Layer manufacturing apparatus and process

Details Layer manufacturing apparatus and process Layer manufacturing apparatus and process

1999-04-29

2002-06-04

Patel, Ramesh (Department: 2121)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S118000, C700S098000, C700S120000, C700S163000, C264S401000, C264S512000, C264S516000, C427S466000, C427S470000, C427S472000, C204S192150, C204S192200, C204S298120

Reexamination Certificate

active

06401002

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to a computer-controlled object-building process and apparatus and, in particular, to an improved process and apparatus for building a three-dimensional object in a layer-by-layer fashion.
BACKGROUND OF THE INVENTION
Solid freeform fabrication (SFF) or layer manufacturing is a new rapid prototyping technology that builds an object layer by layer or point by point. This process begins with creating a Computer Aided Design (CAD) file to represent the image or drawing of a desired object. As a common practice, this CAD file is converted to a stereo lithography (.STL) format in which the exterior and interior surfaces of the object is approximated by a large number of triangular facets that are connected in a vertex-to-vertex manner. A triangular facet is represented by three vertex points each having three coordinate points: (x
1
,y
1
,z
1
,), (x
2
,y
2
,z
2
), and (x
3
,y
3
,z
3
). A perpendicular unit vector (i,j,k) is also attached to each triangular facet to represent its normal for helping to differentiate between an exterior and an interior surface. This object image file is further sliced into a large number of thin layers with the contours of each layer being defined by a plurality of line segments connected to form polylines. The layer data are converted to tool path data normally in terms of computer numerical control (CNC) codes such as G-codes and M-codes. These codes are then utilized to drive a fabrication tool for building an object layer by layer.
This SFF technology enables direct translation of the CAD image data into a three-dimensional (3-D) object. The technology has enjoyed a broad array of applications such as verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, reducing or eliminating engineering changes in production, and providing small production runs.
A commercially available system, fused deposition modeling (FDM) from Stratasys, Inc. (Minneapolis, Minn.), operates by employing a heated nozzle to melt and extrude out a nylon wire or wax rod. The starting material is in the form of a rod or filament that is driven by a motor and associated rollers to move like a piston. The front end, near a nozzle tip, of this piston is heated to become melted; the rear end or solid portion of this piston pushes the melted portion forward to exit through the nozzle tip. The nozzle is translated under the control of a computer system in accordance with previously sliced CAD data. The FDM technique was first disclosed in U.S. Pat. No. 5,121,329 (1992), entitled “Apparatus and Method for Creating Three-Dimensional Objects,” issued to S. S. Crump. A more recent patent (U.S. Pat. No. 5,738,817, April 1998, to Danforth, et al.) reveals a fused deposition process for forming 3-D solid objects from a mixture of a particulate composition dispersed in a binder. The binder is later burned off with the remaining particulate composition densified by re-impregnation or high-temperature sintering. Other melt extrusion-type processes include those disclosed in Valavaara (U.S. Pat. No. 4,749,347, June 1988), Masters (U.S. Pat. No. 5,134,569, July 1992), and Batchelder, et al. (U.S. Pat. No. 5,402,351, 1995 and U.S. Pat. No. 5,303,141, 1994). These melt extrusion based deposition systems are known to provide a relatively poor part accuracy. For instance, a typical FDM system provides an extruded strand of 250 to 500 &mgr;m, although a layer accuracy as low as 125 &mgr;m is achievable. The accuracy of a melt extrusion rapid prototyping system is limited by the orifice size of the extrusion nozzle, which cannot be smaller than approximately 125 &mgr;m in real practice. Otherwise, there would be excessively high flow resistance in an ultra-fine capillary channel. Such a system, however, can provide a relatively fast deposition rate provided a larger-diameter nozzle orifice is utilized.
In U.S. Pat. No. 4,665,492, issued May 12, 1987, Masters teaches part fabrication by spraying liquid resin droplets, a process commonly referred to as Ballistic Particle Modeling (BPM). The BPM process includes heating a supply of thermoplastic resin to above its melting point and pumping the liquid resin to a nozzle, which ejects small liquid droplets from different directions to deposit on a substrate. Sanders Prototype, Inc. (Merrimack, N.H.) provides inkjet print-head technology for model making. Multiple-inkjet based rapid prototyping systems are available from 3D Systems, Inc. (Valencia, Calif.). Inkjet printing involves ejecting fine polymer or wax droplets from a print-head nozzle that is either thermally activated or piezo-electrically activated. The droplet size typically lies between 30 and 50 &mgr;m, but could go down to 13 &mgr;m. This implies that inkjet printing offers a high part accuracy. However, building an object point-by-point with “points” or droplets as small as 13 &mgr;m could mean a slow build rate.
In a series of U.S. patents (U.S. Pat. No. 5,204,055, April 1993, U.S. Pat. No. 5,340,656, August 1994, U.S. Pat. No. 5,387,380, February 1995, and U.S. Pat. No. 5,490,882, February 1996), Sachs, et al. disclose a 3-D printing technique that involves using an ink jet to spray a computer-defined pattern of liquid binder onto a layer of uniform-composition powder. The binder serves to bond together those powder particles on those areas defined by this pattern. Those powder particles in the un-wanted regions remain loose or separated from one another and are removed at the end of the build process. Another layer of powder is spread over the preceding one, and the process is repeated. The “green” part made up of those bonded powder particles is separated from the loose powder when the process is completed. This procedure is followed by binder removal and metal melt impregnation or sintering. Again, ejection of fine liquid droplets to bond a large area of powder particles could mean a long layer-building time.
The selected laser sintering or SLS technique (e.g., U.S. Pat. No. 4,863,538) involves spreading a full-layer of powder particles and uses a computer-controlled, high-power laser to partially melt these particles at desired spots. Commonly used powders include thermoplastic particles or thermoplastic-coated metal and ceramic particles. The procedures are repeated for subsequent layers, one layer at a time, according to the CAD data of the sliced-part geometry. The loose powder particles in each layer are allowed to stay as part of a support structure. The sintering process does not always fully melt the powder, but allows molten material to bridge between particles. Commercially available systems based on SLS are known to have several drawbacks. One problem is that long times are required to heat up and cool down the material chamber after building. In addition, the resulting part has a porous structure and subsequent sintering or infiltration operations are needed to fully consolidate the part.
U.S. Pat. No. 5,555,481, issued on Sep. 10, 1996 to Rock and Gilman, discloses a powder-based layer manufacturing method that is capable of creating parts with spatially controlled material compositions. This technique involves producing parts using two distinct classes of materials. According to this method, a first class material and a second class material are deposited on a surface wherein the first class material forms a three-dimensional shape defined by the interface between the first class material and the second class material. The first class material is unified by subsequent processing such as sintering or fusion-and-solidification, which is followed by removing the second class material from the three-dimensional part made up of first class material. The second class material plays the basic role of serving as a support structure. Upon completion of the deposition procedure for all layers, the green object which has

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