Development of green rapid tooling technologies

Transcription

1 Indian Journal of Engineering & Materials Sciences Vol. 20, August 2013, pp Development of green rapid tooling technologies Chil-Chyuan Kuo* Department of Mechanical Engineering, Ming Chi University of Technology No. 84, Gungjuan Road, Taishan Dist., New Taipei City 24301, Taiwan Received 23 April 2012; accepted 15 April 2013 Rapid tooling technology is regarded as an important method of reducing the cost and time to market in a new product development process. Silicone rubber mold and epoxy-based composites mold are frequently used in the indirect tooling. Based on green manufacturing, a green rapid tooling technology is developed and implemented in this work. This technology provides a new and simple approach for producing the green silicone rubber mold and the green epoxy-based composites mold without appreciable loss of surface roughness. The savings in costs of development in the green silicone rubber mold and green epoxy-based composites mold are about 35.6% and 52.5%, respectively. The saving in cost of development in the large-sized silicone rubber mold fabrication is up to 66.4%. Keywords: Rapid tooling technology, Green manufacturing, Silicone rubber mold, Epoxy-based composites The manufacturing industry is under more pressure due to global competition. To effectively shorten new product development time, rapid prototyping (RP) was developed 1. However, the features of the prototype do not usually meet the need of the end product with the required material. Rapid tooling (RT) technologies are then developed. RT is regarded as a nature extension of RP since it is the technology that uses RP technologies and applies them to the manufacturing of mold inserts 2. Since the importance of RT goes far beyond component performance testing, RT is regarded as an important method of reducing the cost and time to the market in the development of a new product. Several RT technologies are commonly available in industry now. For the purpose of the classification, RT is divided into soft and hard tooling and also indirect and direct tooling. Soft tooling is easier to work with than tooling steels because these tools are created from materials such as epoxy-based composites with aluminum particles, silicone rubber or low-meltingpoint alloys. It is generally known that RT is capable of replacing conventional steel tooling, saving the cost and time in the manufacturing process 3,4. King and Tansey 5 proposed alternative materials for rapid tooling. Ferreira 6 demonstrated the ability of direct metal laser sintering for producing rapid tooling directly from computer aided design data. * jacksonk@mail.mcut.edu.tw Simchi et al. 7 developed an iron based powder blend for rapid tooling using a direct laser sintering process. Wang et al. 8 demonstrated the feasibility of rapid tooling for zinc spin casting using stereolithography and arc metal spray technology. Yarlagadda et al. 9 developed a rapid tooling for the production of sheet metal drawing using a combination of stereolithography and nickel electroforming processes. Ferreira and Mateus 10 develpoed a rapid tooling with conformal cooling channels for plastic injection moulding. Yang and Hannula 11 developed a precision spray forming for rapid tooling. Ferreira 12 manufactured core-boxes for foundry using rapid tooling technology. Zhang et al. 13 developed a rapid hard tooling for injection molding and sheet metal forming using plasma spraying. Khaing et al. 14 fabricated metal prototypes and tools directly from computer aided design data using direct metal laser sintering. Wang et al. 15 presented an automatic method for designing conformal cooling circuits for rapid tooling. Masood and Song 16 developed new materials for use in fused deposition modelling process to fabricate rapid tooling. Dürr et al. 17 fabricated electrical discharge machining electrode using selective laser sintering. Indirect soft tooling is used more frequently in the development of new products than direct tooling because it is fast, simple and cost-effective. It is a well-known fact that the silicone rubber mold is employed frequently because it owns flexible and

