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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Control of the Thermo-Mechanical Environment in Injection Molding
A special tool was designed to allow the injection molding of flat disc geometry under a wide window of thermo-mechanical conditions. This can be achieved by controlled mechanical actions of one of the cavity molding walls, which is able to rotate and move axially (in steady or oscillating modes) during the filling and holding stages. The movements are assured by two servo-actuated electric motors allowing for an accurate control of a previously defined moving sequence.This injection tool was used to mold polypropylene under different thermo-mechanical set-ups, including a filling stage under cavity wall movements (in rotation, compression or expansion modes).Polarized light transmission microscopy and small angle light scattering (SALS) were used to observe and assess the moldings microstructure, including the quantification of the core spherulite size.The results evidence a very large range of microstructural patterns, whose features can be associated to the specifically imposed thermo-mechanical conditions.Furthermore, the evolutions of the microstructure along the disc radius was also assessed.
Study on Mechanical Properties and Material Distribution of Sandwich Plaques Molded by Co-Injection
In the sandwich injection molding process (co-injection), two different polymer melts are sequentially injected into a mold forming a skin/core structure. Sandwich molding is a well established method for producing parts with tailored mechanical performance.In this study the mechanical properties of co-injected plaques have been investigated. Virgin and short glass fiber reinforced (10 and 40%) polypropylene were used in six different combinations of sandwiched layers.Flexural tests were carried out on co-injected samples both parallel and perpendicular to flow direction. Optical microscopy was used to determine the core/skin thickness ratio and to calculate the composite flexural modulus, which was compared to the experimentally measured modulus.
Application and Potentials of Injection Transfer Moulding for Processing Thermoplastics
Injection Transfer Moulding (ITM) is a combination of the well known injection moulding and transfer moulding processes. Although the ITM process provides many advantages compared to conventional injection moulding, ITM is up-to-now only used for the processing of crosslinkable plastics. Research work at the Institute of Plastics Processing (IKV) made the ITM-Process accessible for the processing of thermoplastic materials by use of a newly developed mould.This paper discusses the mould technology, the course of the ITM process as well as the resulting part qualities. Besides, a comparison of the ITM process to conventional moulds with hot runner systems is shown.
Processing Studies in Reactive In-Mold Coating for Thermoplastic Parts
In-Mold Coating (IMC) has been successfully used for many years with Sheet Molding Compound compression molded body panels for the automotive and heavy truck industries. The next logical step is to extend IMC technology to injection molded thermoplastic parts. The objective of this paper is to research the factors that affect IMC flow, cure, and final part appearance. We discuss the rheology of coating candidates for thermoplastic parts and show how it affects the coating process. We use 2D non-steady heat transfer computer code coupled with chemo-rheological analysis to predict cure time. Finally, we present a case study to demonstrate the effect of part thickness and initial molding conditions on cycle time.
Prediction of Production Yields in Injection Molding I
Plastics molders need to continuously improve production efficiency to remain competitive. With increasingly tight specifications driven by Six Sigma quality initiatives, however, such efficiency gains are more difficult to maintain. This paper investigates the use of process capability indices for linear and non-linear regression models based on observed shrinkage data for polypropylene molding parts. Statistical validation of the yield estimates is accomplished through Monte-Carlo analysis. The discrepancy among results indicates that current practices in industry are poor, and care should be taken when using yield prediction methods for process optimization or development.
Novel High Flow Polymers and Their Applications
Novel high flow, low crystallinity polyolefin polymers offer a wide variety of attributes in a broad range of applications. The basic characteristics of these polymers and their usefulness in applications such as hot melt adhesives, flow modification, masterbatches and color concentrates, thermoplastic polyolefins (TPOs), and thermoplastic road markings will be discussed.
A Review of Diffusion in Automotive Polymers
This paper reviews the research over the past number of years on diffusion of fuels and fuel components into polymers used in near engine fluid and fuel delivery systems. The areas investigated cover Fourier Transform Infra-Red (FTIR-ATR) spectrometry and standard immersion procedures to measure the migration of fuel components in a series of fluoropolymer, polyester and polyamide materials at various temperatures.
