JP2007231349A - Metal powder for metal laser sintering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal powder, when fed to metal laser sintering, free from cracks in the vicinity of the joint with a fabrication plate, also precipitating no carbon on the fabricated material, and further capable of obtaining the fabricated material having high strength and high hardness. <P>SOLUTION: The powder of tool steel is a powdery mixture composed of: iron based powder; the powder of nickel or/and a nickel based alloy; the powder of copper or/and a copper based alloy; and graphite powder. In the iron based powder, the content of carbon is reduced to 0.2 to 0.6 wt.%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal powder for use in metal stereolithography to form a sintered layer by irradiating a powder layer made of metal powder with a light beam and laminating this sintered layer. It is.

  A powder layer formed of metal powder is irradiated with a light beam (directional energy beam, for example, a laser) to form a sintered layer, and a new powder layer is formed on the sintered layer and irradiated with the light beam. Thus, a technique for manufacturing a three-dimensional shaped object by repeating the formation of a sintered layer is known. In this technique called metal stereolithography, a characteristic manufacturing method is that a complicated three-dimensional shape can be manufactured in a short time. By irradiating a light beam with high energy density, the metal powder is almost completely melted and then solidified, that is, the modeling density (sintering density) is almost 100%, and the surface of this high-density model is finished. By processing, a smooth surface can be formed, and it can be applied to plastic molds.

  However, in order to obtain such a three-dimensional shaped object by metal stereolithography, the metal powder used for normal powder sintering must satisfy different requirements and have different characteristics. Necessary.

  For example, the particle size of the metal powder needs to be smaller than the thickness of the powder layer. At this time, the smaller the particle size, the higher the powder packing density, and the better the light beam (laser) absorption during modeling. The modeling density can be increased and the surface roughness can be decreased. However, if the powder is too fine and agglomerates, the packing density of the powder decreases, and the powder cannot be spread evenly.

  Also, in order to obtain a certain degree of modeling strength, the bonding area between the laser-irradiated modeling part and the underlying sintered layer must be large and the adhesion strength must be high, The bonding area must be large and the adhesion strength must be high.

  Furthermore, the upper surface of the laser-irradiated portion should not rise so much. When the next powder layer is laid to form the next layer, if the bulge amount exceeds the thickness of the powder layer, the formation of the powder layer itself may be difficult.

  In addition, since the metal powder has adhered to the surface of the modeled object, the processing when performing processing such as cutting finish to remove this unnecessary metal powder and expose the high-density surface It is desirable that the property is good.

  Of course, there should be no large cracks in the appearance, and it is desirable that the internal structure should be free of microcracks in consideration of the case of flowing a fluid (cooling water) inside an injection mold or the like.

  Here, a part or all of the metal powder irradiated with the laser is once melted and then rapidly solidified to form a sintered product. If the bonding area is large and the fluidity is large, the rise is small. Therefore, it is desired that the fluidity when melted is high and the wettability is good.

  From this point of view, the present applicant disclosed in Japanese Patent Application Laid-Open No. 2001-152204 (Patent Document 1) from iron-based powder (chromium molybdenum steel, alloy tool steel), nickel, nickel-based alloy, copper, and copper-based alloy. Proposing metal powder for metal stereolithography including one or more types of non-ferrous powders selected from the group consisting of, and further reducing the number of microcracks that would be problematic in metal stereolithography using this metal powder, No. 3633607 (Patent Document 2), iron-based powder (chromium molybdenum steel, alloy steel for machine structure (non-tool steel)), nickel or nickel-based alloy powder, copper or copper-based alloy powder, A mixed powder for metal stereolithography consisting of graphite powder was proposed. Chromium molybdenum steel is from the point of strength and toughness, copper or copper alloy powder is from the point of wettability and fluidity, nickel or nickel base alloy powder is from the point of strength and workability, graphite powder is from laser It is adopted from the viewpoint of absorption rate and microcrack reduction.

  The latter metal powder for metal stereolithography (mixed powder) has been able to obtain quite favorable results in terms of obtaining a complicated three-dimensional shaped object by laser irradiation and its lamination. It remained as a problem. That is, in metal stereolithography, a mixed powder layer is formed on a modeling plate and sintered to form a modeled object on the modeling plate, but this occurs when the mixed powder melts and solidifies. Due to the shrinkage stress, there is a problem in that peeling (strictly, cracking of the modeled object) occurs in the vicinity of the modeled object and the modeled plate. Moreover, since carbon deposits exist in the modeled object, it becomes a defect, and there is a problem that a smooth surface cannot be formed even if the surface is finished. In the alloy formed by melting the mixed powder, the mixed carbon or the carbon contained in the iron-based powder is considered to have precipitated out of solid solution at the time of alloy formation (solidification). This is because there is almost no force and it spills out of the shaped object during finishing.

Moreover, when this molded article is used as a mold for plastic molding, the durability increases as the strength and hardness increase. Therefore, it is necessary to increase the strength and hardness of the shaped object to the extent that the cutting workability is not impaired.
JP 2001-152204 A Japanese Patent No. 3633607

  The present invention has been invented in view of the above-described conventional problems, and when subjected to metal stereolithography, there is no crack of the modeled object in the vicinity of the joint with the modeled plate, and carbon is deposited on the modeled object. It is an object of the present invention to provide a metal powder that can obtain a molded article having high strength and high hardness without any problems.

  In order to solve the above problems, a metal stereolithographic metal powder according to the present invention is a mixed powder comprising an iron-based powder, a nickel or nickel-based alloy powder, a copper or copper-based alloy powder, and a graphite powder. The iron-based powder is characterized in that it is a tool steel powder whose carbon content is reduced to 0.2 to 0.6 weight percent. The tool steel referred to here means carbon tool steel (JIS G4401), alloy tool steel (JIS G4403), and alloy tool steel (JIS G4404), and only the carbon content is reduced from the original content. 0.2 to 0.6 weight percent is used.

  Peeling (cracking) in the vicinity of the modeling plate is thought to be due to the shrinkage stress that occurs when the metal powder for metal stereolithography irradiated with laser is melted and solidified, but the tool steel has a reduced carbon content. In the metal stereolithography metal powder according to the present invention in which powder and carbon powder are mixed, the expansion that occurs when carbon is dissolved in the tool steel melted by laser irradiation and the shrinkage that occurs during solidification cooling are combined. It is thought that the internal stress (shrinkage stress) of the resulting shaped article is reduced, peeling does not occur in the vicinity of the shaped plate, and alloy components contained in the tool steel generate carbides in the shaped article. In addition, carbon deposition is eliminated, and at the same time, a material having high strength and hardness can be obtained.

  However, if too much graphite is added to reduce microcracks, carbon precipitation occurs, so the graphite powder content is preferably 0.2 to 0.8% by weight. The amount of the iron-based powder is 60 to 80 weight percent, the amount of the nickel or nickel-based alloy powder is 5 to 35 weight percent, the amount of the copper or copper-based alloy powder is 5 to 15 weight percent, Particularly favorable results can be obtained.

  The iron-based powder is preferably a high-speed tool steel powder whose carbon content is reduced to 0.2 to 0.6 weight percent in high strength and high hardness. By using SKH57 steel powder reduced to 2 to 0.6 weight percent, a molded article having high strength and high hardness can be obtained.

  In the metal stereolithography metal powder of the present invention, the tool steel powder whose carbon content is reduced to 0.2 to 0.6 weight percent, nickel or nickel-based alloy powder, copper or copper-based alloy Because of the mixed powder consisting of powder and graphite powder, there is no crack in the vicinity of the joint with the modeling plate in the modeled article, and there is almost no carbon deposition in the modeled article, and the modeled article has high strength and high hardness. Could get.

