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Conventional Processing of Polymer Matrix Composites
Published in Sanjay Mavinkere Rangappa, Jyotishkumar Parameswaranpillai, Suchart Siengchin, Lothar Kroll, Lightweight Polymer Composite Structures, 2020
M.K. Singh, N. Verma, S. Zafar
Thermoforming setup usually consists of the heaters, clamping unit, mold, and air cooling system. The molds should be cleaned after each and every cycle, as materials in the mold can cause a change in the shape of the finished goods. There are mainly three different types of thermoforming processes depending upon the pressure required i.e., pressure forming, vacuum forming, and matched die forming. Vacuum FormingVacuum forming is the technique in which vacuum pressure is used to form the thermoplastic sheet into a certain shape. The placement of thermoplastic sheet is done on the mold surface and is fixed by clamping unit. The sheet is heated up to its softening temperature. The sheet is heated until it is softened and after that, vacuum is applied quickly. A surge tank is provided for the quick pull out of the air. When the vacuum is created, the sheet conforms to the shape of the mold cavity. The formed part is cooled and then ejected from the mold cavity.Pressure FormingThis process is the same as vacuum forming. In this process, the air pressure required is higher than vacuum forming. The preheated plastic sheet is placed on the mold surface, and then air pressure is quickly applied over the sheet. The pressure developed between the pressure box and softened sheet is high. Due to high pressure, the sheet deforms quickly in the mold. The deformed sheet is placed in the mold for some time for cooling.Matched Die FormingMatched die forming is also known as mechanical forming. In match die forming, the mold consists of two parts i.e., the punch and the die. The thermoplastic sheet is heated up to the softening temperature. The preheated sheet is placed onto the surface of the mold and punch pressure is applied on the hot sheet. The presented air in between the die and sheet is removed by application of vacuum pump, and therefore the sheet deforms into the mold shape. The formed part is cooled and ejected from the mold cavity. The important process parameters of the thermoforming process are heating time, heating temperature, vacuum pressure, mechanical pressure, air pressure, cooling time, and ejection mechanism.
Theoretical and experimental study of the free hydroforming of egg-shaped shell
Published in Ships and Offshore Structures, 2022
Jian Zhang, Mingqiang Dai, Fang Wang, Wenxian Tang, Xilu Zhao, Yongmei Zhu
Shells of revolution with positive Gaussian curvatures are widely used as pressure hulls in various underwater vehicles such as submarines, submersibles, torpedoes, gliders, and robots (Kohnen 2009; Błachut 2010; Moorhouse 2015; Cui et al. 2017; Cui 2018). Typical geometries, such as spheres (Pan and Cui 2010), cylinders (Błachut 2015), cones (Błachut 2013), ellipsoids (Ma et al. 2008), toroids (Enoma and Zingoni 2017), and their combinations, have been widely used because of their highly developed design theory and simple manufacturing technology. Atypical geometries, including egg (Zhang, Wang, Wang, Tang, et al. 2017), barrel (Magnucki and Jasion 2013), and longan (Zhang, Wang, Cui, Tang, et al. 2018) shapes, have also received considerable attention because of their low imperfection sensitivity, rational hydrodynamics, and high loading capacity. In particular, egg-shaped shells are a promising geometry for deep pressure hulls (Zhang, Wang, Wang, Tang 2017; Zhang, Zhu, et al. 2017; Zhang, Wang, Cui, Wang, et al. 2018; Zhang, Hua, et al. 2018; Zhang, Hua, et al. 2019; Zhang, Tan, Tang, Wang, et al. 2019; Zhang, Tan, Tang, Zhao, et al. 2019). However, the fabrication of pressure hulls is challenging because such hulls are always fabricated in large sizes and small batches. Traditional multiphase die forming techniques have high process cost, long production time, and high complexity because of the use of many sets of dies and heavy duty presses (Wang et al. 2000; Wang et al. 2005; Yuan et al. 2012; Yuan and Fan 2019).