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3D printing technology is a powerful tool for producing complex shapes with high quality textures. Alongside color and shape, shine is one of the most salient visual aspects of an object.
MIT scientists may have a solution. They developed a combined hardware and software printing system that uses standard paints to finish objects with realistic and spatially varying gloss patterns.
The technology has a wide range of applications: to reproduce fine art, allowing the distribution of near-flawless replicas to museums without access to the originals. Also, it could be useful for creating more realistic looking dentures.
Gloss refers to the sheen and apparent smoothness of a surface. Low-gloss, or dull, the surface is not reflective, like concrete.
Paints that impart a glossy finish tend to be less viscous and dry to a smooth surface. Paints that give a matte finish are more viscous, closer to honey than water. They contain large polymers which, when dried, randomly protrude from the surface and absorb light.
MIT researcher Michael Foshey said: “You have a bunch of these particles sticking out of the surface, which gives you that roughness.”
“But those polymers pose a dilemma for 3D printers, whose thin fluid channels and nozzles aren’t made for honey. They are small and can become clogged easily. “
Reproducing a surface with varying sheen in space takes a lot of work. At first, the scientists printed the object with a high gloss and support structures that covered where a matte finish was desired. Then the support material is removed to give roughness to the final surface.
Foshey said, “There is no way to instruct the printer to produce a matte finish in one area or a glossy finish in another. So, we came up with one. “
The printer was designed with large nozzles. It can deposit paint droplets of various sizes. The paint is stored in the pressurized tank of the printer and a needle valve opens and closes to release droplets of paint on the print surface. A variety of droplet sizes are achieved by controlling factors such as tank pressure and needle valve speed. The greater the quantity of paint released, the greater the droplet deposited. The same goes for the drop release rate.
Foshey said, “The faster it goes, the more it spreads once it hits the surface. So essentially varying all of these parameters to get the drop size we want. “
As expected, the printer achieved variable gloss in space through the midtones. In this strategy, discrete paint droplets are arranged in examples that look like a continuous surface when viewed well.
Foshey said, “Our eyes mix themselves.”
“The printer uses only three standard paints: one glossy, one matte and one in between. By incorporating these paints into its preprogrammed halftone pattern, the printer can produce continuous and spatially varying shades of gloss on the print surface. “
Along with the hardware, Foshey’s team produced a software pipeline to control printer output. First, the user indicates the desired glossy pattern on the surface to be printed. Next, the printer performs a calibration, testing various halftone patterns of the three paints provided. Based on the reflectance of these calibration patterns, the printer determines the correct halftone pattern to use in the final print job to achieve the best possible reproduction.
Scientists demonstrated their results on various “2.5D” objects: mostly flat prints with textures that varied by half a centimeter in height.
Foshey said, “They were impressive. They have more of an idea of what you are trying to reproduce. “
Scientists are now planning to continue developing hardware for use on fully 3D objects.
Journal reference:
- Michal Piovarči et al. Towards a reproduction of variable gloss in space for 3D printing. DOI: 10.1145 / 3414685.3417850
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