Comparison of Properties and Bead Geometry in MIG and CMT Single Layer Samples for WAAM Applications

The process of Wire Arc Additive Manufacturing (WAAM) utilizes arc welding technology to fabricate metallic components by depositing material in a selective layered fashion. Several welding processes exist that can achieve this layered deposition strategy. Gas Metal Arc Welding (GMAW) derived processes are commonly favored for their high deposition rates (1–4 kg/h) and minimal torch reorientation required during deposition. A range of GMAW processes are available; all of which have different material transfer modes and thermal energy input ranges and the resultant metallic structures formed from these processes can vary in their mechanical properties and morphology. This work will investigate single-layer deposition and vary the process parameters and process mode to observe responses in mechanical properties, bead geometry and deposition rate. The process modes selected for this study were GMAW derived process of Metal Inert Gas (MIG) and Cold Metal Transfer (CMT). Characterization of parameter sets revealed relationships between torch travel speeds, wire feed speeds and the specimen properties and proportions. Differences were observed in the cross-sectional bead geometry and deposition rates when comparing MIG and CMT samples though the influence of process mode on mechanical properties was less significant compared to process parameter selection

Investigation of the Mechanical Properties of Friction Drilling with 6082-T6 Aluminium Alloy

Friction drilling is a non-conventional hole-making process suitable for thin-section, ductile metals. During friction drilling, heat is generated due to tool rotation and the resulting flow of metal creates a bushing on the exit side of the hole. The bushing offers a longer engagement length for any subsequent thread making process. The threaded holes in this study were created by friction drilling and thread forming in 6082-T6 aluminium alloy. Four scenarios of the threaded holes were created with four levels of rotation rates of friction drilling processes (2000 rpm to 4000 rpm) and the mechanical properties of the threaded holes were compared. It was shown that 3000–3500 rpm is the optimum range of the rotation rate that achieved the higher load-bearing capacities (i.e., resistance to thread stripping) of 5.0–5.5 kN. In addition, the regions close to the thread surfaces in all scenarios were found to have experienced localised hardening to a hardness from 113 HV to around 125 HV

Extruded Monofilament and Multifilament Thermoplastic Stitching Yarns

Carbon fibre reinforced polymer composites offer significant improvement in overall material strength to weight, when compared with metals traditionally used in engineering. As a result, they are replacing metals where overall weight is a significant consideration, such as in the aerospace and automotive industries. However, due to their laminate structure, delamination is a prime concern. Through-thickness stitching has been shown to be a relatively simple method of improving resistance to delamination. In this paper, monofilament and multifilament fibres of a similar overall diameter were characterised and their properties compared for their suitability as stitching yarns. Dissimilar to other published works which rely on commercially available materials, such as polyparaphenylene terephthalamide, criteria were produced on the required properties and two potentially promising polymers were selected for extrusion. It was found that although the multifilament fibres had a greater ultimate tensile strength, they began to yield at a lower force than their monofilament equivalent

Novel thermoplastic yarn for the through-thickness reinforcement of fibre-reinforced polymer composites

Sewing has attracted a great deal of attention as a method to improve the delamination performance of carbon fibre laminate composites. A critical factor in the commercial exploitation of the technology is the development of a suitable sewing yarn, with other researchers looking at a variety of commercial fibres such as Kevlar. It would appear from the literature that fundamental research into what properties a suitable yarn should have has not been carried out. In this work, a commercial fibre designed for sewing applications was sourced from Toho Tenax (Germany) and used as a control. Unlike in published works, rather than relying on yarns which could be purchased commercially, selection criteria were drawn up and promising polymers identified and then extruded as a yarn. Based on the selection criteria, thermoplastic yarns were extruded using polysulfone, polyethersulfone, polyphenylsulfone and polyetheretherketone. It was found that despite the fact that the commercial fibre had much better mechanical properties as a straight fibre, when it was knotted or looped (to try and simulate the effects of sewing), there was a dramatic decrease in the mechanical properties (the ultimate tensile strength dropped by 88% due to a single knot). There was no significant change in the mechanical properties of the thermoplastic yarns. As a result, it is concluded the thermoplastic fibres created could potentially be better suited for sewing applications compared to commercial fibres such as Kevlar and further work is planned to sew the yarns and test the delamination performance. </jats:p

Elastic Modulus and Flatwise (Through-Thickness) Tensile Strength of Continuous Carbon Fibre Reinforced 3D Printed Polymer Composites

Additively manufactured composite specimens exhibit anisotropic properties, meaning that the elastic response changes with respect to orientation. Both in-plane and out-of-plane mechanical properties are important for designing purpose. Recent studies have characterised the in-plane performance. In this study, however, through-thickness tensile strength of 3D polymer composites were determined by printing of continuous carbon fibre reinforced thermoplastic polyamide-based composite, manufactured using a Markforged Two 3D printer. This paper discusses sample fabrication and geometry, adhesive used, and testing procedure. Test standards used to determine out-of-plane properties are tedious as most of the premature failures occur between the specimens and the tabs. Two types of samples were printed according to ASTM flatwise tension standard and the results were compared to determine the geometry effect on the interlaminar strength. This test method consists of subjecting the printed sample to a uniaxial tensile force normal to the plane. With this method, the acceptable failure modes for tensile strength must be internal to the structure, not between the sample and the end tabs. Micro-computed tomography (µCT) was carried out to observe the porosity. Surface behaviour was studied using scanning electron microscopy (SEM) to see the voids and the distribution of the fibres in the samples. The results showed consistent values for tensile strength and elastic modulus for Araldite glue after initial trials (with some other adhesives) to determine a suitable choice of adhesive for bonding the samples with the tabs. Circular specimens have higher tensile strength and elastic modulus as compared to rectangular specimens