An edge weld is a weld made along the edges of two pieces of metal that are aligned side by side or at a slight angle, with their edges exposed and parallel. It’s most common in sheet metal work, where thin materials need to be joined without adding bulk or distortion to the finished part. Think of it as fusing the very edges of two overlapping or flanged sheets together, rather than welding across a flat surface or into a groove.
How an Edge Joint Is Configured
In an edge joint, the two workpieces are positioned so their edges are adjacent and roughly flush. The weld is then deposited along that shared edge. This differs from a butt joint (where two pieces meet end to end in the same plane) or a lap joint (where one piece overlaps the other and is welded along the face). Edge joints work best when the material is thin enough that the weld can fuse both pieces without requiring deep penetration.
The pieces are sometimes flanged, meaning their edges are bent upward at a right angle before being placed together. This small flange gives the weld more material to fuse into and helps with alignment. On thicker stock, a scarf groove (an angled bevel along the edge) can be machined to improve penetration, though this is less common since edge welds are primarily a thin-material technique.
Where Edge Welds Are Used
Edge welds have a relatively narrow range of applications compared to fillet or butt welds, but they’re the right choice in specific situations. According to TWI, they’re mostly used for joining sheet metal components, though they also appear in tube-to-tubesheet connections in heat exchangers.
Sealing a lid onto a can is a classic example. The lid is pushed into the can body, creating a minimal gap and a self-jigging joint where the parts hold themselves in position. The edge weld then seals the seam. This same principle applies to enclosures, housings, and any container where a clean, sealed edge matters more than raw structural strength.
In tube-to-tubesheet fabrication (common in heat exchangers and boilers), a small raised feature called a pintle is machined onto the tubesheet. The tube slides through the hole and the edge weld joins the tube end to the tubesheet surface. Battery trays, lightweight frames, bellows, and HVAC ductwork are other places you’ll find edge welds in production.
Welding Processes for Edge Joints
TIG welding is the traditional choice for edge welds on thin sheet metal because the welder has precise control over heat input. The focused arc and optional filler wire let you make a clean, narrow bead without overwhelming the thin edges. The tradeoff is speed: TIG requires longer dwell times and often leaves a wider heat-affected zone that can warp long seams.
Fiber laser welding has become a serious alternative on materials between 0.8 and 3 mm thick. The laser beam focuses into a small spot and oscillates across a scan width of 3 to 4.5 mm at 30 to 40 Hz. On 1.5 mm stainless steel, a 1,200-watt system achieves full penetration at only 40% peak power. The result is a much narrower heat-affected zone, significantly less distortion, and often no need for post-weld grinding or straightening. Travel speeds are typically higher than TIG and comparable to or faster than MIG on thin sheet.
Aluminum is especially challenging for edge welds because of its high thermal conductivity and tendency to burn through on thin edges. Laser welding has a clear advantage here, concentrating energy precisely enough to avoid the wide heat-affected zone that plagues TIG on aluminum sheet. MIG welding is generally too aggressive for most edge weld applications, though it remains common on heavier structural joints elsewhere in the same assembly.
Fit-Up and Preparation
Edge welds are unforgiving when it comes to fit-up. Because you’re welding along thin edges with limited material to work with, any gap between the parts makes burn-through far more likely. The general standard for joints involving fillet or tee welds is a maximum gap of 1/8 inch (about 3 mm), with adjustments required if the gap exceeds 1/16 inch. For edge welds on thin sheet, tighter fit-up is better. Self-jigging designs, where one part nests into the other like a lid into a can, are ideal because they naturally minimize the gap.
Before welding, edges should be clean and free of oil, oxide, and mill scale. On aluminum, removing the oxide layer is especially important because aluminum oxide melts at a much higher temperature than the base metal. If tolerances can’t be achieved through initial preparation, edges can be built up with weld material or re-prepped by machining or grinding before the final joint is made.
Clamping is simpler with laser welding because the lower heat input produces less expansion and contraction. With TIG, more elaborate fixturing is sometimes needed to keep parts from pulling apart as the weld cools.
Common Defects and How to Avoid Them
The biggest risk with edge welds is burn-through, where the arc or beam melts entirely through the thin edge instead of fusing the joint. This happens when current is too high, travel speed is too slow, or the gap between parts is too wide. Reducing amperage (or laser power), increasing travel speed, and ensuring tight fit-up are the primary fixes.
Excess reinforcement, where weld metal builds up above the surface of the base material, is another common issue. It’s caused by too much filler wire, excessive current, or slow travel speed. On visible seams this creates an uneven appearance and may require grinding. Overlap, where weld metal flows onto the base material without fusing to it, creates a weak spot that can crack under stress.
Because edge welds involve minimal material thickness, the margin for error on heat input is narrow. Welders often run test beads on scrap pieces of the same thickness before committing to the actual part, dialing in parameters until they achieve consistent fusion without distortion.
Reading Edge Weld Symbols on Drawings
On engineering drawings, welds are represented by standardized symbols rather than cross-sectional illustrations. The edge weld symbol sits on a reference line with an arrow pointing to the joint location. Under AWS standards, symbols placed below the reference line indicate the arrow side of the joint, while symbols above the line indicate the other side. ISO 2553 uses a broken (dashed) reference line for the same purpose.
When no specific dimensions appear next to the symbol, the default assumption is full penetration, meaning the weld should fuse completely through the joint thickness. If partial penetration is acceptable, a depth-of-penetration value appears to the left of the symbol, noted with an “S” prefix followed by the required depth in millimeters or inches.
Strength Limitations
Edge welds are not high-strength structural joints. They work well for sealing, for joining sheet metal where the primary loads are light, and for assemblies where appearance and minimal distortion matter more than load-bearing capacity. If you need a joint to carry significant tensile or bending loads, a butt weld or fillet weld on a lap or tee joint is almost always the better choice. Edge welds excel where the geometry of thin, aligned edges makes other joint types impractical or where the goal is a sealed, low-profile seam rather than maximum strength.