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Procedia Manufacturing 26 (2018) 720–730 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
46th SME North American Manufacturing Research Conference, NAMRC 46, Texas, USA 46th SME North American Manufacturing Research Conference, NAMRC 46, Texas, USA
Effect of surface slope and build orientation on surface finish and Effect ofdimensional surface slope and build orientation on surface finish and accuracy in material jetting processes Manufacturing Engineering Society International Conference 2017, MESIC 2017, dimensional accuracy in material jetting processes 28-30 June 2017, Vigo (Pontevedra), Spain Ali Khoshkhooa*, Andres L. Carranob, David M. Blerschc Ali Khoshkhooa*, Andres L. Carranob, David M. Blerschc
Auburn University, Department of Industrial and Systems Engineering, Auburn, Alabama 36849. USA Costing models forUniversity, capacity optimization in Industry 4.0: Trade-off Georgia Department of Manufacturing Engineering, Auburn, Statesboro, Georgia 30460. USA AuburnSouthern University, Department of Industrial and Systems Engineering, Alabama 36849. USA Auburn University, Department of Biosystems Engineering, Auburn,Statesboro, Alabama 36849. USA Georgia Southern University, Department of Manufacturing Engineering, Georgia 30460. USA between used capacity and operational efficiency a
b b
a
c
c Auburn University, Department of Biosystems Engineering, Auburn, Alabama 36849. USA * Ali Khoshkhoo. Tel.:+1-713-428-1035. a a,* b b E-mail address: Tel.:+1-713-428-1035.
[email protected] * Ali Khoshkhoo.
A. Santana , P. Afonso , A. Zanin , R. Wernke
E-mail address:
[email protected]
a
University of Minho, 4800-058 Guimarães, Portugal
Unochapecó, 89809-000 Chapecó, SC, Brazil Abstract Abstract This work seeks to elucidate the effect of surface slope and build orientation upon the surface finish and dimensional accuracy of specimens by material jetting Specimens a flat area feature (i.e., spherical and This work fabricated seeks to elucidate the effect of processes. surface slope and buildwith orientation uponand the four surface finishdesigns and dimensional accuracy Abstract prismatic hole fabricated and protrusions) were printed two orientations (i.e.,with alonga (XY) and and across (YX) the print head(i.e., direction) and two of specimens by material jetting in processes. Specimens flat area four feature designs spherical and surface slopes (i.e.,protrusions) horizontal (0°) 45°) and scanned with a (i.e., white-light profilometer to quantify the surface texture, areal, and prismatic holeconcept and wereand printed inproduction two orientations along (XY) and across (YX) the print head direction) and two Under the of "Industry 4.0", processes will be pushed to be increasingly interconnected, material ratio parameters for dimensional accuracy and areal The results indicatetothat surface andtexture, build orientation surface slopes (i.e., horizontal (0°) and 45°) and scanned withfidelity. a white-light profilometer quantify theslope surface areal, and information on ainfluence real time and, necessarily, much The more efficient. In that this context, capacity optimization appear toratio havebased a greater on basis the recessed compared theresults protruded ones. The heightslope and volumetric functional material parameters for dimensional accuracyfeatures and areal fidelity. to indicate surface and build orientation goes beyond the traditional aim of capacity maximization, contributing also for organization’s profitability and value. surface toparameters are significant andthe show betterfeatures surfacecompared finish fortothethe0°protruded surface slope 45°.volumetric Also, prismatic and appear have a greater influence on recessed ones.compared The heighttoand functional Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of recessed features might benefit from printing on a 45° sloped surface while the design fidelity of cross-sections in holes surface parameters are significant and show better surface finish for the 0° surface slope compared to 45°. Also, prismatic and protrusions greatly vary depending theoptimization specimen slope. contributions of work include potential for maximization. The study of capacity andThe costing models is this an important research topicthe that deserves recessed features might benefit fromonprinting on a 45° sloped surface while the design fidelity of illustrating cross-sections in holes and increased production, resolution andon fidelity capabilities ifperspectives. 