US20060165546A1

US20060165546A1 - Method and apparatus for manufacturing three-dimensional objects

Info

Publication number: US20060165546A1
Application number: US11/337,079
Authority: US
Inventors: Shigeki Yamada; Hiroyuki Hara
Original assignee: Aisan Industry Co Ltd
Current assignee: Aisan Industry Co Ltd
Priority date: 2005-01-24
Filing date: 2006-01-23
Publication date: 2006-07-27
Also published as: JP2006200030A; DE102006003152A1

Abstract

The present invention teaches a method and an apparatus for manufacturing a three-dimensional object having a smooth outer surface, without any step of removing a surface layer each time a sintered layer is formed so as to manufacture a three-dimensional object consisting of integrally built-up sintered layers. The method may include the steps of: (i) supplying powder particles (10) onto a moving area while heating the powder particles (10) with heat (20) from a high-density energy heat source so as to form a sintered layer (16); and (ii) supplying powder particles 10 onto a moving area on the sintered layer while heating the powder particles (10) with heat (20) from the high-density energy heat source so as to form another sintered layer (18) integrally on the sintered layer (16), wherein the step (ii) is repeated a predetermined number of times.

Description

This application claims priority to Japanese patent application serial number 2005-15483, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field
The present invention relates to a method and an apparatus for manufacturing three-dimensional objects consisting of integrally built-up sintered layers.
2. Description of the Related Art
In order to manufacture three-dimensional objects consisting of integrally built-up sintered layers, Japanese Laid-Open Publication Nos. 2002-115004 and 2003-159755 disclose a rapid prototyping method including the steps of: forming a powder layer of inorganic or organic material on a sintering table; sintering a predetermined portion of the powder layer by irradiating with an optical beam to form a sintered layer; covering the sintered layer with a new powder layer; and repeating the aforementioned steps to form a plurality of sintered layers united together.
According to the aforementioned rapid prototyping method, in which a powder layer is formed and then an optical beam is irradiated on a predetermined portion of the powder layer, unnecessary powder adheres to the sintered and hardened portions because of the heat transferred from the circumference thereof. In this case, the adhered powder forms a low-density surface layer so that the resulting three-dimensional object may not have a smooth and accurate outer surface.
In this respect, Japanese Laid-Open Publication No. 2003-159755 discloses a method including a step of removing the low-density surface layer by a cutting tool or the like each time a predetermined portion of the powder layer is sintered by irradiating with an optical beam to form another sintered layer. However, according to this method, it will be necessary to remove the surface layer each time a sintered layer is formed. This requires additional processing time and costs for the removal step as compared to a method without such a removal step.

