Determination of the causes of weld-metal cracking in high-strength steels and the development of heat-treatable low-alloy-steel filler wires for use with the inert-gas-shielded arc-welding process

"Materials Central, Contract no. AF 33(616)-5878, Project no. 7351."

Welding of Sheet metal using Modified short arc MIG/MAG welding process

In this research work, the results of an investigation dealing with welding of sheet metals with diverse air gap using FastROOT modified short arc welding method and short circuit MAG welding processes have been presented. Welding runs were made under different conditions and, during each run, the different process parameters were continuously monitored. It was found that maximum welding speed and less HAZ are reached under specific welding conditions with FastROOT method with the emphasis on arc stability. Welding results show that modified short arc exhibits a higher electrode melting coefficient and with virtually spatter free droplet transition. By adjusting the short circuit duration the penetration can be controlled with only a small change in electrode deposition. Furthermore, by mixing pulsed MIG welding with modified arc welding the working envelope of the process is greatly extended allowing thicker material sections to be welded with improved weld bead aesthetics. FastROOT is a modified short arc welding process using mechanized or automated welding process based on dip transfer welding, characterized by controlled material deposition during the short circuit of the wire electrode to the workpiece.

The copper cladding of steel by the submerged arc welding method

The literature available on submerged arc welding of copper and copper alloys, submerged arc welding with strip electrodes, and related areas has been reviewed in depth. Copper cladding of mild steel substrates by deposition from strip electrodes using the submerged arc welding process has been successful. A wide range of parameters, and several fluxes have been investigated. The range of deposit compositions is 66.4% Cu to 95.7% Cu. The weld beads have been metallographically examined using optical and electron microscopy. Equating weld beads to a thermodynamical equivalent of iron has proven to be an accurate and simplified means of handling quantitative data for multicomponent welds. Empirical equations derived using theoretical considerations characterize the weld bead dimensions as functions of the welding parameters and hence composition. The melting rate for strip electrodes is dependent upon the current-voltage product. Weld nugget size is increased by increased thermal transfer efficiencies resulting from stirring which is current dependent. The presence of Fe2O3 in a flux has been demonstrated to diminish electrode melting rate and drastically increase penetration, making flux choice the prime consideration in cladding operations. A theoretical model for welding with strip electrodes and the submerged arc process is presented.

Characterization of airborne particles generated from metal active gas welding process

This study is focused on the characterization of particles emitted in the metal active gas welding of carbon steel using mixture of Ar + CO2, and intends to analyze which are the main process parameters that influence the emission itself. It was found that the amount of emitted particles (measured by particle number and alveolar deposited surface area) are clearly dependent on the distance to the welding front and also on the main welding parameters, namely the current intensity and heat input in the welding process. The emission of airborne fine particles seems to increase with the current intensity as fume-formation rate does. When comparing the tested gas mixtures, higher emissions are observed for more oxidant mixtures, that is, mixtures with higher CO2 content, which result in higher arc stability. These mixtures originate higher concentrations of fine particles (as measured by number of particles by cm 3 of air) and higher values of alveolar deposited surface area of particles, thus resulting in a more severe worker's exposure.

Control methods for arc welding power supplies

Welding is one of the most important process of modern industry. Welding technology is used in the manufacture and repair a wide variety of products from different metals and alloys. In this thesis the different aspects of arc welding were discussed, such as stability and control of welding arc, power supplies for arc welding (especially the welding inverters because it is the most modern welding power source). All parameters of power source have influence on the arc parameters and its by-turn influence on quality. The ways of control for arc welding inverter power sources have been considered. Calculations and modeling in Matlab/Simulink were done for PI control method. All parameters of power source have influence on the arc parameters and its by-turn influence on quality.

Laser-TIG hybrid welding process

Joining processes and techniques need to meet the trend of new applications and the development of new materials. The application in connection with thick and thin plates in industrial fields is wide and the joining technology is in very urgent need. The laser-TIG hybrid welding technology can play the respective advantages of both of them. One major advantage of the hybrid laser-TIG welding technology is its efficient use of laser energy. Additionally, it can develop into a high and new advanced welding technology and become a hot spot in both the application and research area. This thesis investigated laser –TIG hybrid welding with the aim of enlightening the reader on its advantages, disadvantages and future areas of improvement. The main objective is to investigate laser-TIG hybrid on the welding of various metals (steels, magnesium, aluminium etc.). In addition, it elaborates on various possible combinations on hybrid laser-TIG welding technology and their benefits. The possibility of using laser-TIG hybrid in welding of thick materials was investigated. The method applied in carrying out this research is by using literature review. The results showed that hybrid laser-TIG is applicable to almost all weldable metals. Also it proves to be effective in welding refractive metals. The possibility of welding with or without filler materials is of economic advantage especially in welding of materials with no filler material. Thick plate’s hybrid laser-TIG welding is showing great prospects although it normally finds its used in welding thin materials in the range of 0.4 to 0.8 mm. The findings show that laser-TIG hybrid welding can be a versatile welding process and therefore will be increasingly used industrially due to its numerous advantages and the development of new TIG arc that enhances its capabilities.

