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A model for arc-cathode attachment in gas metal arc welding is presented. It considers the cathodic heating in the case of a non-refractory iron cathode, with the assumption of the lowering of the local plasma temperature, due to cold metal vapor. It takes the plasma bulk temperature as well as the cathode drop voltage as free parameters and it gives a maximum of heat flux and current density for a cathode surface temperature below boiling temperature. The applicability as a heat source description in a weld pool simulation has been shown, and the temperature field of the cathode was calculated, giving rise to heat flux and current density distributions, which differ significantly from the converntionally used axisymmetric Gaussian distribution. The maximum cathode surface temperature was lower than boiling temperature, which is in agreement with the observeration.

The main aim of this investigation is to study the temperature and electrical resistance of the wire during gas metal arc welding (GMAW), because the wire heating contributes to a considerable extent to the power balance of the welding processes. As a reference, a typical pulsed GMAW process of mild steel with fixed wire feed speed of 4 m min−1 but varying free wire length and varying pulse current has been investigated. Three approaches have been applied for comparison: firstly, the surface temperature of the solid and molten wire parts has been measured with an infrared camera and a two-colour pyrometer with high-speed recording, respectively, and the wire resistance has been determined based on wire geometry and temperature dependent conductivity. Secondly, the resistance of the solid wire and the wire contact in the contact tube has been measured by an electrical probe. Thirdly, short circuit events together with surface temperature determination have been used to estimate the wire resistance. In addition, the temperature dependent conductivity of the corresponding wires has been measured systematically in a specific heating setup. Main results are a wire temperature exponentially decreasing with the distance from the wire tip and almost independent of the pulse current. The overall resistance of the wire part in the current path of the process including the contact tube scales mainly with the free wire length and reaches 13 m in our example for 15 mm free wire length.

Reinforced concrete (RC) is by far the most widely used composite material in the world. Despite the enormous economic importance of RC construction, there is a lack of viable concepts for its digital fabrication. While 3D printing of plain concrete has been pushed forward by a growing research community in recent years, methods for integration of steel reinforcement have only scarcely been researched and little attention has been payed to meet the practical requirements of construction sites and prefabrication plants. Therefore, full-scale implementations of current approaches are hardly available. Based on both, a sound review of R&D for digital fabrication of RC structures and an analysis of practical requirements, the present paper proposes a novel 3D printing process for RC structures, called Additive Manufacturing of Reinforced Concrete (AMoRC), viable for real-world application. In this hybrid process, consisting of an intermittent stud welding process and a continuous concrete extrusion process, segmented steel reinforcing bars are joined to form a three-dimensional reinforcement mesh and simultaneously encased with extruded concrete. The paper describes the conceptual design and development of the process and demonstrates the results of preliminary investigations on its feasibility. As AMoRC enables the operation of rebar welding and concrete extrusion process with synchronized feed rates, combination of both processes in one hybrid print head for digital fabrication of RC is a key-advantage of the proposed method.

In this paper, the voltage drop in pulsed gas metal arc welding (GMAW) is studied, focussing on the contributions of the different sections of wire and arc along the current path and their dependence on arc length and current. A typical pulsed GMAW process of mild steel in the one drop per pulse modus is considered as a reference. Voltage and current have been measured in experiments with fixed wire feed speed for varying arc length and free wire length. The temporally changing geometry of the arc and the molten wire parts has been studied carefully by highspeed imaging and image processing. In particular, the shielding gas and the metal vapour dominated parts of the arc have been captured simultaneously, and conclusions on the length of the current path in the arc column have been drawn. Comparing voltage measurements for the same current and different arc lengths, finally, the sum of cathode and anode sheath voltages as well as the mean electric field strength of the arc column have been determined. Sheath voltages increasing from 18 to 23 V for pulse currents from 350 to 650 A and a mean electric field of about 1.1 V mm −1 in the arc column, which is almost independent of the current, have been obtained. As a consequence, the Ohmic heating in the arc column contributes less than 20% to the overall power budget whereas the contribution of the electrode sheathes is larger than 60%.