A multi-bead overlapping model for robotic wire and arc additive manufacturing (WAAM)

Wire and arc additive manufacturing (WAAM) is a promising alternative to traditional subtractive manufacturing for fabricating large aerospace components that feature high buy-to-fly ratio. Since the WAAM process builds up a part with complex geometry through the deposition of weld beads on a layer-by-layer basis, it is important to model the geometry of a single weld bead as well as the multi-bead overlapping process in order to achieve high surface quality and dimensional accuracy of the fabricated parts. This study firstly builds models for a single weld bead through various curve fitting methods. The experimental results show that both parabola and cosine functions accurately represent the bead profile. The overlapping principle is then detailed to model the geometry of multiple beads overlapping together. The tangent overlapping model (TOM) is established and the concept of the critical centre distance for stable multi-bead overlapping processes is presented. The proposed TOM is shown to provide a much better approximation to the experimental measurements when compared with the traditional flat-top overlapping model (FOM). This is critical in process planning to achieve better geometry accuracy and material efficiency in additive manufacturing

A practical path planning methodology for wire and arc additive manufacturing of thin-walled structures

This paper presents a novel methodology to generate deposition paths for wire and arc additive manufacturing (WAAM). The medial axis transformation (MAT), which represents the skeleton of a given geometry, is firstly extracted to understand the geometry. Then a deposition path that is based on the MAT is efficiently generated. The resulting MAT-based path is able to entirely fill any given cross-sectional geometry without gaps. With the variation of step-over distance, material efficiency alters accordingly for both solid and thin-walled structures. It is found that thin-walled structures are more sensitive to step-over distance in terms of material efficiency. The optimal step-over distance corresponding to the maximum material efficiency can be achieved for various geometries, allowing the optimization of the deposition parameters. Five case studies of complex models including solid and thin-walled structures are used to test the developed methodology. Experimental comparison between the proposed MAT-based path patterns and the traditional contour path patterns demonstrate significant improved performance in terms of gap-free cross-sections. The proposed path planning strategy is shown to be particularly beneficial for WAAM of thin-walled structures

A tool-path generation strategy for wire and arc additive manufacturing

This paper presents an algorithm to automatically generate optimal tool-paths for the wire and arc additive manufacturing (WAAM) process for a large class of geometries. The algorithm firstly decomposes 2D geometries into a set of convex polygons based on a divide-and-conquer strategy. Then, for each convex polygon, an optimal scan direction is identified and a continuous tool-path is generated using a combination of zigzag and contour pattern strategies. Finally, all individual sub-paths are connected to form a closed curve. This tool-path generation strategy fulfils the design requirements of WAAM, including simple implementation, a minimized number of starting-stopping points, and high surface accuracy. Compared with the existing hybrid method, the proposed path planning strategy shows better surface accuracy through experiments on a general 3D component

Advanced Design for Additive Manufacturing: 3D Slicing and 2D Path Planning

Commercial 3D printers have been increasingly implemented in a variety of fields due to their quick production, simplicity of use, and cheap manufacturing. Software installed in these machines allows automatic production of components from computer-aided design (CAD) models with minimal human intervention. However, there are fewer options provided, with a limited range of materials, limited path patterns, and layer thicknesses. For fabricating metal functional parts, such as laser-based, electron beam-based, and arc-welding-based additive manufacturing (AM) machines, usually more careful process design requires in order to obtain components with the desired mechanical and material properties. Therefore, advanced design for additive manufacturing, particularly slicing and path planning, is necessary for AM experts. This chapter introduces recent achievements in slicing and path planning for AM process

Avaliação inicial de uma nova versão para soldagem laser: MIG/MAG duplo-arame

Recently a large number of research and development has been made regarding the use of Laser in welding operations, turning this process into an important tool for a variety of applications. Although it is possible to use Laser as a unique source of heat to promote union of materials, the combination of the beam provided by a Laser system with an arc welding process has become largely studied and applied in the so called hybrid welding. Generally, the final result of such combination is an increase in the weld penetration depth, width and welding travel speed. Despite all these facts, there are many issues still requiring further research and development concerning the use of hybrid welding using Laser and arc welding, including more comprehensive understanding on the various welding phenomena involved and the exploitation of new combinations. This paper describes a new approach for hybrid welding combining LBW with Tandem GMAW (Laser beam placed between the Tandem GMAW wires). The first view on such hybrid process variation is described and some basic aspects regarding its performance are discussed. The Laser beam had a positive effect on the aspect of the weld beads produced and a 10 mm inter-wire distance showed to be the most appropriate among the distances tried.Key words: hybrid welding, LBW, tandem GMAW.Recentemente, várias pesquisas e desenvolvimentos têm sido feitos sobre a utilização de Laser em operações de soldagem, tornando este processo em uma importante ferramenta para uma variedade de aplicações. Apesar de ser possível utilizar o Laser como única fonte de calor para promover a união de materiais, a combinação do feixe produzido pelo sistema de Laser com um processo de soldagem a arco tem se tornado largamente estudada e aplicada na chamada soldagem híbrida. Geralmente, o resultado final é um aumento na penetração e largura do cordão de solda e da velocidade de soldagem. Apesar de todos estes fatos, existem muitas questões que ainda requerem mais investigação e desenvolvimento em relação ao uso de soldagem híbrida usando Laser e soldagem a arco, incluindo um melhor entendimento dos fenômenos de soldagem envolvidos e a exploração de novas combinações. Este artigo descreve uma nova montagem para a soldagem híbrida combinando Soldagem a Laser e MIG/MAG Duplo-Arame (feixe de Laser colocado entre os arames do MIG/MAG Duplo-Arame). Os primeiros resultados do uso deste processo híbrido são apresentados e alguns aspectos básicos com relação à sua performance são discutidos. O feixe de Laser teve um efeito positivo no aspecto dos cordões de solda produzidos e uma distância de 10 mm entre os arames se mostrou ser a mais apropriada dentre as distâncias testadas.Palavras-chave: soldagem híbrida, soldagem a Laser, MIG/MAG duplo-arame

