When I first started reading welding blueprints, projection weld symbols looked like a foreign language. The tiny circles, crosses, and arrows seemed confusing compared to straightforward groove weld symbols. After working with resistance welding specifications for over 15 years, I’ve learned that projection weld symbols are actually quite logical once you understand the pattern.
A projection weld symbol is a standardized graphical symbol used on engineering drawings and blueprints to specify projection welding, a resistance welding process where welds are created at pre-formed projections or embossments on mating parts. The symbol communicates weld location, size, quantity, and processing specifications required for manufacturing.
Projection welding relies on current concentration at designed projection points rather than electrode-defined locations like spot welding. I’ve seen this process used extensively in automotive manufacturing and sheet metal assembly where multiple welds must be made simultaneously with consistent quality.
Understanding Projection Welding
Projection welding creates welds at pre-formed projections or embossments on one or both workpieces. When current flows through the joint, these projections concentrate the electrical current and heat, allowing multiple welds to form simultaneously under electrode pressure.
Quick Summary: Projection welding uses embossed projections on the workpiece to concentrate welding current. The process creates multiple welds in a single cycle, making it faster than spot welding for production applications.
Projection weld symbols indicate the resistance welding process where the weld location is determined by designed projections, not electrode placement. This distinction matters because the symbol tells the welder that joint preparation (creating the projections) happens before welding occurs.
The embossments can be created through stamping, machining, or coining operations. I’ve worked with projections ranging from 0.5mm to 3mm in height, depending on material thickness and welding equipment capacity. The symbol specifies the weld requirements, but the projection design is typically detailed in separate notes or specifications.
AWS A2.4 Standard Reference
AWS A2.4: The American Welding Society standard titled “Standard Symbols for Welding, Brazing, and Nondestructive Examination.” This document defines all welding symbols used in North America, including projection weld symbols, and provides rules for their application on technical drawings.
The AWS A2.4 standard governs projection weld symbols in North America. This specification establishes the uniform method for specifying welded joints on drawings, ensuring clear communication between design engineers and welding personnel. I keep a current copy of A2.4 in my office because symbol interpretations can change between editions.
ISO 2553 serves a similar purpose internationally, with some notable differences in symbol appearance and notation. For this guide, I’ll focus on AWS A2.4 conventions since they’re most common in North American manufacturing. However, I’ve worked with international blueprints and noted that projection symbols remain relatively consistent across standards.
The current edition of AWS A2.4 provides detailed rules for symbol placement, dimensioning, and supplementary information. Understanding this standard helps prevent misinterpretation that could lead to costly welding errors.
Anatomy of a Projection Weld Symbol
Every projection weld symbol consists of several key components that work together to convey complete welding instructions. Let me break down each element from my experience reading thousands of welding prints.
The complete weld symbol assembly includes a reference line, an arrow line, the weld symbol itself, dimensions, and optional supplementary information. Each component has a specific position and meaning defined by AWS A2.4.
Projection Weld Symbol Structure
Reference Line
The reference line is the horizontal foundation of the welding symbol. All other elements attach to or position relative to this line. The reference line serves as the anchor point for symbol placement and determines whether the weld is on the arrow side or other side of the joint.
In my experience, the reference line is the most critical component to understand because symbol positioning relative to this line determines weld location. Weld symbols below the reference line indicate arrow-side welds, while symbols above indicate other-side welds.
Arrow and Arrow Side
The arrow connects the reference line to the weld joint and indicates which side is the “arrow side.” The arrow side designation matters because it determines where the symbol should be placed relative to the reference line.
The arrow side is the joint side toward which the arrow points. When the projection weld symbol appears below the reference line, the weld is on the arrow side. When it appears above, the weld is on the other side (the side opposite the arrow).
Tail
The tail is the optional element extending from the opposite end of the reference line from the arrow. When present, the tail contains reference information, specifications, or process notes that apply to the weld.
I’ve seen tails used for various purposes: specifying welding processes, referencing standards, indicating weld sequence, or providing supplementary notes. An empty tail (no text) has no meaning and can be omitted. The tail should only be included when it contains essential information.
Projection Weld Symbol
The projection weld symbol itself consists of a circle with a cross or dot in the center, resembling a target. This symbol appears either above or below the reference line depending on weld location.
Projection Weld Symbol
AWS A2.4 Symbol
Alternative Symbol
This emblem distinguishes projection welding from other resistance welding processes. Spot welding uses a different symbol (a simple circle), and seam welding has its own designation. The projection symbol’s crossed circle makes it immediately identifiable on drawings.
Dimensions and Specifications
Dimensional information appears around the weld symbol in specific positions. The size (diameter) of each projection weld typically appears to the left of the symbol, while the number of welds may appear in parentheses or in the tail.
Pitch spacing (distance between weld centers) is sometimes specified when multiple projection welds are arranged in a pattern. I’ve seen pitch dimensions placed below the reference line for arrow-side welds or above for other-side welds, depending on the drawing standard being followed.
Dimension Placement Reference
| Location | Information |
| Left of symbol | Weld size (diameter) |
| Right of symbol | Length (if applicable) |
| In parentheses | Number of welds |
| In tail | Process, specification reference |
How to Read Projection Weld Symbols?
Reading projection weld symbols follows a systematic process that I’ve taught to welding students and inspection personnel. Here’s my step-by-step approach for interpreting any projection weld symbol correctly.
