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A rapid thermocycling blow mold with electric heating was used to produce automobile spoiler in the present work. In order to achieve high heating efficiency as well as uniform temperature distribution on mold cavity surface, a multi-objective optimization model was proposed and a hybrid method consisting of design of experiment (DOE), artificial neural network (ANN) and multi-objective genetic algorithm (GA) was developed to optimize the heating system of the mold. The results showed that the method can effectively give the optimal values of design variables. Further, the temperature distribution uniformity on the mold cavity surface was largely improved and the heating efficiency was also guaranteed by using optimal design results.
The use of in-mold pressure and surface temperature sensors was investigated to determine whether they reduced variation in part weight when variation in material viscosity and check ring leakage were introduced to the process. Velocity to pressure transfer when the part was not quite full (2-stage, pack with second stage), after the part was packed with a fast velocity (2-stage, pack with first stage), and after the part was packed with a slow velocity (3-stage) were the injection strategies evaluated. It was found that surface temperature sensors toward the end of fill were the most beneficial in all cases studied.
Crosslinked plastic parts demonstrate prominent performance advantages over the non-crosslinked articles for a wide array of applications. New crosslinkable polyethylene compositions were recently developed which showed outstanding processibility and excellent thermal and mechanical properties, such as increased impact strength, high modulus, and enhanced environmental stress cracking resistance (ESCR). The advancement in balance of melt processibility and solid properties is ideally suited for the rotational molding process, opening opportunities to produce high-performance end-use products, including sporting boat, large agricultural and chemical containers, all-plastic cars, and other outdoor products.
Shawn Shi, Ramani Narayan, Shilpa Manjure, May 2013
Polylactic Acid (PLA) is the most widely available, renewable and compostable polymer with several unique features. However, PLA is poor in its ability to withstand elevated use temperatures above 55 °C. As such it is common practice to either compound PLA with additives that improve its heat deflection temperature or increase its crystallinity in mold or in an extra annealing step for use in injection molded applications. The objective of this research was to study the crystallization of three PLA grades and its effect on thermal properties including compostability. Crystallization was studied using DSC and Talc was used as a nucleating agent. Crystallinity was found to vary from 25% to 60% for the various grades. The PLA was converted into test bars and cutlery and its heat distortion temperature was tested before and after annealing. Additionally, the crystallized cutlery was sent to a local composting facility and was found to disintegrate within 4 weeks, which is much sooner than the requirements of the ASTM D6400 standard of 12 weeks.
Friction behavior of polyethylene terephthalate (PET) in either its amorphous or semi-crystalline form can depend on several factors. Surface microstructure and the resulting forces (Van der Waals), residual stress, the molecular weight distribution (MWD), and contaminants can influence polymer friction. A semi-crystalline polymer, PET exhibits an interesting microstructure sensitive to processing. PET is used for a range of applications with different forms. In some cases it is essential to determine the friction coefficients on molded parts. The current work presents a unique fixture built for measuring the friction of amorphous PET in the form of bottle preforms and stretched PET in the form of empty bottles, collected from high speed injection stretch blow molding (ISBM) equipment. The test frame was developed to accommodate samples with a range of contact areas, contact force, and time. The friction behavior of polymers is known to be dependent on the time and speed of the test. In the current work, dynamic friction between the molded parts were measured at a fixed rotation speed (13 RPM) and averaged over multiple samples. Data has been collected across several variables including change in chemistry, MWD, and processing changes related to cooling time. Friction on amorphous parts was higher than semi-crystalline ones. Time dependent friction behavior was observed irrespective of the microstructure. This suggests the presence of transitory micro surface features, at least on pristine surfaces.
A novel combination approach to producing quality foamed injection molded parts has been investigated. By combining extruded, gas-laden pellets with microcellular injection molding, the processing benefits and material characteristics of using both nitrogen (N2) and carbon dioxide (CO2) as co-blowing agents can be realized, thus yielding features superior to that of using either N2 or CO2 alone. Using an optimal content ratio for the blowing agents, as well as the proper sequence of introducing the gases, foamed parts with a much better morphology can be produced. In particular, extruding N2 gas-laden pellets, followed by microcellular injection molding with higher amounts of CO2, produces a cellular structure that is very fine and dense. In this paper, the theoretical background is discussed and experimental results show that this combined approach leads to significant improvements in foam cell morphology for low density polyethylene (LDPE), polypropylene (PP), and high impact polystyrene (HIPS) using two different mold geometries.
