Study on residual stresses of thin-walled injection molding

The residual stresses of the thin-walled injection molding are investigated in this study. It was realized that the behavior of residual stresses in injection molding parts was affected by different process conditions such as melt temperature, mold temperature, packing pressure and filling time. The layer removal method was used to measure the residual stresses at a thin-walled test sample by a milling machine. This simple method was demonstrated to be adequate for a thin-walled part. Moldings under different conditions were investigated to study the effects of the process conditions on the residual stresses of a thin-walled product using the elastic and viscoelastic models. The mold temperature was found to affect the size of the core region and residual stress on the surface layer of a thin-walled part in our studied range. The packing pressure was insensitive to the residual stresses in the studied high-pressure range. The residual stresses predicted by the viscoelastic model are about the same level and trend as compared to the experimental measurement.     

CE chips fabricated by injection molding and polyethylene/thermoplastic elastomer film packaging methods

This study presents a new packaging method using a polyethylene/thermoplastic elastomer (PE/TPE) film to seal an injection-molded CE chip made of either poly(methyl methacrylate) (PMMA) or polycarbonate (PC) materials. The packaging is performed at atmospheric pressure and at room temperature, which is a fast, easy, and reliable bonding method to form a sealed CE chip for chemical analysis and biomedical applications. The fabrication of PMMA and PC microfluidic channels is accomplished by using an injection-molding process, which could be mass-produced for commercial applications. In addition to microfluidic CE channels, 3-D reservoirs for storing biosamples, and CE buffers are also formed during this injection-molding process. With this approach, a commercial CE chip can be of low cost and disposable. Finally, the functionality of the mass-produced CE chip is demonstrated through its successful separation of phiX174 DNA/HaeIII markers. Experimental data show that the S/N for the CE chips using the PE/TPE film has a value of 5.34, when utilizing DNA markers with a concentration of 2 ng/microL and a CE buffer of 2% hydroxypropyl-methylcellulose (HPMC) in Tris-borate-EDTA (TBE) with 1% YO-PRO-1 fluorescent dye. Thus, the detection limit of the developed chips is improved. Lastly, the developed CE chips are used for the separation and detection of PCR products. A mixture of an amplified antibiotic gene for Streptococcus pneumoniae and phiX174 DNA/HaeIII markers was successfully separated and detected by using the proposed CE chips. Experimental data show that these DNA samples were separated within 2 min. The study proposed a promising method for the development of mass-produced CE chips.     

Device for non-disruptive taking of melt samples from a compounding process and direct injection molding

A concept for taking a sample from a polymer melt stream plus the direct processing of this melt to specimen is presented. Therefore, a melt sampling and direct injection molding (MSIM) device was developed. Process parameters were studied and the set-up was implemented successfully. Using the MSIM device, different thermoplastics were processed and provided specimen characterized. The mechanical material properties from samples of the MSIM process show a good consistency compared with data from conventional processes. The MSIM device can be used in production processes for quality control, e.g. color or mechanical properties, as well as in the field of research and development to reduce development cycles.     

Measurement and quantitative analysis of fiber orientation distribution in long fiber reinforced part by injection molding

The fiber orientation distribution is one of the important microstructure variables for thermoplastic composites reinforced with discontinuous fibers. In this paper, the long fibers in the injection molded part are measured in detail by micro X-ray CT. A three dimensional (3D) structure of the sample is built and two dimensional images are generated for image analysis. The orientation tensor of fibers is calculated in the flow plane. It shows a symmetric distribution of fibers through the thickness direction, which consists of outer skin, transition zone and the core. The skin layer is so thin that it has only one layer of highly oriented fibers. The core layer also has highly oriented fibers but the direction of fibers is different from that in the skin layer. Nevertheless, the clustering of the fibers is characterized quantitatively in the core. The transition zone can be divided into two subzones by the principal directions of the tensor.     

Non-destructive measurement of cavity pressure during injection molding process based on ultrasonic technology and Gaussian process

Non-destructive measurement of the cavity pressure is of great importance for monitoring, optimizing and controlling the injection molding process. However, to date, almost all researches have relied on embedded pressure probes, and holes have to be drilled in the molds. In this paper, a non-destructive cavity pressure measurement method is proposed based on ultrasonic technology and a Gaussian process. According to the pressure-volume-temperature profile, the cavity pressure of a given polymer can be treated as a function of the density and the temperature. Moreover, the cavity pressure is significantly affected by injection hydro-cylinder pressure. Ultrasonic technology is employed to detect the variation of polymer density during injection molding. The Gaussian process is adopted to model the functional relationships between the cavity pressure, the ultrasonic signal, the mold temperature and the injection hydro-cylinder pressure. Experimental results show that the proposed Gaussian process regression model has a better modeling performance than that of the neural network regression model, and the proposed measurement method is capable of measuring the cavity pressure at different processing conditions and measurement locations during injection molding. In general, the proposed method offers several advantages: (1) non-destructive, (2) flexible, (3) no wires, (4) low-cost, and (5) health and safety, so it has great application prospects in injection molding.     

