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1 용접에의한 Metal 3D Printing 의동향 대한용접 접합학회지제 34 권 4 호별책

2 1 ISSN Online ISSN 용접에의한 Metal 3D Printing 의동향 변재규 * 조상명 **, * 부경대학교대학원신소재시스템공학과 ** 부경대학교신소재시스템공학과 Trend of Metal 3D Printing by Welding Jae-Gyu Byun* and Sang-Myung Cho**, *Dept. of Materials System Engineering, Graduate School, Pukyong National University, Busan 48513, Korea **Dept. of Materials System Engineering, Pukyong National University, Busan 48513, Korea Corresponding author : pnwcho@pknu.ac.kr (Received June 14, 2016 ; Revised July 13, 2016 ; Accepted July 29, 2016) Abstract 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. Key Words : Metal 3D printing, Additive manufacturing, Welding 1. 서론 3D printing 은 CAD 로설계된부품의정보를일정한두께의층으로슬라이싱한 STL 파일로변환하여소재를적층제조하는공정을의미하며 AM(Additive manufacturing) 이 ASTM 의공식명칭이다 1,2). 플라스틱소재를사용하는기존의 AM 은소재의용융점이약 100~ 400 로낮아쉽게만들수있었으나, 금속을사용하는 AM은용융점이약 1000~2000 로용융및적층시키기위하여플라스틱 AM 과는달리상당한기술이필요하다. 지난 30년간 RP(Rapid Prototyping) 라는명칭으로 metal AM은꾸준히발전해왔으며분말베드에고에너지열원인레이저와전자빔으로적층하는 PBF(Powder Bed Fusion) 방식으로가장먼저개발적용되었으며, 현재는소재를직접공급하면서열원으로용융 적층하는 DED(Directed Energy Deposition) 방식의 metal AM 이연구 적용되고있다. DED 방식은분말기반, 고체용가재기반으로나뉘며, 선진국에서는생산성이높은고체용가재기반의 DED 방식으로이미항공우주, 국방분야에먼저적용하고있다. 따라서이논문은전반적인 metal AM과용접에의한 AM의연구개발동향을알아보고자한다. 2. Metal AM 의분류 Metal AM 의분류는 Fig. 1 과같이 PBF 방식과 DED Powder bed fusion Powder based AM for metals Powder based Directed energy deposition Fig. 1 Classification of AM Solid filler based Journal of Welding and Joining, Vol.34 No.4(2016) pp1-8

2 방식으로나뉘게된다. PBF 는분말을소재로베드에분말을평평하게분포시킨후고에너지의레이저나전자빔을선택적으로조사하여소결시키거나용융시켜적층하는방법으로서형상의정밀도가우수하나생산성이낮고적층제품의소결및용융균일도가좋지못하여제품의강도와충격치의확보가어려운단점이있다. DED 는소재를직접공급하면서고밀도에너지열원으로용융시켜적층하는방법으로용접과유사하다.

