Electric heating – Metal heating – By arc
Reexamination Certificate
2002-09-09
2004-04-06
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121650
Reexamination Certificate
active
06717106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser sintering apparatus, and particularly to a laser sintering apparatus for forming a three-dimensional model comprising a powder sintered body obtained by exposing a powdered body with a continuously-driven or pulse-driven laser beam in a predetermined-wavelength region that includes ultraviolet and sintering the powdered body.
2. Description of the Related Art
As three-dimensional CAD (Computer Aided Design) systems have recently spread, rapid prototyping systems for forming three-dimensional models in accordance with three-dimensional CAD data generated in virtual space within computers have been used.
Among rapid prototyping systems, an optical forming system was developed and spread in the beginning. In the case of the optical forming system, a three-dimensional model is formed by slicing CAD data at predetermined intervals on a computer to generate a plurality of sets of cross-sectional data, scanning the surface of a liquid photo-curable resin with a laser beam in accordance with the sets of cross-sectional data to cure the resin into layers, and successively laminating the layers of cured resin. As an optical forming method, a free-liquid-level method is widely known in which liquid photo-curable resin is stored in an open-top vessel and layers of cured resin are laminated while a forming table, disposed near the surface of the liquid photo-curable resin, is caused to successively sink from the surface of the resin.
Conventionally, optical forming apparatuses used in the optical forming system have included an apparatus for performing scanning with a laser plotter system and an apparatus for performing scanning with a movable mirror system, as described in an issue titled, Maruya, Yoji. 1992. Hikari zokei shisutemu no kiso, genjou, mondaiten. (Foundation, status quo, and issues in optical molding systems technology.) Kata Gijutsu (Die and Mold Technology)7, no.10:18-23.
FIG. 18
shows an optical forming apparatus according to the laser plotter system. In this apparatus, a laser beam emitted from a laser beam source
250
reaches an XY plotter
256
through an optical fiber
254
provided with a shutter
252
and is irradiated to a surface
266
of a liquid photo-curable resin
262
in a vessel
260
from the XY plotter
256
. Furthermore, X- and Y-directional positions of the XY plotter
256
are controlled by a XY-positioning mechanism
258
provided with an X-positioning mechanism
258
a
and a Y-positioning mechanism
258
b
. Therefore, it is possible to cure the photo-curable resin
262
at predetermined positions of the surface
266
by turning a laser beam, irradiated from the XY plotter
256
, on and off using the shutter
252
while moving the XY plotter
256
in the X and Y directions.
However, a forming apparatus according to the laser plotter system has a problem in that a shutter speed and a plotter moving speed are limited, and forming requires a long time.
FIG. 19
shows an optical forming apparatus according to the movable mirror system using a conventional galvanometer mirror. In this apparatus, a laser beam
270
is reflected from an X-axis rotation mirror
272
and a Y-axis rotation mirror
274
and irradiated to the photo-curable resin
262
. The X-axis rotation mirror
272
controls an X-directional irradiation position by rotating about a Z-axis and the Y-axis rotation mirror
274
controls a Y-directional irradiation position by rotating about the X-axis. In the case of the movable mirror system, it is possible to increase a scanning speed compared to the case of the layer plotter system.
However, even in the case of the optical forming apparatus according to the movable mirror system, it takes 8 to 24 hours to form a three dimensional model of about 10 cm
3
, even when performing high-speed scanning at a rate of, for example, 2 to 12 m/s, because scanning is performed with a very small laser spot. Therefore, forming requires a long time. Moreover, the irradiation region of the laser beam
270
is limited because the laser beam
270
is reflected only when it is incident upon the Y-axis rotation mirror
274
at an angle within a predetermined range. Further, when the Y-axis rotation mirror
274
is disposed at a high position further away from the photo-curable resin
262
in order to widen an irradiation region, problems occur in that the diameter of a laser spot increases and, positioning accuracy and forming accuracy are thereby deteriorated. Positioning accuracy is also deteriorated if a rotation angle of the Y-axis rotation mirror
274
is increased, and the number of pincushion errors increases even though an irradiation range is increased. Moreover, an optical forming apparatus using a galvanometer mirror has problems in that adjustment of an optical system, such as adjustment of an optical axis and correction of distortion, is complex and a size of the apparatus is increased because the optical system thereof is complex.
Furthermore, regardless of the system used in an optical forming apparatus, a high-output ultraviolet laser-beam source is used as a laser-beam source, and a gas laser, such as an argon laser, has generally been used so far. Maintenance of gas lasers, however, such as injection of gas, is troublesome, and moreover, gas lasers are expensive. Therefore, when a gas laser is used, the price of an optical forming apparatus is raised, and the apparatus is increased in size because accessories including a cooling chiller are necessary. In view of this problem, Japanese Patent Application Laid-open (JP-A) No. 11-138645 discloses an optical forming apparatus provided with a plurality of light sources, each capable of irradiating an exposure region with a spot larger than a single pixel in order to conduct multiple exposure of pixels using the plurality of light sources. This apparatus can use inexpensive light-emitting diodes (LED) as the light sources because multiple exposure of pixels is carried out by the plurality of light sources, and it is unnecessary to use light sources that each have a large output.
The optical forming apparatus disclosed in JP-A No. 11-138645 has problems in that it cannot be used for highly detailed forming because the spot size of each light source is larger than a single pixel, many unnecessary operations are performed because multiple exposure of pixels is carried out with the plurality of light sources, and forming requires a long time. Also, the optical forming apparatus has problems in that a size of an exposure portion is increased due to increasing the number of the light sources. Moreover, even when multiple exposure of pixels is carried out with the luminous energy outputted by the LEDs, there is a possibility that sufficient resolution may not be obtained.
A powder laser sintering apparatus, developed subsequent to optical forming apparatuses that use a photo-curable resin, is known among rapid prototyping systems, which are widely used at present. The powder laser sintering apparatus scans the surface of a powdered body with a laser beam in accordance with cross-sectional data of a three-dimensional model generated on a computer. Processing for curing the powdered body, including gradually melting and sintering the powdered body by scanning with laser light, is repeated. A three-dimensional model made of a laminated powdered sintered body is then formed due to the repetition of the processing.
The powder laser sintering apparatus has advantages in that various materials can be selected and it can directly manufacture not only function-evaluation models of superior toughness and precise cast patterns and dies, but also metallic molds and metallic parts, and it has a wide range of applications. Moreover, the laser sintering apparatus is less expensive than an optical forming apparatus and has a high forming speed. Therefore, its use for confirmation of design models is becoming more and more entrenched. However, because the powder laser sintering apparatus also uses a movable mirror system, such as a g
Nagano Kazuhiko
Okazaki Yoji
Elve M. Alexandra
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
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