Narrow Gap flux-cored arc welding of high strength shipbuilding steels

This thesis is part of the Arctic Materials Technologies Development –project. The research of the thesis was done in cooperation with Arctech Helsinki Shipyard, Lappeenranta University of Technology and Kemppi Oy. Focus of the thesis was to study narrow gap flux-cored arc welding of two high strength steels with three different groove angles of 20°, 10° and 5°. Welding of the 25 mm thick E500 TMCP and 10 mm thick EH36 steels was mechanized and Kemppi WisePenetration and WiseFusion processes were tested with E500 TMCP steel. EH36 steel test pieces were welded without Wise processes. Shielding gases chosen were carbon dioxide and a mixture of argon and carbon dioxide. Welds were tested with non-destructive and destructive testing methods. Radiographic, visual, magnetic particle and liquid penetrant testing proved that welds were free from imperfections. After non-destructive testing, welds were tested with various destructive testing methods. Impact strength, bending, tensile strength and hardess tests proved that mechanized welding and Wise processes produced quality welds with narrower gap. More inconsistent results were achieved with test pieces welded without Wise processes. Impact test results of E500 TMCP exceeded the 50 J limit on weld, set by Russian Maritime Register of Shipping. EH36 impact test results were much closer to the limiting values of 34 J on weld and 47 on HAZ. Hardness values of all test specimens were below the limiting values. Bend testing and tensile testing results fulfilled the the Register requirements. No cracking or failing occurred on bend test specimens and tensile test results exceeded the Register limits of 610 MPa for E500 TMCP and 490 MPa for EH36.

Gas tungsten arc welding of NiTi shape memory alloy

Shape memory alloys are characterized by the ability of recovering their initial shape after being deformed and by superelasticity. Since the discovery of these alloys, a new field of interest emerged not only for the scientific community but also to many industries. However, these alloys present poor machinability which constitute a constrain in the design of complex components for new applications. Thus, the demand for joining techniques able to join these alloys without compromising their properties became of great importance to enlarge the complexity of existing applications. Literature shows that these alloys are joined mainly using laser welding. In the present study, similar NiTi butt joints, were produced using TIG welding. The welds were performed in 1.5 mm thick plates across the rolling direction. A special fixture and gas assist device was designed and manufactured. Also a robot arm was adapted to accommodate the welding torch to assure the repeatability of the welding parameters. Welds were successfully achieved without macroscopic defects, such as pores and distortions. Very superficial oxidation was seen on the top surface due to insufficient shielding gas flow on the weld face. The welded joints were mechanically tested and structurally characterized. Testing methods were used to evaluate macro and microstructure, as well as the phase transformation temperatures, the mechanical single and cyclic behaviour and the shape recovery ability. Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), microhardness measurements were techniques also used to evaluate the welded joints. A depletion in Ni in the fusion zone was seen, as well as a shift in Ms temperature. For strain values of 4% the accumulated irrecoverable strain was of about 30% and increased with the strain imposed during cycling. Nevertheless, a complete recovery of initial shape was observed when testing the shape memory effect on a dedicated device that introduces a deformation of 6.7%. That is, the welding procedure does not remove the ability of the specimens to recover their initial shape.

Advanced orbital pipe welding

Since the introduction of automatic orbital welding in pipeline application in 1961, significant improvements have been obtained in orbital pipe welding systems. Requirement of more productive welding systems for pipeline application forces manufacturers to innovate new advanced systems and welding processes for orbital welding method. Various methods have been used to make welding process adaptive, such as visual sensing, passive visual sensing, real-time intelligent control, scan welding technique, multi laser vision sensor, thermal scanning, adaptive image processing, neural network model, machine vision, and optical sensing. Numerous studies are reviewed and discussed in this Master’s thesis and based on a wide range of experiments which already have been accomplished by different researches the vision sensor are reported to be the best choice for adaptive orbital pipe welding system. Also, in this study the most welding processes as well as the most pipe variations welded by orbital welding systems mainly for oil and gas pipeline applications are explained. The welding results show that Gas Metal Arc Welding (GMAW) and its variants like Surface Tension Transfer (STT) and modified short circuit are the most preferred processes in the welding of root pass and can be replaced to the Gas Tungsten Arc Welding (GTAW) in many applications. Furthermore, dual-tandem gas metal arc welding technique is currently considered the most efficient method in the welding of fill pass. Orbital GTAW process mostly is applied for applications ranging from single run welding of thin walled stainless tubes to multi run welding of thick walled pipes. Flux cored arc welding process is faster process with higher deposition rate and recently this process is getting more popular in pipe welding applications. Also, combination of gas metal arc welding and Nd:YAG laser has shown acceptable results in girth welding of land pipelines for oil and gas industry. This Master’s thesis can be implemented as a guideline in welding of pipes and tubes to achieve higher quality and efficiency. Also, this research can be used as a base material for future investigations to supplement present finding.

