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한국정밀공학회지제 33 권제 4 호 pp. 247-255 J. Korean Soc. Precis. Eng., Vol. 33, No. 4, pp. 247-255 ISSN 1225-9071(Print), ISSN 2287-8769(Online) April 2016 / 247 http://dx.doi.org/10.7736/kspe.2016.33.4.247 특집 양동열교수님헌정세션특집 박판성형공정설계및해석의발전 Research History and Recent Trends in the Development of Sheet Metal-Forming Processes 김종봉 1, 이성욱 2, 양동열 2, 정완진 3, Jong-Bong Kim 1, Sung-Uk Lee 2, Dong-Yol Yang 2, and Wan-Jin Chung 3, 1 서울과학기술대학교기계자동차공학과 (Department of Mechanical and Automotive Engineering, Seoul National University of Science and Technology) 2 한국과학기술원기계공학과 (Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology) 3 서울과학기술대학교기계시스템디자인공학과 (Department of Mechanical System Design Engineering, Seoul National University of Science and Technology) Corresponding author: wjchung@seoultech.ac.kr, Tel: +82-2-970-6390 Manuscript received: 2016.2.25. / Revised: 2016.3.21. / Accepted: 2016.3.21. Sheet metal-forming processes such as stamping, deep drawing, bending, shearing, hydroforming, hydromechanical deep drawing, rubber forming, and incremental forming have been widely used in the automotive, aircraft, and ship-building industries. With the expansion of the automotive industry, research on these processes has been remarkably developed in Korea since the 1980s. Here, we review the history of this research as well as recent trends in sheet metal-forming processes. This overview focuses specifically on the results of research in Korea and on the works of Professor D.Y. Yang, in honor of his retirement. KEYWORDS: Sheet metal forming ( 박판성형 ), Process design ( 공정설계 ), Review ( 리뷰 ) 1. 서론 박판성형공정은얇은판재를이용하여원하는제품을성형하는공정으로자동차, 선박, 항공등의산업에서다양하게적용되고있다. 수작업에의한박판제품의성형은아주오래전부터수행되어왔고, 프레스를이용한성형도 1600 년대 1 에이미적용이되었다. 1950 년이후소비시장이커지고양산에의한제품생산이요구되면서박판성형공정은빠른속도로발전한다. 1967 년에현대자동차가설립된후, 1968 년에코티나를처음국내생산하고 1974 년에는국내최초의고유모 델인포니를생산 2 한것으로볼때, 1960년대말에박판성형공정이국내에서이미시작된것으로볼수있다. 하지만, Science Direct 3 를이용한조사결과국내에서체계적인연구가시작되고연구결과가발표된것은 1980년대이후로분석된다. 본연구에서 1980년이후차량경량화및생산성향상요구와선박등의여러분야에서의박판제품수요에부응하기위해대한민국, 특히한국과학기술원양동열교수연구실에서수행된박판성형관련연구성과를중심으로관련국내박판성형공정설계및해석의발전과정을종합하여정리하였다. Copyright C The Korean Society for Precision Engineering This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

