Towards a Robust, Water-Soluble, Lost Core Material – part two: Fiber-Reinforced Salt by Wet Compression Molding

The creation of an ideal surfboard is art. The design and construction depend on the individual surfer’s skill level and type of the required performance. In this research, four fuselage concepts were carefully explored to meet the following unique needs: lightweight, strong, and a fast-manufacturing process. The fuselages were manufactured by compression moulding using skin and core materials. The skin material was selected to be unidirectional (UD) carbon fibre, discontinuous carbon fibre (SMC) and Filava quadriaxial fibre impregnated with epoxy, while the core material was selected to be lightweight PVC foam. To assess the mechanical performance, three-point bending has been performed according to BS-ISO 14125 and validated using Finite Element Analysis (FEA) using Ansys software. As expected, the flexural test revealed that the UD carbon fibre fuselage was the strongest and SMC was the weakest, while large deflection was seen in Filava fibre fuselages before failure, showing great reactive flex that promotes projection during surfing. The experimental results show good agreement with FEA simulation, and the locations of the physical failure in the fuselage matches the location of maximum flexural stress obtained from FEA simulation. Although all fuselages were found to carry a surfer weight of 150 kg, including a factor of safety 3, except the SMC fuselage, due to shrinkage. The Filava fibre fuselages were seen to have a large deflection before failure, showing great flexibility to handle high ocean waves. This promotes the potential use of reactive flex in high performance sports equipment, such as surfing boards. A large shrinkage must be taken under consideration during compression moulding that depends on fibre orientation, resin nature, and part geometry.

Bending and shear improvements in 3D-printed core sandwich composites through modification of resin uptake in the skin/core interphase region

The key to finding relevant process parameters in manufacturing of thermoplastic sandwich panels is an accurate prediction of the temperature at the interface between core and face during manufacturing, as this temperature is critical for the bond between the constituents. In this paper a model for prediction of the temperature distribution within a sandwich panel during manufacturing is presented. The process of face manufacturing by compression molding also is modeled, both for a one-dimensional case using finite difference methods to investigate effects of varying thermal contact conductances, and for a three-dimensional (3D) case using finite element methods to study temperature edge effects. The models are verified by experiments, in which a preconsolidated glass fiber/polyamide 12 laminate is used, partly as a ply in a thicker laminate, partly as face sheet for a sandwich panel. The core material used is polymethacrylimide foam.

Parts with undercuts or hollow sections exploit the maximum lightweight potential due to efficient material usage. However, such geometries are often challenging to produce with ordinary tooling technology, especially in aluminum high-pressure die casting (HPDC). In order to close this gap, this paper investigates flax fiber-reinforced salt made by wet compression molding as a new lost core material that can be removed with water. Three-point bending tests and HPDC experiments characterized the material. The 2D and 3D simulations with aluminum melt and compressible air were carried out in ANSYS Fluent 2023R1. The outlet vent boundary condition is characterized separately to address the geometric features of the outlet vent. Combined with a two-phase flow filling simulation, it allows assessing the actual loads on the lost core material. The simulations show an excellent agreement between the proposed one-dimensional, analytical outlet model and the computational fluid dynamics (CFD) results. The 2D filling simulations are helpful to prove mesh convergence and model simplifications but overestimate the loads. A 3D simulation predicts stress peaks up to 33 MPa for an ingate speed of 64 m/s. Conventional, brittle salt cores with a bending strength of 15 MPa fail under these conditions in the HPDC experiment. In contrast, fiber-reinforced salt cores with bending strengths between 11 and 37 MPa are viable thanks to their toughness, which was demonstrated by a eight to 31 times higher energy absorption than the unreinforced benchmark in the three-point bending tests. With the new robust lost core material, a foundry gains a technology advantage that opens up new markets, e.g., in the mobility sector.

The authors have developed a lateral extrusion process with a lost core. The outline of the process is as follows. First, the cavity of a pipe, or a channel material, is filled up with liquid of a low-temperature melting material. The low-temperature melting material is then solidified to become a soluble core of the pipe. The authors call this soluble core the lost core. Next, the material is compressed longitudinally as a composite billet and extruded in the lateral direction. After deformation, the low-temperature melting material is melted and removed. The process can performed in a compression state to control the precise appearance of the product. This study examines a new core material, alumina powder (alumina ball) bonded with wax, as a core material. A mixing methodology for wax and alumina powder is discussed along with the effect of their mixing ratio on the deformation of the pipe.

Wet Compression Moulding (WCM) provides large-scale production potential for continuously fibre-reinforced structural components due to simultaneous infiltration and draping during moulding. Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficient - a considerable economical advantage. Similar to other Liquid Compression Moulding (LCM) processes, forming and infiltration strongly interact during process. However, the degree of forming is much higher in WCM, which disqualifies a sequential modelling approach. This is demonstrated in this work via experimental characterisation of the interaction between compaction and permeability of a woven fabric and by trials with a transparent double dome geometry, which facilitates an in situ visualization of fluid progression during moulding. In this light, and in contrast to existing form filling approaches, a forming-inspired, three-dimensional process simulation approach is presented containing two fully-coupled macroscopic forming and fluid-submodels. The combined model is successfully benchmarked using experimental double dome trials with transparent tooling.

