JPH08260162A - Laser beam-applied powder compacting method - Google Patents

Abstract

PURPOSE: To compact a powder into an optional shape with high dimensional precision without any die by laminating a powder material in layers, irradiating the region corresponding to the contour of the compact with a laser beam for each layer, heating and sintering the obtained intermediate compact. CONSTITUTION: A compact to be worked is separated into plural parallel layers. A powder material such as metal powder not contg. binder and solvent is layered into unit layer of 0.1-1mm. At least the region corresponding to the contour of the compact is irradiated with a laser beam for each layer of the layered powder material, and the region other than the contour is not irradiated with the beam. The maximum output of the laser beam is controlled to 10-1000 W, and the irradiated region is locally heated and solidified. The succeeding layer of the powder material is laminated on the laser beam-irradiated layer and irradiated with the laser beam. The process is repeated, and the powder outside the contour of the compact is removed after the final layer is irradiated with the laser beam. The intermediate compact thus obtained is entirely heated and sintered to join the layers, and the compact is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder forming process using a laser, and more particularly to a method for forming a powder into a predetermined shape without using a mold such as a metal mold.

[0002]

2. Description of the Related Art The inventor has proposed a powder molding method in which a powder immediately after being extruded from a cylinder is irradiated with a laser beam to be sintered (Japanese Patent Laid-Open No. 61-52,373). In this method, a solvent such as water is added to the powder material so as to give it a caking property, and the shape at the time of being extruded into a rheological shape is maintained.
Then, it is irradiated with laser light to be heated and solidified to be molded. The feature of such a processing method is that powder molding can be performed without using dies and special shape tools, and that products and raw shapes can be realized without generating chips that are difficult to reuse, making it possible to produce a wide variety of products in small quantities. Suitable for production and molding of prototypes.

However, this method has limitations. The shape of the molded product is determined by the rheology when it is extruded from the cylinder and is not suitable for precision molding. In particular, it is difficult to form a step or make a hole, and it is impossible to form an overhang. Many mechanical parts have overhangs that increase the cross-sectional area on the way, and only simple parts can be molded. Furthermore, the inside of the molded body and the surface cannot be heated uniformly. This is because the laser light is several tens nm from the surface.
This is because it reaches only a certain depth and energy is absorbed near the surface. The heat conduction from the surface to the inside is performed by ordinary heat conduction, and the degree of heating differs between the surface and the inside. For this reason, only the surface of the molded body is melted and the inside remains unsintered, or the surface is overheated more than necessary and the precision of the shape is lowered due to the scattering and flow of the powder material.

[0004]

An object of the present invention is to provide a laser-applied powder molding method which has 1) high shape accuracy, 2) high adhesion between layers, and 3) little warpage or thermal deformation in each layer. (Claims 1 to 3). An additional problem in claim 2 is that 4) an arbitrary shape including an overhang can be molded, and 5) a shape collapse does not occur when the intermediate molded body is conveyed, etc., and the shape accuracy is further improved. Especially. Claim 3
6) is to prevent metal contamination by binder residue or solvent residue by molding metal powder without binder such as polyvinyl alcohol or solvent such as water or turpentine oil.

[0005]

The laser-applied powder molding method of the present invention is a method of irradiating a powder material with a laser beam to perform molding, by dividing a molded body to be processed into a plurality of parallel layers,
The powder material is layered one layer at a time, and for each layer, at least an area corresponding to the contour of the molded body is irradiated with laser light, and an area corresponding to the outside of the contour of the molded body is not irradiated with laser light. , The powder material of the next layer is laminated on the layer irradiated with the laser beam so that the laser irradiation is performed,
Repeatedly stacking powder materials and irradiating with laser light, and after irradiating the final layer with laser light, remove the powder corresponding to the outside of the contour of the molded body, leaving the inside unsintered powder. The intermediate molded body of 1 is obtained, and the obtained intermediate molded body is sintered by overall heating to combine the layers to form a molded body (Claim 1).

