Studies on the Width of Rectangular Channels of Fuel Cell Bipolar Plate Using FDM 3D Printer with PLA Filament
Jae-Hyun Kim1, Chul-Kyu Jin2*
<Abstract>
Bipolar plates with channel width of 0.5 mm, 0.4 mm, and 0.3 mm respectively were printed using a 3D printer. The shape of three b ipolar plates was rectangular, the channel depth was 0.5 mm, and the thickness of base was 0.5 mm. The bipolar plate with channel width of 0.5 mm had 45 channels, and their active area was 44.5 mm x 50 mm. The bipolar plate with channel width of 0.4 mm had 57 channels and its active area was 45.2 mm × 50 mm, and the bipolar plate with channel width of 0.3 mm had 75 channels and its active area was 44.7 mm × 50 mm. The bipolar plates were printed using PLA filament. The cross-sectional lengths of the bipolar plates with channel widths of 0.5 mm and 0.4 mm were identical by 96% of the designed cross-sectional length. Whereas the bipolar plate with a channel length of 0.3 mm had a large difference of 25% from the designed cross-sectional length.
Keywords : Active Area, Bipolar Plate, Channel, Fuel Cell, 3D Printing
1 School of mechanical engineering, Kyungnam University E-mail: kth2343@naver.com
2* Corresponding Author, School of mechanical engineering, Kyungnam University E-mail: cool3243@kyungnam.ac.kr
1. Introduction
A fuel cell is an energy conversion device that generates electrical energy through electrochemical reaction between hydrogen and oxygen. Fuel cell is a clean energy technology that does not emit pollutants (SOx, NOx, and CO2 etc.) generated from thermal power generation. The fuel cell stack used in the passenger cars is composed of approximately 400 single cells and a maximum of 120 kW of output is produced by this stack. A single cell consists of an anode bipolar plate, a cathode bipolar plate, and a membrane electrode assembly (MEA). A fuel cell stack which produces an output of 120 kW is coupled with 800 bipolar plates [1-5].
Bipolar plate acts as a pathway that uniformly transfers hydrogen and oxygen to MEA. Bipolar plate shall have various properties like high electrical conductivity, high heat conductivity, low electrical resistance, good electrochemical stability, high corrosion resistance, durable, thin, lightweight, high workability, and low cost.
As materials of b ipolar plate, there are graphite, carbon fiber, and metals (stainless steel, titanium, and aluminum). Currently, only research on stainless steel is focused on manufacturing time and cost. Therefore, bipolar plates are being produced by forming channels through stamping stainless-steel plate with a thickness of 0.1 mm[6-10].
With 3D printing technology, a product in
three-dimensional shape desired by users can be manufactured. Fuel cell bipolar plate can also be manufactured through 3D printing technology. 3D printing technology has been developing since the 1980s when Charles Hull created a stereolithography (SLA) type printer. In 3D printing field, there are technologies such as SLA, fused deposition modeling (FDM), multi jetting modelling (MJM), and selective laser sintering (SLS).
Currently, high technological advancement has been made in the metal 3D printing, enabling printing materials like aluminum, magnesium, stainless-steel, and titanium. In addition, it has been reported that 3D printing was possible with nickel and tungsten that have high melting point. The representative metal 3D printing technologies includes directed energy deposition (DED) and power bed fusion (PBF)[11-13].
In this study, a preliminary experiment was conducted to prepare stainless-steel bipolar plate with micro channels which could not be produced by the stamping. Three types of bipolar plates with variable channel sizes were prepared using the polylactic acid (PLA) filament of FDM 3D printer. It was aimed to search channel width which could be fabricated from the 3D printer. Therefore, magnified images of the channels in three types of bipolar plates printed through 3D printer were measured using a microscope, and the laminated cross-sectional profiles were analyzed. The ob jective of this study is not to fabricate bipolar plates for the target shape with metal 3D printer but to conduct
a b asic study for the next metal 3D printer research that can reduce parameters and working time of the next study.
2. Experimental Method
2.1 3D Modeling of the bipolar plates
To give an output a bipolar plate with 3D printer, first, a b ipolar plate shape was modeled as 3D using the UG NX 10 program. Fig. 1 shows the plan-view of the 3D modeling of the bipolar plate. The bipolar plate was designed to have a size which was applied to a single cell. The bipolar plate was a square-shape, and the height and width were the same 95.6 mm. Eight holes of size Ø7.3 mm for bolted connection to unit fuel cells were made. There were another two holes of Ø2 mm for inflow and discharge of hydrogen or oxygen. One was the inlet and the other was the outlet. The height and width of the inlet and outlet were 45.6 mm and 48.5 mm, respectively.
