parts, towards printing active integrated systems.”