Further, in the present invention, in the first layer and the final layer, a region corresponding to the contour of the molded body and the inner surface thereof are irradiated with laser light, and in the layers other than the first layer and the final layer, A region corresponding to the contour of the molded product and a step portion between the layer and the layers above and below the layer are irradiated with laser light (claim 2). The present invention is further characterized in that a metal powder containing no binder and no solvent is used as the powder material (claim 3).

Here, as the powder material, in addition to the metal powder shown in the examples, any powder that is solidified by heating, such as ceramic powder such as alumina or magnesia, or plastic powder, may be used. It is possible, but particularly important is metal powder such as Fe, Ni, Cr, Co, Zr, W. When using metal powder, if there is a binder such as polyvinyl alcohol or cellulose acetate, or a solvent such as water or turpentine oil in the material, it decomposes during laser light irradiation and subsequent sintering, and the residue remains in the molded body. Pollute. For example, water decomposes by heating and oxidizes the metal, preventing the bonding between layers.
Further, an organic binder such as polyvinyl alcohol or an organic solvent such as turpentine oil is decomposed into a carbon residue upon irradiation with laser light or during sintering, thereby changing the carbon content in the metal.
And, as is well known, the properties of metals are sensitive to the carbon content. Therefore, when the metal powder is used, it is preferably used as a dry metal powder without a binder or a solvent.

In the case of metal, the powder material for layering is preferably dry metal powder as described above. In the case of ceramic, for example, a green sheet prepared by adding a binder or a solvent may be used. good. The thickness of each layer is, for example, about 0.1 to 1 mm, and the thinner the layer, the more precise processing can be performed, but the number of steps increases, so it is preferable to determine the layer thickness within this range. Further, the powder material may have different components for each layer. For example, the first layer and the third layer may be made of corrosion-resistant Ni or Cr.
If the alloy containing Al and the second layer in the middle is pure iron, the pure iron layer can be clad with the corrosion resistant alloy.

Either pulsed oscillation or continuous oscillation can be used for the laser, and the wavelength and oscillation mode are arbitrary. The maximum output is, for example, about 10 to 1000 W, and a CO2 laser having an output of 10 to 100 W is used in the embodiment.

To explain the terminology, since the molded body after sintering generally shrinks from the shape when irradiated with laser light,
Instead of “irradiating the contour of the molded body with laser light”, considering the shrinkage amount, “irradiate the region corresponding to the contour of the molded body with laser light” is set. In the following, the area corresponding to the contour of the molded body will be simply referred to as the contour portion. The step difference between the upper and lower layers means both the step difference between the lower layer and the upper layer and the step difference between the upper layer and the upper layer. Irradiation with laser light is local heating, and the powder is solidified accordingly. This is a kind of sintering, and in order to distinguish from this, ordinary sintering using a furnace, infrared rays, etc. is referred to as sintering by overall heating in this specification.

[0011]

The operation of the invention of claim 1 will be described. The molded body to be processed is divided into layers of about 3 to 20 layers, each layer is laminated, and the contour portion is irradiated with laser light.
The laser light is basically applied to the contour portion, and the outside of the contour portion is not irradiated. Then, the irradiation of the laser beam and the stacking of the next layer are repeated for each layer, and this step is repeated until the final layer is reached. It is not necessary to completely sinter the powder material by irradiating the contour portion with the laser beam, and it is sufficient if the powder material has such strength that the intermediate compact can be taken out and conveyed.

After the irradiation of the laser beam to the final layer is finished, the contour portion is solidified by laser heating, so that the powder inside is confined in the contour portion in an unsintered state. Further, since the final sintering is performed separately from the laser light irradiation, the irradiation energy can be reduced and the thermal deformation of each layer can be reduced. Therefore, each layer does not warp, and there is no thermal deformation or generation of holes due to the scattering or flowing of the powder on the surface. Further, it is possible to prevent the oxidation of each layer during the laser irradiation process and to keep the sinterability of the powder high. The prevention of oxidation of the layer surface is particularly important in the case of metal powder, and it is possible to prevent the oxide film between layers from interfering with the sintering in the sintering process. Since the irradiation energy of the laser light can be reduced, only a specific layer can be laser-heated, and the contour of each layer can be changed to form a complicated shape.

