Magazine Articles
The articles below are from the Spring 2010 Issue of the AILU Magazine
Porosity control in Nd:YAG welding of titanium alloys
Current socioeconomic pressures are driving the demand for weight savings in the commercial aerospace industry. This is necessitating the incorporation of high specific strength materials; such as titanium alloys and carbon fibre reinforced plastic (CFRP) composites, into primary airframe structures. Current manufacturing techniques are machining intensive, and finished components may have uneconomical buy-to-fly ratios compared with structural steels and aluminium alloys. The production of near-net-shape titanium components with a high integrity welding process has the potential to significantly reduce overall component cost; and keyhole laser welding, with its inherent flexibility and capability to produce deep penetration welds with a relatively low heat input, is a viable option for this manufacturing requirement.
A problem for keyhole welding is the formation of porosity in the weld metal, something that is of particular concern in fatigue-sensitive aerospace applications, since the pores can act as sites of increased stress concentration and reduce the fatigue resistance of the welded component. In this paper we describe current progress in the use of a directed jet of inert gas aimed in the vicinity of the laser-material interaction point to reduce weld porosity.
The reliable prevention of weld defects, such as porosity and undercut, is critical if the laser is to be considered as a tool for the mass manufacture of fatigue-sensitive aerospace components. The use of a directed jet has been shown to result in levels of weld metal porosity acceptable against different welding standards (such as AWS D17.1:2001 or internal aerospace standards), with a high degree of confidence. The optimum parameters can be used as a starting point when optimising the process for thicker section titanium alloys.
Jonathan Blackburn and Lin Li - Laser Processing Research Centre, The University of Manchester, Chris Allen and Paul Hilton - Laser and Sheet Processes Group, TWI Ltd, Granta
Park, Cambridge
IMAGE:(a) Butt welds made in 3.25 mm thickness Ti-2.5Cu; (b) Butt welds made in 3.25 mm thickness Ti-6Al-4V. In both cases the left photograph is without and right with the directed argon jet.
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Technical aspects of welding X70 pipe steel with high power fibre laser-GMA-hybrid welding
The use of laser techniques such as CO2-laser-GMA-hybrid longitudinal or spiral welding have been investigated for the production of pipes in a variety of steel grades. In such applications the robustness, mobility and high degree of freedom offered by fibre delivery, gives the fibre laser advantages over the CO2 laser, yet it has not been widely used to date.
This article shows the results for fibre laser-GMA-hybrid welding of pipe steel as a way of welding 14 mm thick section X70 material with the maximum of 8 kW laser power available. Two different wire electrodes were tested for their suitability in this application.
The equipment comprised a fibre laser source, a welding head combined with a welding torch and a welding source with a wire feed unit. Details of equipment and materials is shown in the illustration. For these tests the pipe material was supplied in plate form.
With a maximum of 8 kW laser power available, welding of 14 mm thick material using a hybrid process required at least two weld passes and so a joint was made; a single V-butt joint with root faces of 6 mm and 8 mm and an included angle of 45°.
With a maximum of 8 kW laser power available, welding of 14 mm thick material using a hybrid process required at least two weld passes and so a joint was made; a single V-butt joint with root faces of 6 mm and 8 mm and an included angle of 45°.
The approach described in this article has the advantages of a reduced number of welding passes, a high welding speed for the root pass and less filler wire needed. These are advantages contribute to higher productivity and lower production costs.
Stefan Grünenwald -Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany
IMAGE: Experimental set-up for laser-GMAhybrid welding with 8 kW for pipe production.
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