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Injection Molding

Experimental & Analytical Investigation of Incomplete Filling Defects During Hot Runner Based Inject
halid Alqosaibi | Chandresh Thakur | Hussam Noor | Alaauldeen Duhduh | Animesh Kundu | John Coulter, May 2021

A novel processing innovation called Rheodrop technology is introduced for hot runner based injection molding. The goal is to enable both optimized processing and properties of final molded parts. The technology applies a controlled shear rate to the polymer melt during and/or in between injection molding cycles by rotating the valve pin inside a hot drop nozzle. Doing so can eliminate defects such as incomplete filling which was focused on during this study. This issue was investigated through both simulation and experimental analysis. Moldflow software was utilized to study the effect of melting temperature on cavity filling. Acrylonitrile Butadiene Styrene (ABS) was chosen as a focus material, and three different melt temperature levels were selected. The cavities are perfectly filled at the highest melt temperature level with incomplete filling resulting at the lower levels. Implementation of the Rheodrop technology then produced consistent and complete filling throughout the melt temperature range studied.

Simulative Analysis of the Filling Process in the Two-Component-GITBlow-Process on Organo Sheets
Prof. Dr.-Ing. Elmar Moritzer | Michael Kroeker, May 2021

The combination of different special processes allows the production of complex hybrid component structures with simultaneous function integration, thus opening up a large portfolio of possibilities. One example of this is the combination of back-injection of thermoformed organo sheets with the GITBlow process. An organo sheet is back-injected by two components, whereby one of the two components is additionally formed by the GITBlow process. The separation of the two cavities during the filling process by the formed organo sheet is a challenge not to be underestimated. The investigations refer to the simulative analysis of the filling process of the cavities. Here, the melt displacement into the secondary cavity during the first gas injection and the influence of the separation of the two cavities are considered. Investigations show that the melt temperature, the gas pressure and the injection speed have the greatest influence on the filling of the cavity separation.

Evaluation of Pressure Reduction for Various Materials at Various Length to Thickness Ratios Using An iMFLUX® Constant Pressure Process
William F. Lawless III | Rick A. Pollard | Darien R. Stancell, May 2021

This paper will show that an iMFLUX® constant pressure process can significantly reduce molding pressure requirements compared to conventional velocity controlled injection molding while molding a part with an equal length to thickness ratio. A significant pressure reduction is observed for all materials; regardless of material type or family. All comparisons in this paper are based on the maximum achievable flow length of a conventional velocity controlled process for each material. 

Investigate on the Degree of Assembly for Components in an Injection Family Mold System
Tsai-Wen Lin | Chao-Tsai (CT) Huang | Wen-Ren Jong | Shia-Chung Chen, May 2021

The main target for Design for Manufacturing and Assembly (DFMA) is to integrate multiple components with multiple functions to minimize cost and efforts. In addition, a family mold system has been utilized in industrial manufacturing to make a series integrated components for years. However, there is very few information to the degree of assembly for a single component or components. In this study, we have tried to investigate the degree of assembly using a family mold system with two different components. The study methods include numerical simulation and experimental observation. Firstly, we have adopted packing pressure as the practical operation parameter to affect the variation of degree of assembly. Then the pre-defined characteristic lengths can be utilized to catch the degree of assembly. Results showed that when a higher packing pressure applied in injection molding, it will results in more difficulty in the assembly for Part A and B by numerical prediction. Furthermore, the experimental validation on the degree of assembly based on the characteristic lengths has also performed. The tendency is quite consistent for both numerical simulation and experimental estimation. However, there is some gap between simulation prediction and experimental measurement for the same operation condition setting. It is necessary to make further study in the future.

Characterization of In-Mold Shrinkage Using a Multi-Variate Sensor
Davide Masato | David Kazmer | Rahul Panchal, May 2021

The design of a multivariate sensor is detailed that incorporates a spring-biased pin for measuring in-mold shrinkage. The sensor also includes a piezoelectric ring for measurement of polymer melt pressure and an infrared detector for measurement of the polymer melt temperature and the local mold temperature. As a result, the multivariate shrinkage sensor can accurately measure cavity pressure, melt temperature, ejection temperature, various event timings, and in-mold shrinkage to closely estimate the total shrinkage. The performance of the sensor is validated with a design of experiments for a high impact polystyrene (HIPS) and polypropylene (PP).