When the intermediate compact is taken out, the powder outside the contour portion is unsintered and has no strength, so that unnecessary powder can be easily removed with an air brush or a brush in the laboratory. Therefore, the intermediate compact can be easily taken out of the powder material. When the taken out intermediate compact is sintered in an electric furnace, a gas furnace, an infrared furnace or the like, the powder inside the contour portion is also sintered to obtain a compact. Since the inside of the intermediate molded body is basically unsintered, the sintering activity is high in the sintering process, and the layers are bonded to each other in the sintering process except the contour portion.

When the powder material is laminated as a green sheet, the bottom surface of the first layer and the top surface of the final layer have strength enough to withstand conveyance from the beginning, and the bottom surface and the top surface (top surface) of the intermediate compact are laser-coated. There is no need to illuminate. Even when the green sheet is used, there is a large difference in the strength of the sheet between the contour portion and the outside thereof, and the outside sheet can be easily peeled off. Here, as in claim 2, by irradiating the inside of the contour portion of the first layer and the step portion of the intermediate layer and the inside of the contour portion of the final layer with laser light, even dry powder having no strength, Solidify the bottom and top surfaces of the intermediate molded body and the step,
It can provide strength that can withstand transportation and sintering. If the powder material is a metal powder that does not contain a binder and a solvent, a molded product can be obtained without contamination by these residues or fluctuation in composition.

[0015]

1 to 6 show an embodiment, FIG. 1 shows the processing principle of the embodiment and the structure of a processing apparatus used, and FIG. 2 shows the processing algorithm of the embodiment. In FIG. 1, reference numeral 2 denotes an appropriate CAD device, which inputs a target shape 4 of a molded body, divides it into a plurality of parallel layers, and determines a laser beam irradiation pattern for each layer. The thickness of each layer is, for example, 0.1 to 1 mm
The layer thickness is reduced as the accuracy required for the shape is higher. FIG. 1 shows a laser beam irradiation pattern 8 for the lowermost first layer 6. The irradiation pattern is determined in consideration of the layer thickness and the type of powder material. When the layer thickness and the irradiation pattern of the laser beam are determined by the CAD device 2, this is input to the NC device 10 to perform powder molding processing.

Reference numeral 12 is a laser, and a CO2 laser is used here, but a glass laser, a ruby laser, or a YAG laser is used.
A laser or the like may be used, and for example, a laser having a maximum output of about 10 to 1000 W is used. Laser light is used as a heat source, and the wavelength, oscillation mode, etc. are arbitrary. 14 is a lower die, 16 is an upper die, 18 is a lower pin, and 20 is an upper pin. The upper die 16 and the upper pin 20 compress the powder for each layer before irradiating the laser light to reduce shrinkage during sintering. It is preferable to reduce the porosity of the compact after sintering (hereinafter referred to as a sintered compact) as well as to reduce the porosity. 22 is a hopper for supplying the powder material into the lower die 14. The lower die 14 is set on an XY table (not shown) so that the lower die 14 can be moved under the control of the NC device 10.
The powder can be compressed by the upper pin 20 and the laser beam can be emitted by the laser 12.

As the powder material, in addition to metal powder, ceramic powder, plastic powder, or the like may be used. In addition to dry powder containing no solvent or binder, it may be in the form of a green sheet to which a solvent or binder is added. However, the organic solvent and binder become carbon residue and contaminate the sintered body, and when water is used as the solvent, the metal powder is oxidized and the sinterability is lowered, so the powder material contains the solvent and the binder. No dry powder is preferred. In the example, iron carbonyl was decomposed into powder material,
A dry powder of pure iron containing no solvent or binder was used.

