Page 82 - Welding Robots Technology, System Issues, and Applications

Welding Technology
67
TM
A recent development is the reversal stir welding process (Re-Stir ), developed
by TWI, in which tool rotation is applied as both angular reciprocating, where
reversal is imposed within one revolution, and rotary reversal, where reversal is
imposed after one or more revolutions, instead of continuous rotation as is in
conventional FSW. Re-Stir is basically a cyclic and essentially symmetrical
TM
process. According to TWI Re-stir may become the preferred option for certain
butt, lap, compound lap and spot welding and material processing applications
[55].

2.6 Health and Safety

The major potential hazards of arc welding processes are the high-voltage
electricity, which can injure and kill personnel, the fumes and gases, which can be
dangerous to health, the electric arc radiation, which can injure eyes and burn skin
and the noise that can damage hearing.

The exposure to the high open-circuit voltage of power supplies can cause
dangerous electric shocks, which can be prevented by connecting all the electrical
equipment and work-pieces to a suitable electrical ground. All electric cables
should be suited to the maximum current and must remain insulated and dry.

Fumes and gases are generated in all arc welding processes, being particularly
intense in the flux cored arc welding process. Metal fumes of nickel, chromium,
zinc, lead or cadmium, for example, and gases such as carbon monoxide, ozone
and nitrogen oxides formed in the arc are very harmful to the health [56]. Enough
ventilation or exhaust at the arc, or both must be used in order to keep fumes and
gases from the personnel breathing zone.

The electric arc of GTAW and GMAW processes emits intense radiation in the
ultraviolet range, in the infrared range and also in the visible range. UV radiation
can commonly cause a temporary eye burn, which can be painful for 48 h. A filter
glass should be used by the operator to absorb the radiation in the dangerous
wavelengths, and limit visible light so he can see the joint during the welding
operation. There are two basic types of filter, permanent filters and photosensitive
filters, which react rapidly to the incident light from the arc and darken [55].
Optical density of filters increases with increasing current. The UV also occasions
reddening and irritation of the skin and operators need to be protected by leather,
wool or aluminum coated clothing. Robotic welding systems are generally
protected by enclosures provided with windows with filters for viewing weld area.

Ear protection should be used when noise is excessive in the work area. Special
care must be taken in handling and use of cylinders containing high-pressure and
liquefied gases, which should remain in a vertical position, secured with chains,
when they are being used.