Biuletyn Instytutu Spawalnictwa No. 01/2012

ination of its power and width (duration).
Therefore, these radiation beam parameters
cannot be shaped freely, as one cannot freely
define the duration and emission frequency of
a pulse for the assumed value of the average
power of a radiation beam. The energy of a
pulse cannot exceed the maximum value defined
for a given resonator.
The average power of laser radiation in pulsed
mode is defined as the product of the average
power of the radiation of one pulse P i
,
the duration of this pulse t i
and the number
of pulses per a second expressed through the
frequency of emission f. For a given average
power there is a number of combinations of
the selection of pulse energy and pulse repetition
frequency.
P śr
= P i
× t i
× f = E i
× F (1)
The frequency of a pulse emission is a parameter
closely related to the period of their occurrence
expressed in the following relation:
A weld produced by a laser beam emitted in
pulsed mode is composed of a number of overlapping
spot welds. The degree of overlapping
of individual pulses expressed in percentage,
i.e. the so-called overlap, represents the degree
at which the area of a material molten by
a single pulse overlaps a similar area produced
by the previous pulse. By means of a specific
overlap one can control the amount of heat
supplied to a material being welded, as well as
influence the homogeneity of the structure of
a weld.
The overlap is defined by the rate of the
welding process appropriately selected in relation
to the frequency of pulses. In turn, the
frequency of pulses depends on the pre-defined
power of a pulse and its duration. If an
area molten by a single pulse of a laser beam
takes an elliptic shape (as a result of the pro-
1 ⎡ 1 ⎤
T =
f ⎢
s =
⎣ Hz ⎥ ⎦
(2)
The average energy of laser radiation for
the pulsed operation mode is defined as the
product of the average radiation power and radiation
beam action time.
E śr
=P śr
× t [J] (3)
In the case of single pulse spot welding, an
important parameter is the density of pulse power.
GP
i
Pi
Ei
= =
A t × A
i
⎡ J
⎢
⎣s
⋅ m
(4)
where A represents the focusing area of a
radiation beam.
In the case of a pre-defined average power
of a radiation beam P śr
, the density of the power
supplied to the area unit, i.e. the average
2
⎤
⎥
⎦
area power density, is determined by means of
the following quotient:
GP
śr
=
P
śr
A
⎡ W
⎢
⎣m
2
⎤
⎥
⎦
(5)
The quotient of the area power density GP śr
and radiation beam action time determines the
average area power density:
GEśr = GPśr
× t
⎡ J
⎢
⎣m
(6)
The quantities defined above are presented
in Figure 1.
Fig. 1. Graphic interpretation of average power of pulse
P i
, average power of radiation beam P śr
, pulse energy E i
,
pulse duration t i
, pause time t p
pulse period T
2
⎤
⎥
⎦
6 BIULETYN INSTYTUTU SPAWALNICTWA
NR 01/2012