  Hereinafter, the present invention will be described in detail based on an example of an embodiment. FIG. 1 shows an example of an apparatus for metal stereolithography, and an elevating table 20 that moves up and down by a cylinder in a space surrounded by an outer periphery. Powder layer forming means 2 for forming the powder layer 10 having a predetermined thickness Δt1 by leveling the supplied metal powder with the squeezing blade 21, and a scanning optical system such as a galvano mirror 31 for the laser output from the laser oscillator 30 By irradiating the powder layer 10 via the sintered layer forming means 3 for sintering the metal powder to form the sintered layer 11, and the base portion of the powder layer forming means 2 via the XY drive mechanism 40 The removal means 4 formed by providing the milling head 41 is provided.

  As shown in FIG. 2, the manufacturing of the three-dimensional modeled object in this product is the surface of the modeling plate 22 on the upper surface of the lifting table 20 which is an adjusting means for adjusting the relative distance between the sintered layer forming means and the sintered layer. The first powder layer 10 is formed by supplying the metal powder to the blade 21 at the same time as the blade 21, and the portion of the powder layer 10 to be cured is irradiated with a light beam (laser) L to give the powder. The sintered layer 11 integrated with the modeling plate 22 is formed by sintering.

  Thereafter, the lifting table 20 is slightly lowered, the metal powder is supplied again, and the blade 21 is used to form the second powder layer 10. A light beam (laser) is applied to the portion of the powder layer 10 to be cured. L is irradiated to sinter the powder to form the sintered layer 11 integrated with the lower sintered layer 11.

  By lowering the elevating table 20 to form a new powder layer 10 and irradiating a light beam to make the required portion a sintered layer 11, a desired three-dimensional shaped object is manufactured. Yes, a carbon dioxide laser can be suitably used as the light beam, and the thickness Δt1 of the powder layer 10 is about 0.05 mm when the obtained three-dimensional shaped object is used for a molding die or the like. It is preferable to do this.

  The irradiation path of the light beam is created in advance from three-dimensional CAD data. That is, contour shape data of each cross section obtained by slicing STL data generated from a three-dimensional CAD model at an equal pitch (0.05 mm pitch when Δt1 is 0.05 mm) is used. By irradiating the inside of the contour shape data with a light beam under the condition that the metal powder is melted to obtain a high density, a shaped article having a dense surface after cutting finish can be obtained at high speed.

  Then, the powder layer 10 is formed and the light beam is irradiated to repeatedly form the sintered layer 11. The total thickness of the sintered layer 11 is, for example, the tool length of the milling head 41. When the required value obtained from the above is reached, the removal means 4 is once activated to cut the surface of the shaped object that has been shaped so far. For example, if the tool (ball end mill) of the milling head 41 is capable of cutting with a diameter of 1 mm, an effective blade length of 3 mm and a depth of 3 mm, and the thickness Δt1 of the powder layer 10 is 0.05 mm, 60 layers of fired When the binder layer 11 is formed, the removing means 4 is operated.

  By removing the low-density surface layer of the powder adhering to the surface of the modeled object by cutting by the removing means 4, the high-density part is entirely exposed on the surface of the modeled object by cutting into the high-density part.

  The cutting path by the removing means 4 is created in advance from three-dimensional CAD data in the same manner as the light beam irradiation path. At this time, the machining path is determined by applying contour line processing, but the Z direction pitch does not need to stick to the stacking pitch at the time of sintering, and in the case of a gentle inclination, by interpolating with a finer Z direction pitch, Keep a smooth surface. In addition, although the thing provided with the removal means 4 for the cutting process in the middle of modeling was shown here, you may not have this removal means 4.

  In manufacturing a three-dimensional shaped object in such metal stereolithography, what kind of metal powder is used as described above has a great influence on the point of formability and the quality of the object. However, as this metal powder for metal stereolithography, here there is no cracking of the modeled object in the vicinity of the joint with the modeled plate, there is no precipitation of carbon that could not be completely dissolved in the modeled object, and the strength and hardness Is obtained from a tool steel powder (iron-based powder) whose carbon content is reduced to 0.2 to 0.6 weight percent, nickel or a nickel-based alloy powder, copper or A mixture of copper-based alloy powder and graphite powder is used.

