John Norrish

Advanced welding processes

An introduction to welding processes welding process development trends welding power source technology filler materials for arc welding gases for advanced welding processes advanced gas tungsten arc welding high energy density processes narrow gap welding techniques monitoring and control of welding processes welding automation and robotics.

Automated offline programming for robotic welding system with high degree of freedoms

Although robotics based flexible automation is an intriguing prospect for small to median enterprises in the era of the global competition, the complexity of programming remains one of the major hurdles limiting its applications. This paper presents an automated offline programming (AOLP) method to address this issue. AOLP is software that automatically plans and programs for a robotic welding system with high Degree of Freedoms (DOFs). It takes CAD model as input, and is able to generate the complete robotic welding code without any further programming effort.

Investigation on Welding Arc Interruptions in the Presence of Magnetic Fields: Welding Current Influence

Arc interruptions and, therefore, oscillation in the amount of energy and molten wire delivered to the plate have been observed during tandem pulsed gas metal arc welding (GMAW). It appears that these instabilities are related to the magnetic interaction between the arcs. In order to clarify the possible mechanisms involved, this paper tries to mimic the tandem GMAW arc interruptions. External magnetic fields were dynamically applied to GTAW arcs in constant current mode to verify their resistance to extinction as a function of current level and direction of deflection. High-speed filming was carried out as an additional tool to understand the extinction mechanism. The influence of the welding current level on the arc resistance to extinction was established: The higher the welding current, the more the arc resists to the extinction. The arc deflection direction has minor effect, but arcs deflected backward have more resistance to extinction.

Investigation on Welding Arc Interruptions in the Presence of Magnetic Fields: Arc Length, Torch Angle and Current Pulsing Frequency Influence

Arc interruptions have been observed in tandem pulsed gas metal arc welding (GMAW). This fact, which is likely related to magnetic interaction between the arcs, motivated previous study concerning the influence of the welding current on this phenomenon. In order to promote further understanding, this paper investigates the effects of arc length, torch angle, and high-frequency current pulsing on the arc resistance to extinction. To mimic the situation found in tandem GMAW (magnetic field induced by one arc acting on the other arc), external magnetic fields were applied to gas tungsten arc welding arcs. It was verified that short arc lengths and torch angles set to push the weld pool increase the arc resistance to extinction, whereas the utilization of high-frequency current pulsing tends to weaken the arc resistance to extinction. According to a model devised from the results, the arc extinction takes place if the heat generated inside and the heat transferred into the arc column become insufficient to counterbalance the total heat loss in this arc region.

Preliminary evaluations on laser - Tandem GMAW

Recently there has been considerable research and development activity in the use of lasers for welding operations, turning this process into an important tool for a variety of applications. Although it is possible to use lasers as a unique source of heat to promote union of materials, the combination of the beam provided by a laser system with an arc welding process has been studied widely and applied in the so-called hybrid welding systems. Generally, the final result of such a combination is an increase in the weld penetration depth, width and welding travel speed. Despite these advantages, there are many issues still requiring further research and development concerning the use of hybrid welding using laser and arc welding, including a more comprehensive understanding of the various welding phenomena involved and the exploitation of new combinations. This paper describes an approach for hybrid welding combining a laser with tandem G MAW, in particular placing the laser beam between the tandem GMAW wires. This hybrid process variation is described and some basic aspects regarding its performance are discussed. The laser beam was found to have a positive effect on the appearance of the weld beads produced and best results are obtained if the laser is located halfway between the leading and trailing wires. A 10 mm inter-wire distance was found to be the most appropriate of the separation distances tried. The hybrid process approach was able to increase the welding travel speed or penetration depth significantly in comparison with tandem GMAW (operating in pulsed mode).

3D mapping using a ToF camera for self programming an industrial robot

Automated Offline Programing (AOLP) is a cost effective robot programming method. However, it relies on accurate CAD information of the work environment to perform optimally. Incorrect CAD data is a known source of error for AOLP systems. This paper introduces a new sensor based method of programming that extends the concept of AOLP. Using a ToF camera to map the environment, there is no reliance on CAD data. The problem of motion planning to efficiently map the environment is examined and changes to the motion planning algorithm are proposed and tested.

