Different technologies for metal 3D printing, printed items have many differences. Figure 1: Characteristic differences between preheating and preheating Figure 2: 3 orthophotos of the sample used to confirm the modeling limits Figure 3: Outcome shape results The size of the modeling sample was measured and compared with the design values. The surface roughness was also measured. Design dimensions refer to the orthographic image of FIG. Figure 4: Modeling results for confirming the modeling limits Figure 5: Results of Rotating Bending Fatigue Test
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A metal 3D printer is a device for selectively sintering metal powders for lamination. Currently, there are two main types of sintering heat sources, namely a laser beam method and an electron beam method. The output power and scanning speed of the two methods are different, which is closely related to whether the overall level of the product level is a layer by layer. Preheating will affect the residual stress and powder removal, and the implementation of the target shape will also change. The results of the verification of the Metals & Technology Co., Ltd., which is engaged in the commissioning of metal parts, are summarized below.
According to Nikkei Technology Online, a research institute has compared metal 3D printing technology based on laser beam and electron beam, and the comparison results are as follows.
The research institutes used two typical metal 3D printing devices: the laser beam type "EOSINT M280" (EOS, Germany) and the electron beam type "Arcam A2X" (Arcam, Sweden) as a processing device for the printing of formed parts.
The maximum size of the two models is basically the same, are 250mm square, the minimum thickness of about 50 microns is the main difference is the laser beam or electron beam output power and scanning speed. In terms of output power, the laser beam type is 400W, and the electron beam type is as high as 3500W. The scanning speed, the laser beam type is 7m/s, and the electron beam type is as high as 8000m/s. The gap between the two is huge. The electron beam type utilizes the advantage of the scanning speed, and the shape of the entire layer of the scanning screed is preheated (the temperature of the metal powder is increased) as it is formed, and then the shape of the sintered cross section is started.
1. When the metal powder material is Ti-6Al-4V, the maximum size of EOSINT M280 (EOS, Germany) is 250×250×325mm, Arcam A2X (Arcam, Sweden) is 200×200×380mm, and the stack of EOSINT M280 The thickness is 30 microns or 60 microns, Arcam A2X is 50 microns.
So, how will the warm-up result change? There are currently two major direct impacts (Figure 1). 
The laser beam type does not perform preheating, and the electron beam type performs preheating. As a result, the magnitude of the residual stress and the state of powders other than the molded object will change, and the processes after modeling have advantages and disadvantages.
First, the attachment of the required support varies. This is because the temperature difference of the laser beam type that does not perform preheating becomes large, resulting in a rise in residual stress, and the styling article needs to withstand such residual stress. The support body needs to be firmly attached to the substrate contacted by the first layer, and the size of the support body can be quite large. It is difficult to remove the support from the substrate, so after the modeling, it is necessary to do the final treatment through mechanical processing.
2, support material: In order to prevent the shape of the product's weight caused by deformation of the target shape and additional parts. Need to be removed after modeling.
The electron beam type has a small temperature difference and a low residual stress, so that only the support body supporting the recessed portion can be fully molded. "Apply a thin support body that can be bent by hand. It can be removed slightly by hand or with a slight twist of the pliers."
As described above, the electron beam type is dominant compared with the support (residual stress), but the laser beam type also has advantages. That is powder removability.
In fact, after preheating, the metal powder "will become like a pseudo-sintered state." With the laser beam type, the portion outside the molding range can be directly taken out as a powder, and the electron beam type is preheated so that the powder on the entire molding table is in a slightly solidified state.
This excess part that becomes a pseudo-sintered state can also be removed by sandblasting, but the part that cannot be sprayed is difficult to remove. Parts with complex circuits have the problem of not completely removing excess parts.
Confirm with your own modeling sample
To investigate the impact of powder removal and other factors on the accuracy and shape reproducibility of the actual molded object, the research institute printed Ti-6Al-4V modeling samples using these two methods of 3D printers and compared them (Fig. 2). In order to confirm the following six points, samples were specially designed. These six points include: (1) If there is no support, what is the maximum collapse angle at the time of modeling (extreme model angle), (2) how small transverse holes can be reproduced (lateral hole shape, powder removal), (3) ) The minimum diameter and height of the round bar, (4) the thinnest thickness and height of the plate, (5) the shape of the gap portion and the edge portion, and (6) the shape of the acute angle portion. 
In order to confirm the limit of shape reproduction, samples were prepared which changed the diameter of the hole and the rod, the angle of the stacking direction, and the like. The shape was printed without a support.
