One on the most appealing aspects of Stratasys PolyJet line of 3D printers is the ability to create highly arcuate and detailed parts. While these parts suitable for a wide range of applications including design verification, analysis, and even limited functional testing, where the technology really excels is in creating high quality models for presentations and design reviews. In situations where physical appearance is great concern, companies are choosing to go the extra step of painting models for added realism.
While the results can be impressive painting and the associated prep work can be time consuming and expensive, defeating many of the cost and speed advantages of using 3D printing in the first place. To address this need, some models of Stratasys PolyJet printers allow the creation of models directly from colored resins. With these printers, users can select colors directly in the printer software eliminating the cost and time associated with painting models. This feature is available on all Connex3 printers, as well the new Stratasys J750. Because of the differences architecture of these two product lines, the process for applying color is slightly different for each, with some major improvements being made between the release of the Connex3 platform in 2014 and the release of the Stratasys J750 last year. Objet Connex3 printers have three material bays allowing the user to load up to three different materials simultaneously. Because five materials are necessary to print a 3D model in full color (Yellow, Cyan, Magenta, Black, and White) the first step is for the user to select from one of 14 available color pallets. The first 10 pallets are generated by loading the printer with any 3 of the 5 materials listed above. In each case the user is then able to select one of the 45 individual colors available in the pallet. The remaining 4 pallets are generated by replacing one of the opaque materials with the VeroClear resin. These pallets are also 45 user selectable options, but trade fewer distinct colors for the ability to make those colors transparent.
Once the color pallet has been established for a build, color can be assigned to a part using the material selection dialog box in Objet Studio.
It is also possible to create a single part with multiple colors. This is done by first exporting the part as multiple STL files, and then importing them into Objet Studio with the “assembly” box checked. Once imported, each individual STL file in the assembly can be assigned its own color from the active pallet. While this process is certainly faster and cheaper than painting, the concept of pallets and the need to manually assign colors on a body by body basis do impose some limitations. Only certain combinations of colors can be applied to any given part, and patterns and gradients are essentially impossible. Also assigning more than a small number of colors to the same part is cumbersome and time consuming.
The Stratasys J750 is the latest generation of Polyjet printer from Stratasys and it was designed specifically to address these limitations in the Connex3 architecture. Rather than three material bays the J750 has six. This means that all five necessary materials for printing in full color can be loaded simultaneously and still have one bay available for VeroClear. Rather than selecting one of 45 colors from one of 14 pallets, colors can now be specified using RGB hex values. Additionally with the elimination of pallets, any combination of the over 350,000 colors can be printed together on the same tray at any level of transparency.
Multicolor parts can still be made by the traditional method of importing multiple STL’s, but the J750 software can now also read VRML files in addition to STL’s. Full color models can now be created in programs like Rhino, Blender, or even Photoshop and sent directly to the printer with color data intact. This allows for the printing of patterns, gradients, and other design elements that are difficult if not impossible to create directly in Objet Studio.
Additionally many FEA simulation packages can export results as colored VRML files. Printing analysis results as a colored 3D model can provide a way for engineers to share their work in a way that is far more intuitive and engaging than graphs or static images.
So what about the cost? While it is true that color printing requires companies to keep a larger amount of material on hand, establishing that inventory is a one-time investment. Once a department is up and running, printing with colored resins is only 5% more expensive than using only VeroWhite or VeroBlack. This means that the cost for adding color to a model goes from over $100 per piece for professional painting to a few dollars or less for printing directly in color. Also because the color is applied during printing, it requires no additional time or post processing beyond what is needed for making standard unpainted parts. Depending on utilization, this advantage in terms of speed and part cost can easily make a Connex3 or a J750 printer the most effective and possibly even the most economical option in situations where there is an ongoing need for highly realistic, presentation quality models.