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Conference Proceedings
How Poor Selection of Materials, Design, Tooling and Design Errors Affect the Aesthetics of Plastic Parts and What Designers Need to Know About the Science of Color and Appearance - Part 2
Most engineers and designers come from the metal world. Therefore, many of them make assumptions on the predicted performance of plastic properties based on their metals background.
Unlike metals, the knowledge of color and appearance is extremely important in the case of plastics. Most plastic parts have dual functions— physical performance and aesthetics. Aesthetics are important since very few of the parts need to be painted or otherwise decorated if designed and manufactured with due diligence.
On the other hand, even if we are designing the most aesthetically critical metal components such as exterior automotive parts, we mostly choose the metals and alloys based on the physical properties, weight, and cost. The aesthetics are left to the paint specialist, who will in most cases find a paint system (primer, paint, and application method) that will meet the cost, durability, and cosmetic requirements. In other words, aesthetics and physical properties are quite independent of each other. A vast majority of metal parts meet their aesthetic and environmental requirements just by getting brushed, plated, chromate conversion coated or anodized.
Plastic parts not only need to meet the short-term color and appearance requirements, but also need to be resistant to long term color shift and fading.
This paper is in two parts.
Part 1 - Appearance and Color Factors
- Material
- Design
- Tooling and Processing
Part 2 –The fundamentals of Color and Appearance, Specifications, Measurement and Tolerances
Improving Surface Quality of An Injection Molded Part By Adapting Rapid Heating and Cooling Technology
In injection molding, the cooling stage has significant impact on the overall part quality. Cooling time is a major contributor towards the molding cycle time. In conventional molding, the mold is maintained at a constant temperature for the entire duration of molding cycle. To achieve this, coolant at a constant temperature is pumped through the mold cooling channels. A relatively new molding technology called ‘Rapid Heating and Cooling Molding’ (RHCM) involves varying the inlet temperature of the coolant fluid, so as to maintain the mold temperature relatively hotter during filling stage and reduce the surface temperature to ejection temperature during the packing and cooling stages of the injection molding cycle. RHCM is best achieved with mold designs that allow for conformal cooling ofthe mold. Some of the key benefits of using RHCM are mitigation of weld line effects, improvement in the weld line strength, achievement of high-gloss surface finish, reduction of molding pressures, residual stresses and clamping force.
In this paper, a comparative study is carried out between Conventional and RHCM molding to quantify the benefits of RHCM. The component chosen for this study is arepresentative center bezel part typically seen in automotive industry; a center bezel is used in the interiors of the car, and is required to be of high-quality surface finish and devoid of surface defects such as weld lines. Different materials, i.e., filled and unfilled grades from SABIC were used for this study. The molded parts were evaluated for gloss, L*, a*, b* values, visual defects, weld line appearance and its depth, scratch and mar resistance performance.
Improving Thermal Conductivity of CoContinuous Ternary Composites using Double Percolation Structure
The double percolation structure was used to produce thermally conductive polymeric composites including high density poly (methyl methacrylate) (PMMA)/polyethylene (HDPE)/ carbon nanofiber (CNF) and polypropylene (PP)/PMMA/boron nitride (BN) composites. Microscopy images showed that for both systems, most of fillers were in PMMA phase, confirming the hypothesis of the filler location by the thermodynamic theory. The thermal conductivity of the PMMA/HDPE/ CNF composite was higher than that of the HDPE/CNF and the PMMA/CNF composites with the same content of fillers loading when the CNF concentration got to 16 wt%. In addition, a similar phenomenon was also found when the BN concentration was above 10% in term of the PP/PMMA/BN composites. This study proved that double percolation structure was a useful way to improve the thermal conductivity of the polymer composites.
Improving Thermoforability of IPP Through Multilayer Coextrusion
While the flow forces governing primary melt-based polymer processing techniques, such as extrusion and injection molding, have been extensively studied, characterization of forcesin secondary processes such as thermoforming is limited. In this work we utilize multilayer coextrusion to create an extruded film with 100s of alternating linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP) layers; and by extension, 100s of interfaces. The combination of LLDPE, iPP, and these interfaces decreases the elastic storage modulus (E’) and broadens the rubbery plateau observed via dynamic mechanical analysis (DMA). The broadening of the rubber plateau is correlated with an observed improvement in LLDPE/iPP multilayer thermoformability compared to the homopolymer LLDPE and iPP films.