During the demolding process, high ejection forces can cause a local damage of the plastic part. The plastic part design as well as the design of the demolding system can be verified according to occurring stresses in the part by applying an integrative simulation already in early stage of the product development. This approach consists of a coupling of injection molding simulation and structural simulation. That way it is possible to take account of the process influence on the residual stresses in the plastic part, which may increase the contact pressure between part and mold core. For high ejection speed, it is possible to model a strain rate dependent mechanical material model to get a higher accuracy of the stress results. The validation of the simulation results in real injection molding trials show a good accordance concerning the measured and simulated demolding force.
The numerical simulation of fiber orientation during compression molding (CM) is a crucial and valuable tool for predicting the mechanical reliability of the final part. Considering LFT, advanced models are necessary to obtain accurate results for fiber orientation. The objective of our research is to verify new models which consider reduced strain closure (RSC) and anisotropic rotary diffusion (ARD). Since the initial fiber orientation in the charge will be considered, the first step of this project is to measure it. Using micro computerized tomography (?CT) and Volume Graphics’ (VG) VGStudio MAX image processing software for CT data analysis, the initial fiber orientation of the charge will be obtained. With the help of interpolation functions such as radial basis functions (RBF) the initial fiber orientation can be evaluated at each node of the charge mesh in the CM simulation. Model parameters are fitted by matching the experimental fiber orientation results.
Foamed rubber profiles have found widespread industrial applications. Their cellular structure offers savings potential with respect to component weight, material consumption and costs. The foam structure is generated using chemical blowing agents, which are added to the rubber mixture before processing. Foaming and vulcanisation occur simultaneously in the curing unit. Both processes are adjusted by modification of the rubber mixture, which is currently state of the art for the calibration of the foam quality. There are little systematic approaches to an optimisation of the cellular structure during processing. In a current research project, correlations between processing parameters, polymer structure and foam structure of chemically foamed rubber profiles are systematically analysed and evaluated. A lab scale pin barrel extruder is used for production of chemically foamed rubber profiles with an EPDM-based rubber compound and Azodicarbonamide (ADC) - based blowing agents. In first experiments, the thermal stress of the rubber compound during processing and the extrusion speed have been identified as influencing factors on the cellular structure. A high thermal stress caused by increased processing temperatures leads to a faster scorch of the compound and thus to finer cellular structures with smaller average cell sizes and higher cell densities. With increasing extrusion speed, a finer cellular structure is formed.
A methodical analysis of influencing factors on the cellular structure allows an optimisation of the foamed profiles in terms of their cellular structure and will lead to a guideline for processing. Primary objective of further investigations is the analysis of influencing factors of the curing equipment used on the profile quality.
Silicone rubber profiles are used in an increasing amount of applications, for example in sealing or damping technologies. A cellular structure of the silicone rubber profile enhances the damping properties and leads to a reduction of component weight, material consumption and cost at the same time. For production of cellular rubber profiles, the use of chemical blowing agents is state of the art. However, physical blowing agents such as nitrogen offer ecological, economical and procedural advantages. So far, an application of a physical foaming process on silicone rubber has been difficult due to the sorption properties of the material.
In a current research project, a continuous foaming process for silicone rubber is developed using a modified lab scale extrusion plant. A constant foaming process was realised in first experiments. The silicone rubber profiles are analysed in terms of cellular structure, surface quality and density. Experimental investigations show that the amount of blowing agent injected has a significant influence on density, foam structure and surface roughness. The use of a nucleating agent improves the cellular structures in terms of a smaller average cell size and increased homogeneity. Besides, the foam structure can be influenced by the pressure in the extrusion die. Primary objective of further investigations is the analysis of the influence of silicone rubber material properties on the profile quality.