2 246 INDIAN J. ENG. MATER. SCI., AUGUST 2013 elastic characteristics so that parts with sophisticated geometry can be fabricated easily 18. In addition, the epoxy-based composites mold is frequently employed in the intermediate tooling because this material owns good mechanical properties and high temperature resistance 19. Environmentally conscious design and manufacturing (ECD&M) is a view of manufacturing that includes the social and technological aspects of design, processing, and use of products in continuous or discrete manufacturing industries 20. The objectives of ECD&M include reducing environmental and health risks, improving product quality at lower cost and worker protection. Pursuing the green manufacturing (GM) of products is very beneficial in the alleviation of environment burdens. GM is a renewable way of producing products that do no harm to the environment, which is involved in every aspect of manufacturing processes. Manufacturing industries contribute significantly to prosperity, but also generate many tons of hazardous and non-hazardous waste. Thus, technical development of a green rapid tooling technology is required. In this work, two green rapid tooling technologies are proposed. A simple and cost-effective process for fabricating green rapid tooling is demonstrated to address this important issue. Surface roughnesses of the mold surface were measured using a white-light interferometry (WLI). Characteristics of these technologies are also discussed. Experimental Procedure Figure 1 show the schematic diagram of process flow for fabricating the silicone rubber mold. The amount of silicone rubber required was calculated by multiplying the desired volume of the silicon rubber mold to be made by the density of silicone rubber (1.07 g/cm 3 at 23 C). Depending on the extent of air bubbles in the mixture, the degassing process can range from 25 to 60 min. A vacuum casting system was used for generating a vacuum environment 21 to remove the air bubbles derived from the mixing process of the curing agent and the silicone rubber. Silicone rubber was mixed with a curing agent with a mass ratio of 10:1 thoroughly with a stirrer. The properties of the silicone rubber mold such as durability and mold life are significantly affected by the relative amounts of curing agent and silicone rubber. Thus, calculating the weight of base and curing agent precisely is crucial before mixing. To reduce human error, a user-friendly man-machine interface was developed using Visual Basic program. Figure 2 shows the schematic illustration of process flow for fabricating the green silicone rubber mold. Master model used in this work is a wrench. The process flow is typically the same as the process flow for fabricating a silicone rubber mold 22. The only one difference in the process flow is that the recycled pieces of silicone rubber were placed into the mold frame before pouring the silicone mixture. To evaluate the economic benefits of the green soft tooling technology, a large-sized silicone rubber mold was investigated. Figure 3 shows the process flow for fabricating the large-sized silicone rubber mold. The master model used in this work is a fan guard which was designed by Pro/ENGINEER software. A fan guard RP pattern was fabricated using fused deposition modeling RP system 23. Fan surface was set as parting surface because the silicone rubber mold will be separated easily 24. Table 1 shows the working parameters for fabricating the master model. Figure 4 Fig. 1 Schematic diagram of process flow for fabricating the silicone rubber mold Fig. 2 Schematic illustration of process flow for fabricating the green silicone rubber mold

3 KUO: DEVELOPMENT OF GREEN RAPID TOOLING TECHNOLOGIES 247 Fig. 3 Process flow for fabricating the large-sized silicone rubber mold Table 1 Working parameters for fabricating the RP pattern of master model Material Thickness (mm) Fabrication time(min) Working temperature ( C) P430-ABS shows the schematic diagram of process flow for fabricating the green epoxy-based composites mold. Epoxy resin composite (C1, Devcon) was used to fabricate the mold insert, which consists of 30% epoxy resin filled with 70% aluminum (Al) powder. A special step in the manufacturing processes is that the recycled pieces of epoxy-based composites were placed into the mold frame before pouring the new epoxy-based composites mixture. The master model employed in this work is a wrench. The amount of Fig. 4 Schematic diagram of process flow for fabricating the green epoxy-based composites mold