The transportation and automotive industries are slowly integrating biocomposite materials into products where the economics make sense; this typically means a short manufacturing cycle time, not using expensive prepreg, and with little waste generated from the process. In a previous investigation into the use of biocomposites for electric bus seats and backs, three different material systems (hemp, flax, and pure cellulosic fibers, each paired with a high-bio-content epoxy) and two manufacturing processes (wet layup followed by compression molding, vacuum-assisted resin transfer molding) were investigated, but neither process proved to be viable. In this paper, a relatively obscure process called Wet Compression Molding (WCM) is considered for economical production of the biocomposite bus seats using the same three material systems. Darcy’s law predictions of full impregnation time for a nominally 3.5 mm thick part using experimentally determined permeability values are all less than 2 s. Furthermore, prepreg is not used, and net-shape parts without excess resin show potential. Important design details of the WCM mold set, used in the manufacturing of flat test panels from each material system, that are generally not discussed in the literature include a high-pressure O-ring seal, and semi-permeable membranes covering injection pins and vacuum vents (evacuates trapped air) to prevent resin ingress. Biocomposite laminate specimens are fabricated using the mold set in a thermal press and a vacuum pump. Part characterization includes fiber volume fraction estimates and measurements of thickness, density, flexural modulus, and outer fiber maximum stress at failure. Due to its rapid impregnation with just enough resin, WCM should be considered for the economical manufacture of parts similar in shape and size to electric bus seats and backs.

This paper presents the development of a low-cost water-soluble core material, which is suitable for producing hollow composite structures via high pressure moulding processes, such as compression moulding and resin transfer moulding. The bulk material of the core is sodium chloride (NaCl), which is held together by a water-soluble trehalose binder. The composition of the core has been optimised to provide acceptable dissolution rates and mechanical properties for high volume structural composite applications.The compressive strength of the NaCl core was 57MPa at ambient temperature, which reduced to 20MPa when tested at 120°C. The compressive strength at elevated temperature was approximately 4times higher than for a water-soluble commercial benchmark and 33times higher than a conventional structural closed-cell foam. The specific dissolution rate of the NaCl core was between 0.14 and 1.23kg/(min·m2), depending on processing parameters and the coefficient of thermal expansion was approximately 43×10−6/K. A practical example has been presented to demonstrate how the removable core can be used to produce a representative hollow section of an integrally stiffened panel.

Recently, epoxy resin-based composite structures have been widely used in many engineering applications due to their superior mechanical properties, thermal insulation and acoustic damping. However, to further improve the mechanical performance, several studies indicate significant benefits can be achieved using woven carbon fibers and different core material reinforcements for sandwich composite materials. The present review includes a comprehensive review of the most important composite material manufacturing techniques such as hand layup, spray layup, compression moulding, extrusion compound, filament winding, moulding injection, pultrusion, resin transfer moulding, and vacuum infusion or vacuum-assisted resin transfer, and the advantages of each method. In addition to the mechanical performance of epoxy composites and the possibility of improving these properties by using different strategies to enhance interfacial bonding and mechanical performance. These strategies include the incorporation of nanoparticles, surface modifications, the use of advanced resin systems, and a review of the latest studies in this field. Each approach aims to interaction improvement between carbon fibers and the epoxy matrix, thus enhancing properties such as tensile strength, compression strength, impact resistance, and interlaminar shear strength. To establish a systematic understanding of design criteria, this work intends to summarize all studies in the open literature about this topic. It is concluded that enhancing the mechanical performance of sandwich structural composites depends on the selection of the appropriate manufacturing method, which is determined by material properties, cost considerations, processing requirements, and specific applications.

Package on Package (PoP) is one of the increasingly used high density package solution for package stacking technology in various device manufacturing applications. Normally PoP configurations use a top package with a stacked memory packaging system connected to a bottom logic packaging system via solder joint. To guarantee the assembly yield and reliability of the solder joint between the top package and bottom package, mechanical compliance between these two packages is crucial during package stacking. The industry is constantly working toward reducing the total stack height and current road maps point toward a thinner total stack Z height of PoP configuration. It is necessary to reduce the package height by reducing the mold cap thickness as well as reduce the mold cap clearance, the distance between the top silicon die to the mold top. However, it is one of the increasing challenges to reduce top package thickness maintaining its low warpage behaviors during the reflow process and to avoid bonding wire exposure after laser mark process due to thin mold cap clearance. In this paper, we used the compression mold process to fabricate PoP top package test vehicle with different mold cap thickness at around 80 um mold cap clearance on 14×14 package size, and investigated the effects of various molding compound materials and substrate material properties on PoP top package warpage behaviors during solder reflow process. The substrates are all 100 um thickness and 2 layer structure. As the mold cap thickness gets thinner, the warpage variation during reflow process gets larger. The material property of key component in top PoP package plays a crucial role in warpage performance. The thermo-mechanical properties of molding compounds after compression molding process and substrate materials are very important and mainly determine the warpage level of the top package at room temperature and the warpage behaviors during the reflow profile for the board level assembly with bottom package. The compression mold compound material properties and substrate core materials were optimized to improve the ultra thin PoP top package. The findings and results provide a guideline of the material selection for warpage control in the PoP top package to improve the PoP assembly yield and reliability.

