Additive Manufacturing Strategies

Using an Inkjet Robot On Curved FDM Surfaces to Get the Best of Both Worlds

ST Medical Devices

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Inkjet robot setup with the to-be-painted sneaker (Image: DDMC-Fraunhofer)

So far, 3D creators have experimented with hydrographics, ultrasonic misting, and water marbling as ways to make Fused Filament Fabrication (FFF)-created objects more visually interesting. Now, an Austrian-based group is experimenting with using inkjet printing robots to beautify designers’ creations. The combination of FFF for dimensional accuracy as well as toughness and inkjet for aesthetics could be a very powerful one indeed.

In a paper from the 2018 Fraunhofer Direct Digital Manufacturing Conference in Berlin, the team detailed their efforts in developing a robot that can recognize and stylize curves like an expert artist. This robot would then apply inkjet inks to existing prints. 

Current Methods for Putting Designs on FFF Surfaces

Currently, the most common options for beautifying 3D printed objects are using lasers, hot air, or chemical or mechanical processes. But since 3D printing and inkjet printing are both digital processes, using the latter would allow different designs to be applied to each unique object, and potentially on a large scale.

While this seems straightforward enough, inkjet printing is a particular challenge on 3D objects with curved surfaces. Of several proposed solutions to overcome this problem, the group first took action with developing a robot-powered Inkjet system.

Design Details

Inkjet setup with UR10 robot printing on shoe (Image: DDMC-Fraunhofer)

For the robot’s hardware, the team decided on a Dimatix Printer with Ricoh Gen 4 printing head. This printhead was chosen for its ability to be used in a tilted position (essential for printing on a curved surface), integrated ink heating system, and its compact dimensions. The head’s smaller size allowed for better control between the printing head and the printing surface.

Images were prepared for the robot using a software module that converted vector graphics into raster graphics. Raster images are those made up of a rectangular grid of pixels and are the opposite of vector graphics, which are made up of lines, curves, and 2D points. Once the graphics’ resolutions were converted, color channels separated, and color management processes executed, printing with the robot could begin.

Test Results

Test droplets of ink from the two rows of nozzles on the UR10 robot (Image: DDMC-Fraunhofer)

First, the system’s movement was tested by printing on a flat polymeric foil. Due to vibrations in the robot’s movement, the printed droplet design did not come out perfectly straight (as desired) and each line was slightly different based on the color used.

This is due to the Ricoh Gen’s nozzle design that has nozzle row 2 resting between nozzle row 1. These distinct rows can be supplied with different colors of ink, however the spacing between rows (about 529μm) means that ink is not jetted at the same time. While the result was not perfect, the team noted that the configuration was still serviceable and that “encouraging results could be obtained” with it.

For printing on a 3D object, the team chose to decorate a tennis shoe with a grass-like pattern on the toe and inner and outer quarters. Using the same printhead mounted on a Universal Robots UR10, Stäubli, and Kuka robot systems, the end product was encouraging, if not vaguely reminiscent of the T-shirt spray art you see in kiosks at your local mall.

The team noted too that while this configuration was functional enough, it was far from optimal as it involved near constant movement of the printhead’s orientation, often far from the ideal 90° sideways position.

The Future of 3D Inkjet Robots (and of Art?)

While it still might be some time before we see vivid and beautiful ink designs on complex and curvy 3D printed surfaces, the early results are encouraging. Like with 3D printing itself, the possibilities are limitless, and it’s not too hard to imagine that inkjet printing onto FFF objects could become a whole other art form in and unto itself. One could also use inkjet heads to apply conductive materials, coatings and perhaps even entire electronics to existing FFF parts. By combining the toughness, strength, low cost and durability of FFF parts with the ability of inkjet to add many different kinds of inks this process could fundamentally revolutionize 3D printing. By separating out the process into two steps we could see functional parts with consumer-friendly esthetics emerge. This is a huge step forward for 3D printing and many more teams should look at seeing their 3D printing challenge as something that could be solved with multiple technologies instead of just one. 

Until then, the Austrian crew (and probably many like it) are optimizing each step and component of their process. They’ll also, of course, be doing a lot of testing until they have their state of the art process down to a fine art.

Source: DDMC

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