Christian Hopmann, Clemens Behmenburg, Ulf Recht, May 2013
Injection molding is the most important process to manufacture complex polymer parts. Today, however the injection molding of elastomers almost entirely produces solid workpieces. Functionalized complex hollow components, e. g. for the conduction of medias, are often manufactured in costly multistep processes. The projectile injection technique offers a new approach to easily produce elastomers in a one-step process into complex hollow parts.
In addition to the well-known process variations of the gas (GIT) and water injection technology (WIT), the projectile injection technology (PIT) provides special advantages for the production of elastomeric continuous fiber reinforced hollow bodies, especially considering the residual wall thickness. When using the PIT, a projectile is initially placed on an injector. The melt is injected into the mold cavity afterwards. Subsequently a fluid is then injected into the component interior. The PIT uses the projectile for the actual melt displacement. It is driven by means of the fluid through the device and thereby forms the interior cavity.
Because of the fundamentally different mechanism of melt displacement and cavity formation when using the PIT in comparison to GIT or WIT, in thermoplastic processing standard materials which do not need to be specially modified for FIT can be used. So far, the PIT has not been used for the manufacturing of elastomeric hollow bodies. The target of ongoing investigations is to clarify whether or not the PIT is suitable for elastomeric processing.
Avraam I. Isayev, Tian Liang, Todd M. Lewis, May 2013
The present study is devoted to ultrasonic devulcanization of tire rubber particles of 10 and 30 meshes by means of a new ultrasonic twin-screw extruder. Ultrasonic amplitude and devulcanization temperature were varied at a fixed frequency of 40 kHz. The die pressure and ultrasonic power consumption during devulcanization were recorded. Degree of devulcanization was investigated by measuring the crosslink density, gel fraction and revulcanization behavior. Rubber of 30 mesh exhibited a lower die pressure and higher degree of devulcanization than those of rubber of 10 mesh. Due to the higher level of devulcanization and lower viscosity of devulcanized rubbers at higher amplitudes, the temperature of devulcanized rubbers at the die was reduced with an increase of the ultrasonic amplitude. Cole-Cole plots, crosslink density and gel fraction of devulcanized and revulcanized rubbers, revulcanization behavior, and modulus of revulcanizates separated in two distinct groups based on the level of devulcanization and effect on molecular structure of devulcanized rubber. Revulcanizates with a greater degree of devulcanization exhibited higher elongation at break, while those with a lower degree of devulcanization exhibited higher strength and modulus. Revulcanizates of rubber of 30 mesh exhibited a consistently higher elongation at break. The normalized gel fraction versus normalized crosslink density was described by a unique function independent of the processing conditions and rubber particle size.
Joamin Gonzalez-Gutierrez, Pavel Oblak, Bernd S. von Bernstorff, Igor Emri, May 2013
Polyoxymethylene (POM) is considered a high performance engineering polymer with many applications primarily in the automotive industry. Currently, POM has also found uses in powder injection molding (PIM) technology, where it acts as a carrier medium for metal or ceramic powders during an injection molding process, it is later removed during the debinding step and a solid metallic or ceramic piece is obtained after sintering. The main advantage of using POM in PIM technology is the faster debinding process compare to polyolefin-based feedstock, since POM sublimates into its monomer directly when exposed to an acid vapour. During the process of PIM, the binder has two contradictory requirements: viscosity should be as low as possible when in the molten state, but mechanical properties in the solid state, like toughness, should be as high as possible. One way to lower the viscosity is to use POM with lower molecular weights. It was observed that POM’s viscosity increases with average molecular weight (MW) at a faster rate than impact toughness and it is suggested that a MW of around 40000 g/mol provides the most appropriate combination of strength and fluidity.
Christian Hopmann, Anika van Aaken, Ivo Erler, May 2013
Ultrasonic welding of thermoplastics is a well known and well established industrial process. One of the advantages of this joining process is the extremely short welding time. A disadvantage is the tendency of formation of loose particles during the welding process. Especially in the field of automotive and medical technology there are high demands to the quality and appearance of joined parts. Besides the weld strength the optical appearance of the weld seam and the contamination of the production area can affect the choice of the joining technology. In order to remain competitive the ultrasonic welding process has to be improved.
