- Email: [email protected]
Impact of process parameters on mechanical behaviour in multi-material jetting
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Impact of process parameters on mechanical behaviour in multi-material jetting Arivazhagan Pugalendhi ⇑, Rajesh Ranganathan, Sivakumar Ganesan Department of Mechanical Engineering, Coimbatore Institute of Technology, Civil Aerodrome Post, Coimbatore, Tamilnadu 641 014, India
a r t i c l e
i n f o
Article history: Received 7 November 2019 Accepted 12 December 2019 Available online xxxx Keywords: Additive manufacturing PolyJet technology Multi material jetting Mechanical properties Process parameter
a b s t r a c t PolyJet material jetting is a rapidly growing Additive Manufacturing (AM) technology due to its ability to build precise multi material parts having complex geometries. Mechanical properties of parts fabricated by AM are affected by printing parameters. Examining the strength of AM parts is important, due to the differences with PolyJet technology. The aim of this study is to characterize the effect of process parameters on the mechanical properties of VeroClear and VeroWhitePlus test specimens manufactured with digital material printing mode. Tensile, flexural and shore hardness tests are carried out to determine the mechanical properties of the 3D printed specimens. Findings indicate that the specimens printed in glossy finish are stronger and stiffer than matte finish. From a view of material and material concentration, VeroClear specimens show better results when compared to the mechanical properties of VeroWhitePlus specimens. In addition, comparison between the material consumptions and required printing time to complete the specimens were also carried out. All these test results revealed, VeroClear with glossy finish specimen is more efficient than the other combinations as it is significantly improved. This work provides a selection guideline that can be used to increase the durability of functional parts in wide variety of applications. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
1. Introduction Rapid growth of the Additive Manufacturing (AM) is applied to both commercial and potential research activities for providing better solutions in various sectors since middle of 1980’s to current state of art [1]. In AM, desired three dimensional computer aided design (CAD) model is sliced into two dimensional profiles for a layer-upon-layer building process to obtain the final part [2]. Flexibility in design and tool less fabrication of AM plays a major role in time to market (TTM) which has great impact on the final product cost over traditional tool manufacturing techniques [3]. Due to layer by layer fabrication process, AM samples displays anisotropic behaviour and it causes flaws and voids which may significantly reduce the strength of the final parts [4]. In many cases, material properties provided by the manufacturer are not practically suitable for most of the applications. So, in order to examine the influence of process parameters on mechanical behaviour it is essential for functional parts to deter⇑ Corresponding author. E-mail address: [email protected] (A. Pugalendhi).
mine the life of the 3D printed parts [5]. This study concentrates on examining the mechanical property of the parts fabricated by AM to provide better understanding for selection of process parameters based upon the final application.
2. Literature survey In PolyJet technology, ultraviolet (UV) curable resins are selectively jetted onto a build platform and cured, the recent layer is deposited. Capabilities of this technique allow the fabrication of multi materials in a single print with variety of colours and shore hardness values [6]. Automobile, aerospace and healthcare sectors took a great leap by the application of AM. 3D printed tissues and organs, surgical planning, prosthetics, medicine, medical device and medical imaging creates the revolution in the healthcare to customization and reduces the risk in surgery. In terms of accuracy of 3D printed model, PolyJet models have more accuracy than Selective Laser Sintering (SLS) and 3D inkjet printers (3DP) [7]. Virtual or physical bio-models are used to predict the disorders and complexity in surgery. Pre-operative planning and training can
https://doi.org/10.1016/j.matpr.2019.12.106 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
2
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx
improve the surgical skill of surgeon. Fabrication of patient-specific through AM reduces the cost and time without skilled sculptors over than casted polymer model [8]. In food science and technology, applications of AM allow a novel artistry and customized food items. 3D printed foods are directly used after the proper coating of silicon to meets the food safe regulations. In this regard, it is crucial to ensure the selection of material and process of AM [9]. Comparing the properties of machined stainless-steel insert, direct metal laser sintered (DMLS) bronze alloy insert and PolyJet inserts made by digital ABS to obtain a polypropylene moulded part. Study revealed that, mechanical properties, dimensional tolerances and quality of the AM parts are different from traditional techniques. PolyJet inserts has smoother surface finish than DMLS insert can be used without any polishing. Despite, due to the high temperature differences and low thermal conductivity, PolyJet inserts has highest shrinkage and long cycle time. Optimized cycle and tensile strength of the insert is 80 and 15 MPa [10]. AM is capable to reproduce an accurate ancient and modern artifacts for educational and commercial reasons. Scanning, replication and restoration of artifacts spawn rely in natural history and technology museums. PolyJet 3D printer exhibits wider range of thinking with the help of multi-colour materials [11]. The potential of AM generates new class of functional musical instruments that sounds extreme and resembles the original instruments. Greater accuracy and improved ergonomic factors of 3D printed instruments satisfy both mechanical and acoustic features. By utilising the PolyJet technology, wave whistle and transverse flute are printed in Objet PolyJet printer [12]. Dizon et al. gave a broad review of various AM methods and the effects of the mechanical properties. The cryogenic temperatures, nano filler additions and post processing have also been included. Various test standards and its standardization of test methods has been briefly discussed [13]. Mechanical properties of PolyJet parts are highly influenced by build orientation, layer thickness, type of material, surface finish and post processing [14–16]. Glossy finished PolyJet printed parts have higher fatigue life compared to matte finish [17]. Printing speed and placement of the object does not affect the strength of the final part. The study conducted by Pilipovic´ et al., in PolyJet machine revealed that, specimens of FullCure material has a maximum tensile and flexural strength followed by VeroBlue and VeroBlack. However, these values are lower than data provided by the manufacturer. Similarly, surface roughness is minimum in FullCure