CHARACTERIZATION OF DEVELOPED HYBRID MOLDINGS BY TEXTILE AND SHORT FIBER REINFORCED COMPOSITES

Transcription

1 CHARACTERIZATION OF DEVELOPED HYBRID MOLDINGS BY TEXTILE AND SHORT FIBER REINFORCED COMPOSITES Taiga Saito, Kazuharu Yasuda, Asahi Kasei Corporation Asami Nakai, GIFU University, Akio Ohtani, Kyoto Institute of Technology Abstract Advanced material is developed by using continuous fiber reinforcement to achieve higher strength than can be obtained with injected composite material. High forming performance has been achieved by using the clothlike textile fabric material, made from combined filament yarn. By applying the developed textile composite, parts can be molded with deep drawing and complex shapes with ribs. Moreover, high weld strength has been achieved between the materials of compression molded textile composite and injection molded short fiber reinforced material in hybrid molding. Introduction Target market for developed materials In general, reducing automobile weight by 100 kg improves fuel efficiency by 1 km/l. Weight reduction is especially desired for electric automobiles which have a limited driving range. The target parts of the present study are automotive structural elements. By using the developed textile composites instead of currently used materials for automotive structural members, weight can be reduced by 30 50%. Comparison between metal and resin Figure 1. Strengthtoweight ratio comparison of various resin and metal materials Positioning of developed materials Resin materials used as automotive materials are classified according to reinforcement method as follows. (A) Nonreinforced materials without fiber reinforcement (B) Fiber reinforced thermoplastics (FRTP) with short fiber reinforcement such as chopped strands (C) FRTP with long fiber reinforcement with the same length fiber as pellets (D) Random mat materials with randomly oriented fiber which is longer than long fiber materials (E) Textile made with continuous warp and weft fiber reinforcement (F) Fiber reinforced materials with unidirectional orientation Resin materials have low density compared to metal materials and the strengthtoweight ratio of some resins is higher than that of some metals as shown in figure 1. This means that lighter materials can be used if they have the required strength. However, when there is insufficient absolute strength, it is difficult to replace metal with resin. Therefore, materials with high strengthtoweight ratio are desired. Figure 2. Mechanical properties of nonreinforced and various fiber reinforced resin materials SPE ANTEC Anaheim 2017 / 558

2 The materials of (A) to (C) are molded by injection molding processes and (D) to (F) are molded by compression molding processes. As shown in figure 2, since mechanical strength correlates with the fiber length, the order of strength is from (A) to (F) given the same fiber content among the reinforced materials. Mechanical strength of unidirectional fiber reinforced materials is greater than that of textiles with continuous fiber reinforcement due to unidirectional orientation. Composites such as (E) and (F), which have continuous fiber without breaks during molding, have excellent mechanical strength. This study focused on continuous fiber reinforced materials in category (E). Materials in category (E) consist of fiber reinforcement with resin matrix. Carbon fiber and glass fiber (GF) are generally used as reinforcement. Epoxy resin and polyurethane resin as thermoset resin, and polyamide (PA) and polypropylene as thermoplastics, are used for the matrix resin. These materials are chosen as appropriate by required properties, cost performance, and compatibility of resins and coupling agents for fibers. Issues of FRTP and the purpose of this study Issues of FRTP (1) Mechanical properties of short fiber reinforced composite Attempts have been made to use short fiber reinforced thermoplastics as structural elements. However, short fiber reinforced thermoplastics do not have sufficient mechanical properties for some structural members. (2) Poor forming performance of continuous fiber reinforced composites The plateshaped thermoset prepreg or thermoplastic prepreg are used for compression molding for continuous fiber reinforced composite as the current method of molding. In the case of the thermoplastic preimpregnation plate, the plate is heated prior to inserting into the mold, which has relatively low temperature compared to the heated plate, and the molded part is produced by compression molding after mold closing. By applying this method, there are some difficulties in deep drawing and complex shaped parts, such as poor forming performance and fiber breakage due to the rapid cooling of the heated plate during the compression process. The purpose of this study The purpose of this study is the development of moldings which have excellent mechanical properties and also the development of molding processes for moldings with excellent forming performance. Developed material Experimental Procedure [1] [2] [3] In this study, GF is used as reinforcing material and PA is used as matrix resin. PA fiber (PAF) and GF are combined together to form a filament yarn. The commingled yarn is then woven into a clothlike textile composite as a base material with continuous GF reinforcement as shown in figure 3. PAF/GF comingled yarn Figure 3. Production method of the base material Molding process of developed textile composite Compression molding and hybrid molding, which is a combination of compression and injection molding, are used for the molding process of the developed material. GF (Eglass) having a fineness of 0 dtex and a single yarn number of 400 was used as continuous reinforcing fiber. Leona 470/13BPA having a fineness of 470 dtex and a single yarn number of 13 manufactured by Asahi Kasei Corporation was used as PA fiber (melting point: 25 C). Textile composite having 3/3 twill weave was used for base material. Compression molding process The compression molding process as shown in figure 4 was as follows. (1) Mold opening: The mold is opened. (2) Setting textile composite: The developed textile is set into the mold. (3) Mold closing/compression/cooling (3.1) The mold is closed and the PA is melted by increasing the temperature of the mold higher than the melting temperature of the PA. SPE ANTEC Anaheim 2017 / 559

