The Undercut is an imperfection which is characterized by a groove formation at the weld toe due to overheating at the free edges of base metal or weld metal (of the previous run). This happens when a welder tries to make weld either with high welding current or with fast travel speed.
Moreover, the incorrect usage of gas shielding, wrong welding technique, and position are other primary causes of undercut imperfection.
Undercutting always has been a serious concern in steel welding industries and efforts have been made to resolve this problem in recent years.
Following are the preventions that effectively assist, in reducing the concentration of undercutting in your weld.
1. Correct Heat Input
One of the major causes of undercut in the weld is high heat settings while making a run near to the free edges. This may lead to the overheating and melting of near parent metal or previous weld metal. In order to prevent this, one must take great care of weld heat by reducing the current, when approaching to thinner and free edges.
2. Correct Electrode Angle
As we know welding angles always play a vital role in producing defects free runs. If one makes a run with an incorrect angle which directs more heat to free edges, here in this case weld is more prone to undercuts. For this one must use correct angles (lead, work, electrode, travel, and slope) in order to direct more heat towards thicker components as compared to the free edges.
3. Moderate Travel Pace
Making a weld with high travel pace is another big cause of weld undercutting. In doing so, some portion of parent metal is drained into the molten metal and never came back due to fast solidification, leaving a depression along the edges. It is recommended to travel a weld run with moderate pace because too slow travel also does not give satisfactory results.
4. Right Selection of Gas Shielding
In case of MAG (metal active gas) process, wrong selection of gas shielding is also one major cause of undercuts in a weld. Welding associates must ensure the correct composition of gas according to the requirement of material type and thickness. Use of Carbon dioxide in conjunction with inert gases provides quality results in welding of carbon steels.
5. Correct welding Technique
Problem of undercut also arises when a welder endeavors to make a weld run with excessive weaving style. Codes and standards call for the recommended width of weaving according to the electrode size. Size of weaving should not be exceeded to the acceptable limit, otherwise, the weld may prone to undercut grooves. In order to prevent this one must endeavor either to reduce the size of weaving or to produce the weld with multipass technique.
6. Correct Welding position
Sometimes making a fillet weld in horizontal-vertical position, also results in weld undercuts. In this case, a depression is formed due to inadequate metal filling along the joint edges. In order to prevent this, try to weld in the flat position to ensure the adequate electrode consumption.
7. Use of multi-run technique
This one is the best option to adopt, in order to reduce the level of undercuts in welding. Multi-run technique supports all above-mentioned preventions and helps to produce fine welds with improved mechanical properties.