SUMMARY OF THE INVENTION

It is one object of the present invention to teach a method and an apparatus for manufacturing a three-dimensional object having a smooth outer surface, without any additional steps of removing a surface layer each time a sintered layer is formed so as to manufacture a three-dimensional object consisting of integrally built-up sintered layers.
According to one aspect of the present teachings, a method for manufacturing a three-dimensional object consisting of a plurality of integrally built-up sintered layers is taught that may include the steps of: (i) supplying powder particles onto a moving area while heating the powder particles with heat irradiated from a high-density energy heat source so as to form a sintered layer;. and (ii) supplying powder particles onto a moving area on the sintered layer while heating the powder particles with heat irradiated from the high-density energy heat source so as to integrally form another sintered layer on the previous sintered layer, wherein the step (ii) is repeated a predetermined number of times. This method makes it possible to manufacture a three-dimensional object having a complex and precise shape in a short time and with reduced costs. The three-dimensional object manufactured by the method of the present invention is applicable, for example, to a mold for injection molding having a complex internal structure, or to a part or its prototype having a complex three-dimensional shape.
The method may include further features: that the powder particles are operably supplied onto the moving area so that the surface region of the three-dimensional object has a higher density than the inside region thereof; that the powder particles for forming the inside region of the three-dimensional object have a larger particle diameter than the powder particles for forming the surface region thereof; that the powder particles for forming the inside region of the three-dimensional object are obtained by granulating the powder particles for forming the surface region thereof; that the powder particles for forming the inside region of the three-dimensional object are metal particles while the powder particles for forming the surface region thereof are metal particles mixed with an organic binder; that a supplying rate for the powder particles for forming the inside region of the three-dimensional object is greater than a supplying rate for the powder particles for forming the surface region thereof; that the high-density energy heat source is a laser; that a supplying rate of the powder particles is adjustable; and that the powder particles are selectable from a group of two or more different types of powder particles.
The term “powder particles” herein refers to powder materials or particles that are sintered by heating. The term “sintering” refers to causing at least a portion of powder particles to be softened or melted by heating so as to integrally adhere to the surrounding powder particles on the softened or melted portion. “Sintering” may be either liquid phase sintering, which causes a portion of powder particles to be melted so as to integrally adhere to the surrounding powder particles, or solid phase sintering, which causes powder particles to integrally adhere by contacting each other without melting. Preferably, the powder particles used in the present invention may integrally adhere to each other through solid phase sintering, which enables a three-dimensional object to be formed having a smoother outer surface and a more accurate shape than through liquid phase sintering. Solid phase sintering also enables a three-dimensional object to be formed in a shorter time, because it requires less heating.
The “powder particles” used in the present invention may include, but are not limited to, metal powder particles of steel or stainless steel such as SUS420 or SUS410L, and ceramic powder particles. It is also possible to use a mixture of the aforementioned powder particles.
A process for preparing such powder particles may include, but is not limited to, an atomization process and a mechanical process such as crushing, grinding, and milling. Preferably, powder particles used in the present invention may be prepared to be spherical and as uniform as possible with respect to particle diameter distribution. For example, powder particles pulverized into fine spherical particles through an atomization process are preferable in the present invention. The average particle diameter may include, but is not limited to, the range generally between 1 μm and 100 μm, and preferably between 10 μm and 50 μm. It should be noted that the “average particle diameter” refers to a representative particle diameter corresponding to a cumulative oversize weight percentage of 50% estimated from a cumulative oversize weight percentage versus particle diameter curve.
The “high-density energy heat source” used in the present invention refers to a heat source for locally heating a supplied powder area. For example, a plasma-transferred arc, a non-transferred plasma arc, a laser, or a mixture of these high-density energy heat sources may be used as the high-density energy heat source. In particular, the laser may include a carbon dioxide laser and a YAG laser. Such a heat source may be appropriately selected according to factors such as the type, the volume, and the particle diameters of the powder particles, and the accuracy requirements for forming the surface of the three-dimensional object. Using such a local heating heat source enables the target powder particles supplied onto a predetermined area to be intensively heated and sintered. Also, it is possible to prevent various defects such as lower forming accuracy and deposition of the powder particles onto the surface portions, otherwise caused by heat transferred to areas other than the desired sintering area.