Reference numeral 24 is an Ar cylinder, and the powder lamination and laser light irradiation are carried out in an Ar stream, and the laser light irradiation atmosphere is neutral or reducing. This is to prevent the metal powder from being oxidized by the oxygen in the atmosphere during the irradiation of the laser beam. The atmosphere is not limited to Ar, but a non-oxidizing atmosphere such as N2, CO2, or CO2-H2 is used. When molding the ceramic powder, the atmosphere may be oxidizing. Reference numeral 26 is an airtight chamber for keeping an Ar atmosphere by the Ar air flow from the cylinder 24. The intermediate compact 28 after the laser light irradiation is sintered in an electric furnace 30, a gas furnace or the like.

FIG. 2 shows an algorithm of powder forming processing in the embodiment. When the three-dimensional shape of the molded body is input to the CAD device 2, this shape is divided into a large number of parallel layers according to the required shape accuracy. And the thickness of each layer is, for example, 0.1.
It is about 1 to 1 mm. Next, the irradiation pattern of the laser light to each layer is determined according to the thickness and material of each layer. The irradiation pattern of the laser light is the contour portion of the molded body and the upper surface inside thereof for the first layer, and the contour portion and the step portion between the upper and lower layers for the second and subsequent layers. For the final layer, the contour portion and the upper surface inside thereof are used.

It is preferable that the irradiation energy of the laser beam is maximum with respect to the contour portion and the step portion with respect to the upper and lower layers, the inner upper surface of the final layer is intermediate, and the inner upper surface of the first layer is minimum. This gives priority to the strength of the contour portion, gives the strength of the laser light to the upper surface of the final layer to the extent that powder does not spill, and provides the first layer with the minimum strength as the bottom surface of the intermediate compact 28. This is to suppress the oxidation of the powder while giving it and to improve the adhesion with the second layer. These are the steps in CAD.

Upon completion of these processes, the processes are handed over to the NC device 10 of the laser processing machine, and the laser 12 is used to mold the powder. After the powder of the first layer is filled in the lower die 14 from the hopper 22 and compressed by the upper pin 20, the laser light is irradiated to the contour portion of the powder of the first layer and the upper surface inside the contour portion. When the irradiation of the laser beam on the first layer is completed, the second
Layers after the layer are laminated and compressed by the upper pin 20 for each layer,
Laser light is irradiated to the contour portion and the step portion with respect to the upper and lower layers. Then, with respect to the final layer, the contour part and the upper surface inside thereof are irradiated with laser light.

In the intermediate compact 28 after the irradiation of the laser beam to the final layer, the contour portion, the bottom surface and the upper surface are in a semi-melted or slightly sintered state, and the internal powder remains unsintered. is there. The powder remains dry powder having no strength outside the contour portion, and the lower pin 18 is pushed up to take it out from the lower die 14, and the powder outside the contour portion is removed with a brush or an airbrush to remove the intermediate molded body 28. obtain. Intermediate molded body 28 taken out
Is sent to an electric furnace 30 and sintered at, for example, about 1000 ° C.

Since the irradiation of the laser beam is basically performed on the contour portion and the irradiation to the inside of the contour portion is suppressed, oxidation of the metal powder due to residual oxygen is small. Therefore, in the sintering in the electric furnace 30, the oxide layer between the layers does not hinder the sintering, and the adhesion between the layers is high. Except for the contours, the layers are joined by sintering in an electric furnace 30. Since the irradiation of laser light is suppressed to the contour part etc.,
There is no deformation or warpage of the layer due to overheating, peeling between layers, or scattering of the powder material from the surface of the layer. Further, since the inside of each layer remains unsintered powder, it has high sintering activity and can be uniformly sintered in the electric furnace 30. Since the contour portion is not completely melted and the laser light is irradiated to such an extent that the intermediate compact 28 can be taken out and transported, the contour portion is not deformed or oxidized. Since the laser energy for irradiation can be reduced in this way, only a specific layer can be heated. Therefore, it is possible to prevent the laser-irradiated layer from adhering integrally with the lower layer when the laser beam is irradiated. As a result, it is possible to change the shape of the contour portion for each layer and mold it into an arbitrarily complicated shape. If necessary, finish processing is performed after sintering.