Combined effect of exfoliated graphite/ferrite filled epoxy composites on microwave absorbing and mechanical properties

Sugar palm fibers (SPF) reinforced vinyl ester (VE) composites were prepared in this study. The SPFs were obtained from three different geographical locations: Kuala Jempol (Peninsular Malaysia), Tawau (West Malaysia), and Tasik Malaya (Indonesia). The SPFs were utilized as reinforcement material with a fixed loading of 10 wt.%. The reinforced VE composites were prepared using a wet lay-up compression moulding method. The physical properties examined were water absorption, thickness swelling, and moisture content. To determine the strength of the SPF composites, tests on the tensile, flexural, and impact strength related to mechanical properties were completed. A thermogravimetric analysis (TGA) was completed to observe the thermal properties. This study confirmed that the properties of the composites were affected by the strength of the fiber. The SPF/VE composites obtained from Kuala Jempol had the highest tensile, flexural, and impact strength compared to the SPF/VE composites from Indonesia and Tawua. In addition, SPF Jempol/VE also recorded the highest percentage of water absorption, thickness swelling, and moisture content. A comparison of thermal properties showed that SPF Tawau/VE had highest percentage of mass loss between fibers from the three geographic locations.

In this article, biocomposites derived from a starch-glycerol biodegradable matrix reinforced with jute fibers were fabricated using the wet hand lay-up and compression moulding techniques. Samples having different weight percentages of jute fiber in the starch matrix were analyzed. The fiber’s surface was chemically treated by alkaline sodium hydroxide to improve the interphase bonding between the fiber and the matrix. Tensile tests for the composites were done and the sample with highest tensile strength was selected for further tests that included water absorption (WA), scanning electron microscopy (SEM) and thermal analysis (TA). It has been concluded that the ultimate tensile strength was found to be maximum for the composition of 15% fiber by weight composite as 7.547 MPa without epoxy coating and 10.43 MPa with epoxy coating. The major disadvantage of the biocomposite is its high WA property, which in this study was inhibited by the epoxy resin layer. Herein, the results of various tests done disclose a noteworthy improvement in the overall properties of bio-composite, in comparison to the neat biodegradable starch matrix.

Sandwich panels are extensively used in aeronautical field due to its high strength-to-weight ratio and better energy absorption. In this study, the sandwich panels are fabricated with Kevlar (K) and basalt (B) fibres as face sheets as it has high strength, and thermal stability with polyurethane (PU) foam as core material and investigations are performed to evaluate the energy absorption and mechanical properties of the sandwich panels. The plates are fabricated using compression moulding method. Tests such as inter laminar shear strength test, edge wise compression test, flammability test, drop-weight impact test are performed, and the obtained results are compared. Plate 2 (Kevlar/Kevlar/PU Foam/Kevlar/Kevlar) shows a better shear strength as 4.38N/mm2 and better energy absorption capability whereas, Plate 3 (Basalt/Kevlar/PU Foam/Kevlar/Basalt) shows more compressive strength with value of 13.4N/mm2. Plate 1 (Basalt/Basalt/PU Foam/Basalt/Basalt) shows faster propagation speed when it is in contact with fire.

This paper analyses the lightweight potential of long-fiber-reinforced and local continuous-fiber-reinforced foam injection molded components. Using the LFT-D foam process [7, 13] and breathing mold technology [11, 12], long-glass-fiber-reinforced polypropylene foams were manufactured with a constant weight per unit area and varying density reductions. As the area moment of inertia increases with the wall thickness to the third power, in these investigations small density reductions were sufficient to increase the flexural rigidity by several hundred% compared to a compact reference sample. The fiber length advantage generated by the direct process (injection molding compounding) also meant that even at higher density reductions the ductility was not reduced by the foaming. In order to achieve even better mechanical properties, foam injection molding can be combined with local continuous-fiber reinforcement. To demonstrate the potential, sandwich integral foam components with local continuous-fiber-reinforced facing were produced in-situ in an injection mold and characterized. Fully-consolidated tape blanks and self-reinforced PP fabrics were positioned on both sides of the cavity and heated. Afterwards a gas-loaded melt was injected between them. A short embossing stroke generated sufficient interfacial adhesion between the facing layers and the core material, and the foaming process was initiated by the pressure drop resulting from the precision opening of the injection compression mold.