Inverted Laser Sintering
A novel laser sintering process that replaces the traditional powder-bed setup with a single powder layer coated onto a glass substrate. A selected region of material is fused onto the print from below by an upwards directed laser.
Inverted Printing Process
I developed a novel laser sintering process that replaces the traditional powder-bed setup with a single powder layer coated onto a glass substrate. This upper surface of this piece of glass is first coated with a monolayer of material. A flat print surface is then pressed onto the top surface of this powder. A laser is shined up through the bottom of the glass, selectively heating and fusing some of this material layer to the print surface. Finally, the print surface is raised with the fused material, the glass can be recoated, and the process can repeat, with new powder layers being fused to the existing print. This novel process requires less material than a standard selective laser sintering machine, and the piece can be observed during the entire print cycle due to the lack of surrounding, unfused powder.
Multi-Material Printing
In addition to less material usage and the ability to observe the part during the printing process, this setup enables easy multi-material printing. This is accomplished by simply changing the material powder coated onto the glass between laser cycles. When the print surface is again pressed to the unfused powder layer, the laser can either fuse material in the same layer as the previously fused material or on top of the previous layer. Here, this is demonstrated using thermoplastic polyurethane (white) and Nylon 12 (black).
Multi-Process Printing
To further expand the capabilities of the inverted printing process, additional materials were added to increase functionality. One such material was laser curable resin. Instead of recoating the glass with a secondary powder, an additional glass pane was added to the printing process. The upper surface of this pane was coated with a thin layer of stereolithography resin, much like a standard I-SLA printer. The print surface can then be moved between the powder glass and the resin glass, with material from each being selectively fused into the print. This larger range of materials allows greater control over aspects such as part strength, conductivity and porosity.
Inverted Sintering Embedding
In traditional LS printing processes, the use of a powder-filled print bed prevents users from embedding components during the printing process. This is due to the stacked surrounding regions of unfused powder. However, as the ILS process only uses a single layer of unfused material at a time, embedding objects becomes much simpler. This can be done by printing a few layers to create a chamber for a component to be adhered into. The printing process can then be paused, the object can be inserted, and the process can be continued to cover over the chamber and fully conceal the embedded part.
Inverted Laser Sintering of Metal Powders
I demonstrated the ability of the inverted laser sintering process to manufacture parts composed of metal powder by fabricating a 10-layer part by depositing a layer of copper powder onto a sapphire plate, then pressing the plate against the part being built and sintering the powder onto the part by shining a 14W 445 nm laser through the glass. The process was then repeated multiple times, each time adding a new layer to the component being printed until completion.
