Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 132 (2015) 856 – 863
The Manufacturing Engineering Society International Conference, MESIC 2015
Dimensional and surface texture characterization in Fused Deposition Modelling (FDM) with ABS plus P.J. Nuñeza,*, A. Rivasa, E. García-Plazaa, E. Beamudb, A. Sanz-Loberac a
Universidad de Castilla-La Mancha, E.T.S. de Ingenieros Industriales-Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Avda. Camilo José Cela 3, 13071, Ciudad Real, Spain b Universidad de Castilla-La Mancha, Escuela de Minas e Ingeniería Industrial, Plaza Manuel de Meca 1, 13400, Almadén, Ciudad Real, Spain c Universidad Politécnica de Madrid, Aerospace Materials and Production Department. E.T.S.I. Aeronáutica y Espacio, Plaza Cardenal Cisneros 3, 28040, Madrid, Spain
Abstract Fused Deposition Modelling (FDM) has become extensively used for low-cost printers. Normally, commercial manufacturers of printers only provide information on layer thickness, but no information is given as to dimensional accuracy, and the surface characteristics obtained in manufactured components. The aim of this study was to determine the dimensional accuracy, flatness, and surface texture obtained in FDM rapid prototype with ABS-plus as the model material. In the experimental test, two densities (low, solid) and two layer thicknesses (0.178 mm, 0.254 mm) were used. The best dimensional behaviour was obtained with the configuration of maximum layer thickness (0.254 mm) and solid density (100%) with a The best finish surface and minimum flatness error were obtained with less layer thickness (0.178 mm) and solid density (100%). This study has established the optimum configurations for the manufacture of components with FDM 3D printing and ABS-plus. © by Elsevier Ltd. by ThisElsevier is an open © 2015 2016Published The Authors. Published Ltd.access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015. Peer-review under responsibility of the Scientific Committee of MESIC 2015 Keywords: Additive manufacturing (AM); Fused deposition modelling (FDM); Dimensional accuracy; Flatness; Surface texture.
1. Introduction Fusion Deposition Manufacturing (FDM) technology is ideal for manufacturing functional models, prototypes or components in thermoplastic materials, with excellent mechanical, thermal, and chemical resistance [1]. This
* Corresponding author. Tel.: +0-034-926-295218; fax: +0-034-926-295361. E-mail address:
[email protected]
1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015
doi:10.1016/j.proeng.2015.12.570
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technology involves heating thermoplastic polymer filaments to a temperature close to the point of fusion, through single-extruder or multi-extruders to deposit the material in layers on an X-Y horizontal plane, with varying layers of thickness on the axis perpendicular to the worktable (Z axis). The most frequently used materials are thermoplastics (polythene, polypropylene, polybutylene, polystyrene, polyvinyl chloride, ABS, ABS-plus, polyamide, among others), due to their excellent mechanical, thermal, and chemical characteristics. These materials are particularly suitable for industrial applications since they are easily manageable in their pre-fusion state at low temperatures, gradually harden as they cool down at glass transition temperature, and revert back to their initial properties [1]. The last decade has witnessed an exponential rise in the use of FDM technology given that the manufacture of prototypes and finished products is relatively inexpensive for very short runs. Manufacturers of commercial 3D printers provide information on how to adjust the printer settings on each machine e.g., layer thickness in relation to the vertical Z axis, material density, extrusion speed, extrusion temperature, etc. However, little information is provided in terms of the quality of the product produced, repeatability in positioning the