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금속적층제조기술의국내외개발동향과기술적이슈 대한용접 접합학회지제 34 권 4 호별책 2016. 8

9 ISSN 2466-2232 Online ISSN 2466-2100 금속적층제조기술의국내외개발동향과기술적이슈 강민철 *, 예대희 ** 고근호 ** * 3D 프린팅연구조합 ** 한국마그네슘기술연구조합 International Development Trend and Technical Issues of Metal Additive Manufacturing Min-Cheol Kang*,, Dea-Hee Ye** and Geun-Ho Go** *3D Printing Research Organization, Seoul 06307, Korea **Korea Magnesium Technology Research Association, Changwon 51395, Korea Corresponding author : mkang@3dpro.or.kr (Received July 6, 2016 ; Revised July 19, 2016 ; Accepted July 21, 2016) Abstract Metal parts are produced by conventional methods such as casting, forging and cutting, extrusion, etc. However, nowadays, with additive manufacturing (AM), it is possible to directly commercialize by means of stacking of equipment to the 3D drawing and use of high precision tools such as laser source. Thus, drawing of materials is an important aspect in delivering good products. AM deals with production of lighter aircraft parts and few more three-dimensional molds, it wish to manufacture special medical parts and want to steadily expand the new market area. The cost of related equipment and materials are still expensive and difficult to obtain on a mass production. However, the ability to make changes and lead the innovation in the paradigm of traditional manufacturing process is still effective. In this paper, we introduce metal AM and the principles of the related devices, metal powder production process, and their application. Key Words : Additive manufacturing, Atomization, PBF, DED 1. 개요 전통적인금속부품의생산방법은주조, 단조, 절삭가공, 압출등의방법으로제품을생산하였다면, 적층가공기술은 3D도면과재료, 레이저등을소스로하는적층장비만있으면바로제품화가가능하다. 따라서누구나도면만있으면제품을생산할수있는적층제조기술이 3차산업혁명, 제조업의인터넷혁명 으로불리우며전세계인의관심을한몸에받고있다. 그러나지난 2-3 년간언론보도등으로전지전능한도구로과장된면이있었으나기존전통방식으로제조가불가능한입체냉각몰드, 항공기부품등을더욱경량화하는방향, 그리고개인맞춤형의료용부품등으로새로운시장영 역을꾸준히확장하고있다. 또한아직은관련장비및재료가격이비싸고대량생산이힘들다는한계로회의적인시각도존재하고있다. 그러나기존제조공법으로제조가불가능한제품을만든다는제조업의패러다임의변화와전통적인제조공정을혁신을이끌능력은여전히유효하다. 본고에서는메탈 3D 프린터와관련된장비의원리, 금속분말제조공정, 적용사례등을살펴보고자한다 1,2). 1.1 적층제조기술의분류와작동원리 3D 프린터는공식적인용어가아니며절삭가공 (Subtractive Machining) 과대조되는적층제조 (Additive Manufacturing) 가공식적인 ASTM 용어이다. 이적 Journal of Welding and Joining, Vol.34 No.4(2016) pp9-16 http://dx.doi.org/10.5781/jwj.2016.34.4.9

10 Table 1 Classification of additive manufacturing processes by ASTM Category Binder jetting Material jetting Powder bed fusion Directed energy deposition Sheet lamination Vat photopolymerization Material extrusion Description Liquid bonding agent selectively deposited to join powder Droplets of build material selectively deposited Thermal energy selectively fuses regions of powder bed Focused thermal energy melts materials as deposited Sheets of material bonded together Liquid photopolymer selectively cured by light activation Material selectively dispensed through nozzle or orifice 층제조기술은 Table 1에나타낸바와같이 7가지로분류하고있다. 