Flash and flange weld symbols are specialized graphical notations used on engineering drawings to specify light gauge metal joints where edges are flared or resistance-welded together. Unlike standard groove or fillet welds, these symbols communicate unique joining methods that require specific interpretation skills.
Flash and flange weld symbols indicate light gauge metal welding joints where edges are flared (flange welds) or resistance-welded using heat and pressure (flash/upset welds). Flash and upset weld symbols are always centered on the reference line with no arrow side or other side significance.
I’ve spent years interpreting welding symbols in fabrication shops, and flash and flange welds are some of the most misunderstood symbols on drawings. These specialized welds appear in HVAC ductwork, automotive body panels, and sheet metal fabrication where thick welding beads would be impractical.
Understanding these symbols correctly prevents costly fabrication errors. A misinterpreted flange weld symbol can lead to wrong joint preparation, resulting in weak connections that fail inspection or require expensive rework.
Quick Reference: Flash and Flange Weld Symbols
Quick Summary: There are four main flash and flange weld symbols: Edge Flange, Corner Flange, Flash Weld, and Upset Weld. Edge and corner flange welds use directional symbols placed on the reference line. Flash and upset weld symbols are centered on the reference line with no arrow or other side significance.
| Symbol Type | Text Representation | Key Characteristic | Typical Application |
|---|---|---|---|
| Edge Flange | < (perpendicular line with flare) | Arrow side significance | Sheet metal seams |
| Corner Flange | L-shaped with flare | Arrow side significance | Box corners, ductwork |
| Flash Weld | || (parallel lines centered) | Centered on reference line | Pipe connections, rods |
| Upset Weld | = (equal sign centered) | Centered on reference line | Butt joints, tubing |
Understanding Welding Symbol Basics
Before diving into flash and flange symbols specifically, you need to understand the foundation of all welding symbols. Every welding symbol shares common elements that convey specific information about the weld.
Reference Line: The horizontal line that serves as the anchor for all welding symbol elements. It’s the foundation upon which the entire symbol is built.
The reference line always appears horizontally on the drawing. The arrow extends from one end and points to the joint location. The other end typically has a tail where additional information can be specified.
Symbol placement relative to the reference line determines which side of the joint gets welded. This is a fundamental concept that applies to most weld types, including edge and corner flange welds.
Arrow Side vs. Other Side:
- Symbol below the reference line = weld on arrow side
- Symbol above the reference line = weld on other side
- Symbol on both sides = weld on both sides
Arrow Side: The side of the joint that the arrow specifically points to. This is a critical concept for edge and corner flange welds, which have arrow side significance.
Flash and upset welds are the exception to this placement rule. Their symbols are always centered on the reference line, meaning they have no arrow side or other side significance. I’ll explain why this matters in the flash and upset weld section below.
Flange Weld Symbols: Edge and Corner
Flange welds are used primarily for light gauge metal joints where the edges are flared or flanged to create the weld connection. These are common in sheet metal work, HVAC duct fabrication, and automotive body construction.
There are two types of flange weld symbols you’ll encounter on drawings: edge flange and corner flange. Both have arrow side significance, meaning their placement on the reference line matters.
Edge Flange Weld Symbol
The edge flange weld symbol consists of a horizontal line (the reference line’s perpendicular element) with a flare or curve pointing away from the joint. The symbol resembles a right angle bracket with a curved or flared end.
Text Diagram:
Arrow points to joint
|
V
_________________ (reference line)
|
| (edge flange symbol below line = arrow side weld)
( (flare/curved element)
Edge flange welds are used when joining two pieces of sheet metal along their edges, where one or both edges have been flanged outward. The flanged edges are then welded together to create a strong, flush connection.
When edge flange symbols appear below the reference line:
- The weld is made on the arrow side of the joint
- The flanged edge is on the side the arrow points to
- This is the most common placement for edge flange welds
I frequently see edge flange welds in HVAC ductwork seams and automotive panel joints. The flanged edge creates a natural alignment feature that makes welding easier and more consistent.
Corner Flange Weld Symbol
The corner flange weld symbol is similar to the edge flange but shaped for corner applications. It appears as an L-shaped element with a flare or curve, indicating the metal is flanged at a corner joint.
Text Diagram:
Corner flange joint
|
V
_________________ (reference line)
|
|_ (corner flange symbol below line)
(flare/curved element)
Corner flange welds join two pieces of light gauge metal at a corner where at least one piece has a flanged edge. This creates a boxed corner configuration common in enclosures, cabinets, and ductwork.
