Researchers at the UK Manufacturing Technology Centre (MTC) in Coventry have made significant improvements in the performance of laser drilling aerospace alloys, which could make it possible to drill aero-engines faster. The results were presented by MTC's Sundar Marimuthu at the Association of Industrial Laser Users' (AILU) Industrial Laser Applications Symposium (ILAS) at the end of March in Grantham, UK.
The study in laser drilling was made by adjusting the parameters of a 20kW five-axis quasi-CW fibre laser.
Marimuthu explained at ILAS that, by 2020, aero-engines will contain more than 500,000 holes, approximately a hundred times more than engines built in the 1980s. Holes are currently drilled at a rate of 75 to 80 millimetres per minute, he said, which, while acceptable now, might not be by 2020, and that throughput will have to increase to generate the 500,000 holes in the next generation of aero-engines.
Marimuthu commented that ‘if we can increase the speed of drilling by one or two seconds per hole [across hundreds of thousands of holes], we can hugely reduce the processing time overall.’ He also highlighted that manufacturers cannot just increase drilling speeds without affecting performance: ‘We also have to increase other parameters like the energy, pulse duration, beam overlap or frequency.’
The MTC researchers have therefore been working to increase the performance of laser drilling at faster speeds by experimenting with these parameters, and have observed significant improvements while working with pulse duration and beam overlap.
Marimuthu noted that previous work had suggested that low pulse durations are beneficial to laser drilling, as they correspond to higher peak powers and provide less heat input. ‘This is not what we are seeing however,’ he said. ‘We have observed the best drilling performance at pulse durations of 1.5ms to 2ms.’
The quality of the drilling performance was determined by the thickness of the recast layer – a by-product of laser drilling and cutting that can result in cracking. Higher pulse durations were observed by the MTC team to produce significantly thinner recast than the excessive amounts produced by the more commonly used shorter durations.
The researchers also observed dramatic improvement in laser drilling performance while experimenting with beam overlap. ‘One of our main observations was that at a 50 per cent beam overlap, irrespective of the beam energy or pulse duration, we got much better beam drilling performance and recast thickness,’ commented Marimuthu. Beam overlaps as high as 84 per cent and as low as 22 per cent were also experimented with; however, overlaps of around 50 per cent consistently resulted in the lowest recast thicknesses.
Marimuthu concluded his presentation by informing ILAS attendees that the team should be able to increase the speed of laser drilling without having any effect on the quality of the process.