3D printing equipment could incorporate tilting printathe trays, adaptable protrusions greatly depending the specimen slope. The contributions this work include illustrating potential for contributions fromvary both the practical and theoretical This of paper presents and discusses mathematical print orientation, and local angles,and among others. increased production, resolution fidelity capabilities if 3D printing equipment could incorporate tilting print trays, adaptable model for capacity management based on different costing models (ABC and TDABC). A generic model has been print orientation, and local angles, among others. developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s © 2018The The Authors. Published bymaximization Elsevier B.V. value. trade-offPublished capacityby © 2018 The Authors. Elsevier B.V. vs operational efficiency is highlighted and it is shown that capacity Peer-review under responsibility of the scientific scientific committeeof ofthe NAMRI/SME. © 2018 The Authors. Published by B.V.committee Peer-review under responsibility of Elsevier the 4th International Conference on System-Integrated Intelligence. optimization might hide operational inefficiency. Peer-review under responsibility of the scientific committee of NAMRI/SME. © 2017 The Authors. Published by Elsevier B.V. b
Keywords: 3D printing; additive manufacturing; material jetting; dimensional accuracy; surface finish; surface metrology; design guidelines;
Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference stair-stepping Keywords: 3D printing; additive manufacturing; material jetting; dimensional accuracy; surface finish; surface metrology; design guidelines; 2017. stair-stepping
Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
material layer by layer [1]. The main advantage of AM 1. Introduction technologies to traditional manufacturing is material layercompared by layer [1]. The main advantage of AM 1. Introduction its capability compared to fabricate complex geometry with technologies to any traditional manufacturing is Additive Manufacturing (AM) is a process to create 1. Introduction internal features. AM technologies havegeometry been used in its capability to fabricate any complex with 3-DAdditive specimens from 3-D(AM) model bytoadding Manufacturing is a data process create internal features. AM technologies have been used in 3-DThespecimens 3-Dis model data byinformation adding for companies cost of idlefrom capacity a fundamental and their management of extreme importance
2351-9789 2018 The Authors. Published by Elsevier in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured Peer-review of the scientific committee of NAMRI/SME. 2351-9789 2018responsibility The Authors. Published by Elsevier B.V.hours in several©under ways: tons of production, available of manufacturing, etc. The management of the idle capacity Peer-review under Tel.: responsibility the761; scientific committee NAMRI/SME. * Paulo Afonso. +351 253of 510 fax: +351 253 604of741 E-mail address:
[email protected]
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 4th International Conference on System-Integrated Intelligence. 10.1016/j.promfg.2018.07.082
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industries for design specimens, production tools, and as a final product [2]. A wide variety of AM technologies exists nowadays with different properties in resolution, accuracy, speed, materials, porosity, and mechanical aspects. A comprehensive classification of AM processes is described in the ASTM F2792−12a standard [1]. The standard classifies the AM processes into seven categories: binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, and vat photopolymerization [1]. In the material jetting process, an acrylic photopolymer is projected over the printed object and is cured to its succeeding layer by ultraviolet (UV) radiation. When the layer has cured, the tray drops the equivalent of a layer thickness along the Z-axis, and this procedure is repeated until the part is built. The printing head consists of multiple microjetting heads capable of injecting a 10-30 µm thick layer of resin [2,3]. Numerous studies have analyzed the surface finish of AM technologies such as Fused Deposition Modelling (FDM) [4], Laminated Object Manufacturing (LOM) [5], stereolithography (SL) [6,7], Selective Laser Sintering (SLS) [8], Selective Laser Melting (SLM) [9], Electron Beam Melting (EBM) [9], and High Speed Sintering (HSS) [10]. To date, there are very few efforts that have aimed at the surface finish and dimensional accuracy in material jetting processes [11,12]. Khoshkhoo et al. [13] proposed a method to generate pseudorandomized surfaces with certain surface characteristics with specific Smr, Sa, and Sv values). Surface metrology parameters (i.e., Smr, Sp, Sku, Ssk, Sz, Sq, Sa, and Sv) are used to test the fidelity of the proposed method. Their results showed that the accuracy of metrology parameters are varied depending on the resolution of the machine in different axes. Among selected metrology parameters for validation process, Smr had the lowest average error (5.7 %), while Sv and Sa had the highest average error (33.8 %). Carrano et al. [14] studied natural surfaces (rocks) to understand and engineer desired surface topography with material jetting processes for biofilms in biological applications. There are many design guidelines available that address surface finish and dimensional accuracy in AM processes. These studies (Campbell [15]) suggest minimum wall thicknesses, clearances, and angles for features such as pins, holes, bosses, threads, and overhangs for powder bed fusion and fused deposition processes, or for better surface roughness, mechanical
