The five components of the key instrument are made by electron beam melting, which can transmit hollow box beams and thin walls. But 3D printing is only the first step.
The instrument used in the artist’s rendering is PIXL, an X-ray petrochemical device that can analyze rock samples on Mars. Source of this image and above: NASA / JPL-Caltech
On February 18, when the “Perseverance” rover landed on Mars, it will carry nearly ten metal 3D printed parts. Five of these parts will be found in equipment critical to the rover mission: the X-ray Petrochemical Planetary Instrument or PIXL. PIXL, installed at the end of the cantilever of the rover, will analyze rock and soil samples on the surface of the Red Planet to help assess the life potential there.
PIXL’s 3D printed parts include its front cover and back cover, mounting frame, X-ray table and table support. At first glance, they look like relatively simple parts, some thin-walled housing parts and brackets, they may be made of formed sheet metal. However, it turns out that the strict requirements of this instrument (and the rover in general) match the number of post-processing steps in additive manufacturing (AM).
When engineers at NASA’s Jet Propulsion Laboratory (JPL) designed PIXL, they didn’t set out to make parts suitable for 3D printing. Instead, they adhere to a strict “budget” while fully focusing on functionality and developing tools that can accomplish this task. The assigned weight of PIXL is only 16 pounds; exceeding this budget will cause the device or other experiments to “jump” from the rover.
Although the parts look simple, this weight limitation should be taken into consideration when designing. The X-ray workbench, support frame and mounting frame all adopt a hollow box beam structure to avoid bearing any additional weight or materials, and the wall of the shell cover is thin and the outline more closely encloses the instrument.
PIXL’s five 3D printed parts look like simple bracket and housing components, but strict batch budgets require these parts to have very thin walls and hollow box beam structures, which eliminates the conventional manufacturing process used to manufacture them . Image source: Carpenter Additives
In order to manufacture lightweight and durable housing components, NASA turned to Carpenter Additive, a provider of metal powder and 3D printing production services. Since there is little room for changing or modifying the design of these lightweight parts, Carpenter Additive chose electron beam melting (EBM) as the best manufacturing method. This metal 3D printing process can produce hollow box beams, thin walls and other features required by NASA’s design. However, 3D printing is only the first step in the production process.
Electron beam melting is a powder melting process that uses electron beam as an energy source to selectively fuse metal powders together. The entire machine is preheated, the printing process is carried out at these elevated temperatures, the parts are essentially heat-treated when the parts are printed, and the surrounding powder is semi-sintered.
Compared with similar direct metal laser sintering (DMLS) processes, EBM can produce rougher surface finishes and thicker features, but its advantages are also that it reduces the need for support structures and avoids the need for laser-based processes. Thermal stresses that may be problematic. PIXL parts come out of the EBM process, are slightly larger in size, have rough surfaces, and trap powdery cakes in the hollow geometry.
Electron beam melting (EBM) can provide complex forms of PIXL parts, but to complete them, a series of post-processing steps must be performed. Image source: Carpenter Additives
As mentioned above, in order to achieve the final size, surface finish and weight of PIXL components, a series of post-processing steps must be performed. Both mechanical and chemical methods are used to remove residual powder and smooth the surface. The inspection between each process step ensures the quality of the entire process. The final composition is only 22 grams higher than the total budget, which is still within the allowable range.
For more detailed information on how these parts are manufactured (including the scale factors involved in 3D printing, the design of temporary and permanent support structures, and details on powder removal), please refer to this case study and watch the latest episode of The Cool Parts Show To understand why, for 3D printing, this is an unusual production story.
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Post time: Feb-27-2021