Layer manufacturing using deposition of fused droplets

Details Layer manufacturing using deposition of fused droplets Layer manufacturing using deposition of fused droplets

1999-07-22

2002-06-04

Patel, Ramesh (Department: 2121)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S098000, C700S119000, C700S120000, C700S163000, C264S401000, C264S512000, C264S516000, C427S466000, C427S470000, C427S472000, C204S192150, C204S192200, C204S298120

Reexamination Certificate

active

06401001

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to a computer-controlled object-building system and, in particular, to an improved layer manufacturing system for building a three-dimensional object such as a model, molding tool, microelectronic device and micro-electromechanical system (MEMS) using the deposition of fused droplets.
BACKGROUND OF THE INVENTION
Solid freeform fabrication (SFF) or layer manufacturing is a new rapid prototyping and manufacturing technology. In its most commonly used approach, a SFF system builds an object layer by layer or point by point under the control of a computer. The process begins with creating a Computer Aided Design (CAD) file to represent the geometry of a desired object. This CAD file is converted to a suitable format, e.g. stereo lithography (.STL) format, and 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 vectors or 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.
The SFF technology has found a broad range 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. Although most of the prior-art SFF techniques are capable of making 3-D form models on a macroscopic scale, few are able to directly produce a microelectronic device or micro-electromechanical system (MEMS) that contains micron- or nano-scale functional elements.
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. Patents related to the BPM technology can also be found in U.S. Pat. No. 5,216,616 (June 1993 to Masters), U.S. Pat. No. 5,555,176 (September 1996, Menhennett, et al.), and U.S. Pat. No. 5,257,657 (November 1993 to Gore). Sanders Prototype, Inc. (Merrimack, N.H.) provides inkjet print-head technology for making plastic or wax models. Multiple-inkjet based rapid prototyping systems for making wax or plastic models are available from 3D Systems, Inc. (Valencia, Calif.). Model making from curable resins using an inkjet print-head is disclosed by Yamane, et al. (U.S. Pat. No. 5,059,266, October 1991 and U.S. Pat. No. 5,140,937, August 1992) and by Helinski (U.S. Pat. No. 5,136,515, August 1992). 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 100 &mgr;m, but could go down to 13 &mgr;m. This implies that inkjet printing offers a part accuracy on the order of 13 &mgr;m or worse which, for the most part, is not adequate for the fabrication of microelectronic devices.
Methods that involve deposition of metal parts from a steam of liquid metal droplets are disclosed in Orme, et al (U.S. Pat. Nos. 5,171,360; 5,226,948; 5,259,593; 5,340,090) and in Sterett, et al. (U.S. Pat. Nos. 5,617,911; 5,669,433; 5,718,951; 5,746,844). The method of Orme, et al involves directing a stream of a liquid material onto a collector of the shape of the desired product. A time dependent modulated disturbance is applied to the stream to produce a liquid droplet stream with the droplets impinging upon the collector and solidifying into a unitary shape. The method of Sterett, et al entails providing a supply of liquid metal droplets with each droplet being endowed with a positive or negative charge. The steam of liquid droplets is focused by passing these charged droplets through an alignment means, e.g., an electric field, to deposit on a target in a predetermined pattern.
The above-cited prior art droplet deposition methods suffer from the following drawbacks:
(1) Inkjet print-head based systems have been largely limited to ejection and deposition of polymer droplets with very low melting temperature (Tm) or glass transition temperature (Tg) such as wax, high impact polystyrene (HIPS), and acrylonitrile-butadiene-styrene copolymer (ABS). These materials can only be used to make models for form and fit, but not functional parts. Even with these low melting materials, the droplet sizes have been known to be larger than 13 &mgr;m (normally 50 &mgr;m or larger). When being jetted through an inkjet orifice, the liquid droplets could not go down to a few microns or sub-micron in scale due to the strong viscosity and surface tension effects.
(2) The ejection of metallic or ceramic liquid droplets is expected to be difficult due to the high melting temperatures of these materials. The piezoelectric elements such as lead-zirconate-titanate (PZT) commonly used as an actuator to drive and expel liquid droplets are known to have limited working temperature ranges. They are not particularly suitable for use in a high temperature environment conducive to ejection of metallic or ceramic liquid droplets.
(3) The methods proposed by Orme, et al (e.g., U.S. Pat. No. 5,171,360) and by Sterett, et al. (e.g., U.S. Pat. No. 5,617,911) require a continuous supply of liquid metal droplets. The raw metallic material, normally in bulk quantity in the melt state, has to be maintained in a high temperature for an extended period of time, thereby subject to oxidation. Further, since the supply of liquid droplets is essentially continuous rather than drop-on-demand, it is difficult to prevent droplets from reaching “negative” regions (which are not portions of a cross-section of the object). A mask will have to be used to collect these un-desired droplets. In both cases, the metal droplets arc on the micron scale or larger.
(4) Similarly, in any layer manufacturing method that involves thermal spray (e.g., U.S. Pat. No. 5,301,863), a mask has to be used to screen out undesired droplets.
In U.S. Pat. No. 5,301,863 issued on Apr. 12, 1994, Prinz and Weiss disclose a Shape Deposition Manufacturing (SDM) system. The system contains a material deposition station and a plurality of processing stations (for mask making, heat treating, packaging, complementary material deposition, shot peening, cleaning, shaping, sand-blasting, and inspection). Each processing station performs a separate function such that when the functions are performed in series, a layer of an object is produced and is prepared for the deposition of the next layer. This system requires an article transfer apparatus, a robot arm, to repetitively move the object-supporting platform and any layers formed thereon out of the deposition station into one or more of the processing stations before returning to the deposition station for building the next layer. These additional operations in the processing stations tend to shift the relative position of the object with respect to the object platform. Further, the transfer apparatus may not precisely bring the object to its exact previous position. Hence, the subsequent layer may be deposited on an incorrect spot, thereby compromising part accuracy. The more processing stations that the growing object has to go through, the higher the chances are for the part accuracy to be lost. Such a complex and complicated process necessarily makes the over-all fabrication equipment bulky, heavy, expensive, and difficult to maintain. The equipment also requires attended operation.
The selected laser sintering or SLS technique (e.g., U.S. Pat. No. 4,863,538 issued in September 1989 to Deckard and U.S. Pat. No. 4,94

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