What’s a fillet weld?

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Fillet weld is a basic type of weld used to join flat steel at a 90° angle. It requires proper penetration and heat settings, and the weld wire must travel the same distance on both sides of the joint. It is important to avoid excessive penetration when welding a lap joint. Fillet weld is the most common type of weld and requires training and practice to apply correctly.

Fillet weld is the most common type of weld and is used to join two pieces of flat steel at a 90° angle. It is produced by making a weld bead with a 45° angle on a 90° angle; it resembles a triangle when viewed from the side. Welding is used to fill the area where two pieces of steel meet, giving it its name.
Used to make lap, corner, and “T” joints, fillet weld is the most basic of welds. The depth of the penetration, as in all welds, determines its strength. It is important when creating this type of weld that the weld wire travels the same distance on both sides of the joint. Failure to achieve sufficient penetration on both pieces of the joint will result in a weld that has much lower strength than one with equal distribution on both sides.

A proper fillet weld requires a higher heat setting than a comparable butt weld. The trick to learning how to make a proper fillet is to learn how to properly measure the amount of solder deposited in the joint. A joint with little weld will have a flat-like appearance on the weld bead, which often occurs if the welder is moving too fast. Conversely, a weld that is done too slowly will have a bubbled appearance or appear puddled in the joint. The correct weld should have a flat appearance when viewed from the side.

When a welder uses a fillet to weld a lap joint, it is important that the top corner of the joint does not melt. This requires that the weld be placed below the top edge and that the amount of heat and penetration cannot travel to the edge of the top piece of steel. Careful technique must be practiced by the welder to avoid excessive penetration by moving the weld puddle too slowly. Speed ​​and heat settings are key to getting it right.

While fillet is estimated to fill 80% of all welds, it still requires training and practice to apply correctly every time. It requires such attention simply because it is predominantly used on every construction site. Applied correctly, fillet is the workhorse of all welds.




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