Projection Welding: An Overview

Chonghua (Cindy) JiangAET Integration, Inc.

50388 Dennis Ct. Wixom, MI 48393

Cindy.jiang@aet-int.com

Definition

“Projection welding is an electric resistance welding process that

produces welds by the heat obtained from the resistance to the flow

of the welding current. The resulting welds are localized at

predetermined points by projections, embossments, or intersections”

(Welding Handbook, Vol. 3, Part 2, p50)

Typical Projection Designs

a. Embossed b. Stud-to-Plate c. Annular

Examples of Projection Design

Examples of Various Projection Designs Before and After Welding

(Welding Handbook, Vol. 3, Part 2, p56)

Examples of Annular Projections

(Welding Handbook, Vol. 3, Part 2, p58)

Typical Commercially Available Fasteners Used in Projection Welding

(Welding Handbook, Vol. 3, Part 2, p59)

• Medium Frequency (MFDC) Machine

• AC Machine

• Capacitor Discharge (CD) Machine

Projection Welding Equipment

Projection Welding Equipment (Cont’d)

• Design and location of the projection

• Thickness of the sections

• Thermal and electrical conductivity of the materials

• Heating rate

• Electrode geometry and alloy

• Tooling alignment

• Weld force

Factors Affecting Heat Balance

• Welding Current– Welding current must be at least high enough to create fusion before the

projection has completely collapsed

• Weld Time– Weld time is dependent on the welding current and projection rigidity– Depending on the type of base metal and its surface conditions, multiple

pulses can be applied to yield the desired weld performance

• Electrode/Dies– Proper electrode design and alloy is a major factor in making projection

welds

• Electrode Force– Electrode force is critical for proper projection collapse without expulsion

and formation of a sound weld

Key Process Variables

Formation of Projection Welds

Annular Projection Weld (solid state bonding develops)

Embossed Projection Weld(fused nugget forms)

• Low carbon steel

• Hardenable steels

• Stainless steels-ferritic, martensitic, and austenitic types

• Nickel-base alloys

• Copper alloys

• Aluminum and magnesium alloys

• Titanium alloys

• Coated and plated steels

Materials Suitable for Projection Welding

(Welding Handbook, Vol. 3, Part 2, p63)

Welding Trials on 1.6 mm Magnesium AZ31, AET

Materials Suitable for Projection Welding-Example

Example of Project Weld Property-Microhardness

Microhardness Traverse of Two Projection Welds

0

100

200

300

400

500

600

0 0.05 0.1 0.15 0.2 0.25 0.3Distance (in.)

Mic

roh

ard

nes

s (H

V50

0g)

Weld A Weld B

• Parts preparation– Weld area clean of grease, rust, scale, dirt or shearing burrs– Less variance in part tolerance before welding

• Projection size and shape

• Materials

• Welding technique

• Heat balance

Weld Quality

• Issue: Weld did not pass dye penetrant test and pull test

• Root Causes:– Tooling misalignment– Insufficient forging force at the faying surface

• Actions Taken:– Check tooling misalignment by using carbon imprints between faying surfaces– Increase applied forging force– Adjust welding parameters to get sufficient weld bonding area

Projection Weld Performance Improvement: Example 1

Fracture surface No Bonding

Projection Weld Performance Improvement: Example 2

Intergranular Fracture Mode of a Projection Weld Failed during Service

Base MetalBase Metal

HAZ HAZ

Broken part with Intergranular Fracture

Non-broken Part

• The broken part with IG fracture shows primary ferrite along grain boundary. This generally results in low ductility and fracture toughness. • The base metal microstructure of the broken part with IG fracture is a result of improper heat treatment of the base metal before it was welded.

Projection Weld Performance Improvement: Example 2 (Cont’d)

• Advantages– Versatility– Speed– Ease of automation– Ability to make multiple welds simultaneously– Longer electrode/tooling life

• Limitations– The forming of projection may require an additional step of operation– Limitations on materials projection weldability

Process Advantages and Limitations

• Tubular connections

Projection Welding Applications

Projection Welding Applications (Cont’d)

• Attaching nuts and stud

• Sheet metal assemblies

• Tank fittings and ferrules

• Fusites

Projection Welding Applications (Cont’d)

• Fabricate the metal sandwich plate of large area– Projection welding– Adhesive assisted projection welding

(STS Shipbuilding, South Korea)

(Welding in the World, v 53, n 7-8, p 5-11, 2009)

• Attach nuts and stud

Potential Projection Welding Applicationsfor Shipbuilding