The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Advances in Injection Molding Process / Quality Control
Injection molding process/quality control has been an active research area for many years, especially when part quality requirement is becoming more stringent due to increasing applications of plastics. This paper reviews the state-of-the-art research and developments in injection molding control. It has been found that all the prior studies can be organized into a multiple-level structure system, which consists of one feedforward loop (process setup) and three feedback loops (machine control, process control, and quality control). The three feedback loops are cascaded so that the output from the previous controller becomes the command to the next controller. Numerous variables, models, and control methods have been proposed and employed for different levels of control. However, the real on-line quality control without human's intervention has not been realized primarily due to lack of thorough understanding of the relationship among machine, process, and quality variables and lack of transducers for on-line quality measurement. Based on the research progress to date, it has been concluded that process/quality model and quality sensors are the two most important areas for further advancement in injection molding control.
Evaluation of Weldline Strength of Injection Molded Polystyrene by Surface Milling
Weldline strength of injection-molded polystyrene was evaluated using surface-milled specimens. The surface including a V-notch on an adjacent flow weldline occurring behind an obstructive pin was mechanically milled off and its tensile strength was measured. The strengths of specimens milled 1/5 of the thickness off from each surface were almost the same independent of the distance from the pin. On the other hand, the strengths of specimens without milling decreased once and then increased along the flow direction. It demonstrated that the strength of weldline was dependent on the properties of the surface layer of weldline influenced by stress concentration effect of V-notch and effect of flow stagnation at the area near the pin. The size of the surface layer could be evaluated by the variation of milling depth. The tensile strength increased with an increase of milling depth up to an intrinsic value and hence increased little despite the specimen was milled off deeper. It demonstrated that there was an area in which the bonding of the resin was insufficient at the weldline interface below the V-notch. The depth of the area was ten times larger than the V-notch depth at the area near the pin and decreased along the flow direction.
Mechanical Properties of Weldline in Injection Molded PC/ABS
Relationship between morphology and mechanical properties of weldline in injection-molded PC/ABS blend was investigated by testing specimens sliced along the flow direction. The diameter of ABS particles at the weldline decreased along the direction from the center to the surface of the specimen. The most outside slice showed the lowest strength among all the slices due to stress concentration effect by surface v-notch. In contrast, the adjacent one exhibited the highest strength among all, then the strength decreased gradually toward the center. Thus, the decrease of the diameter of ABS particles coincided with the increase of the strength of the weldline.
The Effect of Processing Factors on Weld Lines in Injection Moulded Nylon 6 Nanocomposites
The effect of process factors on weld lines of nylon 6 nanocomposites was investigated. Eight process factors were evaluated: injection pressure, holding pressure, holding time, back pressure, screw rotational speed, cooling time, melt and mould temperatures. A modified L16 orthogonal array of the Taguchi method with three levels was designed to run injection moulding experiments using a smaller number of samples to determine the most influential parameters. The experimental results were analysed by sensitivity test signal-to-noise (S/N) ratio and analysis of variance (ANOVA). The results show that the principal process factors for single end-gated tensile samples are different to those of double end-gated samples when the weld line occurs. The important process factors of the single end-gated samples are injection pressure and mould temperature, whilst for the double end-gated samples are mould temperature and melt temperature. The temperature factor plays an important role in processing to heal the weld strength by promoting the ability of polymer molecules to diffuse across the weld line boundary, enhancing interfacial strength at the weld region.
The Effects of Tooling Surfaces on Injection Molded Nanofeatures
The composition and surface properties of tooling materials become more critical as the size of the molded features decreases. This work investigates the effect of tooling surfaces with micro and nanoscale features. These tooling surfaces were employed as inserts for micro injection molding. Insert materials included etched and coated silicon wafers with pattern depths of 600 nm and minimum features of 200 nm. Electroformed nickel-based digital versatile disk (DVD) masters were employed as a control because this tooling currently can reproduce features that are 140 nm in depth. The micro and nano-featured parts were molded with high flow polycarbonate over a range of processing conditions. Atomic force microscopy (AFM) was used to characterize the surface topography of molded samples. The goal of this study was to explore the effect of different tooling materials on molded plastic parts with nanoscale features in terms of replication quality and durability of mold surface.
