The effect of copper alloy mold tooling on the performance of the injection molding process

The performance of copper alloy mold tool materials in injection molding has been examined with respect to cycle time, part quality and energy consumption using in‐process monitoring techniques. A mold insert manufactured from conventional tool steel was compared to four identical inserts made from beryllium‐free copper alloys with copper contents ranging from 85 to 96%. Injection molding trials using high density polyethylene and polybutyl terepthalate were performed using a highly instrumented injection molding machine. Results showed that copper alloy mold tools exhibited cooling rates up to 29% faster than conventional tool steel and that cooling rate was related to thermal conductivity of the alloy. Lower cycle times were achievable with copper alloy than for tool steel before part quality deterioration occurred. The results suggest that copper alloy tooling has the potential to achieve significant reductions in cycle time without detriment to the process or product quality. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Reduction of cycle time by addition of silicon carbide filler to syndiotactic polystyrene/glass fiber composites

Reducing cycle time in injection molding process is important because it can save operational cost and increase product yield. Cycle time can be categorized by six criteria, which are metering time, time for closing a mold, packing time, holding time, cooling time, and the time needed to open a mold and to eject the molded product. It was found that the metering time is crucial to predict the cycle time of glass fiber reinforced syndiotactic polystyrene (sPS/GF, 60/40 by weight). In many cases, however, cycle time could be reduced by saving cooling time. This study is motivated by the demand to reduce the cycle time of sPS/GF composite. Since the increase of thermal conductivity leads to the reduction of cooling time, silicon carbide (SiC) is employed to evaluate if it can increase the thermal conductivity of sPS/GF composite. When SiC is added to replace entire GF in sPS/GF composite, the mechanical property of the resulting sPS/SiC (60/40 by weight) composite was not satisfied even though its thermal conductivity was enhanced to about 62 %. Within tolerable ranges in mechanical properties, SiC was added to replace a half amount of existing GF filler. sPS/GF/SiC (60/20/20 by weight) composite achieved the enhancement of thermal conductivity from 0.230 to 0.308 W/m K (34 %) which resulted in the effective reduction of both cooling time and cycle time from 16 to 10 s and from 47 to 38 s, respectively. It should be noted that additional time saving was obtained by 3 s between 6 s in cooling and 9 s in overall cycle time. It can be interpreted by the fact that the increase of thermal conductivity also accelerated the heating rate of sPS/GF/SiC composite.     

Preparation, electrical and elastic properties of new anisotropic expanded graphite-based composites

New composite materials with application to catalyst supports or adsorbents are presented. They are made of compressed expanded graphite of various densities first impregnated by polyfurfuryl alcohol and next pyrolyzed and activated. The resultant materials are monoliths comprising a graphite backbone coated by a thin layer of active carbon. The electrical conductivity and the dynamic elastic moduli are measured on each kind of material, namely before and after carbonization, and finally after activation. The results are shown to be consistent with a percolation phenomenon: the conductivity and the rigidity thresholds are derived, and several theoretical considerations and comparisons with pure expanded graphite are made. The discussion leads to a better understanding of the structure of the materials before and after impregnation, namely the graphite backbone and the graphite-polymer or carbon composites. Besides, their conductive and elastic properties are shown to be very good. Hence, the materials are expected to have fair thermal conductivities, to be electrically regenerable (application as adsorbents) and to have an interesting life time (application as catalyst supports).     