  When the iron-based powder used as the base is a tool steel powder containing a large amount of carbon and alloy components for the purpose of increasing the strength and hardness of the modeled object, the modeled object in the vicinity of the joint with the model plate due to thermal shrinkage during modeling Cracking occurs. The present inventors reduce the carbon content of the tool steel powder that is the base of the mixed powder, and at the same time, by mixing an appropriate amount of graphite powder in the mixed powder, there is no cracking of the molded object, and the molding has high strength and hardness. It has been found that a product can be obtained.

  However, if the reduction amount of carbon in the tool steel powder is large, a modeling defect such as a pore occurs in the modeled object, and if it is severe, a microcrack occurs. The amount of carbon in the tool steel powder is suitably 0.2 to 0.6 weight percent, so that there is no cracking of the modeled object in the vicinity of the joint with the modeled plate, and there is no carbon deposition in the modeled object. In addition, a molded article having high strength and hardness can be obtained.

  In the mixed powder, the low-carbon tool steel powder that is an iron-based powder has a blending amount of 60 to 90 weight percent, a nickel or nickel-based alloy powder blending amount of 5 to 35 weight percent, copper or copper-based powder. It is desirable that the blending amount of the alloy powder is 5 to 15 weight percent and the blending amount of the graphite powder is 0.2 to 0.8 weight percent. When the graphite powder is not mixed or when the blending amount is small, a modeling defect such as a pore occurs in the modeled object, and a micro crack occurs when it is severe. On the other hand, when the amount of graphite powder to be mixed is too large, carbon cannot be completely dissolved in the molded article, and carbon deposition occurs.

In order to obtain a high-strength and high-hardness shaped article, the iron-based powder is preferably a high-speed tool steel powder among tool steels, and more preferably a SKH57 steel powder among high-speed tool steels. .
[Example 1]
High-speed tool steel SKH57 powder (carbon content 1.2%) with non-spherical particles and an average particle size of 20 μm as iron-based powder, and high-speed tool with non-spherical particles and an average particle size of 20 μm with a reduced carbon content Steel SKH57 powder (carbon content 0.4%, see Fig. 3) and non-spherical particles of high-speed tool steel SKH57 powder (carbon content 0.08%) with an average particle size of 20 µm and further reduced carbon content In addition to the types, nickel Ni powder (see FIG. 4) with a spherical particle shape and an average particle diameter of 30 μm, and a copper manganese alloy CuMnNi (for example, Cu-10% Mn-3% Ni) with a spherical particle shape and an average particle diameter of 30 μm Prepare powder (see FIG. 5) and flaky graphite powder (see FIG. 6) having a major axis of 10 μm,
a 70% SKH57 (C: 1.2%)-20% Ni-10% CuMnNi
b 70% SKH57 (C: 0.4%)-20% Ni-10% CuMnNi
c Mixed powder b + 0.5% graphite powder d Mixed powder b + 1.0% graphite powder e 70% SKH57 (C: 0.08%)-20% Ni-10% CuMnNi
f A metal powder for metal stereolithography was prepared with a blending amount of mixed powder e + 0.5% graphite powder. Each% is% by weight. An appearance SEM photograph of the mixed powder c is shown in FIG.

    Metal stereolithography was performed using the metal powders a to f described above. The thickness of the powder layer was 0.05 mm, and the laser used was a carbon dioxide laser (90% output of 200 W output), which was sintered at a laser scan speed of 75 mm / sec and a scan pitch of 0.25 mm.

When laser sintering is performed with the above mixed powder of a, which contains high-speed tool steel SKH57 powder, nickel powder and copper manganese alloy powder whose carbon content is within the range of JIS standard, the bending strength of the shaped article is 2,000 MPa. The Vickers hardness was as high as HV400, but cracks occurred in the modeled object in the vicinity of the modeled plate (see FIG. 8: modeled object peeled off from modeled plate). In addition, a slight amount of carbon deposits was observed inside the shaped object. (See Figure 9)
When laser sintering was performed using the mixed powder b, which was a high-speed tool steel SKH57 powder (components other than carbon and the amount thereof according to JIS standards) in which the amount of carbon in the iron-based powder was reduced to 0.4%, Although the crack of the modeled object in the vicinity of the modeled plate disappeared, when the internal structure of the modeled object was observed, there were a few vacancies as a type of modeling defect (see FIG. 10). The bending strength of the molded article at this time was 1,300 MPa, and the Vickers hardness was HV280.