Effects of Materials when Injection Molding Nano-Scale Features
Although micro parts and features are routinely molded, the performance of polymer melts is not well understood when the part wall thickness is less than 1 mm. In this study, the effects of molding conditions and material properties were determined for the replication of nanoscale features via injection molding. The nanoscale features were part of a thin insert incorporated into a micromold. The performance of high-flow grades of polypropylene, polystyrene, polycarbonate, and polymethylmethacrylate were examined using a design of experiments designed to investigate the effects of melt temperature, mold temperature, injection velocity, and packing pressure on depth ratio and surface quality. Atomic force microscopy (AFM) was employed to measure the molded parts. As expected, higher melt and mold temperatures provided better feature replication. Replication was also material dependent with polypropylene providing the best feature replication.
Injection Molding of Micro-Structured Surfaces
Communication and information technology are branches of industry with a high potential for growth and innovation. Micro-structured light guiding elements made from plastics can e.g. help improving display technology referring to illumination. On the one hand the investigations considered different polymers (PMMA, PC, POM, COC) and on the other hand several test structures. The processing parameters were varied systematically. Especially a high mold surface temperature is a precondition for the accurate reproduction of microstructures, but leads to increased cycle times. Therefore, within the investigations the use of a dynamic heating system by induction was analyzed to heat the cavity surface efficiently. The aim is to improve the molding accuracy and to reduce the formation of orientations in the molded part. Furthermore, new demolding technologies are analyzed using different demolding principles.
Water Assisted Injection Molding for Thermoplastic Materials
This study investigated the water-assisted injection molding of thermoplastic materials. The first part of this report was to develop a water assisted injection-molding system, which included a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. Two types of water injection pins were designed and made to mold the parts. The second part of this report is to test the moldability of the developed system on various thermoplastic materials, including polystyrene, polyethylene, polypropylene, and acrylonitrile-butadiene-styrene. A comparison has been made between the parts molded by water assisted injection molding and gas assisted injection molding. The final goal of this research is to gain better understanding of the moldability of water assisted injection-molded parts, so that steps can be taken to optimize the process. This would provide significant advantages in improving parts quality.
In-Situ Observation of Birefringence during Vibration-Assisted Injection Molding
The phenomenon of birefringence has been widely used in the study of steady state and transient polymer flows as well as for stress analysis but has seldom been applied to the actual injection molding process. The current study utilizes a custom designed mold with built-in windows for observation of the polymer melt within the cavity. A polystyrene melt is viewed through crossed polarizers to reveal the birefringence pattern in the melt during the molding cycle. A high-speed CCD camera is used to record the birefringence patterns in real time throughout the cycle for subsequent analysis. The use of birefringence yields information regarding the molecular orientation of the polymer that can be compared under different processing conditions.
In-Mold Coating of Thermoplastic Substrates: Further Developments
In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. A computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow assuming the coating to be a power law fluid. A packing module is being added to further improve the pressure prediction and achieve desired coating thickness, the preliminary results are presented. Regression based statistical analysis is used to demonstrate the significance of various control variables used in a 1-D IMC flow condition. Data envelopment analysis (DEA) is used to find the optimal compromises between multiple performance measures (PMs) to prescribe the settings of IMC process variables in the 2-D IMC flow case and the location of the injection point on a real part. Case studies are presented for this purpose.
Multi-Component Laminate Moulding (MLM): Process Evaluation
Multi-component Laminate Moulding (MLM) is a novel injection moulding process that can produce multi-layered injection mouldings from at least two thermoplastic compounds. The principle of the process and initial results were presented at the Antec Meeting in 2002. This paper will describe recent developments in the process and the results from moulding trials carried out on combinations of thermoplastics including several engineering thermoplastic compounds. The discussion will highlight the potential benefits of the technology. Reference will be made to the relationship between the mechanical properties and the level of compatibility between the separate components. An assessment of the potential cost saving from the use of the MLM process with engineering resins will also be presented.
Rapid Mold Surface Heating/Cooling Using Electromagnetic Induction Technology
In this study, electromagnetic induction heating is developed to achieve a rapid mold surface heating. Both a single turn of circular coil and a spiral coil were properly designed for induction heating experiments on a flat steel mold plate. Mold surface temperature distribution during induction heating process was measured using infrared thermal image system. Simulation tool was also developed by integration of both thermal and electromagnetic analysis modules of ANSYS. The capability and accuracy of simulations on the induction heating were verified via experiments. To evaluate the practical purpose of induction heating on the real injection molding, a mold plate, roughly about an inset size of cellular phone housing, designed with four cooling channel design and running 12? coolant were utilized for the demo experiment. After 3 seconds’ induction heating, mold surface temperature increases from 110? to 180?. It takes another 21 seconds for mold surface to cool down to 110?. The rapid heating and cooling of mold surface temperatures using induction technology was successfully illustrated via both experiments and simulations.
