Increasing Performance and Energy Efficiency of Gas Metal Arc Welding by a High Power Tandem Process

Standard Gas Metal Arc Welding (Standard GMAW) and a high power Tandem GMAW (TGMAW) process are evaluated with respect to energy efficiency. Current, voltage and overall equipment power are measured and energy consumption is determined. The new key performance indicator Electrical Deposition Efficiency is introduced to reflect the energy efficiency of GMAW processes. Additionally, wall-plug efficiency of the equipment is determined in order to identify the overall energy consumption. Results show that energy efficiency as well as economic process performance can be significantly increased by application of the TGMAW process. Furthermore findings indicate that wall-plug efficiency of the equipment is independent of power level and material transfer mode. A metal plate of 30 mm thick structural steel is joined by Standard GMAW and TGMAW to demonstrate the total energy savings for a real weld. Electricity consumption is reduced by more than 20% using the high power TGMAW process.DFG, 199828953, SFB 1026: Sustainable Manufacturing - Globale Wertschöpfung nachhaltig gestalte

Automatically Welded Tubular X‐Joints for Jacket Substructures: Prediction of the Technical Fatigue Crack Location

To increase the competitiveness of jacket substructures compared to monopiles a changeover from an individual towards a serial jacket production based on automated manufactured tubular joints combined with standardized pipes has to be achieved. Therefore, this paper addresses fatigue tests of automatically welded tubular X-joints focusing on the location of the technical fatigue crack. The detected location of the technical crack is compared to numerical investigations predicting the most fatigue prone notch considering the structural stress approach as well as the notch stress approach. Besides, the welding process of the automated manufactured tubular X-joints is presented

Sustainable technologies for thick metal plate welding

Welding is the most important joining technology. In the steel construction industry, e.g. production of windmill sections, welding accounts for a main part of the manufacturing costs and resource consumption. Moreover, social issues attached to welding involve working in dangerous environments. This aspect has unfortunately been neglected so far, in light of a predominant focus on economics combined with a lack of suitable assessment methods. In this chapter, exemplary welding processes are presented that reduce the environmental and social impacts of thick metal plate welding. Social and environmental Life Cycle Assessments for a thick metal plate joint are conducted for the purpose of expressing and analysing the social and environmental impacts of welding. Furthermore, it is shown that state-of-the-art technologies like Gas Metal Arc Welding with modified spray arcs and Laser Arc-Hybrid Welding serve to increase social and environmental performance in contrast to common technologies, and therefore offer great potential for sustainable manufacturing

Assessing carbon dioxide emission reduction potentials of improved manufacturing processes using multiregional input output frameworks

Evaluating innovative process technologies has become highly important within the last decades. As standard tools different Life Cycle Assessment methods have been established, which are continuously improved. While those are designed for evaluating single processes they run into difficulties when it comes to assessing environmental impacts of process innovations at macroeconomic level. In this paper we develop a multi-step evaluation framework building on multi regional input–output data that allows estimating macroeconomic impacts of new process technologies, considering the network characteristics of the global economy. Our procedure is as follows: i) we measure differences in material usage of process alternatives, ii) we identify where the standard processes are located within economic networks and virtually replace those by innovative process technologies, iii) we account for changes within economic systems and evaluate impacts on emissions. Within this paper we exemplarily apply the methodology to two recently developed innovative technologies: longitudinal large diameter steel pipe welding and turning of high-temperature resistant materials. While we find the macroeconomic impacts of very specific process innovations to be small, its conclusions can significantly differ from traditional process based approaches. Furthermore, information gained from the methodology provides relevant additional insights for decision makers extending the picture gained from traditional process life cycle assessment.DFG, SFB 1026, Sustainable Manufacturing - Globale Wertschöpfung nachhaltig gestalte

Environmental and Social Life Cycle Assessment of welding technologies

Life Cycle Assessment (LCA) and Social Life Cycle Assessment (SLCA) are applied in evaluating possible social and environmental impacts of the state-of-art welding technologies, such as Manual Metal Arc Welding (MMAW), Manual Gas Metal Arc Welding (GMAW), Automatic GMAW and Automatic Laser-Arc Hybrid Welding (LAHW). The LCA results indicate that for 1 meter weld seam, MMAW consumes the largest amount of resources (like filler material and coating on electrodes) and energy, which contributes to comparatively higher environmental impacts in global warming potential, acidification, photochemical ozone creation potential and eutrophication than other chosen processes. With regard to social aspects, the health issues and fair salary are under survey to compare the relative potential risk on human health caused by fumes in different welding technologies, and to indicate the sufficiency of current salary of welders in Germany. The results reflect that the wage status of welders is still fair and sufficient. The manual processes bring much higher potential risk of welders’ health than the automatic processes, especially MMAW

