The Rochester Institute of Technology are constructing a resin-based DLP (Digital Light Processing) 3D printer, using an ordinary overhead projector to project black and white images onto a film of UV curable photopolymer in order to selectively cure/harden the polymer.
The rig pulls a printed object up from the ooze on the build platform where resin is cured with visible light. The bath needs to be a uniformed thickness so that it solidifies correctly when the light hits it from the underside. The build table is made of glass sandwiched between gaskets where it comes in contact with the frame, keeping the liquid in place, while letting the DLP projector shine through.
Students who participate in this ambitious ongoing project are to be invited to design a movable platform upon which the 3D part is printed; determine the best method of adjusting the image size and focus; create a procedure for generating the sequence of black and white images; research different photo-polymers that are available; and design and construct an optics system capable of transmitting light that will cure the selected photo-polymer.
Check out this fast-motion build video to see how each layer is exposed to light, then pulled upward to make room for the next. The build time could be estimated at two hours – one can see a technician replace the extracted resin at regular intervals during the extended real-time process.
The project’s technical and detailed website is a pleasure to browse, including interesting descriptions of problem solving. A snippet of the main problem that last years student team faced is an illustration of the innovation and ingenuity required in this fascinating project:
‘The biggest problem faced by last year’s team was that when the projector cures through an optical medium onto the build platform, the resin sticks to both the optical medium and the build platform.
Despite the implementation of a peeling mechanism that aimed to “peel” the part from the optical medium, the cured resin continued to stick to both the build platform and the optical medium. This resulted in the motor being unable to generate enough torque to raise the build platform.
In exploring ways to overcome this main issue we began by exploring a different method of curing referred to as the top-down method. Previous groups had aimed to put the projector on the bottom and project images through an optical medium into a bath of resin (bottom-up curing). In this method the platform starts at the bottom of the bath of resin and moves up layer by layer.
The top-down method, however, puts the projector above the bath of resin. In this method the platform starts at the top of the bath and moves down layer by layer. The top-down method eliminates the need for the optical medium and therefore does not require any shearing or peeling.
The team explored this idea thoroughly and after a vote decided that the bottom-up method would be used in order to more closely control the accuracy of the part.’
Despite the implementation of a peeling mechanism that aimed to “peel” the part from the optical medium, the cured resin continued to stick to both the build platform and the optical medium. This resulted in the motor being unable to generate enough torque to raise the build platform.
In exploring ways to overcome this main issue we began by exploring a different method of curing referred to as the top-down method. Previous groups had aimed to put the projector on the bottom and project images through an optical medium into a bath of resin (bottom-up curing). In this method the platform starts at the bottom of the bath of resin and moves up layer by layer.
The top-down method, however, puts the projector above the bath of resin. In this method the platform starts at the top of the bath and moves down layer by layer. The top-down method eliminates the need for the optical medium and therefore does not require any shearing or peeling.
The team explored this idea thoroughly and after a vote decided that the bottom-up method would be used in order to more closely control the accuracy of the part.’
Source: edge.rit.edu