Page 69 - Welding of Aluminium and its Alloys

60 The welding of aluminium and its alloys

controlled to provide consistent and high-quality cuts. Typical laser cutting
parameters are given in Table 4.3.
A number of advantages accrue from using a laser for the cutting of weld
preparations:
• Low heat input, resulting in minimal distortion and narrow heat affected
zones.
• Edges that are smooth and perpendicular to the surface and often
require no further cleaning before welding.
• Narrow kerfs and heat affected zones, meaning that more efficient
nesting can be achieved, resulting in material savings.
• Very thin materials can be cut without distortion.
• Very accurate cuts can be made, resulting in more easy assembling for
welding, this giving reduced fit-up time, more accurate fit-up and fewer
weld defects.
• The process is easily automated and can be readily interfaced with other
NC equipment (Fig. 4.7).
The main drawbacks to the use of lasers for the cutting of aluminium are
as follows:
• The capital cost of equipment, which may be in the order of several
hundreds of thousands of pounds for a laser interfaced with suitable
manipulating equipment. A 1.5kW CW Nd-YAG laser interfaced with
a robotic system, together with its appropriate safety equipment will
cost in the region of £250k to £300k at today’s (2002) prices.
• The coupling of the beam with the work surface is not very good since
aluminium can be highly reflective. This means that higher power is
needed to cut an aluminium component than a similar item in steel.
Aluminium may also reflect the beam back into the lens, resulting in
damage, although this problem has lessened with the development of
more accurate lenses and focusing systems.
• Laser cut aluminium may have a heavy dross on the underside of the
cut. Removal of this can make the process non-competitive with other
processes. Higher gas pressures will assist in reducing or eliminating the
problem.
• The cut edges of the age-hardening alloys may contain microfissures
that will need to be removed.

4.4.1 Health and safety

The laser cutting process is a thermal process and therefore metal fume
mixed with the assist gas will be generated. This fume will need to be
removed, preferably by local fume extraction at source. As laser cutting is