Bad welds and causes of rework
Rework in the weld cell essentially means you’re paying for something twice. This makes weld rework a costly proposition for most every manufacturer.
Here are six questions about common issues that require weld rework — and tips for how to best address them in the operation.
Q1: Why do weld appearances look poor and fail inspection?
A: A weld profile that is visually bad is often the main culprit. The beads may be ropey, have undercut or lack fusion at the weld toes, or be inconsistently or improperly sized.
Potential causes of poor weld appearance are:
- Puddle that’s too cold: The puddle must be hot enough to achieve good fusion and produce a good bead profile.
- Improper travel speed: Going too fast and getting too far ahead of the puddle will cause a strung-out puddle that doesn’t flow at the toes.
- Incorrect work angle, travel angle or electrode stickout: Producing good weld beads also requires proper technique, including travel angle and electrode stickout. The work angle should be approximately 45 degrees. When running a pulsed or spray transfer process, contact-tip-to-work-distance should be about 3/4 inch. When running a short-circuit transfer process, it should be about 3/8 inch. Also, with pulsed or spray transfer modes, a 10- to 15-degree travel angle is recommended with a push travel method. Either a drag or push angle is fine with short-circuit transfer mode.
How to address issues with poor weld appearance:
- Proper training: Make sure less experienced welders have proper training. Get tips for reducing welder training time in this article.
- Adjust parameters as needed: Proper wire feed speed is tied to material thickness. With thicker materials, use a faster wire feed speed, which may require an increase in voltage. Training and experience will help welders understand the connection between thickness, wire feed speed and voltage.
- The right shielding gas: The shielding gas for the job is dependent on material type and thickness and the type of arc transfer desired. A good option for pulsed and spray transfer modes is a blend of 90% argon and 10% carbon dioxide. For short-circuit MIG, a good option is a mix of 75% argon and 25% carbon dioxide. Synergic welding systems aid with gas selection as well, recommending gasses to produce the best arc characteristics for the program being used.
Q2: What causes lack of penetration or lack of root fusion?
A: Weld parameters that are too cold or incorrect parameter settings are often the main culprit for lack of fusion. Ensure correct parameter settings and add enough heat. Problems with lack of fusion can also tie back to reading the puddle. Less experienced operators may go too slowly, which causes the arc to get back into the puddle. This increases the risk of lack of fusion or improper penetration. In response, operators may rush to get ahead of the puddle again but end up too fast — and get too far ahead of the puddle. This will cause a strung-out puddle that doesn’t flow at the toes.
Keep the arc at the leading edge of the puddle to get the best fusion and base metal penetration. Also, keep a tear-drop shaped puddle with proper travel speeds.
A welding process switch can also help. Pulsed MIG provides a 28% wider operating window compared to constant voltage MIG. This helps less skilled welders keep more consistent fusion.
|See how a wider operating window can reduce rework:
Q3: How can I reduce weld spatter and post-weld clean up?
A: The transfer mode plays a key role in how much spatter is produced. For example, if you’re welding very thin material or out of position, it may require a short-circuit transfer mode. However, this will produce much more spatter than other transfers. Short-circuit transfer can also limit puddle fluidity and result in lack of fusion or penetration on thicker materials. A switch to pulsed MIG will produce a flatter, more fluid bead and greatly reduce spatter levels. In addition, pulsed MIG is able to maintain a clean arc transfer regardless of the wire speed setting.
Excess spatter can also be caused by improper parameters and using the wrong shielding gas.
|See how pulsed MIG welding can reduce spatter: