THERMOPLASTIC PREPREG INSERT INJECTION MOLDING COMPOSITES: MECHANICAL AND ADHESIVE PROPERTIES. Introduction

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1 THERMOPLASTIC PREPREG INSERT INJECTION MOLDING COMPOSITES: MECHANICAL AND ADHESIVE PROPERTIES Badin Pinpathomrat, Akihiko Imajo, Supaphorn Thumsorn, Hiroyuki Hamada Kyoto Institute of Technology, Kyoto, Japan Abstract Thermoplastic composites are widely applied to automotive industry. They are lightweight, high specific strength and modernly process by injection molding. Automotive parts are mostly bolt joining and using an adhesive. An insert-injection molding is a process that can be applied reinforcing or decorative material to produce complex injection molding parts. The insert-injection molding is the process that is injected melted polymer around the inserted material placed in the molded cavity. Hence, inserted injection molding is introduced for adhering automotive parts without using bolts or the adhesive. In this study, two types of thermoplastic prepregs inserted were glass fiber/polypropylene (GF/) prepreg and carbon fiber/polyamide 6 (CF/6) prepreg. GF/ resin is injected to GF/ prepreg while GF/6 resin is injected to CF/6 prepreg. The role of adhesion between inserted part and injected resin on the mechanical property is measured by tensile and bending testing. The unidirectional of prepreg improved tensile and flexural strength of the insert-injection molding composites. Mechaical properties and microscope observation indicated that the main failure mode of the insert-injection molding was the structure failure mode. The structural failure and adhesive failure modes were founnd in the composites with the unidirectional GF/ prepreg and GF/ injected molding. Introduction Thermoplastic composites are found in various applications such as parts of automobiles, aerospace and construction due to their advantages in high specific strength with an excellent performance, structural efficiency and modernly process by injection molding [1]. The industry parts are mostly bolt joining and using an adhesive. Insert-injection molding process is an advanced injection molding technology that uses dissimilar material to produce complex part [2-3]. This unique manufacturing process combines metal and plastic, ceramics, or multiple combinations of materials, components and plastic into a single unit. The insert injection molding process is molded specimen by injected melted polymer to the inserted part that placed in the injection molded cavity then an adhesive single bonding between the inserted part and the injected polymer [4-6]. Hence, the insert-injection molding is introduced for adhering automotive parts without using bolts or the adhesive. On the other hand, the insert-injection molded, also called two stages sequential insert molding, is the injection molding process using rigid substrate or the flexible material. The insert can either be incorporated at the time of the molding process or can be inserted as post molding operation. However, there is less information on the insert-injection molding process. In this study, we would like to introduce the composites prepreg as the inserted in this molding process. The prepreg represents as a sheet molding with the ideal properties, leading to reinforcement of material and successful use for various applications [7]. This study focused on the insert-injection molding process. Two types of thermoplastic prepregs inserted are GF/ prepreg and CF/6 prepreg. GF/ resin is injected to GF/ prepreg while CF/6 resin is injected to CF/6 prepreg. The role of adhesion between inserted part and injected resin on the mechanical property was measured by tensile and bending testing. In order to investigate the effect of prepreg orientation and number of the inserted parts on mechanical properties of the GF/ prepreg and GF/

2 inserted-injection molding system was investigated. On the other hand, the effect of unidirectional and woven of CF/6 prepreg inserted part on the properties of this specimen was characterized. The adhesive behavior and fracture mode of the specimen were observed by optical and scanning electron microscope. Materials and Sample Preparation Experimental The 20 wt% glass fiber reinforced polypropylene (GF/) (Grade GWH42) was supplied by Sumitomo Chemical Co., Ltd, Japan. The 30 wt% glass fiber reinforced polyamide 6 (GF/6) (Grade A1030BRL) was provided by Unitika Limited, Japan. Both GF/ and GF/6 were injected to mold cavity, which had dimensions of 150x10x3.5 mm according to ASTM standard D638 by injection molding (TOYO MACHINERY & METAL CO., Ltd, TI- 30F6, Japan). Two types of thermoplastic prepregs inserted are GF/ prepreg (Grade MCP 1228) and CF/6 prepreg (Grade MCP 1223), which were provided by Maruhachi Corporation, Japan. Both of prepergs were cut to dimension of 150 mm long x 10 mm wide x 0.3 mm thick as the inserted parts. The inserted part was put in the mold cavity before injected with polymer resin. Table 1 summarizes the processing conditions for the insertinjection molded specimens. Table 2 tabulates a code of specimen of insert-injection molding. Figure 1 shows photographs of the insert-injection molded with various inserted parts. Table 1: Materials and the injection molding parameters. Condition Values Prepreg size 150 mm x 10 mm x 0.3 mm Prepreg (GF/) Unidirectional Prepreg (CF/) Unidirectional, Woven fabric Holding pressure 20 MPa Barrel temperature C Cooling time 15 s Table 2: Specimen designation. No Code Inserted part (Prepreg) Prepreg directions Injected part Inserted part position 1 Normal - - GF/ - 2 GF/ Unidirectional GF/ one side 3 GF/ Unidirectional GF/ both sides 4 Normal - - GF/ - 5 CF/ Unidirectional GF/ one side 6 CF/ Unidirectional GF/ both sides 7 CF/ Woven fabric GF/ one side 8 CF/ Woven fabric GF/ both sides Characterization Tensile test was carried out by using Instron universal testing machine (Instron model 4206, USA) at 115 mm of grip distance with testing speed of 1 mm/min. Three-point bending test was done with testing speed of 1 mm/min at span length of 48 mm. Morphology of fractured surface of the insert injection molded specimens was observed by optical microscope and scanning electron microscopy (SEM) (JSM 5200, JEOL, Japan).