In Situ Injection Molding Thermotropic Liquid Crystalline Polymer Reinforced Nylon 6 Composites With MWCNTS Filler
Thermotropic liquid crystalline polymer (TLCP), Vectra B, and nylon 6 (PA6) along with multi-walled carbon nanotubes (MWCNTs) forming multi-scale composites were processed via injection molding, yielding in-situ nanocomposites. Within this research, optimal injection molding processing conditions, in particular the temperature profile, for the production of MWCNTs filler reinforced in-situ composites were established. The optimized processing condition was aimed to minimize thermal degradation of PA6 and maintain mechanical properties of the composite. With the help of one percent addition of MWCNTs filler, the strength of the in-situ nanocomposites in the transverse to fluid flow direction was enhanced by 28%, while maintaining other tensile properties. MWCNTs also could help reduce the anisotropy in the nanocomposite. The experimental tensile results quantitatively followed the estimated values by the rule of mixture, which indicated PA6 had no thermal degradation.
incorporating Unmodified Lignin into Flexible Polyurethane Foams Formulation
Industries that use polyurethane foam are looking for new sustainable and greener material to replace the petroleum-based polyols. Lignin produced as byproduct of pulp and paper and bioethanol industries is a suitable natural polymer to replace petroleum-based polyol in formulation of PUs. The emphasis was to study effect of different lignins obtained from different chemical processes and plant sources on the structural, mechanical and thermal properties of PU flexible foam and to achieve maximum lignin substitution. Additionally, we were interested to find correlation between lignin properties and performance of lignin-based PU foams to identify which lignin properties would affect the performance of developed lignin-based flexible PU foams and find the most suitable lignins for this application. It was seen that lignins isolated through organosolv process were better for PU fiexible foam applications. Overall, substitution of polyol with lignin increased compression strength, support factor, tear propagation strength and tensile strength of the developed PU foams.
Increasing the Process Window of Single-screw Extruders Operated with Regrind
A feed zone geometry was developed which adapts the specific throughput when processing regrind to that of virgin material without adjustable means. This leads to an enlarged process window of the extruder. For this, the filling zone of a single-screw extruder was increased and a conical section was implemented in the feed zone which was designed with helical grooves. The experimental investigations with a 35mm extruder show that a complete alignment of the specific throughput is possible depending on the enlargement of the filling zone, the grooving as well as the angle of the conical section. Here, the self-adjusting compression is used which varies depending on the material’s particle shape. Additionally, approaches for the three-dimensional description of the throughput behavior using the discrete element method are shown. The uneven shape of regrind particles is transformed into so called superquadrics.
Influence of Additive Type On the Properties of Polyolefin Blends
The aim of this work was to compare the effects of compatibilisation with different additives on the properties of polyolefin blends, made from different PP and PE grades, to mimic the mixed polyolefins found in post-consumer waste and investigate ways to improve the properties of these mixtures.
We found, that it is possible to compatibilize such polyolefin blends via the addition of ethylene-octen- or olefinic-block copolymers, where the type of copolymer shows an influence on the properties achievable. Also the blends show differently improved impact behavior, depending on the polyolefin which builds the major phase of the blend. These results show that it is possible to recycle such mixed polyolefin streams towards a suitable material with reasonable properties.
Influence of Variothermal Temperature Control on the Weld Line Quality of Extrusion Blow Molded Articles
Extrusion blow moulding enables the cost-effective production of plastic hollow bodies with complex geometries and different volumes. The majority of the components are used as packaging articles for the consumer goods- and food industries or as technical components, e.g. in the automotive and chemical industries. Extrusion blow moulded products are often failing at the weld line. The quality of joint depends mainly on the welding temperature. In order to improve this critical area, the IKV is investigating the use of variothermal temperature control of the blow mould. This brings the advantage of being able to locally increase the temperature of the blow mould. By using this temperature control concept, the results show a significant improvement in the quality of the weld line.
Inline Surface Activation in the Multi Injection Molding Process
Surface activation by plasma is a widely used process technology for connecting several components to each other. Usually, the activation takes place outside the injection molding machine as an additional step. With the development of the InMould-Plasma technology, the surface activation is fully integrated in the injection molding process, which eliminates an additional process step. Therefore, a plasma nozzle is directly connected to the mold. The plasma runs along a defined channel and activates the substrate surface in the closed mold. Through the technology, a strong bond of originally incompatible materials has been achieved. Without a surface activation, there is no adhesion of polypropylene (PP) and thermoplastic polyurethane (TPU). Studies on the peel strength of PP with TPU show that a treatment time of 5 s can drastically increase the material compatibility and achieve a peel strength of > 12.5 N/mm over the entire treatment area.
