• 한국기계가공학회지
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• 제21권5호
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• pp.91-97
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• 2022

The Directed Energy Deposition (DED) is a representative metal additive manufacturing method. Owing to its strong point of repairment, its application is gradually spreading in aerospace applications, power generation, military components, and mold making. 5-axis cladding is needed to repair damage, such as wear and scratches on cylindrical surfaces to circular-shaped parts, including sleeves and liners. Furthermore, the condition of cladding on inclined parts must also be considered to prevent interference between the nozzle and the part. In this study, the effects of changes in scanning speed due to the 5-axis control system and differences from the height of laser beam irradiation due to inclination are evaluated among the items that should be additionally considered in 5-axis cladding compared to 3-axis cladding. Moreover, the trends of the width and height of the clad are identified by different tilting angles via single line cladding. Lastly, cladding methods on cylindrical surfaces at various angles are proposed to enhance the clad quality and post-processing efficacy. These results can be applied with 5-axis cladding on inclined surfaces, including cylindrical surfaces.

• 한국분말재료학회지
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• 제27권3호
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• pp.219-225
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• 2020

The directed energy deposition (DED) process of metal 3D printing technologies has been treated as an effective method for welding, repairing, and even 3-dimensional building of machinery parts. In this study, stainless steel 316L (STS316L) and Inconel 625 (IN625) alloy powders are additively manufactured using the DED process, and the microstructure of the fabricated STS316L/IN625 sample is investigated. In particular, there are no secondary phases in the interface between STS316L and the IN625 alloy. The EDS and Vickers hardness results clearly show compositionally and mechanically transient layers a few tens of micrometers in thickness. Interestingly, several cracks are only observed in the STS 316L rather than in the IN625 alloy near the interface. In addition, small-sized voids 200-400 nm in diameter that look like trapped pores are present in both materials. The cracks present near the interface are formed by tensile stress in STS316L caused by the difference in the CTE (coefficient of thermal expansion) between the two materials during the DED process. These results can provide fundamental information for the fabrication of machinery parts that require joining of two materials, such as valves.

• 한국산업융합학회 논문집
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• 제25권6_1호
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• pp.941-952
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• 2022

In this study, additive manufacturing technology was applied to restore a planner miller that was unusable due to aging. The drive spur gear of the planner miller was inoperable due to many defects in the teeth. The shape of the defective gear teeth was restored by deposition of the defective teeth using the DED method. However, as the location of the deposition head and the location of the set origin became farther, the deposition shape was different from the modeling shape. Nonetheless, since the modeling of the deposition part was designed to be larger than the tooth shape of the original gear, it was possible to completely restore all gear teeth through post-processing. The arrangement interval of the flow lines of the deposition part was narrower than that of the substrate. The hardness of the substrate was 172 HV, and that of the deposition part was 345 HV, which was twice as high as that of the substrate.

• 한국기계가공학회지
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• 제20권12호
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• pp.113-122
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• 2021

Complicated residual stress distributions occur in the vicinity of a deposited region via directed energy deposition (DED) process owing to the rapid heating and cooling cycle of the deposited region and the substrate. The residual stress can cause defects and premature failure in the vicinity of the deposited region. Several heat treatment technologies have been extensively researched and applied on the part deposited by the DED process to relieve the residual stress. The aim of this study was to investigate the residual stress characteristics of a specimen fabricated by DED and a quenching process using thermomechanical analyses. A coupled thermomechanical analysis technique was adopted to predict the residual stress distribution in the vicinity of the deposited region subsequent to the quenching step. The results of the finite element (FE) analyses for the deposition and the cooling measures show that the residual stress in the vicinity of the deposited region significantly increases after the completion of the elastic recovery. The results of the FE analyses for the heating and quenching stages further indicate that the residual stress in the vicinity of the deposited region remarkably increases at the initial stage of quenching. In addition, it is observed that the residual stress for quenching is lesser than that after the elastic recovery, irrespective of the deposited material.

• 한국기계가공학회지
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• 제20권9호
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• pp.1-10
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• 2021

Recently, the repair and recycling of damaged mechanical parts via metal additive manufacturing processes have been industrial points of interest. This is because the repair and recycling of damaged mechanical parts can reduce energy and resource consumption. The directed energy deposition(DED) process has various advantages such as the possibility of selective deposition, large building space, and a small heat-affected zone. Hence, it is a suitable process for repairing damaged mechanical parts. The shaft is a core component of various mechanical systems. Although there is a high demand for the repair of the shaft, it is difficult to repair with traditional welding processes because of the thermal deformation problem. The objective of this study is to propose a repair procedure for a damaged shaft using the DED process and discuss its applications. Three types of cases, including a small shaft with a damaged surface, a medium-size shaft with a worn bearing joint, and a large shaft with serious damage, were repaired using the proposed procedure. The microstructure and hardness were examined to discuss the characteristics of the repaired component. The efficiency of the repair of the damaged shaft is also discussed.

