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This study investigates the relations between processing conditions and morphology of injection molded structural foams. The samples were produced by adjusting five process parameters (blowing agent concentration, mold temperature, melt temperature, injection pressure, and back pressure) at four different levels. The experiments were based on the design of experiments (DOE) analysis with a Taguchi the optimum conditions to produce high quality foams in terms of low skin thickness, small cell sizes, and narrow cell size distribution combined with low foam density and high cell density. The conclusions revealed that blowing agent concentration and injection pressure were the most influential factors. Using the optimum conditions predicted from the DOE, a validation test was performed and confirmed the results. POLYM. ENG. SCI., 49:949-959, 2009. (C) 2009 Society of Plastics Engineers, INTRODUCTION Injection molding of structural foam is one of the most suitable approaches to produce parts having a foamed core sandwiched between two unfoamed skins. This structure is known to [...]

The structure and mechanical properties of injection-molded polypropylene along the flow direction were investigated in this article. A remarkable difference was found in morphology and mechanical properties of the injection-molded parts along the flow direction. The three-layered structure (namely the skin, subskin, and core layer) showed a gradient distribution along the flow direction. The IR and WAXD results showed that the orientation of the subskin layer in the gate part is much higher than that in the far part. DSC analysis results indicated that the two parts (gate part and far part) of injection-molded bar has the same degree of crystallinity that should not be responsible for the mechanical difference of the two parts. According to the measurement of residual internal stress, there is large difference between the gate part and far part, which is the main reason leading to the difference of impact behavior. The annealing treatment eliminated the internal stress, so the mechanical difference between the two parts decreased and the fracture type of the far part changed from brittle to ductile. POLYM. ENG. SCI., 49:703-712, 2009. [C] 2009 Society of Plastics Engineers, INTRODUCTION Injection molding is one of the most widely used processing methods for the manufacture of plastic products. Because of the different thermomechanical history the melt undergoes, the injection-molded parts [...]

Solid freeform fabrication processes offer the manufacturing flexibility for tools with low thermal inertia and internal conformal channels for rapid thermal cycling in injection molding. This article analyzed each step of a rapid thermal cycling process and provided quantitative guidance for tooling design. The proposed design methodology was tested on a three-dimensional (3D) printed benchmark tool with truss support. Rapid cooling test on the benchmark tool resulted in the mold time constant shorter than 2.3 s and the cavity temperature uniformity better than 3 ° C. Preliminary tests demonstrated the technical feasibility of using a solid freeform fabrication process to fabricate low thermal inertia tools for improved heat management in injection molding. POLYM. ENG. SCI., 49:305-316, 2009. [C] 2008 Society of Plastics Engineers, INTRODUCTION Many thermoplastic manufacturing processes, such as molding and forming, involve repetitive cycles of heating, filling, cooling, and ejection. Rapid heating and cooling of the tool is always desirable for [...]

The injection molding of a microfeatured component, a diffractive optical element, was studied. The component has a wave-like pattern on the surface, with amplitude 0.5 µm and wavelength 3 µm. Two different polymers were used: a polymethylmethacrylate and an ethylene-norbornene copolymer (cyclic olefin copolymer). The topography was investigated using white light interferometry (WLI), atomic force microscopy (AFM), and scanning electron microscopy (SEM). A new WLI-based technique is proposed for rapid quantification of the replication of periodic surface patterns. This technique gives almost the same information regarding the degree of replication as AFM but can be performed much faster. Quantitative data on the degree of replication as function of processing conditions are presented. At optimal conditions, almost perfect replication is obtained using both materials. At suboptimal conditions, it is observed that the degree of replication increases with increasing injection velocity and increasing mold temperature, with similar characteristics for both materials. The difference in replication quality between the two materials seems to be related to the different temperature dependencies of the viscosities. POLYM. ENG. SCI., 48:2134-2142, 2008. [C] 2008 Society of Plastics Engineers, INTRODUCTION In his visionary talk 'There's plenty of room at the bottom' given in 1959 at Caltech, Richard Feynman suggested plastic materials as ideal candidates for rapid replication of parts [...]

For microinjection molding, it is envisaged that cavity surface roughness plays an important role in the cavity filling of polymer melt. This article presents an experimental investigation into the surface roughness effects on the flow area of a microthickness disk through injection molding. Three core inserts, each of which has different surface roughness on its two semicircular halves but with the same roughness mean lines, were machined and formed the mold cavity. The difference in flow area (or volume) between these two semicircular halves of the molded part was investigated by varying the mold and melt temperatures. Regressive analysis of the significance of mold and melt temperatures and cavity thickness on the surface roughness effects was carried out. Experimental results obtained indicated that the flow area on the smoother half is larger than that on the rougher half during cavity filling. For the same surface roughness, its effect on cavity filling is a function of mold temperature, melt temperature, and cavity thickness. An increase in mold temperature or melt temperature will result in smaller surface roughness effect on the flow area. When cavity thickness is reduced, the surface roughness effect will become more significant. Moreover, a larger difference in the surface roughness between the two semicircular halves of the insert will result in a larger difference in the flow area between the two halves of the molded part. POLYM. ENG. SCI., 48:490-495, 2008. © 2008 Society of Plastics Engineers, INTRODUCTION In recent years, plastic microparts have been used extensively in various fields such as medical technology, biotechnology, optics, telecommunication, and microfluidics. Examples of products include pressure sensors, biological reactors, [...]

