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Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Influence of Flow Rate and Inlet Geometry on the Thermal Efficiency of a Water Flow CalorimeterAbstract: The main aim of the present work is to analyze the influence of water flow rate and inlet geometry on the arc thermal efficiency of a continuous water flow calorimeter. The experimental procedure consists of varying water flow rate and testing three different calorimeter inlet seal geometries: straight seal, conical diffuser seal and seal with water flux obstacle. The experiments were designed and the results evaluated based in a one-factor statistical analysis of variance, in this case the inlet calorimeter water flow. The welding beads were deposited on low carbon steel pipes by Gas Metal Arc Welding -GMAW process, using the same parameters and welding time. The highest average thermal efficiency is 80.5% to water flow of 4 l/min, with a low statistical error, using the conical diffuser seal inlet geometry, whereas for smaller or higher flow rates the measured efficiency values were lower. The inlet with straight seal model shown all the arc thermal efficiency values with slightly lower numerical values compared with conical diffuser, while the seal with flux obstacle exhibited high statistical error.

WAAM (Wire-Arc-Additive-Manufacturing) is an additive manufacturing process which uses arc welding to produce metal parts. This process is prone to heat accumulation, i.e. a progressive increase of the interlayer temperature and molten pool size, having detrimental consequences on the material properties and on the workpiece integrity. This paper investigates the effect of air jet impingement, an active cooling technique, to prevent heat accumulation, on the surfaces of WAAM workpieces. A reference test case was manufactured using traditional free convection cooling and air jet impingement. The workpiece temperature was measured using Ktype thermocouples. The manufactured surfaces were measured using a coordinate measuring machine and compared in terms of deposition efficiency, deposit height and average arithmetical deviation. The temperature results highlight that air jet impingement is effective in preventing the occurrence of heat accumulation. The surface data highlight that air jet impingement increase the deposited height and the surface waviness with a consequent decrease of the deposition efficiency.

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Weld bead geometry is a critical factor for determining the quality of welded joints, for this the welding process input parameters play a key role. In this study, the relationships between welding process variables and the size of the weld bead produced by pulsed GMAW process were investigated by a neural network trained with Bayesian-Regulation Back Propagation algorithm and a second degree regression models. A series of experiments were carried out by applying a Box-Behnken design of experiment. The results showed that both models can predict well the bead geometry. However, the neural network model had a slightly better performance than the second-order regression model. Both models can be used for further analyses and using them may surmount or reduce the need of experimental procedures especially in thermal analysis validations of welding finite element modelling.

In this work, AISI H13 tool steel build-ups were produced through wire arc additive manufacturing (WAAM). The cold metal transfer (CMT), low spatter control (LSC) and pulsed synergic (PS) current deposition modes were compared. Similar deposition strategy was employed in order to attempt to evaluate the influence of energy input on geometrical and mechanical properties of the deposits. To evaluate the mechanical properties of the deposits, hardness and tensile tests were carried out. Microstructures were analysed in optical microscope. As a result of the intrinsic characteristics of each current waveform and adjustments of the heat source used to perform the deposits, the heat input value was similar for CMT and PS mode and lower for the LSC mode. The CMT deposit was the tallest and widest. Temperatures were higher using the PS deposition mode. The hardness values for all deposits were higher than the usual ones for this tool steel. The microstructure was composed by hard phases, and the precipitates at grain boundaries were responsible for the brittle fracture observed in tensile specimens.

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