Investigations at the institute of plastic processing show, that the formation of loose particles during the welding process can be minimized by making use of an infrared preheating.
Because of the preheating the first phase of the ultrasonic welding process - when the particles are abraded – can be shortened or even avoided entirely.
Christian Hopmann, Clemens Behmenburg, Torben Fischer, Anna Funk, May 2013
The rapid developments in microsystems technology over the last decades have led to an increased demand for micro components in various areas of everyday life. Due to their complexity and low component masses additional requirements must be considered for the injection molding of micro components made of thermoplastics. Especially the reproducible plasticizing of the required amount of material is still a major challenge for conventional plasticizing units. Hence these units are not designed for a micro-oriented production, the required micro component qualities can only be achieved at the cost of an increased material consumption.
In recent years, micro injection molding machines that are specifically designed for the production of micro-molded parts have been developed. These machines often separate the injection from the plasticizing by utilizing a separate injection system. This system is adapted in its dimensions to the small injection volumes and thus permits a better overall resolution of the injection process while reducing the material throughput at the same time. These Systems, however, show procedural disadvantages. Besides the increased technological complexity of these systems, the desired homogenizing of commonly used three-section screws is not achieved.
This poster presents a new plasticizing concept developed by the Institute of Plastics Processing (IKV), Aachen, Germany, in corporation with ARBURG GmbH + Co KG, Loßburg, Germany. The concept, the so-called ‘inverted plastication’, is based on the kinematic reversal of the screw flights’ arrangement. It is characterized by the position of the screw flights, which are attached to the inside of the plasticizing cylinder. This also includes the feed section which provides sufficient flight depths for standard granulate. The injection piston is mounted coaxially within the cylinder. Due to the lack of the screw flights the injection piston is exposed to lower mechanical stresses and therefore featu
Christian Hopmann, Anna Funk, Johannes Marder, May 2013
For the reliable design of statically or dynamically loaded lightweight structures made of fibre reinforced plastics (FRP), a wide knowledge of the material-specific failure behaviour is necessary. Depending on their loading conditions laminates made of FRP fail by one of the macroscopic failure modes named fibre fracture, inter-fibre fracture or delamination. When structures made of FRPs are designed to be used in load bearing applications the evaluation of their load carrying capacity in compression parallel to fibre direction is of primary interest. For this purpose, a vast number of research investigations, whose main objective is linked to determining the compression strength of a structure out of FRPs, has been carried out. Influencing factors, which have been considered, are fibre properties, fibre volume content, non-linear matrix properties, interface properties, residual stresses, fibre misalignment and ply waviness.
An additional influence factor which has not yet been discussed in literature is the influence of the load history. Shear loading and loading transverse to fibre direction lead to microscopic damages – so called micro-cracks – which accumulate in fibre-reinforced plastics at increasing static load or cyclic loading conditions long before the first macroscopic damage occurs. Furthermore, they influence the compression strength parallel to the fibre direction. In this poster results of a numerical model will be presented. The model allows for the investigation of the effect of micro-cracks on the fibre longitudinal compressive strength. The micro-cracks are introduced in form of fibre/matrix debonding as well as matrix cracking. The results show, that micro-damage highly affects the fibre longitudinal strength properties, depending on the extent and the location of the damage.
Increasing demands on plastic components, increasing cost pressure and the demand of a higher efficiency of the production lines lead, inter alia, to an ongoing development of mold technologies. The high requirements for blow molded hollow articles are met by using coextrusion technology. The core of a coextrusion blow molding machine is the die head. The main tasks of a die head are to divert the flow direction of the melt, to form a parison and to bring together the different polymer melts.
Common die heads are spiral mandrel dies, side-fed dies or spider-type mandrel dies. In current research activities at IKV the mold concept of a pancake die (stack die), which is already established in blown film extrusion, is tested in the coextrusion blow molding process. The focus of the research is on short material and color change times, low production costs, flexible applications of the mold as well as on the product quality. To simplify a possible industrial implementation, advantages and disadvantages of the die head concerning the extrusion of the parison, the wall thickness distribution and the properties of the hollow articles are worked out in comparison with conventional die heads. Practical testing of the mold is accompanied by the simulation of the flow process.