3 2 방식으로나뉘게된다. PBF 는분말을소재로베드에분말을평평하게분포시킨후고에너지의레이저나전자빔을선택적으로조사하여소결시키거나용융시켜적층하는방법으로서형상의정밀도가우수하나생산성이낮고적층제품의소결및용융균일도가좋지못하여제품의강도와충격치의확보가어려운단점이있다. DED 는소재를직접공급하면서고밀도에너지열원으로용융시켜적층하는방법으로용접과유사하다. DED 는정밀도가낮아후가공이필요한단점이있지만, 생산성이높고재현반복성이뛰어나며강도와충격치가높은장점을가진다. Fig. 2와같이제품의생산성, 크기, 형상의정밀도와해상도에따라다양한 metal AM 방식이사용된다 3). 이러한 DED 방식은고에너지의레이저나전자빔을이용하여동축으로분말을송급및적층하는분말기반 DED, 용접과유사하게고체용가재를송급하여다양한열원으로용융및적층하는고체용가재기반 DED 로분류된다. 3. PBF process Table 1은 metal AM 공정의적층방식과소재에따른분류이다. PBF 는분말과레이저열원을기반으로하는독일EOS사에서 SLS(Selective Laser Sintering) 공정을시작으로발전하고있으며, 유럽의레이저업체에서대부분의공정노하우를가지고있다. 현재는용융방식의 SLM(Selective Laser Melting) 공정이주로레이저업체에의해개발되어지고있다. 현재 PBF 공정은장치와소재의개발에이어모니터링기술이활발히연구개발중이다. 4. DED process 4.1 분말기반 DED 분말을기반으로한 DED 방식은미국의 Optomec 에 (d) Decreased resolution & complexity (c) (e) (f) 20cm Machining (g) Increased deposition rate & part size Fig. 2 Comparison of surface finish and deposition rate between powder-feed/-bed and wire-feed technologies. Titanium 3D-micro framework-structure based on a diamond lattice fabricated using powder bed electron beam melting. A powder-feed-directed light fabrication of 316 stainless steel hemispherical shapes. (c) Three as consolidated powder-feed laser consolidation IN-625 samples with surface roughness 1 2 μm. (d) A large samples fabricated by WAAM from Cranfield University. (e) 2219 Al airfoil produced by wire-feed EBF3. (f) As-deposited sample made by wire-feed LAM (AeroMet) with stair stepping surface, and g shows the sample after surface machining 3) 300 Journal of Welding and Joining, Vol. 34, No. 4, 2016

용접에의한 Metal 3D Printing 의동향 3 Table 1 Classification of metal AM process PBF DED Material Power source Process Company Deposition rate Powder based Solid filler based Laser SLS(Selective Laser

Electron beam EBM(Electron Beam Melting) ARCAM 0.1~0.2kg/h Laser Electron beam GTAW, GMAW arc GMAW arc LENS(Laser Engineered Net Shaping) Optomec 0.1~2kg/h DMD(Direct Metal Deposition) DM3D 0.

4 용접에의한 Metal 3D Printing 의동향 3 Table 1 Classification of metal AM process PBF DED Material Power source Process Company Deposition rate Powder based Solid filler based Laser SLS(Selective Laser Sintering) EOS, 3D systems, TPM, Farsoon, etc. 0.1~0.2kg/h DMLS(Direct Metal Laser Sintering) EOS 0.1~0.2kg/h SLM(Selective Laser Melting) SLM Solutions, 3D systems, Realizer, 0.1~0.3kg/h Concept laser, etc. Electron beam EBM(Electron Beam Melting) ARCAM 0.1~0.2kg/h Laser Electron beam GTAW, GMAW arc GMAW arc LENS(Laser Engineered Net Shaping) Optomec 0.1~2kg/h DMD(Direct Metal Deposition) DM3D 0.1~2kg/h DMT(Direct Metal Tooling) InssTek 0.1~2kg/h CLAD(Construction Laser Additive Direct) BeAM 0.1~2kg/h EBAM(Electron Beam Additive Manufacturing) Sciaky ~9kg/h WAAM(Wire Arc Additive Manufacturing) Cranfield Univ. ~4kg/h DML(Direct Metal Lamination) MUTOH ~4kg/h ADED(Arc Directed Energy Deposition) EWI ~4kg/h IFF(Ion Fusion Formation) Honeywell ~3kg/h Plasma arc RPD(Rapid Plasma Deposition) Norsk titanium ~6kg/h GTAW arc STAM(Super-TIG Additive Manufacturing) Super-TIG welding ~7kg/h Laser scanner Visual camera Light source(top) Light source(side) Light source(front) Build cylinder Window of camera-view Feed cylinder Working plane Fig. 3 Visual inspection system principle and example image of deposited powder bed generated by craeghs et al. 4) Laser Camera Scanner mirror Pixels Diode scanner Semi transparent Mirror Mirror Reflecting laser wavelength Transmitting observation wavelength Gray value Meltpool Pixels Fig. 4 Schematic showing arrangement of photodiode and camera and an example output from the camera system showing varying intensity values (right) achieved 5) 대한용접 접합학회지제 34 권제 4 호, 2016 년 8 월 301

4 Semi-reflective mirror Laser Coaxial view Nozzle Side view Powder nozzle Vp Powder stream Front view V d i Melt pool d i Δh Melt-pool Substrate H Δh Fig.