The development of fiber orientation in injection molding was manipulated by a special molding tool, the RCEM mold, which imposes a rotation action by one of the cavity surfaces during the filling stage. Center-gated disc moldings were produced from glass fiber reinforced polypropylene with different cavity rotation velocities, inducing distinct distributions and levels of fiber orientation. The morphologies of the moldings were characterized by optical and electronic microscopy. The through-thickness profiles of fiber orientation were assessed by means of the orientation tensor, and the relationship between the processing thermo-mechanical environment and the fiber orientation was established. At high rotation velocities, the resulting fiber orientation pattern is mainly controlled by the rotational motion, inducing a much more homogeneous through-the-thickness fiber orientation distribution, with a preferential alignment on the circumferential direction. POLYM. ENG. SCI., 48:395-404, 2008. © 2007 Society of Plastics Engineers, INTRODUCTION The manipulation of fiber orientation during injection molding is a well-established route to enhance the mechanical properties and dimensional stability of glass fiber reinforced injection molded parts [1]. The [...]

Injection molding is one of the most common processes for cost-effective mass production of micro-plastic parts. When the dimensions of the part, and thus the cavity of the mold, are small, microscale factors which are normally neglected in the analysis of conventional injection molding may play an important role. This investigation addresses the effects of mold surface roughness on the injection of polymer melt, which is a non-Newtonian fluid, during the filling stage of microinjection molding. The surface roughness effect on the volume of the mold cavity is discussed. A simple, but effective model, to describe the conductivity and the specific heat of the surface roughness is proposed. Subsequently, by employing the finite volume method and the level set method, a numerical procedure incorporating the proposed surface roughness model to describe the flow behavior of the polymer melt in the cavity is implemented. Finally, simulation on the melt flow injected into a microdisk cavity is performed using the proposed model and the results are found to be in good agreement with experiment. POLYM. ENG. SCI., 47:2012-2019, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION Injection molding is one of the most common processes for cost-effective mass production of microplastic parts. Many researchers have carried out extensive numerical and experimental analysis on the optimization [...]

Ultrasonic technology provides a powerful and noninvasive method of in-process measurement during injection molding and extrusion. Changes in the velocity, attenuation and reflection coefficients of high frequency sound waves can be related to the state and conditions of the materials through which they propagate. The velocity of an ultrasonic wave changes with density and elastic moduli; this allows information on solidification and material properties to be collected during the molding cycle. The time of flight of the wave is a function of velocity and path length. This paper shows that it can be correlated with the residual wall thickness of polymer in the mold during gas assisted injection molding. POLYM. ENG. SCI., 47:1730-1739, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION An ultrasonic measurement technique has been employed during gas assisted injection molding (GAIM). GAIM is a high added value injection molding process involving partial filling of the injection-molding cavity [...]

High-frequency proximity heating was used to rapidly heat injection molds. The principle is based on the proximity effect between a pair of mold inserts facing each other with a small gap and forming a high-frequency electric loop. Because of the proximity effect, the high-frequency current will flow at the inner surfaces of the facing pair, thus selectively heating the mold surface. With this method, the electrical insulation layer beneath the mold surface can be eliminated, resulting in a mold insert made of a single metal. A mold with a cavity of 25 x 50 [mm.sup.2] was constructed with careful design on its electrical, structural, and thermal performance. Air pockets with reinforcing ribs were embedded right beneath the mold surface for enhancing the heating performance. The resulting mold cavity can be rapidly heated from room temperature to about 240°C in 5 s with an apparent heating power of 93 W/[cm.sup.2]. The new mold heating method was applied to thin-wall molding and micromolding, and in all testing cases, short cycle times less than a minute were achieved. POLYM. ENG. SCI., 46:938-945, 2006. © 2006 Society of Plastics Engineers, INTRODUCTION It is a common practice in thermoplastic injection molding that the mold temperature stays at a preset constant temperature well below the softening temperature of the thermoplastic polymer. Auxiliary [...]

A. I. ISAYEV, [*] The injection moldings of isotactic polypropylenes with various molecular weights were simulated using finite difference method. In the simulations, the unified crystallization model proposed in our [...]

INTRODUCTION The conversion of platelet-filled thermoplastics into finished products, such as injection and blow-molded articles containing aluminum flake, gives rise to visual defects associated with melt flow characteristics such as [...]

INTRODUCTION The sandwich molding process consists of injecting sequentially two or more polymers. The first polymer entering into the mold will be the skin material of the final part, and [...]