Polymer Processing—An Introduction

This article discusses technologies focused on processing plastic materials or producing direct tools used in plastics processing. The article focuses on extrusion and injection molding, covering applications, materials and their properties, equipment, processing details, part design guidelines, and special processes. It also covers the functions of the extruder, webline handling, mixing and compounding operations, and process troubleshooting. Thermoforming and mold design are covered. Various other technologies for polymer processing covered in this article are blow molding, rotational molding, compression molding, transfer molding, hand lay-up process, casting, and additive manufacturing.

NUMERICAL ANALYSIS OF INFUSION STRATEGIES IN VACUUM ASSISTED RESIN TRANSFER MOLDING (VARTM) PROCESS

The Liquid composite Molding (LCM) process, such as Vacuum Assisted Resin Transfer Molding (VARTM), offers a fast and high-quality production of composites laminates. In the VARTM process, the simulation tool is found beneficial to predict and solve composite manufacturing issues. The part quality is dependent on the resin mold filling stage in the VARTM process. The infiltration of resin into a porous fibrous medium is taken place during the resin mold filling stage. The permeability has a crucial role during the resin mold filling stage. In this study, simulation of resin infusion through multiple injection gates is discussed. The various infusion schemes are simulated to identify defect-free composite manufacturing. The simulation approach is applied to five different stacking sequences of reinforcements. In this transient simulation study, permeability and resin viscosity is essential inputs for the resin flow. The simulation approach found that a gating scheme plays a vital role in mold filling time and defect-free composite fabrication. It is found that the line gating system can be useful for fast mold filling over the point gating system.

RESIN FLOW SIMULATION DURING THE RTM METHOD OF COMPOSITES PRODUCTION

Processes of plastic injection molding are often under analyzes in industry and science. Many of these considerations apply to epoxy resins with additional reinforcement, often with glass or carbon fiber inside the closed mould. The simulations of injection molding processes in the production of composite elements is not as common, as thermoplasts. Hence the idea to carry out the work described in this article. The RTM (Resin Transfer Molding) method is dedicated to serial production with the possibility of producing visual carbon fiber elements for aesthetic reasons. Simulations can help to better refine the products. This allows to take appropriate precautions and solve many issues before implementation. The article presents possible situations that could occur in real conditions. Various shapes models were prepared as basis of the numerical calculations. The analyses highlighting the possible issues were performed. The influence of resin pressure and flow rate on the final product was also considered. The aim was to present the characteristic phenomena and their causes that often occur in reality to technologists working with the RTM. Conclusions related to the work carried out are included. Based on the analyzes and conclusions drawn, it is possible to improve the quality of production processes.

Optimizing Bladder Resin Transfer Molding Process to Manufacture Complex, Thin-Ply Thermoplastic Tubular Composite Structures: An Experimental Case Study

The bladder molding process is primarily used in sporting applications but mostly with prepregs. Bladder-Assisted Resin Transfer Molding (B-RTM) presents the tremendous potential to automate and mass produce the complex hollow-composite profiles. Thin-ply, non-crimp fabrics (NCFs) provide excellent mechanical, fracture toughness, and vibration damping properties on top of the weight saving it offers to a final product. However, these fiber architectures are difficult to inject due to the resistance they provide for the polymer flow using the liquid injection process. Therefore, it is mandatory to optimize the process parameters to reduce the time for injection and simultaneously achieve better consolidation. This work presents a first, detailed, experimental case study to successfully inject a low-permeability, thin-ply, complex, thermoplastic tubular structure, and the effect of process parameters, boundary conditions, the associated manufacturing challenges, and proposed solutions are deliberated in this paper.

DAMAGE EVOLUTION IN NON-CRIMP FABRIC CARBON FIBER/EPOXY MULTI-DIRECTIONAL LAMINATES UNDER QUASI-STATIC TENSION

An experimental study was performed to characterize the evolution of damage in a unidirectional Non-Crimp Fabric (NCF) carbon fiber/snap-cure epoxy composite under in-plane quasi-static tensile loads. The NCF composites were manufactured using a High Pressure-Resin Transfer Molding (HP-RTM) process and comprised a fast-curing epoxy resin and heavy tow unidirectional carbon fiber NCF layers. Laminates with stacking sequences [0/±45/90] and [±45/0 ] were subjected to axial and transverse quasi-static tensile loads and an in-situ Edge replication (ER) technique was used to capture the damage evolution at predefined intervals. An imprint of the composite microstructure, as observed on the edges of a test coupon, was created on a cellulose acetate replicating tape, which was then observed under the microscope. The onset and progression of ply cracks and delamination, which were the two major damage modes present, were quantified and correlated with the stress-strain curves and changes in stiffness. The influence of stacking sequence and ply thickness are also captured.

Compression Resin Transfer Molding Using Inflatable Seals

Compression resin transfer molding using inflatable seals is a new variant of LCM (“Liquid composite molding”) processes, which uses the inflatable seals to compress the fiber reinforcements and drive the resin to impregnate the fabric preform, resulting to fill the entire mold cavity. During resin injection, the preform is relaxed. Consequently, the resin enters easily and quickly into the mold cavity. After, the necessary resin is injected into the mold cavity, the compression stage takes place, in a stepwise manner, by swelling the inflatable seals. The objective of this paper is to present this new process and study the effect of the number of inflatable seals on the filling time.