Accuracy and mechanical properties of multiparts produced in one mold in microinjection molding

The use of plastic materials with added fillers has become a potential alternative due their versatility and the ease of batch fabrication. Recently, micromolding has become a new branch of injection molding. One mold can be used to produce multiparts that weigh no more than a few milligrams and whose precision in terms of dimension is on the order of a few microns. This work investigates the shrinkage and accuracy of multiparts in one mold used in microinjection molding. In addition, the wear and mechanical properties of polymer composites with added fillers are systematically studied. Experiments showed that microparts with a 1.5 mm outer diameter were well duplicated, with clear structural definition. The average deviation in dimension was less than 20 μm. The resulting composites with 20–25 wt% glass particles exhibited significant improvement in shrinkage, wear resistance, and mechanical strength. In addition, wear loss was minor, and lubrication was not needed when the roughness of the wearing surface was less than 0.064 μm. POLYM. ENG. SCI., 45:1471–1478, 2005. © 2005 Society of Plastics Engineers     

Processing and property improvement of polymeric composites with added ZnO nanoparticles through microinjection molding

The use of nanoparticulates in polymeric materials has become a potential alternative for organic–inorganic composite materials because of their versatility in property modification and ease of batch fabrication. This paper investigates the kneading and mechanical properties of polypropylene (PP) with added nano‐ZnO powder in sizes of 10–30 nm, through batch kneading and microinjection molding processes. The results show that the PP microgears with added ZnO nanoparticles are well replicated with clear structural definition. The resulting composites with a small amount of nanofiller added exhibit significant improvement in wear resistance and mechanical properties. The possible strengthening and wearing mechanisms is discussed based on the investigation of the worn and fractured surfaces of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6009–6016, 2006     

The mechanical and tribological properties of PTFE filled with PTFE waste powders

Polytetrafluoroethylene (PTFE) composites filled with PTFE waste offer interesting combination of tribological properties and low cost. PTFE composites waste was mechanically cut and sieved into powders. PTFE composites filled with PTFE waste powders were prepared by compression molding. Friction and wear experiments were carried out in a reciprocating sliding tribotester at a reciprocating frequency of 1.0 Hz, a contact pressure of 5.5 MPa, and a relative humidity of (60 ± 5)%. PTFE materials slid against a 45 carbon steel track. Results showed that a PTFE composite (B) filled with 20 wt % PTFE waste exhibited a coefficient of steady‐state friction slightly higher than that of unfilled PTFE (A), while wear resistance over two orders of magnitude higher than that of unfilled PTFE (A). Another PTFE composite filled with PTFE waste and alumina nanoparticles exhibited the highest wear resistance among the three PTFE materials. This behavior originates from the effective reinforcement of PTFE waste as a filler. It was experimentally confirmed that the low cost recycling of PTFE waste without by‐products is feasible. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1035–1041, 2007     

塑料配电柜的研制和应用

研制了一种塑料配电柜，该塑料配电柜由改性树脂经注塑成型或者热压成型加工制作而成。另外，根据塑料配电柜的不同要求有的塑料配电柜中还使用了尼龙网或钢丝网或者钣金件骨架，这样既保证了塑料配电柜的绝缘性能，又增加了塑料配电柜的刚性，同时还增加了塑料配电柜对电磁辐射的屏蔽性能，试验结果表明，该塑料配电柜耐老化、免油漆、耐雨水冲刷、耐腐蚀、绝缘性能好、电磁波屏蔽性能佳、加工工艺简啦、生产制作成本低廉，综合性能优于会属材料制作而成的配电柜。     

Effect of the processing molding temperature on the crystalline structure and properties of acrylonitrile‐butadiene rubber/trinylon thermoplastic vulcanizates

The effect of the processing molding temperature on the properties and crystalline structure of acrylonitile‐butadiene rubber (NBR)/nylon 6,66,1010 (trinylon) thermoplastic vulcanizates (TPV) was studied. With decreasing molding temperature, the stress at 100% and elongation at break of TPV changed slightly, and the solvent resistance of TPV improved. The best conditions for processing molding were 170°C and 12 min. The crystalline structure of the nylon continuous phase in TPV was investigated by X‐ray diffraction, polarized optical microscopy, and differential scanning calorimetry. The results show that the crystalline structure of the nylon phase in TPV was more perfect/orderly and formed α‐crystalline structure at a processing molding temperature of 170°C. Therefore, the oil resistance of NBR/trinylon TPV clearly improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1374–1379, 2006     

