welding in shipbuilding may 10-11, 2011 seattle, washington projection welding: an overview chonghua...
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Projection Welding: An Overview
Chonghua (Cindy) JiangAET Integration, Inc.
50388 Dennis Ct. Wixom, MI 48393
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