Space Systems Academic Group
Rapid Prototyping / Additive Manufacturing (3D Printer).
The NPS Space Systems Academic Group procured in July 2008 through FISC San Diego a Fortus 400mc (link to Fortus web site where product and materials information can be found) rapid prototyping machine through school funds. The machine employs fused deposition modeling (FDM) for additive manufacturing of three-dimensional parts from computer-aided design (CAD) geometry. This Wiki is intended to provide information for potential users of the machine. The 3D printer is open to the NPS community on a cost-reimbursable basis for appropriate activities, e.g. instructional parts, research, and thesis projects. Interested in producing parts? Contact Dan Sakoda and provide the following information (login to Wiki required to access link).
Information needed with (.stl) job request:
NPS Department or Group:
Research or Instruction:
Material Provided by:
Approx. size (provide units) Length x Width x Height:
How does it work?
CAD models are imported in the stereo lithography (.STL) file format to the printer software. After orienting the part for the build, the software then slices horizontal build planes and creates toolpaths for each slice of the part based on the configuration of the machine and user-selectable parameters. Once print jobs are generated, another software application is used to arrange them on the build area and send them to the machine. In this way, time can be saved by printing a number of parts, as long as they can fit within the envelope of the machine and the build footprint.
The tool path is defined by contour lines that outline the part, and raster, or fill lines. Parts can be made as completely solid, or to save on material and time as a sparse build, where the internal volume is similar to a honeycomb structure. By default, each alternating layer is raster-filled in alternating directions for higher strength. This figure shows the build parameters of a simple block part.
How Do You Remove The Support Material?
There are two kinds of support material: The break-away support system (BASS) and the soluble support system. We generally use the BASS system, as the removal of the soluble support requires immersing the part into an alkaline bath. However, if there are fine features, the soluble support system may be the best solution. Depending on the part and the state of the solution, parts may require a few hours to a day or so to fully remove the support material.
The Break-Away Support System, as the name implies, is a support material that is broken away from the part. The material is a polyphenylene ether / high impact polystyrene blend [from the MSDS]. Appropriate personal protective equipment (PPE) should be worn, i.e., safety glasses and working gloves. The BASS support material can be pulled or broken away using carving tools, dental picks, and pliers. A video posted from Stratasys demonstrates this (Oops! looks like he forgot to wear safety glasses).
What Can Be Printed?
The maximum build volume is 16 x 14 x 16 in. (406 x 356 x 406 mm). Parts which would be difficult (or impossible) to machine can be readily printed as a single part. Some post-printing work may be necessary to remove support material and/or finish the surface properties depending on how the parts are to be used. Since the part is built in the vertical direction, one slice at a time, it may be necessary to have a sacrificial support structure on which to build. Any cantilevered feature would need this, for example. Either a break-away support material or a soluble support material is used. ABS plastic requires a soluble support. Polycarbonate material parts can use either a break-away support or the soluble support. When using a soluble support material, the part is placed in an alkaline bath to melt away the support material. This allows the possibility of fine features. The break-away support system is faster to remove, but small features on the part may break away, as well.
The following figures comprise a gallery of parts printed from the Fortus 400mc 3D Printer (note: not an exhaustive representation of output) The first two figures show the CAD model and the 3D part of a female head printed for MOVES as a part of their studies on tangible 3D virtual humans (Dr. Amela Sadagic). Prototype assemblies can be built from individual parts to verify a working design such as the control moment gyro (CMG) (Mike Ross/Mark Karpenko).
Below, are pictures of follow-on work of the assembled (actual) CMG and a 3D-printed support structure for mounting on a test bed.
The next figures represent working assemblies, such as the MAE Spacecraft Robotics platform (Dr. Marcello Romano) built from a number of 3D-printed parts for the structure and its next-generation version, a Physics Robotics (Dick Harkins) project that utilizes a number of 3D parts for housings, and working parts such as the 'whegs' that propel the platform over terrain and obstacles. Or a wheel with 'Paddle' features bolted together.
2015 Version of Physics robot for littoral experimentation.
Sometimes, a simple bracket is needed to hold an instrument or sensor, such as the figure below with an inertial measurement unit mounted by an RP bracket (1 hour, 11 minutes to build) on a pendulum for a thesis project (Xiaoping Yun, advisor).
NPSAT1 Half-Scale Model Assembly.
An interesting innovative use of 3D-printed parts was done in building laser reflectors to do large-scale modal testing. Here, the large bi-focal mirror in the basement of Halligan Hall is outfitted with a number of reflectors printed on the Fortus 400mc. Some post-printing work was done to yield a good reflective surface.
