Resistance Spot Welding Monitoring System and Method
A resistance spot welding monitoring system includes a plurality of sensors coupled to a resistance spot welding system to receive welding data produced during a welding operation. The monitoring system further includes a nugget prediction system. The welding data is indicative of welding parameters used to produce the weld nugget. The nugget prediction system retrieves the welding data and predicts a nugget size based upon the welding data received from the plurality of sensors. Additionally, the nugget prediction system generates a nugget size signal. The monitoring system also includes an indicator that receives the nugget size signal and notifies an operator of a predicted nugget size.
1 . A resistance spot welding monitoring system, comprising:
a plurality of sensors adapted to be coupled to a resistance spot welding system for receipt of welding data, wherein the welding data is indicative of the welding parameters used to produce a weld nugget;
a nugget prediction system coupled to the plurality of sensors and configured to retrieve the welding data, wherein the nugget prediction system is operable to predict a nugget size based upon the welding data received from the plurality of sensors, and to generate a nugget size signal; and
an indicator coupled to the nugget prediction system and operably receiving the nugget size signal, wherein the indicator notifies an operator of a predicted nugget size.
2 . The resistance spot welding monitoring system of claim 1 , wherein the welding data include electrical energy data and contact area data used to form the weld nugget.
3 . The resistance spot welding monitoring system of claim 2 , wherein the contact area is a function of a dynamic resistance associated with a welded plurality of materials.
4 . The resistance spot welding monitoring system of claim 2 , wherein the electrical energy data further comprises:
a welding current and a tip voltage associated with a pair of electrodes of the resistance spot welding system.
5 . The resistance spot welding monitoring system of claim 2 , wherein the welding data further comprises at least one of the following:
material thickness data;
welding time;
electrode force; and
dynamic resistance.
6 . The resistance spot welding monitoring system of claim 1 , wherein the nugget prediction system is further operative to determine whether a severe expulsion occurs during a welding operation.
7 . The resistance spot welding monitoring system of claim 6 , wherein the nugget prediction system ignores the nugget size whenever a severe expulsion is determined.
8 . The resistance spot welding monitoring system of claim 6 , wherein the nugget prediction system compares a detected expulsion to a predetermined expulsion threshold to determine whether a severe expulsion has occurred.
9 . The resistance spot welding monitoring system of claim 8 , wherein the detected expulsion is indicative of a sudden drop in dynamic resistance when a dynamic resistance for the weld nugget is compared with at least one previously obtained dynamic resistance.
10 . The resistance spot welding monitoring system of claim 1 , wherein the nugget prediction system further comprises a user interface configured to allow an operator to input at least one of the welding parameters.
11 . The resistance spot welding monitoring system of claim 1 , wherein the nugget size is predicted based on
d
n
2
=
α
0
+
α
1
(
E
h
)
+
α
2
(
d
c
2
·
Δ
t
h
)
+
α
3
(
d
c
·
Δ
t
)
+
α
4
F
,
wherein h is the thickness of the material, d n is the nugget size, ΔT m is the temperature increase from the room temperature to the melting temperature of the plurality of materials 20 , Δt is the welding time, F is the electrode force, αs are calibrated coefficients of the linear equation, and d c is the contact area.
12 . A method for monitoring resistance spot welding, comprising:
sensing welding data associated with a welding operation forming a weld nugget within a plurality of materials, wherein the weld data is indicative of welding parameters used to produce the weld nugget;
predicting a nugget size of the weld nugget based upon the welding parameters; and
notifying an operator of a predicted nugget size.
13 . The method of claim 12 , further comprising:
determining whether a severe expulsion occurred during the welding operation; and,
ignoring the predicted nugget size whenever the severe expulsion is determined.
14 . The method of claim 13 , wherein determining whether the severe expulsion occurs further comprises:
comparing a detected expulsion associated with the weld nugget to a predetermined severe expulsion threshold.
15 . The method of claim 14 , wherein the severe expulsion occurs when a detected expulsion for the weld nugget is above the predetermined severe expulsion threshold.
16 . The method of claim 15 , wherein the detected expulsion is indicative of a sudden drop in dynamic resistance when a dynamic resistance for the weld nugget is compared with at least one previously obtained dynamic resistance.
17 . The method of claim 12 , wherein the welding parameters further comprise at least one of the following:
electrical energy;
contact area;
material thickness data associated with each of the plurality of sheet metals;
welding time;
dynamic resistance; and
electrode force.
18 . The method of claim 17 , wherein the contact area is a function of the dynamic resistance associated with forming the weld nugget.
19 . The method of claim 18 , wherein the dynamic resistance is determined by
R
T
=
∫
0
h
ρ
r
1
A
x
x
=
∫
0
h
ρ
r
1
π
(
r
+
r
e
(
1
-
x
h
)
)
2
x
=
ρ
T
h
π
r
(
r
+
r
e
)
,
wherein r is a contact radius at the electrode to surface interface, r e is the difference between the contact radius at the surface-to-surface interface and the electrode-to-interface surface, h is a thickness of each of the plurality of metal materials, T o is an ambient temperature of a welding zone, k 1 and k 2 are heat transfer coefficients related to thermal conductivities of the pair of electrodes 18 and the plurality of materials, A t is the contact area at the pair of electrodes 18 to surface interfaces, and A s is the side surface area of the lumped volume, where ρ T is a temperature dependent electrical resistance.
20 . The method of claim 12 , wherein the nugget size is determined by
d
n
2
=
α
0
+
α
1
(
E
h
)
+
α
2
(
d
c
2
·
Δ
t
h
)
+
α
3
(
d
c
·
Δ
t
)
+
α
4
F
,
wherein h is the thickness of the material, d n is the nugget size, ΔT m is the temperature increase from the room temperature to the melting temperature of the plurality of metal materials, Δt is the welding time, F is the electrode force, as are calibrated coefficients of the linear equation, and d c is the contact area.