Hypertrophic cardiomyopathy is characterized by alterations of the mitochondrial calcium uniporter complex proteins: insights from patients with aortic valve stenosis versus hypertrophic obstructive cardiomyopathy

Introduction: Hypertrophies of the cardiac septum are caused either by aortic valve stenosis (AVS) or by congenital hypertrophic obstructive cardiomyopathy (HOCM). As they induce cardiac remodeling, these cardiac pathologies may promote an arrhythmogenic substrate with associated malignant ventricular arrhythmias and may lead to heart failure. While altered calcium (Ca2+) handling seems to be a key player in the pathogenesis, the role of mitochondrial calcium handling was not investigated in these patients to date.Methods: To investigate this issue, cardiac septal samples were collected from patients undergoing myectomy during cardiac surgery for excessive septal hypertrophy and/or aortic valve replacement, caused by AVS and HOCM. Septal specimens were matched with cardiac tissue obtained from post-mortem controls without cardiac diseases (Ctrl).Results and discussion: Patient characteristics and most of the echocardiographic parameters did not differ between AVS and HOCM. Most notably, the interventricular septum thickness, diastolic (IVSd), was the greatest in HOCM patients. Histological and molecular analyses showed a trend towards higher fibrotic burden in both pathologies, when compared to Ctrl. Most notably, the mitochondrial Ca2+ uniporter (MCU) complex associated proteins were altered in both pathologies of left ventricular hypertrophy (LVH). On the one hand, the expression pattern of the MCU complex subunits MCU and MICU1 were shown to be markedly increased, especially in AVS. On the other hand, PRMT-1, UCP-2, and UCP-3 declined with hypertrophy. These conditions were associated with an increase in the expression patterns of the Ca2+ uptaking ion channel SERCA2a in AVS (p = 0.0013), though not in HOCM, compared to healthy tissue. Our data obtained from human specimen from AVS or HOCM indicates major alterations in the expression of the mitochondrial calcium uniporter complex and associated proteins. Thus, in cardiac septal hypertrophies, besides modifications of cytosolic calcium handling, impaired mitochondrial uptake might be a key player in disease progression

Ein Beitrag zur Lösung des inversen Wärmeleitungsproblems in der Schweißsimulation