specimens compared to others [18]. Exposure time of UV light, machine’s warm-up time, storage time and validity of the raw material affects the mechanical properties of the PolyJet printed parts. The manufacturer provided data of VeroWhitePlus values of elastic modulus is close to the upper boundary and ultimate tensile strength, which exceeds the upper boundary. Geometry of the printed parts is highly affected by nozzle blockage [19]. So, assessment of the mechanical properties and their geometrical accuracy, minimum feature size and repeatability is most important [20]. Through experimental work of Rajendra Boopathy and Sriraman, compressive and impact loads on 5 layer sandwich multimaterial (3 layer of VeroWhitePlus) has a better energy absorbing capability compared to single VeroWhitePlus material, 2 layer (equally shared VeroWhitePlus and TangoPlus) and 3 layer sandwich multi-material (Centre layer is TangoPlus) [21]. Mueller et al. tested the interfaces of VeroWhitePlus and TangoBlackPlus in single-material interfaces, on-the-fly mixing of materials and multi-material interfaces. Multi material printing of PolyJet technology is similar to the conventional composite materials. Material properties of VeroWhitePlus material are similar to the commercial ABS. When the size of the part is larger than the inclusion size,
composite effect of digital material gives better result. Mixing ratios, different material combinations and direction of load plays a major role in composite effect. Rigid materials have uniform layer heights than flexible materials [22]. Meisel et al. measured the viscoelastic properties of PolyJet digital materials by using Dynamic mechanical analysis (DMA). Material composition and voxel dithering pattern affects the storage and loss modulus. In digital material, property of the final part is similar to the concentration of the dominant material [23]. Classical lamination theory is used to determine the directional specific mechanical properties of multi-material structured specimens printed by PolyJet 3DP. This study reports, shear strength is higher in angle ply laminate, both tensile and flexural is higher in quasiisotropic laminate [24]. In PolyJet machine, there is an option to print the single material part with mixture of other material by mixed tray method. This research work investigates the mechanical behaviour of tensile, flexural and shore hardness of the VeroClear and VeroWhitePlus material. By this study, selection of suitable material and their surface finish for specific application becomes easy.
3. Experimental details 3.1. Materials and methods In this study, mechanical behaviour of the standard specimens fabricated by Stratasys Objet260 Connex2 is determined by tensile, flexural and shore hardness tests. The Objet260 Connex2 printer consists of assembly of eight parallel print heads, two UV lights and one roller to flatten the printed surface, which moves in X and Y direction. Four print heads are owed to two model materials and four to support materials. Photo-curable materials are deposited in the required area in build tray through nozzles of the print heads. Build tray moves downwards direction of Z axis after curing the previous layer. This machine has extensive range of materials with different material properties; it prints any product with more than one material property simultaneously in a single part. Non-toxic gellike photopolymer of FullCure 705 is used as a support material. High-resolution layer accuracy of 16-m (High Quality-HQ) and 30m (High Speed-HS & Digital Material-DM), with a tray size of 255 252 200 mm. HQ and HS comes under single material mode, where only one model material is deposited on the end product. In DM mode or multi material mode, deposits more than one model materials on end product by mixed part, mixed tray and digital material approaches. Mixed tray method offers single material printing in DM mode. This study investigates the mechanical properties of VeroClear and VeroWhitePlus which are suitable to form and fit testing in wide range of industrial application. All test specimens are printed in mixed tray approach in DM mode by introducing the small sample object having the dimensions of Ø5 0.5 mm. Here, model materials bays are loaded with both VeroClear and VeroWhitePlus materials. In this condition, a sample object can be printed along with the required material using alternate material. Then test results are compared with standard values provided by manufacturer as shown in Table 1. Because, except three mechanical properties (Polymerized density, Ash content, Colour) of VeroClear and VeroWhitePlus, all other properties are same, where, practically it is not possible. VeroClear material is used in medical devices, eyewear and light cover and white colour opaque material of VeroWhitePlus is used in medical devices and electronic housings. All the test specimens are fabricated with both matte (M) and glossy (G) finish, matte finish wraps the entire surface in support material and glossy finish is free from the support material on specimen’s
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
3
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Mechanical properties of VeroClear and VeroWhitePlus (Source: Stratasys). Material
Mechanical Properties
Test Method
Value (Metric Unit)
VeroClear and VeroWhitePlus
Tensile Strength Elongation at Break Modulus of Elasticity Flexural Strength Flexural Modulus Izod Notched Impact Shore D Hardness
ASTM ASTM ASTM ASTM ASTM ASTM –
50–60 MPa 10%–25% 2000–3000 MPa 75–110 MPa 2200–3200 MPa 20–30 J/m 83–86 D
top surfaces. In this regard, four cases were discussed in this research paper: named as matte finished VeroClear specimens (VC-M), glossy finished VeroClear specimens (VC-G), matte finished VeroWhitePlus specimens (VW-M) and glossy finished VeroWhitePlus specimens (VW-G).
3.2. Specimen preparation and testing standards Fig. 1 illustrates the dimensions of all test specimens, standards and its orientation with respect to print head moving direction. Four dumbbell shaped tensile specimen (ASTM D638) is used for tensile test to determine the tensile strength and elongation at break [25]. Four rectangle shaped flexural specimen (ASTM D790) is used for flexural test to determine the flexural strength and flexural modulus [26]. Due to same thickness, both tensile and flexural specimens are printed in single job, linearly aligned along the Y axis and equally spaced. Dimensions of tensile, flexural specimens and its printing direction are shown in Fig. 1a and 1b respectively. The tensile and flexural tests were performed by Zwick universal testing machine; capacity ranges of 0–100 KN, speed of 50 mm/min and constant environment of 72° F. Shore hardness specimen is printed in a separate single print job in XY direction and the specimen dimensions are shown in Fig. 1c. For detecting the shore hardness value, a circular disc shaped shore hardness specimen (ASTM D2240) is tested by shore D durometer [27]. It measures the indenter’s depth of penetration produced by applied load with specified time and having the capacity ranges of 0–100 HD, accuracy of 0.5 HD in 68–70° F temperature.
