Fiber Laser Blanking of Coil Strips at Extreme-Speed Extreme-Power

By: Dr. Charles Caristan and Jay Finn

Air Liquide Industrial US LP, Automatic Feed Company

The blanking process consisting of cutting flat panels directly out of a metal coil is practiced in the automotive industry to the tune of 10 MM tons of steel coils processed each year for the North American market alone.  Up until now, CO2 laser-cutting technology is almost exclusively used to produce low-volume prototype blanks, whereas when it comes to high volume production, nearly 100% is still manufactured exclusively mechanically with shears and press die-blanking systems which hold high throughput and piece cost advantages.

Today, advances in high power fiber laser technologies yield resonators with energy efficiency more than double that of CO2 lasers while almost doubling the processing speed performance when compared to same power CO2 lasers.  Fiber-laser processing at “extreme power extreme speed” reverses the high throughput and piece cost advantages in favour of laser processing in new niche applications.

However, the transition from development to “laserfacturing”, the art of industrial manufacturing with lasers, must be done deliberately by understanding the physics of the cutting and keyhole welding processes and solving the new challenges posed by thermal lensing induced focus shifts and by rising defects rates when processing at “extreme power extreme speed”.

The present work studies special zinc sulphide material made lenses of bifocal and toroidal shapes.  A multimode 5kW fiber laser emitting at 1.07 micron wavelength with a Beam Parameter Product, (BPP) of 5 mm.mrad was used for the experimental part of the work.  Laser beam dimensions caustics through the toroidal and bifocal lenses were measured with a digital beam scanner and plotted in almost perfect agreement with the results of a judicious analytical beam propagation calculation.

Applications to fiber laser welding with an oblong focused beam spot on the workpiece instead of a small circular spot confirm a notably superior welding efficiency and stability demonstrated in previous works with CO2 lasers.

Applications to fiber laser cutting of advanced strength steel with a Bifocal lens confirm an expected 20% increase in cutting speed, when compared to cutting with a standard lens, as previously demonstrated with CO2 lasers as well.  A current project for fiber laser-blanking directly from coil strips predicts a substantially favourable piece cost advantage when compared to press die-blanking. It also results in leaner manufacturing by eliminating blanking-dies and coil slitting operations.  Laser-blanking is found to be substantially more energy efficient than press die-blanking by enabling fiber laser cutting at “extreme power extreme speed” and by significantly reducing material waste.