How to use metal 3D printers in repairing metal parts and practical examples

In recent years, 3D printer technology (Additive Manufacturing; AM) has been used to maintain after-sales service for a huge number of product types after the production of a wide variety of products. It plays an important role in repair function. In addition to reducing lead times, metal AM also helps reduce costs, digitize parts, and maintain supply chains. For example, when replacing a damaged metal part, it is necessary to start by creating a blueprint and mold. It can be regenerated by processing. For that purpose, it is necessary to understand the typical design process in metal AM.

1.First of all

In recent years, AM has played an important role in small and medium volume production, spare parts and repair functions in maintaining post-production after-sales service for a wide variety of products. AM not only reduces lead times, it also reduces costs, digitizes parts, and helps maintain supply chains. For example, in the infrastructure industry, metal parts have been damaged in an old plant, etc., and the company that manufactures the parts no longer exists, causing a problem in the supply of parts. In this case, you will have to find another manufacturing company, or in the worst case, you will have to start from making blueprints and molds, which will incur a large work cost. However, by utilizing scanning technology and the features of AM, it is possible to regenerate only the defective parts by overlaying and machining while maintaining quality, thereby avoiding costs.

This paper describes the repair process (design and manufacturing process) in the event that a metal part (hereafter referred to as this product) used in the infrastructure industry or other industries is damaged, using scanning technology and metal AM. Masu. In this paper, we will explain the process of repairing a damaged part of an infrastructure device with metal AM. After that, a test piece and a hypothetical part (part A) are created, and a tensile test is performed on the test piece using a testing machine, until quantitative comparative evaluation of a single material and multiple materials (overlay material). to hold. It does not refer to practices such as infrastructure industries and other industries that utilize turbine blades.
‍Note : This report is a report created by 3D Printing Corporation, assuming the use of AM and scanning technology for "turbine blades" used in "infrastructure industry and other industries". This is only an explanation of the process based on hypotheses, and we do not conduct molding or durability experiments on actual parts.

Fig 1: Turbine blade made with a 3D printer

Table 1 Prerequisites

2. [AM process] Prerequisites

Assuming that metal parts are damaged, we will explain the manufacturing process when using a metal 3D printer as a repair or repair method. Prerequisites are shown in Table1.

In addition, in this article, we will use Meltio450, a metal 3D printer that uses the wire DED method, which is one of the DED (Direct Energy Deposition) methods. Metal powder materials are the mainstream of metal 3D printers, but this machine utilizes metal wires. There are roughly two types of 3D printers for metal wires: the DED method and the WAAM method. The reasons for using the metal wire method and the reason for using this machine, which is the DED method, are as follows.

The reason for using the DED method instead of the WAAM method is the amount of heat input. In the WAAM method, when repairing damaged metal parts with a metal 3D printer, the amount of heat input is large, so it is necessary to consider thermal deformation. This is because a large amount of heat input causes thermal deformation of the part, which adversely affects performance. (*Analysis and analysis of thermal deformation of metal parts subject to repair and repair due to heat input will be introduced in another column.)

The reason for using metal wire is that it is easy to operate, has low operating costs, and is inexpensive. A metal 3D printer that utilizes metal powder can form high-precision products with little or no support material. However, metal 3D printers that use metal powder have a high cost of introducing ancillary equipment, etc., and due to the nature of powdered materials, there is a high risk of dust explosions, etc., and operations tend to be complicated and difficult to operate. In addition, the manufacturing cost per product is high. It also requires a lot of care to maintain the build and maintenance.

For the above reasons, we decided that Meltio450, which uses the wire DED method, is effective for improving the performance of metal parts.

3. [AM process] Scraping damaged parts to create a foundation

Meltio450 in this article is a 3-axis 3D printer, so it can only form films in the Z-axis direction. Therefore, when overlaying using a 3-axis 3D printer, first cut the damaged product horizontally from the ground, and then cut the modeled part as shown on the right side of Fig. 1 according to the specifications of the 3D printer. It is necessary to prepare (≒ cut) the part. By doing this, the remaining part (hereinafter referred to as the base material) with a flat base for film deposition in the Z-axis direction is completed.

Fig 2: Left) Before cutting the damaged part Right) After cutting the damaged part

Fig 3: Cutting part A

4. [AM process] 3D scan of the defective part (② in Fig. 4)

In "3", the unevenness caused by the damage between the damaged part and the base material was flattened. However, as it is, it is not possible to build up the missing part with a 3D printer. The 3D printer can finally print after following the steps shown in Fig. 4.

3D printers start with data. In order to print instructions to a 3D printer on an already existing object like the base material in this case, it is necessary to create accurate digital data that is as close as possible to the dimensions of the object in the physical world. This is called "Net Shape [1]" . To create such precise digital data, we primarily utilize technologies that convert the physical world to digital, such as 3D scanning technology. The procedure for this is shown in Fig. 4.

An operator uses a 3D scanner to collect surface information (point cloud data) of objects in the physical world and create rough 3D (mesh) data.

