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Multi-material 3D printing using stereolithography: an optimization approach,’ authored by Daniel Daniel Bandeira, Marta Pascoal, Artur Mateus, and Miguel Reis Silva, explores further uses of different composites in SLA (featuring a digital light processing system) as they create hybrid parts by adding polymer resin to another pre-existing object such as metal or ceramic.

In this type of work, there is always the concern that the structure could block the laser beam, resulting in ‘shaded’ regions. Here, the researchers attempt to overcome that issue upon analyzing the laser projection, and then calculating how many DLP emitters are needed to solve the problem—and in this case, with galvanometer mirror scanners installed on the side walls of the printer serving as emitters.

Printing area

“For the sake of the stability of the system, the emitters are considered to be fixed along the printing process, while they may reflect the laser beam at specific angles,” state the researchers, who had the task of analyzing the voxels reached by each emitter, and examining further how laser projections are affected by their positioning. To do so, they created an integer optimization model for figuring out the minimum number of emitters, along with their locations.

An algorithm for determining which voxels could be reached by the emitters was created:

“It is assumed that a set of m voxels have to be reached by the laser light, which may be sent from a set of n possible emitter positions, or simply n emitters. One of the emitters is placed at the central position of the top wall of the printer. The remaining are n − 1 emitters the positions of which have to be determined.”

Once emitter positions are realized, and in place upon printing, the researchers state that the emitter reaches a particular voxel by maximizing θ, the incidence angle of the laser light—affecting how it reaches the layers being printed and the distortion of the product.

(a) Printing area and object to be printed; (b) Intermediate cross section of the object to print

As the study progressed, the team worked to solve the multi-material issue with computational experiments:

“The computational experiments carried out have shown that the use of additional galvanometer scanners may be an alternative for implementing multi-material 3D printing. For all tests, theoretical solutions were obtained that satisfy the imposed constraints,” concluded the researchers. “Two parameters were calculated as measures of the quality of the determined solutions, the outer area, formed by the regions polymerized beyond the object voxels, and the inner area, formed by the regions of the object voxels that remained unpolymerized. Both depend on the incidence angle of the laser beam at the printing layers.”

“On the one hand, for the considered case study, the outer area was always null. On the other, the values of the inner area were around 70%. In principle these values could be improved by skipping the simplification that it is enough that the laser reaches the center of the voxels. Also, in practice finishing techniques could be used to overcome high values for Aout or small values for Ain. Future work includes performing further experiments for more complex case studies, as well as to studying the possibility of using other printing methodologies different from galvanometer mirror scanners.”

3D printing with SLA and DLP offers so many opportunities to users around the globe in a wide range of capacities with researchers working on projects like making bioresins for DLP 3D printing, creating multimaterials for airjet DLP, and developing faster, higher resolution methods. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Projection of the laser light in a voxel

[Source / Images: ‘Multi-material 3D printing using stereolithography: an optimization approach’]
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