In particular, the high-density energy heat source may heat powder particles supplied on a predetermined area either concurrently with or immediately subsequent to the supply of the powder particles. Thus, it is possible to intensively heat the target powder particles supplied onto a predetermined area, which results in preventing the heat from transferring to a portion surrounding the target portion to be sintered and hardened. Further, since there exist no extra powder particles surrounding the target portion to be sintered and hardened, it is possible to prevent unnecessary powder particle depositions, which are caused by transferred heat, onto the three-dimensional object to be obtained. As a result, without removing the low-density surface layer by a cutting tool or the like each time a sintered layer is formed, it is possible to manufacture a three-dimensional object having a smooth and accurate outer surface.
According to another aspect of the present invention, an apparatus is taught for manufacturing a three-dimensional object consisting of a plurality of integrally built-up sintered layers that may include: a powder particle supplying device for supplying powder particles at a adjustable supplying rate; a high-density energy heat source for heating the powder particles supplied by the powder particle supplying device; and a driving device for moving an area onto which the powder particles are supplied by the powder particle supplying device.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the claims and the accompanying drawings, in which:
FIG. 1 is a schematic view showing one representative embodiment of a sintered layer forming process;
FIG. 2 is a perspective view of a three-dimensional object formed on a work table according to the present invention; and
FIG. 3 is a cross-sectional view of the three-dimensional object taken along the line III-III shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide an improved method and apparatus for manufacturing a three-dimensional object. Representative examples of the present invention, which examples utilize many of these additional features and teachings both separately and in conjunction with one another, will now be described in detail. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings.
As shown in FIG. 1, powder particles 10 are heated and sintered into sintered layers 16 and 18. It should be noted that the boundary lines between the sintered layers 16 and 18 are shown in FIG. I for the convenience of the explanation, although the sintered layers 16 and 18 are actually integrally built-up as shown in FIGS. 2 and 3. In particular, the powder particles 10 are supplied onto a work table 14 from a powder supplying nozzle 12. The nozzle 12 is moved in a predetermined direction so that the supplied powder area is moved. Thus, while the area, onto which the powder particles 10 are supplied, is moved, the powder particles 10 supplied onto the area are heated by a laser beam 20 downwardly irradiated from a laser as a high-density energy heat source. Accordingly, the powder particles 10 are sintered by heating so as to be formed into a sintered layer 16. Preferably, the thickness of the sintered layer 16 may be configured operably within, but is not limited to, the range between 0.01 mm and 0.5 mm.
In order to form a new sintered layer 18, the powder particles 10 are supplied from the powder supplying nozzle 12 onto the sintered layer 16, which has been previously built up on the work table 14. Thus, while the area, onto which the powder particles 10 are supplied, is moved with the nozzle 12, the powder particles 10 supplied onto the area are heated by the laser beam 20 irradiated from the laser. Accordingly, the new sintered layer 18 is integrally formed on the previous sintered layer 16. The thickness of the new sintered layer 18 may preferably be configured operably within, but is not limited to, the range between 0.01 mm and 0.5 mm.
By repeating the aforementioned process a predetermined number of times, in which a new sintered layer 18 is formed on the previous sintered layer 16 in a layer-by-layer manner, it is possible to manufacture a three-dimensional object consisting of a plurality of integrally built-up sintered layers.
Further, by controlling the two-dimensional shape of each sintered layer, a three-dimensional object may be manufactured in a desired shape. In particular, it is required to control the trajectory of the moving area onto which the powder particles 10 are supplied. This is achieved, for example, by controlling the physical relationship between the nozzle 12 and the table 14. In this case, either the nozzle 12 or the table 14 may be moved to control the physical relationship therebetween. It will of course be appreciated that both the nozzle 12 and the table 14 may be moved. In order to move the nozzle 12 and/or the table 14, a conventional feed mechanism or an XY drive unit driven by linear motors and the like may be used.