D638 D638 D638 D790 D790 D256
4. Results and discussion Table 2 infers that consumption of model material 1 (M1), model material 2 (M2), support material and required printing time to complete the each test specimens. From this table VC-M case takes maximum material consumption and printing time compared to other cases. Due to the additional support materials, material consumption and printing time is higher in matte finished specimens compared to glossy finished specimens. VC-G and VWG has the same printing time for all specimens. Table 2 values clearly exhibit that the printing details depends upon the required model material. After the cleaning of support materials from 3D printed specimens, standard testing was performed on specified testing specimens. Fig. 2 illustrates the tested specimens for tensile strength, flexural strength, and shore hardness of all cases. The tensile test results of specimens based on tensile strength (a) and elongation at break (b) as shown in Fig. 3. In Fig. 3a, the X axis denotes the sample number and Y axis denotes the tensile strength in MPa. The average tensile strength of the VC-G has highest value of 53.6 MPa and VW-M has lowest value of 43.15 MPa. By comparing the finish types, average tensile strength of VC-G is found to be 15.89% higher than VC-M, and VW-G is 3.36% higher than VW-M. Similarly, Comparing the material type with same finish, VC-G is 20.17% higher than VW-G and VC-M is 7.18% is higher than VW-M. Additionally, in an average tensile strength value of VC-G is deviated by 7.27% from standard average tensile strength value (57.5 MPa). From the tensile test, obtained elongation at break results are shown in Fig. 3b. The average elongation at break of the VW-M
Fig. 1. Dimensions of test specimens and its printing direction (a) Tensile specimen; (b) Flexural specimen; (c) Shore hardness specimen.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
4
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 2 Details of PolyJet printed test specimens. S. No
Test Specimens
Quantity
Case
1
Tensile and Flexural
4 and 4
2
Shore Hardness
1
VC-M VC-G VW-M VW-G VC-M VC-G VW-M VW-G
Fig. 2. Tested specimens of all tests.
has highest value of 28.75%, followed by VC-G (24.5%), VW-G (23.5%) and VC-M (21.5%). Value of VW-M is exceeds the upper boundary of the standard value (10–25%). Comparing the VW-M and VW-G, VC-M and VC-G, percentage of deviation in average elongation at break is 22.34% and 13.95% respectively. In matte finish, VW-M is 33.72% higher than VC-M. In glossy finish, VW-G is 4.25% lower than VC-G.
Material Consumption (Grams)
Build Time (Minutes)
M1 (VC)
M2 (VW)
Support
96 94 4 2 5 5 1 1
33 6 103 98 2 1 6 6
131 30 62 30 7 3 5 3
137 79 87 79 34 24 25 24
Fig. 4 displays the flexural test results of specimens based on flexural strength (a) and flexural modulus (b). Fig. 4a shows the flexural strength results of all cases. The average flexural strength of the VC-G has highest value of 49.1 MPa and VW-M has lowest value of 35.12 MPa. By comparing the finish types, average flexural strength of VC-G is 13.65% higher than VC-M and VW-G is 8.46% higher than VW-M. Similarly, Comparing the material type with same finish, VC-G is 28.87% higher than VW-G and VC-M is 22.98% is higher than VW-M. Average flexural strength value of all the cases is lower than standard value (75–110 MPa). Highest average flexural strength value of VC-G is deviated by 88.39% from standard average flexural strength value (92.5 MPa). From the flexural test, obtained results of flexural modulus are shown in Fig. 4b. Average flexural modulus values from highest to lowest are VC-G is 1352.5 MPa, VC-M is 1232.5 MPa, VW-M is 1070.25 MPa and VW-G is 991.25 MPa. From this result, all the values are found to be lower than standard table value (2200– 3200 MPa). Comparing the VC-M and VC-G, VW-M and VW-G, percentage of deviation in average flexural modulus is 9.73% and 7.96% respectively. In glossy finish, VC-G is 26.37% higher than VW-G. In matte finish, VC-M is 24.33% higher than VW-M. Fig. 5 displays the shore hardness values for all cases. The X axis denotes the trail number and Y axis denotes the shore hardness in scale D value. The average shore hardness of the all the cases are more or less equal. Despite, all the values are lower than standard table value (83–86 D). Both VC-G (81.37D) and VW-G (81D) secures the first two places. Similarly, VC-M (80.37D) and VW-M (79.62D) secures the last two places. Average shore hardness value of VC-G deviated by 3.84% from standard value. From the above, it could be concluded that glossy finished VeroClear (VC-G) specimens have better mechanical property than others. Due to the minimum support material consumption, free from support material contact and faster printing time, glossy finished specimen is realized to have better mechanical property than
Fig. 3. Tensile test results (a) Tensile strength; (b) Elongation at break.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx
5
Fig. 4. Flexural test results (a) Flexural Strength; (b) Flexural modulus.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements We gratefully acknowledge the financial support for establishing the Centre of Excellence in Manufacturing Sciences at Coimbatore Institute of Technology, Coimbatore; India from Ministry of Human-Resource Development (MHRD), Government of India where this R&D work is carried out. References Fig. 5. Shore Hardness.
matte finished specimens. The results reveal that VeroClear specimens are better than VeroWhitePlus specimens. Because, printing time and material consumptions of VeroWhitePlus specimens are higher than VeroClear specimens.
5. Conclusions The objective of this paper is to investigate the mechanical behaviour of the VeroClear and VeroWhitePlus materials in Objet260 Connex and printed in DM mode. Comparing to standard value, there is a difference in obtained values. Through this research study, following are the major findings: In both materials, glossy finish gives better result when compare to matte finish. VC-G specimen gives higher tensile strength (53.6 MPa), which is 20.17% than VW-G. VW-M specimen gives higher elongation at break (28.75%), which is 33.72% than VC-M. Flexural strength (49.1 MPa) 28.87% and flexural modulus (1352.5 MPa) 26.37% are good in VC-G compared to VW-G. In shore hardness, there is a minor difference in all cases. However, VC-G value is 0.46% higher than VW-G. Findings from current study, analysis can be used for better design of functional parts and new product development to improve the durability and reliability.