流水线上机械手克隆转换开关改性塑料的选择

转换开关是用在工业生产自动流水线机械手中一种易磨损和大量消耗的塑料制品,以前依靠外国进口,花费了大量外汇。由于转换开关的精度极高,甚至超过金属件的制造精度。故不仅要求制品在成型加工过程中不能有微小的变形,甚至需要严格控制塑料的收缩量。使得所有成型孔的精度达到IT6级以上,平面度不大于0.02 mm,圆柱度不大于0.01 mm。通过对亚光微珠增强聚碳酸脂改性材料的选择,实现控制了制品变形量和提高了耐磨性的目的,通过超高精度孔的二次限制工艺的实施,使得制品孔的精度可达到IT4级以上,圆柱度为0.002 mm以内。国产转换开关完全取代了进口产品,且其精度和寿命远高于进口产品,为超高精度注射件加工创出了一种新方法,也为有关单位节约了大量外汇。     

Prediction of polymer pellet conveying behavior in microinjection molding machine

The higher requirements in dosage accuracy and material strength for products with micro features have made the solid conveying process in microinjection molding machines very important. Problems such as starve feeding and process instability will adversely affect quality more in microinjection molding than bigger parts. Studies have been carried out on the conveying of discrete solid polymer pellets in the plasticizing unit of microinjection molding machines using a newly developed discrete element modeling method to simulate polymer particle movements in the screw channel. The model takes into consideration the influences of adhesion and gravity. The effect of inclination of the conveying screw on the speed of solid conveying is investigated with both simulation and experimental approaches. The results of simulations agree with the results of experiments qualitatively. POLYM. ENG. SCI. 46:1608–1612, 2006. © 2006 Society of Plastics Engineers     

Injection molding with an additive manufactured tool

This study examines the viability of using additively manufactured injection molding tools for short run proof‐of‐concept plastic parts by assessing the quantity and quality of molded parts. Prototyping injection molded parts traditionally can be very expensive, but with improved additive manufacturing materials and techniques such costs could be reduced. To prove this, plastic tools were made by using PolyJet and Fused Deposition Modeling out of Digital ABS, FullCure 720, and ULTEM 1010 materials in this study. The test tools were then compared to the standard P20 metal tool by molding acetal, polycarbonate (PC), and polypropylene (PP) in each tool type. The molded parts were analyzed for processing effects on part shrink, physical, and mechanical properties. Testing concluded that parts molded with additively manufactured tools performed comparably to parts made on a P20 tool. However, the quantity of satisfactory parts molded in acetal and PC were consistent with the literature at 10–100 parts. Conversely, molding in PP suggested that processing with additive manufactured tools could exceed 250 parts. POLYM. ENG. SCI., 59:1911–1918, 2019. © 2019 Society of Plastics Engineers     

Abrasive/Erosive Wear on MMCs in Plastic Molds as a Function of Volumetric Flow Rates and Glass Fiber Distribution

In injection molding wear of components is pronounced in positions with high flow rates of melt. The platelet‐wear‐test is an established method for comparative assessment of wear resistance of tool materials in such regimes. Within this study three metal matrix composites: two hard metals and one powder metallurgical steel were investigated. Results show non‐linear wear rates with increasing amount of plastic melt processed. The reasons were found in the viscous dissipation, which is based on high volumetric flow rates and the small wear gap, leading to a temperature rise, which are detrimental especially for the PM‐steel. Analysis of the processed glass fiber‐filled polymer showed dramatic decrease of fiber length due to the processing through the wear gap. This entails a high amount of free fiber ends, resulting in higher load for the surfaces through micro chipping. POLYM. ENG. SCI., 59:E302–E311, 2019. © 2018 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.     

Feasibility study of thin microinjection molded components

The trend toward the miniaturization of parts has created a strong demand for the manufacturing of precision‐molded miniature polymeric components, due to their high productivity and cost‐effectiveness. The objective of this study is the investigation of the filling behavior and dimensional accuracy of thin microinjection‐molded components using chemical blowing agents and wood fibers. In order to investigate the dimensional stability of the miniature molded parts, a micromold was designed and manufactured using a precision micromilling machine. The flow pattern of the thin molded components was experimentally investigated using different materials: pure linear low‐density polyethylene (LLDPE), foamed LLDPE, and wood fiber LLDPE composite. The results indicate that viscosity significantly affects the flow patterns. Filling behavior of the molded parts was also investigated using commercial flow software. Dimensional accuracy and shrinkage of the molded parts were measured using various gauges. Controlling the cell size, cell density, and distribution of foamed parts was especially difficult for thin micro components; however, the results showed that use of chemical blowing agents can improve the flow ability of the thin components in the microinjection molding process. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Plastic films with improved adhesion on integrated circuit packages for laser marking