extruder, dimensional and geometric precision, surface texture, which are crucial data for establishing elements such as dimensional and geometric tolerance, surface finish, and correct printer set-up and functioning, and the manufacture of prototypes. Thus, the aim of this study was to assess the quality parameters for the manufacture of products using FDM with ABS-plus in a commercial mid-range 3D printer from a geometric perspective to determine dimensional precision, flatness error, and the characterization of surface texture. This data is vital for determining the quality of the final product, and provides users essential information on the tolerance of FDM technology in additive manufacturing (AM) by commercial 3D printers. 2. Experimental Procedure For the experimental design a Dimension Elite 3D Printer (Stratasys) was used, with ABSplus-P430 thermoplastic as the modeling material, whose properties are described in Table 1, Table 2 and Table 3. The soluble support material (SST) is dissolved in an acid-aqueous solution provided by Stratasys, a solution that is deposited in the SCA-1200 Stratasys system to dissolve and eliminate the supports of the printed workpiece, with controlled temperature, time and mechanical agitation. The model material can be mechanized, polished, coated or painted. The materials, model, and support, cure inside the impression chamber during the printing process. This printer allows for two layers of thicknesses: 0.178 mm and 0.254 mm; and three densities of model interior fill: low density (10%), high density (50%), and solid (100%). Table 1. Mechanical Properties of ABS plus-P430 Mechanical Properties
Test Method
XZ Axis
ZX Axis
Flexural Strength (Method 1)
ASTM D790
58 MPa
35 MPa
Flexural Modulus (Method 1)
ASTM D790
2.100 MPa
1.650 MPa
Flexural Strain at Break (Method 1)
ASTM D790
2%
2%
Tensile Strength, Ultimate (Type 1)
ASTM D638
33 MPa
Tensile Strength, Yield (Type 1)
ASTM D638
8 MPa
Tensile Modulus (Type 1)
ASTM D638
2.200 MPa
Tensile Elongation at Break (Type 1)
ASTM D638
6%
Tensile Elongation at Yield (Type 1)
ASTM D638
2%
IZOD Impact, notched (Method A, 23°C)
ASTM D638
106 J/m
Rockwell Hardness
ASTM D785
109.5
For dimensional inspection, a Derby 454 coordinate measurement machine (Brown and Sharpe Etalon) was used, and a 3D stylus Tesastar-i, with axis ranges: X-457 mm, Y-508 mm, Z-406 mm; resolution of 0.001 mm; and repeatability is defined by R=0.004+0.005L/1000, where L is the machine axis length. Surface texture and the flatness error were measured using a Talysurf CLI 1000 3D profiler (Taylor Hobson), which is a scanning surface topography instrument that moves the workpiece under a stationary gauge head.
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Talysurf CLI 1000 has a measuring envelope of 100 mm on the three axis (X, Y, Z). The device has a continuous measurement of surface roughness 2D and 3D, surface topography, and microgeometric measurement [2]. The Talysurf CLI 1000 system uses a non-contact chromatic length aberration (CLA) gauge with a 300 µm range; maximum height measurement of 300 µm; resolution on the Z axis of 10 nm; 300 mm/s speed; and step height repeatability of 2 nm. Table 2. Thermal Properties of ABS plus-P430 Thermal Properties
Test Method
Value
Heat Deflection (HDT) @ 66 psi ASTM
ASTM D648
96°C
Heat Deflection (HDT) @ 264 psi
ASTM D648
82°C
Glass Transition Temperature (Tg)
DSC (SSYS)
108°C
Coefficient of Thermal Expansion
ASTM E831
8.82E-05 mm/mm/°C
Table 3. Electrical properties of ABS plus-P430 Electrical Properties
Test Method
Value Range
Volume Resistivity
ASTM D257
2.6E15 - 5.0E16 ohm-cm
Dielectric Constant
ASTM D150-98
2.3 - 2.85
Dissipation Factor
ASTM D150-98
0.0046 - 0.0053
Dielectric Strength
ASTM D149-09, Method A, XZ Orientation
130 V/mil
Dielectric Strength
ASTM D149-09, Method A, ZX Orientation
290 V/mil