Injection Family Molds Productivity Using CAD/CAE Tools
The main purpose of this study was to evaluate the efficiency of a injection family mold for produce security caps for pharmaceutical bottles using the computer aided design (CAD) and the computer aided engineer (CAE) tools. Such caps are made of two pieces: an internal and an external. A conventional four cavity mold with removable cores, as well as, an eight cavity family mold, both with an x" type distribution was evaluated. A manufacturing cost analysis for both molds was done finding the eight cavity mold as the cheapest one to be used for manufacturing such caps. The feasibility of these molds depends on the production cycle time the labor work shifts and the price of the injection mold."
Tool Development for Semiautomatic Design of Moulds
This paper presents the work developed for last years in TIIP, Associate Unit to CSIC, in order to make easier and faster, the task of designing a thermoplastic injection mould. During a mold design, there is a great amount of repetitive tasks that makes the designer loose a lot of time.The work presented consists of a semiautomatic software that covers the complete generation of the mould, according to standard components. It also allows the most suitable orientation of the part into the mould, according to specified criteria, and the generation of its parting surface, and cavities.The software has a very easy and intuitive running, and it follows the methodology of mould design developed in TIIP.
The Integration of Informational Functions in the Chain from Idea to Manufacturing of Molds for Injection Molding
Tooling has lived through substantial changes. The toolmaker has been, first of all, the designer and maker in one and the same person. Then, in the second part of the 20th century the division took place in the form of the increased specialization. Three function specialists: the mold designer, function makers of mold elements, and the assembling operators, toolmakers exist. The introduction of computers caused new redistribution of tasks. The mold designer activities (CAD) are followed by the mold manufacturing-planning phase (CAP), which includes also the software development for NC-equipment (CAM). The function element makers started to disappear they are materials machining-operators. A new reintegration, of part and mold designer functions will be discussed.
Thermoforming Prototype Mold Evaluation using a CAE Software
The main objective of this project consisted on the development of a measure container prototype and its mold, using Computer-Aided Design (CAD) / Computer Aided Engineer (CAE) / Computer Aided Manufacture (CAM) tools, through a 3D program and a simulation software of the thermoforming process, to determine the geometry corrections in the part design. The part prototype was carried out by using the material deposition rapid prototyping (RP) technique and the mold prototype was carried out for the machine technique. To evaluate both prototypes, the results obtained in a thermoforming machine and in a simulation software were compared.
Processing Strategies for Rotational Molding of Integral Skin Polyethylene Foams
This paper focuses on the study of the single-shot rotational foam molding technology for producing integral skin polyethylene foams. In this context, parametric studies over the mold rotational speed and in-mold temperature transition have been conducted. In conjunction with the utilization of the particle size difference between foamable and non-foamable resins, it has been found that increased mold rotational speeds can significantly improve the crucial separation of the time of formation of the skin layer from that of the foam layer. The proposed processing strategies secure the formation of a distinct layer of solid skin surrounding the high quality foamed polyethylene core.
Experimental Study on the Mixing and Segregation of Granular Particles in Rotational Molding
The nature of powder flow and its effect on particle deposition in rotationally molded parts is studied in this work. Experiments were carried out to see the effects of various parameters such as powder characteristics and operating conditions on the deposition pattern. Models for cohesive forces were developed and their effects on particle movements were estimated. Results indicate that the polymeric powders are cohesive enough to prevent size segregation at room temperature. When heating, the particles become sticky and a relatively new phenomenon of cohesive segregation is seen.
Single Site Polyethylene Resins with Enhanced Processability for Rotational Molding Applications
The performance of a new generation of single site polyethylene resins is compared to that of conventional Ziegler-Natta (Z/N) resins. Results from rotational molding trials showed that under comparable molding conditions, the mechanical properties of parts produced from single-site resins superior to those of Z/N resins. Moreover, the densification of the single site resins is complete at significantly shorter residence time in the oven versus Z/N resins. The processing window is wider and shifted to lower temperatures for the single site resins compared to the Z/N resins. The enhanced densification arises from faster dissolution of bubbles formed during the heating cycle.
The Effect of Surface Tension on the Sintering of Polyethylene Copolymers and Blends in Rotational Molding
Polymer sintering is a formation of a homogenous melt through the coalescence of powder particles during the heating cycle of rotational molding. Although the importance of surface tension in rotational molding has been recognized as one of the most important controlling parameters, there is only limited information on the role of surface tension in rotational molding.The objective of this work was to develop an experimental technique for characterizing the surface tension of materials used in rotational molding. The effect of surface tension on sintering was investigated. This paper summarizes the results of the effect of surface tension on the rotomoldability of selected polyethylene copolymers and blends.
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