Multi-Seam Tracking With a Portable Robotic Welding System in Unstructured Environments

Most welding manufacturing of the heavy industry, such as shipbuilding and construction, is carried out in an unstructured workspace. The term Unstructured indicates the production environment is irregular, changeable and without model. In this case, the changeable workpiece position, workpiece shape, environmental background, and environmental illumination should be carefully considered. Because of such complicated characteristics, the welding is currently being relied on the manual operation, resulting in high cost, low efficiency and quality. This work proposes a portable robotic welding system and a novel seam tracking method. Compared to existing methods, it can cope with more complex general spatial curve weld. Firstly, the tracking pose of the robot is modeled by a proposed dual-sequence tracking strategy. On this basis, the working parameters can be adjusted to avoid robot-workpiece collision around the workpiece corners during the tracking process. By associating the forward direction of the welding torch with the viewpoint direction of the camera, it solves the problem that the weld feature points are prone to be lost in the tracking process by conventional methods. Point cloud registration is adopted to globally locate the multi-segment welds in the workpiece, since the system deployment location is not fixed. Various experiments on single or multiple welds under different environmental conditions show that even if the robot is deployed in different positions, it can reach the starting point of the weld smoothly and accurately track along the welds.

Development of a Multidirectional Wire Arc Additive Manufacturing (WAAM) Process with Pure Object Manipulation: Process Introduction and First Prototypes

Wire Arc Additive Manufacturing (WAAM) with eccentric wire feed requires defined operating conditions due to the possibility of varying shapes of the deposited and solidified material depending on the welding torch orientation. In consequence, the produced component can contain significant errors because single bead geometrical errors are cumulatively added to the next layer during a building process. In order to minimise such inaccuracies caused by torch manipulation, this article illustrates the concept and testing of object-manipulated WAAM by incorporating robotic and welding technologies. As the first step towards this target, robotic hardware and software interfaces were developed to control the robot. Alongside, a fixture for holding the substrate plate was designed and fabricated. After establishing the robotic setup, in order to complete the whole WAAM process setup, a Gas Metal Arc Welding (GMAW) process was built and integrated into the system. Later, an experimental plan was prepared to perform single and multilayer welding experiments as well as for different trajectories. According to this plan, several welding experiments were performed to decide the parametric working range for the further WAAM experiments. In the end, the results of the first multilayer depositions over intricate trajectories are shown. Further performance and quality optimization strategies are also discussed at the end of this article.

Mixed Reality-Enhanced Intuitive Teleoperation with Hybrid Virtual Fixtures for Intelligent Robotic Welding

This paper presents an integrated scheme based on a mixed reality (MR) and haptic feedback approach for intuitive and immersive teleoperation of robotic welding systems. By incorporating MR technology, the user is fully immersed in a virtual operating space augmented by real-time visual feedback from the robot working space. The proposed robotic tele-welding system features imitative motion mapping from the user’s hand movements to the welding robot motions, and it enables the spatial velocity-based control of the robot tool center point (TCP). The proposed mixed reality virtual fixture (MRVF) integration approach implements hybrid haptic constraints to guide the operator’s hand movements following the conical guidance to effectively align the welding torch for welding and constrain the welding operation within a collision-free area. Onsite welding and tele-welding experiments identify the operational differences between professional and unskilled welders and demonstrate the effectiveness of the proposed MRVF tele-welding framework for novice welders. The MRVF-integrated visual/haptic tele-welding scheme reduced the torch alignment times by 56% and 60% compared to the MRnoVF and baseline cases, with minimized cognitive workload and optimal usability. The MRVF scheme effectively stabilized welders’ hand movements and eliminated undesirable collisions while generating smooth welds.

Pipe Welding Machine Modernization

There are the results of pipelines rolled joints welding machine modernization. The machine is designed using a welding rotator, linear electric drives, stepper motors, CNC system. The machine is controlled by a CNC system according to ISO 6983-1: 2009. The machine consists of: stepping rotary device, welding torch stepping device, controlled TIG welding power source, controlled welding wire feeder, welding current control system, workpiece rotation control system and welding torch. The welding torch movement trajectory controlling software has been created. It allows to weld by any type of welding torch recommended movements. The modernizing machine allows welding the pipelines rolled joints in automatic mode both in one pass and in multi-pass. The machine can be used for industrial pipeline elements welding, for welding modes testing, for studying the effect of welding modes on the quality of pipeline welds. The results can be adapted for sheet structures welding using the standard commands of the ISO 6983-1: 2009 standard. The results can be adapted to industrial welding robots control. The welding machine can be used for MIG / MAG welding and surfacing.