Composite Material Transmission Cross Member Feasibility
General Motors’ next generation full-size truck frames are currently 80 pounds over their targeted weight. By replacing the current steel transmission cross member on General Motors’ full-size trucks through the application of a composite material transmission cross member, a substantial weight reduction will be achieved. Reducing the weight of General Motors’ full-size trucks will consequently increase the fleet-wide fuel economy for the company’s truck line, allowing CAFE requirements to be met more easily.
Novel Polymer Modifier Improves the Flow Characteristics of TPO Compounds
The enhancement of one particular performance parameter in a Thermoplastic Polyolefin (TPO) is often tied to a decrease in another property. This trade-off is evident in the balance between compound viscosity and impact performance. While low melt index elastomers will result in higher impact performance, the increase in compound viscosity is undesired. This paper discloses the utility of adding ultra-low viscosity modifiers to a TPO to achieve high flow while retaining impact performance.
Thin-Wall Injection Molding Using Rapidly Heated Molds
While gains are achieved via cost reduction and increased portability, thinner and smaller parts encounter more difficulty in molding because of the frozen layer problem. Due to coupled filling and cooling involved in standard injection molding, the relative contribution of the frozen layer in the total part thickness drastically increases as the part thickness decreases, thus resulting in increased difficulty of flow. Resin providers recommend using high speed and high pressure to alleviate the increased molding difficulty. However, the high-speed and high-pressure strategy appears inadequate when molding ultra thin wall parts and microstructures and cannot be efficiently used for delicate structures due to localized high stresses. A thin-wall molding process, wherein the mold surface is rapidly heated during the filling stage, was investigated in this paper. By rapidly raising the mold temperature to above the polymer melting temperature, thin-wall cavities can be easily filled without frozen layer induced flow resistance. Characteristics of this molding process were studied and compared with those of standard injection molding with the aid of molding simulation. A thin-wall molding process for an electrical connector is used to demonstrate the advantages of the new molding strategy over the high-speed and high-pressure molding strategy.
New Intermeshing Pin Mixer for Injection Molding
It is well known that reorientation of interfaces is key to efficient distributive mixing. However, how to achieve reorientation is not well known. This paper describes how interfaces can be reoriented in screw extruders and which method leads to the most effective reorientation. A new mixing device was developed to achieve highly efficient reorientation. This mixer can produce excellent mixing quality over a short axial length, as short as one diameter.This makes it possible to incorporate this new mixer into the non-return valve of an injection molding screw. Results will be presented from injection molding studies that compare the mixing action of the new mixing non-return valve to other mixing devices.
Molding of Microstructures and High Aspect Ratio Features
The challenge of replication of microstructures by injection molding depends very much on the size and the aspect ratio of the features as well as the size of the area covered with such structures. The filling of the structure has to compete with the filling of the underlying thicker substrate. The degree of filling of structures with high aspect ratios is investigated in a mold with a single continuous thin wall section attached to a flow leader for a large number of thermoplastic polymers. The degree of filling of the thin wall part is found to depend very much on the distance from the gate. Materials with the smallest pressure drop in the flow leader tend to give the best filling. Processing conditions do not have a strong influence except for the injection speed which can change the filling picture even qualitatively. It is found that the degree of achieved filling depends mainly on the local ‘time-to-pressure’, which is inversely related to the slope of the pressure rise curve. Numerical simulation overpredicts the achieved filling of the thin section for all investigated polymers.
Effects of Mold Gating on Shrinkage and Warpage of Injection Molded Parts
A laser printer frame, which is one of the tightest tolerance injection-molded parts in a printer, was simulated using injection molding simulation software fromMoldflow® Corporation. The part was simulated with different types of gating, including multi-gate cold and hot runner systems. The simulations were used to predict the part deformation using the different gating options. The optimized gating was determined by minimizing the part’s shrinkage and warpage. The optimized gating was used in the production mold for the frame. The predicted part shrinkage and warparge was in good agreement with the actual frame deformation.
