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Elastomers and Composites Vol. 51, No. 4, pp. 301~307 (December 2016) Print ISSN 2092-9676/Online ISSN 2288-7725 DOI: https://doi.org/10.7473/ec.2016.51.4.301 Temperature Analysis of Nozzle in a FDM Type 3D Printer Through Computer Simulation and Experiment Jung Hyun Park, Min-Young Lyu, Soon Yong Kwon *, Hyung Jin Roh *, Myung Sool Koo *, and Sung Hwan Cho * Product Design and Manufacturing Engineering, Graduate School of Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 139-743, Republic of Korea * Samyang Central R & D Center, 730 Daedeokdae-ro, Yuseong-gu, Daejeon, Republic of Korea (Received December 6, 2016, Revised December 8, 2016, Accepted December 9, 2016) Abstract: Additive manufacturing (AM), so called 3D Printing is a new manufacturing process and is getting attraction from many industries. There are several methods of 3D printing. Among them fused deposition modeling (FDM) type is most widely used by reason of cheap maintenance, easy operation and variety of polymeric materials. Articles manufactured by 3D printing have weak deposition strength compared with conventionally manufactured products. Deposition strength of FDM type 3D printed article is highly dependent of deposition temperature. Subsequently the nozzle temperature in the FDM type 3D printing is very important and it is controlled by heat source in the 3D printer. Nozzle is connected with heat block and barrel, and heat block contains heat source. Nozzle becomes hot through heat conduction from heat source. Nozzle temperature has been predicted for various thermal boundary conditions by computer simulation and compared with experimental measurement. Nozzle temperature highly depends upon thermal conductivities of heat block and nozzle. Simulation results are good agreement with experiment. Keywords: 3D printing, fused deposition modeling, nozzle temperature, heat block, thermal conductivity Introduction 3D printing기술은플라스틱가공기술들중한가지방법으로다품종소량생산에적합한기술이며현재산업계에서주목받고있는기술이다. 1,2 3D printing은기존플라스틱성형방법인사출또는압출성형등으로가공하기어려운복잡한형상의제품을금형없이단기간내에제작할수있어매우경제적이다. 이러한 3D printing의적용분야는금형, 건축, 디자인, 우주항공, 그리고의료분야까지다양하다. 3-7 3D printing 기술은적층기술에따라 ASTM 규격에의해 binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, vat photopolymerization으로나뉜다. 8 이가운데 material extrusion에해당하는 fused deposition modeling (FDM) 은필라멘트형태로제공되는열가소성플라스틱을 nozzle부로공급시키고 nozzle부의 heat block 에의해용융된재료를한층씩적층하여제품을제작하는방식이다. 