Hi all,
Lately there has been a lot of buzz about the metal print material that Shapeways has been offering. There seems to be some confusion about what this stuff is and how it is printed. I have been working as a consultant, helping to develop finishing and coloring procedures for this material and I would like to help the community understand this remarkable process and material. So here are a few basics.
1. THE PRINT PROCESS:
The
printer first spreads a thin (.1mm) layer of stainless steel powder onto a
build platform. An industrial print head then dispenses a liquid binder onto the first layer of metal powder. The print head moves along the X and Y axis just like an inkjet printer to describe whatever you want printed. One thin layer at a time. Once the first layer is printed the build platform moves downward (Z axis) one increment and another layer of powdered metal is spread on top of the first. There is a frame (build box)around the build platform so the unbound powder does not spill off the platform. This process is repeated until the entire object is consolidated. It takes about 10 hours for every 1" of build height! The excess (unbound powder) is now removed leaving a relatively fragile mass of powdered stainless held together with binder, think of this as
green, unfired ceramic. At this point the object is only about 60% in density.
2. INTO THE FURNACE:
The next step involves a cycle through a
controlled atmosphere furnace. The green print is now placed into the furnace along with a quantity of bronze powder. As the temperature rises the binders begin to vaporize. Then the bronze material begins to melt and is wicked up into the stainless mass. The temperature continues to rise to the point at which the particles of stainless fuse together (sintering). The hot mass is now approximately 85% in density. The furnace now begins it's return to room temperature. This cycle takes about 18 hours.
3. FINISHING THE GOODS
If the Gods have been smiling you now have a wonderful pile of new prints. At this stage the prints have a clean but rough surface. Print lines are obvious and the texture is unpleasant to the touch. Several options are available for surface conditioning. Just about any method employed in the metals industry can and will work. However, this metal material really is different than any others. It is a true composite of two dissimilar metals. The stainless component is quite hard. The bronze component is soft and gummy. The material is quite strong but somewhat brittle. It is much like malleable cast iron in terms of strength. Thin parts will bend a little before they snap. The good news is that it can be silver soldered with a gas torch. For removing and blending contour lines a rotary hand piece with carbide and diamond burs work best for rapid cut down. It can be milled, drilled or tapped but carbide tooling is a must. This composite is hard and abrasive stuff! It is possible to get a mirror finish but it takes a LOT of time. Small parts without a lot of surface detail or thin projecting sections can be finished in high energy centrifugal tumblers. The "Ring Poems" and "Cufflinks" are finished this way. Because this material is so hard,
vibratory type finishing equipment does little more that brightening. Vibes will not remove print lines! Once you get the surface conditioned, objects can be left as is or additional coloring procedures can be carried out. Certain chemical solutions will produce nice
patina finishes. Shades of brown and black are possible. However, blues and greens are almost impossible because the chemicals that color the bronze component will also corrode (rust) the stainless component. NOT pretty! I can't tell you how many tests I've run trying for a nice green patina. Although Shapeways is not offering it......... yet, the composite can be electroplated with gold or nickel.
Hope this sheds a little light on the subject. I know this material is expensive. But it really does require a whole lot more than printing with plastics. And hey, it's METAL! Unless you want to do it yourself, I think you will find that having a short run or one of a kind object cast commercially would be no less costly (probably more). The folks who make this metal printing possible are truly 21st century alchemists.