WAAM TECHNOLOGY OPTIMIZED BY OFF-LINE 3D ROBOT SIMULATION

WAAM (Wire + Arc Additive Manufacturing) is an alternative additive technology that combines an electric arc as a heat source, filler material in the form of a wire for welding and cladding individual weld passes so as to ultimately achieve the closest shape of produced components. Nowadays, when it is modern to digitize the manufacturing production, this process can also be designed using off-line programming tools and 3D simulations of the robot that welds the whole structure. This study deals with the comparison of three structured continuous welds using different weld metal transfers. From the results of the first two processes (dip transfer and IAC process), optimization was achieved using the CMT process and the welding path correction. As the filler material, the low-alloyed solid wire electrode for shielded arc welding of quenched and tempered fine grained structural steels, Böhler Union X 90 (G 89 6 M Mn4Ni2CrMo) with 1 mm in diameter, was used. Obtained samples were subjected to standard technological tests. The results of these tests are used to determine new parameters to ensure stability of this technology. The experiment confirmed that off-line programming will greatly influence the speed and quality of the welding track programs. The results prove that, by combining off-line welding path optimization with an optimized CMT welding process, we can achieve a stable WAAM process

Advanced Functions of a Modern Power Source for GMAW Welding of Steel

This paper evaluates the use of a modern welding power source equipped with advanced arc control functions. At the Laboratory of Welding Technologies of CTU in Prague we have focused on GMAW welding of steel using Sigma Galaxy, a modern welding power source produced by Migatronic. Sigma Galaxy is equipped with functions called Intelligent Arc Control and Sequence Repeat. According to the manufacturer, controlling an arc by these functions should significantly stabilize the welding process, lower the heat input and the deformation, and improve the weld quality. To evaluate the benefits of these functions completely, single V butt welds were performed on S275J2 structural steel 10 mm in thickness (2 weld layers: root+capping layer) in PF and PG positions. Welding was monitored by the Welding Information System, and was compared with standard GMAW welding. The results have shown that these “intelligent” functions offer significant advantages for steel welding, especially in vertical and overhead positions, because they lower the heat input and improve the weld metal control

The Czech Republic on the UN Security Council: The Rwandan Genocide

The Rwanda civil war that in 1994 degenerated into a slaughter of the country’s Tutsi, amounting to genocide, was possibly the world’s most devastating blood- bath of the 1990s. In 1994, the newly formed Czech Republic took up its place as a non-permanent member of the UN Security Council; Karel Kovanda was the Czech Ambassador at the time. Drawing on internal documents of the Czech Foreign Service and on his own private notes, as well as on a wealth of published information, Kovanda details in this personal memoir the step-by-step evolution of the Rwandan tragedy as he and his delegation perceived it, and the Czech reaction to it. He repeatedly highlights the information gap: on the one hand, insufficient and biased information provided by the UN Secretariat; on the other hand, the detailed, accurate, and timely information his delegation received from NGOs. Kovanda estimates that during the first weeks, the Security Council gave perhaps 80% of its attention to the civil war between Rwandan government forces and the Rwandan Patriotic Front (RPF) and 20% to how to handle the difficult position of UNAMIR, the peacekeeping operation then on the ground in Rwanda. Only after weeks of delay did the Security Council even start to come to grips with the ongoing genocide—a term that Ambassador Kovanda was the first to employ publicly in an official UN meeting. While focusing on Rwanda proper, Kovanda also explains and describes the sometimes little-known mechanisms that play a role in the day-to-day workings of the Security Council: the role of the UN Secretariat, informal consultations, groupings of Security Council members, and so on

Změna mechanických vlastností hliníkových slitin typu Al-Zn-Mg-Cu po svařování

V následujícím příspěvku jsou prezentovány výsledky experimentu, který byl proveden na oboustranném tupém svarovém spoji hliníkové slitiny EN AW 7022 a spočíval ve sledování změny tvrdosti v závislosti na čase po svaření. Hliníková slitina tohoto typu patří k vysoce pevným materiálům a svařováním může dojít k degradaci mechanických vlastností. Z tohoto důvodu byl změřen průběh tvrdosti ve svarovém spoji (v oblasti základního materiálu, svarového kovu a tepelně ovlivněné oblasti). Měření tvrdosti bylo provedeno 1., 7., 21., 70. a 175. den po svaření vzorku, experiment potvrdil nárůst tvrdosti vlivem procesu přirozeného stárnutí, jenž je v souladu s předpokládanými výsledky a s výzkumem ostatních autorů. Tvrdost ve svarovém kovu se zvýšila na 80 % původní hodnoty základního materiálu a v tepelně ovlivněné oblasti až na 93 % hodnoty základního materiálu. Elektronovou mikroskopií bylo zjištěno chemické složení svarového kovu a přechodové oblasti

Numerical modeling of two-dimensional heat-transfer and temperature-based calibration using simulated annealing optimization method: Application to gas metal arc welding