용융된재료가 nozzle을통해적층되는모습을 Figure 1에나타내었다. FDM type 3D printing은제품제작비용이비교적저렴하며장비조작방법이간편하다. Corresponding author E-mail: mylyu@seoultech.ac.kr 또한다양한열가소성플라스틱을적용할수있어 3D printing 기술들가운데가장많이사용되고있는기술이다. FDM type 3D printing에관한연구들은다양하게진행되고있으며대표적으로적층물의기계적강도에관한연구, 적층물의휨변형에대한연구그리고재료압출현상에관한연구등이있다. 9-15 FDM type 3D printing으로제작한조형물의강도는일반적인플라스틱성형방법인사출성형으로제작한제품의강도보다현저히떨어진다. 적층물의강도는적층하는방향, 적층속도, 적층온도, chamber 온도, layer 두께등에영향을받으며이가운데적층온도가적층강도에가장큰영향을미친다. 13,15 따라서 FDM type 3D printing에서는적층온도의조절이조형물의강도에매우중요한역할을한다. 또한 3D printer 시스템에설정하는온도는 heat block에위치한열선의온도이며실제로필라멘트와접촉하는 nozzle 내부의온도는시스템설정온도보다낮을것으로예상된다. 그렇기때문에 nozzle부의온도분포에대한연구가필요하다. 본연구에서는컴퓨터해석을통해다양한경계조건을적용하여 FDM type 3D printer nozzle부의온도분포를파악하였다. 그리고컴퓨터해석을통해분석한 nozzle 내부의온도와실험을통해측정된 nozzle 내부의온도를비교하여 nozzle

302 Jung Hyun Park et al. / Elastomers and Composites Vol. 51, No. 4, pp. 301-307 (December 2016) Figure 1. Extrusion of molten filament at the nozzle of FDM type 3D printing. Figure 4. Photo (left) and 3D model (right) of heat block. 부온도의정확성을확인하고자하였다. Experimental 1. 연구모델 Figure 2는 FDM type 3D Printer에사용되는노즐부의구조이다. 노즐부는필라멘트형태의재료가통과되는 barrel (Figure 3), 열선이삽입되는 heat block(figure 4) 그리고 heat block에서가열된필라멘트가일정한두께로압출되는 nozzle (Figure 5) 로구성되어있다. Figure 3~5에 barrel, heat block 그리고 nozzle의형상과치수를각각나타내었다. Figure 5. Photo (left) and 3D model (right) of nozzle. 2. 재료 Figure 2. Photo of nozzle area in the FDM type 3D printing and 3D model. Barrel의소재는 stainless이며 stainless barrel 내부에 PTFE (Polytetrafluoroethylene) 소재의튜브가삽입되어있다. PTFE 는용융온도가 325 o C~330 o C로내열성이좋으며열전도율이낮아 barrel 내부의 filament에대한열전달을최소화시킬수있다. 16 Barrel 내부의 filament가 T g 이상의온도로가열되면 nozzle까지재료가제대로공급되지않는다. 따라서 barrel 안쪽소재로 PTFE가사용되고있다. Heat block의재료는열전도도가높은 aluminum이사용되었고 nozzle 또한열전도도가높은재료인황동으로제작되었다. 각부품의열적물성을 Table 1에나타내었다. 3. 해석을위한모델링 FDM type 3D printer 의온도분포해석에사용한모델은 Figure 3. Photo (left) and 3D model (right) of barrel. Table 1. Thermal Property of Nozzle, Heat Block and Barrel Part Material Thermal conductivity (W/mm o C) Nozzle Brass 124 Heat block Aluminum 167 Barrel(Outer) Stainless 15.3 Barrel(Inner) PTFE 0.261