적층제조기술은이미 20여년전에 RP(Rapid Prototyping) 기술로활용된기술이나최근원천기술이일부해제되면서개발에가속이붙었고대중화를앞당기는상황이되었다. 플라스틱의경우수지의다양화, 엔지니어링플라스틱의도입뿐만아니라금속, 세라믹등소재의다양화가진행되고산업체의활용도가확장되고있다. 특히금속적층제조에사용되는소재는 분말기반형 와이어기반형 박판기반형으로나눌수있다. 분말기반형은금속분말을아토마이저방식등으로급랭하여구형화된분말을대부분사용하며 Powder Bed Fusion(PBF) 와 Directed Energy Deposition (DED) 방식이대표적으로널리사용된다. 와이어기반형은용접의원리와똑같이베이스에와이어를용융시켜용융풀을형성한후기계가공으로마무리하는형태로서대표적인방법이 EBF(Electron Beam Freeform Fabrication) 가있다. 박판기반형은금속박판시트를여러층을적층하여초음파로접합시키는방법등이있으나와이어기반형과함께형상자유도가떨어져잘사용하지않는방식이다. 제조설계단계에서공정을미리전제로하여주조, 단조, 압출, 프레스등의공정을염두에두기때문에모든디자인이나기구설계가전통적인제조공법을고려한설계가중요하다. 그러나적층제조기술은엔지니어가설계한그대로를기존전통공정에서만든수없는어떠한제품도제작이가능하다. 즉복잡한냉각채널을가지는냉각몰드의경우기계가공으로는복잡한냉각수채널을제조할수없으나 Fig. 1에서보듯이금형표면에따라내부냉각채널을제조가가능해짐에따라사출금형이나다이캐스팅금형의경우제품의함몰이나수축을최대한줄일수있게설계가가능하여최종제품의불량률을줄이고생산성을올릴수있다. 둘째는 Complexity for free 이다. Fig. 2는항공기에사용되는브라켓으로내부를중공화하거나강성이요구되지않는영역을가감히제거할수있는최적설계 (topology optimization) 를보여준다. 이러한설계는동일한구조강성을확보가가능하고소재절감및경량화에도기여할수있는장점이있다. 셋째는 Potential elimination of tooling 이다. 기업들이프로토타입이나시제품생산시필요한금형비용을대폭줄일수있어도전적인제품개발이가능한것도큰매력이다. 미국의 Rocket Lab 은뉴질랜드에 Photo by Mincheol kang Fig. 1 Injection mold core with conformal cooling 1.2 왜적층제조기술인가? 지금까지기업들은소비자가좋아할만한상품을개발해대량생산해서최대한많이판매하는것을목표로삼았다. 그러나적층제조기술을이용하면다양한소비자의욕구를충족시킬수있는맞춤형다품종소량생산이가능하다. 소비재중심에서생산기반형의적층제조기술이주목받는가운데이기술의장점에대해설명하고자한다 3-6). 첫째는 Freedom of design 이다. 항상엔지니어는 Fig. 2 Design optimization of mounting bracket for aerospace 308 Journal of Welding and Joining, Vol. 34, No. 4, 2016

금속적층제조기술의국내외개발동향과기술적이슈 11 Fig. 3 The Rutherford rocket engine(rocket Lab) 서로켓개발을진행하며적층제조기술을적극적으로도입하여저비용화를실현했다고한다. 로켓2단에 9대의엔진을장착하여인젝터, 터보펌프등의주요추진체밸브등을타이타늄합금으로제조하여로켓을 500 만달러미만으로발사할수있다고밝히고있다. 보잉은항공기소형부품 300 여종을 3D프린터로제작중에있으며기타미사일부품, 전투기등방산관련부품과신차개발등에도적용사례와저비용화를실현한사례들이속속공개되고있다. 2. 적층제조기술에사용되는장비와금속소재 2.1 적층제조용장비 메탈적층제조장비는크게두가지로분류할수있다. 첫번째는 Powder Bed Fusion (PBF) 방식이다. 이방식은 Table 2에보듯이분말공급장치에서일정한면적을가지는분말베드에수십μm의분말층을깔고레이저또는전자빔을설계도면에따라선택적으로조사한후한층한층씩용융시켜쌓아올라가는방식이다. PBF 방식은 SLS(Selected Laser Sintering) 또는 SLM(Selected Laser Melting), Laser Cursing, DMLS(Direct Metal Laser Sintering) 등의용어도혼용하고있으나그원리는동일하다. 두번째방식은 DED(Directed Energy Deposition) 방식이다. 이방식은보호가스분위기에서분말을실시간으로공급하여고출력의레이저를사용하여공급즉시용융되어적층해나가는방식이다. PBF 와 DED 는각각장단점을아래표에정리해두었으며, 전세계장비판매량은비교적정밀하고형상자유도구현에유리한 PBF 방식이월등히많다. PBF 방식은독일의 ConceptLaser, EOS, SLM 등이독일회사가 70% 이상의시장점유율을가지고있으며우리나라에서는윈포시스, 스맥, 센트롤등이개발에성공하여시판하고있다 7,8). 2.2 적층제조용금속분말의특징 3D프린터용금속분말은 PBF 방식은구형을사용하며제조방식은 Fig. 4에나타낸바와같이가스 Atomisation 으로제조하며고주파로봉재의금속을가열후가스를분사하는 EIGA(Electrode Induction Melting Gas Table 2 Comparison of PBF and DED technologies CRITERIA POWDER BED FUSION DIRECTIED ENERGY DEPOSITION Laser Scanner Processing direction Melting area Schematic Diagram Coater Powder overflow Deposited material Dilution area Power stream Laser beam Shield gas Powder supply Melt pool Workplace Build speed 5-20 cm³/h (~40-160 g/h) Up to 0.5 kg/h (~70 cm³/h) Accuracy +/- 0.02-0.05 mm/25 mm +/-0.125-0.25 mm/25 mm Detail capability 0.04-0.2 mm 0.5-1.0 mm Surface quality Ra 4-10 μm Ra 7-20 μm Max. part size 800 mm 400 mm 500 mm 2,000 mm 1,500 mm 750 mm Materials Steel, Al,Ti, CoCr, Ni base alloy, bronze Steel, Ti, Ni base alloy, ceramic Typical application Molds and die(tool inserts), Implants All types of component Repair of worn components Modification of tooling for re-use Shaft, ducts, airfoils and coating 대한용접 접합학회지제 34 권제 4 호, 2016 년 8 월 309

12 (a) Electrode induction melting gas atomization Wire straightener Plasma torches Gas exhaust to filtration and recirculation Wire feedstock Water-cooled jacket (b) Plasma atomisation (wire feeding) Vacuum Inert gas Spindle Brush asesembly Motor Rotating electrode Chamber Plasma arc torch Inert gas (c) Plasma rotating electrode process Fig. 4 Atomization processes for spherical metal powder Atomization), 와이어를공급하여플라즈마로가열하여분사하는방식, 봉재를고속으로회전하며플라즈마를가열하는방식등이구형화분말제조에유리하여주조사용된다. 분말의크기는제조회사마다차이가있지만레이저를사용하는 ConceptLaser 및 EOS 의경우 25-55μm를, 전자빔을사용하는 Arcam 사는 50-100 μm, MIM을대체할초소형부품제작용은 1-5 μm를사용하는것으로알려져있다 9,10). 이구상화분말을제조하는업체는 AP&C, Sandvik, Höganäs, TLS Technik, H.C.Stark 등이제조를하고있다. 분말에대한요구조건은구형화도, 유동도, Tap density, 산소및질소농도등이매우까다로운편이며 Table 3에요구조건과측정방법등을나타내었다. 2.3 금속분말의종류와응용분야기존의분말야금방법은분말을성형압축시켜소결등여러공정을거치게되나적층제조기술을활용하면단순하게금속분말박스내에서국부적인용융과융착이발생되어부품이탄생하는것이다. 이방식을사용하면스크랩등의재료손실도없고유사한디자인이나형상변경에대한설계변경이자유롭다는장점이있다. 또한기존주조방법으로제조가불가능한언더컷, 다중공형태제품의생산이가능하며, 두께도 0.3mm 이하로제작가능하여정밀한부품제조가가능하고 Netshape 성형이가능하기때문에성형이후기계가공공정을대폭줄일수있다. 그러나적층제조에사용될수있는금속은많지않고잉곳등원소재에비해 20-30 배로가격또한고가이다. 그이유는분말제조기술이난이도가높고각합금마다적층조건이다르며현재로서시장확대가되지않았기때문이다. 현재사용되는금속은순타이타늄및그합금, 스테인레스합금류, 알루미늄합금, Fe-Cr- Table 3 Measurement methods and requirement for additive manufacturing metal powder Requirement Why? Measurement Spherical Shape Flowability High Packing Layer, Surface area and Low Porosity SEM, BET analysis Hall Test : ASTM 8214 MPIF 03 Carney Test : ASTM B964 Low Porosity Sound Microstructure SEM Particle Size Uniform Melting SEM, Laser Diffraction Purity Low Oxygen and Nitrogen Contents ON Analyzer Tap to Apparent Density Ratio Powder Packing Hausner or carr, Tapped densitytester Chemical Composition Uniform Mechanical Properties ICP-OES, XRD 310 Journal of Welding and Joining, Vol. 34, No. 4, 2016

금속적층제조기술의국내외개발동향과기술적이슈 13 Materials name Material type Typical applications MaragingSteel MS1 18 Mar 300/1.2709 StainlessSteel GP1 StainlessSteel PH1 NickelAlloy IN718 NickelAlloy IN625 CobaltChrome MP1 Stainless steel 17-4/1.4542 Hardenable stainless 15-5/1.4540 Inconel 718, UNS N07718, AMS 5662, W.Nr 2.4668 etc. Inconel 625, UNS N06625, AMS 5666F, W.Nr 2.4856 etc. CoCrMo superalloy, UNS R31538, ASTM F75 etc. Injection moliding series tooling; Engineering parts parts; Engineering and medical parts; Engineering