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ExOne’s ProMetal 3D Printing

One of my favorite types of 3D printing is the 420Stainless/bronze composite from ExOne. It’s a powder-based process that is very similar to the Z-corp (Now owned by 3D Systems) plaster printers. The processes fall under the same 3D printing patent licensed from MIT. An organic binder “glues” the powder together, and a series of carefully developed processing steps burn out the binder and replace the voids in the powder with bronze. This is an odd mix, since these metals are not very similar. You could not weld them, and this is not an alloy, but a mottled mix of about 60% steel and 40% bronze. Here is a close up of a polished ring:

The metal grains vary in size, but they look about about 25-50 microns in diameter. The crevice in the image is a layer boundary. The polishing process removes projecting roughness, but is not aggressive enough to remove depressions. The material and process produce a very nice aged, textured look. There is always a small flat spot on a model where a stem allowed bronze to flow into the part, but they are much more free of defect than raw DMLS parts, and the price is far less. Aside from the pleasing appearance, the material is resistant to oxidation and very strong (about the same as structural steel).

The metal printed Time Keeper, available customized on Shapeways

The mixed bronze gives the metal a slightly warmer hue than regular steel, and depending on some variables in the process, can come out mildly golden in color. I was curious about the composition of the metal, and measured it with an X-ray spectrometer. The elemental composition in the sample I took was:

Iron 45.00%, Copper 40.30%, Chromium 9.97%, Tin 3.58%, Cobalt 0.58%, Manganese 0.31%, Silver 0.17%, Palladium, 0.05%, Nickel 0.02%

Not much nickel, surprisingly. This mixture has a lot of chromium, but not more than typical stainless steel. The lack of nickel interesting to me partly because, apart from being a common component of stainless steel, nickel works well with copper, the main non-ferrous component in the material, so this is the opposite of what I would have guessed. ExOne has a lot of variations on their process, and can do huge parts up to a meter square, weighing hundreds of pounds. Using this material for years, I keep finding more and more good uses for it. Unfortunately this process needs huge vacuum ovens, so we won’t be doing this at home, but the number of installations is increasing, and even Shapeways has plans to purchase their own setup eventually.

The Most Metal Moment in 3D Printing

The Morning Star is an an incarnation of beauty and danger. It is a 3D-printed sculpture of wood and steel, built by myself in collaboration with ExOne. It weighs about 15 pounds. The sphere of points is about 7.5 inches in diameter. It was printed in four pieces, and the chain portion was printed all at once. The craftsmen at ExOne polished up the points and gave it a nice dark patina for an aged look. The handle was CNC cut from mahogany in five radial sections. The base was CNC cut from oak. Both wood sections were finished with natural oils.

The spike ball design, created in Wings3D

The raw printed parts


Attaching the printed chain

Carefully brazing the chain

Polishing the points

Applying the dark patina

Milling the handle

The completed Morning star on its display base

The Morning Star was featured in the art gallery at the Rapid 3D-printing Conference. It got a great response, and I’m proud to say it was the only piece without a “Do Not Touch” sign. In fact, I ensured there was a signing asking for interaction- this is tactile art!

Afterward, I had a concept to have this brutal piece, made of one of the strongest 3D-printed materials, interact with one of the weakest materials- uninfiltrated Zcorp prints made of gypsum powder. Without reinforcing resin, those parts are very fragile and take great care to move without damage. I created a mesh of the Skull from the Visible Human dataset, and shaded reddish brown it with ambient occlusion in Meshlab. This darkened the crevices and made the entire inside dark red. The skull is life-size and took a lot of work to empty the loose powder from the small holes.

From there, I had a plan to modify the greenhouse in my backyard into a Smash House. I credit Whit, my roommate at the time, for the creative name for this structure dedicated to smashing things with a big metal spike ball.

Welcome to the Smash House

The side of the greenhouse was cut away, the bare frame was painted firecracker red, and a platform was built on the side to mount several cameras. I bought a special camera capable of filming up to 1000 frames per second, though it was used in the 240 fps mode to maintain decent resolution. A hinged apparatus was built to support the morning star, and also to mount a first-person view camera. I had a few friends over to assist in setup and filming.

Right before the smash, I spritzed the skull with water to further reduce its strength, increase its weight, and mitigate dust from the impact. The skull was aligned just off-center so more of the face would be visible in the shot. The ball was aligned just above the lower jaw in the hope that it would remain there as the top of the skull was obliterated. It worked perfectly.


The shot could not have gone off any better. The face was pulverized, leaving the broken lower jaw almost where it stood. The skull tilted backward just as the lowest point wedged it against the ground. The point split it right down the center (along the grain direction), and the two halves of the cranium were sent flying in opposite directions. Smash.

