Jukka Martikainen

Conditions for achieving high-quality welds in the plasma-arc keyhole welding of structural steels

Abstract The present investigation describes the possibilities and the technological conditions for welding structural steels, especially high-strength steels, reproducibly and with high quality. The investigation comprises butt welding with an I-groove in the flat, horizontal vertical and vertical positions, and root welding of thick plates in the flat position. The investigation presents the welding-parameter combinations which results in the best quality welds. It has been shown that mechanized plasma keyhole welding is a very useful method for structural steels. It can compete successfully with common MIG/MAG and SAW welding as well as with electron and laser-beam welding, especially in large applications such as in the welding of large plates, box girders, tanks and pressure vessels, and large diameter pipes.

Determination of fracture toughness using the area of micro-crack tracks left in brittle materials by Vickers indentation test

In this article, a new method has been presented for the estimation of fracture toughness in brittle materials, which enjoys improved accuracy and reduced costs associated with fracture toughness testing procedure compared to similar previous methods, because a vast range of specimens with irregular cracks can be accommodated for testing. Micron-sized alumina powders containing 0.05 wt% magnesium oxide (MgO) nanoparticles were mixed and also together with 2.5 vol%, 5 vol%, 7.5 vol%, 10 vol%, and 15 vol% of silicon carbide (SiC) nanopowders separately. By making and testing various types of ceramics with different mechanical properties, and considering the irregular cracks around the indented area caused by Vickers diamond indenter, a semi-empirical fracture toughness equation has been obtained.

The effect of the relative location of laser beam with arc in different hybrid welding processes

Hybrid welding requires that several parameters are properly adjusted in order to reach high weld quality. One of the main setup parameters of hybrid welding is the order of the different power sources. The selection partly depends on the results desired for welding whether it is gap bridging, penetration depth, welding speed, melting efficiency, process stability, control of weld width, porosity reduction or weld appearance. In this paper we have studied how the placement of the different sources in laser hybrid welding influences the overall weld quality. The paper is based on an analysis of the results of various studies carried out by different research groups. The process is analyzed with regard to process parameters, the type and thickness of the base material, power and beam quality together with the optical parameters of the laser system applied.Hybrid welding requires that several parameters are properly adjusted in order to reach high weld quality. One of the main setup parameters of hybrid welding is the order of the different power sources. The selection partly depends on the results desired for welding whether it is gap bridging, penetration depth, welding speed, melting efficiency, process stability, control of weld width, porosity reduction or weld appearance. In this paper we have studied how the placement of the different sources in laser hybrid welding influences the overall weld quality. The paper is based on an analysis of the results of various studies carried out by different research groups. The process is analyzed with regard to process parameters, the type and thickness of the base material, power and beam quality together with the optical parameters of the laser system applied.

Aluminium alloys welding processes: Challenges, joint types and process selection

Aluminium and its alloys have gained increasing importance in structural engineering due to advantageous properties such as light weight, ease of machining and corrosion resistance. This article presents surface-related challenges facing aluminium welding, specifically weld process limitations and joint limitations. The methodological approach is a critical review of published literature and results based on eight industrial welding processes for aluminium and six joint types. It is shown that challenges such as heat input control, hot cracking, porosity and weldable thickness vary with the process used and that there is no optimal general weld process for all aluminium alloys and thicknesses. A selection table is presented to assist in selection of the optimal process for specific applications. This study illustrates that knowledge of weld limitations is valuable in selection of appropriate weld processes.

Trends in Joining Dissimilar Metals by Welding

The welding of dissimilar materials finds a wide variety of applications in the fields of industrial construction and manufacturing, where the characteristic features of the different materials are optimized for the desired application to result in cost effectiveness and value addition. Non-fusion welding methods such as solid state welding and high energy beam welding are more popular for welding dissimilar metal combinations, due to fewer complications, than fusion welding, which melts the base metal and forms brittle intermetallic compounds (IMCs) that may lead to failure. Various factors have to be considered when assessing the feasibility of welding dissimilar metals and producing a sound weld joint. This paper presents a broad classification of the most commonly used welding processes for dissimilar materials, discusses some of the commonly used welding processes with examples of some common material combinations, critical factors for good welding, and practical difficulties arising from the physical and chemical properties of materials. From the findings, it can be inferred that continuous improvement and research is still required in the field of dissimilar metal welding, particularly in the light of increasing demand for tailored material for modern engineering and industrial applications.

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.

Prediction of Liquation Crack Initiation in Al-Mg-Si Alloy Welded Joints

Heat-treatable 6005-T6 alloy welded joints were studied experimentally and theoretically. The joints were gas tungsten arc and gas metal arc welded, bead-on-plate with 4043 and 5356 alloy filler metals. The temperature dependences of mechanical properties (yield stress, elastic modulus, thermal strain and characteristic ductility curve) under welding conditions were obtained using the 3800 Gleeble System. The unknown volume heat source parameters were found by application of inverse modeling. The three-dimensional heat conduction and thermomechanical problems were solved numerically. Liquation cracking criterion in terms of accumulated plastic strains was proposed. Strain vs temperature curves for the partially melted zone were calculated and compared with the ductility curve. The proposed technique allows the prediction of liquation cracking in arc welding of the 6005-T6 alloy.

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.

Sensing in Aluminum Alloy Welding

With the emerging trends of automation of welding technology for high volume manufacturing and use of aluminum for lightweight construction, continuous efforts have been undertaken to improve sensing and data acquisition for automated welding of aluminum and its alloys. This work aims to present and compare various sensing methods i.e. touch sensing, through-arc seam tracking (TAST), vision and composite sensing for automated fusion welding of aluminum alloys. Sensing technologies used for sensing of the seam and weld process are analyzed with focus on difficulties specific to aluminum alloy welding. It is found that the automated welding of aluminum is a well-established subject and that solutions for most industrial automated aluminum welding needs can be developed by integrating ongoing advancement in the field of sensor technology.

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.