For the experimental tests, workpieces were designed (Figure 1a) 20 mm in length on the X and Y axis, and 10 mm in length on the Z axis. This design allows for a sufficient sampling surface (20x20 mm2) for the analisis of surface texture and flatness. Table 4 shows the workpiece manufacturing conditions, with the analysis of each parameter on two levels, by combining the two layer thicknesses produced by the 3D printer: 0.254 mm and 0.178 mm; and the minimum and maximum density of model interior fill: sparse low density (10%) and solid (100%). Table 4. Tested parameters Test
Layer thickness (mm)
Density (%)
1
0.254
100
2
0.254
10
3
0.178
100
4
0.178
10
For the evaluation of dimensional precision on the Z-Y and Z-X lateral faces, 9 points were distributed along the contours and in the centre of each face, and 13 points on the top (X-Y) face as shown in Figure 1. More points were used on the upper face since it was larger (20x20 mm2), and exhibits greater geometric problems due to the positioning of the material during the curing process. Surface texture and flatness error were measure by sampling a 10x10 mm2 area on the edge of the surface and the centre point, as shown in Figure 1, on the surface of the upper face of the workpiece. The surface was measured using a laser scanning resolution of 304, at 30 μm intervals, and a speed of 30 mm/s. All of the workpieces were placed in the same manufacturing position. The area selected (Figure 1b) encompassed the area closest to the workpiece contour, which was expected to have the maximum height on the upper face of the workpiece, and the central area, which was expected to have the lowest surface area. This sampling area was used for determining the maximum flatness deviation of the upper surface of the workpiece. Surface texture is assumed to be uniform, though there may be variations or grooves in the sampling area, given that maximum texture variations occur between the contour and the central area of the upper surface of the workpiece.
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(a)
(b)
Fig. 1. (a) Sampling points under analysis. (b) Scanned sampling area.
For the characterization of surface texture, two areal roughness parameters [3-13] were used i.e., the Arithmetic mean height Roughness Sa, and the Root Mean Square height Roughness Sq. The Sa parameter quantifies the deviations in height of the surface points in relation to the mean reference plane, according to Eq. 1:
ܽݏൌ
ͳ ඵ ȁݖሺݔǡ ݕሻȁ݀ݕ݀ݔ ܣ ܣ
(1)
The Sq parameter determined the quadratic height of the measured surface, which was determined by Eq. 2: ͳ ݍݏൌ ඨ ඵ ʹ ݖሺݔǡ ݕሻ݀ݕ݀ݔ ܣ ܣ
(2)
For the characterization of flatness, the parameter the Root Mean Square Flatness Deviation (fltq) [14, 15] was defined by Eq. 3:
݂݈ ݍݐൌ ඨ
σሺ݉ͳ ݔ ݉ʹ ݕെ ʹሻʹ ሺ݊ െ ʹሻሺ݉ͳʹ ݉ʹʹ ͳሻ
(3)
where
ݖൌ ݉ͳ ݔ ݉ʹ ݕ
(4)
and ݉ͳ ൌ
σ ʹ ݕσ ݖݕെ σ ݕݔσ ݖݕ σ ʹ ݔσ ʹ ݕെ ሺσ ݕݔሻʹ
(5)
݉ʹ ൌ
σ ʹ ݔσ ݖݕെ σ ݕݔσ ݖݕ σ ʹ ݔσ ʹ ݕെ ሺσ ݕݔሻʹ
(6)
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3. Results Table 5 shows the results obtained in the dimensional control of the manufactured workpieces. In the first row the nominal values for workpiece length on each axis (X, Y, Z), and the nominal volume are shown. The next rows show the values obtained for each workpiece, with the mean value for each axis and the nominal deviation. The last two columns show the value of the volume calculated for each workpiece, with the data obtained, and the deviation with the nominal volume. Table 5. Results obtained for dimensional quality control Length No. Test (mm)
Error
Length
Error
Length
Error
(mm)
(mm)
(mm)
(mm)
(mm)
Axis Z Nominal 10
Volume (mm3)
Axis X
Axis Y
Volume
20
20
4000
Error (mm3)
1
9.984
-0.016
20.036
0.036
19.975
-0.025
3995.787
-4.213
2
10.526
0.256
20.019
0.019
19.981
-0.019
4102.396
102.396
3
10.175
0.175
19.983
-0.017
19.895
-0.105
4045.191
45.191
4
10.262
0.262
20.027
0.027
19.989
-0.011
4108.081
108.081