[1] D.L. Bourell, D.W. Rosen, M.C. Leu, The roadmap for additive manufacturing and its impact, 3D Printing Add. Manuf. 1 (1) (2014) 6–9. [2] H. Bikas, P. Stavropoulos, G. Chryssolouris, Additive manufacturing methods and modelling approaches: a critical review, Int. J. Adv. Manuf. Technol. 83 (1– 4) (2016) 389–405. [3] G.L. Goh, S. Agarwala, G.D. Goh, H.K.J. Tan, L. Zhao, T.K. Chuah, W.Y. Yeong, Additively manufactured multi-material free-form structure with printed electronics, Int. J. Adv. Manuf. Technol. 94 (1–4) (2018) 1309–1316. [4] I. Gibson, D. Rosen, B. Stucker, Direct digital manufacturing, Additive Manufacturing Technologies, Springer, New York, 2015, pp. 375–397. [5] B.H. Lee, J. Abdullah, Z.A. Khan, Optimization of rapid prototyping parameters for production of flexible ABS object, J. Mater. Process. Technol. 169 (1) (2005) 54–61. [6] Stratasys Ltd, PolyJet Materials, Stratasys Ltd, 2013. [7] M. Ramola, V. Yadav, R. Jain, On the adoption of additive manufacturing in healthcare: a literature review, J. Manuf. Technol. Manage. 30 (1) (2019) 48– 69. [8] Y.L. Yap, Y.S.E. Tan, H.K.J. Tan, Z.K. Peh, X.Y. Low, W.Y. Yeong, C.S.H. Tan, A. Laude, 3D printed bio-models for medical applications, Rapid Prototyping J. 2 (2) (2017) 227–235. [9] J. Lipton, J. Witzleben, V. Green, C. Ryan, H. Lipson, Demonstrations of additive manufacturing for the hospitality industry, 3D Printing Add. Manuf. 2 (4) (2015) 204–208. [10] G.A. Mendible, J.A. Rulander, S.P. Johnston, Comparative study of rapid and conventional tooling for plastics injection molding, Rapid Prototyping J. 23 (2) (2017) 344–352. [11] D.B. Short, Use of 3D printing by museums: Educational exhibits, artifact education, and artifact restoration, 3D Printing Add. Manuf. 2 (4) (2015) 209– 215. [12] A. Kantaros, O. Diegel, 3D printing technology in musical instrument research: reviewing the potential, Rapid Prototyping J. 24 (9) (2018) 1511–1523. [13] J.R.C. Dizon, A.H. Espera Jr, Q. Chen, R.C. Advincula, Mechanical characterization of 3D-printed polymers, Add. Manuf. 20 (2018) 44–67. [14] J.W. Stansbury, M.J. Idacavage, 3D printing with polymers: challenges among expanding options and opportunities, Dent. Mater. 32 (1) (2016) 54–64. [15] A. Cazón, P. Morer, L. Matey, PolyJet technology for product prototyping: tensile strength and surface roughness properties, Proc. Inst. Mech. Eng., Part B: J. Eng. Manuf. 228 (12) (2014) 1664–1675. [16] J.M. Chacón, M.A. Caminero, E. García-Plaza, P.J. Núñez, Additive manufacturing of PLA structures using fused deposition modelling: effect of
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
6
[17] [18] [19]
[20]
[21]
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx process parameters on mechanical properties and their optimal selection, Mater. Des. 124 (2017) 143–157. J.P. Moore, C.B. Williams, Fatigue properties of parts printed by PolyJet material jetting, Rapid Prototyping J. 21 (6) (2015) 675–685. A. Pilipovic´, P. Raos, M. Šercer, Experimental analysis of properties of materials for rapid prototyping, Int. J. Adv. Manuf. Technol. 40 (1–2) (2009) 105–115. J. Mueller, K. Shea, C. Daraio, Mechanical properties of parts fabricated with inkjet 3D printing through efficient experimental design, Mater. Des. 86 (2015) 902–912. L. Rebaioli, I. Fassi, A review on benchmark artifacts for evaluating the geometrical performance of additive manufacturing processes, Int. J. Adv. Manuf. Technol. 93 (5–8) (2017) 2571–2598. V. Rajendra Boopathy, A. Sriraman, Energy absorbing capability of additive manufactured multi-material honeycomb structure, Rapid Prototyping J. 25 (3) (2019) 623–629.