한국정밀공학회지제 33 권제 4 호 pp. 247-255 April 2016 / 248 2. 박판성형공정의발전과정 2.1 연구의시작 (-1980 년대 ) 박판성형공정관련한국제적인연구결과를분석하기위해 1900년이후국제저널에발표된논문수를집계하여 Fig. 1에도시하였다. 조사는여러저널데이터베이스 (DB) 중에서 Science Direct 3 에서만검색을하였고, 조사에사용된키워드는 Sheet Forming 이고 Engineering 및기계관련저널만대상으로하였다. 그렇기때문에 Science Direct 에서검색이되지않은다른논문들은누락이되었을수있다. Fig. 1은전세계적으로발표된논문의수와그중에서대한민국연구자가포함된논문의수를보여준다. 세계적으로는 1960년대이전에박판성형공정에대한논문이발표가되고있다. Hill 4 은 1950년에디프드로잉과네킹등에대해연구하였고, 이후 1960년대에 Naziri와 Pearce 5 는판재의이방성이플랜지주름발생에미치는영향을, Bramley와 Mellor 6 는이방성및변형율속도가스트레치성형에미치는영향을연구하였다. 대한민국연구자가포함된논문은 1980년대부터발표가되기시작했다. Lee, 7 Suh, 8 Chung, 9 Kim 10 그리고 Kim 11 이포함된논문은미국이나호주등의외국에서발표되었고, 국내에서발표한논문은 Kim과 Kim, 12 그리고 Kim과 Yang 13,14 에의해서처음발표되었다. Kim 과 Kim 12 은이방성을고려하여박판의성형한계변형율을예측하였고, Kim과 Yang 13,14 은처음으로질점좌표계 (Convective Coordinate) 에기반한유한요소수식화를통해정수압벌징공정과디프드로잉공정에서소재의변형을해석하였고이방성을고려하여디프드로잉공정에서귀 (Earing) 의발생을예측하였다. 1990년대이후국내의연구도세계적인연구흐름과같이급속하게발전한다. 최근국제적인저널의수와 DB가많아지는추세를감안하면더많은연구결과가발표되고있는것으로사료된다. Fig. 1에서발표된논문의수가 10년단위로 2 배중가하고있음을알수있다. 또한, 국내연구자가포함된연구결과는전세계적으로발표되는논문의약 5.5-8.5% 이다. 국내에서도박판성형공정에대한연구가활발하게진행되고왔고, 2010년이후에는다소비중이줄어드는것을알수있다. Fig. 1 Number of international journal articles written by global and Korean researchers (Searched DB: Science Direct, Keywords for title and abstract: Sheet forming, Category: Engineering) 2.2 연구의확장및다양화 (1990-2009) 1990 년대와 2000 년대에는박판성형공정에관한연구가크게확장되고다양화되는시기라고볼수있다. 가장큰연구방향은박판성형공정해석을위한유한요소법프로그램개발 15-24 과유한요소법을이용한공정해석 15-25 이었고, 그외에도주름 (Wrinkling) 의발생해석, 25-30 상계해법을이용한해석, 31 성형성분석, 32-37 항복함수 38-40 등의분야에대한연구도활발하게진행되었다. 용접판재 (Tailor Welded Blank) 적용, 41-44 하이드로포밍, 36,45-48 하이드로미케니컬디프드로잉, 49-50 롤포밍, 51-54 블랭크최적설계 55-57 와같은다양한공정에대한연구도활발하게수행되었다. Kim 과 Yang 13,14 에의해개발된프로그램을기반으로 Yang, Chung, Shim, 15 Yoon 등, 16,20 그리고, Jung 과 Yang 17 은수렴성개선및접촉처리추가, 15 탄소성쉘요소의개발, 16,20 외연적 (Explicit) 시간적분방법 17 적용, 그리고연속체요소 (Solid Element) 23 를개발하여적용하였다. Fig. 2 는개발된코드를이용하여정사각형컵성형을해석한결과를보여준다. 20 또한 Huh 등 18 은굽힘이고려된멤브레인요소를개발하여박판성형공정을해석하였다. Kim 등은분기이론 (Bifurcation Theory) 을탄소성유한요소법에적용하여내연적방법으로는처음으로 Fig. 3 에보인박판성형공정에서발생하는주름을해석하였고, 30 Chung 등, 55 Lee 와 Huh, 56 그리고 Park 등 57 은이상성형 (Ideal Forming) 이론과유한요소법으로초기블랭크형상을최적화하였다. Fig. 4 는 Lee 와 Huh 56 가설계한최적블랭크형상을보여준다.

한국정밀공학회지 제 33 권 제 4 호 pp. 247-255 April 2016 / 249 Fig. 6 The line array roll set for incremental rolling of doubly curved plates61 Fig. 2 Tool surfaces and initial blank (left) for the analysis of square cup drawing and analysis results (right) at the punch stroke of 15 mm20 Fig. 7 Emboss patterns formed using an electromagnetic force71 Fig. 3 Predicted wrinkling shape (left) and experimental results (right) at the stroke of 20 mm and 5 kn of blank holding force30 Fig. 4 Calculated initial blank shape (right) from the desired mesh geometry (left)56 Fig. 5 Octagonal cones with flat (left) and convex (right) surface formed by incremental sheet forming60 레이저 포밍,58 점진성형 (Incremental Forming)52,53,59-61 에 대한 연구도 1990년대 이후 시작이 되었다. Fig. 5는 Park과 Kim60이 일점 점진성형으로 성형한 제 품을, Fig. 6은 Shim 등61이 제안한 점진적 롤링 성 형으로 선박용 판재를 성형하는 모습을 보여준다. 적용 재료 측면에서도 경량화 요구로 인해 알루미 늄,36-39,49,50,62,63 타이타늄,64 마그네슘64-66과 같은 경 량화 소재의 성형과 관련된 연구도 시작이 되었고, 결정소성 (Crystal Plasticity)67-69에 대한 연구도 시작 되었다. Lee 등66은 마그네슘 판재의 비대칭 가공경 화 (Anisotropic/Asymmetric Hardening) 를 고려하여 탄성회복을 해석하였다. 2.3 최근의 연구 (2010-) 2010년 이후에는 이전에 검토가 되었던 전자기 성형,70-73 점진 성형,74-77 레이저 성형,78 고속 물 성,79 국부 가열 성형,80 샌드위치 판재 개발 및 성 형,81,82 고온 성형83 등의 공정에 대한 심화 연구, 결정소성학84,85 적용의 심화연구 등이 진행이 된다. Fig. 7은 Noh 등71이 전자기 성형으로 성형한 판재 의 형상이고, Fig. 8은 Kim 등79이 성형 속도를 변화 시키면서 구한 성형한계도이고, Fig. 9는 Seong 등81 이 개발한 샌드위치 판재를 굽힘 성형한 시편이다. 그리고, 자동차가 고급화함에 따라 박판 성형 제품의 급격한 곡률부에서 발생하는 약 0.5 mm 이 하의 미세굴곡86-88에 대한 관심도 커지고 있다. Chung 등86은 유한요소법 결과에서 미세굴곡을 정 확하게 예측하기 위한 방법을 제시하고 실험 결과 와 비교하여 제안한 방법의 신뢰성을 검증하였다. Fig. 10은 미세굴곡을 예측하고 측정한 결과를 보 여준다.