• 한국분말재료학회지
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• 제25권3호
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• pp.220-225
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• 2018

The microstructure and mechanical characteristics of SUS630 specimens fabricated using the direct energy deposition (DED) process are investigated. In DED, several process parameters such as laser scan speed, chamber gas flow, powder carrier gas flow, and powder feed rate are kept fixed; the laser power is changed as 150 W, 180 W, and 210 W. As the laser power increases, the surface becomes smooth, the thickness uniformity improves, and the size and number of pores decreases. With the increase in laser power, the hardness deviation decreases and the average hardness increases. The microstructure of the material is columnar; pores are formed preferentially along the columnar interface. The lath-martensite phase governs the overall microstructure. The volumetric fraction of the retained austenite phase is measured to increase with the increase of laser input power.

• Journal of Welding and Joining
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• 제34권4호
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• pp.1-8
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• 2016

Metal AM(Additive Manufacturing) has been steadily developed and that is classified into two method. PBF(Powder Bed Fusion) deposited in the bed by the laser or electron beam as a heat source of the powder material and DED(Directed Energy Deposition) deposited by varied heat source of powder and solid filler material. In the developed countries has been applying high productivity process of solid filler metal based DED method to the aerospace and defense sectors. The price of the powder material is quite expensive compared to the solid filler metal. A study on DED method that is based on a solid filler metal is increasing significantly although was low accuracy and degree of freedom.

• 한국압력기기공학회 논문집
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• 제19권1호
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• pp.11-19
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• 2023

Additive manufacturing technology, called as 3D printing, is one of fourth industrial revolution technologies that can drive innovation in the manufacturing process, and thus should be applied to nuclear industry for various purposes according to the manufacturing trend change in the future. In this paper, we performed tensile tests of 3D printed stainless steel 316L as-built specimens manufactured by two types of technology; DED (Directed Energy Deposition) and PBF (Powder Bed Fusion). Their mechanical properties (tensile strength, yield strength, elongation and reduction of area) were compared. As a result of comparison, the mechanical properties of the PBF specimens were slightly better than those of DED specimens. In the same additive type of specimens, the tensile and yield strength of specimens in the X and Y direction were higher than those in the Z direction, but the elongation and ROA were lower.

• KEPCO Journal on Electric Power and Energy
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• 제7권1호
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• pp.129-135
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• 2021

Recently, additive manufacturing (AM) technology such as powder bed fusion (PBF) and directed energy deposition (DED) are actively attempted as consumers' needs for parts with complex shapes and expensive materials. In the present work, the effect of processing parameters on the mechanical properties of 316L stainless steel coupons fabricated by PBF and DED AM technology was investigated. Three major mechanical tests, including tension, impact, and fatigue, were performed on coupons extracted from the standard components at angles of 0, 45, 90 degrees for the build layers, and compared with those of investment casting and commercial wrought products. Austenitic 316L stainless steel additively manufactured have been well known to be generally stronger but highly vulnerable to impact and lack in elongation compared to casting and wrought materials. The process-induced pore density has been proved the most critical factor in determining the mechanical properties of AM-built metal parts. Therefore, it was strongly recommended to reduce those lack of fusion defects as much as possible by carefully control the energy density of the laser. For example, under the high energy density conditions, PBF-built parts showed 46% higher tensile strength but more than 75% lower impact strength than the wrought products. However, by optimizing the energy density of the laser of the metal AM system, it has been confirmed that it is possible to manufacture metal parts that can satisfy both strength and ductility, and thus it is expected to be actively applied in the field of electric power section soon.

• 한국기계가공학회지
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• 제20권7호
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• pp.33-40
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• 2021

Current industrial flow is directed toward reducing the usage of raw materials by reusing parts, which is referred to as a circular economy (CE). Repair is one of the most value-added approaches in CE, which can be efficiently accomplished via additive manufacturing. The repair technology of metallic parts via the directed energy deposition process, which includes the selective removal and redeposition of damaged regions of metallic parts. Residual stress characteristics depend on the shape of the part and the shape of the redeposition region. The objective of this study is to investigate the effects of the radius and corner position of the substrate on the residual stresses for repair by using finite element analysis (FEA). The residual stress distribution of the 45° angle groove at the edge of the circular shape models on the outer and inner radii was analytically investigated. The analysis was accomplished using SYSWELD software by applying a moving heat source with defined material properties and cooling conditions integrated into the FEA model. The results showed a similar pattern of concentrated stress distribution for all models except the 40-mm and 60-mm radii, for which the maximum stress locations were different. The maximum residual stresses are high but lower than the yield strength, suggesting the absence of cracks and fractures due to residual stresses.