The trajectory of the area onto which the powder particles 10 are supplied may be defined by three-dimensional CAD data or the like of the three-dimensional object to be obtained. For example, the trajectory may be defined by contour data corresponding to each cross-section of the three-dimensional object to be obtained. Or otherwise, when a prototype of a part, for example, is to be manufactured, a geometrical shape sensor such as an optical sensor is used to measure the geometrical shape of the surface on the target part. Based on the measured geometrical shape data, the trajectory of the area may be defined onto which the powder particles 10 are supplied.
Preferably, the trajectory of the area onto which the powder particles 10 are supplied may appropriately be compensated, for example, by interposing a compensation calculation while the sensor recognizes each shape of a sintered layer that is being actually formed. Such a compensation technique is particularly useful when a layer to be formed with powder particles 10 has either a contraction or an expansion property during the heating and sintering. When powder particles 10 are used that may cause a layer to be contracted during the heating and sintering, the trajectory is preferably controlled by the movement of the nozzle 12 so as to trace a contour shape slightly larger than the actual contour shape corresponding to the target cross-section of the three-dimensional object to be obtained. On the other hand, when powder particles 10 are used that may cause a layer to be expanded during the heating and sintering, the trajectory is preferably controlled by the movement of the nozzle 12 so as to trace a contour shape slightly smaller than the actual contour shape corresponding to the target cross-section of the three-dimensional object to be obtained. It should be noted that the trajeciory of the area onto which the powder particles 10 are supplied by the nozzle 12 may be controlled by such as a conventional numerical control device.
When a prototype of a part having a certain three-dimensional shape is manufactured, the prototype is required to be accurately reproduced to the original shape of the target part. In this case, as long as the reproducibility of the outside appearance of the target part is maintained, the inside region of the prototype may not be required to be manufactured in high density. Namely, the highest priority is given to the outside appearance of the target part being manufactured in high density, while the inside density of the target part may not required to be uniform with the outside density.
Thus, it is preferable to supply powder particles 10 so that the surface region of the three-dimensional object to be obtained has higher density than the inside region thereof. The “three-dimensional object to be obtained” described above refers to a three-dimensional object to be manufactured by a manufacturing method according to the present invention. The “surface region” of the three-dimensional object to be obtained refers to a portion near the outside surface of the three-dimensional object, or a portion in particular from the outer surface to a predetermined depth, such as a depth generally in a range from 0.1 mm to 10 mm.
Also, the “inside region” of the three-dimensional object to be obtained refers to a portion inside of the “surface region,” or toward the center of the three-dimensional object. The sentence “the surface region of the three-dimensional object to be obtained has higher density than the inside region thereof” refers to a density relationship between the surface region and the inside region, while the boundary therebetween is not required to be particularly distinct. The boundary may be formed in such a manner that the density of the three-dimensional object gradually decreases from the surface region to the inside region.
By way of example, FIGS. 2 and 3 show a three-dimensional object 30 manufactured according to the present invention. A surface region 32 is formed with sintered layers of a higher density, while an inside region 34 is formed with sintered layers of a lower density. Since the surface region 32 is formed with high-density sintered layers, the accurate reproducibility of the original part may be maintained even if the three-dimensional object 30 is formed with a complex shape. Thus, it is possible to manufacture a prototype generally having the same shape as the three-dimensional shape of the original part. It should be noted that the surface region 32 shown in FIG. 2 is not formed on the top and bottom surfaces, but is formed around the side surfaces of the inside region 34.
Further, since the surface region 32 is formed with high-density sintered layers, it is possible to minimize the distortion generally caused in the three-dimensional object 30 by thermal contraction and the like. Thus, even if the three-dimensional object 30 to be obtained is larger than conventional objects, the accurate reproducibility of the three-dimensional shape may be ensured.
Still further, since the surface region 32 is formed with high density, it is possible to manufacture the three-dimensional object 30 having the surface region 32 with a sufficient strength.
It should be noted that the aforementioned prototyping according to the present invention may be achieved with reduced costs and increased speed as compared to the case where the three-dimensional object 30 is entirely manufactured with a uniform high density, since the present invention enables the inside region 34 to be formed with a lower density so as to save the amount of the powder particles otherwise consumed.
In summary, in order to form the surface region 32 with a higher density while forming the inside region 34 with a lower density, at least one of the following processes may be performed:

