3D PRINTING OF CONTINUOUS FIBER REINFORCED PLASTIC

Transcription

1 3D PRINTING OF CONTINUOUS FIBER REINFORCED PLASTIC Masaki NAMIKI 1, Masahito UEDA 1, Akira TODOROKI 2 Yoshiyasu HIRANO 3, Ryosuke MATSUZAKI 4 1 Nihon University, Kanda-surugadai, Chiyoda, Tokyo, , JAPAN 2 Tokyo Institute of Technology, Ookayama, Meguro, , JAPAN 3 Japan Aerospace Exploration Agency, Osawa, Mitaka, Tokyo, , JAPAN 4 Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, , JAPAN ABSTRACT 3D printing technique of continuous carbon fiber reinforced thermoplastic (CFRTP) was developed based on fused deposition modeling. In this study, poly-lactic acid was used as matrix material and continuous carbon fiber as reinforcement material. In-site fiber impregnation was adopted. A PLA filament and a continuous carbon fibers were separately supplied and then mixed in a heater before ejection. A CFRTP tensile test specimen of dumbbell shape was made by the developed 3D printer. Tensile test results showed improvement of tensile stiffness and strength by continuous fiber reinforcement. Tensile properties were, however, slightly smaller than those expected by rule of mixture. Fracture surface observation showed some gaps between filaments, which suppressed improvement of tensile properties of the CFRTP. 1. INTRODUCTION 3D printer is widely adopted as a next generation manufacturing, which produces a complicated three dimensional part without expensive mold or tool [1-3]. The cost of 3D printer was drastically dropped, particularly noticeable for thermoplastic fused deposition modeling [4, 5]. In the meantime, carbon fiber reinforce plastic (CFRP) has been used as a structural material of an aircraft and an automotive because of its superior specific stiffness and strength. 3D printer can be applied for 3D manufacturing of CFRP part because CFRP was based on plastic material. 3D printing of composite materials has been reported, in which particles or short fibers were used as reinforcement [6-7]. The additives were previously mixed into thermoplastic filament and supplied to a 3D printer, as substitute for conventional thermoplastic filament. It is, however, not reported the fabrication of continuous fiber reinforced plastic by 3D printer although continuous fiber reinforcing was needed for CFRP to demonstrate the superior mechanical property. In this study, continuous carbon fiber reinforced thermoplastic (CFRTP) was fabricated by 3D printer which was based on fused deposition modeling. CFRTP tensile specimens were made by the 3D printer. Mechanical property in tension increased by continuous carbon fiber reinforcement. It was shown that 3D printing technique was applicable to make continuous carbon fiber reinforced thermoplastic. Point to be improved was also found from the experimental results to fully demonstrate mechanical advantage of the CFRTP fabricated by the 3D printer.

2 2.1 3D printing of CFRTP 2. EXPERIMENTATION Poly-lactic acid (PLA) was used as a matrix material. A PLA filament used was commercially available type. The diameter was 1.75mm. A PAN based carbon fiber (T800S-10E, Toray) was used as reinforcement. Continuous carbon fiber was used to fully exert the superior mechanical property. Carbon fiber was used as-is; sizing of the carbon fiber was for epoxy. Mechanical property of the carbon fiber is shown in Table 1. Commercially available 3D printer (Fused deposition modeling) was used. The printer head was modified to fabricate continuous fiber reinforced plastic. Schematic drawing of the modified printer head was shown in Figure 1. In this study, in-site fiber impregnation into matrix was adopted. A PLA filament and a carbon fiber bundle ( 1000 fibers) were separately supplied and brought together in the heater. Then, the PLA filament was heated and melted in the main-heater and carbon fiber was impregnated into the PLA filament. The carbon fiber impregnated filament was ejected from the nozzle. An enlarged photo of 3D printing of CFRTP is shown in Figure 2. 3D printing process was same to the conventional fused deposition modeling. There was a preheater for carbon fiber. Carbon fiber was previously heated to promote impregnation into the PLA filament. The diameter of the nozzle was 1.4mm. Relatively large nozzle diameter was used in this pilot study to prevent clogging of carbon fibers. Layer resolution was relatively low because of the wide diameter of the nozzle. Nozzle diameter need to be reduced to increase layer resolution. Filament (PLA) Fiber drive gear Motor Motor Filament drive gear Carbon fiber bundle Pre-heater & thermometer Nozzle Main heater & thermometer Heat table Figure 1. Schematic of printer head

3 2.2 Tensile specimen A CFRTP tensile specimen was fabricated by the 3D printer. The tensile specimen was shown in Figure 3(a). Figure 3(b) shows migration path of nozzle; the specimen was fabricated traversable way. The same line was traced four times to form four layer. Total thickness of the specimen was about 4mm. y x Figure 2. 3D printing of CFRTP Loading direction Thickness: 4mm 10mm 80mm 200mm 20mm (a) Specimen dimension Finish point Start point y (Transverse direction) x (Longitudinal direction) z (Thickness direction) (b) Migration path of nozzle Figure 3. CFRTP tensile specimen

