336
Y. Shi et al.
Fig. 10.17 Welding circuit [31]
the weld seam, i.e. partial and complete penetration, can be artificially maintained.
For K-TIG welding, a rear keyhole is present in the full penetration state while it is
not present in the partial penetration state.
To give an exposition to the above phenomenon, ‘frequency delay’, circuit of the
welding system (shown in Fig. 10.17) must be analyzed.
Jarvis [33] pointed out the arc resistance as Eq. (10.20).
=
ω g L a
A e sin θ
∼ =
ω g L a
I sin θ
(10.20)
where the resistivity of Ar is represented as ω g ; the tip angle is represented as θ ; the
arc column length is represented as L a ; and the emission area of the cathode is A e .
Defining k =
ω
sin θ
, V a , the arc voltage can be derived as Eq. (10.21):
V a = V ao + k L a
(10.21)
Due to the DC welding property, the inductance in the welding circuit is convincing
enough to be ignored. Hence, V s , the output voltage of the welding power supply, is
able to be derived as the following equation:
V s = V p + V a = V ao + I R p + k L a
(10.22)