The beautiful shots from five different cameras were assembled into a video, shown below.

Morning Star – The Most Metal Moment in 3D Printing

Thanks to ExOne and everyone else who helped me on this project, which may very well be the most Metal moment in 3D printing.

The 3D-printed Bra

Mardell models a 3D printed top with flexible elastomeric cups

3D printing is perfect for creating items perfectly fit for one person. It has already been applied successfully for prosthetic limbs, joint implantsorthopedic implants and inserts, orthotics, orthodontics, hearing aids, and many more advanced medical applications. Now that people with those rarer conditions have been helped, it’s time for 3D printing to move into applications that help the masses. 75–85% of women who wear bras are wearing the wrong size. By combining 3D scanning, custom software, and 3D printing, millions of women can live more comfortably. I am collaborating with two female industrial designers in Brooklyn who are working on just such a project, and I’m working on exploring a variety of other potential problems and solutions. Using scanning to determine size is very easy, but am taking on the much harder problem of matching and creating the desired curvature and structure. On September 21st, I showed an example design at World Maker Faire in New York that featured 3D-printed elastomeric cups. They are perfectly fit to the wearer using 3D scanning. In this case, the natural shape was ideal, and the function was only to support and preserve, with no shaping required. In cases where a sculpting of form is desired, there is an opportunity for benefit, but a fairly complicated geometry problem to achieve the perfect fit and comfort. I’m making good progress, and this project is tied in with others I’m working on, so expect to hear more about it very shortly.

3D Laser-machining of Acrylic

I have been using an Epilog laser cutter in an unconventional way lately, using it’s raster imaging mode to vaporize materials using repeated passes in an attempt to reproduce fine scale shapes from a “displacement map” image (similar to engraving, just much deeper with predictable dimensions). The most noticeable issue is that, at the 40-watt power level of the machine I am using, the acrylic material is not propelled away from the work surface in the way that high-energy lasers can do. With powerful pulse lasers, very fine cuts can be made in even metals, because the material is instantly vaporized and flies away quickly due to the expansion of the gases. This leaves very little debris at the cut, and does not allow time for the heat to propagate to nearby material, localizing the effects only to the intended area.

You can see the main problem here is that the vaporized material cannot be removed from the area quickly enough. Even with an active vapor-curtain to remove smoke, much of the material still ends up condensing back onto the surface, where it interferes with subsequent passes. There is also some non-linearity in the cut depth (the curvature of the ramp), most likely due to the short focal depth of the laser. This can be compensated for by either shifting the platform upward between passes, or by applying a lookup-table to the gradient to normalize the cutting response. There is also some waviness in the depth that appears to be from vibration in the carriage as it scans over the surface.

Here I attempted a laser-machined acrylic box that needs no assembly, only a heating stage to slump the pieces into position. Note that in addition to the miter-cut edges to join the walls, there are also channels cut in the sides to allow a top to slide into place. After the laser does its work, the acrylic  “snow” is cleaned from the piece. It is then flipped over, supported on the inside of the bottom surface, and heated until the walls swing down into position.

Flowing Forms – Experimentation in 3D Printed Wearable Tech

3D printing creates perfectly adapted forms with unlimited complexity. It follows that the ideal applications for it should play on its strengths, where using other approaches would be difficult or impossible. One of the major promises of using 3D printing for wearable designs is that is can reduce or eliminate the extensive labor required for assembly. When it comes to functional apparel that integrates wiring, fluid lines, air-flow, mechanical devices or fasteners, having everything produced at once is a huge advantage. The sections can be produced separately so the printer does not have to be the size of a person. Correctly sized, integrated fittings hold the tubes in place.

Body-conforming mesh topology derived from a 3D scan

Some experiments I have in the works are designed to integrate pathways for air/fluid or wiring, and are designed to do so without a lot of manual modeling. The path of the channel is derived from the 3D geometry of the scanned body, so the tubing lines follow the body curvature exactly. There are also some interesting aesthetic possibilities offered by these new structures, which can become part of the design rather than being tacked on top of it or covered by it. The designs are inherently organic. These first attempts look like internal organs more than something produced by a machine.

Inside surface of the tubing study

There are a lot of possibilities for building functional structures using these techniques. The most accessible and easily applied are for cooling and ventilation applications, but after some successful prototypes, the applications will be extended to channels for EL-wire or fiber optic lighting, then wiring, and finally liquids, which I anticipate to be the most challenging. Current production processes for materials that are appropriate structurally also require some access to remove support material, so some advancement in materials, processes, or both must be developed for practical transfer of liquids.