Influence of Cross-Wind on CO2 Arc Welding of Carbon Steel

The purpose of this study is to develop a novel welding torch with high wind resistance, which can be used for welding outside a building under strong cross-wind. In this paper, a parametric study was carried out using different torch nozzle designs and shield gas flow rates for their optimization. The gas flow around the torch nozzle exit was visualized through the shadowgraph method to evaluate the interaction between the shielding gas flow and the cross-wind. Nitrogen fraction in a weld bead was measured for confirming the shielding effect. Furthermore, CFD simulation was also carried out for obtaining shielding gas flow velocity at the torch nozzle exit. From the result of the above experiments and simulation, effective parameters for improving the shielding effect against the cross-wind were comprehensively discussed. As a result, the nitrogen fraction was found to be decreased by increasing the averaged vertical gas velocity at the torch nozzle exit. For achieving this, it is especially effective to decrease the nozzle diameter or increase the gas flow rate.

Synthesis of Fuzzy Logic Mathematical Model for Adaptive Control of the Mig/Mag Surfacing

A functional transformer with fuzzy logic is synthesized, which allows to get the estimations of weld beads height and width at the arbitrary values of entry parameters: wire feed speed and torch transverse oscillations amplitude. The influence of these input parameters on the base metal penetration and beads geometric parameters, welded using MIG/MAG process, were studied. Surfacing was performed by a robotic system with an arc power supply "Fronius TPS- 320i", which operated in the mode of arc process synergetic control. The formation of both individual beads and surfacing layers at different overlap coefficients has been studied. The arc surfacing process was realized in a mixture of protective gases (Ar+18%CO2) using a welding wire Св-08Г2С with a 1.0 mm diameter. Surfacing speed – 4 mm/s, frequency of welding torch oscillations – 1 Hz. The obtained experimental dependences of beads width and height, as well as the length of the welding pool can be used in both: creating of multi-pass MIG/MAG surfacing program for robotic restoration of critical purposes parts surfaces, and in preparing of FEM model of MIG/MAG surfacing.

Control of forming process of truss structure based on cold metal transition technology

Purpose The purpose of this paper is to study the wire and arc additive manufacturing (WAAM) method and path planning algorithm of truss structure parts, to realize the collision-free rapid prototyping of truss structures with complex characteristics. Design/methodology/approach First, a point-by-point stacking strategy is proposed based on the spot-welding mode of cold metal transfer welding technology. A force analysis model of the droplet is established, which can be used to adjust the posture of the welding torch and solve the collapse problem in the WAAM process of the truss structure. The collision detection model is developed to calculate the interference size between the truss structure and the welding torch, which is used to control the offset of the welding torch. Finally, the ant colony algorithm has been used to optimize the moving path of welding torch between truss with considering the algorithm efficiency and collision avoiding and the efficiency of the algorithm is improved by discretizing the three-dimensional workspace. Findings A series of experiments were conducted to prove the validity of the proposed methods. The results show that the wire feeding speed, welding speed are the important parameters for controlling the WAAM process of truss parts. The inclination angle of the welding torch has an important influence on the forming quality of the truss. Originality/value The force analysis model of truss structure in the WAAM process is established to ensure the forming quality and a collision-free path planning algorithm is proposed to improve forming efficiency.

Features of Filler Wire Melting and Transferring in Wire-Arc Additive Manufacturing of Metal Workpieces

In this paper, we present the results of a study on droplet transferring with arc space short circuits during wire-arc additive manufacturing (WAAM GMAW). Experiments were conducted on cladding of single beads with variable welding current and voltage parameters. The obtained oscillograms and video recordings were analyzed in order to compare the time parameters of short circuit and arc burning, the average process peak current, as well as the droplets size. Following the experiments conducted, 2.5D objects were built-up to determine the influence of electrode stickout and welding torch travel speed to identify the droplet transferring and formation features. Moreover, the current–voltage characteristics of the arc were investigated with varying WAAM parameters. Process parameters have been determined that make it possible to increase the stability of the formation of the built-up walls, without the use of specialized equipment for forced droplet transfer. In the course of the research, the following conclusions were established: the most stable drop transfer occurs at an arc length of 1.1–1.2 mm, reverse polarity provides the best drop formation result, the stickout of the electrode wire affects the drop transfer process and the quality of the deposited layers. The dependence of the formation of beads on the number of short circuits per unit length is noted.