Molding processes comparison

A negative photoresist, SU-8 (Microchem), was used in the microreactor mold process for preparing the PDSM-E microreactors. When exposed to ultraviolet light, material may be removed via a wet etching process leaving high-definition features in micrometer dimensions. Additionally, a microreactor has been constructed in silicon onto which layer-bylayer self-assembled polyelectrolytes and enzymes are deposited. This system is being used for comparison with the PDMS-E system performance. 

There may be a requirement for surface finish, molded-in color, textured surface, or other conditions the plastic material is to meet (Chapter 2). The different processes may be able to provide only one surface to be smooth or both sides are smooth. Important that smooth be identified since it has many meanings to different people. Surface finish can be more than just a cosmetic standard. It can also affect product quality, mold cost, and delivery time. The Society of Plastics Engineers/Society of Plastics Industries standards range from a No. 1 mirror finish to a No. 6 grit blast finish. A mold finish comparison kit consisting of six hardened tool steel pieces and associated molded pieces is available through SPE/SPI. 

In comparison to sized molded containers from the blow-molded process, tubing process containers are made lighter in weight and provide more precisely controlled dimensions than blow-molded containers. The walls and bottom thickness are more uniform, and, hence, are more suited for use in automatic inspection systems. Clear and light-resistant glass compositions can be used in the tubing process. 

The dynamics of the molding process are determined through control of different but related machine elements such as motors, heaters, servovalves, etc. These machine elements are typically controlled via a hierarchical closed loop control architecture as shown in Fig. At the innermost level, only the machine elements are regulated by real time comparison of the desired machine set points with the machine feedback, such that the difference (or error) is used to correct the process. At the second level, state variables such as melt temperature and melt pressure are controlled to track prespecified profiles and provide more precise control of the state of the melt. At the outermost level, the machine inputs are adjusted by the machine operator to improve the quality of the part through specification of better set points given feedback of part quality. 

Microinjection Moiding for Microfiuidics Appiications, Fig. 6 Comparison of variotherm molding process and conventional molding process (Reprinting with permission) [17]... 

Gunes, l.S. and Ersoy, O.G. (2007) Effects of injection molding processing parameters on appearance related optical properties of styrene-acrylonitrile copolymer and comparison with... 

Table 2. Comparison of Injection-Molding Process for Various Products with and without Microcellular Structure ...

The injection pressure of injection-molding process decreases substantially because of the presence of dissolved gas, which lowers the viscosity. The cycle time is also substantially reduced because of the elimination of the liold and pack time and also because of about 25% reduction in cooling time. Table 2 presents a comparison of the injection-molding process with and without the dissolved gas (see Injection Molding). 

Second, the low melt viscosity of SPS formulations helps to reduce molded-in stress from the injection molding process. The data in Figure 15.7 show typical melt viscosities of SPS in comparison with other semicrystalline thermoplastics. The low melt viscosity of SPS results in low hydraulic pressures during injection molding, which helps to minimize molded-in stress. Low viscosity also contributes to SPS s ability to fill complex parts with thin walls and its relative lack of flash during injection molding. 

Fig. 3.30 Comparison of pressure die casting and injection molding processes for the manufacture of a critical surface finish.

S Stretch and S Crosby. A comparison of four closed-mold processes for the manufacture of large plastic parts. SPI Structural Plastics Symposium, Philadelphia, 1988. 

Table II. Comparison of Ceramic Injection Molding Process with Organic Binder and Preceramic Polymer Binder ...

Comparison of fiber length distributions for IP Retainers from various long fiber IM and ECM molding processes. 

An on-line technique for quantifying part shrinkage rate in the mold has been developed. The technique consists of measuring post-hold cavity pressure decay rate inside the mold during the injection molding process. A comparison of the technique as applied to amorphous and semi-crystalline polymers will be presented. 

In this investigation compounding and molding are integrated in order to minimize the exposure time of the natural fibers to temperatures above 200°C. The specific process entails twin screw extrusion with fiber addition half way down the extruder barrel, formation of a hot log and immediately compression molding a test plaque. The material also is coarsely ground and injection molded for comparison. 

In this paper, a true 3D thermal flow solver incorporated with the Giesekus viscoelastic constitutive model is developed to simulate melt flow in the injection molding process. The mold filling of a typical plate part is analyzed to study the flow-induced residual stress. Finally, the comparison between experiment and simulation for an industrial part demonsfiates the capability of the present methodology. 

Tensile bars were molded. Variation in process conditions was eliminated by using the same injection molding process based on a two stage velocity - position transfer process. Tensile bars were then aged for 140 days at 60°C in the ovens. Each tensile bar was then tensile tested to determine the changes in ultimate elongation in comparison to time aged. 

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