Various plastic films of a melting point above 170°C were selected for IC package in laser marking. These films include: (1) polyacetal, (2) polycarbonate, (3) polyester, and (4) nylon. They are in a form of a homogeneous layer, polymer blend, or multilayer structure. The plastic films were plasma treated and laminated onto the molded compound through transfer molding process. No extra process was introduced except for slight modification of the mold for film placement. The film molded IC package was evaluated in terms of adhesion, laser marking, and thermal and humidity resistance. Design of experiment was employed for the adhesion study. The results indicated that the polymeric material and film thickness were the key parameters affecting film adhesion. Careful selection of the plastic film made it possible for self‐triming during product ejection. Two kinds of plastic films, namely, nylon and polyester, were finalized as laser markable and moldable materials. The laser marking effects of the film‐molded packages were comparatively better than those of the nonfilm‐molded packages. These two films were molded into IC packages and tested for thermal and humidity resistance. The results showed that polyester film‐molded packages exhibited superior reliability in thermal shock tests (1000 cycles) and unbias cooker tests (72 h). © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 758–766, 2002; DOI 10.1002/app.10321     

可熔型芯在注射成型中的应用

以低熔点合金为可熔型芯材料,注射成型形状复杂的30%玻纤增强尼龙66中空塑料件。介绍可熔型芯材料的组成及配制方法、可熔型芯的成型、塑料件注射成型过程,以及可熔型芯的熔出。结果表明,用低熔点合金制作可熔型芯材料并用于塑料件注射成型技术可行,工艺控制可靠,但塑料件制作成本高,只能用于附加值较高的塑料件上。     

Flow properties of polymer melt in longitudinal ultrasonic‐assisted microinjection molding

Microplastic parts are usually fabricated by microinjection molding (µIM) which is an effective and low cost method. But the defects, such as short shot, often appear during fabricating plastic parts with high aspect ratio structures or complex shapes. a longitudinal ultrasonic‐assisted microinjection molding (LUµIM) method effectively improve the molding quality. In the paper, the mechanism that the ultrasonic vibration impacts on the polymer melt is investigated. Considering from the point view of energy effect, mechanical energy transmission, and mechanical energy conversion, which are divided from the energy of ultrasonic vibration, are analyzed. The model of energy transmission and a new rheological equation including the parameters of ultrasonic vibration are established to describe the rheological behavior of polymer melt in microcavity. The simulation results show that the ultrasonic vibration improves the viscosity field and the velocity field in complex shaped microcavity, and leads to a better filling capability and uniformity of the polymer melt. This research achievement can be used to guide the process flow and parameter selection of LUµIM. POLYM. ENG. SCI., 57:797–805, 2017. © 2016 Society of Plastics Engineers     

Microstructure and wear properties of plasma‐sprayed aluminum–silicon–polyester coatings

Powder coatings, which are made by plasma‐spraying processes, are being used in industrial applications because of their wear resistance, chemical resistance, and high impact strength even at low service temperatures. These factors increase the importance of plastic and plastic‐based coatings in industrial applications. In this study, an aluminum–silicon–polyester‐based composite coating was applied by plasma‐spraying processes with and without an intermediate bond coat (Ni–Al). The effects of the coating thickness, intermediate bond coat, and processes parameters on the microstructure and wear properties of the coating were studied experimentally. The wear properties of the coatings were determined according to ball‐on‐disk procedure. The microstructures of the coating were examined by optical microscopy and scanning electron microscopy. The results indicated that the plasma‐spraying current and thickness had a strong influence on the wear resistance and microstructural properties of the aluminum–silicon–polyester coating. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3609–3614, 2006     

Bi‐axial self‐reinforcement of high‐density polyethylene induced by high‐molecular weight polyethylene through dynamic packing injection molding

Previously, bi‐axial self‐reinforcement of high‐density polyethylene (HDPE) was achieved through a uni‐axial shear stress field introduced by dynamic packing injection molding technology. Here, further improvement of tensile strength along the flow direction (MD) was achieved by blending a small amount of high‐molecular‐weight polyethylene (HMWPE) with HDPE, while the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional moldings. Tensile strengths in both flow and transverse directions were considerably enhanced, with improvements from 23 MPa to 76 MPa in MD and from 23 MPa to 31 MPa in TD. The effect of HMWPE content and molding parameters on tensile properties was also investigated. The tensile strength along MD was highly dependent on HMWPE content, oscillating cycle, mold temperature, melt temperature and packing pressure, while that along TD was insensitive to composition and processing parameters within the selected design space. According to the stress–strain curves, samples with HMWPE produced by dynamic packing injection molding had a special tensile failure mode in MD, different from both typical plastic and brittle failure modes. There were no yielding and necking phenomena, which are characteristic during tensile testing of plastic materials, but there was still a considerably higher elongation compared to those of brittle materials. However, in TD, all dynamic injection molding samples exhibited plastic failure as did typical conventional injection molding samples. Copyright © 2006 Society of Chemical Industry     