and medical parts; High temperature turbine parts etc. parts; High temperature turbine parts etc. parts; Engineering, medical, dental CobaltChrome SP2 CoCrMo superalloy Dental restorations Titanium Ti64 Aluminium ETC Table 4 Metal powder and applications for additive manufacturing Ti6Al4V, TiAl6V4 ELI AlSi10Mg, AlSi12 CL 80CU(Bronze), Yellow gold(18 carat), Silver alloy(930 sterling) parts; Aerospace, motor sport etc. parts; Engineering, automotive etc. Arts and Jewelry Table 5 Mechanical properties of metal materials for additive manufacturing Materials Condition T.S [MPa] Y.S [MPa] Elong.[%] Aluminum AlSi10Mg as built 280-355 235-250 1-3 Aluminum AlSi12 as built 310-325 170-220 2-3 Tool steel 1.2709 heat-treated 1900 1800 2-3 Tool steel 1.2083 (stainless) heat-treated 1700 1600 >2 Stainless steel 1.4404 as built 570 470 >15 Titanium TiAl6V4 heat-treated 1060-1120 980-1040 10-18 Cobalt-Chrome ASTM F75 as built 1100-1350 910-1010 8-13 Nickel-base alloy Inconel 718 as built, at 20 1400 1100 10 Ni 강, 마르에이징강, Inconel 초내열합금, 귀금속등에제한적으로사용되고있으며 Table 4에분말의종류및응용분야를 Table 5에기계적성질을나타내었다 11). 2.4 메탈프린팅제품응용사례메탈프린팅제품의응용분야는크게금형, 치과및의료분야, 자동차, 우주항공, 전자기기등으로나눌수있으며현재의적용분야와미래의적용가능분야를 Table 6에나타내었다 12). 우주항공분야는 Airbus, GE 등에서활발하게진행되고있다. 터빈브레이드, 연소기부품, 각종브라켓, 연료노즐등등가시적인성과등이속속보고되고있으며주로사용하는소재는 Inconel 초내열합금및타이타늄, CoCr 합금등이주로사용된다. 그러나적층소재의열응력, 피로강도, creep 특성등에대한보다신뢰성을확보해야만적용분야가증가할것으로보인다. 의료분야는특히개인맞춤형으로제작되기때문에기존방식보다신속하고가격이저렴한장점이있다. 활용되는사례는치과용각종크라운, 고관절비구컵등인공뼈, 두개골손상후머리임플란트, 척추임플란트, 각종수술용도구등에도많이사용되고있다. 주된재료는 Co-Cr 합금및 Ti 합금이널리사용되고있으며국내에도확산되고있어향후시장규모가크질것으로보인다. 대한용접 접합학회지제 34 권제 4 호, 2016 년 8 월 311

14 Table 6 Current and future applications of additive manufacturing in the industry Industry Current applications Future applications and technical problem Concept model and prototype Small parts: nozzle, bracket Special light and high strength parts Deformation, fatigue, thermal stress etc. Large structure parts: wings, main body Complex engine part: turbine blade Electronic devices Prototype parts Motorsports parts Parts for discontinued models Ligthweight automotive parts by optimized design Private motor racing parts Heat sink for hot conductivity Prostheses and implant Medical equipment and model dental implants Biodegradable implant Parts of bio robot Manufacturing and test for modeling Personal jewelry and watch Cooling cannel Personal special product High strength mold Cooling cannel for die casting and hot forming Fig. 5 Prototype parts of automobile Fig. 7 Aerospace parts(up: F-15 part made by DED process, down: combustor made by PBF process) Fig. 6 Medical and dental parts 자동차분야는양산용이라기보다는주로프로토타입용으로많이제작되며, 일부모터스포츠용의튜닝제품, 단종모델의부품제작에활용된다. 최근디젤직분사엔진용연료분사장치를개발하여연료효율을향상시켰다고보고가있어직접제조한부품이양산차에적용될 312 Journal of Welding and Joining, Vol. 34, No. 4, 2016

