Rapid prototyping describes various techniques for fabricating a three-dimensional prototype of an object from a computer model of the object. One technique is three-dimensional printing, whereby a printer is used to fabricate the 3-D prototype from a plurality of two-dimensional layers. In particular, a digital representation of a 3-D object is stored in a computer memory. Computer software sections the representation of the object into a plurality of distinct 2-D layers. Alternatively, a stream (sequential series) of instructions for each incremental layer maybe entered directly, e.g. a series of images. A 3-D printer then fabricates a thin layer of bound material for each 2-D image layer sectioned by the software. Together, the layers are printed one on top of the other and adhere to each other to form the desired prototype.
Three-dimensional powder-liquid printing technology has been used to prepare articles such as pharmaceutical dosage forms, mechanical prototypes and concept models, molds for casting mechanical parts, bone growth promoting implants, electronic circuit boards, scaffolds for tissue engineering, responsive biomedical composites, tissue growth promoting implants, dental restorations, jewelry, fluid filters and other such articles.
Three-dimensional printing is a solid freeform fabrication technique/rapid-prototyping technique in which thin layers of powder are spread onto a surface and selected regions of the powder are bound together by the controlled deposition (“printing”) of a fluid. This basic operation is repeated layer-by-layer, with each new layer formed on top of and adhered to the previously printed layer, to eventually make three-dimensional objects within a bed of unbound powder. When the printed objects have sufficient cohesion, they may be separated from the unbound powder.
Systems and equipment assemblies for three-dimensional printing of articles are commercially available or in use by others: Massachusetts Institute of Technology Three-Dimensional Printing Laboratory (Cambridge, Mass.), Z Corporation's 3DP and HD3DP™ systems (Burlington, Mass.), The Ex One Company, L.L.C. (Irwin, Pa.), Soligen (Northridge, Calif.), Specific Surface Corporation (Franklin, Mass.), TDK Corporation (Chiba-ken, Japan), Therics L.L.C. (Akron, Ohio, now a part of Integra Lifesciences), Phoenix Analysis & Design Technologies (Tempe, Ariz.), Stratasys, Inc.'s Dimension™ system (Eden Prairie, Minn.), Objet Geometries (Billerica, Mass. or Rehovot, Israel), Xpress3D (Minneapolis, Minn.), and 3D Systems' Invision™ system (Valencia, Calif.).
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Three-dimensional printing systems that employ radial or polar coordinate-based printing systems are disadvantageous because having each jetting position located at a different radial position requires that the surface speed of the substrate underneath the each jetting position will vary. The surface speed will be greatest for the jetting position furthest from the center of rotation. This can be compensated for by normalizing the print density across all jetting positions by either adjusting the input images or possibly the drive frequency. However, these methods of compensation simply cause objects printed radially to emulate each other as opposed to true replicates. The angle of entry of the droplets into the powder bed will also vary with radial position again creating subtle differences in the objects printed at different locations. Alignment and interleaving of multiple print heads is another disadvantage to radially printing. Although feasible it is more complex than for Cartesian systems.
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