Channels were arranged between the inlet and outlet. When hydrogen was introduced into the inlet, it flew along the channel and moved to the MEA. The unreacted hydrogen gas was discharged to the outlet. Active area (AxB) where chemical reaction took place was calculated by multiplying the width (A) and height (B) of the channel. The bipolar
plates desired to fabricate in this study were of three types with different width (w) of the channels and width (s) of the ribs. Fig. 2 shows the cross-sectional shape of the bipolar plate. The cross-sectional shape of the channel was square. Table 1 shows the key dimensions of modelled three bipolar plates. The base thickness (t) of the bipolar plate was the same as 0.5 mm, and so was the channel depth (d) as 0.5 mm. Therefore, the thickness (d+t) of the bipolar plate became 1 mm. The channel width and rib
Fig. 1 Plan-view of 3D modeling of the bipolar plate with micro channels in fuel cell
Fig. 2 Section-view of three bipolar plate channels : (a) BP1, (b) BP2 and (c) BP3
width were adopted as parameters in the experiment since these were factors that were highly correlated with manufacturability.
In this study, the channel width and rib width were set to the same. The channel width of the first bipolar plate (BP1) was 0.5 mm, and the channel width of the second bipolar plate (BP2) was 0.4 mm. While, the channel width of the third bipolar plate (BP3) was 0.3 mm. The number of arranged channels as well as the active area differed depending on the channel width and rib width.
Fig. 3 shows the enlarged images of the channel parts of three bipolar plates. The numbers of the channels in BP1, BP2, and BP3 were 45, 57, and 75, respectively. As can be seen from Table 1, the active areas
of BP1, BP2, and BP3 were 44.5 mm x 50 mm, 45.2 mm x 50 mm, and 44.7 mm x 50 mm, respectively.
To print the three types of bipolar plates with a 3D printer, the part file was converted to stereolithography (STL). The STL file was then again converted to G-code using IdeaMaker program.
2.2 3D Printing of the bipolar plates
The 3D printer device used in the experiment was a FDM type 3D printer. FDM type is a mode of lamination wherein thermoplastic material is heated to a semi-solid state and extruded to laminate the material layer by layer. PLA filament was used to print the b ipolar plate. Tab le 2 shows the physical properties of PLA filament.
The printing conditions for printing the b ipolar plate are presented in Tab le 3. The extrusion temperature was set to 205 ℃, and bed temperature was set to 60 ℃. Nozzle diameters and printing speeds were 0.4 mm and 50 mm/s for BP1 (channel width 0.5 mm), and 0.4 mm and 40 mm/s for BP2 (channel width 0.4 mm), respectively. Meanwhile, the channel width of the BP3 was 0.3 mm, thus (a)
(b)
(c)
Fig. 3 Plan-view at channels of three bipolar plates : (a) BP1, (b) BP2 and (c) BP3.
No. w s d t X Y
BP1 0.5 0.5
0.5 0.5 44.5
50
BP2 0.4 0.4 45.2
BP3 0.3 0.3 44.7
Table 1. Dimensions of the bipolar plates
(unit : mm)
the nozzle diameter was set to 0.3 mm. Since the channel width was quite narrow, the printing speed was set to 30 mm/s considering printing failure. The working times depending on the printing conditions were 2 hours and 38 min. for BP1, 3 hours and 9 minutes for BP2 and 3 hours and 41 minutes for BP3.
2.3 Analysis method of Printed bipolar plates
Lamination conditions of the printed bipolar plate were investigated with a digital microscope. The enlarged images against plane of the channel were examined and enlarged cross-sectional images were also examined after cutting the channel. The lengths of the cross-section were also measured.
3. Experimental Results
The plan-views of the three bipolar plates printed from the 3D printer are presented in Fig. 4. Fig. 4(a) shows the bipolar plate with channel width and rib width of 0.5 mm and 0.5 mm, respectively. Fig. 4(b) shows the bipolar plate with channel width and rib width of 0.4 mm and 0.4 mm, respectively.
Meanwhile, Fig. 4(c) shows the bipolar plate with channel width and rib width of 0.3 mm and 0.3 mm, respectively. Since the channel width was quite narrow, three types of the bipolar plates looked printed well.
The images with a digital microscope b y magnifying the plane to observe the printed bipolar plate in more detail are presented in Fig. 5. ① is the image in the bend area where the channel was bent by 90°, and ② presents the image of the center. There was no area where channels were blocked, or rib was not laminated in any location in all Property Testing
standard Typical Value Density
[g/cm3] ISO 1183 1.17-1.24 Tensile strength
[MPa] ISO 527 46.6±0.9
Elongation at Break
[%] ISO 527 1.90±0.21
Young's Modulus
[MPa] ISO 527 2636±330
Bending Modulus
[MPa] ISO 178 3283±132
Bending Strength
[MPa] ISO 178 85.1±2.9
Impact Strength
[KJ/m²] ISO 179 2.68±0.16 Table 2. Properties of Polylactic Acid filament
Conditions BP1 BP2 BP3
Values Extrusion temperature
(℃) 205
Bed temperature (℃) 60 Layer thickness (mm) 0.1 Nozzle diameter (mm) 0.4 Extrusion width (mm) 0.4 0.3 Printing speed (mm/s) 50 40 30 Working time (min) 158 189 221 Table 3. 3D printing conditions
three bipolar plates. However, rib width at the bend area by 90 degree was laminated thicker compared to other locations in all three bipolar plates. In Fig. 5(a), BP1 (channel width 0.5 mm) had several places where the rib thicknesses were not uniform near the bend area. BP2 (channel width 0.4 mm) in Fig. 5(b) shows the rib width uniform in general even at bend areas. BP2 had uniform rib widths in all the positions compared with BP1. On the contrary, BP3 (channel width 0.3 mm) in Fig. 5(c) had rib
(a)
(b)
(c)
Fig. 5 Magnified plan-view of printed three bipolar plates : (a) BP1, (b) BP2 and (c) BP3.