Influence of Chemical Blowing Agents on the Filling Behavior of Wood-Plastic-Composite Melts
Elmar Moritzer | Felix Flachmann, May 2021

A major challenge in the injection molding of wood fiber reinforced thermoplastics, so-called Wood-Plastic-Composites (WPC), lies in the flow anomalies that occur during the cavity filling process. The melt front is brittle and breaks open at unpredictable points. Particularly at wood contents above 40 % by weight stream flow (jetting phenomenon) caused by wall slipping occurs more frequently, which in turn leads to undesired weld lines. In this study, an analysis method is presented, which allows a quantitative evaluation of the filling process. The methodology is applied to different WPC formulations. Higher wood content, low viscous matrix polymers and coarser particles lead to poorer filling behavior overall. In order to reduce the flow anomalies, chemical blowing agent is added to the WPC. This should reduce the viscosity and thus the elasticity of the melt. It has been shown that reducing the viscosity has no positive influence on the filling behavior. An improvement could only be achieved with the lowest viscosity formulation. However, the explanation for this is seen in the comparatively lower resistance of the melt to the expansion of the blowing agent, as a result of which the melt is pressed more strongly against the mold wall and wall slipping is thus rather suppressed.

Fischer-Tropsch Hydrocarbons as Processing Aids in Injection Molding: An Overview
Stefan de Goede | Pieter van Helden | Steve Torchia | Philip Richards, April 2021

Polymer producers and converters are continuously evaluating potential options to reduce costs by producing faster, reducing energy consumption, reducing scrap and improving article properties. Recently, however, sustainability and overall environmental impact have also become prominent themes for converters, as a result of the pressure to minimize the footprint of the plastics industry on the environment. Polyolefin blown film and injection molding are large polymer conversion market segments that have received significant attention in terms of equipment improvements and formulating principles. Processing aides are commonly used in blown film extrusion and injection molding. Specifically in injection molding, silicone spray is used to ease the removal of the article from the mold, thereby saving cycle time. Silicone spray is, however, difficult to remove from the final part. An alternative is to use higher molecular weight Fischer-Tropsch (FT) hydrocarbons as a polymer processing aide and mold release agent due to good compatibility with the polymer compound matrix. This paper gives an overview of the use of FT hydrocarbons as processing aides in injection molding. Examples of more than 15 years of experience in the global marketplace, ranging from the production of small to large articles, are shown. Formulating with these hydrocarbons allows the converter to reduce cycle time, produce faster to reduce labor, to reduce energy consumption and improve certain properties of the injection molded article. Ultimately FT as a polymer processing aide could be an important tool to a converter to reduce manufacturing costs and improve quality.

Comparative Study of Filled and Unfilled PLA Produced Via Injection Molding and 3D Printing
Chethan Savandaiah | Bernhard Plank | Julia Maurer | Juergen Lesslhumer | Georg Steinbichler |, April 2021

This study investigates the impact of two different processing methods, Injection molding (IM) and 3D printing (3Dp), on Neat/unfilled polylactic acid (NPLA) and the short carbon fibers (SCFs) filled polylactic acid (SPLA). Furthermore, the resulting processing conditions and its influence on mechanical properties, such as tensile, flexural, notched Charpy impact test, and heat deflection temperature (HDT) along with the process-induced effects, such as fiber length distribution and voids were studied. The process-induced voids were evident in all the computed tomography (CT) scans, 3Dp specimens have higher void volume fraction compared to no visible voids in IM specimens. Similarly, the mechanical test results such as tensile, flexural and notched Charpy impact test follow the trend for 3Dp SPLA and IM SPLA. On the contrary, 3Dp 0° and ±45° NPLA tensile test results are comparable to IM NPLA, whereas 3Dp 0° NPLA has the highest impact resistance compared to injection molded NPLA and SPLA as well as 3Dp SPLA specimens, indicating the annealing effect induced by the heated 3D printing bed along with increased void volume fraction. Furthermore, the HDT study indicates the maximum serviceable temperature of both NPLA and SPLA remained comparable regardless of the processing method. Moreover, the change in fiber length distribution for SPLA injection molded and extruded filament specimens were negligible.

