It should be remembered that welding over weld metal is actually a very common occurrence. Multi-pass welds after all are manufactured by welding over weld metal! There are also many accepted procedures in which welds overlap.
Materials such as mild, low carbon and carbon-manganese steels, are considered to be very tolerant to heat input and may accept at least two or more re-weld operations. In the case of low alloy steels, re-welds will be governed by the heat-treated condition in which they were supplied.
Running over the top of an existing weld will add little, if any strength to the joint as you're having to penetrate the new weld material, not the parent metal.
The adhesive encapsulates the weld (see Figure 3). But at the spot of the weld, there is just metal-to- metal contact, a conductive path. The reason why the rule has always been to not weld in the same spot twice, is that the metal has been compressed at that point and hardened.
So if the item was welded originally, it should be weldable again for repair, right? Yes, but only if you know the materials and their conditions and whether they still are exactly as they were at fabrication time—no heat treatment or other surface conditioning has been introduced.
A good weld should be visually appealing, with a smooth and uniform weld bead that shows proper fusion and penetration. Bad welds, on the other hand, may contain defects like porosity, pinholes, or slag on the weld surface, which can compromise the strength and reliability of the weld.
1: The minimum distance between welds should be at least four times the thickness of the thinner part joined, but not less than 1 inch (25 mm).
But most company specification will give some minimum distance that you have to maintain between two nearby welds. This is to avoid overlapping of heat affected zones. The thumb rule is that the minimum distance between adjacent butt welds is 1D. If not, it is never closer than 1-1/2″.
The drill bit method is the least resource-dependant as you only need a drill and some drill bits, and a center punch for the removal of the spot welds. As far as what drill bits to use, grab something small to start, like a 1/8-inch bit, but a 5/16-inch bit will be used for the majority of the removal.
Welded joints are normally stronger than bolted joints, in great part because their material does not have the perforations needed for bolted joints. The manufacturing process is the determining factor when it comes to joint strength: bolted joints offer simplicity, but welded joints provide higher strength.
TIG welding is the hardest form of welding to learn for a variety of reasons. The process of TIG welding is slow and takes time to get used to as a beginner. A TIG welder requires a foot pedal to feed the electrode and control the variable amperage while maintaining a steady hand at the welding torch.
The overhead position is the most challenging welding position, as gravity can cause the weld metal and slag to fall out of the joint.
Signs of a bad weld include: Burnout, no filler metal used, wide flat bead without distinct bead pattern, erratic beads, tungsten inclusion, porosity and/or undercutting.
The weld is as smooth as possible. If you see cracking along the weld, it's a sign of a poor MIG weld. Any lack of uniformity or dips that cause the bead to lack straightness are bad signs as well. Also, if the bead is too thin it will lack proper strength.
Depends on a lot of things including thickness of base metals, job requirements and operator skills. Generally you want tight fit up, but 1/4 inch is common on inspected structural jobs. Sometimes a filler plate is added and another weld made. Sometimes an engineers approval is required.
There's no Code requirement for the minimum distance between welds. A figure "pulled off the air" that is very used in prefabricating shops and jobsites is that the minimum distance should be three times the pipe diameter.
2 Root openings (gap) between parts to be fillet welded shall not exceed 3/16 in., except in cases involving plates 3 in. or greater in thickness.
A weld would be stronger, but the HAZ surrounding the weld would be the weak point. Most engineers only allow one bend on a piece of reinforcing bar because it reduces it's strength so much. But they never allow welding on it in my experience, so a bend may be better if done properly.
Cold Welding
In fact, without the protective coating of oxygenation, parts made of the same type of metal will stick together in space fairly easily. The atoms in each part have no way of knowing they are separate pieces in a vacuum, so they stick together.
Any steel up to 1.5mm is best welded without a gap, though a small gap or perhaps between 1/2 the thickness of the steel can be useful on steel thickness 2mm or above.
Defects which are welded over, and not melted out, can suffer locally intensified strain age embrittlement by static or dynamic strain ageing at the region of concentrated strain at the flaw tip, leaving a planar defect with its tip in a region of low toughness (Dawes M G).
Yes, he can, according to Kevin. Because a primary purpose of a TIG welder is to melt metal, move metal, and push metal around, he shows in this short how-to video how to use those capabilities to clean up an ugly MIG weld. This is particularly helpful in butt joints, where it is hard to grind.
Any kind of debris, dirt, oxides, or other particles on the metal will disrupt the weld, creating a final weld that is porous and not uniform. Since any porous nature in the weld means pockets of weakness, you want to avoid anything that will result in a porous weld.