Applications include:
- HVAC duct corners and connections
- Electrical enclosure corners
- Sheet metal box construction
- Automotive trunk and hood edges
Both edge and corner flange weld symbols maintain arrow side significance. Their position relative to the reference line indicates which side receives the weld. This is different from flash and upset welds.
Flash and Upset Weld Symbols
Flash and upset welding are resistance welding processes that differ significantly from flange welding. These processes use electrical resistance, heat, and pressure to join metals without filler material.
Flash Welding: A resistance welding process that creates a weld by rapidly heating the mating surfaces with an electric current, then forcing them together under pressure. The flashing action expels molten metal, creating a forged joint.
Upset Welding: A resistance welding process similar to flash welding but without the flashing action. The parts are heated and then forged together under pressure in a single motion.
What makes flash and upset weld symbols unique is their placement rule. Unlike other weld symbols, these are always centered on the reference line with no arrow side or other side significance.
Flash Weld Symbol:
Flash weld symbol (centered on reference line)
|
__||__||________ (reference line)
flash symbol centered
OR
|
____||__||______ (reference line)
flash symbol centered (same meaning either way)
Upset Weld Symbol:
Upset weld symbol (centered on reference line)
|
__==__==__________ (reference line)
upset symbol centered
OR
|
____==__==________ (reference line)
upset symbol centered (same meaning either way)
Why Are These Symbols Centered?
Flash and upset welding processes create symmetrical joints on both pieces being joined. Unlike flange welds where one side may be flanged differently, flash and upset welds affect both pieces equally throughout the entire cross-section.
This is why AWS A2.4 and ANSI standards specify that flash and upset weld symbols must be centered on the reference line. There’s no “arrow side” or “other side” because the weld penetrates and affects both sides identically.
I’ve seen fabricators confused by this convention. They look for arrow side information that doesn’t exist. Remember: if you see a weld symbol centered on the reference line, it’s a flash or upset weld, and the joint is welded completely through both pieces.
Dimensions and Surface Contour Symbols
Flash and flange weld symbols often include dimensional information and surface contour requirements. Understanding these supplementary symbols is essential for proper fabrication.
Dimensioning Flange Welds
Flange weld dimensions typically specify:
- Height of flange: The vertical dimension of the flared edge
- Radius at point of tangency: The curve radius where flange meets base metal
- Root opening: Gap between pieces before welding
Dimensions appear on the same side of the reference line as the weld symbol. For edge and corner flange welds, this means dimensions are placed below the reference line for arrow-side welds and above for other-side welds.
Dimension Format Example
Example: A dimension reading “0.12 (h) 0.25 (r)” indicates a flange height of 0.12 inches and a radius of 0.25 inches at the tangency point where the flange begins.
Surface Contour Symbols
Surface contour symbols indicate the desired finished appearance of the weld surface. These supplement the basic weld symbol with additional finishing requirements.
| Contour Symbol | Text Representation | Meaning |
|---|---|---|
| Flat | – (straight line) | Weld surface flush with base metal |
| Convex | arc (curved upward) | Weld surface raised above base metal |
| Concave | cup (curved downward) | Weld surface below base metal surface |
Contour symbols are placed above the weld symbol when no finish method is specified. If a specific finishing method (grinding, machining, etc.) is required, a letter is added below the contour symbol.
I’ve seen many fabricators overlook contour symbols, leading to rejected parts. Always check for contour requirements before welding, especially for visible assemblies or parts that mate with other components.
Step-by-Step: Reading a Flash or Flange Weld Symbol
After teaching welding symbol interpretation to apprentices for years, I’ve developed a systematic approach that prevents errors. Follow these steps when reading any flash or flange weld symbol.
Step-by-Step Reading Method
Step 1: Identify the reference line and arrow direction. The arrow points to the joint location on the part.
Step 2: Determine the weld symbol type. Is it an edge flange, corner flange, flash, or upset weld symbol?
Step 3: Check symbol placement. Is it above, below, or centered on the reference line?
Step 4: For flange welds: determine if weld is on arrow side (below line) or other side (above line). For flash/upset: placement doesn’t matter (centered).
Step 5: Read all dimensions and specifications. Note size, length, spacing, and any special requirements.
Step 6: Check for contour symbols and finishing requirements.
Step 7: Review the tail for process specifications, reference standards, or supplementary notes.