Temperature Analysis of Nozzle in a FDM Type 3D Printer Through Computer Simulation and Experiment 303 Figure 6. Assembled model of barrel, heat block, and nozzle for simulation. barrel, heat block 그리고 nozzle을 assembly한모델이며 Figure 6에모델링형상을나타내었다. Figure 7. Surfaces to assign boundary conditions for simulation. 4. 해석방법 열전달은단위시간당온도차이에의한열에너지의이동으로전도, 대류그리고복사이렇게 3가지방식으로구분된다. FDM type 3D printer nozzle부의열전달은주로부품간의전도그리고대기와 nozzle간의대류에의해이루어진다. 식 (1) 과 (2) 에전도와대류에의한열전달방정식을차례로나타내었다. q = ka dt ----- dx q = ha( T s T ) (1) (2) q는단위시간당열유동량 (heat flow), k는재료의열전도도 (thermal conductivity), T는온도, A는표면적, h는열전달계수 (heat transfer coefficient), T s 는재료의표면온도그리고 T 는주변온도를나타낸다. 본연구에서는상용유한요소해석소프트웨어인 ANSYS WORKBENCH를이용하여정상상태에서해석조건에따른 FDM type 3D printer nozzle부의열전달해석을진행하였다. 해석에서기본경계조건을부여하는위치를 Figure 7에나타내었다. Nozzle, heat block 그리고 barrel은모두완전히붙어있다고가정하여 bonded 조건을적용하였다. 대기 ( 상온 25 o C) 중에있는 nozzle의외부표면과내부표면, heat block 의외부표면그리고 barrel의외부표면과내부표면에대류조건을적용하였고열전달계수 (h) 는 20W/m 2o C이다. 그리고 heat block에위치한열선삽입부에온도를설정하였다. 해석은위에언급한경계조건을기본조건으로하여해석하였다. 그리고재료의 thermal conductivity를기본조건의 1/2배그리고 1/3배로설정하여온도분포를비교분석하였다. 또한 heat block 외부표면에단열조건을주었을때의온도분포 Figure 8. Mesh generation for simulation. 를비교하였다. 그리고 barrel 부에강제대류조건을적용하였을때온도분포결과값과기본조건의결과값을비교하였다. FDM type 3D printer nozzle 부의 barrel이높은온도로가열되는것을방지시키기위해 barrel 부분에 fan이설치되어있다. 따라서 barrel 외부표면에강제대류조건을적용하여자연대류조건을적용하였을때와비교해보았다. 강제대류계수는자연대류계수의 10배인 200 W/m 2o C로적용하였다. 부품간의접촉조건에따른온도분포를파악하기위해각부품간의 contact 조건을 no separation 조건을적용하여기본조건인 bonded조건을적용하여해석한결과값과비교하였다. Bonded 조건은부품간접촉면이떨어지지않고미끄러짐도불가능하게하는조건이고 no separation 조건은부품간접촉면이떨어지지않고미끄러짐만가능하게하는조건이다. 해석을위한 3차원메시는사면체요소와육면체요소의조합으로총 219,725개의요소로 Figure 8과같이형성하였다.

304 Jung Hyun Park et al. / Elastomers and Composites Vol. 51, No. 4, pp. 301-307 (December 2016) Figure 9. Location of temperature measurement and photo of measurement. 5. 온도측정 유한요소해석을통해구해진 nozzle부의온도분포결과값과실제 nozzle부의온도를비교하기위해접촉식온도미터를이용하여 nozzle 내부의온도를측정하였다. 측정장비는 FLUKE 사 ( 미국 ) 의 FLUKE-53-2B 온도미터를사용하였다. 측정정확도는 0.05%+0.3 o C이며측정가능온도범위는 250 o C~1767 o C이다. 본연구에서는 3D printer 온도설정을 210 o C, 230 o C 그리고 250 o C로하여 nozzle 내부의온도를측정하고해석값과비교하였다. Figure 9에온도측정위치와측정모습을나타내었다. Results and Discussion 1. 재료의열전도도에따른온도분포 Figure 10은기본조건을적용하여해석한온도분포결과값이며 Figure 11은재료의열전도도를기본조건에서 1/2배그리고 1/3배로설정하여해석하였을때노즐의온도분포이다. Heat block 열선삽입부의온도를 230 o C로설정하였을때 Figure 11. Temperature distribution in the nozzle for various thermal conductivities. 기본조건에서 nozzle의최대온도는 229.59 o C이며최저온도는 nozzle 출구부분에서 227.9 o C로나타난다. 재료의열전도도를기본조건에서 1/2배그리고 1/3배로적용하였을때노즐에서의최대온도는각각 229.22 o C, 228.86 o C이며최저온도는노즐출구에서각각 225.9 o C, 223.96 o C이다. 재료의열전도도가낮아질수록열전도율이떨어져노즐의온도가다소낮아지는것을알수있다. 2. 단열조건에따른온도분포 Figure 10. Temperature distribution in barrel, heat block, and nozzle for basic condition. Heat block 외부표면에대류조건 (basic condition) 을적용하였을때의온도해석결과값 (Figure 12(a)) 과단열조건을적용