4 248 INDIAN J. ENG. MATER. SCI., AUGUST 2013 epoxy-based composites was calculated by the size of master model. The curing agent and epoxy-based composites in weight ratio of 1:112 was mixed thoroughly with a stirrer. The mixing process of Al powder and epoxy resin is very important because the uniform distribution of the Al powder in the epoxy resin provides a great effect on the mechanical property of mold insert. A defect-free mold insert was made using a vacuum casting device because the vacuum condition offers the epoxy resin composite to be poured into the mold frame fluently. Depending on the extent of air bubbles in the mixture, the degas process can range from 30 to 80 min. When the green part of mold insert was made, a stepwise post cure process for mold insert was performed in a convection oven (DH400, Deng Yag) to ensure the completion of curing reaction of the composite materials. Figure 5 shows the temperature profile used for the post cure process of epoxy-based composites mold insert. The green mold insert was first cured at 55 for 2 h followed by 121 for 2 h and 204 for 2 h. Finally, a fully dense mold insert was obtained. Surface roughnesses of the mold surface were measured using a WLI (vertical resolution 0.1 nm, horizontal resolution 0.5 µm, Chroma 7502). The sampling area was chosen to be 50 µm 50 µm. The arithmetic average roughness value (R a ) was used to quantify the surface finish, which is the average displacement of the peaks and valleys measured with respect to a mean line. successfully cast from the green silicone rubber mold because silicone rubber owns high elasticity and low surface energy 25. High elasticity gives the wax pattern to be demolded without damage or breakage during demolding process. Low surface energy gives the wax pattern to be separated from green silicone rubber mold with small releasing force. The total volume of green silicone rubber mold was approximately 1,607,560 mm 3. The green silicone rubber mold can be fabricated only by the use of new silicon rubber with the volume of 1,000,418 mm 3 because the recycled silicone rubber with the volume of 607,142 mm 3 was embedded in the manufacturing process. Thus, the savings in costs of silicone rubber mold fabrication is about 35.6%. This result shows that the green silicone rubber mold meets the requirements of recycling waste resources. Figure 8 shows the WLI images of surface of master model and mold surface of the green silicone rubber mold. The average roughness of the mold surface is approximately 153 nm, showing the green silicone rubber owns the desired mold surface. To evaluate the economic benefits of the green silicone rubber mold, a large-sized silicone rubber mold was fabricated. Figure 9 shows the core and Results and Discussion Figure 6 shows the core and cavity halves of green silicone rubber mold. As can be seen, the surfaces of both core and cavity own the desired surface finish. Figure 7 shows that a wrench made of wax was Fig. 6 Core and cavity halves of green silicone rubber mold Fig. 5 Temperature profile for the post cure process of epoxybased composites mold inserts Fig. 7 Wax pattern of wrench cast from green silicone rubber mold

5 KUO: DEVELOPMENT OF GREEN RAPID TOOLING TECHNOLOGIES 249 Fig. 8 WLI images of (a) surface of master model and (b) mold surface of the green silicone rubber mold cavity halves of green large-sized silicone rubber mold. Figure 10 shows the WLI images of surface of master model and mold surface of the large-sized silicone rubber mold. The average roughness of the mold surface is approximately 216 nm due to largesized silicone rubber mold owns good replication fidelity 26. In general, the medical knife is widely employed to part the core and cavity after the silicone rubber mold is cured. Especially, the main advantage of this method is that the core and cavity can easily be fabricated without the use of medical knife because the parting surface was fabricated in advance via silicone rubber materials. This is a key technology for making a large-sized silicone rubber mold because separating the core and cavity using medical knife is a sophisticated process in the large-sized silicone Fig. 9 (a) Core and (b) cavity halves of a large-sized silicone rubber mold rubber mold. Figure 11 shows that a fan guard made of polyurethane was successfully cast from the largesized silicone rubber mold using the casting procedure. A large-sized silicone rubber mold can be fabricated successfully only by the use of new silicon rubber with the volume of 6,056,148 mm 3 because the recycled silicone rubber with the volume of 11,975,000 mm 3 was embedded in the manufacturing process. The savings in costs of silicone rubber mold fabrication is up to 66.4%. This implies that the cost reduction in the manufacturing process increased with increasing the size of silicone rubber mold. Thus, green rapid tooling technology is a cost-effective method for fabricating a large-sized silicone rubber mold. Figure 12 shows the core and cavity halves of the green epoxy-based composites mold. Figure 13 shows

6 250 INDIAN J. ENG. MATER. SCI., AUGUST 2013 Fig. 12 Core and cavity halves of the green epoxy-based composites mold Fig. 10 WLI images of (a) surface of master model and (b) mold surface of the large-sized silicone rubber mold Fig. 13 WLI image of mold surface of the green epoxy-based composites mold Fig. 11 Polyurethane pattern of fan guard cast from the largesized silicone rubber mold the WLI images of mold surface of the green epoxybased composites mold. The average roughness of the mold surface is approximately 114 nm, showing the mold insert is suitable for manufacturing optical components using injection molding. Figure 14 shows that a wrench made of wax was successfully cast from the green epoxy-based composites mold using the casting procedure 27. The savings in costs of epoxybased composites mold fabrication is about 52.5%. The green epoxy-based composites mold can be employed in the intermediate tooling to produce a small quantity of working samples by plastic injection