FIG. 3 shows the filling state of the powder in the lower die 14 and the irradiation pattern of the laser 12. The figure shows a state in which the irradiation of the laser beam up to the third layer has been completed, where 32 is the contour portion, 34 is the inside of the contour portion of the first layer, and 36 is the step portion. In the figure, it is assumed that there is no step between the third layer and the next fourth layer, and the inside of the contour of the third layer is not irradiated with laser light.

FIG. 4 shows an irradiation pattern of the laser 12 on the intermediate compact 40 having steps. 42 is the first layer,
Reference numeral 44 is an intermediate layer having a step, and 46 is a final layer. Illustration of the other layers is omitted. In the embodiment, the contour portion 32 is scanned with the laser 12 while being pulse-oscillated, and the laser light is emitted in a dot shape. Was continuously oscillated for scanning and irradiation. In addition, the laser 1
2 may be continuously oscillated and irradiated. By the laser irradiation, the contour portion 32 is semi-melted or partially sintered and solidified, and the inside 34 of the first layer 42, the step portion 36, and the inside 48 of the final layer are slightly sintered and solidified. Therefore, the intermediate compact 40 is taken out from the lower die 14 in a state where only the outer surface of the intermediate compact 40 is solidified. Inside the intermediate compact 40, the powder remains unsintered and can be uniformly sintered in the electric furnace 30.
Further, since the heating by the laser 12 is slight, it is possible to prevent the oxidation of the metal powder to improve the adhesion between the layers, and also to prevent the deformation such as the warp of each layer due to the heating and the generation of the holes and cracks due to the scattering of the material. The state of the powder 50 when taken out from the lower die 14 is shown in the lower portion of FIG.

5 and 6 show an example in which the bevel gear 52 is molded according to the embodiment. The material used is pure iron powder obtained by decomposing iron carbonyl, which is a dry powder containing no binder or solvent. Powder materials are stacked in order from bottom to top in FIG.
The thickness of each layer is 0.3 mm. The line of FIG. 5 shows the irradiation pattern of the laser 12, FIG. 5 shows the state seen from the lower side of FIG. 6, and the four concentric circles in the center show the irradiation pattern of the laser light to the inside of the first layer and the surroundings. The dense line of contour 3
The irradiation pattern to 2 is shown. The irradiation conditions of the laser light are: pulsed output with an output of 65 W at the contour portion 32 and a duty ratio of 13%, an oscillation frequency of 300 Hz, a laser beam power density of 1.38 × 10 ⁵ W / cm ² , and an irradiation from the laser 12. The distance was 95 mm, and the beam feed rate was 400 mm / min. In the inside 34 of the first layer, the laser 12 continuously oscillates with an output of 27 W and the power density is 5.48 × 10 ³ W / cm ² ,
Irradiation distance is 110mm, beam speed is 400mm
/ Min., Laser 12 outputs 15 W inside the last layer 48
Continuous oscillation, the power density is 7.28 × 10 ⁴ W / c
m ² , irradiation distance is 100 mm, beam feed rate is 40
It was set to 0 mm / min. The residual oxygen concentration in the airtight chamber 26 was about 0.5%. With regard to the laser energy per surface area of the intermediate compact, considering the strip-shaped portion having the width of the beam diameter of the laser light as the contour portion 32, the contour portion 32 is the largest, the inside 48 of the final layer is next to this, and the first layer is the second layer. Inside 34
Is the lowest. The intermediate compact after laser irradiation is converted into an electric furnace 30.
And sintered at 1000 ° C. for 5 minutes to obtain a bevel gear shown in FIG.

As is clear from FIG. 6, the machining accuracy is high,
It could be processed into a gear shape. Further, no voids or cracks were observed between the layers, the surface was smooth and free of roughness or holes, and no warpage was observed on the upper surface of the last laminated layer in FIG. This indicates that even if a large number of layers are laminated, no warpage occurs and a complicated shape with overhang can be formed.