(a) supplying fewer powder particles for forming the surface region 32 than for forming the inside region 34;
(b) supplying powder particles at a lower supplying rate for forming the surface region 32 than for forming the inside region 34, wherein the “supplying rate” refers to the supplying amount of powder particles per unit of time;
(c) supplying powder particles 10 of smaller particle diameter for forming the surface region 32, while supplying powder particles 10′ of larger particle diameter for forming the inside region 34, wherein the terms “smaller” and “larger” refers to the relationship of particle diameters between the powder particles 10 for forming the surface region 32 and the powder particles 10′ for forming the inside region 34;
(d) supplying powder particles 10 to form the surface region 32, while supplying granulated powder particles 10′ prepared by granulating the powder particles 10 of the same type supplied to form the surface region 32, wherein the particle diameter of the granulated powder particles 10′ are larger than that of the mere powder particles 10 due to the granulation; and
(e) supplying metal powder particles 10 to form the surface region 32, while supplying metal powder particles 10′ mixed with an organic binder to form the inside region 34.

By performing at least one of the processes (a) to (e), powder particles 10, 10′ may be supplied so that the surface region 32 of the three-dimensional object 30 to be obtained is formed with a higher density, while the inside region 34 thereof is formed with a lower density. Thus, it is possible to manufacture the three-dimensional object 30 having a surface region 32 formed with a high density and high strength, while having the inside region 34, which is not seen, formed with a low density.
In the process (c), larger powder particles 10′ are supplied to form the inside region 34 so that less thermal energy is required to heat and sinter the powder particles 10′. This is because larger powder particles 10′, which have fewer contact areas with other powder particles 10′ than the smaller powder particles 10, generally require less thermal energy to soften or melt the contact areas. This may also contribute to reduced costs and increased speed in manufacturing the three-dimensional object 30.
In the process (d), the granulated powder particles 10′ for forming the inside region 34 are prepared by granulating the smaller powder particles 10 supplied for forming the surface region 32. Thus, the three-dimensional object 30 is manufactured with the surface region 32 formed with a higher density, while the inside region 34 is formed with the larger, granulated powder particles 10′. Also, since both the surface region 32 and the inside region 34 are sintered with the same type of powder particles, a binding affinity may be increased between the surface region 32 and the inside region 34 so that the binding strength therebetween may be enhanced. As a result, it is possible to prevent such defects as a release between the surface region 32 and the inside region 34.
In the process (e), the metal powder particles 10′ mixed with an organic binder may be prepared as granulated powder particles, which may be obtained by processes of: mixing metal powder particles with a synthetic resin binder; heating the binder-mixed particles into a slurry form with the melted binder; atomizing the slurry into droplets with a spray dryer; and solidifying the droplets into granulated powder particles. In this case, the average particle diameter of the granulated powder particles may include, but is not limited to, the range generally between 50 μm and 1000 μm, and preferably between 100 μm and 500 μm. Further, the organic binder may include, but is not limited to, a polyester resin. In the present invention, the organic binder integrally surrounding the powder particles 10′ may be removed due to the heat during sintering. This may make it easier to form the inside region 34 with a lower density.
In order to supply the powder particles 10, 10′ onto a predetermined area, a powder particle supplying device may preferably be adjustable in the supplying rate of the powder particles 10, 10′, or selectable in the type of powder particles 10, 10′.
Thus, in order to manufacture a three-dimensional object 30 consisting of a plurality of integrally built-up sintered layers, the following apparatuses may used:

(f) apparatuses that include a powder particle supplying device for supplying powder particles at an adjustable supplying rate; a high-density energy heat source for heating the powder particles supplied by the powder particle supplying device; and a driving device for moving an area onto which the powder particles are supplied by the powder particle supplying device; and
(g) apparatuses that include a powder particle supplying device for supplying powder particles selectable from a group of two or more different types of powder particles; a high-density energy heat source for heating the powder particles supplied by the powder particle supplying device; and a driving device for moving an area onto which the powder particles are supplied by the powder particle supplying device.