This systematic approach prevents the most common interpretation errors I see in fabrication shops. Rushing through symbol reading leads to mistakes that cost time and money to correct.
Real-World Applications
Understanding when and where flash and flange welds are used helps with symbol interpretation. These specialized welds appear in specific industries and applications.
HVAC and Sheet Metal:
Edge and corner flange welds are standard in HVAC duct fabrication. The flanged edges create self-aligning joints that weld quickly and consistently. I’ve seen miles of ductwork joined using corner flange welds in commercial construction projects.
Automotive Industry:
Flash welding connects automotive components like wheel rims, exhaust parts, and structural members. The process creates strong, consistent joints suitable for high-volume production. Many suspension components are flash-welded at the factory.
Electrical Enclosures:
Corner flange welds create sealed corners in electrical cabinets and control panels. The flanged edge design allows for consistent weld penetration and good appearance on visible enclosures.
Pipe and Tubing:
Flash welding joins pipes and tubing in applications requiring consistent, strong butt joints. The process creates a forged joint with properties matching the base metal.
Common Mistakes When Reading Flash and Flange Weld Symbols
After reviewing thousands of fabrication drawings and inspecting countless weldments, I’ve identified recurring interpretation errors. Avoiding these mistakes prevents rework and rejected parts.
Mistake 1: Misinterpreting Arrow Side for Flash/Upset Welds
Fabricators sometimes look for arrow side information on flash and upset weld symbols, but these symbols are always centered on the reference line. There is no arrow side or other side significance for flash and upset welds.
Mistake 2: Confusing Flange with Flare Groove Symbols
Flange weld symbols look similar to flare-bevel and flare-V groove symbols. The key difference is that flange welds are for light gauge metal with flanged edges, while flare groove welds are for heavier sections with grooved joints.
Mistake 3: Ignoring Contour Requirements
Surface contour symbols are frequently overlooked, leading to welds that don’t meet specifications. Always check for contour symbols above the weld symbol and any finishing methods specified.
Mistake 4: Missing Dimensional Information
Fabricators sometimes weld without checking all dimensions. Flange height and radius dimensions are critical for proper fit-up. Always verify all dimensional requirements before welding.
Mistake 5: Not Checking Tail Information
The tail of the welding symbol contains important information including welding process, specification references, and special requirements. Ignoring tail information leads to non-compliant welds.
These mistakes are easily avoided with careful symbol reading and a systematic approach. Taking an extra minute to verify all symbol details prevents hours of rework.
Frequently Asked Questions
How is a flash weld indicated on the welding symbol?
A flash weld is indicated by two parallel lines placed on and centered on the reference line. The symbol resembles the equals sign (=) positioned in the center of the horizontal reference line. Unlike most weld symbols, flash weld symbols have no arrow side or other side significance.
What does flash mean in welding?
Flash welding is a resistance welding process that joins metals by heating them with electric current until molten, then forcing them together under pressure. The flashing action expels impurities and creates a forged joint. The process produces strong, consistent welds without filler metal.
Where are flange weld symbols placed on the reference line?
Edge and corner flange weld symbols are placed either above or below the reference line to indicate other side or arrow side welds respectively. Unlike flash and upset welds, flange weld symbols have arrow side significance. Placement below the line means arrow side, above means other side.
What is the difference between flash and upset welding?
Flash welding creates a visible flashing action as molten metal is expelled from the joint before forging. Upset welding heats the parts without visible flashing, then forges them together in a single motion. Both use resistance heating and pressure, and both use centered symbols on the reference line.
What are welding symbols used for?
Welding symbols are graphical notations on engineering drawings that communicate weld requirements without extensive written notes. They specify weld type, size, length, location, and other requirements using standardized symbols. This system ensures clear communication between designers and welders per AWS and ANSI standards.
Summary
Flash and flange weld symbols communicate specialized joining methods for light gauge metal and resistance welding applications. Edge and corner flange welds use directional symbols with arrow side significance, while flash and upset welds are centered on the reference line.
Understanding these symbols prevents fabrication errors and ensures proper joint preparation. The systematic reading method I’ve outlined helps you interpret symbols correctly every time. Reference AWS A2.4 and ANSI standards for complete symbol specifications.
Practice reading symbols on actual drawings to build confidence. The more you work with these symbols, the more natural the interpretation becomes. Start with simple symbols and gradually work up to complex drawings with multiple weld types and specifications.