(a)
(b)
(c)
Fig. 4 Printed three bipolar plates by FDM 3D printer : (a) BP1, (b) BP2 and (c) BP3.
widths almost non-uniform at the center and near bend. In addition, the shape of the smallest bend was printed in a circle instead of a quadrangle. The reason why width of ribs are not uniformly printed at bend area is considered to be a problem that occurs only in FDM printers.
The images measured by magnifying the cross-sectional shape of the channel with a digital microscope are presented in Fig. 6.
The shape of the laminated ribs is similar with that of compressed spring. Since the
layer thickness of the 3D printer was 0.1 mm, ribs were laminated in five layers. The ribs of BP1 (channel width 0.5 mm) in Fig.
6(a) and the ribs of BP2 (channel width 0.4 mm) in Fig. 6(b ) were laminated in a quadrangle which made the channel shape also a quadrangle. However, there were barreled parts where the lower layers laminated first, spread to both the sides. BP3 (channel width 0.3 mm) in Fig. 6(c) had a shape of the channel and rib not laminated like the cross-section of modeling. The laminated rib shape was similar with that of trapezoid. In some cases, the ribs were bent, so the lower parts of the channels were blocked.
The dimensions (w, s, d, and t) of the cross-sections for the printed three bipolar plates are presented in Table 4. The cross-sectional lengths were measured from the cross-sectional images using a digital microscope. The lengths were measure at the laminated layers and the positions were also marked between the layers. The mean values and standard deviation values of the measured data are presented in Table 4. As seen from the cross-sectional shapes in Fig.
(a)
(b)
(c)
Fig. 6 Magnified section-view of printed three bipolar plates : (a) BP1, (b) BP2 and (c) BP3.
BP1 BP2 BP3
AVG SD AVG SD AVG SD
w 0.481 0.029 0.386 0.035 0.222 0.086 s 0.521 0.031 0.425 0.028 0.379 0.069 d 0.513 0.014 0.515 0.013 0.428 0.058 t 0.514 0.018 0.519 0.019 0.542 0.062 Table 4. Channel dimensions of printed three
bipolar plates
6, BP1 (channel width 0.5 mm) and BP2 (channel width 0.4 mm) measured to be 96%
identical to the designed cross-sectional length. However, since the length of the laminated layer position and the length between the layers were slightly different, the standard deviation for the channel width and the rib width was large. BP3 (channel width 0.3 mm) had a difference in the measured length by about 25% compared to the designed cross-sectional length. In case of BP3, the printing speed is set to 30 mm/s and the extrusion width is set to 0.3 mm, b ut the printing is not performed properly.
This is considered to be impossible because the diameter of the applied nozzle is 0.4 mm. If the nozzle diameter is applied to 0.2mm, it is judged that printing is possible.
4. Conclusions
In this study, bipolar plates with channel width of 0.5 mm, 0.4 mm, and 0.3 mm were prepared using a PLA filament of the FDM 3D printer. The printable channel width could be drawn from the cross-sectional shape of the printed b ipolar plate. The obtained results are as follows.
(1) No channel of the three types of printed bipolar plates was blocked. At the vicinity of the bend, there is a part where the width of the rib is rather non-uniformly laminated. In the areas where the channels were bent by 90°, the rib widths were
laminated thicker than those of other areas.
(2) The cross-sectional lengths of the b ipolar plates with a channel width of 0.5 mm and 0.4 mm were identical b y 96% of the designed cross-sectional length. In addition, the channel shapes were also quadrangle. In the bipolar plate with channel width of 0.3 mm had areas where the lower parts of the channels were blocked, and the lengths were greatly different by 25% from the designed cross-sectional length. Therefore, the rectangular channel length printable by a 3D printer was found to b e 0.4 mm in width and 0.5 mm in depth.
Acknowledgment
This results was supported by "Regional Innovation Strategy (RIS)" through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(MOE) (2021RIS-003). This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea Government(MSIT) (No. NRF-2020R1F1A1067912).
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(Manuscript received November 07, 2021;
revised December 01, 2021; accepted December 03, 2021)