Intelligent Hybrid Hot Runner System for Optimized Polymer Products
A novel “Rheo drop” concept is developed to advance the process of injection molding with hot runner systems. It controls shear rate during injection molding process in the hot drops, allowing us to process the material at lower temperatures since the viscosity can be reduced by increasing shear instead of increasing the temperature. Also, maintaining lower viscosity at the hot drop will prevent slug formation that causes incomplete filling defects when manufacturing thin walled parts. This innovative idea is suitable for temperature sensitive materials as they might degrade when subjected to excessive heat for longer periods. Analytical and experimental investigations were performed to validate the developed “rheo drop” concept. Simulations were performed using ANSYS fluent and the results confirmed that the concept was able to produce a sufficient amount of shear to significantly reduce the dynamic viscosity between injection molding cycles. To validate the concept experimentally, a hot runner mold was modified to retrofit the rheo drop technology. The results showed that the new concept was able to solve one of the molding significant issues, which is a defect that is caused by incomplete filling.
Internal Damping and Its Variblity of Polyamide 6.6-Based Materials
This paper should help engineers and designers to make best possible use of PA66-based engineering materials in the context of components that are subject to vibration or the damping of vibrations in automotive. It will provide results from material testing, discuss these results and provide guidance, how these measurement results translate into components.
Proven concept to reduce the propagation of vibrations is the use of elastomer elements as damper for example at bearing points within the suspension system or in engine mounts. With thermoplastics being introduced to also the rigid parts of these systems, there is an additional potential to eliminate vibrations thanks to the viscoelastic behavior of this class of materials.
PA66-based materials are widely used for components in the engine compartment and the suspension system because of their capability to provide sufficient mechanical properties, thermal stability and chemical resistance. The goal of this paper is, to highlight the influence of glass fiber reinforcement, impact modification and humidity content on the damping behavior of PA66-based materials and to explain the variability of the internal damping as a function of these variables.
Investigation of Glass Bubbles iM16K Polyamide 12 Composites for Selective Laser Sintering
Selective Laser Sintering is an additive manufacturing technique that has been increasingly exploited in small-batch production to supplement traditional polymer processing techniques. Integrating specialized additives with PA12 SLS powder allows for the production of parts with tailored properties. 3MTM Glass Bubbles iM16K offers the possibility to reduce SLS powder cost, reduce part weight, and improve mechanical performance. Both intrinsic and extrinsic properties and their effects on SLS processing have been investigated. Tensile testing revealed the average Young’s modulus could be improved by 30% at 5 wgt% loadings, while maintaining ultimate tensile strength.
Keynote: Structural Characterization of Hybrid Composites with Graphene to Increase the Use of Light Weight
Injection molded composites have been used effectively in automobiles, but there is still a need for the development of lighter and greener materials. Hybrid composites, composites with multiple kinds and length scales of fillers, present the opportunity for exciting new material breakthroughs and the opportunity for finely engineer the performance of the manufactured materials. This study presents the structural testing results for a hybrid composite composed of a blend of glass fibers with graphene nano-platelets within a PA6 matrix. This blend is chosen to meet the high demands of the automotive industry for select under the hood applications. The results presented in this work demonstrate that the addition of less than 1% by mass of graphene nanoparticles can allow the reduction of glass fillers by nearly 25% with only a minimal reduction in performance while reducing the density increase relative to the neat polymer by nearly 20%.
Long- and Short-Term Tensile Strength and Morphology of Joined Beta-Nucleated Polypropylene Parts
This paper presents the results of static short-term and long-term tensile tests for beta-nucleated joined polypropylene samples by the hot plate welding process. In the present study different dimensionless joining displacements are accounted for. The results show that high short-term tensile strength does not directly transfer to high long-term tensile strength. The morphology of the weld seam in the joined samples is examined by means of transmitted and reflected light microscopy. For the dimensionless joining displacements of 0.75 and 0.95, stretched spherulites are obtained. X-Ray diffraction can be used as a tool for qualitative and quantitative analysis and eventually for differentiation of samples of various joining displacements.