[22] J. Mueller, D. Courty, M. Spielhofer, R. Spolenak, K. Shea, Mechanical properties of interfaces in inkjet 3D printed single-and multi-material parts, 3D Printing Add. Manuf. 4 (4) (2017) 193–199. [23] N.A. Meisel, D.A. Dillard, C.B. Williams, Impact of material concentration and distribution on composite parts manufactured via multi-material jetting, Rapid Prototyping J. 24 (5) (2018) 872–879. [24] M. Sugavaneswaran, G. Arumaikkannu, Additive manufactured multi-material structure with directional specific mechanical properties based upon classical lamination theory, Rapid Prototyping J. 24 (7) (2018) 1212–1220. [25] ASTM D638-14, Standard Test Method for Tensile Properties of Plastics, ASTM International, West Conshohocken, PA, 2014. [26] ASTM D790-15e2, Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials, ASTM, International, West Conshohocken, PA, 2015. [27] ASTM D2240-15, Standard Test Method for Rubber Property— Durometer Hardness.” ASTM International, West Conshohocken, PA, 2015.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Impact of process parameters on mechanical behaviour in multi-material jetting Arivazhagan Pugalendhi ⇑, Rajesh Ranganathan, Sivakumar Ganesan Department of Mechanical Engineering, Coimbatore Institute of Technology, Civil Aerodrome Post, Coimbatore, Tamilnadu 641 014, India
a r t i c l e
i n f o
Article history: Received 7 November 2019 Accepted 12 December 2019 Available online xxxx Keywords: Additive manufacturing PolyJet technology Multi material jetting Mechanical properties Process parameter
a b s t r a c t PolyJet material jetting is a rapidly growing Additive Manufacturing (AM) technology due to its ability to build precise multi material parts having complex geometries. Mechanical properties of parts fabricated by AM are affected by printing parameters. Examining the strength of AM parts is important, due to the differences with PolyJet technology. The aim of this study is to characterize the effect of process parameters on the mechanical properties of VeroClear and VeroWhitePlus test specimens manufactured with digital material printing mode. Tensile, flexural and shore hardness tests are carried out to determine the mechanical properties of the 3D printed specimens. Findings indicate that the specimens printed in glossy finish are stronger and stiffer than matte finish. From a view of material and material concentration, VeroClear specimens show better results when compared to the mechanical properties of VeroWhitePlus specimens. In addition, comparison between the material consumptions and required printing time to complete the specimens were also carried out. All these test results revealed, VeroClear with glossy finish specimen is more efficient than the other combinations as it is significantly improved. This work provides a selection guideline that can be used to increase the durability of functional parts in wide variety of applications. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
1. Introduction Rapid growth of the Additive Manufacturing (AM) is applied to both commercial and potential research activities for providing better solutions in various sectors since middle of 1980’s to current state of art [1]. In AM, desired three dimensional computer aided design (CAD) model is sliced into two dimensional profiles for a layer-upon-layer building process to obtain the final part [2]. Flexibility in design and tool less fabrication of AM plays a major role in time to market (TTM) which has great impact on the final product cost over traditional tool manufacturing techniques [3]. Due to layer by layer fabrication process, AM samples displays anisotropic behaviour and it causes flaws and voids which may significantly reduce the strength of the final parts [4]. In many cases, material properties provided by the manufacturer are not practically suitable for most of the applications. So, in order to examine the influence of process parameters on mechanical behaviour it is essential for functional parts to deter⇑ Corresponding author. E-mail address: [email protected] (A. Pugalendhi).
mine the life of the 3D printed parts [5]. This study concentrates on examining the mechanical property of the parts fabricated by AM to provide better understanding for selection of process parameters based upon the final application.
2. Literature survey In PolyJet technology, ultraviolet (UV) curable resins are selectively jetted onto a build platform and cured, the recent layer is deposited. Capabilities of this technique allow the fabrication of multi materials in a single print with variety of colours and shore hardness values [6]. Automobile, aerospace and healthcare sectors took a great leap by the application of AM. 3D printed tissues and organs, surgical planning, prosthetics, medicine, medical device and medical imaging creates the revolution in the healthcare to customization and reduces the risk in surgery. In terms of accuracy of 3D printed model, PolyJet models have more accuracy than Selective Laser Sintering (SLS) and 3D inkjet printers (3DP) [7]. Virtual or physical bio-models are used to predict the disorders and complexity in surgery. Pre-operative planning and training can
https://doi.org/10.1016/j.matpr.2019.12.106 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
2
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx
improve the surgical skill of surgeon. Fabrication of patient-specific through AM reduces the cost and time without skilled sculptors over than casted polymer model [8]. In food science and technology, applications of AM allow a novel artistry and customized food items. 3D printed foods are directly used after the proper coating of silicon to meets the food safe regulations. In this regard, it is crucial to ensure the selection of material and process of AM [9]. Comparing the properties of machined stainless-steel insert, direct metal laser sintered (DMLS) bronze alloy insert and PolyJet inserts made by digital ABS to obtain a polypropylene moulded part. Study revealed that, mechanical properties, dimensional tolerances and quality of the AM parts are different from traditional techniques. PolyJet inserts has smoother surface finish than DMLS insert can be used without any polishing. Despite, due to the high temperature differences and low thermal conductivity, PolyJet inserts has highest shrinkage and long cycle time. Optimized cycle and tensile strength of the insert is 80 and 15 MPa [10]. AM is capable to reproduce an accurate ancient and modern artifacts for educational and commercial reasons. Scanning, replication and restoration of artifacts spawn rely in natural history and technology museums. PolyJet 3D printer exhibits wider range of thinking with the help of multi-colour materials [11]. The potential of AM generates new class of functional musical instruments that sounds extreme and resembles the original instruments. Greater accuracy and improved ergonomic factors of 3D printed instruments satisfy both mechanical and acoustic features. By utilising the PolyJet technology, wave whistle and transverse flute are printed in Objet PolyJet printer [12]. Dizon et al. gave a broad review of various AM methods and the effects of the mechanical properties. The cryogenic temperatures, nano filler additions and post processing have also been included. Various test standards and its standardization of test methods has been briefly discussed [13]. Mechanical properties of PolyJet parts are highly influenced by build orientation, layer thickness, type of material, surface finish and post processing [14–16]. Glossy finished PolyJet printed parts have higher