Spot weldability Lesson Objectives When you finish this

Spot weldability Lesson Objectives When you finish this lesson you will understand: • Concept of Spot Weldability • Electrode arrangements Learning Activities 1. View Slides; 2. Read Notes, 3. Listen to lecture 4. Do on-line workbook Keywords: Current Level, Current Range, Lobe Curve, Electrode Life, Peel Test, Nugget Size, Button Size, Interfacial Failure, Shunting Effect, Multiple Direct Electrodes, Series Electrodes, Electrode Tooling

Process Characteristics as a Measure of Weldability • Current Level • Current Range & Weldability Lobe • Process Deterioration – Characterization of the loss in weld size at constant welding conditions – Characterization of the variation in process requirements for maintaining welds of an adequate quality Peel Test Used As Measure

Button Size as a Measure of Weld Quality Button Diameter

Modes of Failure in Spot Welds Full Button Irregular Button Interfacial Failure

Process Characteristics as a Measure of Weldability • Current Level • Current Range & Weldability Lobe • Process Deterioration – Characterization of the loss in weld size at constant welding conditions – Characterization of the variation in process requirements for maintaining welds of an adequate quality Peel Test Used As Measure

Nugget Diameter vs. Weld Current Expulsion Acceptable Nuggets Minimum Nugget Diameter Small Nuggets Weld Current Nominal Current

Process Characteristics as a Measure of Weldability • Current Level • Current Range & Weldability Lobe • Process Deterioration – Characterization of the loss in weld size at constant welding conditions – Characterization of the variation in process requirements for maintaining welds of an adequate quality Peel Test Used As Measure

Nugget Diameter Current Range & Weldability Lobe Acceptable Nuggets Minimum Nugget Diameter Small Nuggets Weld Current Weld Time Expulsion Time A Smaller “Brittle” Nuggets Time A Lobe Curve Acceptable Nuggets Weld Current Expulsion Level

Process Characteristics as a Measure of Weldability • Current Level • Current Range & Weldability Lobe • Process Deterioration – Characterization of the loss in weld size at constant welding conditions – Characterization of the variation in process requirements for maintaining welds of an adequate quality Peel Test Used As Measure

Process Deterioration Weld Diameter Minimum Acceptable Diameter Number of Welds

Shunting Effect IB IA B A Itotal = IA + IB I A RA = I B RB IB/Itotal = 1 - RB/(RA + RB) [Reference: Resistance Welding Manual, p. 1 -7, RWMA]

Multiple Direct Electrodes Series Electrode

Tooling for Multiple Welding Pressure Adjustment Screw Stud and Jam Nuts Equalizing Bar Compression Spring Split and Clamped to Electrode Flexible Conductors Slip-Fit Workpiece Lower Electrode (a) (b) [Reference: Resistance Welding Manual, p. 17 -8, RWMA]