Temperature Analysis of Nozzle in a FDM Type 3D Printer Through Computer Simulation and Experiment 305 Figure 12. Comparison of temperature distribution in the heat block and nozzle for convection and insulation condition. Figure 13. Comparison of temperature distribution for convection and forced convection condition. 하였을때의온도해석결과값 (Figure 12(b)) 을비교하였다. 대류조건을적용하였을때 heat block과 nozzle의최대온도는각각 230 o C, 229.59 o C이며최저온도는 227.41 o C 그리고 227.9 o C이다. Heat block 외부표면에단열조건을적용하였을때 heat block과 nozzle의최대온도는각각 230 o C, 229.77 o C이며최저온도는각각 228.25 o C, 228.44 o C이다. 대류조건을적용한경우대기와 heat block사이의대류에의해 heat block의열이대기중으로전달되어단열조건을적용하였을때보다 heat block과 nozzle의온도가약간낮게분포하는것을확인할수있다. 3. 강제대류조건에따른온도분포 Barrel부에자연대류조건 (basic condition) 을적용하였을때와강제대류조건을적용하였을때의 nozzle부의온도분포를 Figure 13에나타내었다. Barrel 외부표면에강제대류를적용하였을때자연대류조건을적용하였을때보다 barrel의온도가 37.46 o C로낮아졌으며 nozzle의온도또한다소낮게분포하는것을알수있다. Barrel 부의강제대류는 nozzle의온도에크게영향을주지않았다고판단된다. 4. 부품간접촉조건에따른온도분포각부품간의 contact조건을 bonded 조건 (basic condition) 으로적용하였을때와 no seperation 조건을적용하였을때의온도분포해석결과비교그림을 Figure 14에나타내었다. 두해석결과값에차이가없는것으로보아 contact 조건에크게영향을받지않는것을확인할수있다. 5. 컴퓨터해석결과값과실험값비교유한요소해석을통해구한노즐부의온도분포결과값과실제노즐부의온도를비교하기위해접촉식온도미터를사용하여노즐내부의온도를측정하였다. Figure 15(a) 는 heat block 열선삽입부의온도를 210 o C로설정하였을때의해석결과이며 Figure 15(b) 는실제노즐내부의온도측정값이다. 해석결과노즐내부의온도는약 209 o C~208 o C이며측정값은약 208.2 o C로해석결과와유사하였다. Figure 16는온도설정을 230 o C로하였을때의해석결과값 (Figure 16(a)) 과실험을통한측정값 (Figure 16(b)) 이다. 해석결과노즐내부의온도는약 229.5 o C~227.9 o C로나타났으며측정값은약 227.5 o C

306 Jung Hyun Park et al. / Elastomers and Composites Vol. 51, No. 4, pp. 301-307 (December 2016) Figure 16. Comparison of computational result and measurement for 230 o C of heat source. Figure 14. Comparison of temperature distribution for contact condition. Figure 17. Comparison of computational result and measurement for 250 o C of heat source. 247.7 o C로나타났으며측정값은약 248 o C로나타났다. 이또한해석결과값과측정값이매우유사하였다. Conclusion Figure 15. Comparison of computational result and measurement for 210 o C of heat source. 로비슷한결과를보였다. Figure 17에온도설정을 250 o C로하였을때의해석결과값 (Figure 17(a)) 과측정값 (Figure 17(b)) 을나타내었다. 해석결과노즐내부의온도는약 249.5 o C~ 본연구에서는 FDM type 3D printer의 nozzle부에서재료의열전도도에따른온도분포, 단열조건에따른온도분포, 대류조건에따른온도분포그리고부품간 contact 조건에따른온도분포를컴퓨터해석을통해관찰하였다. 그리고컴퓨터해석을통해구해진온도분포결과값과실제실험을통해측정한노즐내부의온도분포결과값을비교하였다.