fatigue life compared to matte finish [17]. Printing speed and placement of the object does not affect the strength of the final part. The study conducted by Pilipovic´ et al., in PolyJet machine revealed that, specimens of FullCure material has a maximum tensile and flexural strength followed by VeroBlue and VeroBlack. However, these values are lower than data provided by the manufacturer. Similarly, surface roughness is minimum in FullCure specimens compared to others [18]. Exposure time of UV light, machine’s warm-up time, storage time and validity of the raw material affects the mechanical properties of the PolyJet printed parts. The manufacturer provided data of VeroWhitePlus values of elastic modulus is close to the upper boundary and ultimate tensile strength, which exceeds the upper boundary. Geometry of the printed parts is highly affected by nozzle blockage [19]. So, assessment of the mechanical properties and their geometrical accuracy, minimum feature size and repeatability is most important [20]. Through experimental work of Rajendra Boopathy and Sriraman, compressive and impact loads on 5 layer sandwich multimaterial (3 layer of VeroWhitePlus) has a better energy absorbing capability compared to single VeroWhitePlus material, 2 layer (equally shared VeroWhitePlus and TangoPlus) and 3 layer sandwich multi-material (Centre layer is TangoPlus) [21]. Mueller et al. tested the interfaces of VeroWhitePlus and TangoBlackPlus in single-material interfaces, on-the-fly mixing of materials and multi-material interfaces. Multi material printing of PolyJet technology is similar to the conventional composite materials. Material properties of VeroWhitePlus material are similar to the commercial ABS. When the size of the part is larger than the inclusion size,
composite effect of digital material gives better result. Mixing ratios, different material combinations and direction of load plays a major role in composite effect. Rigid materials have uniform layer heights than flexible materials [22]. Meisel et al. measured the viscoelastic properties of PolyJet digital materials by using Dynamic mechanical analysis (DMA). Material composition and voxel dithering pattern affects the storage and loss modulus. In digital material, property of the final part is similar to the concentration of the dominant material [23]. Classical lamination theory is used to determine the directional specific mechanical properties of multi-material structured specimens printed by PolyJet 3DP. This study reports, shear strength is higher in angle ply laminate, both tensile and flexural is higher in quasiisotropic laminate [24]. In PolyJet machine, there is an option to print the single material part with mixture of other material by mixed tray method. This research work investigates the mechanical behaviour of tensile, flexural and shore hardness of the VeroClear and VeroWhitePlus material. By this study, selection of suitable material and their surface finish for specific application becomes easy.
3. Experimental details 3.1. Materials and methods In this study, mechanical behaviour of the standard specimens fabricated by Stratasys Objet260 Connex2 is determined by tensile, flexural and shore hardness tests. The Objet260 Connex2 printer consists of assembly of eight parallel print heads, two UV lights and one roller to flatten the printed surface, which moves in X and Y direction. Four print heads are owed to two model materials and four to support materials. Photo-curable materials are deposited in the required area in build tray through nozzles of the print heads. Build tray moves downwards direction of Z axis after curing the previous layer. This machine has extensive range of materials with different material properties; it prints any product with more than one material property simultaneously in a single part. Non-toxic gellike photopolymer of FullCure 705 is used as a support material. High-resolution layer accuracy of 16-m (High Quality-HQ) and 30m (High Speed-HS & Digital Material-DM), with a tray size of 255 252 200 mm. HQ and HS comes under single material mode, where only one model material is deposited on the end product. In DM mode or multi material mode, deposits more than one model materials on end product by mixed part, mixed tray and digital material approaches. Mixed tray method offers single material printing in DM mode. This study investigates the mechanical properties of VeroClear and VeroWhitePlus which are suitable to form and fit testing in wide range of industrial application. All test specimens are printed in mixed tray approach in DM mode by introducing the small sample object having the dimensions of Ø5 0.5 mm. Here, model materials bays are loaded with both VeroClear and VeroWhitePlus materials. In this condition, a sample object can be printed along with the required material using alternate material. Then test results are compared with standard values provided by manufacturer as shown in Table 1. Because, except three mechanical properties (Polymerized density, Ash content, Colour) of VeroClear and VeroWhitePlus, all other properties are same, where, practically it is not possible. VeroClear material is used in medical devices, eyewear and light cover and white colour opaque material of VeroWhitePlus is used in medical devices and electronic housings. All the test specimens are fabricated with both matte (M) and glossy (G) finish, matte finish wraps the entire surface in support material and glossy finish is free from the support material on specimen’s
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
3
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Mechanical properties of VeroClear and VeroWhitePlus (Source: Stratasys). Material
Mechanical Properties
Test Method
Value (Metric Unit)
VeroClear and VeroWhitePlus
Tensile Strength Elongation at Break Modulus of Elasticity Flexural Strength Flexural Modulus Izod Notched Impact Shore D Hardness
ASTM ASTM ASTM ASTM ASTM ASTM –
50–60 MPa 10%–25% 2000–3000 MPa 75–110 MPa 2200–3200 MPa 20–30 J/m 83–86 D
top surfaces. In this regard, four cases were discussed in this research paper: named as matte finished VeroClear specimens (VC-M), glossy finished VeroClear specimens (VC-G), matte finished VeroWhitePlus specimens (VW-M) and glossy finished VeroWhitePlus specimens (VW-G).
3.2. Specimen preparation and testing standards Fig. 1 illustrates the dimensions of all test specimens, standards and its orientation with respect to print head moving direction. Four dumbbell shaped tensile specimen (ASTM D638) is used for tensile test to determine the tensile strength and elongation at break [25]. Four rectangle shaped flexural specimen (ASTM D790) is used for flexural test to determine the flexural strength and flexural modulus [26]. Due to same thickness, both tensile and flexural specimens are printed in single job, linearly aligned along the Y axis and equally spaced. Dimensions of tensile, flexural specimens and its printing direction are shown in Fig. 1a and 1b respectively. The tensile and flexural tests were performed by Zwick universal testing machine; capacity ranges of 0–100 KN, speed of 50 mm/min and constant environment of 72° F. Shore hardness specimen is printed in a separate single print job in XY direction and the specimen dimensions are shown in Fig. 1c. For detecting the shore hardness value, a circular disc shaped shore hardness specimen (ASTM D2240) is tested by shore D durometer [27]. It measures the indenter’s depth of penetration produced by applied load with specified time and having the capacity ranges of 0–100 HD, accuracy of 0.5 HD in 68–70° F temperature.