  Next, when laser sintering is performed with the mixed powder c according to the present invention in which 0.5% by weight of graphite powder is added to the mixed powder b, there is no crack of the molded object in the vicinity of the modeling plate (see FIG. 11: modeling plate). There was no peeling of the molded object from No.), and a molded object without a modeling defect was obtained (see FIG. 12). The bending strength of the molded article at this time was 1,700 MPa, the Vickers hardness was HV340, and both strength and hardness were improved as compared with the molded article from the mixed powder b.

  Furthermore, when laser sintering was performed with the mixed powder d obtained by adding 1.0 wt% graphite powder to the mixed powder b, there was no crack of the molded object in the vicinity of the modeling plate, but the modeled article with many carbon deposits was obtained. (See FIG. 13). However, the bending strength of the molded article was 1,900 MPa, the Vickers hardness was HV380, and both the strength and hardness were further improved.

  Next, laser sintering was performed using mixed powder e in which high-speed tool steel SKH57 powder in which the carbon content of the iron-based powder was reduced to 0.08% was blended with nickel powder and copper-manganese alloy powder. Although there was no crack of the modeled object in the vicinity of the modeled plate, when the internal structure of the modeled object was observed, there were many vacancies and microcracks (see FIG. 14), and the bending strength of the modeled object was 100 MPa, Vickers The hardness was as low as HV170.

Further, laser sintering was performed with a mixed powder f obtained by adding 0.5% by weight of graphite powder to the mixed powder e. Although there was no crack of the modeled object in the vicinity of the modeled plate, the same holes as in the case of the mixed powder b were observed (see FIG. 15). This molded article had a bending strength of 1,500 MPa and a Vickers hardness of HV280.
[Example 2]
High-speed tool steel SKH51 powder (carbon content 0.85%) with non-spherical particles and an average particle size of 20 μm, nickel Ni powder with spherical particles and an average particle size of 30 μm, and spherical particles with an average particle size of 30 μm A copper-manganese alloy CuMnNi (for example, Cu-10% Mn-3% Ni) powder and a flake graphite powder having a major axis of 10 μm,
g 70% SKH51 (C: 0.85%)-20% Ni-10% CuMnNi
h Metal powder for metal stereolithography was prepared with a blending amount of mixed powder g + 0.5% graphite powder, and metal stereolithography was performed using these metal powders. Each% is% by weight. The conditions of the thickness of the powder layer, the laser used, the scan speed of the laser, and the scan pitch are the same as those in Example 1.

  When laser sintering is performed with the above-mentioned mixed powder of g in which high-speed tool steel SKH51 powder having a carbon content (0.85%) within the range of JIS standard, nickel powder, and copper-manganese alloy powder is blended, there is no modeling defect. A modeled object was obtained (see FIG. 16), its bending strength was 1,500 MPa, Vickers hardness was HV320, and a modeled object with high strength and hardness was obtained, but small cracks were formed in the modeled object in the vicinity of the modeled plate. There has occurred.

Next, when laser sintering is performed with a mixed powder h in which 0.5% by weight of graphite powder is added to the mixed powder g, the strength and hardness of the molded product is improved as compared with the mixed powder g (the bending strength is 2). , 200 MPa, Vickers hardness was HV375), but the molded object in the vicinity of the modeling plate was not broken, and a slight amount of carbon was generated inside the molded object (see FIG. 17).
[Example 3]
Non-spherical alloy tool steel SKD11 powder with an average particle size of 20 μm (carbon content 1.5%) and non-spherical alloy tool steel SKD11 powder with an average particle size of 20 μm and reduced carbon content (carbon content 0) 0.4%), a nickel Ni powder having a spherical particle shape and an average particle diameter of 30 μm, a copper manganese alloy CuMnNi (for example, Cu-10% Mn−3% Ni) powder having a spherical particle shape and an average particle diameter of 30 μm, Prepare flaky graphite powder with a long diameter of 10 μm,
i 70% SKD11 (C: 1.5%)-20% Ni-10% CuMnNi
j 70% SKD11 (C: 0.4%)-20% Ni-10% CuMnNi
k Metal powder for metal stereolithography was prepared with a blending amount of mixed powder j + 0.5% graphite powder, and metal stereolithography was performed using these metal powders. Each% is% by weight, and the conditions of the thickness of the powder layer, the laser used, the laser scanning speed, and the scanning pitch are the same as those in Examples 1 and 2.

