While the majority of desktop 3D printers are based on FDM/FFF technology, other technologies such as Stereolithography (SLA) are coming on strong as patent expiration and lower prices increase their availability. With that said there are also other reasons why SLA has not caught on just yet, namely the inability to print with multiple materials and colors, like one can with dual extrusion FDM/FFF machines. This limits the colors of a print as well as the ability to have support material which differs from the main object being fabricated.
XZEED 3D Printer
In comes Reinout Holtrup, a student of industrial design at the University of Twente in the Netherlands. For his bachelor assignment he decided to take on these very issues by creating a prototype for a DLP 3D printer which can print with up to 5 materials/colors at once. Clearly something which had never been done before with a DLP printer, he certainly had his work cut out for him. For those who are unaware, Digital Light Processing (DLP) 3D printing uses a projector to cure a photosensitive resin one layer at a time. Such processes allow for incredibly accurate prints since movement during the print process only occurs along the Z-axis.
The machine that Holtrup created for this project is called the XZEED Multi-Material DLP Printer, and I must admit it appears to be quite the breakthrough once the process can be polished up a bit. Basically what he does is create a 
The XZEED printer uses the bottom-up approach where an object is built upside down in the vat of resin, on the bottom side of a build platform. When one material is done printing, the next vat of material that’s required will horizontally move under the build platform as the DLP projector projects light up through the bottom curing the new material. One problem that Holtrup had to overcome was the issue of an object sticking to the vat floor. This clearly is not something you’d want to occur if you plan on changing vats mid-print. He decided to use a layer of oxygen permeable PDMS on the vat floor, which would inhibit the curing process because of its oxygen permeable attributes. This enables multiple vats to be automatically swapped in and out of the print area on a whim.
The entire machine was conceptualized and built by Holtrop who decided to use a Megatronics V3 motherboard loaded with Marlin firmware to control the whole thing, along with a 24V 15A power source. For the projector he opted to go with a Benq PB7230 DLP beamer that works at an XGA resolution of 1024 x 768, but since he needed to project such a small image at a tiny distance he installed a 5mm spacer in between the DMD chip and the lens assembly. As for the body, he simply laser cut sheets of medium-density fibreboard, making it sturdy and solid enough to perform the movements required. There were also a total of 55 parts which were 3D printed themselves which made up the machine. This included nut housings, linear bearing housings, mirror clips, etc.
Certainly this is an innovative approach to overcome some of the shortfalls within the SLA/DLP processes. Where Holtrup takes this project next will certainly be interesting as I’m sure there are many individuals out there interested in such a technology. Let’s hear your thoughts on this multi-material, multi-vat 3D printer. Discuss in the XZEED forum thread on 3DPB.com.
