Spot Welding Parameters Basic Calculation

𝐸 = 0.241𝑃𝑡w .........................(1) where E : Energy (J)

*Calculation for AC spot welding P : Power (W) tw : Weld time (sec) = 0.241𝐼2𝑅𝑡w .........................(2) where I : Welding Current (A) R : Panel Contact Resistance (Ω) = JvSL .........................(3) where Jv : Melting energy (J/mm3) S : Surface contact (mm2)

L : Total plate thickness combination (mm)

= Jv[π𝑑2

4]L ........................(4) where d : Required nugget diameter (mm)

Since 𝑑 = 4 𝑡min for general spot point

= 5 𝑡min for important spot point

Where 𝑡min : Min thickness of panel combinations

So, 0.241𝐼2𝑅𝑡 = Jv[π(4 𝑡min)2

4]L .......(5) Combination eqn (2) & eqn (4)

= Jv[π4𝑡min]]L .............(6)

Final equation;

𝐼 = Jv[π4𝑡min]]L

0.241𝑅𝑡w

2 ..............(7) *Used for minimum nugget diameter requirement (general)

= Jv[π

𝑑 2

4]L

0.241𝑅𝑡w

2

....................(8) *Used for specific required nugget diameter

Note :

Steel type Melting Energy Contact Resistance

Low Carbon Steel 9.7 J/mm3 100 μΩ

Aluminum 2.9 J/mm3 75 μΩ

Replace 𝐸 = 0.241𝑃𝑡w to 𝐸 = 0.37𝑃𝑡w for MFDC / DC spot welding calculation

𝐹w = 250𝑡min .............................(9) where 𝐹w = Welding Force (kg) - target

*Go to Quadratic approximation for best data fitting (refer reference) – No 11

𝑡w = 10𝑡min .............................(10) where 𝑡w = Weld time (cycle) – 50 hz

𝑡hold = 3 ~ 5 𝑐𝑦𝑐𝑙𝑒𝑠.................... where 𝑡hold = Hold time (cycle) – 50 hz

*𝑡squeeze - Pneumatic Gun : Min 17 cycle – Min time require for applied force to stable at 80%

- Servo Gun (robot) : 0 cycles – Using integrated robot function (robot will send

signal once applied force is stable to welding

controller)

Servo Gun : 4 cycle – Min time require for applied force to stable

References

1. Spot Welding Process Sequence

2. Relationship between welding force & resistance

𝐹w = 𝑃w𝐴 .............(1) where Fw : Weld Force

Pw : Weld Pressure A : Contact Area

R = 𝜌𝐿

𝐴 ........(2) where R : Resistance, Ω

So, A = 𝜌𝐿

𝑅 ........(3) ρ : Resistivity , Ω/mm

L : Total plate thickness combination (mm)

A : Contact Area, mm2

Combine eq (1) & (3)............

𝐹w = 𝑃w𝜌𝐿

𝑅 ........................(4) 𝐹w α 1 𝑅 .... Force ↑ Resistance ↓

3. Relationship between welding force & welding current

𝑃p = 𝑉𝐼 = 𝐼2𝑅 .................................................(5) where Pp : Weld Power

Combine eq (4) & (5)............

𝐹w = 𝑃w𝜌𝐿𝐼2

𝑃p ............................(6) 𝐹w α 𝐼2 .... Force ↑ Current ↑

*Lobe curve sample from Lobe Curve Generator – Welding Force vs Weld Current

4. Welding Condition Graph (Base on formulas)

Using derived formulas as above, the new plot (yellow & blue colours) are published against original

welding chart to confirm the accuracy of the formulas. Also, the Lobe Curve estimator was

programmed to view weldability region as following sample;