Diffraction line profile analysis of 3D wedge samples of Ti-6Al-4V fabricated using four different additive manufacturing processes

Wedge‐-shaped samples were manufactured by four different Additive Manufacturing (AM) processes, namely selective laser melting (SLM), electron beam melting (EBM), direct metal deposition (DMD), and wire and arc additive manufacturing (WAAM), using Ti‐-6Al‐-4V as the feed material. A high‐-resolution powder diffractometer was used to measure the diffraction patterns of the samples whilst rotated about two axes to collect detected neutrons from all possible lattice planes. The diffraction pattern of a LaB6 standard powder sample was also measured to characterize the instrumental broadening and peak shapes necessary for the Diffraction Line Profile Analysis. The line profile analysis was conducted using the extended Convolution Multiple Whole Profile (eCMWP) procedure. Once analyzed, it was found that there was significant variation in the dislocation densities between the SLMed and the EBMed samples, although having a similar manufacturing technique. While the samples fabricated via WAAM and the DMD processes showed almost similar dislocation densities, they were, however, different in comparison to the other two AM processes, as expected. The hexagonal (HCP) crystal structure of the predominant α‐-Ti phase allowed a breakdown of the percentage of the Burgers\u27 vectors possible for this crystal structure. All four techniques exhibited different combinations of the three possible Burgers\u27 vectors, and these differences were attributed to the variation in the cooling rates experienced by the parts fabricated using these AM processes

Mitigation of thermal distortion in wire arc additively manufactured Ti6Al4V part using active interpass cooling

In this study, active interpass cooling using compressed CO2 was innovatively employed in the wire arc additively manufactured Ti6Al4V process with the aim of mitigating part distortion. A comparative analysis between simulation and experimental results was performed to explore the effects of active interpass cooling on the thermal behaviours, geometric features and distortion levels of deposit. The results show that active interpass cooling with CO2 gas is an effective means of reducing Wire arc additive manufacturing (WAAM)-part distortion by increasing heat dissipation and reducing heat accumulation within the deposition. It can contribute to a maximum reduction of 81% in longitudinal distortion and 69% in transverse distortion for the wall structures produced in this study. Compared to the cooling gas flow rate, cooling time alternation is more effective in mitigating WAAM-part distortion due to more effective heat dissipation per unit time. The findings reveal that using active interpass cooling in WAAM can offer significant cost and build-time savings, as well as providing conditions for the improvement of WAAM-part quality

Additive manufacture of titanium alloys using integrated robotic GTAW welding

Additive manufacturing (also known as rapid prototyping, shape metal deposition or near net manufacture ) is becoming an important option for low volume production of complex parts. Much of the recent effort has been devoted to laser based processes using powder feedstock and 3D printing techniques; these techniques are well suited to producing smaller complex structures in a wide range of materials. The current paper describes a technique for cold wire GTAW deposition of titanium alloys using robotic welding and integrated post weld machining; the approach is suitable for producing much larger parts. The techniques involved and resultant weld quality will be discussed

Verstatile welding power source controller for research and product development

The diminishing cost and increasing speed of microprocessors has made them ubiquitous in modern welding control equipment, whether it is mass produced or custom made for research purposes

Control of the short-circuit gas metal arc welding process using instantaneous current regulation

The performance of the short-circuit gas metal arc welding (GMAW) process under the control of two current-controlled techniques is investigated in detail using a custom built, high performance power source. The objective of these techniques is to provide significant improvements in process control compared to that obtained by using conventional constant voltage power sources. The first control technique, described as open loop , has a fixed, preprogrammed response to key events within the process that define various states of the weld cycle. The response parameters are adjusted to suit the wire feed speed, welding travel speed and shielding gas mixture. Adaption to the requirements of the process occurs automatically, since the timing of the responses is determined solely by events at the weld. This technique produces stable, low-spatter welds with excellent bead appearance across a very wide range of wire feed speeds and contact tip to workpiece distance (CTWD values. Operation does not depend on synchronising the weld cycle frequency with the natural frequency of the weld pool. The technique also significantly decouples key welding parameters such as peak arc length, fusion area, and short-circuit metal transfer characteristics. Following investigation of this technique, a new approach is proposed. This closed loop control aims to regulate the size of the droplet formed at the end of the electrode on a cycle-by-cycle basis. A model of the instantaneous melting rate is developed to predict droplet size. A novel method is used to estimate the CTWD using through the arc sensing techniques. The objectives of this technique are to increase process stability and to further reduce spatter. These aims were achieved under a limited set of operating conditions. The performance of this second technique is influenced by weld pool oscillation but the key benefit of parameter decoupling is retained. The theoretical development of both techniques and experimental validation of their performance is detailed in this thesis