With respect to the apparatus (f), an example of the powder particle supplying device with an adjustable supplying rate of powder particles 10 is disclosed in Japanese Laid-Open Publication No. 2003-302281, which is owned by the applicant of the present invention and is hereby fully incorporated herein by reference. The device includes an ultrasonic vibration powder supplier. Such device enables the supplying rate of the powder particles 10 to be finely controlled. Or otherwise, when the powder particles 10, 10′ are supplied for forming a sintered layer, the supplying rate may be switched between a higher supplying rate of the powder particles 10 for the surface region 32 and a lower supplying rate of the powder particles 10′ for the inside region 34. Using such a device may eliminate the necessity for a plurality of supplying devices configured with the different supplying rates. Thus, it is possible to manufacture the three-dimensional object 30 with reduced costs and increased speed.
With respect to the apparatus (g), an example of the powder particle supplying device with a selectable type of powder particles 10, 10′ is disclosed in Japanese Laid-Open Publication No. 2002-273201, which is also owned by the applicant of the present invention and is hereby fully incorporated herein by reference. The device includes a plurality of supplying hoppers, which enable the type of powder particles 10, 10′ to be selectable, if required, from a group of two or more different types of powder particles. In the aforementioned manner, a plurality of different types of powder particles 10, 10′ may be prepared in one device so that powder particles 10, in a smaller average particle diameter, are selected to be supplied for forming the surface region 32, while powder particles 10′, in a larger average particle diameter, are selected to be supplied for forming the inside region 34. Therefore, a plurality of supplying devices may not be required to be used according to the different types of powder particles 10, 10′ to be supplied. Thus, it is possible to use one powder particle supplying device for manufacturing the three-dimensional object 30 with reduced costs and increased speed.
In addition, the surface region 32 may be formed by a high-density energy heat source such as a laser, while the inside region 34 may be formed by a non-transferred plasma arc or a cold spray technique. The cold spray technique is a spray technique in which the powder particles are supplied with a high velocity gas jet from a high pressure gas supply.
The driving device in the apparatuses (f) and (g) may move either the powder supplying nozzle 12, which is provided in the powder particle supplying device, or the work table 14, onto which sintered layers are formed. It will of course be appreciated that both the nozzle 12 and the table 14 may be moved. In order to move the nozzle 12 and/or the table 14, a conventional feed mechanism or an XY drive unit driven by linear motors and the like may be used.
By way of example, a manufacturing system may be constructed so that the high-density energy heat source such as a laser for the surface region 32 may be aligned with respect to a high pressure gas jet device such as a cold spray for the inside region 34, with a powder particles supplying device and a workpiece-moving table included.
As described above, according to the present invention, a method and an apparatus are provided for manufacturing a three-dimensional object having a smooth outer surface, without any additional steps of removing a surface layer each time a sintered layer is formed so as to manufacture a three-dimensional object consisting of integrally built-up sintered layers. Such a manufacturing method or apparatus requires less thermal energy to heat and sinter the powder particles so as to contribute to reduced costs and increased speed in manufacturing the three-dimensional object. This also has the effect of saving an amount of the powder particles otherwise consumed.

EXAMPLE

A more specific embodiment of the present invention will be described below. In this representative embodiment, a Model PF-01 disc-type powder feeder, available from Nihon Welding Rod Co., Ltd., Japan, was used as the powder particle supplying device. A Model 2012H CO₂laser having a 50C oscillator, a rated power of 5 kW, and an argon shielding gas, available from Mitsubishi Electric Corporation, Japan, was used as the high-density energy heat source. Further, two types of powder particles, as shown in Table 1, are used as the powder particles in this representative embodiment.