Role of heat transfer and thermal conductivity in the crystallization behavior of polypropylene‐containing additives: A phenomenological model

The thermal conductivity of a filler and the thermal conductivity of a composite made from that filler influence the heat‐transfer process during melt processing. The heat‐transfer process from the melt to the mold wall becomes an important factor in developing the skin–core morphology. These aspects were examined in this study. The thermal conductivity of polypropylene–filler composites was estimated with a standard model for various fillers such as calcium carbonate, talc, silica, wollastonite, mica, and carbon fibers. The rate of cooling under given conditions, including the melting temperature, mold wall temperature, mass of the composite, and filler content, was estimated with standard heat‐transfer equations. The time to attain the crystallization temperature for polypropylene was evaluated with a regression method with differential temperature steps. The crystallization curves were experimentally determined for the different fillers, and from them, the induction period for the onset of crystallization was estimated. These observations were correlated with the expected trends from the aforementioned formalism. The excellent fit of the curves showed that in all these cases, the thermal conductivity of the filler and composite played a dominant role in controlling the onset of the crystallization process. However, the nucleation effects became important in the later stages after the crystallization temperature was attained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2994–2999, 2003     

Development of rapid heating and cooling systems for injection molding applications

The injection molding process has several inherent problems associated with the constant temperature mold. A basic solution is the rapid thermal response molding process that facilitates rapid temperature change at the mold surface thereby improving quality of molded parts without increasing cycle time. Rapid heating and cooling systems consisting of one metallic heating layer and one oxide insulation layer were investigated in this paper. Design issues towards developing a mold capable of raising temperature from 25°C to 250°C in 2 seconds and cooling to 50°C within 10 seconds were discussed. To reduce thermal stresses in the layers during heating and cooling, materials with closely matched low thermal expansion coefficient were used for both layers. Effects of various design parameters, such as layer thickness, power density and material properties, on the performance of the insert were studied in detail with the aid of heat transfer simulation and thermal stress simulation. Several rapid thermal response mold inserts were constructed on the basis of the simulation results. The experimental heating and cooling response agrees with the simulation and also satisfies the target heating and cooling requirement.     

Effects of inserts on the injection molding process

Injection molds often contain blocks of dissimilar material for improved cooling; they may also contain blocks of movable metal as a means of ejecting large parts from the mold. In this case, the blocks of metal are made of the same material, but the resistance at the interface between them has a marked influence on the cooling in the local area near the interface. In many other cases, inserts may be required because of wear in a particular mold section, or because efficient mold design is needed to produce similar parts. Hence, any mathematical model for analysis of heat transfer in injection molds must be general enough to apply to interfaces with and without gaps (i.e., with and without resistance to the flow of heat at the interface) for similar, as well as dissimilar, materials. A new and accurate model for prediction of heat transfer in heterogeneous (zoned) molds is presented in this paper. Through the solution of real problems with this model, the effects of differing material properties and interfacial thermal resistance are studied and the results are reported. It is observed that inserts have both local and global effects on the injection molding process; the overall ejection time for a part may be shortened, and the surface appearance of a part may be improved by correct placement of inserts.     

热适应复合材料应用于电子器件散热的研究进展

热适应复合材料是具有适合要求的热导率或热膨胀系数的一种复合材料。综述了高导热系数的快速热响应复合材料及可控热膨胀系数复合材料的研究进展,并介绍了热适应复合材料在电子器件散热领域的应用。     

复合材料热膨胀成型工艺研究与应用

简要叙述热膨胀工艺的原理和成型工艺过程，对热膨胀芯模的材料性能和设计、制造进行试验，分析影响膨胀压力的因素，并与热压罐成型工艺进行性能对比。以硅橡胶材料制作的芯模与钢模组合使用制备碳纤维复合材料制件，应用效果较好。研究表明，该工艺适用于多腔体复合材料制件的整体共固化成型。     

Internal cooling in rotational molding—A review

Rotational molding suffers from a relatively long cycle time, which hampers more widespread growth of the process. During each cycle, both the polymer and mold must be heated from room temperature to above polymer melting temperature and subsequently cooled to room temperature. The cooling time in this process is relatively long due to the poor thermal conductivity of plastics. Although rapid external cooling is possible, internal cooling rates are the major limitation. This causes the process to be uneconomical for large production runs of small parts. Various researchers have strived to minimize cycle times by applying various internal cooling procedures. This article presents a review of these methods, including computer simulations and practical investigations published to date. The effects of cooling rate on the morphology, shrinkage, warpage, and impact properties of rotationally molded polyolefins are also highlighted. In general, rapid and symmetrical cooling across the mold results in smaller spherulite size, increased mechanical properties and less potential warpage or distortion in moldings. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers.     