3D parts were also used in thesis research to validate an optics design for an experimental nano-satellite imaging platform.
A summer intern project was supported with parts printed from the 3D printer to build the frame of a high-altitude balloon (HAB) platform. The platform supports electronics, a battery, a GoPro camera, GPS receiver and beacon.
Below, a clock escapement was put together as an instructional demonstration in the Physics Dept.
Below, is a 3D printed form to support a thin-walled aluminum part for machining. Because of the thin walls and odd shape, it would be difficult to hold the piece for the machining setup and tolerances can be lost due to vibration and bending while the part undergoes its machining / milling process.
Another example of a tooling part that was easily printed for use is shown, below. The part is an adapter between a box wrench and a 1/4-inch drive torque wrench that was needed for some tight work spaces where the torque wrench couldn't reach.
Production of multiple-copies of parts – here's a production run of an array of (7x4=) 28 copies of a part. Note that efficiencies in packing can be gained by creating the full array in CAD and exporting the array as a single (.STL) part for processing, making sure the array fits within the build envelope.
STL File Requirements
If you're using one of the NPS-licensed CAD programs, it's very likely you can export your part geometry into the .STL file format. Here are some settings for the more popular CAD programs. It's best to have your model in English Inch units, but millimeters will work, also. The basic settings for export deal with Angle Tolerance (how much the normals of the surface triangle can deviate from one another), and Deviation (how much the mesh is allowed to deviate from the CAD part).
- File > Save As
- Save as type: STL (*.stl)
- Set the slider on Deviation to about 0.0003 for inch / 0.003 for mm
- Leave the Angle slider alone
- Give it a file name and save to a directory where you have read-write privileges.
Screenshot of SolidWorks (2015) STL Export.
NX 11 (and later)
- File > Export > STL...
- Output Type: (Binary)
- Select the solid body (or bodies) to export
- Provide the path where the .STL file will be saved
- Chordal Tolerance 0.0003 (inch) / 0.003 (mm)
- Angular Tolerance: 10.0 (deg) – this value affects the 'stair-stepping' of curved surfaces; You can use a value as low as 1.0 deg.
Screenshot of NX11 STL Export.
It's always a good idea to try importing your STL file to see that it is what you expect. If your CAD program is a solid modeler, it's good to check that the volume of the CAD part matches the volume of the imported STL file.
Stratasys "Best Practices" PDF document describing some other CAD programs and how to export STL files can be found here. (Note: Login to the ERN is required).
Read this article on the "Top 7 Common Mistakes in Designing Parts for Additive Manufacturing" (from QuickParts).
What Does It Cost?
Approximate cost (part material alone) is about $2.30 per cubic inch. Canisters of material and support come in 92 cubic inch canisters and cost about $200 each (educational pricing), depending on the type of material. Note that some waste is involved with calibration parts and in the normal operation of the machine. In order to build parts, it is requested that part material be purchased. Unfortunately, material can only be purchased per canister. Generally, the SSAG 3D Printer only uses polycarbonate (PC) for the part material, and the 'Break-Away Support System' (BASS) for support material. This removes the need to deal with alkaline baths for dissolving the soluble support. However, if soluble support is required, the Physics Department may allow use of their support removal bath (check for size limitations).
Materials' part numbers are as follows: for the white polycarbonate (PC) (P/N: 310-20100); and its respective Break-Away Support System (BASS) for Fortus 360/400/900mc (P/N: 310-30100).
The following are vendors that I'm aware of that provide consumable materials for the Fortus 400mc:
- Stratsys (http://www.fortus.com/)
- Go-Engineer (http://www.goengineer.com/Products/Fortus)
- Cap-Inc (https://www.capinc.com/capstore/fortusmaterial)
How Do I Dispose of 3D Printer Material?
3D-printed parts can be recycled as recyclable plastic. For specific questions, contact the Environmental Office (x2841).
Does it outgas in a vacuum?
A concern for any material in space or for research is whether they outgas -- will they be a source of contamination. NASA has performed testing to determine the amount of outgassing of various (read many, many) materials in a vacuum. The numbers provided are in TML (percent of total mass loss), CVCM (percent of collected volatile condensable materials) and WVR (percent of water vapor regained). For more information on the NASA outgassing tests, see http://outgassing.nasa.gov. The Stratasys polycarbonate (PC) material was tested and results are favorable for use in space, of course, verification should be done to ensure the specific application is consistent with the NASA test results. Below is the output from the NASA on-line outgassing report (when doing a search on "Stratasys"):