Thermoplastic is the only material we use at this point in time. It is very versatile however. Combine that with some clever geometry and some solid engineering skills and you have quite an amazing capability in computer controlled manufacturing.
Bulk filler materials would be powders added to thermoplastic to increase its stiffness, toughness, or wear resistance. plaasjaapie has experimented with MarbleDust blended with CAPA: http://reprap.blogspot.com/2006/03/potential-support-material.html
Common filler materials used with thermoplastics include glass fiber and talc.
Cements are slurries that consist of a mixture of powdered solids suspended in a liquid solution of water and various chemical agents. As they are deposited from a syringe or SlurryDepostionHead, the wet filament hardens and bonds to the lower dry cement structure.
See James Low's work on depositing Polycell Fine Surface Polyfiller from a syringe here: http://reprap.blogspot.com/2006/05/support-material-conclusions.html http://reprap.blogspot.com/2006/05/refill-of-syringe.html http://reprap.blogspot.com/2006/05/support-material-extruder.html
Also see VikOlliver's work on a cement extrusion head component (under HighTemperatureMaterials.)
See also Behrokh Khoshnevis's work on using the "contour crafter" - a large robot that moves a slurry head around to print houses and buildings out of portland cement.
Ceramic materials are similar to cements, consistng of a mixture of powdered solids suspended in a liquid such as water and various chemical agents and binders. Traditionally in pottery, the wet clay is shaped, and then allowed to dry. After the liquid is evaporated away, the ceramic is called leather-hard or more commonly, greenware. The greenware is fired in a kiln - this firing sinters the material in the object, fusing the powdered solids into a larger solid mass. This step is referred to as bisque-firing or biscuit-firing. The biscuit wear or bisque may be as much as 15% smaller than the orginal wet clay object. If supports are needed for the wet clay object to prevent slumping or deformation during drying, these supports are usually made from wet clay, as they will shrink at the same rate.
Ceramic materials are also slipcast, where a fluid solution of water and clay particles is poured into a plaster mold. After the object dries and hardens, it is removed from the mould and fired.
Kaolin clay with mixed with class F fly ash is almost as cheap as dirt, and if fired above 1050°C, becomes a strong porcelain. Fly ash particles are normally smaller than 100 micrometers. Kaolin clay drys green very rapidly compared to most clays, though still very slowly compared to what is needed for rapid prototyping.
Ceramic materials are interesting because this way we can reprap scalpels, kitchen knives, and bike sprockets. A ceramic knife or sprocket has to be fired to porcelain temperatures, above 1050°C, which is hotter than typical pottery.
See: Joe Cesarano's work at Sandria Lab: "Robocasting: Joe Cesarano develops breakthrough way of fabricating ceramics"
In Cesarano's method, a two dimensional clay pattern is printed, then powder spread over the entire surface including the clay, then another two dimensional clay pattern is printed. When all layers have been printed, a three dimensional clay object, of clay mixed with powder, is buried in fine powder. It is apt to disintegrate during powder removal.
Possibly the object can be fired, powder and all to produce a less fragile clay object, the powder brushed away, and the ceramic then fired to full temperature.
It may be useful to speak to Mr. Cerarano about his work; perhaps we can reprap a SlurryDepositionHead ...
See: AG Cooper et.al. "Fabrication of high quality ceramic parts using Mold SDM" paper: http://www-rpl.stanford.edu/files/paper/1999/sff1999a.pdf Google Scholar search: http://scholar.google.com/scholar?hl=en&safe=off&q=fabrication+of+ceramic+parts+using+mold+sdm&spell=1
A useful keyword for internet and library searchs is Engineering Ceramics e.g. http://scholar.google.com/scholar?q=engineering%20ceramics&ie=UTF-8&oe=UTF-8&hl=en
We have not yet examined adding microscopic pigment particles to thermoplastic to color the objects we produce. We may end up using a five color print head, CMYKV, for Cyan, Magenta, Yellow, Black, and Virgin (bulk, uncolored material).
Friendly Plastic(TM) is available in a range of colours, and also in a luminous version. Samples ave been acquired...
For an interesting, and (probably not-at-all useful) discussion of pigment, as applied to watercolor paint, see: http://www.handprint.com/HP/WCL/pigmt1.html
See also, via handprint.com:The authoritative source on synthetic organic pigments is 'Industrial organic pigments' by Willy Herbst and Klaus Hunger (Wiley, 1997), billed as "everything there is to know about organic pigments."
ConductiveMaterials can serve as CircuitBoard traces, wiring, antennae, electro magnets, and faraday cages, along with actual electrical components such as capacitors, resistors, and inductors.