3 (3.2) The material then solidifies by decreasing the temperature of the mold below the melting temperature of the PA. (4) Mold opening: The mold is opened. (5) Mold release: The molded part composed of PA as the matrix resin with GF as the reinforcing material is removed. Figure 4. Process of compression molding Hybrid molding process The hybrid molding process as shown in figure 5 was as follows. (1) Mold opening: The mold is opened. (2) Setting textile composite: The developed textile composite is set into the mold. (3) Mold closing/compression/injection/cooling (3.1) The mold is closed and the PA is melted by increasing the temperature of the mold higher than the melting temperature of the PA. (3.2) The molten material of PA with short GF is injected into the mold from the injection cylinder. (3.3) The material solidifies as the temperature is decreased below the melting temperature of the PA. (4) Mold opening: The mold is opened (5) Mold release: The hybrid molded part composed of a compressed portion and an injection molded portion is removed. The forming of the complex shaped molded part with deep drawing and ribs was achieved by the developed textile composite, which was better than the molded parts that could be achieved with the thermoplastic preimpregnation plate, as shown in figure. Conditions for preparing the prepreg were as follows. A stack of seven layers of developed cloth were set into a flat mold at 300 C and compression molded for 5 min under 8 MPa, then cooled to 80 C and solidified. Finally, the plate material having a thickness of 2 mm was taken out. Molding conditions of prepreg were carried out as follows. The plateshaped substrate was heated with IR heater until the surface temperature reached 300 C. Immediately after heating by IR heater, compression molding was carried out at a mold temperature of 80 C and clamping force of 8 MPa for 5 minutes. Molding conditions of the developed material were as follows. The developed material was set into the mold and compression molded at 300 C and clamping force of 8 MPa for 5 minutes. Then it was cooled to 80 C and solidified before the molding was taken out. Figure. Comparison of formability Left: Developed material Right: Prepreg material (2) High strength The molded part has higher strength without breaking continuous fiber by using the developed textile composite. (3) High weld strength Figure 5. Compressioninjection hybrid molding process Results Results of molding [3] (1) Excellent formability By raising the mold temperature above the melting temperature of the PA during the holding pressure process in injection molding, high weld strength is achieved between the compressed material and the injected material. Result of formability A box shaped mold with 420 mm length, 320 mm width, 115 mm height and 3 mm base thickness as shown in figure 7 was used to examine the formability. The box shaped molding also has three ribs with 3 mm width and 2 SPE ANTEC Anaheim 2017 / 50

4 mm, 4 mm and mm height respectively. It also has gridlike ribs with 3 mm width and 4 mm height. As a result, the compression molded part with ribs is achieved without any breaking of continuous GF as shown in figure 8. Moreover, the molded part, which has high dimensional accuracy, with complex shape and ribs is produced by hybrid molding using the optimum conditions of compression molding and injection molding as shown in figures 9 and 10. Figure 10. Rib shape produced by hybrid molding Weld strength Tensile tests were carried out on bar specimens cut from the hybrid molded part. Results showed that the weld strength between the compressed part and injected part was higher than the strength of the injected part as shown in figure 11. Figure 7. Part dimensions for formability examination Figure 11. Weld strength of hybrid molding Figure 8. Rib shape produced by compression molding Figure 12 (A) shows the cross section of the weld portion between the injected material and compressed material of the hybrid molded part. The black portion is the injected material and the white portion is the thermoplastic resin in the compressed material. The continuous GF (warp shown with dotted line and the weft shown with solid line) is inserted into the injected resin as shown in figure 12 (B). It is believed that the weld strength is increased by the reinforcing effect of GF as mentioned above, and therefore the fracture was located in the injected material portion. The weld structure is constructed due to the mechanism in which pressed material and injected material combine under the state of good fluidity and proper pressure. Figure 9. Part made by hybrid molding 1: Formed by compression molding (white) 2: Formed by injection molding (black) SPE ANTEC Anaheim 2017 / 51

5 Conclusion The new textile composite has been developed by woven commingled yarn of PAF and GF. It is clothlike and more flexible than thermoplastic preimpregnation plate. This study focused on the formability of moldings by using this developed composite. The developed textile composite shows high forming performance on both the compression molded part and the hybrid molded part with deep drawing and complex shapes. (A) (B) Figure 12. Cross section of weld portion 1: Injection resin (black) 2: Compression resin (white) 3: Warp GF of compression material 4: Weft GF of compression material By raising the temperature of the mold above the melting temperature of the PA during the injection process, high weld strength is achieved between the compressed material and injected material. References Mechanical Properties Mechanical properties are shown in table 1. The molded part made using the developed textile composite has excellent mechanical properties such as mechanical strength, modulus, and impact strength. [1] Obara K. Japan Patent Kokai (2012) [2] Yamaguchi S et. al., Japan Patent Kokai (2013) [3] Yamaguchi S et. al., Japan Patent Kokai (2013) [4] T=PDF&U=0&CULTURE=jaJP&E=4785 Table 1. Mechanical Properties Property U nit D evelopm ent M aterial C om posite M aterial M olding M ethod Polyam ide Short G lass Fiber C om posite M aterial Polyam ide C ontinuous G lass Fiber C om pressi on M olding Injection M olding A vera N um b Stand A vera ge er of ard ge M easu D eviat rem en ion ts G lass Fiber C ontent w t% 5 Tensile Strength M Pa 430 FlexuralStrength M Pa N um b Stand er of ard M easu D eviat rem en ion ts 50[4] 237[4] 371 [4] [4] FlexuralM odulus G Pa 20 Energy to J/2m M axim um Force m (H igh speed Puncture Test) 13 4 Note: Data shown are typical values obtained by proper testing methods and should not be used for specification purposes. SPE ANTEC Anaheim 2017 / 52