Figure 1: Photograps of insert-injection molding specimen.

and specimen, respectively. The maximum load of the insert-injection specimen was higher than neat GF/ and GF/.

(a) Tensile test (b) Bending test Figure 3: Load-displacement curves of (a) tensile test and (b) bending test of specimens. Tensile strength and flexural strength are presented in Figure 4.

3 Figure 1: Photograps of insert-injection molding specimen. Results and discussion Mechanical properties of insert-injection molding Figure 2 and Figure 3 show typical load displacement of tensile and bending test in the inseret-injection molding of specimen and specimen, respectively. The maximum load of the insert-injection specimen was higher than neat GF/ and GF/. (a) Tensile test (b) Bending test Figure 2: Load-displacement curves of (a) tensile test and (b) bending test of specimens. (a) Tensile test (b) Bending test Figure 3: Load-displacement curves of (a) tensile test and (b) bending test of specimens. Tensile strength and flexural strength are presented in Figure 4. It can be seen that tensile strength of the insert-injection molding specimen exhibited higher values than the neat GF/ and GF/ as shown in Figure 4 (a). GF/ prepreg improved tensile strength of the insert-injection molding of GF/ about 35-40% in and. On the other hand, CF/ prereg increased tensile strength values of the insert-injection molding specimen about 32% in and 136% in. The prepreg inserted would support and better enhance the tensile strength of the specimen when using the double side insertion. However, tensile strength of the specimen decreased when using the inserted

4 of CF/ prepreg from woven fabric. The maximum of tensile stress of the insert-injection molding was found in when using CF/ prepreg in unidirectional with both or double side insertion. It was considered that the direction of unidirectional prepreg was able to resistant damage under tension loading than woven prepreg. This inserted technique can increase the failure resistance under the tension loading by inserted one or both side of unidirectional prepreg to the insert-injection molding composite. In addition, the stiffness of GF/6 is higher than GF/, which required high load value during tensile test in the system. Likewise, flexural strength of the insert-injection molding was greater improved when using double side of the prepreg insertion with unidirectional as depicted in Figure 4 (b). The flexural strength was improved about 27% in and 50% in as compared to neat GF/ and GF/, respectively. It was considered that the prepreg was under a compression load, which processed on buckling and kinking of the prepreg [8]. Hence, the flexural stress of and was lower than the neat polymers. Tensile stress (MPa) (a) Figure 4: (a) Tensile srtrength and (b) flexural strength of and insert-injection molding. The knee point of tensile curves is represented to the initial fracture stress and the initial fracture strain in the composites [9]. Figure 5 presents the initial fracture stress and the initial fracture strain of the insert-injection molding specimens. All of the insert-injection molding specimens were required higher stress and strain than neat reinforced polymers before the initial crack was occurred as shown in Figure 5 (a) and (b), respectively. It was attributed to partly adhesion in the insert-injection molding specimens. Flexural stress (MPa) (b) Initial fracture stress (MPa) (a) Initial fracturestrain (%) (b) Figure 5: (a) Initial fracture stress and (b) Initial fracture strain of and insert-injection molding. Morphology and fracture behaivor of inserted injection molded Figure 6 depicts photographs of tensile fractured specimens and their SEM photographs. Both of and were broken after tensile testing. From SEM photographs, GF from prepreg was remaining in both of insert-injection molding of specimens. Hence, the failure modes of these specimens were structural failure of GF/ as the injected part and GF/ prepreg as the inserted part as well as adhesive failure in the specimens. On the other hand, in Figure 7, there was no CF remaining in the CF-GF/ insert-injection molding

$It was considering that the initial fracture was occurred in GF/ inject parted and the crack rapidly$ growth till failure in, -W-1 and.

$On the contrary, tensile fractured of shows structural failure of the inserted CF/ prepreg and the$ injected GF/ as presented in Figure 7 (b).