금속적층제조기술의국내외개발동향과기술적이슈 15 Table 7 Global market share and outlook of additive manufacturing Classification 2013($billion) 2014($billion) 2018($billion) CAGR AM equipment market 7 13 54 50.1% Service and Material Market 18 25 108 43.8% Total market 25 38 162 45.7% SLM Solutions 11% Renishaw 5% Realizer 6% Farsoon 2% Wuhan Binhu 7% Trumpf 5% EOS 19% 3D Systems 4% Arcam 11% Concept Laser 30% Fig. 8 Sales performance of metal AM equipment(2015) 수있는부품도다수있을것으로전망된다. 그외 RFID 삽입을위해제작되는금형, 귀금속을활용한각종장신구등에도수요가있다 13). 적층제조시장은크게장비, 소재, 적층제조한완제품, 교육및소프트웨어등으로크게나눌수있다. Table 7 에 2018 년까지각분야에대한시장전망을보여주고있으며 2013 년보다 2018 년에는연평균 45.7% 의성장으로 5년사이 6.5 배의시장이형성될것으로예상하고있다. 이중 Roland Berger 사의조사에따르면금속과관련된시장은장비시장은 30%, 소재는 20%, 관련서비스시장은 30% 를차지하며장비의경우 2023 년 77억유로로예상하고있다 14). 금속분말시장의경우전체적층제조소재시장의 5.9% 를차지하고있으며 2015 년약 600 톤정도의수요가있었으며, 2023 년 4,800 톤으로금속장비보급에따른수요가 8배이상으로증가할것으로예상하고있다. 2015 년전세계메탈프린터매출은그림 8에나타낸바와같이총 264 백만달러로 ConceptLaser, EOS, SLM 등독일기업이 70% 이상차지하고있으며후발주자인미국의 3D Systems 에서도단기간에매출실적이상승되고있다. 향후경사기능재료나 MMC 등복합소재에대한기술개발, 인쇄전자용나노급분말의수요도발생될것으로예상되는바소재시장의지속적인확대가예상된다. 3. 결론 적층제조기술이대중들에게알려진것은불과수년이지났으며과거만능의도깨비방망이처럼포장이되어세간의관심을한몸에받았으나최근에는그열풍이다소잠잠한감이있다. 그러나최근피규어등등의생활소품에서생산기반형부품의성공사례가속속나오고있으며금속부품의관심도는급증하고있다. 해외적층제조설비사들도대형화와적층속도증가를위한멀티레이저시스템, 적층결함실시간검사기능, 고정밀화및초소형부품제조등많은혁신이진행되고있다. 우리나라도윈포시스, 스맥, 센트롤, 인스텍등의장비개발이가속화되고있으며적층제조용분말의개발성공소식도들려오고있다. 현재적층제조기술에있어서금속분야의응용범위가제한적이었으나국내에도장비보급이확산되고있어각종금형제작, 의료분야, 로봇부품, 방산및자동차부품제조도점차확산될것으로예상된다. 향후 KFX 사업등에서도금속적층기술을도입할예정으로있어그전망은밝다고할수있다. 국내외적으로플라스틱부품을 3D 프린터로부품을제조하는기술은도입기를지나성숙기로접어들고있으나, 금속으로제조하는기술은선진국에대비하여기술격차가크게뒤떨어지지않는도입성장기이기때문에우리나라도장비제작을비롯해서보다는시장규모가더큰금속분말소재및응용분야를확장하는것이시급하다. References 1. Mincheol Kang, Proceedings of KFS., (2013) (in Korean) 2. 3D-PRO, 3D printing symposium, (2014) (in Korean) 3. 3D-PRO, 3D printing technical seminar, KIM, (2014) (in Korean) 4. Mincheol Kang, Current metal 3D printing and meaning, 3D Printing, 8(2014) (in Korean) 5. Mincheol Kang, 3D printing in the automobile industry of Germany, 3D Printing, 10(2014) (in Korean) 6. Mincheol Kang, Proceedings of KPMI, (2014) (in Korean) 7. IRS Global, Reprot-3D printing market, technology, and business strategy, (2015) (in Korean) 8. IRS Global, Reprot- 3D printing business for new industrial revolution, (2016) (in Korean) 대한용접 접합학회지제 34 권제 4 호, 2016 년 8 월 313

16 9. Mincheol Kang, Inside 3D Printing Conference & Expo, KINTEX (2016) 10. Rachel Gordon, Inside 3D Printing Conference & Expo, KINTEX (2016) 11. Mincheol Kang, Ji-hoon Yu, Journal of KPMI. 22(6), (2015), 452 (in Korean) 12. Smartech, Additive Manufacturing Opportunities in the Metal Powder Industry, (2014) 13. Wohlers Associates, Wohlers Report-3D Printing and Additive Manufacturing State of the industry Annual Worldwide Progress Report, (2014) 14. RolandBerger, Additive manufacturing-opportunities in a digitalized production, (2015) 314 Journal of Welding and Joining, Vol. 34, No. 4, 2016