Simulation models of welding processes allow us to predict influence of welding parameters on the temperature field during welding and by means of temperature field and the influence to the weld geometry and microstruc-ture. This article presents a numerical, finite-difference based model of heat transfer during welding of thin sheets. Unfortunately, accuracy of the model depends on many parameters, which cannot be accurately prescribed. In or-der to solve this problem, we have used simulated annealing optimization method in combination with presented numerical model. This way, we were able to determine uncertain values of heat source parameters, arc efficiency, emissivity and enhanced conductivity. The calibration procedure was made using thermocouple measurements of temperatures during welding for P355GH steel. The obtained results were used as input for simulation run. The results of simulation showed that represented calibration procedure could significantly improve reliability of heat transfer model

Advanced Functions of a Modern Power Source for GMAW Welding of Steel

This paper evaluates the use of a modern welding power source equipped with advanced arc control functions. At the Laboratory of Welding Technologies of CTU in Prague we have focused on GMAW welding of steel using Sigma Galaxy, a modern welding power source produced by Migatronic. Sigma Galaxy is equipped with functions called Intelligent Arc Control and Sequence Repeat. According to the manufacturer, controlling an arc by these functions should significantly stabilize the welding process, lower the heat input and the deformation, and improve the weld quality. To evaluate the benefits of these functions completely, single V butt welds were performed on S275J2 structural steel 10 mm in thickness (2 weld layers: root+capping layer) in PF and PG positions. Welding was monitored by the Welding Information System, and was compared with standard GMAW welding. The results have shown that these “intelligent” functions offer significant advantages for steel welding, especially in vertical and overhead positions, because they lower the heat input and improve the weld metal control

Numerical modeling of two-dimensional heat-transfer and temperature-based calibration using simulated annealing optimization method: Application to gas metal arc welding

Simulation models of welding processes allow us to predict influence of welding parameters on the temperature field during welding and by means of temperature field and the influence to the weld geometry and microstructure. This article presents a numerical, finite-difference based model of heat transfer during welding of thin sheets. Unfortunately, accuracy of the model depends on many parameters, which cannot be accurately prescribed. In order to solve this problem, we have used simulated annealing optimization method in combination with presented numerical model. This way, we were able to determine uncertain values of heat source parameters, arc efficiency, emissivity and enhanced conductivity. The calibration procedure was made using thermocouple measurements of temperatures during welding for P355GH steel. The obtained results were used as input for simulation run. The results of simulation showed that represented calibration procedure could significantly improve reliability of heat transfer model. [National CEEPUS Office of Czech Republic (project CIII-HR-0108-07-1314) and to the Ministry of Education and Science of the Republic of Serbia (project TR37020)

Multi-objective calibration of the double-ellipsoid heat source model for GMAW process simulation

The scope of application of simulation models in welding is limited by the accuracy of their output results. This paper presents a calibration procedure for a 3-D quasi-stationary model of heat transfer for gas metal arc welding. The double-ellipsoid heat source used in this model has five input parameters whose value cannot be specified accurately. To estimate these values, we employed a multi-objective calibration procedure with two objective functions using the paretosearch optimization algorithm. Objective functions represented the error between simulated and experimentally observed values of penetration depth and weld bead width during gas metal arc welding of P355GH steel plates. All input parameters were assumed to be a power function of line energy. To reduce computational time, we replaced the numerical model with a response surface methodology metamodel based on an optimal set of simulation results from the numerical model. The results of the simulations based on calculated values of input parameters for the heat source model showed excellent matching with the experimental results

Plasma Jet Sputtering as an Efficient Method for the Deposition of Nickel and Cobalt Mixed Oxides on Stainless-Steel Meshes: Application to VOC Oxidation

Hollow cathode plasma sputtering is an advantageous method of preparing catalysts in the form of thin oxide films on supports. Such catalysts are particularly suitable for processes such as catalytic total oxidation of volatile organic compounds (VOCs), representing an economically feasible and environmentally friendly method of VOC abatement. Catalysts with Ni:Co molar ratios of 1:4, 1:1, and 4:1 were prepared on stainless-steel meshes and compared with single-component Ni and Co oxide catalysts. The properties of the catalysts were characterized by EDX, SEM, powder XRD, temperature-programmed reduction (H2-TPR), Raman spectroscopy, and XPS. Powder XRD revealed the formation of various crystalline phases that were dependent on molar the Ni:Co ratio. NiO and Co3O4 were identified in the single-component Ni and Co oxide catalysts, whereas Ni-Co mixed oxides with a spinel structure, together with NiO, were found in the catalysts containing both Ni and Co. Raman spectra of the catalysts prepared at high working pressures showed a slightly lower intensity of bands, indicating the presence of smaller oxide particles. The TPR profiles confirmed the improved reducibility of the Ni-Co oxide catalysts compared to the single-component Ni and Co catalysts. Catalytic activity was investigated in the deep oxidation of ethanol and toluene, which were used as model volatile organic compounds. In ethanol oxidation, the activity of sputtered catalysts was up to 16 times higher than that of the commercial Cu-Mn oxide catalyst EnviCat® VOC-1544. The main benefits of the sputtered catalysts are the much lower content of Ni and Co oxides and a negligible effect of internal diffusion. Moreover, the process of plasma jet sputtering can be easily implemented on a large scale