Quick Summary: Start at the arrow, identify the weld side from symbol position, read dimensions left-to-right, check the tail for specifications, and verify supplementary symbols. Follow this order every time for consistent interpretation.
- Locate the arrow – Find which joint the arrow points to and identify the arrow side of the joint
- Check symbol position – Symbol below the line means arrow-side weld; above means other-side weld
- Read size dimension – Look left of the symbol for weld diameter or size
- Check for quantity – Look for numbers in parentheses indicating multiple welds
- Examine the tail – Review any reference information or specifications
- Note supplementary symbols – Check for contour, finish, or other special symbols
- Verify against drawing notes – Cross-reference with general notes or specifications
Arrow Side vs Other Side Placement
Symbol position relative to the reference line is the most critical factor in determining weld location. This is where I see most interpretation errors occur on the shop floor.
Symbol Position Guide
The weld is made on the side of the joint toward which the arrow points. This is the most common placement for projection weld symbols.
The weld is made on the side opposite the arrow. The arrow points to one side, but the weld occurs on the reverse side.
I’ve found it helpful to physically point at the drawing and trace the arrow to the joint, then flip my finger to the opposite side if the symbol is above the reference line. This simple physical action prevents the mental slip of misidentifying the weld side.
Multiple Projection Welds
Projection welding’s advantage is making multiple welds simultaneously. Symbols often indicate multiple projections through quantity designations and pattern information.
The number of welds typically appears in parentheses near the symbol: (6) indicates six projection welds. When multiple welds are arranged in a pattern, the drawing may include a separate detail view showing projection locations and spacing.
I’ve worked with automotive subassemblies where a single symbol represented 12-16 projection welds made in one cycle. The symbol specified the weld size and quantity, while a separate detail showed the exact projection layout.
Spot Weld vs Projection Weld Symbols
Spot welding and projection welding are both resistance welding processes, but their symbols differ in important ways. I’ve seen these symbols confused many times, leading to process errors.
Symbol Comparison Table
| Characteristic | Spot Weld Symbol | Projection Weld Symbol |
| Symbol Shape | Simple circle | Circle with cross or dot |
| Weld Location | Determined by electrode position | Determined by part projections |
| Process Type | Single weld per electrode contact | Multiple welds possible per cycle |
| Typical Use | Sheet metal overlap joints | Assemblies with embossed projections |
| Joint Preparation | None required | Requires formed projections |
Visual Symbol Comparison
Spot Weld
Simple circle
Projection Weld
Crossed circle
The key difference I look for is the cross or dot inside the circle. This internal element identifies the symbol as a projection weld rather than a spot weld. Missing this distinction has caused more than one fabrication error in shops I’ve visited.
Common Applications and Industries
Projection welding appears in various manufacturing applications where multiple welds must be made efficiently. I’ve encountered projection weld symbols in several industries:
Body structural components, brackets, subassemblies
Enclosure assemblies, chassis components, grounding points
Cabinet frames, mounting brackets, hardware attachment
Stamped assemblies, welded nuts and studs, fastener attachment
Weld nuts and weld studs represent common projection welding applications. The threaded fastener itself has built-in projections that create the weld points when resistance welding equipment applies current and pressure.
I’ve worked extensively with automotive applications where projection welding joins brackets to body panels. The process allows multiple attachment points in a single cycle, dramatically improving production efficiency compared to individual spot welds.
Frequently Asked Questions
What is a projection weld symbol?
A projection weld symbol is a standardized graphical symbol on engineering drawings that specifies projection welding. It consists of a circle with a cross or dot in the center, placed on a reference line with an arrow pointing to the weld joint. The symbol indicates that welds will be created at pre-formed projections on the workpiece rather than at electrode contact points.
How do you read projection weld symbols?
Read projection weld symbols by starting at the arrow and identifying which joint it points to. Check if the symbol appears below (arrow side) or above (other side) the reference line. Read dimensions left of the symbol for weld size. Look for numbers in parentheses indicating multiple welds. Check the tail for process specifications. Verify against drawing notes and general specifications.
What is the difference between spot weld and projection weld symbols?
Spot weld symbols use a simple circle, while projection weld symbols use a circle with a cross or dot inside. Spot welding location is determined by electrode placement, while projection welding location is determined by pre-formed projections on the part. Projection welding can create multiple welds in one cycle, whereas spot welding typically creates one weld per electrode contact.
What does the arrow side mean on a weld symbol?
The arrow side is the joint side toward which the arrow points. When the weld symbol appears below the reference line, the weld is made on the arrow side. When the symbol appears above the reference line, the weld is made on the other side (opposite the arrow). This positioning convention applies to all welding symbols per AWS A2.4 standard.
What is AWS A2.4 standard?
AWS A2.4 is the American Welding Society standard titled “Standard Symbols for Welding, Brazing, and Nondestructive Examination.” It establishes the uniform system for specifying welded joints on technical drawings used in North America. The standard defines symbol shapes, dimensions, placement rules, and supplementary information formats for all welding processes including projection welding.
Where are projection welds typically used?
Projection welds are commonly used in automotive manufacturing for body components and brackets, electronics for chassis and enclosures, appliance manufacturing for cabinet frames, and sheet metal fabrication for attaching weld nuts and studs. The process excels when multiple welds are needed in a consistent pattern and when production speed is critical.