Die vorliegende Arbeit liefert einen Beitrag zur Lösung des inversen Wärmeleitungsproblems in der Schweißsimulation. Die Ermittlung des dreidimensionalen und transienten Schweißtemperaturfeldes stellt den wichtigsten aber derzeit auch aufwendigsten Teil der Simulationskette dar. Die Lösungsstrategie basiert auf dem Ansatz, dass das für die direkten Lösungen verwendete phänomenologische Simulationsmodel innerhalb kurzer Berechnungszeiten das Ergebnis liefert. Diese Anforderung ist maßgeblich für die Anwendung numerischer Optimierungsverfahren zur Bestimmung optimaler Modellparameter. Das direkte Simulationsmodel beruht auf funktionsanalytischen Lösungen der partiellen Differentialgleichung der Wärmeleitung. Im Speziellen werden Wärmequellen mit einer volumetrischen Energiedichteverteilung eingesetzt, deren Wirkbereich begrenzt ist. Neben der bekannten normalen und exponentiellen Energiedichteverteilung wird die analytische Lösung für eine parabolische Energieverteilung hergeleitet. Des Weiteren werden die analytischen Lösungen erweitert, so dass die Bewegung von Wärmequellen auf beliebig orientierten Trajektorien berücksichtigt werden kann. Ein weiterer Schwerpunkt der Arbeit ist die Kalibrierung der Wärmequellenmodelle gegen experimentelle Referenzdaten. Hierbei wird ein multidimensionales Optimierungsproblem gelöst. Dabei wird der globale Parameterraum mit Hilfe einer auf Zufallszahlen basierenden Methodik analysiert. Die Lösung des Optimierungsproblems erfordert jedoch zunächst die Kenntnis der Modellsensitivität bei Variation der Modelleingangsparameter. Es konnte gezeigt werden, dass sich insbesondere analytische Verfahren aufgrund des geringen Rechenbedarfs eignen, multidimensionale Sensitivitätsstudien durchzuführen. Die eingesetzte heuristische Methode zur Lösung des inversen Wärmeleitungsproblems wird zur Rekonstruktion von Temperaturfeldern realer Schweißexperimente eingesetzt. Es kann gezeigt werden, dass das Temperaturfeld einer Laserstrahl- sowie Laser-MSG Hybridschweißung basierend auf extrahierten Referenzdaten des Makroschliffes sowie Temperaturzyklus rekonstruiert werden konnte. Zusätzlich werden numerische Studien mit dem Ziel durchgeführt, zu evaluieren, welche experimentellen Referenzdaten notwendig sind, um ein dreidimensionales transientes Schweißtemperaturfeld eindeutig zu charakterisieren. Hierbei wird der Einfluss der Referenzdaten auf die Charakteristik der zu minimierenden Zielfunktion untersucht. Die effiziente Lösung des inversen Wärmeleitungsproblems beruht auf zwei wesentlichen Aspekten: das Vorhandensein schneller direkter Lösungen der Temperaturfeldgleichung sowie eine sinnvolle Komplexität des Optimierungsproblems. Für die in dieser Arbeit entwickelte parabolischen Energiedichtverteilung konnte in diesem Kontext gezeigt werden, dass eine Reduktion der Komplexität des Optimierungsproblems die Gesamtlösungszeit des inversen Wärmeleitungsproblems signifikant verringert. Die im Rahmen dieser Arbeit gewonnen Erkenntnisse bezüglich einer effizienten Lösung des inversen Wärmeleitungsproblems in der Schweißsimulation können auch auf numerische Wärmeleitungsmodelle übertragen werden.The present thesis provides a contribution to the solution of the inverse heat conduction problem in welding simulation. The solution strategy is governed by the need that the phenomenological simulation model utilised for the direct solution has to provide calculation results within short computational time. This is a fundamental criterion in order to apply optimisation algorithms for the detection of optimal model parameter sets. The direct simulation model focuses on the application of functional-analytical methods for solving the corresponding partial differential equation of heat conduction. In particular, volume heat sources with a bounding of the domain of action are applied. Besides the known normal and exponential distribution, the models are extended by the introduction of parabolically distributed heat sources. Furthermore, the movement on finite specimens under consideration of curved trajectories has been introduced and solved analytically. The calibration of heat source models against experimental reference data involves the simultaneous adaptation of models parameters. Here, the global parameter space is searched in a randomised manner. However, an optimisation pre-processing is needed to get information about the sensitivity of the weld characteristics like weld pool dimension or objective function due to a change of the model parameters. Because of their low computational cost functional-analytical models are well suited to allow extensive sensitivity studies which is demonstrated in this thesis. For real welding experiments the applicability of the simulation framework to reconstruct the temperature field is shown. In addition, computational experiments are performed that allow to evaluate which experimental reference data is needed to represent the temperature field uniquely. Moreover, the influence of the reference data like fusion line in the cross section or temperature measurements are examined concerning the response behaviour of the objective function and the uniqueness of the optimisation problem. The efficient solution of the inverse problem requires two aspects, namely fast solutions of the direct problem but also a reasonable number of degrees of freedom of the optimisation problem. Hence, a method was developed that allows the direct derivation of the energy distribution by means of the fusion line in the cross section, which allows reducing the dimension of the optimisation problem significantly. All conclusions regarding the sensitivity studies and optimisation behaviour are also valid for numerical models for which reason the investigations can be treated as generic

Wire Arc Additive Manufacturing with Novel Al-Mg-Si Filler Wire—Assessment of Weld Quality and Mechanical Properties

Wire arc additive manufacturing enables the production of near-net shape large-volume metallic components leveraging an established industrial base of welding and cladding technology and adapting it for layer-wise material deposition. However, the complex relationship between the process parameters and resulting mechanical properties of the components still remains challenging. In case of high-strength Al-Mg-Si aluminum alloys, no commercial filler wires are yet available due the high susceptibility of solidification cracking as well as the necessary efforts to obtain acceptable mechanical properties. To address this need, we evaluated a novel filler wire based on AlMg0.7Si doped with a Ti5B1 master alloy to foster fine equiaxed grains within the deposited metal. The correlation between the process parameters and component quality was examined by analyzing the size and distribution of pores as well as the grain morphology. Furthermore, we evaluated the influence of different post-weld heat treatment strategies to achieve mechanical properties corresponding to the reference wrought material. We demonstrated that fine equiaxed grains in the weld metal reduced the susceptibility of solidification cracking significantly. The novel AlMg0.7Si-TiB (S Al 6063-TiB) filler wire facilitated wire arc additive manufacturing of high-strength aluminum components with mechanical properties that were almost as superior as the corresponding wrought base material.BMBF, 01LY1615D, KMU-innovativ - Verbundprojekt Klimaschutz: Energieeffiziente Leichtbaukonzepte durch den Einsatz von 3D-Metalldruck und neuartigen Aluminiumlegierungen (LightPrint) - Teilprojekt 4: Schweißtechnische Verarbeitun