한국정밀공학회지제 33 권제 4 호 pp. 247-255 April 2016 / 250 3. 결론 자동차, 선박, 항공기산업에매우중요한공정의하나인박판성형공정의국내에서의연구발전과정을정리하였다. 국내에서는산업발전과연구기반의확충에따라 1980 년대에연구가시작되었고, 1990 년부터 2010 년까지대한민국의산업발전과함께다양한분야에서많은연구가수행되었고연구논문의수나질이세계적인수준으로발전되었다. 초기에는유한요소법을이용한연구가주를이루었으나점차공정및재료에대한연구로저변이확장되었다. 2010 년이후에는경량화, 고부가가치공정, 그리고재료물성등으로연구의흐름이전환되는것을알수있었다. 후기 Fig. 8 Comparison of the static (0.0008-0.0017/s) FLC with the high speed (68-118/s) FLC of DP590 79 이연구는서울과학기술대학교교내연구비의지원으로수행되었습니다. REFERENCES Fig. 9 U-Bending experiments of the sandwich plate with sheared dimple cores 81 Fig. 10 (a) Measured, (b) Predicted surface deflections in an automobile exterior panel 1. Esteves, A., The Long History of the Pressing of Metals, Interempresas.net, https://www.interempresas. net/metalforming/articles/10544-the-long-history-ofthe-pressing-of-metals.html (Accessed 23 March 2016) 2. Naver, Hyundai Motor Group, http://terms.naver. com/entry.nhn?docid=652864&cid=43167&categoryi d=43167 (Accessed 29 March 2016) 3. Science Direct, ScienceDirect, http://www.sciencedirect. com (Accessed 29 March 2016) 4. Hill, R., The Mathematical Theory of Plasticity, Oxford University Press, pp. 272-286, 1950. 5. Naziri, H. and Pearce, R., The Effect of Plastic Anisotropy on Flange-Wrinkling Behaviour during Sheet Metal Forming, International Journal of Mechanical Sciences, Vol. 10, No. 9, pp. 681-694, 1968. 6. Bramley, A. N. and Mellor, P. B., Some Strain-Rate and Anisotropy Effects in the Stretch-Forming of Steel Sheet, International Journal of Machine Tool Design and Research, Vol. 5, No. 1-2, pp. 43-55, 1965. 7. Lee, D. and Zaverrl Jr., F., Neck Growth and Forming Limits in Sheet Metals, International Journal of Mechanical Sciences, Vol. 24, No. 3, pp. 157-173, 1982.

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한국정밀공학회지제 33 권제 4 호 pp. 247-255 April 2016 / 255 84. Jung, K. H., Kim, D. K., Im, Y. T., and Lee, Y. S., Crystal Plasticity Finite Element Analysis of Texture Evolution during Rolling of FCC Polycrystalline Metal, Materials Transactions, Vol. 54, No. 5, pp. 769-775, 2013. 85. Kim, J. B. and Yoon, J. W., Necking Behavior of AA 6022-T4 Based on the Crystal Plasticity and Damage Models, International Journal of Plasticity, Vol. 73, pp. 3-23, 2015. 86. Chung, W. J., Chung, Y. C., and Kim, W. S., A Robust Prediction Method of Surface Deflection Using Stoning Simulation and Curvature Analysis, Steel Research International, Vol. 86, No. 8, pp. 886-893, 2015. 87. Kim, J. H. and Chung, W. J., A Study on the Surface Deflection in Rectangular Embossing Considering Planar Anisotropy, Transactions of Materials Processing, Vol. 22, No. 6, pp. 310-316, 2013. 88. Thuillier, S., Le Port, A., and Manach, P.-Y., Surface Defects in Sheet Metal Forming: A Simulative Laboratory Device and Comparison with FE Analysis, Proc. of American Institute of Physics Conference, DOI No. 10.1063/1.3623693, pp. 839-846, 2011.

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