[1] Net Shape: Net, unmultiplied final shape

① Cutting the base material (if necessary)

② Scanning

③ 3D design creation and adjustment

④ Slice (layer generation)

⑤ Print

⑥ Completion of post-processing (cutting, etc.)

Fig 4: Procedure from "3D data" to "completion"

5. [3D data correction and creation (Fig. 4 ③)] Data correction

In "4", the information of the material world was converted into digital data. The accuracy of digital data depends on the specifications and performance of the 3D scanner and the environment in which the measurement is performed, and today it is possible to create highly complete digital data from the first measurement. However, the mesh data lacks precision for use in 3D printers. Therefore, it is necessary to convert the mesh data to higher-dimensional data (hereinafter referred to as 3D CAD data, etc.). At present, the shortage is supplemented by the assistance of the automatic generation function by software and the hands of humans (engineers, etc.).

Fig 5: Flow of data conversion

Fig 6: State at the time of data creation

6. [Correction and creation of 3D data (Fig. 4 ③)] Creation of data

Now that the 3D CAD data of the base material has been completed, we can start creating data for repair and repair (hereinafter referred to as overlay data). This time, based on the 3DCAD data created in "5", we will redesign the missing part of this product. Here, the premise that must be kept in mind when redesigning is the machining process.

When considering cutting as a premise, if only the same volume as the defective part is built up, the finished product after cutting will be smaller than the net shape. In order to prevent this, it is necessary to add excess thickness to the damaged part (see Fig. 8). A shape that is as close as possible to the finished product is called a "Near-Net Shape [2] ".

[2] Near-Net Shape: Near-Net Shape

Fig 7: Part A after cutting

Fig 8: Near net shape data after redesign

7. Build-up of defect part (Fig. 4 ④⑤)

Utilizing the redesign data, it will be possible to start repairs and repairs with metal 3D printers. The method of depositing a wire on the base material is almost the same as the conventional welding technology such as MIG welding. Masu. If the reference point deviates, the base material and the redesign data will deviate, making it impossible to form a film normally. In addition to 3-axis metal 3D printers, there are also 5-axis and 6-axis metal 3D printers that utilize robots and positioners.

After aligning the reference points, the printed specimen will look like Fig. 10/Fig. 11/Fig. 12. We were able to create a model that assumes the reproduction of a near-net shape in which the missing part is built up with excess thickness on the base material.

Fig 9: Part A after padding

Fig 10: Inconel printed on SKD11 block

Fig 11: Side view of the finished model

8. [Post-processing (Fig. 4 ⑥)] Cutting

Including this article, it is impossible to achieve high-precision dimensional tolerances only by repairing and repairing with a metal 3D printer. Machining such as cutting must be included in the process.

From the near net shape, the excess thickness is cut out to the product (≒ net shape) that has achieved the dimensional tolerance by a cutting machine (Fig. 13). Machining was not performed in this article.

Fig 12: Simplified drawing of the cutting process of excess wall

9. [Post-processing (Fig. 4 ⑥)] Cut off the test piece from the plate (EDM)

If it is necessary to remove the product from the plate after machining is complete, EDM (Electrical Discharge) is used to separate it (see Fig. 13).

Fig 13: Left) Mold for specimen Middle) Mold during EDM Right) Finished specimen

10. Tensile test

Cut the object created in Fig. 10/Fig. 11 with EDM as shown in Fig. 13, and cut 3 each of "SKD11 (specimen A group)" and "SKD11 + Nickel718 (specimen B group)". I made it (Fig. 14/Fig. 15/Fig. 16). The specimens in this article are not heat treated. As you can see from Fig. 15, as long as you visually check the cross-section of the joint where the build-up starts, you can see that the appearance is nicely fused.

Fig 14: Cross section of test piece (upper: Nickel718, lower: SKD11)

Fig 15: Test piece created

Fig 16: Specimen cross-section (left: outer cross-section, right: side)

Tensile tests were performed on the prepared specimens of groups A and B using an in-house precision universal testing machine (Fig. 17). The results are shown in Fig. 18. Group B was slightly weaker than group A, and the displacement was half that of group A due to fracture at the joint. In terms of strength, we believe that the results were good enough to say that both counties had the same strength. We are also considering doing tensile tests after making the printed Nickel718 specimens.

Fig 17: SHIMAZU precision universal testing machine AGX-V2
Fig 18: Tensile strength and strain
Table 2: Tensile test results

11. Conclusion

In this paper, we have explained the repair process (design and manufacturing process) when assuming cases where metal parts used in the infrastructure industry and other industries are damaged, using scanning technology and metal AM. In addition, we were able to derive the tensile strength of the base material and the overlaid base material by conducting a tensile test on the prepared test piece (without heat treatment).

Along with the commentary, we demonstrated the process of actually regenerating only the defective part through the test piece by overlaying and machining. In the tensile test of the test piece, we were able to obtain the same tensile strength results for one material and multiple materials by quantitative comparative evaluation of one material and multiple materials (build-up materials).

In the future, we plan to create a heat-treated test piece, conduct a tensile test, and perform cutting processing of hypothetical molded parts.


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