電表端蓋塑料件注塑模設(shè)計-抽芯注射模含14張CAD圖,電表,塑料件,注塑,設(shè)計,注射,14,cad An experimental study of the water-assisted injection molding of glass ?ber ?lled poly-butylene-terephthalate (PBT) composites Abstract The purpose of this report was to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate (PBT) composites. Experiments were carried out on an 80-ton injection-molding machine equipped with a lab scale water injection system, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The materials included virgin PBT and a 15% glass ?ber ?lled PBT composite, and a plate cavity with a rib across center was used. Various processing variables were examined in terms of their in?uence on the length of water penetration in molded parts, and mechanical property tests were performed on these parts. X-ray di?raction (XRD) was also used to identify the material and structural parameters. Finally, a comparison was made between water-assisted and gas-assisted injection molded parts. It was found that the melt ?ll pressure, melt temperature, and short shot size were the dominant parameters a?ecting water penetration behavior. Material at the mold-side exhibited a higher degree of crystallinity than that at the water-side. Parts molded by gas also showed a higher degree of crystallinity than those molded by water. Furthermore, the glass ?bers near the surface of molded parts were found to be oriented mostly in the ?ow direction, but oriented substantially more perpendicular to the ?ow direction with increasing distance from the skin surface. 2006 Elsevier Ltd. All rights reserved. Keywords: Water assisted injection molding; Glass ?ber reinforced poly-butylene-terephthalate (PBT) composites; Processing parameters; B. Mechanical properties; Crystallinity; A. Polymer matrix composites; Processing 1. Introduction Water-assisted injection molding technology [1] has proved itself a breakthrough in the manufacture of plastic parts due to its light weight, faster cycle time, and relatively lower resin cost per part. In the water-assisted injection molding process, the mold cavity is partially ?lled with the polymer melt followed by the injection of water into the core of the polymer melt. A schematic diagram of the water-assisted injection molding process is illustrated in Fig. 1. Water-assisted injection molding can produce parts incorporating both thick and thin sections with less shrinkage and warpage and with a better surface ?nish, but with a shorter cycle time. The water-assisted injection molding process can also enable greater freedom of design, material savings, weight reduction, and cost savings in terms of tooling and press capacity requirements [2–4]. Typical applications include rods and tubes, and large sheet-like structural parts with a built-in water channel network. On the other hand, despite the advantages associated with the process, the molding window and process control are more critical and di?cult since additional processing parameters are involved. Water may also corrode the steel mold, and some materials including thermoplastic composites are di?cult to mold successfully. The removal of water after molding is also a challenge for this novel technology. Table 1 lists the advantages and limitations of water-assisted injection molding technology. Water assisted injection molding has advantages over its better known competitor process, gas assisted injection molding [5], because it incorporates a shorter cycle time to successfully mold a part due to the higher cooling capacity of water during the molding process. The incompressibility, low cost, and ease of recycling the water makes it an ideal medium for the process. Since water does not dissolve and di?use into the polymer melts during the molding process, the internal foaming phenomenon [6] that usually occurs in gas-assisted injection molded parts can be eliminated. In addition, water assisted injection molding provides a better capability of molding larger parts with a small residual wall thickness. Table 2 lists a comparison of water and gas assisted injection molding. With increasing demands for materials with improved performance, which may be characterized by the criteria of lower weight, higher strength, and a faster and cheape production cycle time, the engineering of plastics is a process that cannot be ignored. These plastics include thermoplastic and thermoset polymers. In general, thermoplastic polymers have an advantage over thermoset polymers in terms of higher impact strength, fracture resistance and strains-to-failure. This makes thermoplastic polymers very popular materials in structural applications. Poly-butylene-terephthalate (PBT) is one of the most frequently used engineering thermoplastic materials, which is formed by polymerizing 1.4 butylene glycol and DMT together. Fiber-reinforced composite materials have been adapted to improve the mechanical properties of neat plastic materials. Today, short glass ?ber reinforced PBT is widely used in electronic, communication and automobile applications. Therefore, the investigation of the processing of ?ber-reinforced PBT is becoming increasingly important [7–10]. This report was made to experimentally study the waterassisted injection molding process of poly-butylene-tere-phthalate (PBT) materials. Experiments were carried out on an 80-ton injection-molding machine equipped with a lab scale water injection system, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The materials included a virgin PBT and a 15% glass ?ber ?lled PBT composite, and a plate cavity with a rib across center was used. Various processing variables were examined in terms of their in?uence on the length of water penetration in molded parts, which included melt temperature, mold temperature, melt ?lling speed, short-shot size, water pressure, water temperature, water hold and water injection delay time. Mechanical property tests were also performed on these molded parts, and XRD was used to identify the material and structural parameters. Finally, a comparison was made between water-assisted and gas-assisted injection molded parts. 