Figure 2a shows the behaviour of the dimensional deviation of the workpieces analysed. The combination of maximum layer thickness (0.254 mm), and solid density of model interior fill (100%), workpiece 1, was the only combination which showed good dimensional results on all three axis, with deviations ranging from 16 µm to 36 µm. In the other combinations analysed, the Z axis showed strong dimensional deviations ranging from 175 µm to 262 µm. Density of model interior fill was the parameter affecting most dimensional precision on the Z axis i.e., the two low density combinations (10%) showed the worst results, with deviations ranging from 256 µm to 262 µm. Moreover, layer thickness influenced dimensional control on the Z axis, more so than density of model interior fill. The minimum layer thickness (0.178 mm) worsened dimensional precision with 175 µm deviation above the nominal for solid density (100%). The worst result was obtained with a minimum thickness layer (0.178 mm), and low density of (10%), with a deviation of 262 µm. These results show that with the vertical Z axis, and sparse low density (10%) good dimensional control is not achieved during the curing of the model material due to the lack of homogeneity arising from the discontinuities in the structure of the inner filling. Moreover, the addition of more layers had a similar effect due to the greater number of layer-layer interfaces in the material. The best dimensional control on the Z axis was achieved with greater homogeneity in the inner modelling material, and in the layer-to-layer interface due to the fewer number of layers, with the best results being obtained with a layer thickness of 0.254 mm and a solid density (100%). The X axis showed the best dimensional control in all of the workpieces analysed, with dimensional deviations ranging from 19 µm to 36 µm in all of the combinations of layer thickness and density of model interior fill. Moreover, the Y axis also showed good overall behaviour with deviations ranging from 11 µm to 25 µm, except in workpiece 3 (0.178 mm, 100%) where the deviation was 105 µm. Dimensional precision on both axis was not primarily determined either by the curing of the material or by structural homogeneity, but by the precision and repeatability in the positioning of the extruder, probably because this printer begins each layer by printing the contours with two runs of the model solid material (100%), prior to printing the model interior fill. The dimensional deviation on the Y axis of workpiece 3 (0.178 mm, 100%), may be due to an error in positioning the extruder rather than the manufacturing conditions of the layer. Overall, this printer offers good dimensional precision on the X and Y axis, regarding the layer thicknesses permitted by the extruder, but on the Z axis the behaviour was not uniform according to the manufacture's configuration, with dimensional deviations of 262 µm for low density (10%), which comes close to the maximum layer thickness (254 µm). Though volumetric deviations (Figure 2b), were conditioned by the dimensional deviations on the Z axis, they provided a global perspective of the dimensional behaviour of the different printing configurations. Workpiece 1
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(0.254 mm, 100%) exhibited the best dimensional precision with an error of a4.2 mm3, much better than the results obtained with the other combinations. The worst results were obtained with workpiece 2 (a102.4 mm3), and workpiece 4 (a108.1 mm3) with a model interior fill density of 10%. Workpiece 3 (0.174 mm, 100%) showed an intermediate volumetric deviation of a45.2 mm3. These results show that volumetric and dimensional precision are both conditioned by the density of model interior fill, with good behaviour obtained with solid density (100%), and large deviations with low density (10%). To a lesser extent, layer thickness influenced these results, the optimum configuration was a maximum layer thickness of 0.254 mm and solid density of model interior fill (100%).
(b)
(a)
Fig. 2. (a) Dimensional deviations. (b) Volumetric deviations.
