Like any manufacturing or fabrication process, the welding operation is subject to human error. When weld defects occur as a result of a problem with welding operator’s technique or poor equipment settings, it can cause costly downtime and rework, not to mention, frustration.
When a weld defect is discovered, welding operators must know how to rectify the situation as quickly as possible. Faster troubleshooting can add value to the welding operation through increased productivity and improved quality.
Following are some common weld defects, along with suggestions for quick troubleshooting.
Porosity is among the most common of weld defects. It can develop in many types of material — from aluminum to galvanized and carbon steel — and is the result of gas becoming trapped in the weld metal. Porosity can appear at any point on the weld, along its length, and on the inside (subsurface) or outside of the weld.
Inadequate shielding gas coverage is among the biggest culprits of porosity, and can be addressed in several ways. First, check the regulator or flow meter for adequate gas flow, increasing it as necessary. Also, check the gas hoses and welding gun for possible leaks, and block off the welding area if drafts are present.
Other potential causes preventing proper shielding gas coverage include using too small of a nozzle, spatter build up in the nozzle, or incorrect contact tip recess. Solutions include using a large enough nozzle to shield the weld pool fully with shielding gas, keeping the nozzle clean, and following the consumable manufacturer’s recommendation for contact tip recess.
Porosity, as shown here, is among the most common weld defects. It can appear at any point on the weld, along its length, and on the inside (subsurface) or outside of the weld.
Other causes and remedies for porosity include:
– Having dirty base material. Always be sure to follow proper cleaning procedures.
– Extending the wire too far from the nozzle. A good rule of thumb is to extend the wire no more than ½ in. past the nozzle.
– Wet or contaminated shielding gas cylinders. Replace damaged cylinders.
– Damaged filler metals. Low hydrogen filler metals can pick up moisture. Always follow proper storage requirements.
Lack of fusion and cold lap
Cold lap and lack of fusion are terms for weld defects that are often used interchangeably; however, they are different and can occur independent of or in conjunction with one another.
Lack of fusion results from the weld metal failing to completely fuse to the base metal or to the preceding weld bead in multi-pass applications. An incorrect welding gun angle and incorrect travel speeds are leading causes of this weld defect. Correct the problem by maintaining a 0- to 15-degree gun angle during welding and keeping the arc on the leading edge of the weld pool. To maintain the correct arc position, increasing travel speeds is sometimes necessary. Insufficient heat can also cause lack of fusion and can be remedied by increasing voltage settings or wire feed speeds.
Cold lap occurs when the weld overfills and overlaps the toes of the weld. Like lack of fusion, incorrect travel speeds can cause the problem. When the weld pool absorbs most of the energy of the arc, as opposed to the base material, cold lap is more likely to happen. Increasing travel speeds can help the weld fill in more smoothly and prevent this problem.
Lack of fusion is the result of the weld metal failing to fuse completely to the base material or to the preceding weld bead in multi-pass applications. This close-up side view of a weld shows where the weld and base material didn’t fuse.
Weld metal penetrating through the base material is known as burn through and is Materials less than 1/8 in. or around 12 gauge are especially susceptible to burn through. Excessive heat is the main cause of burn through. To help rectify this weld defect, lower the voltage or wire feed speed.. Also, consider increasing travel speeds, particularly when welding on thin aluminum, which is especially prone to heat buildup.
Excessive spatter can appear when using a variety of different filler metals, including solid wires and flux-cored wires, particularly the self-shielded variety, as well as stick electrodes. This defect results when the weld puddle expels molten metal and scatters it along the weld bead, resulting in molten metal that fuses to the base. Typically, spatter needs to be removed mechanically, by scrapping or grinding.
Excessive spatter can also occur because of insufficient shielding gas, dirty base materials, too high of voltage, too high of travel speeds and too long of wire or stickout. Ensuring proper shielding gas flow, cleaning base materials thoroughly, lowering the given weld parameter settings and using a shorter stickout can help.
When a gas mixer does not feed a consistent gas blend or has been incorrectly adjusted, it can change the arc characteristic and result in increased spatter. For example, if an application requires a conventional 75 percent argon and 25 percent CO2 shielding gas blend and this weld defect develops, the mixer might be delivering too much CO2. Check the mixer and adjust as needed.
For self-shielded flux-cored wires, be certain to weld with straight polarity (electrode negative) and use a drag technique when welding to minimize potential spatter buildup. While using flux-cored or metal-cored wires, too low of voltage could produce an excessive amount of spatter. Adjust as needed. The wrong size contact tip, a worn contact tip or the wrong contact-tip-to-nozzle recess can also cause excessive spatter and should be addressed.
When a weld defect appears, it’s important for welding operators to be able to quickly rectify the situation.
Concave and convex weld beads
Regardless of the welding process, the goal is to create a smooth, flat weld bead. Welds that are too concave or too convex can compromise the integrity of the finished product and in some cases can be considered a weld defect..
Concave weld beads are particularly prevalent when welding in vertical-down applications and are the result of working against gravity. It is difficult to keep the weld pool in the joint in this position, so the weld tends to be thinner at the throat. A good remedy is to adjust the welding parameters to a lower setting so the weld pool is less fluid and more able to fill in the joint. If a concave weld bead appears in the flat or horizontal position, it is typically the result of too high of voltage, too slow of wire feed speed or too fast of travel speed. Reduce these factors accordingly.
Convex weld beads present themselves as high, ropey-looking welds, and generally happen in flat and horizontal welding. They are the result of too cold of weld parameters for a given material thickness. Increase the voltage accordingly.
Using the wrong shielding gas for a given wire can also cause a convex weld bead. For example, if an application calls for a mixed argon shielding gas, but the welding operator uses 100 percent argon, the weld pool will not be fluid enough, preventing the weld from penetrating the joint. Instead, it will build up on top of the weld bead. To prevent this defect, follow the recommended welding procedure and be sure to use the correct polarity for the given wire.
Crater cracks are small cracks that develop at the end of the weld. They can happen during any welding process and are sometimes called shrink cracks. This weld defect occurs when the weld crater has not been fully filled when completing a pass; the weld pool solidifies and the center of the crater pulls from the center of the weld bead. This is especially common in welding aluminum.
To prevent crater cracks, pause at the end of the weld to ensure enough filler metal has filled the weld pool or “back step” to fill it, moving back from the end of the weld, then forward. Some welding operators choose to solve crater cracks by pausing and welding a “curlicue” at the end of a pass. A “double trigger” technique also works. With this technique, the operator (in a MIG welding application) releases the trigger, pulls it again to start the weld, and then releases the trigger again to fill the crater.
Some wire feeders feature crater functions that can remedy this problem. To activate this function, the welding operator releases the trigger and the system automatically fills the crater.
In some applications, particularly those using submerged arc welding, run-off tabs are a common way to prevent crater cracks. These are metal tabs that the welding operator tacks to the end of the joint and welds over, thereby eliminating any opportunity for a crater to form.
While not an exhaustive list of possible weld defects, those discussed here are common across many types of materials and welding processes. To minimize costs and labor for rework, as well as downtime spent addressing weld defects, take a systematic approach for troubleshooting each defect. Look at any variables such as welding parameters or techniques that have changed during the course of welding during a shift or from shift to shift and consider their potential impact on the problem. Then consider these tips as potential remedies.
As with any portion of the welding process, should a problem persist, consult with a trusted welding distributor, or filler metal or welding equipment manufacture for assistance.