The present invention relates to the fabrication of three-dimensional objects using additive process modeling techniques. More particularly, the invention relates to modeling machines which form three-dimensional objects by depositing modeling material onto a substrate mounted to a modeling platform.
Additive process modeling machines make three-dimensional models by building up a modeling medium, usually in planar layers, based upon design data provided from a computer aided design (CAD) system. A mathematical description of a physical part to be created is split into (usually) planar layers, and those layers are individually shaped and applied to produce the final part. Three-dimensional models are used for functions including aesthetic judgments, proofing the mathematical CAD model, forming hard tooling, studying interference and space allocation, and testing functionality. The dominant application of layered manufacturing in recent years has been for rapid prototyping.
Examples of apparatus and methods for making three-dimensional models by depositing solidifiable modeling material are described in Crump U.S. Pat. No. 5,121,329, Batchelder, et al. U.S. Pat. No. 5,303,141, Crump U.S. Pat. No. 5,340,433, Batchelder, et al. U.S. Pat. No. 5,402,351, Crump et al. U.S. Pat. No. 5,503,785, Abrams et al. U.S. Pat. No. 5,587,913, Danforth, et al. U.S. Pat. No. 5,738,817, Batchelder, et al. U.S. Pat. No. 5,764,521 and Comb et al. U.S. Pat. No. 5,939,008, all of which are assigned to Stratasys, Inc., the assignee of the present invention. An extrusion head extrudes solidifiable modeling material in a fluent strand (also termed a “bead” or “road”) from a nozzle onto a base. The base comprises a modeling substrate which is removably affixed to a modeling platform. The extruded material is deposited layer-by-layer in areas defined from the CAD model, as the extrusion head and the base are moved relative to each other by mechanical means in three dimensions. The finished model is removed from the substrate. A solidifiable material which adheres to the previous layer with an adequate bond upon solidification is used as the modeling material. Thermoplastic materials have been found particularly suitable for these deposition modeling techniques.
Other additive process manufacturing techniques similarly build-up models on a support surface, including depositing UV curable polymers as in Masters U.S. Pat. No. 5,134,569; jetting droplets of material as in Gothait U.S. Pat. No. 6,658,314; extruding a settable plastic in vertical strips as in Valaaara U.S. Pat. No. 4,749,347; laser welding deposition as in Pratt U.S. Pat. No. 5,038,014; stacking and adhering planar elements as in DiMatteo U.S. Pat. No. 3,932,923; and applying shaped layers of paper as in Hull U.S. Pat. No. 5,192,559.
The support surfaces or substrates used in additive process modeling techniques must stabilize a model as it is built and allow removal of the model when it is complete. Typically, it is preferred that a model under construction be strongly adhered to its modeling substrate. Strains generated within the modeling material tend to warp the deposited structures unless the structures are supported in their correct orientation. Strong adherence to the substrate serves to prevent warpage and avoid localized shrinkage in foundation layers. Also, in some deposition processes, there are external forces that act on the deposited structures, such as pull from an extrusion nozzle, and centripetal acceleration on parts that are not stationary. Adherence of the model to the substrate must be sufficient to resist these forces. Delamination of a foundation layer from the substrate during the building of the object can result in a total failure in forming the object.
Further, since the substrate is a defining surface for the object being built, the substrate itself must be held in a well-defined configuration. Typically, the substrate is held in a configuration approximating a plane.
In rapid prototyping systems sold by Stratasys, Inc., a preferred substrate material has been a polymer foam. The porosity and compressibility of foam allows foundation layers of modeling material to be buried into the foam, which increases stability of the model as is it built up. The Crump '329 and '433 patents disclose a foam plastic material for use as a modeling substrate. A blue polystyrene material manufactured by Dow-Corning Corp. under that name and having a compression strength of 30 psi is identified as particularly suitable coarse, porous structure.
The foam substrate has been mounted onto a tray outside of the modeling machine, with spears inserted through side walls of the tray and pressed into the foam to engage the foam from all sides. The tray is then placed on the modeling platform within the modeling machine, and locked into place. After the object is formed, the tray is removed from the modeling machine and the foam is broken away from the object.
More recently, Stratasys® modeling machines have used a foam slab mounting system which eliminates the use of the tray and spears. This slab substrate mounting system is disclosed in Calderon et al. U.S. Pat. No. 6,367,791, also assigned to Stratasys, Inc., which describes that a slab substrate (e.g., foam) is mounted in a modeling machine by sliding it between two parallel rails having knife edges which cut into the sides of the substrate.
The Stratasys® modeling machines have also used a flexible sheet substrate held down on a platform by vacuum forces, as is disclosed in the Comb et al. '008 patent.
The Crump '329 and '433 patents further disclose modeling on a wire mesh sandpaper substrate, and on a water-soluble wax. The Batchelder et al. '521 patent discloses a sheet of magnetic material for use as a modeling substrate, wherein the modeling platform includes a magnet for attracting the sheet.
While foam substrates have found substantial use, the foam materials used in the prior art produce dust when broken away from the object. The presence of dust creates a risk that the dust may contaminate bearings and bushings in the modeling machine. Also, the foam is not reusable, due to foundation layers being buried into the foam. Thin-sheet substrates produce no dust, but have required hold-down systems which add cost, size and weight to the modeling machine.