Fusion zone geometries, cooling rates and solidification parameters during wire arc additive manufacturing

In this paper, the current status of advanced gas metal arc welding (GMAW) process developments and recent research on heat input determination is presented. After a brief review of the basic requirements for welding procedure control, the way in which welding fabrication standards may accommodate these developments is discussed. This paper is specifically intended to address potential issues with fabrication standards where welding procedural control is used but should also provide guidance to researchers and welding engineers on the various process developments and their implications. The scope of the paper is restricted to GMAW and is focused on standards that relate to the fabrication of ferritic steels, although the principles discussed may be relevant to other arc processes and material groups.

Recent gas metal arc welding (GMAW) process developments: the implications related to international fabrication standards

In this investigation, the fabrication of functionally graded structures of SS316L to Ni-based alloys were studied, using the novel technique 3D plasma metal deposition. Two Ni-based alloys were used, a heat resistance alloy Ni80-20 and the solid-solution strengthened Ni625. Different configurations were analyzed, for the Ni80-20 a hard transition and a smooth transition with a region of 50% SS316L/50% Ni80-20. Regarding the structures with Ni625, a smooth transition configuration and variations in the heat input were applied. The effect of the process parameters on the geometry of the structures and the microstructures was studied. Microstructure examinations were carried out using optical and scanning electron microscopy. In addition, microhardness analysis were made on the interfaces. In general, the smooth transition of both systems showed a gradual change in the properties. The microstructural results for the SS316L (both systems) showed an austenite matrix with δ-phase. For the mixed zone and the Ni80-20 an austenite (γ) matrix with some M7C3 precipitates and laves phase were recognized. The as-built Ni625 microstructure was composed of an austenite (γ) matrix with secondary phases laves and δ-Ni3Nb, and precipitates M7C3. The mixed zone exhibited the same phases but with changes in the morphology.

/pdf/functionally-graded-ss-316l-to-ni-based-structures-produced-14j51ocbje.pdf

Functionally Graded SS 316L to Ni-Based Structures Produced by 3D Plasma Metal Deposition

Numerical simulation of arc, metal transfer and its impingement on weld pool in variable polarity gas metal arc welding

https://depositonce.tu-berlin.de/bitstream/11303/11253/1/sproesser_etal_2016.pdf

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

A study was carried out to measure the effective efficiency of different gas shielded arc welding processes and investigate the role of influence coefficients on the process efficiency. A new system to measure the integrated heat flow in welding processes was developed and further investigated. By this system, it can be shown how e.g. electrical and welding torch parameters, as well as material and gas parameters directly influence the efficiency of the welding process. Through this, it is possible to raise the efficiency of welding (processes for example by reducing the wire speed, using helium gas or increasing the distance of the welding torch to the metal plate. Contrary, increasing the current, welding speed or voltage reduces the process efficiency. The difference between the lowest and highest achievable value of efficiency can be more than 15 % for one specific welding process. In addition to the conventional welding processes like gas tungsten arc welding (GTAW), gas metal arc welding (GMAW) and plasma welding also latest technologies, such as heat reduced processes (for example controlled dip arc with or without wire pullback) and high performance welding processes were analysed. In this manuscript, primarily the new technology for measuring the efficiency is presented. Furthermore, different influence coefficients and their effects on the overall efficiency of welding processes are described. Finally, the differences between measured efficiencies and fixed values of efficiencies for welding processes given in standards are discussed. The efficiencies of the latest heat reduced and high performance welding processes are given. The results verify that the parametrical influence on the efficiency of welding processes is huge, so that it is not recommended to work with fixed efficiency values for example in modeling and simulation.

New Findings On The Efficiency Of Gas Shielded Arc Welding

Within this manuscript, the comprehensive heat flow, as well as the energy balance for gas-shielded arc welding processes based on experimental investigations is discussed. The main focus lies on the gas metal arc welding (GMAW) process which is further analysed. Different calorimetric measurement methods and results for the separate determination of the energy content of droplet and welding arc as well as energy input into the component are presented. Additionally, heat losses to the surrounding atmosphere and the cooling energy of the external cooling power source system are analysed. The mean droplet temperatures are within a range of T
 dr = 2,350 … 2,700 °C. The studies also show that a specific manipulation of the droplet temperature during the welding process is not possible and droplet temperature depends on several parameters. Increasing the wire feed speed, reducing the diameter of the filler material or increasing the stick out length result in an increase of the droplet temperature. The analyses allow to conclude that the welding arc is mainly responsible for the weld seam penetration and the droplet temperature only contributes in a minor manner. Preliminary experiments also show that the heat input into the component is highly influenced by the selection of welding parameters. Measurements confirm that it is possible to increase the efficiency of welding processes for example by reducing the wire feed speed, using carbon dioxide shielding gas or increasing the stick out length. On the contrary, increasing the current or voltage or reducing the shielding gas flow reduces the process efficiency. The difference between the lowest and highest achievable value of efficiency can be more than 15 % for one specific welding process.

Calorimetric analyses of the comprehensive heat flow for gas metal arc welding

The efficiency as well as the knowledge of the energy flow of welding processes is a fundamental coefficient to realize high-quality joints. The increasing use of high-strength materials with a small processing range as well as the demand to simulate resulting component properties increase the demand of exact knowledge of the heat input. Experiments show that the heat input into the component is highly influenced by the selection of welding parameters. Measurements confirm that it is possible to increase the efficiency of welding processes for example by reducing the wire feed speed in gas metal arc welding (GMAW), using carbon dioxide shielding gas or increasing the stick-out length. On the contrary, increasing the current or voltage or reducing the shielding gas flow reduces the process efficiency. The difference between the lowest and highest achievable value of efficiency can be more than 15 % for one specific welding process. In this work, the efficiencies of different groups of welding processes are compared. Due to the use of unique measurement systems and systematical analyses of influencing parameters, a comprehensive overview for different welding processes is possible for the first time.

Determination of energy flows for welding processes

To reach the goal of weight reduction, modern thermo-mechanically processed micro-alloy steels are increasingly used to replace carbon-manganese structural steels. The processing window for welding these newer materials is much smaller, so it is important to accurately determine the rate of heat input, the t8/5-value (cooling rate) and also to ensure that the desired cooling rate is achieved in production. Variations in the welding process, welding parameters welded joint configuration, welding position, and layer structure change the rate of heat input into the component. At the same time, the arcing efficiency is affected by configuration and position. In combination, these parameters can affect the cooling behavior by more than 60%. Various welding processes and parameters are analyzed and the potential errors are discussed. Following this, the impact of these errors is illustrated with reference to practical measurements. The summation of the possible errors shows that it is difficult in practice to achieve the desired mechanical and metallurgical characteristics, as well as theoretically predicting these values, and also calculating or simulating properties such as distortion, microstructure, or residual stresses. The work presented here, together with recommendations for adjustment of published efficiency values as well form factors to calculate the t8/5-value (cooling rate), is expected to make a significant contribution to improve the quality of welded joints.

Reducing potential errors in the calculation of cooling rates for typical arc welding processes

The lowering of the German occupational exposure limit from 3 mg/m3 to 1.25 mg/m3 by 2018 and the high health hazard from tubular cored electrodes shows the need to determine and minimize the emiss...

Mario Kusch

Papers

New Findings On The Efficiency Of Gas Shielded Arc Welding

Calorimetric analyses of the comprehensive heat flow for gas metal arc welding

Determination of energy flows for welding processes

Reducing potential errors in the calculation of cooling rates for typical arc welding processes

Flux cored arc welding – determination and reduction of fume emission rates