6) 서동축으로분말을공급하면서레이저를열원으로하는 LENS(Laser Engineered Net Shaping) 공정을개발하여 DED 의토대를마련하였다.

2 고체용가재기반 DED 로고체용가재를송급하는방식인 WAAM (Wire Arc Additive Manufacturing) 을연구개발중이다 20-25).

중국의 Harbin Institute of Technology 에서는 GMAW 아크를열원으로비젼센서를통한적층폭과높이를제 Welding torch 미국의 NASA Langley lab.

5 4 Semi-reflective mirror Laser Coaxial view Nozzle Side view Powder nozzle Vp Powder stream Front view V d i Melt pool d i Δh Melt-pool Substrate H Δh Fig. 5 DMD experiments - Experimental set-up and associated diagnostics; detail of the laser-powder-melt-pool interaction zone (H = apparent external height of the melt-pool, Δh = additive layer height) 6) 서동축으로분말을공급하면서레이저를열원으로하는 LENS(Laser Engineered Net Shaping) 공정을개발하여 DED 의토대를마련하였다. 분말기반의 DED 는레이저업체에따라 DMD(Direct Metal Deposition), DMT(Direct Metal Tooling) 7), CLAD(Construction Laser Additive Direct) 등다양한이름으로연구개발중이다. 4.2 고체용가재기반 DED 로고체용가재를송급하는방식인 WAAM (Wire Arc Additive Manufacturing) 을연구개발중이다 20-25). 인도의 IIT(Indian Institute of Technology) Bombay 에서는 CMT(Cold Metal Transfer) 를사용하여 CNC 와결합한 metal AM장치를연구개발중이다 26-28). 중국의 Harbin Institute of Technology 에서는 GMAW 아크를열원으로비젼센서를통한적층폭과높이를제 Welding torch 미국의 NASA Langley lab. 에서개발하여미국 Sciaky 사로기술이전된 EBAM(Electron Beam Additive Manufacturing) 공정은진공상태에서고체용가재를송급하여전자빔으로용융 적층하는방식으로서용착속도가 9kg/h 로전세계에서가장높은생산속도를가지며북미지역에서연구가활발히이루어지고있다 8-15). 미국의 Nottingham Univ. 16,17), Kentucky Univ. 18,19) 등은 GMAW 아크열원을사용하여적층경로와적층제품의방향에따른기계적물성을측정하였다. 영국 Cranfield Univ. 에서는 GMAW, GTAW, PAW등의아크열원으 Welding torch Deposited sample Deposited sample Gun motions Wire feeder Molten alloy Re-solidified puddle alloy EB Gun Electron beam Prior deposit Substrate Direction of part motion Z Y X Process coordinate system Fig. 6 Schematic diagram of the EBAM process 11) (c) Welding torch Deposited test piece Fig. 7 Machine experimental set up for SAM edgetek machine ABB robot (c) friction stir welding machine 24) 302 Journal of Welding and Joining, Vol. 34, No. 4, 2016

용접에 의한 Metal 3D Printing의 동향 5 Up and down positions of the torches 3-axis HLM machine (only Fronius TPS 4000 is fully visible: The power Supply and wire feeder of TPS 2700 CMT is kept outside) Two

8 The 3-axis hybrid layered manufacturing machine at IIT bombay28) Structured light vision sensor Motoman Up20 Welding system Bead image Control cabinet Planning and slicing system Fig.