基于多孔支撑体的形状稳定复合相变储能材料的研究进展

固-液相变材料（PCMs）是热能储存（TES）技术发展的关键因素,然而一些固有的问题如泄漏和热导率低等严重制约了相变材料的性能。因此,选择合适的方法构建形状稳定的复合相变材料（FSCPCMs）,并有效地提高其热导率是实现相变材料实用化的重要前提。多孔载体封装相变材料为构建具有高储能密度和优异热传输性能的定形复合相变材料提供了一条有效的途径。本文对不同FSCPCMs的制备、结构热学性能、应用等方面进行了综述,详细总结和讨论了孔径和几何形状、表面改性、作用力、组成等因素对FSCPCMs相变行为的影响。重点介绍了具有高热导率、高负载率和高潜热的新型多孔复合相变材料的设计和应用。最后,基于理论、数值和实验方法,展望了FSCPCMs在约束结构中的相变和多尺度传热方面未来的研究方向及其在能源转换方面的商业化应用。     

高导热高介电BT/SiC/PA6复合材料的制备及性能研究

以聚酰胺(PA6)为基体,氮化硅(SiC)为导热填料,钛酸钡(BT)为介电填料,通过热压法制备出系列复合材料;研究了不同粒径填料的搭配对材料导热与介电性能的影响。结果表明:在填充量较低时,使用混合粒径导热填料能产生一定的级配效应,从而提高复合材料的导热性能。总填充量为26%时,以4∶1的比例,用粒径为0.5~0.7μm和3μm的SiC共同填充PA6,制备获得了最高导热系数为0.9198W/(m·K)的复合材料,而不同粒径、不同功能的混合功能填料还能产生协同效应,进一步提升材料的导热性能并使材料同时获得较好的介电性能,当SiC填充量为20%,BT填充量为20%时,复合材料的导热系数达到1.1110W/(m·K),介电常数到达16(100Hz),损耗保持在0.075(100Hz)左右。     

Failure mechanisms in stereolithography injection molding tooling

Stereolithography tooling is a form of rapid tooling that has been used to injection mold limited runs of prototype parts. However, the process is not well understood and tooling life for fine mold features is difficult to predict. Injection molding processing conditions and feature geometry affect the number of parts that can be made before a mold fails. To study the effects of feature geometry, general purpose polystyrene parts were injection molded in molds made of DSM Somos 7110 stereolithography resin. The ACES build style was used, and no polishing was performed on the mold. The experimental results were compared with theoretical models developed for the two failure mechanisms for raised features in a stereolithography mold—failures during injection due to the flow pressure of the injected polymer; and failures during ejection, whereby the part pulled out a feature of the mold. Injection failures occurred in taller mold features due to the force of flow and the feature's geometry. Ejection failures occurred in the shorter features when the stress from the ejection force (distributed over the bond area) exceeded the yield strength of the mold material. Models were developed to predict the number of parts that a mold could make before mold features break off and were validated through experimental results.     

High Thermal Conductivity Nanocomposites Based on Conductive Polyaniline Nanowire Arrays on Boron Nitride

With the development of soft electronics, conductive composites are garnering an increasing amount of attention. The electrical conductivity, thermal conductivity, and electrical stability of conductive composites are all very important. In particular, the thermal conductivity of conductive composites is critical to the stability of their conductive properties. However, little is reported on thermal management in conductive systems. Herein, sufficiently hydroxylated boron nitride nanosheets (BN‐OH)@polyaniline (PANI) composite nanosheets with a high thermal conductivity and outstanding conductance stability are reported. PANI nanowire arrays are aligned vertically on BN‐OH. This well‐ordered nanostructure provides the means to form a good conductive and thermally conductive path. Notably, the composite through‐plane thermal conductivity is 2.1 W m^?1 K^?1(≈1000% that of pure PANI) and that the resistivity of the composite is 1.38 Ω cm. Importantly, the resistivity of the composite remains unchanged after 1 h of work. The results show that this composite has prospective applications for use in soft electronics.     

