Raimo Suoranta

State-of-the-art of advanced gas metal arc welding processes: Dissimilar metal welding:

The manufacturing industry has for many years shown interest in opportunities offered by the welding of dissimilar metals, for example, in transportation to reduce vehicles weight and in power plants, to fit heterogeneous working conditions. Early gas metal arc welding (GMAW) processes had limited control of heat input, but advanced GMAW processes of the last decades offer new perspectives for welding dissimilar metals. The study review briefly dissimilar metal welding (DMW) and investigates advanced GMAW processes with emphasis on their general operating principles and arc control. Experiments performed on dissimilar metals using GMAW processes are then reviewed, highlighting those made using advanced gas metal arc welding processes. The study collates data from scientific literature on fusion dissimilar metal welding, advanced gas metal arc welding processes and experiments conducted with conventional GMAW. The study shows that the welding procedure specification is an important factor in dissimilar metal welding. Advanced GMAW processes have significant potential in fusion welding of dissimilar metals in the case of ferrous metals, ferrous and non-ferrous metal combinations and non-ferrous metals of different grades. Accurate control of heat input allows more effective prediction of intermetallics and better control of post heat treatments. Increased understanding of advanced processes will permit development of more suitable specifications of gas metal arc welding procedures for dissimilar metal welding. Process flexibility and adaptability to robotic mass production will allow for wider application of this process and the avoidance of costly alternative methods.

Real Time Non-Destructive Testing Methods of Welding

This work presents a review of the three most efficient non-destructive testing methods. The methods are radiography, eddy current and ultrasonic inspection. These particular techniques were chosen because they are able to cover most of the industrial needs for welding joint inspection. The aim of this work is to present the physical background of operation for the given methods, discuss their benefits, limitations, and typical areas of application, and compare them with each other. In the first part of this work, all three methods and their variations are described in detail with schemes and figures which represent their working principles. It appears that, although all the given methods can detect all types of flaws in welded joints, they have their specific limitations. For example, ultrasonic testing is able to detect defects only in certain directions. The eddy current technique is also sensitive to defect direction, but it can be applied for inspecting conductive materials only. The main flaw of radiography is the resolution: it is not usable for very fine defects. The second part of the work is for comparing the testing methods and for drawing the conclusions. The methods are compared according to the possible materials, defect types and their position, as well as the possible areas of application. This part gives the background for choosing a proper welding joint testing method for certain applications in the welding industry.

Welding of Ultra High Strength Steels

The ongoing need to reduce the weight of products while increasing strength has resulted in new generation steel manufacturing using special heat treatments to produce High Strength Steels (HSS) and Ultra High Strength Steels (UHSS) with up to 1700 MPa tensile strength. The high strength level of these steels makes it possible to produce structures with a considerable weight and cost reduction, and such steels have been adopted in the automotive industry and for mobile heavy equipment. Welding of UHSS is, however, not without its complications and welding processes for these steels need careful attention. For instance, their high susceptibility to cracking and Heat Affected Zone (HAZ) softening are risks that need to be borne in mind when choosing welding parameters. This research work discusses the difficulties and challenges of successful welding of UHSS. Common welding methods used in welding of UHSS are briefly reviewed to gain a better understanding of the effects of different welding parameters and methods. The paper finds that UHSS can be satisfactorily welded with laser welding, electron beam welding, resistance welding, and conventional arc welding methods, but the quality of the weld is dependent on appropriate control of several parameters and variables of the welding processes.