TABLE 1


Details of Powder Particles

No.	Type of Powder Particles	Material	Average Particle Diameter

1	Spherical Powder	SUS420		30 μm
2	Granulated Powder	SUS410L	200 μm (Granulated from
			10 μm Powder Particles)

As shown in FIG. 2, by using the aforementioned devices, a three-dimensional object 30 having an outside dimension of 100 mm×100 mm×100 mm was manufactured. As shown in Table 1, with respect to the surface region 32, the powder particles of No. 1 were used. Manufacturing parameters for the surface region 32 were: a laser power of 2.8 kW; a laser spot diameter of 1.0 mm; and a speed for moving the powder particle supplied area of 1000 mm/min. With respect to the inside region 34, the powder particles of No. 2 shown in Table 1 were used. Manufacturing parameters for the inside region 34 were: a laser power of 2.0 kW; a laser spot diameter of 3.0 mm; and a speed for moving the powder particle supplied area of 4000 mm/min. It should be noted that the laser spot diameter for the inside region 34 was greater than that of the surface region 32. Also, the moving speed for the inside region 34 was greater than that of the surface region 34. These parameter settings contributed to achieving higher-speed manufacturing.
The three-dimensional object 30 obtained as above was formed with an outside appearance with a high density. The appearance was generally comparable to a three-dimensional object manufactured entirely with spherical powder particles. Also, the time spent in the manufacturing was 2.0 hours for the surface region 32, 4.8 hours for the inside region 34, and 6.8 hours in total, which was approximately one third as long as compared to a manufacturing time through a conventional layer-building prototyping method. Thus, it has been found that the manufacturing method of the present invention can achieve significantly high-speed prototyping.

Claims

1. A method for manufacturing a three-dimensional object formed from a plurality of integrally built-up sintered layers, comprising the steps of:

(i) supplying powder particles onto a moving area while heating the powder particles with heat irradiated from a high-density energy heat source so as to form a sintered layer; and

(ii) supplying powder particles onto a moving area on the sintered layer while heating the powder particles with heat irradiated from the high-density energy heat source so as to form another sintered layer integrally on the sintered layer,

wherein the step (ii) is repeated a predetermined number of times.

2. The method as in claim 1, wherein the powder particles are operably supplied onto the moving areas so that the surface region of the three-dimensional object to be obtained has higher density than the inside region thereof.

3. The method as in claim 1, wherein the powder particles, for forming the inside region of the three-dimensional object to be obtained, have a larger particle diameter than the powder particles for forming the surface region thereof.

4. The method as in claim 1, wherein the powder particles, for forming the inside region of the three-dimensional object to be obtained, are prepared by granulating the powder particles for forming the surface region thereof.

5. The method as in claim 1, wherein the powder particles, for forming the surface region of the three-dimensional object to be obtained, are metal powder particles while the powder particles for forming the inside region thereof are metal powder particles mixed with an organic binder.

6. The method as in claim 1, wherein a supplying rate for the powder particles, for forming the inside region of the three-dimensional object to be obtained, is greater than a supplying rate for the powder particles for forming the surface region thereof.

7. The method as in claim 1, wherein the high-density energy heat source is a laser.

8. The method as in claim 1, wherein a supplying rate of the powder particles is adjustable.

9. The method as in claim 1, wherein the powder particles are selectable from a group of two or more different types of powder particles.

10. An apparatus for manufacturing a three-dimensional object formed from a plurality of integrally built-up sintered layers, comprising:

a powder particle supplying means for supplying powder particles in a adjustable supplying rate;

a high-density energy heat source for heating the powder particles supplied by the powder particle supplying means; and

a driving means for moving an area onto which the powder particles are supplied by the powder particle supplying means.

11. A method for manufacturing a three-dimensional object having a surface region and an inside region, both of the regions formed from a plurality of integrally built-up sintered layers, comprising the steps of:

(i) supplying first powder particles while heating and sintering the first powder particles into a plurality of sintered layers forming the surface region of the three-dimensional object; and

(ii) supplying second powder particles while heating and sintering the second powder particles into a plurality of sintered layers forming the inside region of the three-dimensional object,

wherein the average particle diameter of the second powder particles is greater than the average particle diameter of the first powder particles.

12. The method as in claim 11, wherein the second powder particles are prepared from a same powder type as the first powder particles.

13. A three-dimensional object having a surface region and an inside region, both of the regions formed from a plurality of sintered layers integrally built-up, wherein the three-dimensional object is manufactured by the method as in claim 11.

14. A three-dimensional object having a surface region and an inside region, both of the regions formed from a plurality of sintered layers integrally built-up, wherein the three-dimensional object is manufactured by the method as in claim 12.