Method to Determine Screw Performance and Product Quality during Manufacturing Process
During the extrusion process, whether it is film, sheet or injection molding, the need to obtain consistent quality and output requires an extensive quality control program. Unfortunately, these operations are time consuming and wasteful, often requiring many pounds of extrudate be expended before the desired result is achieved.Also, as extrusion equipment becomes worn, output rates decline and product quality gradually falls, often going unnoticed, until significant problems occur.Thirdly, when a new screw purchase is required, time-consuming laboratory trials are normally set up to evaluate screws from different manufacturers before deciding the best one for that particular operation.To quickly assess changes in operation conditions, whether from day-to-day running, equipment performance or assessing new equipment, a concept has been developed for an extrusion product, which utilizes the principal of mixing two colors to achieve a homogeneous third color. Observing the homogeneity of the third color mix and the flow pattern it generates will indicate the screw performance and the quality of the product. This is a quick, efficient way to test the process without sacrificing product or running time.A series of experiments was performed to evaluate two different screw designs in an injection molding process. In addition, molded parts from the same mold but the different screw designs were evaluated for quality consistency. In a separate trial, the amount of wear on production screws and barrels in a color compounding process were evaluated.This paper is based on these experiments and prospective new products.
The Role of CAE in the Design of a TPV Weatherseal System
Computer aided engineering has impacted the design process of weatherseal systems by reducing the number of prototypes needed to create a part. Finite Element Analysis is useful in predicting compression load deflection and frictional forces. Advances in FEA include how forces change over time and loading; stress relaxation, cyclic loading, compression set, and elastic recovery. This paper follows the design and prototyping of a unique weatherseal system and highlights the role of CAE.
Materials and Design Trends in Exterior Automotive Plastic Applications
This paper examines material and design trends in exterior automotive plastic applications. Plastics are widely used in exterior automotive applications. With the many different exterior applications, this paper concentrates specifically on fascia, body side moldings/ claddings, rocker moldings, wheel flare, and cowl vent leaf catchers. Examination of the material and design trends for these exterior applications is accomplished by benchmarking a number of OEMs. Insight into future material and design trends is gained by identifying the drivers.
Frozen Layer Effect on Measuring the Internal Cavity Pressure during Injection Molding
Experimental and theoretical studies of internal cavity pressure during injection molding of a spiral tube cavity were carried out. The frozen layer thickness and the evolution of internal cavity pressure were calculated using a commercial software (C-MOLD). The evolution of the internal cavity pressure was recorded during injection molding of polystyrene into a spiral tube mold. To explain the differences observed between the calculated and measured internal cavity pressure, a pressure correction factor (PCF) was introduced based on the plane stress theory. This factor was determined by analyzing the stress state in the melt and calculating the frozen layer thickness near the mold wall. The corrected and experimental pressures have been compared to validate the applicability of the pressure correction factor.
Study of Cavity Pressure and its Prediction during Injection Molding
Cavity pressure is an important injection molding parameter. It is regarded as a good indicator of molded part quality and injection machine control performance. It not only indicates the material condition in the mold but also affects the microstructure and part quality. On the other hand, almost all users prefer better accuracy of CAE simulation. The discrepancy results from neglecting some important factors, such as the pressure-dependent viscosity, variable heat transfer coefficient, and variable material properties. The goal of the study is to understand how pressure-dependent viscosity, heat capacity, heat transfer coefficient, juncture pressure loss and pvT-data affect pressure prediction, and the importance of each parameter. Then the method to improve the prediction accuracy will also be discussed.
Cooling Versus Process Stability: Stable or Not, Here We Ship
The combination of increased quality standards and just in time (JIT) production has yielded a series of issues for injection molders. While striving to maintain high quality and a JIT posture they are often faced with the potential for scrap molded during start up procedures. An often-unseen contributor to start up scrap is the stabilization period required by the mold. Until the mold has reached temperature equilibrium, consistent production is questionable. Building process tolerance to this instability and accurately predicting the amount of time required for equilibrium are the two logical solutions to solve this problem. This research focused on the use of various injection mold core materials to determine their effect on process equilibrium.
A Comparison of Position, Cavity Pressure, and Ultrasound Sensors for Switch/Over Control in Injection Molding
A mold has been constructed with a continuous wave ultrasound transducer installed, along with post gate and end of fill cavity pressure transducers. Signals from these transducers and the position signal from the injection ram were used in turn to control the switch/over from injection to packing phase on a standard industrial injection molding machine. The accuracy with which this point was identified was measured for each sensor. The results show that cavity pressure and ultrasound are significantly more repeatable as switch/over sensors than the ram position sensor.
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