Low- and High-Pressure Foam Injection Molding of Polypropelene/Talc Through Chemical and Physical Foaming Agents
Recent research in the area of advanced polymer processing has demonstrated the potential of foaming agents to introduce additional functionality within injection molded components. In this research, Talc filled Copolymer Polypropylene (PP) ISO standard tensile bars were produced through low- and high-pressure foam injection molding (FIM). Two chemical blowing agents (CBA), Microcell® 548 and TecoCell® H1, in addition to N2, a physical blowing agent (PBA), were processed at both low-pressure and high-pressure configurations. The 2 foaming configurations were used to create parts with weight reductions of 12.6% and 8.8%, respectively. The samples foamed through CBAs produced stronger mechanical parts in both tensile and flexural modulus. Also, low-pressure foaming through CBA produced parts that had near-perfect surface finishes, matching that of conventional molding. High-pressure foaming through PBA showed an improved surface finish compared to low-pressure (through PBA) but was still inferior to that of the CBA foamed parts.
Machine Calibration Effect on the Optimization through Design of experiments (DOE) in Injection Mold
Quality issue is one of the most important concerns in injection molding. However, before executing mass production, how to retain good quality is one of the crucial factors in injection molding. To retain good quality, it is commonly using CAE to assist from original design to revision and to fabrication. However, even using CAE, it doesn’t guarantee the quality factors obtained from CAE can be applied to real experiments. Moreover, the design of experiment (DOE) method has been utilized into injection molding product development. Today, there are still some challenges when people using DOE in injection molding. In this study, we have designed one injection molding system to define quality factor based on a circle plate. Then, we have tried to perform a series virtual DOE testing for injection molding using CAE to optimize the process condition. Furthermore, we also performed real DOE experiment to verify the virtual DOE concept. Finally, we will discuss about the machine calibration effect on the accuracy of quality comparison. Results shows that before machine calibrated, both virtual CAE-DOE and real DOE optimization can provide better quality for injection parts. However, there is some difference between the virtual and real DOE results. To find out why the difference between the virtual and real DOE results happened, we have investigated the machine feature and tried to calibrate it. After machine calibrated, the difference between the virtual and real DOE results has been improved by 58%.
Machine Learning and Multi-Objective Optimization of Industrial Extrusion
A three-level multivariate control system is described that transforms a vector of machine inputs to a vector of virtual process states, and then these virtual process states to key performance objectives. The multivariate system is implemented on a 150 mm (6 inch) screw diameter producing approximately 500 kg/hr of polyvinyl chloride (PVC) film having a nominal width around 1 m (37 inch) and a nominal thickness of 0.38 mm (0.149 inch). Validation is performed with respect to modeling and optimization of three performance objectives including production rate, energy efficiency, and process capability. The results suggest significant gains with respect to the Pareto optimality (efficient frontier) of energy efficiency and process capability.
Mechanical Properties of Electrospun Fibers from Ozone-treated Lignin
Ligninis a viableprecursor alternative for electrospun carbon fiber. Purification of lignin typically involves chemicals. Ozone treatment is an environmentally-friendly approach to purify lignin. In this study, electrospinning of untreated and ozone-treated lignin was conducted with polyethylene oxide (PEO) as an aid-polymerto form submicron fibrous mats. Morphology and mechanical properties of the electrospun fibers were investigated. Electrospun ozone-treated lignin fibers showedspherical shapes attached to smooth fibers, characterized as beads-on-a-string (BOAS) morphology. It was found that longer duration of ozone treatment resulted in decreased average fiber diameter while increasing bead density, changing spindle-like beads into spherical beads. Ozone treatment did not have significant influence on the strain at failure of the electrospun lignin mats. Bead formation reduced the tensile strength and the elastic modulusof the electrospun fibers. Medium ozone consistency and short reaction duration were found to be the optimum conditions where highest tensile strength and elastic modulus were achieved.
Method for Determining Cooling Time in Injection Molding Using Infrared Thermography
Injection molders face confusion about the best way to determine cooling time. Many methods exist to estimate cooling time, but disagreement among results and fundamental flaws create error that leads to extra work, long cycle times, and a loss of profitability for molders. This paper proposes a new method for determining cooling time at the injection molding machine using infrared thermography and DMA data to relate part ejection temperature to dimensional stability. Experiments showed evidence that dimensional stability is linked to material modulus, which would allow molders to choose cooling times based on required dimensional stability by relating measured ejection temperatures to specific modulus values using DMA data.
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