Table 6 shows the results obtained for the measurements of surface texture of the manufactured workpieces, with values for the parameter Arithmetic Mean Height Roughness (Sa) from a6.4 to a12.4 µm, and the Root Mean Square Height Roughness (Sq) from a8.7 to a15.9 µm. These textures were midrange surface finish values comparable to those obtained using other rapid prototyping techniques [16], and manufacturing processes [17]. Figure 3 shows the parameters thickness of layer and density of model interior fill which decisively influenced surface finish, due to the interaction between both parameters, with behaviour varying according to the level of each parameter. With maximum layer thickness (0.254 mm), the density of model interior fill significantly improved surface finish Sa from a12.4 µm to a7.9 µm. The analysis of the behaviour of the low density (10%), showed that reducing layer thickness improved surface finish Sa from a12.4 µm to a7.5 µm. The general behaviour indicated that lower layer thickness and increased density of model interior fill achieved the best surface finish in all of the workpieces analysed. The best surface finish (Sa = a6.4 µm, Sq = a8.66 µm) was obtained in workpiece 3, with less layer thickness (0.178 mm) and a solid density of (100%). The values were twice as high (Sa = a12.4 µm, Sq = a15.9 µm) with greater layer thickness (0.254 mm) and lower density (10%), which offered the worst results in workpiece 2. These results show solid density of model interior fill (100%) enabled the optimum surface finish due to material continuity during the curing stage. The minimum thickness layer (0.178 mm) obtained the best surface texture with the slowest extrusion speed that produced finer grooves on the layer-layer interface.
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Table 6. Areal roughness surface values. Layer thickness
Density
Sq
Sa
(mm)
(%)
(µm)
(µm)
1
0.254
100
10.20
7.95
2
0.254
10
15.90
12.40
3
0.178
100
8.66
6.44
4
0.178
10
10.40
7.49
No. test
Fig. 3. Roughness variation Sa and Sq in the workpieces analyzed.
Table 7 and Figure 4 shows the flatness error that measures the highest deviation between the highest point and the lowest of the evaluated surface. The values shown in Table 7 are incremental values, with the highest area located on the border of the upper surface of the workpiece, and the central area being lowest. As shown in Table 7, Figure 4 the flatness error (fltq) values ranged from a6.4 µm to a12.7 µm, the minimum flatness error was obtained for workpiece 3 (0.178 mm, 100%) with fltq = a6.4 µm, and the maximum error was obtained for workpiece 2 (0.254 mm, 10%) with fltq = a12.7 µm. The values obtained for workpieces 1, 3, and 4 were similar, bearing in mind the maximum variation of the flatness error of a1 µm, which entailed a small incremental difference in flatness. Most notably, the flatness error of workpiece 2 doubled that of workpiece 3. This was because the maximum layer thickness (0.254 mm) required more time to cure for the crystallization of the material, and the layer with the low density of model interior fill (10%) was less rigid, leading a reduction in the dimensional control of the central area of the layer, resulting in a loss of thickness. Table 7. Flatness values . No. test
Layer thickness
1
Density
Fltq
(%)
[µm]
0.254
100
7.25
2
0.254
10
12.70
3
0.178
100
6.39
4
0.178
10
7.36
(mm)
Fig. 4. Flatness variation (fltq) in the workpieces analized.
