Selective laser sintering with optimized raster scan direction

Details Selective laser sintering with optimized raster scan direction Selective laser sintering with optimized raster scan direction

2002-07-26

2004-01-13

Evans, Geoffrey S. (Department: 1725)

Electric heating

Metal heating

By arc

C219S121800, C700S119000, C700S166000

Reexamination Certificate

active

06677554

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 relatively new field of rapid prototyping has provided significant improvements in providing high strength, high density, parts useful for design verification and in pilot production. “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 at those portions of the powder layer that correspond to a cross-section of the article in that layer. 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, 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, the next layer of powder is then dispensed, and the process is repeated, with fused portions of later layers fusing to fused portions of previous layers (as appropriate for the article), until the article is complete.
More detailed descriptions of the selective laser sintering technology are provided by U.S. Pat. No. 4,863,538, U.S. Pat. No. 5,132,143, and U.S. Pat. No. 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 “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 which are 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
, which is controlled by motor
116
to move upwardly and lift a volume of powder into chamber
102
. Two feed 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 2500plus 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 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.
FIG. 2
illustrates a portion of target surface
104
at which four cross-sections
50
of one or more articles are being formed in a top layer of powder according to a conventional selective laser sintering method. In this example, cross-sections
50
are equally-sized rectangles, but at different angular orientations from one another relative to the x-y plane of target surface
104
. As shown in
FIG. 2
, each of these cross-sections
50
are formed by raster scans of the laser beam across the powder of target surface
104
, along scan lines
62
. Also as shown in
FIG. 2
, each of the scan lines
62
are parallel to the x-axis in the coordinate system of target surface
104
; as such, the x-axis is the “fast” scan axis for the raster scan of the laser beam, while the y-axis is the “slow” axis as it is the direction in which the raster scans advance upon completion of each scan.
According to the conventional technique illustrated in
FIG. 2
, the number of uniformly spaced raster scan lines
62
required to form a given cross-section
50
depends upon the orientation of the cross-section
50
in the x-y coordinate plane of target surface
104
. In this example, four scan lines
62
are required to scan horizontally-oriented cross-section
50
a
. Eighteen and fifteen scan lines are required for angularly oriented cross-section
50
c
and
50
b
, respectively. Vertically oriented cross-section
50
d
requires thirteen scan lines
62
. The spacing of scan lines
62
is s

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