Ever since I first used a Polyjet 3D printer, I’ve loved its multi-material capabilities. Flexible materials can be difficult to work with in 3D printing, but Polyjet technology not only handles it reliably, but allows the user to designate which parts of a model need to be flexible or rigid. By blending flexible and rigid resins together, a spectrum of Digital Materials can be created ranging from super soft, semi-flexible and rigid yet non-brittle.
So I started a project that takes advantage of Polyjet technology to create an interactive pull-test. This is used as a qualitative way for people to feel the difference in toughness and flexibility amongst Digital Materials.
My first design challenge was making sure the handles of my demo tool were designed to be comfortable, yet utilize the bare minimum of material used to make them. I opted to print the first handle prototype on the F370 FDM 3D printer to make sure the handles were comfortable. Holding the first iteration… it just felt a little too thin, so slight design changes were made and a second model printed which fit the hand much better.
This gave way to the first Polyjet prototype that had both handles, and the flexible test center. After a few people around the office pulled on it and tears started developing, it became obvious that having a set of handles, with replaceable flexible centers, would be beneficial. Even though the Agilus Polyjet material can withstand a fair amount of abuse, it still has its limits. Creating swappable centers adds functionality to the pulling demonstration by allowing centers of different shore values to be used.
This design is mostly composed of revolve functions, the majority of which all stem from a basic sketch. This makes changing the design simple. To create the rubber-like grip sections, short revolve features were created, then patterned around the same axis. One handle and half of the flexible center section were modeled, then mirrored to create the full assembly.
When I’m designing multi-material Polyjet parts, I like to design all bodies within one Part in SOLIDWORKS. This helps to make sure that the parts either stick together as designed, or have the appropriate tolerance, without having to worry about getting those features just right in an Assembly. I’ve outlined the process below on going from a SOLIDWORKS design in one Part, to a multi-material print on the Objet Polyjet printer.
Right click on “Solid Bodies” in the feature panel, and select “save bodies”.
Click the button labeled “Auto-assign Names”, followed by the “Browse” button under the “Create Assembly” section. This creates a SolidWorks Assembly of parts from the different bodies, and maintains their alignment. I recommend placing all of these files in a single folder.
The newly-created Assembly should open automatically. Select “File>Save As”, and select STL. Under “options”, make sure the box next to “Save all components of an assembly as a single file” is unchecked.
In Objet Studio, select “Import”, and select every file associated with the Assembly. Check the box next to “Import as Assembly”, so that the position of each STL will be preserved.
The specific body can then be selected by clicking on it on the tray, or selecting it in the object tree. A material can be assigned to it using the toolbar at the top of the application.
Polyjet 3D printing technology allows designers to combine flexible and rigid materials like never before. In the context of this project, I used those capabilities to create a pulling rig so that people looking into adopting Polyjet technology in their design process can feel the quality and capabilities of the materials. As a designer and engineer, it’s a good day any time I have an excuse to leverage the Objet’s capabilities.