A Valid Design Prediction Approach of 3D Metal-Printed Mold Manufacturing
Yann-Jiun Chen, May 2020

In plastic part production, 3D metal printing is a leading manufacturing method for fast, waste-less, and high-accuracy way for making molds with conformal cooling channels. In this automotive power supply test-seat assembly case, the development process combines injection molding simulation, 3D metal printing technology and real experiments to demonstrate an effective mold development approach. Simulation-driven conformal cooling design minimizes the mold temperature difference and significantly reduces part deformation from the traditional straight-line cooling design. Through 6 sets of distance detection, the product dimensions are optimized and can improve the fitting of the three assemblies.

An Investigation of the Crystallinity in Vibration Assisted Injection Molded Poly-Lactic Acid
Peng Gao, May 2020

Vibration assisted injection molding (VAIM) is a process in which a controlled oscillatory movement is introduced to the injection screw during injection molding. This research was focused on the effect of processing parameters on crystallinity and the crystal structures of poly-lactic acid (PLA) during VAIM. It was observed that vibration assisted injection molded PLA products have higher crystallinity than conventionally molded PLA products under similar conditions. Additionally, the cycle time for fabricating PLA parts can be reduced utilizing VAIM without significant loss of crystallinity. The growth of α´ phase of PLA during VAIM and conventional injection molding process was investigated utilizing an X-Ray diffraction technique. A slight phase change from α´ to α phase can be observed in VAIM samples fabricated under certain conditions. The mean size of crystal structures decreased as VAIM frequency increased to 30Hz.

Analyzing the Machine-specific Process Behavior for Automated Adaption of Setting Parameters
Pascal Bibow, May 2020

As injection molding represents a highly automated, but to the same extend complex manufacturing process to produce e.g. plastic parts without the necessity of post-processing, many efforts focus on compensating fluctuations and reproducing part quality. Injection molding simulation therefore offers the opportunity to determine a valid operating point even before start of production. However, the machine-specific process behavior and the individual machine setup limit transferability of simulated process parameters. Standardized interfaces like OPC-UA for continuous communication with the injection molding machine offer plenty of data from the running production process. Machine data about e.g. screw movements thereby reflect the real-time machine behavior. By analyzing the injection phase at varying injection flow, dosing volume and nozzle temperature with respect to the resulting part weight and the melt cushion, a machine-specific transmission behavior has been observed to adjust settings on different machines based on OPC-UA data.

Blending Scholarly Knowledge and Practioner Know-How To Successfully Injection Mold A Complex Part
Jeremy Dworshak, May 2020

A complex piece of sporting equipment was molded to customer satisfaction, meeting critical dimensions despite complicated tooling and the use of a crystalline resin. Combining modern simulation techniques and industry expertise proved to be a winning strategy in solving this challenge. The use of post-molding, warp controlling fixtures was completely eliminated from the legacy production process, leading to improved part performance and plant efficiency.

Direct Compounding of Long Glass Fiber-reinforced Plastics in the Injection Molding Process
Marius Wittke, May 2020

Currently, only specially treated and compacted carbon fiber recycles can be fed into the twin screw extruder. In this paper, different delivery forms of fibers are characterized in terms of the product quality. The differences between the fibers for twin screw extrusion is illustrated.

Comparison of Fiber Orientation Results of a Moldflow®-implemented pARD-RSC Model to µCT Scans
Sandra Saad, May 2020

Fiber-reinforced polymers have gained popularity in various industries over the past years, as they allow the reduction of products' structural weight without compromising on performance. The material and mechanical properties of such polymer composites are mainly dependent on those of the fibers included in the polymer matrix. It is therefore crucial to be able to predict the fiber orientation in the injection-molded part during the design process. Simulation techniques offer an efficient and cost-friendly way to perform such predictions early on in the development process. However, accurate simulative predictions necessitate precise material models. Therefore, in this work, the prediction accuracy of three fiber orientation models are compared to experimental fiber orientation data obtained from high-resolution x-ray micro-computed tomography (µCT) scans for two different geometries. The models used to describe the fiber orientation in the Moldflow® simulation are a Solver API-implemented pARD-RSC model with shear-fitted parameters, an MRD model with Moldflow® default parameters and an RSC model with Moldflow® default parameters. Through the performed comparison, it was found that today’s state-of-the-art models are still unable to predict the fiber orientation for variant flow regimes and different part geometries accurately. This shortcoming was mainly highlighted for elongational flows.