D638 D638 D638 D790 D790 D256
4. Results and discussion Table 2 infers that consumption of model material 1 (M1), model material 2 (M2), support material and required printing time to complete the each test specimens. From this table VC-M case takes maximum material consumption and printing time compared to other cases. Due to the additional support materials, material consumption and printing time is higher in matte finished specimens compared to glossy finished specimens. VC-G and VWG has the same printing time for all specimens. Table 2 values clearly exhibit that the printing details depends upon the required model material. After the cleaning of support materials from 3D printed specimens, standard testing was performed on specified testing specimens. Fig. 2 illustrates the tested specimens for tensile strength, flexural strength, and shore hardness of all cases. The tensile test results of specimens based on tensile strength (a) and elongation at break (b) as shown in Fig. 3. In Fig. 3a, the X axis denotes the sample number and Y axis denotes the tensile strength in MPa. The average tensile strength of the VC-G has highest value of 53.6 MPa and VW-M has lowest value of 43.15 MPa. By comparing the finish types, average tensile strength of VC-G is found to be 15.89% higher than VC-M, and VW-G is 3.36% higher than VW-M. Similarly, Comparing the material type with same finish, VC-G is 20.17% higher than VW-G and VC-M is 7.18% is higher than VW-M. Additionally, in an average tensile strength value of VC-G is deviated by 7.27% from standard average tensile strength value (57.5 MPa). From the tensile test, obtained elongation at break results are shown in Fig. 3b. The average elongation at break of the VW-M
Fig. 1. Dimensions of test specimens and its printing direction (a) Tensile specimen; (b) Flexural specimen; (c) Shore hardness specimen.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
4
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 2 Details of PolyJet printed test specimens. S. No
Test Specimens
Quantity
Case
1
Tensile and Flexural
4 and 4
2
Shore Hardness
1
VC-M VC-G VW-M VW-G VC-M VC-G VW-M VW-G
Fig. 2. Tested specimens of all tests.
has highest value of 28.75%, followed by VC-G (24.5%), VW-G (23.5%) and VC-M (21.5%). Value of VW-M is exceeds the upper boundary of the standard value (10–25%). Comparing the VW-M and VW-G, VC-M and VC-G, percentage of deviation in average elongation at break is 22.34% and 13.95% respectively. In matte finish, VW-M is 33.72% higher than VC-M. In glossy finish, VW-G is 4.25% lower than VC-G.
Material Consumption (Grams)
Build Time (Minutes)
M1 (VC)
M2 (VW)
Support
96 94 4 2 5 5 1 1
33 6 103 98 2 1 6 6
131 30 62 30 7 3 5 3
137 79 87 79 34 24 25 24
Fig. 4 displays the flexural test results of specimens based on flexural strength (a) and flexural modulus (b). Fig. 4a shows the flexural strength results of all cases. The average flexural strength of the VC-G has highest value of 49.1 MPa and VW-M has lowest value of 35.12 MPa. By comparing the finish types, average flexural strength of VC-G is 13.65% higher than VC-M and VW-G is 8.46% higher than VW-M. Similarly, Comparing the material type with same finish, VC-G is 28.87% higher than VW-G and VC-M is 22.98% is higher than VW-M. Average flexural strength value of all the cases is lower than standard value (75–110 MPa). Highest average flexural strength value of VC-G is deviated by 88.39% from standard average flexural strength value (92.5 MPa). From the flexural test, obtained results of flexural modulus are shown in Fig. 4b. Average flexural modulus values from highest to lowest are VC-G is 1352.5 MPa, VC-M is 1232.5 MPa, VW-M is 1070.25 MPa and VW-G is 991.25 MPa. From this result, all the values are found to be lower than standard table value (2200– 3200 MPa). Comparing the VC-M and VC-G, VW-M and VW-G, percentage of deviation in average flexural modulus is 9.73% and 7.96% respectively. In glossy finish, VC-G is 26.37% higher than VW-G. In matte finish, VC-M is 24.33% higher than VW-M. Fig. 5 displays the shore hardness values for all cases. The X axis denotes the trail number and Y axis denotes the shore hardness in scale D value. The average shore hardness of the all the cases are more or less equal. Despite, all the values are lower than standard table value (83–86 D). Both VC-G (81.37D) and VW-G (81D) secures the first two places. Similarly, VC-M (80.37D) and VW-M (79.62D) secures the last two places. Average shore hardness value of VC-G deviated by 3.84% from standard value. From the above, it could be concluded that glossy finished VeroClear (VC-G) specimens have better mechanical property than others. Due to the minimum support material consumption, free from support material contact and faster printing time, glossy finished specimen is realized to have better mechanical property than
Fig. 3. Tensile test results (a) Tensile strength; (b) Elongation at break.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx
5
Fig. 4. Flexural test results (a) Flexural Strength; (b) Flexural modulus.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements We gratefully acknowledge the financial support for establishing the Centre of Excellence in Manufacturing Sciences at Coimbatore Institute of Technology, Coimbatore; India from Ministry of Human-Resource Development (MHRD), Government of India where this R&D work is carried out. References Fig. 5. Shore Hardness.
matte finished specimens. The results reveal that VeroClear specimens are better than VeroWhitePlus specimens. Because, printing time and material consumptions of VeroWhitePlus specimens are higher than VeroClear specimens.
5. Conclusions The objective of this paper is to investigate the mechanical behaviour of the VeroClear and VeroWhitePlus materials in Objet260 Connex and printed in DM mode. Comparing to standard value, there is a difference in obtained values. Through this research study, following are the major findings: In both materials, glossy finish gives better result when compare to matte finish. VC-G specimen gives higher tensile strength (53.6 MPa), which is 20.17% than VW-G. VW-M specimen gives higher elongation at break (28.75%), which is 33.72% than VC-M. Flexural strength (49.1 MPa) 28.87% and flexural modulus (1352.5 MPa) 26.37% are good in VC-G compared to VW-G. In shore hardness, there is a minor difference in all cases. However, VC-G value is 0.46% higher than VW-G. Findings from current study, analysis can be used for better design of functional parts and new product development to improve the durability and reliability.