Vik Olliver has fabricated a circuit board, mentioned on the blog here: http://reprap.blogspot.com/2005/05/first-successful-silver-paint-circuit.html This consists of a hot glue circuit board, with traces made from conductive silver paint. This work is also documented in the wiki here (###missing link###)
There are two types of conductive material, intrinsically conductive material and conductor filled material.
other conductive materials
Examples of intrinsically conductive material include conductive plastics such as castable Polyacetylene (PA), along with Polyaniline, PEDOT, Polythiophenes, BESB http://en.wikipedia.org/wiki/Conducting_polymers
RepRap researchers are currently experimenting with at least 3 ways to rapid prototype metal parts: A plastic-extruding RepRap can print plastic forms for casting metal; A plastic-extruding RepRap can be slightly modified to melt a few very-low-melting-point metals; A few researchers are working on directly printing steel, titanium, and other high-temperature metals.
There are also the metals that can be printed in a reprap such as Wood's metal, Field's metal, Rose metal, Galinstan, NaK and some alloys of indium and bismuth. Or there's the metal we're most familar with lead or antimony-based electrical solder. http://en.wikipedia.org/wiki/Fusible_alloy
Conductor filled material
Conductor filled material is reprappable material that has a conductive filler added to it. Examples include buckytubes, carbon black, and powdered metal, such as aluminum flakes or stainless steel fibers
See VikOlliver's work on using IcingSugar here: http://reprap.blogspot.com/2005/05/icing-on-cake.html
The main problem with icing sugar is that it takes ages to dry. Hot air does not help - the sugar dissolves in the water and the whiole thing turns to hot syrup.
There has been quite a bit of discussion about reprapping chocolate. This would have to be done extruded from a syringe or by feeding thick rods into an extrusion head. Chocolate's taste and mouthfeel are shaped by its crystal structure - depending how it was melted and fabricated, chocolate can settle into one of six crystals. In more traditional food preparation, processing the chocolate correctly is called "tempering" the chocolate.
"Let's see, icing covers the sweet end of things, we still need salty, crunchy, and greasy extrudates in order to cover the four snack groups, and fabricate proper snack foods." -Brett
Biomedical Researcher Jordan Miller talks about using RepRap for research in Regenerative Medicine. The RepRap technology used to make delicious snack foods may lead to good sugar lattices / scaffolding, a key technology that could save the lives of people currently on liver and kidney transplant waiting lists. "Open Source is a Philosophy, Not a Checkbox" "Why I’m Registered to be an Organ Donor"
We can use materials such as LiquidLatexRubber and RoomTemperatureVulcanizingSilicone to create flexible elements such as gaskets, hinges, and moulds.
PreciousMetalClay (PMC) is a mixture of finely powdered silver or gold, mixed with an organic binding agent. The PMC object is worked similarly to normal clay, and then sintered using a torch or furnace. PMC is sold in small syringes or small envelopes, and is rather more expensive then precious metal sold as ingots or casting grains.
We can reprap jewelry by loading PMC into a syringe in a reprap.
It may also be interesting to fabricate our own metal clay out of say, tin or steel dust and some binders such as gum arabic or shellac and vegetable oil, printing the material, and then firing the resultant extrudate using a torch.
Refractory Materials are materials which do not break down when exposed to high temperatures. These include the high temperatures reached when casting metal. We'll probably use RefractoryMaterials as an investment or a CeramicShell for metal casting.
When a jeweler prepares a small wax model for casting, he or she places the wax in a small cylindrical metal flask and fill the remaining volume with an investment. This investment is basically refractory plaster; it consists of water added to a mixed powder of gypsum, silica flour, and cristobalite, along with small amounts of chemical modifiers and a strengthening agent such as fiberglass. He or she then places the flask in a small furnace to burn out the wax and then pours metal into the hot flask.
When a sculptor prepares a larger wax model for casting , he or she coats it in a 1 to 2 cm layer of CeramicShell. He or she does this by dipping the wax model into a ceramic slurry - a mixture of water, silica flour, and liquefied plastic. This forms a thin wet coating on the model. This wet layer is then dusted with a refractory aggregate - silica or zircon sand. The process is repeated to build up the 1 to 2cm layer. The ceramic shell is then placed in a furnace to burn out the wax, and metal is poured into the hot shell.
Here what we are interested in doing is depositing a CeramicShell from a SlurryDepostionHead as we build up the model out of thermoplastic. We can then remove the object from the reprap, place it in a furnace to burn out the thermoplastic, and pour metal into the ceramic shell.
For another example of high temperature materials, see VikOlliver's work on a cement extrusion head component (under HighTemperatureMaterials.)
There are a number of water-soluble waxes available to experimenters and fabricators. While their compositions are generally secret, they may be based on polyethylene glycol (PEG). PEG is a flexible, non-toxic water-soluble wax-like polymer, used in cosmetics, toothpaste, and Dr. Pepper, along with who-knows-what else.
Please send an email to the user list or post in the forums if you have any other ideas.
-- Main.SebastienBailard - 16 Jun 2006