7 KUO: DEVELOPMENT OF GREEN RAPID TOOLING TECHNOLOGIES 251 Fig. 14 Wax pattern of wrench cast from the epoxy-based composites mold molding at the first development stage for a new product. The life time of the epoxy-based composites mold inserts is about 5000 shots in plastic injection molding because the thermal conductivity of epoxybased composites is inferior to the tool steel 28. To enhance the heat extraction capacity of the plastic injection molding, further investigation is required to embed the conformal cooling systems in the mold insert for increasing the productivity. Also, the copper block is strongly recommended as the backing material for mold insert. The anti-adhesion treatment of mold surface to prevent sticking problem during plastic injection molding is also an important issue that needs to be further addressed. To increase life time of mold, functional coating on the mold surface is still required 29. In addition, micro sensors can be embedded into the mold insert for monitoring temperature change during injection molding process to ensure quality of products molded 30,31. Conclusions Two green rapid tooling technologies for lowering the cost and reducing the production time in the development of a new product have been demonstrated in this work. This technology provides a new simple manufacturing route for the production of green rapid tooling with the desired surface finish. This green rapid tooling technology provides the savings in costs of development in the green silicone rubber mold and green epoxy-based composites mold about 35.6% and 52.5%, respectively. Besides, the savings in costs of development in the large-sized silicone rubber mold fabrication is up to 66.4%. The green rapid tooling technology has broad market application prospects in the development of new products with large volume such as the bumper of a car or a television set cover. Acknowledgement This work was financially supported by the National Science Council of Taiwan under contract no. NSC E References 1 Gill S S & Kaplas M, Mater Manuf Process, 24 (2009) Palcic I, Balazic M, Milfelner M & Buchmeister B, Mater Manuf Process, 24 (2009) Sustarsic B, Dolinsek S, Jenko M & Leskovsek V, Mater Manuf Process, 24 (2009) Kuo C C, Mater Manuf Process, 27 (2012) King D & Tansey T, J Mater Process Technol, 121 (2002) Ferreira J C, J Mater Process Technol, (2004) Simchi A, Petzoldt F & Pohl H, J Mater Process Technol, 141 (2003) Wang J, Wei X P, Christodoulou P & Hermanto H, J Mater Process Technol, 146 (2004) Yarlagadda P K D V, Ilyas I P & Christodoulou P, J Mater Process Technol, 111 (2004) Ferreira J C & Mateus A, J Mater Process Technol, 142 (2003) Yang Y & Hannula S P, Mater Sci Eng A, 477 (2008) Ferreira J C, J Mater Process Technol, (2004) Zhang H, Wang G, Luo Y & Nakaga T, Thin Solid Films, 390 (2001) Khaing M W, Fuh J Y H & Lu L, J Mater Process Technol, 113 (2001) Wang Y, Yu K M, Wang C C L & Zhang Y, Comput-Aided Des, 43 (2011) Masood S H & Song W Q, Mater Des, 25 (2004) Dürr H, Pilz R & Eleser N S, Comput Ind, 39 (1999) Kuo C C & Lin Z Y, Mater Wiss Werkst, 42 (2011) Ma S, Gibson I, Balaji G & Hu Q J, J Mater Process Technol, 192 (2007) Kundrak J, Mamalis A G, Gyani K & Markopoulos A, Mater Manuf Process, 21 (2006) Kuo C C & Lai M Y, Indian J Eng Mater Sci, 18 (2011) Kuo C C, Lin C Y & Wu X Z, Development of an adjustable mold box for making silicone rubber mold, Proc of IEEE Int Conf on Industrial Engineering and Engineering Management, Macau, China, 7-10 Dec 2010, pp Kuo C C, Tsou Y C, Chen B C, Mater Wiss Werkst, 43 (2012) Pritam C, Reddy N V, J Mater Process Technol, 209 (2009) Chung S, Im Y, Kim H, Jeong H, Dornfeld D A, Int J Mach Tools Manuf, 43 (2003) Jena R K, Yue C Y, Lam Y C, Tang P S & Gupta A, Sens Actuat B: Chem, 163 (2012) Rahmati S, Rezaei M R & Akbari J, Tsinghua Sci Technol, 14 (2009) Ong N S, Zhang H & Woo W H, Mater Manuf Process, 21 (2006) Wilden J & Wank A, Mater Wiss Werkst, 32 (2001) Saha H & Pramanik C, Mater Manuf Process, 21 (2006) Schober A, Fernekorn U, Lübbers B, Hampl J, Weise F, Schlingloff G, Gebinoga M, Worgull M, Schneider M, Augspurger C, Hildmann C, Kittler M & Donahue M, Mater Wiss Werkst, 42 (2011)