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properties or lower fabrication cost or time [15,16]. Phan and Masood [17] tested spherical and prismatic protrusions to evaluate the accuracy level and surface roughness of the FDM process. Different nozzle tip sizes were used in this study, which concluded that both tip size and build orientation affect the dimensional accuracy and surface finish. Other efforts have targeted the effects of size, build orientation, and build location on the dimensional accuracy of flat surfaces of material jetting processes. It was found that the surface finish is affected by build orientation and size of the specimen, whereas part location has a smaller influence. It is recommended that XY orientation (parts’ longest dimension along the printing head direction) has the best dimensional accuracy. [3, 18]. Udroiu et al. [19] studied the effects of build type (glossy and matte), and Kumar et al. [20] investigated the effects of surface slope on the average roughness of fabricated specimens in a Polyjet process respectively. It is shown that both build type and surface slope significantly affect the average roughness of fabricated specimens. However, there are very few studies available to provide design guidelines for material jetting processes. Meisel and Williams [21] studied minimum resolvable feature size and the self-supporting angle in the absence of support material to establish a set of design for additive manufacturing (DfAM) guidelines for material jetting [21]. This study suggests some design guidelines, including channels and holes, should be larger than 50 mm2 and minimum resolvable feature sizes should be larger than 0.897 mm in diameter. It was also found that orientation was a statistically significant factor and that to achieve the minimum self-supporting angle, critical angled faces should be oriented in the YX direction in the build tray. Several other studies [11–14] have pushed the fabrication limits on resolvable feature sizes but have stopped short of proposing quantitative guidelines. Stair-stepping is one of the major artifacts on the printed surfaces due to sloping part features. The stairstepping effect happens when a surface orientation is not orthogonal to the axis of the source of energy. This study aims at uncovering the effects of stair-stepping on surface parameters. Also, there currently is a need for understanding and quantifying the conditions that affect surface finish and dimensional accuracy produced with material jetting technologies. This work aims at understanding the impact of surface angle and build orientation parameters in material jetting additive manufacturing on surface finish and dimensional accuracy. The contributions of this effort
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include laying the foundation for design guidelines for material jetting technology that will benefit the user community and industry. 2. Materials and methods Four features (spherical and prismatic protrusions and holes), as well as a flat area, were modeled in Solidworks® (Dassault Systemes, SolidWorks Corp., Waltham, MA) (Figure 1). Three replicates of each specimen were fabricated to the best possible surface finish option (i.e., glossy) from the machine. The specimens were fabricated with an Objet30 (Stratasys Ltd., Eden Prairie, MN) printer with a 28 µm target layer thickness. The height and length of designed features are 800 μm and 1600 μm respectively. These feature sizes were chosen with two considerations: the limitation of the optical profilometer (ST-400 Nanovea, Irving, California) in the Z-axis (approximately 900 μm); and dimensional accuracy of printed features with sizes greater than 700 μm is higher than 90%. The specimens were printed one at a time in the middle of the build tray to minimize the distorting effect of a possible cooling gradient caused by the edge of the tray. All features were designed and arranged in a matrix layout on each specimen and each row, with each column containing all representative feature types in a pseudo-randomized position order (Figure 1). Prior this experiment, a preliminary trial was conducted to determine the levels of each factor. The preliminary experiment examined two factors: surface slope with three levels (0° (horizontal), 45°, and 90° (upright)) and build orientation with two levels,
Fig. 1Computer models of (a) horizontal (0°) and (b) sloped (45°).