4. Conclusions This study analysed the dimensional precision, the flatness error, and the surface texture obtained with FDM with ABS plus FDM in order to establish the quality ranges for 3D professional printing. This user information is essential in order to precisely establish the exact geometric and dimensional tolerance ranges, and surface finishes that the machine can offer. From the analysis of the results obtained, the following conclusions may be drawn. The largest dimensional deviation was obtained in the configuration of modelling material exhibiting most discontinuities owing to both the density of model interior fill and the number of layer-layer interfaces. This was due to poorer dimensional control in the contraction of the cured material and the lack of continuity, which resulted in the uneven behaviour during curing. The best dimensional behaviour was obtained with the configuration of maximum layer thickness and density of model interior fill (0.254 m, 100%) with a maximum deviation length of
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a36 µm on the X-Y-Z axis, and a volumetric deviation a4.2 mm3. The worst results were obtained with a minimum thickness layer (0.174 mm), and the lowest density (10%), a dimensional deviation of a262 µm, and a volumetric deviation of a108.1 mm3. The Z axis, which was perpendicular to the layer, exhibited the worst dimensional behaviour with the greatest deviations due to the positioning of the layer, and the effect of gravity during curing. The factor influencing most dimensional precision was density of model interior fill, more so than layer thickness. The parameters layer thickness and density decisively influenced surface finish, with a mutually important interaction between both parameter, with a difference in behaviour according to the level of each parameter. The general behaviour showed less layer thickness and an more density of model interior fill provided the best surface finish in all of the workpieces analysed. The best finish surface was obtained in workpiece 3 (Sa = a6.4 µm, Sq = a8.66 µm), with less layer thickness (0.178 mm) and solid density (100%). Optimum surface finish was obtained with this layer configuration due to material continuity during the curing and the finer grooves in the layer-layer interface. The minimum flatness error was obtained with the least thickness layer (0.178 mm) and solid density (100%), with a fltq a6.4 µm. The flatness error increased with layer thickness of (0.254 mm) and a low density (10%), with a fltq of a12.7 µm, and an important reduction in thickness in the central area of the layer owing to the poorer dimensional control in the contraction of the material due to less rigidity of the layer during curing. This study has established the optimum configurations for the manufacture of components with FDM 3D printing and ABS-plus, controlling with precision the minimum and maximum dimensions per axis, volumetric tolerance, surface texture ranges, and flatness error that can be obtained with different printer configurations. This study has determined the dimensional precision, and the characterization of flatness and surface texture. References [1] Gibson, D. Rosen, B. Stucker, Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing, Springer, 2015. [2] D.J. Whitehouse. Handbook of Surface and Nanometrology, CRC Press, 2010. [3] ISO 25178-2, Geometrical product specifications (GPS) - Surface texture: Areal - Part 6: Classification of methods for measuring surface texture, 2012. [4] ISO 25178-3:2012 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 3: Specification operators. [5] ISO 25178-3:2012 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 3: Specification operators. [6] 50. ISO 25178-6:2010 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 6: Classification of methods for measuring surface texture. [7] ISO 25178-601:2010 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 601: Nominal characteristics of contact (stylus) instruments. [8] ISO 25178-602:2010 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 602: Nominal characteristics of non-contact (confocal chromatic probe) instruments. [9] ISO 25178-604:2013 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 604: Nominal characteristics of non-contact (coherence scanning interferometry) instruments. [10] ISO 25178-605:2014 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 605: Nominal characteristics of non-contact (point autofocus probe) instruments. [11] ISO 25178-70:2014 Geometrical product specification (GPS) -- Surface texture: Areal -- Part 70: Material measures. [12] ISO 25178-701:2010 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 701: Calibration and measurement standards for contact (stylus) instruments. [13] ISO 25178-71:2012 Geometrical product specifications (GPS) -- Surface texture: Areal -- Part 71: Software measurement standard. [14] ISO 12781-1:2011 Geometrical product specifications (GPS) -- Flatness -- Part 1: Vocabulary and parameters of flatness. [15] ISO 12781-2:2011 Geometrical product specifications (GPS) -- Flatness -- Part 2: Specification operators. [16] R. Ippolito, L. Iuliano, A. Gatto, Benchmarking of Rapid Prototyping Techniques in Terms of Dimensional, CIRP Annals - Manufacturing Technology (Impact Factor: 2.54). 01/1995; 44(1):157-160. DOI: 10.1016/S0007-8506(07)62296-3. [17] Degarmo, E. Paul; Black, J T.; Kohser, Ronald A., Materials and Processes in Manufacturing, Wiley, 2003.
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