Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Productivity of digital fabrication in construction: Cost and time analysis of a robotically built wall

The construction industry is a major economic sector, but it is plagued with inefficiencies and low productivity. Robotics and automated systems have the potential to address these shortcomings; however, the level of adoption in the construction industry is very low. This paper presents an investigation into the industry-specific factors that limit the adoption in the construction industry. A mixed research method was employed combining literature review, qualitative and quantitative data collection and analysis. Three focus groups with 28 experts and an online questionnaire were conducted. Principal component and correlation analyses were conducted to group the identified factors and find hidden correlations. The main identified challenges were grouped into four categories and ranked in order of importance: contractor-side economic factors, client-side economic factors, technical and work-culture factors, and weak business case factors. No strong correlation was found among factors. This study will help stakeholders to understand the main industry-specific factors limiting the adoption of robotics and automated systems in the construction industry. The presented findings will support stakeholders to devise mitigation strategies.

Robotics and automated systems in construction: Understanding industry-specific challenges for adoption

Wire and arc additive manufacturing : Opportunities and challenges to control the quality and accuracy of manufactured parts

The present work addressed the challenges of identifying applicable Non-Destructive Testing (NDT) techniques suitable for inspection and materials characterization techniques for Wire and Arc Additive Manufacturing (WAAM) parts. With the view of transferring WAAM to the industry and qualifying the manufacturing process for applications such as structural components, the quality of the produced parts needs to be assured. Thus, the main objective of this paper is to review the main NDT techniques and assess the capability of detecting WAAM defects, for inspection either in a monitoring, in-process or post-process scenario. Radiography and ultrasonic testing were experimentally tested on reference specimens in order to compare the techniques capabilities. Metallographic, hardness and electrical conductivity analysis were also applied to the same specimens for material characterization. Experimental outcomes prove that typical WAAM defects can be detected by the referred techniques. The electrical conductivity measurement may complement or substitute some destructive methods used in AM processing.

Non-destructive testing application of radiography and ultrasound for wire and arc additive manufacturing

The adoption of wire and arc additive manufacturing (WAAM) in the market has been retained by the need to find a suitable method to ensure the quality of the parts produced. WAAM processes build up parts through the deposition of weld beads, consequently components with rough finish surfaces are characteristics of the method. Non-destructive testing (NDT) by ultrasonic (UT) method, namely the phased array technique (PAUT), is usually used to detect these defects in welding. However, the roughness of the parts represents a challenge for the UT application, since these variations influence the interaction between the emitted UT beam and the component. This study is thus focused on assessing the capability of detecting WAAM defects. The effectiveness of phased array ultrasonic testing to detect defects in aluminium WAAM components with several degrees of surface finish was evaluated. Simulations were first performed with CIVA software to characterize the beam emitted and select the probes and inspection parameters. Afterwards, physical inspections were performed on three reference specimens. Experimental outcomes prove that PAUT techniques are suitable for WAAM defects detection, including sizing, morphology and location. In addition, the experimental results were consistent with the simulated ones. The probes were able to overcome the limitations caused by the surface roughness of the samples, for a maximum of 89.6 μm average waviness profile. Also, defects ranging from 2 to 5 mm were characterized, in size and depth. These preliminary results represent an essential step for the development of an NDT system for inspecting WAAM parts.

Phased Array Ultrasonic Inspection of Metal Additive Manufacturing Parts

The use of robots in architectural construction has been a research field since the 1980s. Driven by both productive and creative concerns, different systems have been devised based on large-scale robotic structures, mobile robotic units or flying robotic vehicles. By analyzing these approaches and discussing their advantages and limitations, this paper presents an alternative strategy to automate the building construction processes in on-site scenarios. The SPIDERobot is a cable-robot system developed to perform assembly operations, which is driven by a specific Feedback Dynamic Control System (FDCS) based on a vision system. By describing and illustrating this research work, the authors argue about the advantages of this cable robot system to deal with the complexity and the scale of building construction in architecture.

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The SPIDERobot: A Cable-Robot System for On-site Construction in Architecture

Cable-driven robots have received some attention by the scientific community and, recently, by the industry because they can transport hazardous materials with a high level of safeness which is often required by construction sites In this context, this research presents an extension of a cable-driven robot called SPIDERobot, that was developed for automated construction of architectural projects The proposed robot is formed by a rotating claw and a set of four cables, enabling four degrees of freedom In addition, this paper proposes a new Vision-Guided Path-Planning System (V-GPP) that provides a visual interpretation of the scene: the position of the robot, the target and obstacles location; and optimizes the trajectory of the robot Moreover, it determines a collision-free trajectory in 3D that takes into account the obstacles and the interaction of the cables with the scene A set of experiments make possible to validate the contribution of V-GPP to the SPIDERobot while operating in realistic working conditions, as well as, to evaluate the interaction between the V-GPP and the motion controlling system The results demonstrated that the proposed robot is able to construct architectural structures and to avoid collisions with obstacles in their working environment The V-GPP system localizes the robot with a precision of 0006 m, detects the targets and successfully generates a path that takes into account the displacement of cables Therefore, the results demonstrate that the SPIDERobot can be scaled up to real working conditions

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A cable-driven robot for architectural constructions: a visual-guided approach for motion control and path-planning

Technological innovation has been an important driving force in architecture, enabling and inspiring architects and engineers by giving them new tools for solving existing problems. In the last two decades, the exploration of digital design and fabrication technologies has stimulated the development of a variety of interests and strategies to materialize increasingly complex and customized solutions in architecture, with traditional building materials.Reinforced concrete is the most widely used material in the building industry today and throughout its history has been the subject of vast research into its performance as a construction material and its tectonic potential in architecture. As such, the introduction of digital fabrication processes in concrete construction represents the biggest prospect for renovation of our built environment and at the same time, presents particular difficulties and opportunities, which are now being addressed. In an effort to investigate the alternative design and material possibilities in concrete emerging from the use of digital fabrication technologies in architecture, this paper proposes a focused view of digital fabrication applied to concrete construction with two areas of research. By framing the research in the context of reference works in concrete architecture of the 20th century, this paper describes and illustrates taxonomy of existing and possible types of integration of digital fabrication technologies in concrete architecture in the realms of Practice and Research.This characterization allows the authors to frame the relation between material, technology and architecture in different environments regarding the same material, extracting a clear image of existing processes, their potential and shortcomings, as well as expectations for future developments.

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José Pedro Sousa

Papers

Non-destructive testing application of radiography and ultrasound for wire and arc additive manufacturing

Phased Array Ultrasonic Inspection of Metal Additive Manufacturing Parts

The SPIDERobot: A Cable-Robot System for On-site Construction in Architecture

A cable-driven robot for architectural constructions: a visual-guided approach for motion control and path-planning

Digital Fabrication Technology in Concrete Architecture