Fillet welding is the most commonly used welding technique for joining steel structures during the welding process. As a result, welders often encounter several types of fillet welds, each with different patterns.
So how can we ensure that we weld fillet welds correctly and produce high-quality fillet welds that meet the necessary requirements? Today, I would like to give a brief introduction to this topic.
1. Selection of base metal
Let us take the size 200 test panel made of Q355 as an example for a brief introduction.
2. Selection of welding materials
Welding material: E5015 (J507) welding rod should be used, the drying temperature should be 350 ℃, heat preservation should be 1 hour, and the welding wire should comply with the national standard ER50-6 (American standard ER70S-6).
3. Cleaning before welding
For fillet welding, it is essential to clean both sides of the weld within a range of 15 to 20 mm. The surface of the plate must be free from any film of oxide, rust, oil or water, which can be removed with a grinding wheel or through chemical treatment.
4. Fixing the mounting point
Ideally, the weld gap for fillet welding should be kept as small as possible. Point fixation is generally performed on the back of the plate, with the length of point fixation being around 10 mm. Normally, two or three points are sufficient for fixing, as illustrated in the diagram below:
5. Welding parameters
|
Weld bead distribution |
Welding level |
Electrode diameter mm |
Welding current A |
Welding voltage |
mms welding speed |
Heat input KJmm |
|
a=7mm |
1 |
3.2 |
120-140 |
/ |
/ |
/ |
|
2, 3 |
4.0 |
160-180 |
/ |
/ |
/ |
6. Welding operation
Support weld
1.1 Electrode angle and electrode handling method
The electrode angle for flat root fillet welding is illustrated in the figure. To ensure proper welding, strike the arc on the left side of the test plate and perform short arc welding.
Use a straight electrode to weld on the right and align the arc with the top angle of the root. Press the bow to ensure that the top angle and two side plates are fused.
When carrying out backing welding, use the method of moving the electrode in a straight line for oscillation. Fast welding without wobble can also achieve the required penetration.
During the beginning and end of a welding operation, magnetic polarization blows are common, which can negatively impact the quality of the weld. To mitigate this, it is necessary to adjust the angle of the welding rod appropriately.
Typically, pointing the arc toward the molten pool can help control the magnetic bias blow and ensure a higher quality weld.
As shown in the figure.
1.2 Weld bead joint
The arc must start 10mm in front of the crater in the joint. As the elongated arc moves rapidly toward the crater, fill the crater along its shape and proceed with normal welding.
Cover welding
Before welding, it is important to remove any slag and welding spatter from the root pass to avoid slag inclusion defects.
The cover must be welded twice, starting with the lower weld bead followed by the upper weld bead.
When welding the bottom weld bead, the arc must be aligned with the lower edge of the root weld bead and the electrode must be moved in a straight line with an electrode angle greater than 45°.
When welding the top weld bead, the arc must be aligned with the top edge of the root weld bead. The electrode may oscillate sideways while moving in a straight line, with an electrode angle less than 45°, as shown in the figure below:
Schematic diagram of each pavement layer
Fillet size representation
Projection fillet weld
Built-in fillet weld
Theoretical Throat: The vertical distance from the root of the joint to the chamfer in the largest inscribed right triangle drawn on the fillet weld profile.
Effective Throat: The minimum distance from the surface of the fillet weld to the root of the weld minus the raised portion.
Actual Throat: The shortest distance between the surface of the fillet weld and the root of the weld.
For concave fillet welding, as there is no convex part, the effective throat is the same as the actual throat.
Leg Size: The distance from the root of the joint to the tip of the fillet weld.
Weld Toe: The point of intersection between the weld surface and the base metal.
When determining the size of a fillet weld, it is important to determine whether the weld is convex or concave.
Convex fillet welds have a slightly protruding weld surface, which is related to the height of the protrusion.
The height of the bulge of a fillet weld is equivalent to the height of the reinforcement of a channel weld.
If there is a dent in the weld, it means the weld surface is bulging.
For convex and concave shapes, the weld size of a fillet weld with equal leg height is expressed as “the straight edge of the largest isosceles right triangle obtained from the fillet weld profile (two legs have equal length)”.
As a result, the weld leg size of a convex fillet weld is equal to the size of the weld, while the weld leg size of a concave fillet weld is slightly smaller than the length of the weld leg.