4 Carbon fibers were only aligned to the longitudinal direction (loading direction). It means no carbon fibers in the transverse direction (y-direction) and thickness direction (z-direction). Therefore, the mechanical property of the tensile specimen is orthotropic. Transverse and thickness directional reinforcing by carbon fibers is also possible although it is not shown here because it is beyond the scope of this paper. Fiber volume fraction was 1.0% which was determined by supplied amount of carbon fiber and PLA. Tensile specimen was also fabricated using PLA without carbon fiber to compare reinforcing effect of continuous carbon fibers. A PLA filament and a carbon fiber bundle were heated up to 210ºC in the main heater. The carbon fiber bundle was not pre-heated in this study. Temperature of the heat table was fixed to 80ºC. Feeding speed of the PLA filament and the carbon fiber was 100m/min. Moving speed of nozzle head was also fixed to 100 mm/min. 2.3 Tensile test Quasi-static tensile tests of CFRTP and PLA tensile specimen were performed using a universal testing machine (AG-IS, Shimadzu). Crosshead speed was 1.0 mm/min. Strain gage was mounted on a surface of the specimen to measure strain. Shoulder parts of the specimen was directly clamped by wedge grip of the testing machine, and tensile load was applied to the specimen. 3.1 Tensile test 3. RESULTS Tensile stress versus tensile strain curves of CFRTP and PLA were shown in Figure 4. Tensile tests were performed five times. Average tensile modulus and strength of CFRTP and PLA were shown in Table 1. Tensile modulus of CFRTP was higher than that of PLA due to fiber reinforcement. Tensile modules of CFRTP was calculated by rule of mixture. E = V E + ( 1 V ) E (1) f f f m 120 Tensile stress [MPa] CFRTP PLA Tensile strain [%] Figure 4. x-directional tensile stress tensile strain curves of CFRTP and PLA

5 Table 1 x-directional tensile test results Caron fiber [8] PLA CFRTP Tensile modulus 294 GPa 3.4 GPa 5.8 GPa Tensile strength 5880 MPa 57.1 MPa 90.0 MPa Where E, E f and E m is Young s modulus of CFRTP, carbon fiber and PLA, respectively. Since the fiber volume fraction was 1.0% Young s modulus of CFRTP was expected to be 6.3GPa. Experimental result showed 10% lower Young s modulus. Tensile strength of the CFRTP was also expected to be 115MPa by rule of mixture. The tensile strength was 90MPa, which was 20% lower tensile strength. Although the mechanical property was a little lower than expected, proper reinforcing effect was obtained for the CFRTP fabricated by 3D printer, showing 70% increase on Young s modulus and 60% increase on tensile strength. 3.2 Observation of fracture Fractured CFRTP specimen after tensile test was shown in Figure 5. Fiber pull out was observed due to fracture. Figure 6 shows a scanning electron microscope image of the fracture surface. The carbon fibers were impregnated into the PLA filament in the heating process just before the ejection. Carbon fibers were, however, not fully embedded in the PLA filament but partly on the Figure 5. Tensile failure of CFRTP specimen z y x Figure 6. Fracture surface of CFRTP tensile specimen

6 surface. Pre-heating of the carbon fiber improves the impregnation although it was not executed in this study. There were some gaps between PLA filaments due to low layer resolution, which suppressed improvement of tensile strength. Fine processing with small nozzle diameter is required to reduce the gaps between filaments. 4. CONCLUSIONS Continuous carbon fiber reinforced thermoplastic was fabricated by the modified 3D printer using in-site fiber impregnation. Tensile test of the CFRTP specimen was performed to shows the applicability of the manufacturing technique. The results obtained in this paper are summarized as follows. 1. A PLA filament and a continuous carbon fiber bundle were separately supplied and mixed in heater just before ejection. CFRTP tensile specimen was fabricated using conventional fused deposition modeling. 2. Young s modulus and tensile strength of PLA was increased by continuous carbon fiber reinforcement although those were slightly lower than expected by rule of mixture. 3. SEM image of fracture surface showed that the carbon fiber was not fully embedded in the PLA filament but partly on the filament. Gaps were observed between the filaments due to lower resolution of the 3D printer, which suppressed improvement of the composite mechanical property. References 1. Yana, Xue. Gu, P. A review of rapid prototyping technologies and systems. Computer- Aided Design 28 (1996): Rengier, F. Mehndiratta, A. Tengg-Kobligk, H. Zechmann, C. M. Unterhinninghofen, R. Kauczor, H.-U. Giesel, F. L. 3D printing based on imaging data: review of medical applications. International Journal of Computer Assisted Radiology and Surgery 5 (2010): Berman, Barry. 3-D printing: The new industrial revolution. Business Horizons, 55 (2012): Jones, Rhys. Haufe, Patrick. Sells, Edward. Iravani, Pejman. Olliver, Vik. Palmer, Chris. Bowyer, Adrian. RepRap - the replicating rapid prototype. Robotica 29 (2011): Kelly, James. Daniel, Patrick, Printing in Plastic; Build your own 3D printer. Apress, Kumar, S. Kruth, J.-P. Composites by rapid prototyping technology. Materials & Design 31 (2010): Pidcock, Geoffrey. Panhuis, Mark. Extrusion Printing: Extrusion Printing of Flexible Electrically Conducting Carbon Nanotube Networks. Advanced Functional Materials, 22 (2012): Toray Technical Data sheet, No.CFA-019.