A quality and cost approach for welding process selection

The aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of Quality and Costs. A case study was used. The welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: SMAW, GTAW, pulsed GTAW, GMAW with CO2 and Ar based shielding gases and pulsed GMAW. For Quality analysis geometrical aspects of the beads were considered and for Cost analysis, welding parameters and consumable prices. Quantitative indices were proposed and evaluated. After that, evaluation of both Quality and Costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.

Green welding in practice

Efficient production and consumption of energy has become the top priority of national and international policies around the world. Manufacturing industries have to address the requirements of the government in relation to energy saving and ecologically sustainable products. These industries are also concerned with energy and material usage due to their rising costs. Therefore industries have to find solutions that can support environmental preservation yet maintain competitiveness in the market. Welding, a major manufacturing process, consumes a great deal of material and energy. It is a crucial process in improving a product’s life-cycle cost, strength, quality and reliability. Factors which lead to weld related inefficiencies have to be effectively managed, if industries are to meet their quality requirements and fulfil a high-volume production demand. Therefore it is important to consider some practical strategies in welding process for optimization of energy and material consumption. The main objective of this thesis is to explore the methods of minimizing the ecological footprint of the welding process and methods to effectively manage its material and energy usage in the welding process. The author has performed a critical review of the factors including improved weld power source efficiency, efficient weld techniques, newly developed weld materials, intelligent welding systems, weld safety measures and personnel training. The study lends strong support to the fact that the use of eco-friendly welding units and the quality weld joints obtained with minimum possible consumption of energy and materials should be the main directions of improvement in welding systems. The study concludes that, gradually implementing the practical strategies mentioned in this thesis would help the manufacturing industries to achieve on the following - reduced power consumption, enhanced power control and manipulation, increased deposition rate, reduced cycle time, reduced joint preparation time, reduced heat affected zones, reduced repair rates, improved joint properties, reduced post-weld operations, improved automation, improved sensing and control, avoiding hazardous conditions and reduced exposure of welder to potential hazards. These improvement can help in promotion of welding as a green manufacturing process.

An Application of Augmented Reality (AR) in the Teaching of an Arc Welding Robot

Augmented Reality (AR) is an emerging technology that utilizes computer vision methods to overlay virtual objects onto the real world scene so as to make them appear to co-exist with the real objects. Its main objective is to enhance the user’s interaction with the real world by providing the right information needed to perform a certain task. Applications of this technology in manufacturing include maintenance, assembly and telerobotics. In this paper, we explore the potential of teaching a robot to perform an arc welding task in an AR environment. We present the motivation, features of a system using the popular ARToolkit package, and a discussion on the issues and implications of our research.

Unbalanced Three-Phase Induction Motors Starting and Arc Welding Machines Short-Circuit Modeling

Three-Phase Induction Motors (TIM) and Arc Welding Machines (AWM) are loads of special behavior widely used in industrial and commercial installations, and therefore may contribute significantly to the deterioration of the quality of energy supplied by utilities. This paper proposes a modeling in constant power of the unbalanced TIM starting using Genetic Algorithm (GA) and AWM short-circuit based on their statics characteristics curves. The proposed models are compared with the conventional models in the literature. The results showed the good performance of the proposed models, allowing a more precise analysis of the real requests of these loads.

Effects Of The Flash Welding Process On Mechanical And Microstructural Properties Of Structural Steel Joints Assessed Using Dest

ASTM A529 carbon¿manganese steel angle specimens were joined by flash butt welding and the effects of varying process parameter settings on the resulting welds were investigated. The weld metal and heat affected zones were examined and tested using tensile testing, ultrasonic scanning, Rockwell hardness testing, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy in order to quantify the effect of process variables on weld quality. Statistical analysis of experimental tensile and ultrasonic scanning data highlighted the sensitivity of weld strength and the presence of weld zone inclusions and interfacial defects to the process factors of upset current, flashing time duration, and upset dimension. Subsequent microstructural analysis revealed various phases within the weld and heat affected zone, including acicular ferrite, Widmanstätten or side-plate ferrite, and grain boundary ferrite. Inspection of the fracture surfaces of multiple tensile specimens, with scanning electron microscopy, displayed evidence of brittle cleavage fracture within the weld zone for certain factor combinations. Test results also indicated that hardness was increased in the weld zone for all specimens, which can be attributed to the extensive deformation of the upset operation. The significance of weld process factor levels on microstructure, fracture characteristics, and weld zone strength was analyzed. The relationships between significant flash welding process variables and weld quality metrics as applied to ASTM A529-Grade 50 steel angle were formalized in empirical process models.