Adhesive strengths between glass fiber‐filled ABS and metal in insert molding with engraved and embossed metal surface treatments

Metal and plastic can be bonded in a single molding process by metal insert molding, in which a metal is inserted into a mold and a plastic resin is then injected. However, the adhesive strength at the interface between the metal and plastic is weakened by the difference in the shrinkage ratio and inherent differences between the materials in the metal insert molding. This study reports the treatment of a metal surface that is followed by inserting the metal into a mold to increase the adhesive strength between the metal and glass fiber (GF)‐filled acrylonitrile butadiene styrene (ABS). A laser process was used for an engraving surface treatment and a plating process was performed for an embossed surface treatment of the metal. In addition, the adhesive strength between the metal and GF‐filled ABS was evaluated after the insert molding process was completed. Particles such as glass beads, ceramic beads, artificial diamonds, and aluminum oxides were employed in the plating process. The adhesive strength varied depending on the surface treatment of the metal. In particular, the adhesive strength significantly increased when an undercut shape was formed at the metal surface. The best adhesive strength with GF‐filled ABS was found in the metal specimen plated using aluminum oxide particles. POLYM. ENG. SCI., 59:E93–E100, 2019. © 2018 Society of Plastics Engineers     

Electron‐beam processing of nylon 6 and HNBR blends. Part II: development of high strength,heat‐ and oil‐resistant thermoplastic elastomers

The effects of electron‐beam irradiation on morphology, mechanical properties and on the heat and hot oil resistance of the thermoplastic elastomeric blend of 30:70 and 70:30, nylon 6 and hydrogenated nitrile rubber (HNBR) were investigated over the dose range 0–8 Mrad. The insoluble content of blends increased with increase in the radiation dose. The morphology of the blend was studied in scanning electron microscopy, with special reference to the effect of radiation prior to processing via injection molding. Irradiated pellets showed better mechanical properties after injection molding compared with irradiated sheets at low radiation dose. The observed differences in mechanical properties are explained on the basis of morphology of the blend. The blend properties were also found to have a strong dependence on nylon content. It was found that the blends rich in nylon had superior mechanical properties, hot oil and solvent resistance, whereas blends with higher HNBR content had better set and heat resistance. The effect of radiation on interaction in these blends was also evaluated and was found to induce possible inter‐chain crosslinking in the blends. Copyright © 2006 Society of Chemical Industry     

A new composition–processing–property relationship for studying the tensile modulus‐phase plastic blends

Based on thermodynamic principles, a composition–processing–property relationship for predicting the modulus properties of multiphase plastic blends has been developed. This relationship describes the relative modulus of the blend in terms of the volume fraction and the index for the degree of mixing of an inclusion‐polymer in the matrix‐polymer. The relative modulus is defined as the ratio between the modulus of the blend and that of the matrix polymer. These blends include a nylon 6,6/polymethyl methacrylate(PMMA) system mixed using an injection molding process arid a nylon 6/ethylene‐vinyl acetate copolymer system mixed using a corotational extrusion process. Based on the values determined for the mixing index of the nylon 6,6/PMMA blends, a relationship between the mixing index and the fill time used in the injection molding has been developed. The results also imply that the degree of mixing of the blend mixed using a correlation extrusion process is better than that of the blend processed using an injection molding process. Using the above results, we now can scientifically develop new plastic blends and design optimum processing conditions for various automotive applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The occurrence of surface roughness in gas assist injection molded nylon composites

Gas assist injection molding has increasingly become an important industrial process because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that limit the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composities. The materials used were 15 % and 35% glass‐fiber filled nylon‐6 composites. Experiments were carried out on an 80‐ton injection molding machine equipped with a high‐pressure nitrogen‐gas injection unit. Two “float‐shape” axisymmetric cavities were used. After molding, the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature, mold temperature, melt filling speed, short‐shot size, gas pressure, and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness results mainly from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure.     

旋塑汽车后备箱盖设计

主要介绍高分子材料成型的汽车后备箱盖设计流程,为了满足汽车轻量化需求,使用高分子材料代替原有金属冲压件,同时为了满足旋塑成型需求,对塑料后备箱盖的成型工艺进行了优化分析,其中包括内部金属嵌件形式方面的优化和嵌件使用应力的计算。结果表明,通过滚塑工艺成型的后备箱盖可以在保证后备箱盖功能、满足人机工程学功能的基础上减轻后备箱盖的质量达到87%,实现了汽车的轻量化设计。