Page 171 - Welding of Aluminium and its Alloys

154 The welding of aluminium and its alloys

8.5 Nd-YAG laser interfaced with a robot. Courtesy of TWI Ltd.

Since the early 1990s the power available from the solid state lasers has
increased so that a pulsed 3kW laser is capable of welding speeds of up to
2.3 metres per minute in 1.5mm thick 5XXX alloys. Gas shielding, similar
to that for CO 2, can be achieved using either argon, helium or nitrogen fed
co-axially with the beam or from a simple side port. Gas shielding of the
underbead will also give an improvement in the surface finish.
High-power diode lasers (HPDLs) are also being investigated and it is
likely that they will become commercially available in the near future.There
are several advantages with this type of laser, price and low maintenance
being two. With the recent improvements in optics, HDPLs are capable of
4
2
achieving power densities of 5 ¥ 10 W/cm and, with wavelengths of around
800nm, are producing good results when used to weld aluminium.
8.3.3 Welding defects

CEN standards are being developed to cover the quality assurance and
quality control of laser welds in a range of metals, for example EN ISO
13919-1 and EN 288 part 15. ASME IX already has requirements regard-
ing procedure approval testing of laser welds. A brief summary of laser
welding defects is included in Table 8.2.

8.3.4 Arc augmented laser welding
There have been a number of relatively new developments where the laser
has been combined with the arc from a conventional welding power source.