Temperature Analysis of Nozzle in a FDM Type 3D Printer Through Computer Simulation and Experiment 307 Nozzle부재료의열전도도가낮을수록 nozzle부의온도가다소낮게분포하였다. Heat block에단열조건을적용한경우와대류조건을적용한경우를비교해보면단열조건을적용하였을때대기로열이빠져나가지못하여대류조건을적용하였을때보다 nozzle부의온도가다소높게분포하는것을확인할수있었다. Barrel 부에강제대류조건을적용하였을때자연대류조건을적용하였을때보다 barrel의온도는크게낮아졌으나 nozzle의온도는크게변하지않았다. 그리고부품간의 contact 조건을 bonded 조건을적용한경우와 no seperation 조건을적용한경우의해석결과값의차이는없었으며이를통해 contact조건은온도분포해석에영향이없음을확인할수있었다. 또한컴퓨터해석을통해구해진온도값과실험을통해노즐내부의온도를측정한결과값이매우유사한결과를보였다. 이상의결과로 heat block의 heat source 온도는 nozzle의온도를잘제어하고있음을확인할수있었다. Acknowledgments 본논문은산업통상자원부산업핵심기술개발사업으로지원된연구결과입니다 (10051680, 3D 프린팅용친환경고강도고분자소재개발 ). References 1. B. C. Gross, J. L. Erkal, S. Y. Lockwood, C. Chen, and D. M. Spence, Evaluation of 3D printing and its potential impact on biotechnology and the chemical sciences, Analytical Chemistry, 86, 3240 (2014). 2. D. Dutta, F. B. Prinz, D. Rosen, and L. Weiss, Layered manufacturing: current status and future trends, Journal of Computing and Information Science in Engineering, 1, 60 (2001). 3. S. J. Jung and T. H. Lee, Study of Trends in The Architecture and The Economic Efficiency of 3D Printing Technology, Journal of the Korea Academia-Industrial Cooperation Society, 15, 6336 (2014). 4. E. Bassoli, A. Gatto, L. Iuliano, and M. Grazia Violante, 3D printing technique applied to rapid casting Rapid Prototyping Journal, 13, 148 (2007). 5. S. Bose, S. Vahabzadeh, and A. Bandyopadhyay, Bone tissue engineering using 3D printing, Materials Today, 16, 496 (2013). 6. K. T. Han, Research on Die Machining using 3D Printing and CAM System, Journal of the Korea Society For Power System Engineering, 18, 91 (2014). 7. S. C. Joshi and A. A. Sheikh, 3D printing in aerospace and its long-term sustainability, Virtual and Physical Prototyping, 10, 175 (2015). 8. ASTM F2792-12a, Standard Terminology for Additive Manufacturing Technologies, ASTM International (2012). 9. T. M. Wang, J. T. Xi, and Y. Jin, A model research for prototype warp deformation in the FDM process, The International Journal of Advanced Manufacturing Technology, 33, 1087 (2007). 10. L. Xinhua, L. Shengpeng, L. Zhou, Z. Xianhua, C. Xiaohu, and W. Zhongbin, An investigation on distortion of PLA thin-plate part in the FDM process, The International Journal of Advanced Manufacturing Technology, 79, 1117 (2015). 11. S. H. Ahn, M. Montero, D. Odell, S. Roundy, and P. K. Wright, Anisotropic material properties of fused deposition modeling ABS, Rapid Prototyping Journal, 8, 248 (2002). 12. S. J. Park, J. H. Park, K. H. Lee, and M.-Y. Lyu, Deposition Strength of Specimen Manufactured Using Fused Deposition Modeling Type 3D Printer, Polymer (Korea), 40, 846 (2016). 13. M. Roxas, Fluid dynamics analysis of desktop-based fused deposition modeling rapid prototyping, Doctoral dissertation, University of Toronto, (2008). 14. B. N. Turner, S. Robert, and A. G Scott, A review of melt extrusion additive manufacturing processes: I. Process design and modeling, Rapid Prototyping Journal, 20, 192 (2014). 15. Q. Sun, G. M. Rizvi, C. T. Bellehumeur, and P. Gu, Effect of processing conditions on the bonding quality of FDM polymer filaments, Rapid Prototyping Journal, 14, 72 (2008). 16. D. M. Price and M. Jarratt, Thermal conductivity of PTFE and PTFE composites, Thermochimica Acta, 392, 231 (2002).