Arc Welding 101: Minimizing defects from welding starts, stops
Q: I am having trouble making welds that are all the same length when using GMAW. How can I create tie-ins that are all in line with each other and spaced out as they should be?
A: It is understood throughout the industry that most weld defects are attributed to weld stops and starts. We automate (or change from manual to semiautomatic) to improve cycle time and quality. Most of that quality improvement comes from eliminating starts and stops. Welding starts can lead to overlap, incomplete fusion, and slag inclusion, while stops typically lead to cracks and undercut.
Some of these discontinuities may be considered acceptable, but stacking them on top of one another in a multipass weld is just flirting with disaster.
Stops and starts are a necessary evil in welding. We can minimize their negative effects, however, through techniques during manual welding and through weld data settings for semiautomatic and automated welding.
In GMAW those weld settings that can be added to many wire feeders include:
- A burnback that keeps the wire stickout as short as possible will help with your next arc start.
- A three-second postflow protects the wire and keeps it clean.
- A preflow (0.2 second) ensures the shielding gas covers the area before an arc is struck.
- A slow run-in speed of -100 to -200 will reduce the “snap” that often occurs when initially striking an arc.
- Increasing the start by 1 or 2 volts will also reduce the snap.
As for your welding technique:
- When striking an arc, begin ahead of the desired start point (1½ times the weld size). After you strike the arc, back up quickly to the desired start point then begin your weld. This will almost eliminate any overlap (cold lap) that is common with weld starts.
- When extinguishing the arc, weld to the desired stop point then back up (1½ times the weld size). This will fill the weld crater, slow the cooling rate, fill the undercut, and reduce the chances of a crater crack.
You could probably search the Internet for an article on weld stops and starts and get plenty of horror stories. In that same search you will find oodles of “pixie dust” salesmen with quick-fix products or equipment that claim to take all those troubles away.
Stick with common sense. Equip your feeders with the settings that help improve weld starts and stops, and be sure to use good welding techniques.
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