Spot welding

1. Principle

2. Equipment

3. How to set parameters

4. Maintenance

Pressurization

Spot weldingSpot welding is the process that two metal plates are pinched between the pure copper or copper alloy rod shaped electrodes and a large current is flown through the electrodes for a short period of time while two metal plates are pressurized strongly to produce round shaped nugget (after solidification of weld metal) .

　 * The nugget part cannot be seen from the outside and only slight concave part that has beenpushed by the electrode remains.

Controller

Transformer Copper alloy electrode

Copper alloy electrode

Pressurization

Welding part

Rod shaped electrode

87

BASICS

PrincipleQ Joule heat (Cal)t Time ( sec ) J Current density (A/mm2)S 　 Area (mm2)I Current (A)

Q is in proportion to JQ is in proportion to t J is in inverse proportion to S2

J is in proportion to I2 CURRENT SETTING is very importantTIP DIA CONTROLL is very important

WELDING TIME SETTING is important

Temperature

Melting point Around 1500℃　 (Iron)

Q (Joule heat) melts material

I = V / R R is determined by Pressure Pressure SETTING is important

Current

Burning

FlashNug

get D

IA

Current effect

TIP DIA

Nug

get D

IA

Burning Flash

Tip DIA effect

Nug

get D

IA

Pressure

Flash

Burning

Pressure effectN

ugge

t DIA

Welding time

ElectricityConsumption

Welding time effect

L Overall length (cm) t Time (sec.)S Cross-sectional area (cm2) I Current (A)R Resistance () Specific resistance (volume resistivity) (cm)

Calorific value of resistance of columnar objectThe following shows the calorific value Q (cal) when the current (I) is flown for “t” sec.

Resistance heating

I

L

S

Q =0.24·I2·R·t (cal)

=0.24·I2· ·L/S·t (cal)

=0.24· ·I2/S2·L·S2/S·t (cal)

=0.24· ·(I/S)2·L·S·t (cal)

=0.24· ·J 2·V·t (cal) 　

Current density J= I/S (A/cm2) Volume V = L ･ S (cm3)

Q is in proportion to JJ is in inverse proportion to S2

J is in proportion to I2

I = V / R

Principle Support document

Condition to do spot welding

Public

Generator1. Stable in-coming Voltage

2. Enough capacity for distributing power to machines

3. Electricity feedback controller with POKAYOKE function

4. Tip cooling water supply

5. Lathing machine to maintain Tip DIA

Knowledge & awareness about risk of spot welding No

Quit spot weldingYes

How to set parameters

1. Know thickness to be welded, from DRG

2. Decide DIA of TIP based on STD

3. Decide type of TIP

4. Set current , welding time and pressure temporary , based on STD

5. Do breakage test and Check Nugget DIA, and appearance

6. If NG then go back to 4

7. If OK enough then continues test up to breakage to happen

8. TIP maintenance frequency will be half of how many times can be welded

TIP DIA

Nug

get D

IA

Burning Flash

Tip DIA effect

Main factor

First factor

Tuning

How to maintain Quality and parameters

Date Time Part No Part NoCurrent (KA) Welding

Time（∞） Air pressure TIP Change Nugget DIAJudgment Sign Approver Day of

Approval9.5±0.2　 20 3～ 3.5 Every 200 hits φ3.8以上

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

                  OK or NG      

Calibration of Current controller > once / year

Change points controlCheck timing must contains at least below timings

Start of Job is MustEnd of job is MustBefore Tip changeAfter Tip change

Thickness Min Average0.8 2.7 3.11 3 3.5

1.2 3.3 3.81.6 3.8 4.42 4.2 5

2.3 4.5 5.32.6 4.8 5.63.2 5.3 6.3

CLASS C

DIA of Nugget

JIS - Z - 3140

≒ 3 　√ t

ノギス

CHECK 　 SHEET

ＴＰ各種

監督者確認後ＴＰ

破壊試験後ＴＰ

手持ち側破壊治具SPARE TIP

Counter

ＴＰを差込む

固定側破壊治具

Welding defects and causes

Surface flash

Excessive concave

Insufficient pressure Too much current Foreign body between sheets Tip DIA too narrow

Cause of defect Standard nugget shape

Tip is too narrow or too much current

Inside flash

Tip is too narrow or too much current

No nugget / No fusion which have occurred in Japan

1. Forgetting to change PRG when part changed2. Power capacity was not enough 3. Operator changed current due to flash ( Parameter was not set properly)4. TIP DIA was controlled by filing & visual check5. Current separation due to touching of JIG to electrode

3. Part names of resistance welding equipment

Spot welding　 Part names

of equipment Controller　 Microcomputer controlled

constant current timer

CylinderPressure gauge

Cooling water　 Water supply port 　 Drain port

Tip holder

Tip

Foot switch

Toroidal coil

Secondary conductor (shunt)Arm

92

６ –３ ．抵抗溶接機の電極　

抵抗溶接の電極材　・・・　主な電極形状（ａ） （ｂ） （ｃ） （ｄ） （ｅ） （ｆ）

ﾎﾟｲ ﾝﾄ形

ﾄﾞｰﾑ形

円錐台形

ﾗｼﾞｱｽ形

平面形

ｽﾄﾚｰﾄ・　　　　ｵﾌｾｯﾄ形

（Ｐ 形）

（Ｃ 形）

（Ｄ 形）

（Ｒ 形）

（Ｆ 形）

（Ｅ 形）

97

(3) Spot intervals

Strength of spot welding joint and shunting current

10 　　　　　 20 　　　 30 　　 40 　　 50 　　　　 100 　　　　 200 　　 300 　 400 　

Interval between spots 　 (mm)

Tens

ile s

hear

ing

stre

ngth

(kgf

)

Shunting current by spot welding

Existing welding spot

Reactive current

Interval between the spots is approx. 17 times larger than the sheet thickness.

As the plate thickness is thicker, the effect is larger.Recommended by RWMA.

120

500

1000

2000

3000

4000

400

300

200

100

1mm+1mm(Existing welding spot: 1) 1mm+1mm

(Existing welding spot: 2)

3.2mm+3.2mm　　 (Existing welding spot: 2)

3.2mm+3.2mm　　 (Existing welding spot: 1)

11. Points to note in designing

Points to note in designing

(2) Edge distance

(3) Intervalbetween spots

(1) Nugget diameter D = (4 to 6)×T1/2 (Finally, it is important to also consider the cost.)

10 times larger than the sheet thickness.

17 times larger than the sheet thickness (Great care is needed when the sheet thickness is large.)

10t 17t(4 to 6)t

(3) Interval between spots

121

11. Points to note in designing