Offline Programming for a Complex Welding System Using DELMIA Automation

This paper presents an offline programming (OLP) system for a complex robotic welding cell using DELMIA Automation. The goals of this research are aimed at investigating the feasibility of taking a commercially available robotic simulation package, DELMIA, and to use a Visual Basic Automation interface to reduce the programming time by creating automated ‘modules’ to carry out some of the tasks in the OLP process. The paper first investigates and presents the structure of OLP as a discreet method of individual steps. These steps are then evaluated for their potential as an automation candidate. The methods in which these steps are automated are then presented. A general analysis of the developed OLP system was carried out, providing a scope for future research and development.

THE EFFECT OF VOLTAGE AND METAL TRANSFER MODE ON PARTICULATE FUME SIZE DURING THE GMAW OF PLAIN CARBON STEEL

Particulate welding fumes can enter unciliated airways, or may even be absorbed through the skin, possibly to the detriment of the health of welders. The size and shape of the particulates will determine their ability to infiltrate the human body. Hence, the sensitivity of particulate fume size to welding parameters such as arc voltage (20–36 V) and metal transfer mode (dip, globular and spray) was assessed. Transmission electron microscopy (TEM) imaging was used for determining particulate fume size and it was found to be an accurate, reproducible, and relatively simple technique. The results revealed a higher percentage of ultra fine particulates (i.e. in < 20 nm and 20–40 nm intervals) in ‘low welding voltage’ fume plume compared with ‘high welding voltage’ fume plume. Fundamentally, the fume plume created during dip metal transfer at low welding voltages (20–26 V) had much lower levels of particulate fume concentration compared with spray metal transfer at high welding voltages (30–36 V). TEM also revealed that for the range of welding voltages and metal transfer modes investigated, the particulates produced were predominantly less than 100 nm in diameter and spherical. Spherical particles (< 100 nm) have been reported elsewhere to reach the alveoli in rats and, hence, may be of relevance with respect to the health of welders. Slightly faceted crystalline particulates and fume particle sizes of up to 800 nm in diameter were also observed with TEM. It should be noted that the agglomeration behaviour of these particulates in the fume plume is considered important but not entirely understood. The particle size results suggest that the key to welder safety is to minimize cumulative exposure to particulate fume over their working life, irrespective of the welding parameters used. Innovative fume extraction techniques, clean workshops, automated welding, and low welding fume consumables should all form part of an integrated solution to help ensure the health and well-being of welding personnel.

Arc Welding Processes for Additive Manufacturing: A Review

Arc-welding based additive manufacturing techniques are attracting interest from the manufacturing industry because of their potential to fabricate large metal components with low cost and short production lead time. This paper introduces wire arc additive manufacturing (WAAM) techniques, reviews mechanical properties of additively manufactured metallic components, summarises the development in process planning, sensing and control of WAAM, and finally provides recommendations for future work. Research indicates that the mechanical properties of additively manufactured materials, such as titanium alloy, are comparable to cast or wrought material. It has also been found that twin-wire WAAM has the capability to fabricate intermetallic alloys and functional graded materials. The paper concludes that WAAM is a promising alternative to traditional subtractive manufacturing for fabricating large expensive metal components. On the basis of current trends, the future outlook will include automated process planning, monitoring, and control for WAAM process.

Directed electrochemical deposition of conducting polymer filament on screen-printed array

Conducting polymer has been deposited electrochemically to produce a fine sensing filament. Two approaches used to produce directed electrochemical p olymerization h ave been i nvestigated. W ith the h elp o f p latinum w ire, a fine conducting polymer filament across the tracks of the array can be produced very quickly. Alternatively by scribing the surface of the array, a fine score could be formed across the tracks of the array. High surface charge density would be formed around the edges during the electrochemical deposition to encourage the growth of a polymer filament across each track as directed by the electric field. An increase in sensitivity of the filament sensor over the broad conventional sensor in ethanol vapour has been observed.