The newly released TPU 92A material from Stratasys for their F123 series 3D printers is a great addition to the FDM family of materials. TPU material is an elastomer, meaning it lets your produce flexible and elastic parts - opening new doors for prototyping with FDM technology. TPU is best suited for applications such as overmolds, seals, hinges, and gripper pads. To print with TPU material, all that’s required is a simple software upgrade, a small component upgrade, and a new swappable TPU print head. To help you get the best results, we’ve got some best practices you should consider.
While it is a great material to use, TPU can be a tricky material to work with at times; it should not be treated the same as traditional thermoplastics. Since TPU is not rigid, it can sometimes be difficult to achieve consistency while the machine pushes and pulls on the material while printing. It may be helpful to think of TPU material flow as having ‘inertia’; it doesn’t start or stop quickly. Whenever your 3D printer must stop material flow in order to transition the location of the tool head, it takes somewhat longer to stop than other materials. Likewise, TPU material will initially have reduced flow when it resumes.
Part Orientation is Important
Longer, uninterrupted cross-sections reduce material flow interruptions as compared to small disconnected or isolated sections. So, when printing with TPU material, it’s best to orient a part to minimize those starts and stops. (How important is orientation to your 3D model? We discussed that here.)
Another tip for reducing the number of defects in your part is to print one piece at a time. The Purge Tower (which is mandatory for TPU) has the effect of priming the tip and wiping the tip, and always prints before anything else. Building one part at a time allows the machine to transfer directly from the purge tower to the part, reducing the opportunity for error. In order to print multiple parts simultaneously, I’ve also personally found that printing one purge tower per part is the best solution. Simply Export a CMB for each part in GrabCAD Print, and then combine the CMBs into one build (alternately, Control Center can also be used to build the combined Pack). This way the tip is always primed and wiped by a sacrificial purge tower in between parts.
Use Insight 3D Printing Software
Insight 3D printing software is Stratasys’ most advanced FDM slicer and is compatible with all Production Stratasys FDM 3D printers. Insight allows much finer control over Toolpath parameters than GrabCAD Print and can be especially useful for TPU material. (Unfamiliar with GrabCAD Print software? Here’s what you should know). Two of the most important settings in Insight are toolpath “Contour Width” and “Linked Contours”.
Linked Contours affects the start/stop point of perimeter toolpaths (i.e., “Contours”). For areas with multiple contours (e.g., any layer in a Sparse-filled part), the default behavior is to extrude the outermost contour, stop flow, move, then extrude the next Contour, etc. When Contours are Linked, material flow doesn’t stop - all the concentric contours are printed as a single extrusion. This reduces interruptions in material flow on each layer, keeping the flow of TPU more consistent.
Contour Width allows the width of toolpaths to be adjusted to better fill each layer. This is especially important in regions with thin walls - if the width of a wall is not an even multiple of the Contour Width, the wall will have a gap in the middle. Note: When previewing the sliced layers of your model, pay attention to any regions that have tight infill or small air gaps between wall contours. Adjusting the toolpath width and the number of contours can remove these gaps and small infills, which will increase the strength and quality of your part. These options can be used in conjunction with Variable Width Remnant Fill to provide better fill in problematic areas.
To locate these Insight settings, follow these simple steps:
- Laugh Insight through GrabCAD Print or a Desktop launcher
- Select your F123 Series printer from the Modeler Setup command, with TPU as the material
- Select Toolpaths > Setup from the main menu on the top of the Insight Application
- On the right side of the screen click the white and black Advanced Toolpath Parameters button
- In the Toolpaths Parameters window check the Link Contours box
- Under the Contours section, adjust the Contour Width field as needed to improve fill in thin wall sections
If you’ve been printing with TPU material for a while, you may notice some buildup on the model tip. This buildup can cause thin strands/hairs to cling to the tip while printing and affect material flow from the tip. I recommend checking for this buildup and removing it before you begin printing as it’s the simplest way to ensure a great looking part.
I hope you find these TPU material best practices handy. If you haven’t already, check out part one. For more information about the Stratasys F123 Series or TPU 3D printing material, contact us.
About the Author
Ryan Henigan is a 3D printing enthusiast and Intern in Fisher Unitech’s 3DP Operations Department. Ryan has been involved in FIRST Robotics for over 15 years as a lead design, pit crew member, and mentor. Ryan is currently studying Mechanical Engineering at Lawrence Technological University.