Inki Min, Seokkwan Hong, Jeongjin Kang, Kyunghwan Yoon, May 2013
As the adoption of injection molding technology increases, injected-molded optical products require higher dimensional accuracy and optical stability than ever before. Recently, many alternative injection molding techniques have been adopted to increase the stability of optical and dimensional characteristics such as injection/compression molding or rapid heating cycle molding. In the present study we have focused on the optical anisotropy, i. e. birefringence as a significant factor which affects the function of many optical components. Four different molding methods, i.e., conventional injection molding(CIM), injection/compression molding(ICM), rapid heat cycle molding (RHCM) and rapid injection/compression molding(RICM=ICM+RHCM) were chosen to investigate the optical anisotropy of 7 inch LGP by examining the gap-wise and in-plane distribution of birefringence and extinction angle. Gap-wise birefringence was measured at every 5 mm following the center line of flow direction from gate to the end of part by a polarizing microscopy and in-plane birefringence was evaluated under the polariscope optical setup. As a result, for the cases of CIM and RHCM-only the maximum value of in-plane birefringence was about -1.0 x 10-4 near the gate and decreases to almost zero, which is general behavior in injection-molded parts. On the contrary, for the cases of ICM and RICM the maximum birefringence was less than -0.5 x 10-5 near the gate, which is less than half of CIM and RHCM-only. And, for the gapwise distribution of birefringence, two extra birefringence peaks near the center region showed the effect of packing pressure, which came from the extra flow during packing stage in CIM. In RHCM, those two inner peak values were reduced because of relaxation of molecular orientation at rather high temperature. Furthermore, in ICM, quite constant distribution of birefringence of -2.75 x 10-5 could be found over the whole region except the wall. For the combination of compression and
Karim Bahroun, Henrik Behm, Christian Hopmann, Rainer Dahlmann, May 2013
Plasma processes constantly gain importance in the field of plastics processing. For instance, microwave (MW) enhanced plasma polymerization of silicon organic precursors is one of the most effective techniques to create permeation barriers (SiOx-coating) for plastics. These layers have extremely low permeation coefficients to several media. For the deposition of high barrier coatings on flexible substrates it is necessary that the barrier effect is maintained even under high strain. Unfortunately for some applications silicon oxide barrier coatings on flexible polymers are likely to fail at low strain levels.
One possible approach to overcome the poor elongation properties and to avoid a loss in barrier properties under strain poses the deposition of multilayer stacks. The main goal is to prevent crack formation and crack propagation through the entire multilayer stack by incorporating decoupling intermediate layers. Besides MW-excited plasmas also capacitive coupled plasmas (CCP) may be used.
In this study polyethylene terephthalate (PET) films are coated using different multilayer setups. Besides the excitation type for the deposition of the incorporated layers also the order of the stack forming layers is varied. Tensile tests as well as oxygen permeation measurements are carried out in order to identify the influence on barrier and elongation properties.
Karim Bahroun, Henrik Behm, Christian Hopmann, May 2013
Plasma processes constantly gain importance in the field of plastics processing. Due to their macromolecular structure plastics do not offer sufficient barrier functionality against oxygen and water vapor permeation, which is a key demand in a variety of applications. A common solution in plastics processing is the deposition of thin silicon oxide layers (SiOx) using microwave (MW) excited plasma processes. Unfortunately for some applications silicon oxide barrier coatings on flexible polymers are likely to fail at low strain levels.
One possible approach to overcome the poor elongation properties and to avoid a loss in barrier properties under strain poses the deposition of multilayer stacks. The main goal is to prevent crack formation and crack propagation through the entire multilayer stack.
In this study polyethylene terephthalate (PET) films are coated in a roll-to-roll process using different multilayer setups. Besides the material of the incorporated layers (silicon oxide / hydrocarbon) also the order of the stack forming layers is varied. Tensile tests as well as oxygen permeation measurements are carried out in order to identify the influence on barrier and elongation properties.
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