Selective laser sintering with interleaved fill scan

Details Selective laser sintering with interleaved fill scan Selective laser sintering with interleaved fill scan

2002-07-26

2004-02-17

Paladini, Albert W. (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S118000, C219S121640, C264S497000

Reexamination Certificate

active

06694207

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
This invention is in the field of rapid prototyping, and is more specifically directed to the fabrication of three-dimensional objects by selective laser sintering.
The field of rapid prototyping of parts has, in recent years, made significant improvements in providing high strength, high density, parts for use in the design and pilot production of many useful articles. “Rapid prototyping” generally refers to the manufacture of articles directly from computer-aided-design (CAD) data bases in an automated fashion, rather than by conventional machining of prototype articles according to engineering drawings. As a result, the time required to produce prototype parts from engineering designs has been reduced from several weeks to a matter of a few hours.
By way of background, an example of a rapid prototyping technology is the selective laser sintering process practiced in systems available from 3D Systems, Inc. of Valencia, Calif., in which articles are produced from a laser-fusible powder in layerwise fashion. According to this process, a thin layer of powder is dispensed and then fused, melted, or sintered, by laser energy that is directed to those portions of the powder corresponding to a cross-section of the article. Conventional selective laser sintering systems, such as the SINTERSTATION 2500plus system available from 3D Systems, Inc., position the laser beam by way of galvanometer-driven mirrors that deflect the laser beam. The deflection of the laser beam is controlled, in combination with modulation of the laser itself, to direct laser energy to those locations of the fusible powder layer corresponding to the cross-section of the article to be formed in that layer. The laser may be scanned across the powder in raster fashion, with modulation of the laser effected in combination therewith, or the laser may be directed in vector fashion. In some applications, cross-sections of articles are formed in a powder layer by fusing powder along the outline of the cross-section in vector fashion either before or after a raster scan that “fills” the area within the vector-drawn outline. In any case, after the selective fusing of powder in a given layer, an additional layer of powder is then dispensed, and the process repeated, with fused portions of later layers fusing to fused portions of previous layers (as appropriate for the article), until the article is complete.
Detailed description of the selective laser sintering technology may be found in U.S. Pat. Nos. 4,863,538, 5,132,143, and 4,944,817, all assigned to Board of Regents, The University of Texas System, and in U.S. Pat. No. 4,247,508 assigned to 3D Systems, Inc., all incorporated herein by this reference. Laser power control systems for selective laser sintering systems are described in U.S. Pat. No. 6,085,122, issued Jul. 4, 2000, and in U.S. Pat. No. 6,151,345, issued Nov. 21, 2000, both assigned to 3D Systems, Inc., and also incorporated herein by reference. By way of further background, U.S. Pat. No. 5,352,405, issued Oct. 4, 1994 assigned to 3D Systems, Inc., and incorporated herein by reference, describes a method of scanning the laser across the powder in a selective laser sintering apparatus to provide a uniform time-to-return of the laser for adjacent scans of the same region of powder, thus providing uniform thermal conditions over the cross-section of each of multiple parts within the same build cylinder.
The selective laser sintering technology has enabled the direct manufacture of three-dimensional articles of high resolution and dimensional accuracy from a variety of materials including polystyrene, NYLON, other plastics, and composite materials such as polymer coated metals and ceramics. Polystyrene parts may be used in the generation of tooling by way of the well-known “lost wax” process. In addition, selective laser sintering may be used for the direct fabrication of molds from a CAD database representation of the object to be molded in the fabricated molds; in this case, computer operations will “invert” the CAD database representation of the object to be formed, to directly form the negative molds from the powder.
FIG. 1
illustrates, by way of background, the construction and operation of a conventional selective laser sintering system
100
. As shown in
FIG. 1
, selective laser sintering system
100
includes a chamber
102
(the front doors and top of chamber
102
not shown in
FIG. 1
, for purposes of clarity). Chamber
102
maintains the appropriate temperature and atmospheric composition (typically an inert atmosphere such as nitrogen) for the fabrication of the article.
The powder delivery system in system
100
includes feed piston
114
, controlled by motor
116
to move upwardly and lift a volume of powder into chamber
102
. Two powder pistons
114
may be provided on either side of part piston
106
, for purposes of efficient and flexible powder delivery, as used in the SINTERSTATION 2500 plus system available from 3D Systems, Inc. Part piston
106
is controlled by motor
108
to move downwardly below the floor of chamber
102
by a small amount, for example 0.125 mm, to define the thickness of each layer of powder to be processed. Roller
118
is a counter-rotating roller that translates powder from feed piston
114
to target surface
104
. Target surface
104
, for purposes of the description herein, refers to the top surface of heat-fusible powder (including portions previously sintered, if present) disposed above part piston
106
; the sintered and unsintered powder disposed on part piston
106
will be referred to herein as part bed
107
. Another known powder delivery system feeds powder from above part piston
106
, in front of a delivery apparatus such as a roller or scraper.
In conventional selective laser sintering system
100
of
FIG. 1
, a laser beam is generated by laser
110
, and aimed at target surface
104
by way of scanning system
142
, generally including galvanometer-driven mirrors that deflect the laser beam. The deflection of the laser beam is controlled in combination with modulation of laser
110
itself, to direct laser energy to those locations of the fusible powder layer corresponding to the cross-section of the article to be formed in that layer. Scanning system
142
may scan the laser beam across the powder in a raster-scan fashion, or in vector fashion. Cross-sections of articles are often formed in a powder layer by scanning the laser beam in vector fashion along the outline of the cross-section in combination with a raster scan that “fills” the area within the vector-drawn outline.
Referring now to
FIGS. 2
a
through
2
c
, the relationship of successive fill scans among multiple parts in the same build cylinder, and among successive scanned layers, in conventional selective laser sintering processes will be described.
FIG. 2
a
is a plan schematic view of a portion of a layer of powder at target surface
104
at which cross-sections
152
a
,
154
a
,
156
a
, are being formed in the current layer of powder, for three different parts or objects being fabricated in the build cycle. These cross-sections
152
a
,
154
a
,
156
a
are formed, in this example, by a combination of vector outlining and raster scan fills, as discussed above. As shown in the cross-sectional view of
FIG. 2
c
, vector outline scans
160
define the outer boundaries of each of cross-sections
152
a
,
154
a
,
156
a
, and fill scans
162
fill the interior of each of cross-sections
152
a
,
154
a
,
156
a
in a raster scan manner. The vector outlines
160
are not shown in
FIG. 2
a
(and
FIG. 2
b
), for the sake of clarity.
FIG. 2
b
illustrates, in plan view, the scanning of cross-sections
152
b
,
154
b
,
156
b
in the next layer of powder.
As shown in
FIGS. 2
a
through
2
c
, the rastering of fill scans
162
are carried out in an “x-fast” manner, in which each scan of the laser beam is parallel to the x-axis. Conversely, the “slow” axis in this example is the

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