[1] D.L. Bourell, D.W. Rosen, M.C. Leu, The roadmap for additive manufacturing and its impact, 3D Printing Add. Manuf. 1 (1) (2014) 6–9. [2] H. Bikas, P. Stavropoulos, G. Chryssolouris, Additive manufacturing methods and modelling approaches: a critical review, Int. J. Adv. Manuf. Technol. 83 (1– 4) (2016) 389–405. [3] G.L. Goh, S. Agarwala, G.D. Goh, H.K.J. Tan, L. Zhao, T.K. Chuah, W.Y. Yeong, Additively manufactured multi-material free-form structure with printed electronics, Int. J. Adv. Manuf. Technol. 94 (1–4) (2018) 1309–1316. [4] I. Gibson, D. Rosen, B. Stucker, Direct digital manufacturing, Additive Manufacturing Technologies, Springer, New York, 2015, pp. 375–397. [5] B.H. Lee, J. Abdullah, Z.A. Khan, Optimization of rapid prototyping parameters for production of flexible ABS object, J. Mater. Process. Technol. 169 (1) (2005) 54–61. [6] Stratasys Ltd, PolyJet Materials, Stratasys Ltd, 2013. [7] M. Ramola, V. Yadav, R. Jain, On the adoption of additive manufacturing in healthcare: a literature review, J. Manuf. Technol. Manage. 30 (1) (2019) 48– 69. [8] Y.L. Yap, Y.S.E. Tan, H.K.J. Tan, Z.K. Peh, X.Y. Low, W.Y. Yeong, C.S.H. Tan, A. Laude, 3D printed bio-models for medical applications, Rapid Prototyping J. 2 (2) (2017) 227–235. [9] J. Lipton, J. Witzleben, V. Green, C. Ryan, H. Lipson, Demonstrations of additive manufacturing for the hospitality industry, 3D Printing Add. Manuf. 2 (4) (2015) 204–208. [10] G.A. Mendible, J.A. Rulander, S.P. Johnston, Comparative study of rapid and conventional tooling for plastics injection molding, Rapid Prototyping J. 23 (2) (2017) 344–352. [11] D.B. Short, Use of 3D printing by museums: Educational exhibits, artifact education, and artifact restoration, 3D Printing Add. Manuf. 2 (4) (2015) 209– 215. [12] A. Kantaros, O. Diegel, 3D printing technology in musical instrument research: reviewing the potential, Rapid Prototyping J. 24 (9) (2018) 1511–1523. [13] J.R.C. Dizon, A.H. Espera Jr, Q. Chen, R.C. Advincula, Mechanical characterization of 3D-printed polymers, Add. Manuf. 20 (2018) 44–67. [14] J.W. Stansbury, M.J. Idacavage, 3D printing with polymers: challenges among expanding options and opportunities, Dent. Mater. 32 (1) (2016) 54–64. [15] A. Cazón, P. Morer, L. Matey, PolyJet technology for product prototyping: tensile strength and surface roughness properties, Proc. Inst. Mech. Eng., Part B: J. Eng. Manuf. 228 (12) (2014) 1664–1675. [16] J.M. Chacón, M.A. Caminero, E. García-Plaza, P.J. Núñez, Additive manufacturing of PLA structures using fused deposition modelling: effect of
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106
6
[17] [18] [19]
[20]
[21]
A. Pugalendhi et al. / Materials Today: Proceedings xxx (xxxx) xxx process parameters on mechanical properties and their optimal selection, Mater. Des. 124 (2017) 143–157. J.P. Moore, C.B. Williams, Fatigue properties of parts printed by PolyJet material jetting, Rapid Prototyping J. 21 (6) (2015) 675–685. A. Pilipovic´, P. Raos, M. Šercer, Experimental analysis of properties of materials for rapid prototyping, Int. J. Adv. Manuf. Technol. 40 (1–2) (2009) 105–115. J. Mueller, K. Shea, C. Daraio, Mechanical properties of parts fabricated with inkjet 3D printing through efficient experimental design, Mater. Des. 86 (2015) 902–912. L. Rebaioli, I. Fassi, A review on benchmark artifacts for evaluating the geometrical performance of additive manufacturing processes, Int. J. Adv. Manuf. Technol. 93 (5–8) (2017) 2571–2598. V. Rajendra Boopathy, A. Sriraman, Energy absorbing capability of additive manufactured multi-material honeycomb structure, Rapid Prototyping J. 25 (3) (2019) 623–629.
[22] J. Mueller, D. Courty, M. Spielhofer, R. Spolenak, K. Shea, Mechanical properties of interfaces in inkjet 3D printed single-and multi-material parts, 3D Printing Add. Manuf. 4 (4) (2017) 193–199. [23] N.A. Meisel, D.A. Dillard, C.B. Williams, Impact of material concentration and distribution on composite parts manufactured via multi-material jetting, Rapid Prototyping J. 24 (5) (2018) 872–879. [24] M. Sugavaneswaran, G. Arumaikkannu, Additive manufactured multi-material structure with directional specific mechanical properties based upon classical lamination theory, Rapid Prototyping J. 24 (7) (2018) 1212–1220. [25] ASTM D638-14, Standard Test Method for Tensile Properties of Plastics, ASTM International, West Conshohocken, PA, 2014. [26] ASTM D790-15e2, Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials, ASTM, International, West Conshohocken, PA, 2015. [27] ASTM D2240-15, Standard Test Method for Rubber Property— Durometer Hardness.” ASTM International, West Conshohocken, PA, 2015.
Please cite this article as: A. Pugalendhi, R. Ranganathan and S. Ganesan, Impact of process parameters on mechanical behaviour in multi-material jetting, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.106