6 용접에 의한 Metal 3D Printing의 동향 5 Up and down positions of the torches 3-axis HLM machine (only Fronius TPS 4000 is fully visible: The power Supply and wire feeder of TPS 2700 CMT is kept outside) Two torches mounted on the spindle head Fig. 8 The 3-axis hybrid layered manufacturing machine at IIT bombay28) Structured light vision sensor Motoman Up20 Welding system Bead image Control cabinet Planning and slicing system Fig. 9 Schematic diagram of the experimental set-up32) 어하는 알고리즘을 만들었으며, 적층 제품의 열응력과 잔 류응력을 해석하였고29-33), Jiaotong Univ.34), Shanghai Univ.35)등에서는 PAW 아크를 열원으로 공정최적화 변수를 연구개발 중이다. 일본의 Osaka Univ.에서는 GTAW의 아크 열원으 로 TiAl, TiNi, NiAl등의 이종재 적층방법에 대하여 연구하였으며36-38) Tokyo Univ.에서는 GMAW 아크 열원을 사용한 metal AM 장치를 MUTOH사와 함께 연구 개발하였다39). 독일EADS에서는 레이저열원에 고 체용가재를 송급하는 공정을 주로 연구개발 중이며40,41), 레이저 열원과 GTAW열원으로 제작된 제품의 기계적 물성에 대하여 평가하였다42). 벨기에의 Leuven Univ.에 서는 고체용가재 기반의 레이저열원 적층방식에서 GTAW 아크로 열원을 변경하여 Ti-6Al-4V 제품의 기계적 물 성을 평가하고 있다43-45). 호주의 Wollongong Univ.에서는 GTAW와 GMAW 의 아크를 열원으로 하여 Ti-6Al-4V 제품의 적층경로 최적화 및 적층 후 가공경로 최적화에 관한 연구를 진 행 중이다46-51). 국내에서는 KIST에서 GMAW의 아크를 열원으로 적 층 경로 최적화 및 기계적 물성 평가를 하였고52-53), SuperTIG Welding에서 GTAW의 아크를 열원으로 C-fillTungsten electrode Plasma arc welding head Z Argon atmosphere X Y Shielding device Welding wire Additive direction Deposited direction Microhardness direction Tensile specimens Substrate Fig. 10 Schematic drawing of thin-wall deposited by PPAM process35) 대한용접 접합학회지 제34권 제4호, 2016년 8월 303

6 Water tank Welding torch Water pipe Shield gas container X Welding torch Z Welding wire Feeder Substrate Welding machine Water level control B Y NC data input PC Direct metal lamination unit Fig.

PBF 에서고체용가재기반의 DED 로옮겨가는추세이다. 이는 Ti, Inconel 과같은특수분말소재의가격에비해고체용가재가저렴하고생산성또한고체용가재기반의 DED 가우수하기때문이다. 이에따라낮은정밀도와자유도를가짐에도불구하고고체용가재를기반으로하는 DED 방식의공정에관한연구가눈에띄게증가하고있었다.

전세계적으로생산성향상 Bead width Bead height END Fig. 12 Automated process planning for robotic WAAM system 51) Appearance Cross section Fig. 13 STAM at super-tig welding Co., ltd. References 1.