longest dimension along (XY), and across (YX) the printing head direction (Figure 2) to examine the feasibility and repeatability of the conditions. Those specimens with a 90° surface slope required significant coverage of the features with support material due to their location in the cantilever. The removal of this amount of support material required a combination of mechanical scraping and the use of chemical solvents and resulted in undesired alteration of the original surface. Consequently, the experimental orientation level of 90° was discarded. The specimens with a 45° surface slope required minimal support material below the protruded features and inside the depressions so its removal was possible with a waterjet system which did not affect the features or surface. The flat area was printed without any support material, so no post-processing was required. Therefore, two levels of surface slope (0° and 45°) and two levels of build orientation (XY and YX) were considered in this study.
Fig. 2 Specimen orientation and surface slope.
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The flat area was characterized by twenty-three surface texture parameters established by the ISO 25178-2 standard [22], and the features were analyzed by estimating dimensional and areal fidelity. For this purpose, surface profiles were taken with an axiochromatic white-light profilometer (ST-400 Nanovea, Irving, California). Selected flat areas of 10 mm × 10 mm were scanned by a step size of 10 µm in X and Y directions and acquisition with a rate of 1000 Hz and a cut-off length of 0.8 mm. In all reading setups, the missing points accounted for less than 5% of the total raw data. The Abbott Curve (Figure 3) represents the cumulative probability density function of the surface profile’s height and extrapolates numbers of functional surface and volumetric parameters including the distance between the highest and lowest level of the core surface (Sk), the average height of the protruded peaks above the core surface (Spk), and the average height of the protruded dales below the core surface (Svk), peak material volume (Vmp), core material volume (Vmc), core void volume (Vvc), valley void volume (Vvv) [23–25]. Based on the ISO 25178 standard, the bearing ratio thresholds, 20% (Smr1) and 80% (Smr2) are considered for the Abbott Curve to measure the functional parameters. The Smr1 and Smr2 represent the percentage limits of the core roughness profile [25]. Figure 3 (a) and (b) show the functional (i.e., stratified and volumetric) parameters in Abbott Curve. In addition to the Abbot Curve parameters, height parameters and spatial parameters were considered to analyze the effect of stair-stepping on
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surface quality. The list of all studied parameters with their definitions is presented in Table 3 in Appendix A. Dimensional and areal fidelity have been studied in all three axes. For assessing the dimensional accuracy, the geometrical features, the deviations from the design targets (i.e., length (FL), height (FH), and the projected area in XY plane (AL)) have been analyzed through white-light profilometry. The actual diameter and length have been measured for spherical and prismatic features after excluding the ledges created by the creep-like flow of uncured material immediately after deposition. The profiles are analyzed by the Mountain® software (Digital Surf, Professional 3-D7.0, Besancon, France). The features of each replicate were scanned once, and two surface profiles in X and Y directions were taken. For each feature, ten measurements were made to measure length, diameters, height, depth, projected areas in XZ and YZ planes as well as side angles in X and Y direction. Several statistical analyses were performed to examine the dimensional and areal fidelity of the printed features. Several 22 factorial analyses were conducted to study the effects of surface slope, build orientation, and their interactions on the dimensional accuracy of printed features. These included one-way ANOVA and Tukey’s pairwise comparisons. Then, ttests were performed to compare the length of features fabricated on 45° sloped surfaces along the width (FLW) and the slope (FLS) of the specimens.
Fig. 3 (a) 2D and (b) volumetric functional parameters of Abbott Curve.
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3. Results 3.1. Flat surface characterization Twenty-three 22-factorial analyses performed to observe the effects of surface slope (0° and 45°) and build orientation (XY and YX) on each of the surface parameters. The results are summarized in Table 1. Broadly, the height, functional material ratio, and functional volume groups stood out with the most statistically significant parameters. In height parameters, the surface slope is significant at p
