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The Importance of Force and

Displacement

Resistance Welding Training

Marty MewborneProduct Engineer

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Resistance Welding Diagram:

EQUIPMENT

PROCESS

MATERIALS

WELDINGSUCCESS

MATERIALCONTROL

OPTIMIZEDSETTINGS & MONITORING

Part Positioning, Electrode Maintenance, etc.

Composition,Plating, Hardness,

Geometry, etc.

Power Supply, Weld Head, Electrodes, etc.

EQUIPMENTSELECTION

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Weld Heat = I2Rt – Thermal Loss

Weld CurrentNote:

Thermal Loss is the heat sinking into the parts, electrodes and tooling.

where:

I = weld current, amperesR = resistance of work pieces, ohmst = duration of current, seconds

Weld Heat Formula

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How Electrode Force Affects Contact Resistance:

High Force Reduces Contact Resistance

Low Force Causes High Contact Resistance

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Poor Weld Force Control Results in:

Weld splash Excessive part deformation

Wide variations in weld strength

Inconsistent weld heat

Reduced electrode life

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Weld Study:

Application: .032” Diameter Nichrome Wire; 90° Cross Wire Weld

Pull Strength vs. Current for 14, 16, 18, & 20 lbs Electrode Force:

30

40

50

60

70

80

90

100

500 600 700 800 900 1000

Current (KA)

Pu

ll S

tren

gth

(lb

s)

20 lbs

18 lbs16 lbs

14 lbs

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Pull Strength vs. Displacement:

Application: .032” Diameter Nichrome Wire; 90° Cross Wire Weld:

Pull StrengthElectrode 20 24.4 33.8 54.6 47.2 54.6 61.4 62.8Force (lbs) 18 28.8 38.8 54.2 58.4 97.4 79 94.2

16 22 37.2 57.8 58.2 65 67.6 66.614 38 42 60.2 57 64 61.2 7112 54 54.6 63.2 52.2 62 47.2 53.610 27.6 59.6 56.8 68.2 91.2 64.4 56.68 22.8 54 51.2 47.8 51.4 55.6 50.66 31.6 43.8 65.4 56.2 59.4 54 364 35.6 38.6 56.8 56.8 51.8 46.8 53.4

Weld Current (A): 400 500 600 700 800 900 1000

Pull Strength of 60 lbs or Greater is Highlighted

DisplacementElectrode 20 1 3 4 6 8 9 12Force (lbs) 18 1 3 4 6 7 10 12

16 2 3 5 6 8 10 1214 2 3 5 6 8 11 1312 3 4 5 7 9 11 1410 2 4 4 7 8 10 138 3 5 6 7 9 11 146 3 3 5 6 8 10 134 2 4 5 6 8 11 14

Weld Current (A): 400 500 600 700 800 900 1000

Displacement of .009” - .012” is Highlighted

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Weld Head Actions:

Approach

Impact

Squeeze

Fire

Follow-up

Hold

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Force Control Methods:

Manual Foot Pedal

Pneumatic Direct Air Coil Spring Proportional

Pressure Control EZ-AIR

Cam Driven Electronic

Servo Motor Electro Magnetic

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Electrode Force vs. Time for Force Fired Weld Head:

ElectrodeForce

Time

Final Force

Firing Force

Weld Current

150 msec Squeeze

Time

Hold Time

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Electrode Force vs. Time for Two Different Operators:

Electrode Force

Time

Firing Force

Final Forces

Weld Current

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Solenoid No. 2

Air Cylinder

Fixed 78 psi Regulator

Exhaust

85 to 130 psi Shop Air Solenoid

No. 1

Solenoid No. 3

EZ-AIR Overforce Protection:

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Electrode Force vs. TimeBefore and After EZ-AIR:

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Proportional Pressure Control:

Force can be controlled and programmed using a Proportional Valve:

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Force Monitoring:

Force can be monitored using a Load Cell:

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Displacement Monitoring:

Sensor Options:• LVDT (Linear Variable

Differential Transformer)• Linear Encoder

Uses:• Part Detection• Measure Weld Collapse• Weld To Displacement

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Weld to Displacement:

Measure Initial Part Thickness

Measure Final

Thickness

Cut Off Current at Displacement

Limit

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Built-in or External Monitoring:

HF27 (Built-In) MG3 (External)

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Resistance Welding Diagram:

EQUIPMENT

PROCESS

MATERIALS

WELDINGSUCCESS

MATERIALCONTROL

OPTIMIZEDSETTINGS & MONITORING

Part Positioning, Electrode Maintenance, etc.

Composition,Plating, Hardness,

Geometry, etc.

Power Supply, Weld Head, Electrodes, etc.

EQUIPMENTSELECTION