2. Experimental procedure 2.1. Materials The materials used included a virgin PBT (Grade 1111FB, Nan-Ya Plastic, Taiwan) and a 15% glass ?ber ?lled PBT composite (Grade 1210G3, Nan-Ya Plastic, Taiwan). Table 3 lists the characteristics of the composite materials. 2.2. Water injection unit A lab scale water injection unit, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit, was used for all experiments [3]. An ori- ?ce-type water injection pin with two ori?ces (0.3 mm in diameter) on the sides was used to mold the parts. During the experiments, the control circuit of the water injection unit received a signal from the molding machine and controlled the time and pressure of the injected water. Before injection into the mold cavity, the water was stored in a tank with a temperature regulator for 30 min to sustain an isothermal water temperature. 2.3. Molding machine and molds Water-assisted injection molding experiments were conducted on an 80-ton conventional injection-molding machine with a highest injection rate of 109 cm3/s. A plate cavity with a trapezoidal water channel across the center was used in this study.Fig. 2 shows the dimensions of the cavity. The temperature of the mold was regulated by a water-circulating mold temperature control unit. Various processing variables were examined in terms of their in?uence on the length of water penetration in water channels of molded parts: melt temperature, mold temperature, melt ?ll pressure, water temperature and pressure, water injection delay time and hold time, and short shot size of the polymer melt. Table 4 lists these processing variables as well as the values used in the experiments 2.4. Gas injection unit In order to make a comparison of water and gas-assisted injection molded parts, a commercially available gas injection unit (Gas Injection PPC-1000) was used for the gasassisted injection molding experiments. Details of the gas injection unit setup can be found in the Refs. [11–15]. The processing conditions used for gas-assisted injection molding were the same as that of water-assisted injection molding (terms in bold in Table 4), with the exception of gas temperature which was set at 20℃. 2.5. XRD In order to analyze the crystal structure within the water-assisted injection-molded parts, wide-angle X-ray di?raction (XRD) with 2D detector analyses in transmis-XRD samples, the excess was removed by polishing the 40 kV and 40 mA. More speci?cally, the measurements were performed on the mold-side and water-side layers of the water-assisted injection-molded parts, with the 2h angle ranging from 7 to 40 . The samples required for these analyses were taken from the center portion of these molded parts. To obtain the desired thickness for the sion mode were performed with Cu Ka radiation at samples on a rotating wheel on a rotating wheel, ?rst with wet silicon carbide papers, then with 300-grade silicon carbide paper, followed by 600- and 1200-grade paper for a better surface smoothness. 2.6. Mechanical properties Tensile strength and bending strength were measured on a tensile tester. Tensile tests were performed on specimens obtained from the water-assisted injection molded parts (see Fig. 3) to evaluate the e?ect of water temperature on the tensile properties. The dimensions of specimens for the experiments were 30 mm · 10 mm · 1 mm. Tensile tests were performed in a LLOYD tensiometer according to the ASTM D638M test. A 2.5 kN load cell was used and the crosshead speed was 50 mm/min. Bending tests were also performed at room temperature on water-assisted injection molded parts. The bending specimens were obtained with a die cutter from parts subjected to various water temperatures. The dimensions of the specimens were 20 mm · 10 mm · 1 mm. Bending tests were performed in a micro tensile tester according to the ASTM D256 test. A 200 N load cell was used and the crosshead speed was 50 mm/min. 3. Conclusions This report was made to experimentally study the waterassisted injection molding process of poly-butylene-tere-phthalate (PBT) composites. The following conclusions can be drawn based on the current study. 1. Water-assisted injection molded PBT parts exhibit the ?ngering phenomenon at the channel to plate transition areas. In addition, glass ?ber ?lled composites exhibit more severe water ?ngerings than those of non-?lled materials. 2. The experimental results in this study suggest that the length of water penetration in PBT composite materials increases with water pressure and temperature, and decreases with melt ?ll pressure, melt temperature, and short shot size. 3. Part warpage of molded materials decreases with the length of water penetration. 4. The level of crystallinity of molded parts increases with the water temperature. Parts molded by water show a lower level of crystallinity than those molded by gas. 5. The glass ?bers near the surface of molded PBT composite parts were found to be oriented mostly in the ?ow direction, and oriented substantially perpendicular to the ?ow direction with increasing distance from the skin surface. 8 參考文獻(xiàn) [1] Miguel S′anchez-Soto . Optimising the gas-injection moulding of an automobile plastic cover using an experimental design procedure. Spain.2006 [2] Integrated microfluidic systems for automatic glucose sensing and insulin injection