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Optimised Laser welding Implementation Via Enabling Research

TWI is working with CAV Advanced Technologies, Leonardo Helicopters and TISICS Titanium Composites, and supported by the MTC, the NITC at Queen’s University Belfast and IPG Photonics, in an Innovate UK initiative to help the UK aerospace industry supply chain understand and develop near-net-shape titanium alloy and titanium metal matrix composite fabrication possibilities, using advances in laser welding, fixtures, gas shielding and NDT.

Project background

The production cost and/or weight of many aerospace structures made from titanium alloys would benefit from developments in, and a wider understanding of, what laser welding and its associated technologies are capable of when applied to titanium alloys and metal matrix composites (MMCs). 

Appropriately developed laser welding procedures could, for example, be used to replace sealed and riveted assemblies (such as has already been done for some aluminium structures). With the inclusion of MMCs in to certain structures, greater weight savings could also be made, without compromising performance.

Work programme

Following an initial definition of their requirements, TWI is assisting a number of UK companies supplying aircraft and helicopter parts, choosing suitable welding equipment supported by IPG Photonics, and then developing specific laser beam welding procedures for their applications.

The process tolerances of the welding approaches being developed for different thicknesses of joints between Ti alloys, or between Ti alloys and Ti MMCs, are being examined and, along with the MTC and NITC, the resulting qualities and properties of the welds are then being evaluated.

TWI is also developing gas shielding and weld plume control solutions complementary to certain application needs, in line with fixture innovations being developed at the MTC.

With the possibility of fibre-delivered, robotic laser welding of certain parts, suitable path programs, access issues, etc, are also being modelled, offline, by the NITC, ahead of case study demonstrations planned towards the end of the project.

These will involve thin section stake welding as a means of replacing riveting in firewalls and bulkheads,  thin section butt welding for leading edge structures, and thicker section butt welding for connections between MMC tubes and Ti alloy end fittings.

For further information about this project and the opportunities it can bring your company in terms of innovations in fixtures, laser welding, gas shielding and non-destructive inspection, please email contactus@twi.co.uk for further details.

A riveted Ti alloy aerostructure: a helicopter engine firewall
A riveted Ti alloy aerostructure: a helicopter engine firewall
An example laser stake welded lap joint (left) and the values of shear strength (in MPa) that can be achieved using different welding approaches
An example laser stake welded lap joint (left) and the values of shear strength (in MPa) that can be achieved using different welding approaches
Example thermocouple traces recorded during laser welding: Part of the experimental proof that short time/high temperature incursions can be tolerated by Ti MMCs in the vicinity of laser joints
Example thermocouple traces recorded during laser welding: Part of the experimental proof that short time/high temperature incursions can be tolerated by Ti MMCs in the vicinity of laser joints
Views of laser stake welded four-part/three-weld coupons for mechanical property testing
Views of laser stake welded four-part/three-weld coupons for mechanical property testing
A robot-driven steerable gas shielding and plume control device, facilitating high quality omni-directional shielding during seam welding of sheet assemblies
A robot-driven steerable gas shielding and plume control device, facilitating high quality omni-directional shielding during seam welding of sheet assemblies
Thin section stake welding
Thin section stake welding
Thin section butt welding - Laser surface scan (top) showing weld undercuts <50µm in depth, metallographic cross-section (bottom left) and photograph (bottom right) of small scale thin section butt weld, before dressing
Thin section butt welding - Laser surface scan (top) showing weld undercuts <50µm in depth, metallographic cross-section (bottom left) and photograph (bottom right) of small scale thin section butt weld, before dressing
Thick section butt welded Ti/MMC strut demonstrator - Strut demonstrator assembly (top left), laser butt weld in 6mm wall thickness strut (top right) and laser butt welded and dressed 4mm wall thickness precursor for mechanical property testing
Thick section butt welded Ti/MMC strut demonstrator - Strut demonstrator assembly (top left), laser butt weld in 6mm wall thickness strut (top right) and laser butt welded and dressed 4mm wall thickness precursor for mechanical property testing