7 6 Water tank Welding torch Water pipe Shield gas container X Welding torch Z Welding wire Feeder Substrate Welding machine Water level control B Y NC data input PC Direct metal lamination unit Fig. 11 Direct metal rapid fabrication machine 37) 4-axis control machine 2D path planning 3D Slicing Bead modeling Weld setting Input layer Hidden layer Output layer Robot code generation Machining 을위하여 PBF 에서고체용가재기반의 DED 로옮겨가는추세이다. 이는 Ti, Inconel 과같은특수분말소재의가격에비해고체용가재가저렴하고생산성또한고체용가재기반의 DED 가우수하기때문이다. 이에따라낮은정밀도와자유도를가짐에도불구하고고체용가재를기반으로하는 DED 방식의공정에관한연구가눈에띄게증가하고있었다. CAD modeling START Wire-feed rate Travel speed er 54-56) 를사용하여용융 적층하는공정을개발하였고 57), 적층방향에따른기계적물성을평가하였고, 공정최적화를연구개발중이다 58-61). 5. 결론 본리뷰논문에서는용접에의한 metal AM과관련한연구동향을알아보았다. 전세계적으로생산성향상 Bead width Bead height END Fig. 12 Automated process planning for robotic WAAM system 51) Appearance Cross section Fig. 13 STAM at super-tig welding Co., ltd. References 1. ASTM, F a, Standard Terminology for Additive Manufacturing Technologies 2. Terner, Mathieu. "The Current State, Outcome and Vision of Additive Manufacturing." Journal of Welding and Joining (Vol. 33, No. 6) (2015), Ding, Donghong, et al., Wire-feed additive manufacturing of metal components, technologies, developments and future interests. The International Journal of Advanced Manufacturing Technology (2015), Craeghs, Tom, et al., Online quality control of selective laser melting. Proceedings of the Solid Freeform Fabrication Symposium, Austin, TX. (2011) 5. Berumen, Sebastian, et al., Quality control of laser-and powder bed-based Additive Manufacturing (AM) technologies. Physics procedia, 5(2010), Gharbi, Myriam, et al., Influence of various process conditions on surface finishes induced by the direct metal deposition laser technique on a Ti-6Al-4V alloy. Journal of Materials Processing Technology 213(5) (2013), Kim, Woosung, et al. "Effects and Application Cases of Injection Molds by using DED type Additive Manufacturing Process." Journal of Welding and Joining 32.4 (2014), Watson, J. K., et al., Development of a prototype lowvoltage electron beam freeform fabrication system. (2002) 304 Journal of Welding and Joining, Vol. 34, No. 4, 2016

8 용접에의한 Metal 3D Printing 의동향 7 9. Taminger, Karen, and Robert A. Hafley, Electron beam freeform fabrication, a rapid metal deposition process, (2003) 10. Taminger, Karen M., and Robert A. Hafley, Electron beam freeform fabrication for cost effective near-net shape manufacturing, (2006) 11. Stecker, S., et al., Advanced Electron Beam Free Form Fabrication Methods & Technology, Session 2 (2006), Seufzer, W. J., and K. M. Taminger, Control methods for the electron beam free form fabrication process, NATIONAL AERONAUTICS AND SPACE ADMIN LANGLEY RESEARCH CENTER HAMPTON VA, (2007) 13. Mitzner, Scott, et al., Grain refinement of freeform fabricated Ti-6Al-4V alloy using beam/arc modulation, (2012) 14. Fox, Jason, and Jack Beuth, Process mapping of transient melt pool response in wire feed E-beam additive manufacturing of Ti-6Al-4V, Solid Freeform Fabrication Symposium, Austin, TX, (2013) 15. Gockel, Joy, Jack Beuth, and Karen Taminger, Integrated control of solidification microstructure and melt pool dimensions in electron beam wire feed additive manufacturing of Ti-6Al-4V, Additive Manufacturing, 1 (2014), Dickens, P. M., et al., Rapid prototyping using 3-D welding, Proc. Solid Freeform Fabrication Symp, (1992) 17. Everton, Sarah K., et al., Review of in-situ process monitoring and in-situ metrology for metal additive manufacturing, Materials & Design, (2016) 18. Zhang, Yu Ming, et al., Automated system for welding-based rapid prototyping, Mechatronics 12(1) (2002), Zhang, YuMing, et al., Weld deposition-based rapid prototyping, a preliminary study, Journal of Materials Processing Technology 135(2) (2003), Almeida, P. S., and S. 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02-18-수정(2).hwp 6 Ti-6Al-4V 의 AM 에서기계적성질에미치는 Interpass Peening 의영향 ISSN 2466-2232 Online ISSN 2466-2100 변재규 * 이희준 ** 조상명 ***, * 부경대학교대학원신소재시스템공학과 ** 현대로템 ( 주 ) 중기사업본부 *** 부경대학교신소재시스템공학과 The Effect of Interpass Peening