5. Lobe Curve Generator (from equations) – Weld Time vs Weld Current

*Improved Lobe Curve Generator

6. AC vs DC Spot Welding Comparison

7. Lobe Curve Sample (Experimental Data)

8. Welding Stepper Program Sample

3SPCC (1.2) x SPCD-SD (1.4)

x SPRC 40 (2.0)5.5mm 250kgf

Graph Part Combination Nugget Diameter (Standard) Welding Pressure

Graph 3

6 8 10 12 14 16 18 206000

7000

8000

9000

10000

11000

12000

13000

14000

Weld Time (cycle)

Wel

d C

urre

nt (

A)

Weld Current versus Weld Time Graph

weld_current_total vs. weld_time_total fit 1weld_current_total_NF vs. weld_time_total_NF fit 2weld_current_total_SP vs. weld_time_total_SP fit 3

Required Nugget Diameter : 5.5mm

Spatter Region

No Fusion Region

Small Nugget Region

Applicable Region

0 420 840 1260 1680 2100 2520 2940 3360 3780 4200

9500

9700

9900

10100

10300

10500

10700

10900

11100

11300

Weld Count (no)

Wel

ding

Cur

rent

(A)

Welding Current Setting versus Welding Current Actual

Welding Current Setting

Welding Current (Actual)

WASIS

STEPPER 0 STEPPER 1 STEPPER 2 STEPPER 3 STEPPER 4 STEPPER 5 STEPPER 6 STEPPER 7 STEPPER 8 STEPPER 9

CURRENT

(kA)11.3 9.5 9.7 9.9 10.1 10.3 10.5 10.7 10.9 11.1 11.3

WTM 7 3 3 3 4 4 5 5 5 6 6

WELD COUNT 1~420 1~420 421~840 841~1260 1261~1680 1681~2100 2101~2520 2521~2940 2941~3360 3361~3780 3781~4200

WELD TIME

(cycle)13 13

PRESSURE

(kgf)250 250

UNDERBODY ROBOT UB053 / 054 (WELDING PARAMETER SETTING)

9. Stepper versus Typical Welding Comparison (Sample)

10. Weld Force Quadratic Approximation

11. Electrode Force Effect on Lobe Curve Range (Sample from experiments)

6 8 10 12 14 16 18 20 22

6500

7000

7500

8000

8500

9000

9500

10000

10500

11000

11500

Weld Time (cycle)

Weld

Curr

ent

(A)

Electrode Pressure Effect on Applicable Region (Between Standard Nugget & Spatter Region)

Press_160_current_std vs. Press_160_weld_time_std

fit 1

Press_160_current_spatter vs. Press_160_weld_time_spatter

fit 2

Press_200_current_std vs. Press_200_weld_time_std

fit 3

Press_200_current_spatter vs. Press_200_weld_time_spatter

fit 4

160 kgf

200 kgf

Spatter Region

Small Nugget Region

12. Shear Load versus Weld Nugget diameter

2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1

1000

2000

3000

4000

5000

6000

7000

8000

Nugget Diameter, d [mm]

Shear

Load,

F [

N]

Shear Load Graph (Ordinary Weld)

SPCE Shear vs. Nugget Diameter

fit [<390 MPa]

SPFC490 Shear vs. Nugget Diameter

fit [390MPa<TS<490MPa]

SPFC580 Shear vs. Nugget Diameter

fit [490MPa<TS<580MPa]

SPFC780 Shear vs. Nugget Diameter

fit [580MPa<TS<780MPa]

SPFC980 Shear vs. Nugget Diameter

fit [780MPa<TS<980MPa]

SPFC >980 Shear vs. Nugget Diameter

fit [TS>980]

3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

Nugget Diameter, d [mm]

Shear

Load,

F [

N]

Shear Load Graph [Critical Weld]

<390 MPa

fit [<390MPa]

390MPa < TS<490MPa

fit [390<TS<490]

490MPa<TS<580

fit [490<TS<580]

580<TS<780MPa

fit [580<TS<780

780<TS<980MPa

fit [780<TS<980]

TS>980

fit [TS>980]

13. Temperature Distribution During Spot Welding

14. Dynamic Resistance Measurement (IJAME)

15. Welding Heat Distribution (SAE)