On the difference in material structure and fatigue properties of nylon specimens produced by injection molding and selective laser sintering

This paper describes the influence of dynamic tension/compression loading on notched and unnotched nylon specimens fabricated by Injection Molding (IM) and Selective Laser Sintering (SLS). The main objective of this work is to analyze and describe the differences in material structure and fatigue properties of as-built nylon parts produced by IM and SLM from the same polyamide 12 powder. The differences in dimensional quality, density, surface roughness, crystal structure and crystallinity are systematically measured and linked to the mechanical fatigue properties. The fatigue properties of the unnotched SLS specimens are found to be equal to those of the unnotched IM specimens. The presence of pores in the sintered samples does not lead to rapid failure, and the microvoid coalescence failure mechanism is delayed. The notched specimens show more brittle failure and increased fatigue resistance which is caused by local notch-strengthening. The results enable improved understanding of the difference in material structure and fatigue behavior of selective laser sintered and injection molded polyamide.     

Process dependence of pressure-specific volume-temperature measurement for amorphous polymer: Acrylonitrile-butadiene-styrene

The process dependence of pressure-specific volume-temperature (pvT) measurement for an amorphous polymer, acrylonitrile-butadiene-styrene (ABS), was investigated. The influences of different measurement processes (heating, cooling, compression, and decompression with different rates) were considered in the pvT measurements. The pvT measurements of isobaric cooling and heating with different cooling and heating rates (2, 5, and 10 °C/min) and isothermal compression and decompression with different compression and decompression rates (up to 920 bar/s) were conducted. The testing temperature ranged between 40 and 230 °C and the pressure ranged between 20 and 2200 bar. The obtained results demonstrated that the pvT diagram will be significantly different depending on the direction in which the pressure or temperature is changing and also on the rate of the change. Isobaric pvT diagrams are different between cooling and heating. Fast cooling accelerates phase transitions, while fast heating reverses. Specific volume at the same pressure and temperature in decompression process is lower than that in compression. Compression and decompression leads to different pvT curves. Compression and decompression rates have different effects on specific volume in different states.     

Reinforcement of solid‐melt interfaces for semicrystalline polymers in a sequential two‐staged injection molding process

The solid‐melt interfaces between polyethylene (PE) and polyamide 6 (PA6) reinforced by in situ reactive compatibilization in a sequential two‐staged injection molding process has been studied in this work. The effects of the maleic anhydride grafted PE content and processing parameters, such as injection pressure, injection speed, melt temperature, and mold temperature, on the interfacial adhesion were investigated experimentally. The results of the interfacial adhesion characterized by lap shear measurement showed that the interfacial temperature and heat transfer between PE and PA6 interfaces play a very significant role in the bonding process. The fracture surfaces of the specimens prepared at different calculated interfacial temperature were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), which suggested that the fracture failure changes from adhesive to cohesive failure with increasing interfacial temperature. The contribution of crystalline parts of the in situ formed copolymers to the enhancement in interfacial adhesion also was determined by DSC analysis. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1112–1124, 2009     

Optimization of injection‐molding process for mechanical properties of polypropylene components via a generalized regression neural network

This study analyzed contour distortions, wear and tensile properties of polypropylene (PP) components applied in the interior coffer of automobiles. A hybrid method integrating a trained generalized regression neural network (GRNN) and a sequential quadratic programming (SQP) method is proposed to determine an optimal parameter setting of the injection‐molding process. The specimens were prepared under different injection‐molding conditions by changing melting temperatures, injection speeds, and injection pressures. Average contour distortions at six critical locations, wear and tensile properties were selected as the quality targets. Sixteen experimental runs, based on a Taguchi orthogonal array table, were utilized to train the GRNN and then the SQP method was applied to search for an optimal setting. The trained GRNN was capable of predicting average contour distortions, wear and tensile properties at various injection‐molding conditions. In addition, the analysis of variance (ANOVA) was implemented to identify significant factors for the molding process and the proposed algorithm was compared with traditional schemes like the Taguchi method and the design of experiments (DOE) approach. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimization of Processing Parameters for Minimizing Warpage of Large Thin-walled Parts in Whole Stages of Injection Molding

This study investigated total warpage of a type of motorcycle seat support made of polypropylene（PP） during the entire process of injection molding and free-cooling after demolding. Finite element modeling（FEM） analysis for injection molding and its associated thermal deformation was carried out in the study. The effects of processing parameters on warpage occurring in different stages were analyzed by Taguchi optimization method. It was found that packing pressure is the major factor that affects warpage in the injection stage, whereas cooling time is the major factor in free-cooling stage. From an overall evaluation, melt temperature affects the total warpage most, followed by cooling time, packing pressure, packing time and mold temperature. The result proved that optimum parameters for minimizing final warpage of the injected parts can be obtained only when the deformation in the entire manufacturing process is addressed in both molding and demolding stages.     