A photograph of the printed sample shape is shown in Figure 3. From the design dimensions, the part with dimensions of 20mm and 30mm has an accuracy of less than 0.1mm, while the part with dimensions of 105mm (sample width) produces an error of more than 0.3mm. This result is slightly worse than the directory parameter, but "it can be improved by adjusting the lamination conditions, but it is only a reference value." 
Let's take a look at the results of verifying these six points (Figure 4). 
Both the laser beam type and the electron beam type have good and bad parts reproducibility of the shape.
(1) With respect to the extreme modeling angle, it was confirmed that all the devices collapsed at an angle of about 30 degrees with respect to the horizontal plane. It does not happen at 40 degrees, so angles below 40 degrees should be modeled with supports.
(2) With respect to the lateral hole, in the laser beam type, the hole having a φ (diameter) of 0.5 mm is deformed, but the φ of 1 to 10 mm can reproduce the shape of the hole and remove the powder.
In the electron beam type, a hole with a φ of 0.5 to 8 mm is blocked. This is because preheating causes spurious sintering, and when sandblasting is performed, small-diameter holes cannot be sprayed. “If it is a straight shape, it can be removed with a wire, etc. However, if it is a structural part with a complex shape such as a cooling water pipe, it should be difficult to remove the powder.â€
(3) The minimum diameter of the round bar and (4) the thinnest thickness of the plate, the laser beam type has advantages. Taking a round bar as an example, a laser beam type can reproduce a φ0.29 mm round bar for a design value of φ 0.3 mm, while an electron beam type designates a circle of φ0.75 mm when the design values ​​are φ 0.3 mm and φ 0.5 mm. Baton. It is estimated that because the laser beam type does not exhibit spurious sintering, only the scanned portion is almost exactly sintered.
However, in the slender shape of such a thin shape, the electron beam type is more dominant in terms of the height in the stacking direction. When using a laser beam type to shape the sheet, the maximum height of 0.3mm is only 7.3mm. The estimation is due to the fact that the residual stress in the model leads to deformation, causing interlayer misalignment.
(5) In terms of the shape of the gap portion and the edge portion, the actual shape of the object is slightly narrower than the design value, in which the laser beam type has a relatively small deviation and is more excellent in reproducibility. (6) The shape of the acute angle portion is also more excellent in the laser beam type shape reproducibility, and the electron beam type is not caused by the shape collapse caused by the deformation.
Increased fatigue strength through HIP treatment
The shape reproducibility of a three-dimensional model using a 3D printer is described above, and the mechanical strength of the three-dimensional model is next examined. The research institute company verified the characteristic change by HIP treatment of high pressure gas under high temperature environment.
In recent years, metal 3D printers have greatly improved the density of stereoscopic models by improving the quality of powders and the output of heat sources. However, tiny bubbles (stomatals) still remain in the three-dimensional model. The company's observation of the cross-section found that "there are multiple air holes below 20 μm after molding."
The company crushes these air holes through HIP treatment. Implementation of density measurements confirmed that the density has improved*3. In terms of mechanical strength, the tensile strength decreased after HIP treatment, but the elongation at break was improved. Both the laser beam type and the electron beam type "have achieved an excellent value than the plate sold as ordinary titanium 64 before and after the HIP treatment".
Observing the cross-section structure, it was found that since the laser beam type is not preheated, the temperature change is fierce. From the point of view of the structure, the shape is very close to the structure after the solution and aging treatment. However, due to the preheating of the electron beam type, the shape of the tissue looks like a needle-like structure. The growth direction of the grains grows toward the direction of the buildup. Due to the heating by HIP treatment, both of them become acicular.
What is expected to be greatly improved through HIP treatment is fatigue strength. The research institute company implemented a rotary bending fatigue test and found that both the laser beam type and the electron beam type increased the fatigue limit by HIP treatment (Fig. 5). 
Laser beam fatigue strength (stress amplitude) is slightly higher. However, by implementing HIP treatment, the fatigue strength is greatly increased and the two are basically the same.
Specifically, from the stress amplitude (fatigue strength) after carrying out 107 fatigue tests, the stress amplitude of the laser beam type single body (post-molding state) is 360 to 370 MPa, and the electron beam type monomer is approximately 250 MPa. After HIP treatment, it was confirmed that the strength increased to 600 MPa.
The results of the validation conducted by the research institute company on the shape reproducibility and mechanical strength of the metal 3D printer were described above. These verifications are only carried out by the company under the current layered conditions. Yamamoto stated that "In order to achieve a better shape, we will also vigorously develop the conditions for the accumulation of the product." 76.png)