Creating A Skin-Core Structure With Foamed Phenolic Resins In An Injection Molding Process
Martin Bayer, May 2020

The research of foam injection molding for thermosetting materials is still in an early stage. Recent studies focused on the process of volumetric underfilling, but open pore structures and gradients over the flow path were obtained. This paper gives an insight into a novel process variant, which makes the production of skin-core structures possible. It is shown, how an expanding mold technique enables the production of components with a solid skin layer and a foamed core in an injection molding process with phenolic resins. In an experimental design, packing pressure time and mold temperature are identified as the main influencing parameters. Their impact on the skin layer’s height as well as the surface quality of the specimen are discussed. Finally, a model description of the processes leading to the formation of these foam structures is proposed.

Dynamic Variable Gate of Mold and its Application to Injection Molded Part Quality
Min-Chi Chiu, May 2020

As sensors evolve, their application has expanded. Mold related processes and technologies have become a focus of technology research and development. Mounting sensors in the mold cavity has become a trend in recent years. Since heretofore data has largely been limited to feedback data from the injection molding machine, control of the sensor data is the key to exploring the filling behavior of the molten melt in the cavity.In this study we created a dynamic variable-gate design in the mold. In combination with sensors to collect real-time data in the mold cavity during the injection stage, experiments were conducted to explore the course of shear heat and pressure drop generated by the melt passing through the gate when the gate thickness is varied. Therefore, the dynamic variable-gate design parameters such as gate thickness, advance delay time, and forward distance are discussed herein. To understand whether the gate thickness changes in the injection process, the influence of different parameters on the product shrinkage, product weight, and tensile strength are explored.

Enhanced Filling of Injection Molds By Microstructured Cavity Surfaces
Magnus Orth, May 2020

The main objective of this paper is to evaluate the influence of microstructured injection mold cavity walls on cavity filling. Thermoplastic material has been tested with a variety of micro structured molds. The area density of the structures has been varied and the flow length of the plastic melt using constant filling pressure has been measured. Microstructures applied on one side of the injection mold significantly extend the flow length of the molten plastic. In addition, depending on the processing viscosity, there is an optimum structure area density for the longest possible flow paths. This knowledge is therefore valuable in production to realize longer flow paths with the same machine technology.

Experimental Wear Data Acquisition for Condition Monitoring in Injection Molding Machines
Sebastian Fruth, May 2020

Condition Monitoring and Predictive Maintenance are big fields of research in the context of Industry 4.0. The ability of determining the state and predicting the lifetime of specific components can have a big economic impact. As datasets from production containing wear data are rare, it makes sense to generate this data in laboratory experiments. In this paper we present methods for implementing condition monitoring of injection molding screws and non-return valves. After developing key indicators, wear datasets are generated in laboratory experiments and the results are compared to the theoretical considerations.

Glass Reinforced PA 66 Compound with Improved Flowability for Thin Wall Applications
Mo Meysami, May 2020

Glass reinforced polyamide compounds are widely used in various applications. Many of these applications require a material with high flowability to allow the molders to properly manufacture parts with thin walls and complex geometries. In this study, a flow enhancing additive is used to improve the flowability of a glass reinforced polyamide 66 compound. Flow characteristics of the new formulation were studied using various characterization methods. Test results showed that physical and mechanical properties were maintained very well while flowability of the modified formulation was enhanced significantly compared to the control material.

Hot Runner Molding of Bioplastics and Recyclates
Davide Masato, May 2020

The interest for molding of bioplastics and recyclates is continuously increasing, not only with increased awareness of sustainability issues but also in response to regulatory mandates to reduce environmental impact. Bioplastics and biopolymers have been successfully derived from renewable resources, however their commercial adoption remains hindered by the lack of processing experience. Degradation issues are a potential concern for manufacturers, especially for hot runner injection molding. In this work, the performance and thermal stability of three commercial biopolymers and a recycled resin were characterized and compared to a reference synthetic polypropylene. The results indicate that bioplastics can be readily processed by hot runner injection molding by following design and processing rules similar to those conventionally implemented for synthetic resins. Minor degradation and quality issues are solved by routine optimization of processing parameters.

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