$(a) (b) Figure 6: Tensile fracture and SEM photographs of (a) and (b).$ $(a) (b) (c) (d) Figure7:Tensile fracture and SEM photographs of (a), (b), (c) and (d).$ $Figure 8: SEM photographs of tensile fractured surface of at (a) injectd and (b) inserted part.$

5 specimens. It was considering that the initial fracture was occurred in GF/ inject parted and the crack rapidly growth till failure in, -W-1 and. Although the CF/ prepreg supported the specimens without tearing, the tensile strength of these specimens was low. The failure mode of, and was structural failure. On the contrary, tensile fractured of shows structural failure of the inserted CF/ prepreg and the injected GF/ as presented in Figure 7 (b). In addition, the adhesive failure was also found in this specimen, which we could observe a residual GF/ in the prepreg inserted part as depicted in Figure 8. (a) (b) Figure 6: Tensile fracture and SEM photographs of (a) and (b). (a) (b) (c) (d) Figure7:Tensile fracture and SEM photographs of (a), (b), (c) and (d). Matrix cracking Residual of GF/ 50 µm 50 µm (a) (injected part, GF/) (b) (inserted part, CF/ prepreg) Figure 8: SEM photographs of tensile fractured surface of at (a) injectd and (b) inserted part. Figure 9 and Figure 10 show optical photographs of the specimens after bending test. From the results, it would indicate that the main failure mode of the insert-injection molding was the structural failure. It can be seen that the fracture of the specimens was more occurred with one side of the unidirectional prepreg insertion both in the GF/ and GF/ specimens. In addition, the specimen with woven frabic prepreg insertion was less adhesion and easily broken after compression load as presented in Figure 10 (c) and (d).

(a) (b) Figure 9: Optical photographs of GF/ insert- injection molding specimens after bending test.

Conclusions The effect of fiber direction in prepreg inserted of adhesive interface on the adhesive property of the insert-injection molded was presented.

Tensile strength and flexural strength of the insert-injection molding were better improved with double side insertion of the unidirectional prepreg.

$The failure mode of the specimens was the structural failure, which the fracture was occurred both in the prepreg-inserted part and the polymer-injected part.$ The insert-injection molding process presented a benefit for fabrication of joint materials and reinforcing composites. Bibliography 1. Yoshio N., Robert D.

The insert-injection molding process presented a benefit for fabrication of joint materials and reinforcing composites. Bibliography 1. Yoshio N., Robert D.

M., Ramach A., Composites Science and Technololy, Vol. 186, pp. 265, 2007. 4. Davim J.P., Reis P., Antonio C.C., Composites Science and Technololy, Vol. 64, pp. 289, 2004. 5.

6 (a) (b) Figure 9: Optical photographs of GF/ insert- injection molding specimens after bending test. (a) (b) (c) (d) Figure 10: Optical photographs of GF/ insert- injection molding specimens after bending test. Conclusions The effect of fiber direction in prepreg inserted of adhesive interface on the adhesive property of the insert-injection molded was presented. The prepreg inserted had bonding with injection part by injection molded process and promotes an adhesion between the inserted and injected parts. Tensile strength and flexural strength of the insert-injection molding were better improved with double side insertion of the unidirectional prepreg. However, the woven structure was not promoted tensile and bending properties of CF/- GF/ insert-injection molding. The failure mode of the specimens was the structural failure, which the fracture was occurred both in the prepreg-inserted part and the polymer-injected part. It can be noted that the insert-injection molding composites were required higher stress than neat reinforced polymers before the initial crack was occurred. The insert-injection molding process presented a benefit for fabrication of joint materials and reinforcing composites. Bibliography 1. Yoshio N., Robert D., Handbook of Semiconductor Manufacturing Technology. New York: Marcel Dekker; Ryosuke M, Motoko S., Akira T., Composites Part A, Vol. 39, pp. 154, Mohan N.S., Kulkarni S.M., Ramach A., Composites Science and Technololy, Vol. 186, pp. 265, Davim J.P., Reis P., Antonio C.C., Composites Science and Technololy, Vol. 64, pp. 289, O'Higgins R.M., McCarthy M.A., McCarthy C.T., Composites Materials, Vol. 40, pp. 269, Bohse J., Journal of Acoustic Emission, Vol. 22, pp. 208, Wulfsberg J., Herrmann A., Ziegmann G., Lonsdorfer G., Stöɞ N., Fette M., Procedia Engineering, Vol. 81, pp , Budiansky B., Fleck N.A., Mechanics USA 1994, Applied Mechanics Reviews, Vol. 47, No. 2, part 2, pp. S246-S250, Nakai A., Osada T., Hamada H., Takeda N., Composites Part A, Vol. 32, pp , 2001.

MECHANICAL AND ADHESIVE PROPERTIES OF ARAMID/NYLON INSERT INJECTION MOLDING COMPOSITES

MECHANICAL AND ADHESIVE PROPERTIES OF ARAMID/NYLON INSERT INJECTION MOLDING COMPOSITES Badin Pinpathomrat, Hiroyuki Hamada Kyoto Institute of Technology, Kyoto, Japan Abstract A new joining method called