Orthogonal optical force separation simulation of particle and molecular species mixtures under direct current electroosmotic driven flow for applications in biological sample preparation

Presented here are the results from numerical simulations applying optical forces orthogonally to electroosmotically induced flow containing both molecular species and particles. Simulations were conducted using COMSOL v4.2a Multiphysics® software including the particle tracking module. The study addresses the application of optical forces to selectively remove particulates from a mixed sample stream that also includes molecular species in a pinched flow microfluidic device. This study explores the optimization of microfluidic cell geometry, magnitude of the applied direct current electric field, EOF rate, diffusion, and magnitude of the applied optical forces. The optimized equilibrium of these various contributing factors aids in the development of experimental conditions and geometry for future experimentation as well as directing experimental expectations, such as diffusional losses, separation resolution, and percent yield. The result of this work generated an optimized geometry with flow conditions leading to negligible diffusional losses of the molecular species while also being able to produce particle removal at near 100% levels. An analytical device, such as the one described herein with the capability to separate particulate and molecular species in a continuous, high‐throughput fashion would be valuable by minimizing sample preparation and integrating gross sample collection seamlessly into traditional analytical detection methods.     

Current-sensing atomic force microscopy for analyzing conformations and properties of polymer membranes for fuel cells

The three-dimensional structures of polymer membranes are different at surfaces and inside bulks, and thus, in general, physical/chemical properties are also different. Morphologies and properties of membrane surfaces are now visualized by current-sensing atomic force microscopy. The increase in performances of a single cell is discussed based on the three-dimensional structures of the polymer membrane, anion-exchange membrane as an example, used for fuel cells. Other reports on Nafion®, proton-exchange membrane, are also introduced to show the importance of this microscopic method.     

Optimization of a molecular mechanics force field for polyoxometalates based on a genetic algorithm

A stochastic technique based on genetic algorithms was implemented to develop new force fields by optimizing molecular mechanics (MM) parameters. These force fields have been optimized for inorganic compounds such as polyoxometalates (POMs) and especially for type‐I polymolybdate and polytungstate clusters. Focussing on the methodology of the development of the force fields, they were tested for the prediction of structural parameters, comparing the MM optimized structures with the geometry obtained after an optimization based on density functional theory. Results show that the genetic algorithm converges toward an optimum combination of parameters which successfully reproduces POMs structures with a high degree of accuracy. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Topographical properties of polymer films deposited in capillaries for electrophoretic separations of large organic molecules

Topography and thickness of hydrophilic polymer coatings of fused-silica capillaries for capillary electrophoresis (CE) were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and profilometry. Three hydrogels, poly(2-hydroxyethyl methacrylate) [poly(HEMA)], poly(diethylene glycol monomethacrylate) [poly(DEGMA)], and poly(triethylene glycol monomethacrylate) [poly(TEGMA)], were deposited using two procedures, either by simple physical sorption of the polymers, or by derivatization of the capillary wall surface with glycidyl methacrylate (EPMA) followed by polymerization of the appropriate monomers. The performance of the modified capillaries was tested under CE conditions (decrease in the electroosmotic flow, EOF dependence on pH, separation of milk and standard proteins). It has been found that the most important property of the polymer coating is its thickness, whereas its topography and the degree of its hydrophobicity are less significant. Film deposition by physical adsorption is preferable to polymerization on the derivatized surface.     

Preparation and characterization of nanometer‐thin freestanding polymer foils for laser‐ion acceleration

We report on the production and characterization of polymer‐based ultra‐thin (sub 10 nm) foils suited for experiments on laser‐ion acceleration in the regime of radiation pressure acceleration. Beside the remarkable mechanical stability compared with commonly used diamond‐like‐carbon foils, a very homogeneous layer thickness and a small surface roughness have been achieved. We describe the technical issues of the production process as well as detailed studies of the mechanical stability and surface roughness tests. The capability of producing uniform targets of large area is essential for advanced laser‐ion acceleration projects which are dealing with high repetition rate and extended measurement series, but might also be useful for other applications which require ultra‐thin and freestanding substrates of high quality. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1355–1360