[0028]

According to the present invention, the following effects can be obtained (claims 1 to 3). 1) Workability is good because the limited part such as the contour part is irradiated with the laser light and the inside of the molded body is not sintered by the laser light. 2) As a result, there is no thermal deformation or warpage due to laser overheating, no scattering of powder, etc., and the shape accuracy is high. 3) A large number of layers can be laminated, and a complicated shape can be formed by changing the shape of the contour of each layer. In particular, if the layer thickness is reduced, precise molding can be performed. 4) Since the final sintering is performed separately from laser irradiation, the whole can be sintered uniformly, the shape accuracy is high, and the strength is high. Along with this, the adhesion between layers is high. 5) Only a specific layer can be laser-heated, and the lower layer does not unnecessarily adhere to the layer irradiated with laser light. 6) Even in the contour portion, it is sufficient that it has strength to withstand conveyance by laser light irradiation, and it is not necessary to completely sinter. For this reason, the shape of the contour portion is less likely to be deformed. 7) No need for cutting oil, no environmental pollution associated with this, and no cutting chips. 8) No mold required, suitable for high-mix low-volume production and prototype production. 9) It is possible to produce composite members with different compositions for each layer.

According to the invention of claim 2, the following additional effects can be obtained. 10) Any shape including overhang can be formed without using a green sheet. 11) Even if the green sheet is not used, the intermediate molded body does not lose its shape during transportation. According to the invention of claim 3, the following additional effects can be obtained. 12) No binder or solvent is required, so contamination by these residues does not occur. 13) Due to 2) and 6), oxidation of each layer is suppressed and the adhesion between layers is high.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic principle of a laser-applied powder molding method in an embodiment.

FIG. 2 is a process chart of an example

FIG. 3 is a diagram showing a filling state of powder in a die and an irradiation pattern of laser light in an example.

FIG. 4 is a diagram showing an irradiation pattern of laser light in an example.

FIG. 5 is a diagram showing an irradiation pattern of laser light on a bevel gear manufactured by a laser-applied powder molding method according to an embodiment.

FIG. 6 is a photograph showing the metallographic structure of the bevel gears manufactured in the examples.

[Explanation of symbols]

2 CAD device 32 Contour part 4 Target shape of molded body 34 First layer inside 6 Layer 36 Stepped portion 8 Irradiation pattern 40 Intermediate molded body 10 NC device 42 First
Layer 12 Laser 44 Intermediate layer 14 Lower die 46 Final layer 16 Upper die 48 Final layer Internal 18 Lower pin 50 Powder 20 Upper pin 52 Bevel gear 22 Hopper 24 Ar cylinder 26 Airtight chamber 28 Intermediate compact 30 Electric furnace

Claims (3)

[Claims] 1. A method for forming a powder material by irradiating it with a laser beam, wherein a molded body to be processed is divided into a plurality of parallel layers, and the powder material is layered one by one, and each layer is formed in layers. At least the area corresponding to the contour of the molded body is irradiated with laser light, and the area corresponding to the outside of the contour of the molded body is not irradiated with laser light, and the powder of the next layer is formed on the layer irradiated with laser light. By stacking the body material and performing the laser irradiation described above,
Repeatedly stacking powder materials and irradiating with laser light, and after irradiating the final layer with laser light, remove the powder corresponding to the outside of the contour of the molded body, leaving the inside unsintered powder. The laser-applied powder molding method, characterized in that the intermediate molded body of (1) is obtained, and the obtained intermediate molded body is sintered by overall heating to bond each layer to form a molded body. 2. In the first layer and the final layer, a region corresponding to the contour of the molded product and the inner surface thereof are irradiated with laser light, and the layers other than the first layer and the final layer are covered with the molded product. The laser-applied powder molding method according to claim 1, wherein the region corresponding to the contour and the step between the layer and the layers above and below the layer are irradiated with laser light. 3. The laser-applied powder molding method according to claim 1, wherein a metal powder containing no binder and no solvent is used as the powder material.