  When laser sintering is performed with the above mixed powder of i, which is a mixture of alloy tool steel SKD11 steel powder, nickel powder and copper manganese alloy powder with carbon content (1.5%) within the range of JIS standard, immediately after the start of modeling Cracks occurred in the modeled object in the vicinity of the modeling plate, making powder lamination impossible and modeling stopped.

  Subsequently, when laser sintering was performed using the mixed powder j in which the iron-based powder was SKHD11 steel powder with the carbon content reduced to 0.4%, the above-described cracked structure in the vicinity of the modeling plate disappeared. When the internal structure of the modeled object was observed, there were a few micro cracks which are a type of modeling defect (see FIG. 18). The bending strength of the molded article at this time was 700 MPa, and the Vickers hardness was HV210, which was slightly low.

  Next, when laser sintering is performed with the mixed powder k according to the present invention in which 0.5% by weight of graphite powder is added to the mixed powder j, there is no crack in the molded object near the modeling plate, and there is no modeling defect. Was obtained (see FIG. 19). The bending strength of the molded article at this time was 1,200 MPa, the Vickers hardness was HV250, and both strength and hardness were slightly improved as compared with the molded article of the mixed powder j.

It is a schematic perspective view of an example of the apparatus which performs metal stereolithography using the metal powder of an example of embodiment of this invention. It is explanatory drawing same as the above. It is a SEM photograph of the high speed tool steel SKH57 powder which reduced the carbon content of a non-spherical particle form same as the above. It is a SEM photograph of the spherical particle-like nickel powder same as the above. It is a SEM photograph of the spherical particulate copper manganese alloy powder same as the above. It is a SEM photograph of flaky graphite powder same as the above. It is a SEM photograph of mixed powder same as the above. It is a cross-sectional photograph of the modeling object modeled with the mixed powder a in the vicinity of the modeling plate. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder a. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder b. It is a cross-sectional photograph of the modeling object modeled with the mixed powder c in the vicinity of the modeling plate. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder c. ( It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeled object modeled with the mixed powder d. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeled object modeled with the mixed powder e. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder f. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder g. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder h. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder j. It is a cross-sectional photograph of 40 times magnification of the test piece cut out from the modeling object modeled with the mixed powder k.

Explanation of symbols

2 Powder layer forming means 3 Sintered layer forming means 22 Modeling plate L Light beam

Claims (4)

  A metal powder for metal stereolithography, which forms a sintered layer by irradiating a powder layer made of metal powder to form a sintered layer and obtains a desired three-dimensional shaped object by laminating the sintered layer. A mixed powder composed of a nickel-based powder, a nickel or nickel-based alloy powder, a copper or copper-based alloy powder, and a graphite powder, and the iron-based powder has a carbon content of 0.2-0. Metal powder for metal stereolithography, characterized in that it is a powder of tool steel reduced to 6 weight percent.   60-90 weight percent of iron-based powder, 5-35 weight percent of nickel or nickel alloy powder, 5-15 weight percent of copper or copper alloy powder, graphite The metal powder for metal stereolithography according to claim 1, wherein the blending amount of the powder is 0.2 to 0.8 weight percent.   The metal powder for metal stereolithography according to claim 1 or 2, wherein the iron-based powder is a high-speed tool steel powder whose carbon content is reduced to 0.2 to 0.6 weight percent.   The metal powder for metal stereolithography according to claim 3, wherein the iron-based powder is a powder of high-speed tool steel SKH57 whose carbon content is reduced to 0.2 to 0.6 weight percent.