树脂基复合材料用耐高温水溶性模具材料性能研究

本文采用了耐高温水溶性胶粘剂制备了水溶性模具,通过调节水溶性模具材料各组分配比,研究了水溶性模具的溶解性能和压缩性能,从而确定了制备水溶性模具的最佳工艺条件。另外还对水溶性模具的热性能、热膨胀系数、干燥时间、耐温性等性能进行了研究。研究结果表明:此种水溶性模具材料耐温达220℃,溶解性能和压缩性能能满足树脂基复合材料成型的要求,制备出的复合材料具有空隙率低(空隙率小于0.7%)等优点。     

Design and development of ceramic-based composites with tailored properties for cutting tool inserts

A successful approach to the development of tailored cutting tool materials requires the development of innovative concepts at each step of manufacturing, from the material design, synthesis of composite powders, to their processing and sintering. In this paper, a computational design approach is applied in the development of reinforced ceramic-based cutting tool inserts with tailored structural and thermal properties. Several potential filler materials are considered at the material design stage for the improvement of structural and thermal properties of a selected matrix material. Properties, such as an improved thermal conductivity and reduced coefficient of thermal expansion are essential for an effective cutting tool insert to absorb thermal shock at varying temperatures. In addition, structural properties such as elastic modulus have to be maintained within a moderate range. A mean-field homogenization theory and effective medium approximation using an in-house code are applied for predicting potential optimum structural and thermal properties for the required application. This is done by considering the effect of inclusions as a function of volume fraction and particle size in the ceramic base matrix. Single inclusion composites such as alumina-silicon (Al₂O₃-SiC) and alumina-cubic boron nitride (Al₂O₃-cBN) as well as hybrid composite such as alumina-silicon-cubic boron nitride (Al₂O₃-SiC-cBN) are developed using the Spark Plasma Sintering (SPS) process in line with the designed range of filler size and volume fraction to validate the computational results. It is found that the computational material design approach is precise enough in predicting the target properties of a designed hybrid composite material for cutting tool inserts.     

Experimental and numerical analysis of flow behavior in the FASTRAC liquid composite manufacturing process

The success of resin infusion during liquid composite processing depends on several factors; including the complete impregnation of the dry performs, the processing conditions, and the tooling used during processing. New process developments based on the Fast Remotely Actuated Channels (FASTRAC) process aid the infusion with the creation of preferential resin flow paths using a non-contact tooling. Experiments to understand and study the infusion behavior with the presence of the FASTRAC non-contacting tooling have been performed, and compared with vacuum-assisted processes without such tooling. Experimental studies indicate that the infusion time with FASTRAC channel configurations is significantly less despite the additional volume regions to be infused during processing. The use of a non-contacting interchangeable tool, the improved infusion behavior, and the significant reduction in the infusion time provide significant advantages for processing advanced composite systems, including the potential to use high viscosity resin systems, and process automation. The process simulation models of the experimental configurations based on the thin shell model configurations have been compared with experimental observations. Studies indicate that the process simulation models and approaches employed clearly emulate the infusion behavior seen when the channels are present, validating the modeling strategies employed. Similar simulation approaches will thus be effective to study and understand various FASTRAC tooling configurations while processing complex composite structures. Polym. Compos. 25:384–396, 2004. © 2004 Society of Plastics Engineers.     

高导热石墨材料微观结构与其导热性能的关系研究

考察了以膨胀石墨为原料制备的高导热炭材料（高导热石墨块、高导热石墨片）与以中间相沥青为原料制备的高导热炭材料（高导热石墨膜）在微观结构及导热性能上的差异。研究表明：由中间相沥青为原料制备的高导热石墨膜的石墨化度较高、La和Lc更大。高结晶石墨块、高导热石墨片、高导热石墨膜的热导率由高到低的顺序为：高导热石墨膜〉高导热石墨块〉高导热石墨片。     

脂肪酸相变储能材料热性能研究进展

在以往所研究的相变材料中,脂肪酸由于展现出优越的性能,得到了研究者更多的关注,但同样存在相变温度不适宜和导热性能差等热性能问题。本工作通过现有文献对脂肪酸相变储能材料的热性能进行系统分析,提出了脂肪酸与脂肪酸、脂肪醇及石蜡复合3种有效解决相变温度不适宜的方法;针对导热性能差提出了多孔材料吸附、添加碳材料或金属粒子和微胶囊化3种高效易行的强化传热方式,进而说明这一领域目前研究重点。同时,对脂肪酸储能材料的相变性能、导热增强方法及导热增强剂进行了比较,分析了各自的优缺点。最后,对脂肪酸相变储能材料热性能研究的不足之处进行了探究,并指出了制备出更多能应用于建筑节能和纺织等领域的脂肪酸相变储能材料和着重研究脂肪酸与石蜡的复合等进一步研究方向。     

Thermal conductivity augmentation of composite polymer materials with artificially controlled filler shapes

Plastics or polymers of high thermal conductivity are highly desired in various industries. Adding fillers of high thermal conductivity to the base materials is a solution to make composite plastics of high thermal conductivity. Previous researches were focused on increasing the thermal conductivity of the composite materials by increasing the filler content and the thermal conductivity of the fillers. Relatively little attention was paid to the optimization of filler shapes. In this study, the effects of the filler shapes on the thermal conductivity of the composite materials are investigated, where the filler shapes are artificially designed. Heat conduction between the base materials and the artificially designed fillers is modeled. It is found that the filler shapes have great impacts on the effective thermal conductivity of the composite materials. Of the various shapes, the double Y shaped fillers are found to be the best choice for composite materials in which the fillers are distributed randomly. In future industrial applications, new filler shapes, such as double Y, Y, quad Y shaped, I and T shapes should be specially produced to replace the traditional fillers shapes: particles, fibers or slices. At last, composite materials made of paraffin wax and steel fillers of ten shapes are fabricated to simulate and validate the results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39550.     

High thermally conductive PLA based composites with tailored hybrid network of hexagonal boron nitride and graphene nanoplatelets

Bio‐based polymers and multifunctional polymeric composites are promising for the development of new environmentally sustainable materials and are becoming increasingly popular compared to their oil based counterparts. This research aims to develop new multifunctional bio‐based polymer composites with improved thermal conductivity and tailored electrical properties to be used as heat management materials in the electronics industry. A series of parametric studies were conducted to clarify the science behind the hybrid composites' behavior and their structure‐to‐property relationships. Using bio‐based polymers [e.g., polylactic acid (PLA)] as the matrix, heat transfer networks were developed and structured by embedding hexagonal boron nitride (hBN) and graphene nanoplatelets (GNP) in a PLA matrix. The effects of random uniform thermal hybrid networks of hBN‐GNP on improving the effective thermal conductivity (k_eff) of produced composites were studied and compared. Composites were characterized with respect to physical, thermal, electrical, and mechanical properties for practical application in the electronics industry. The use of high thermally conductive hybrid filler systems, with optimized filler content, was found to promote the composites' effective thermal conductivity to more than 12 times over neat PLA. The thermally conductive composite is expected to provide unique opportunities to injection mold three‐dimensional, net‐shape, lightweight, and eco‐friendly microelectronic enclosures with superior heat dissipation performance. POLYM. COMPOS., 37:2196–2205, 2016. © 2015 Society of Plastics Engineers