The research component of this proposal is to determine which quality related problems can and cannot be detected with process controls as compared to after-the-fact NDE. For example, the loss of shielding gas is readily detected with an imbalance in the voltage/amperage output characteristics that are part of modern welding power sources. Some forms of cracking are related to inadequate preheat, and the preheat sensors should enable detection of these problems. However, it is not currently known whether all bridge-quality concerns can be detected with process sensors.
This proposal involves the integration of the pre-weld sensor output, during welding output, post welding quality surface measurements and NDE results in a way that will enable better quality welds on a first pass basis, eliminating the creation of welds that require repair. For example:
1) Sensors that detect pre-welding conditions such as joint fit-up and profile, and preheat measurement can create “no-go” conditions that preclude welding until the conditions are corrected.
2) Sensors that measure arc instability can be used to shut down welding operations until corrected.
3) Sensors that detect weld surface profiles a foot or two behind a completed weld can stop welding operations if the output characteristics are non-conforming. For long welds, such as web-to-flange fillet welds, production can be stopped instead of the continued creation of less than ideal welds.
4) Linkage of NDE results to the production conditions (pre-weld, during weld and post welding sensor outputs) can help identify the conditions under which weld discontinuities are created, enabling adjustments to the acceptable pre-weld and during welding outputs.
5) The welding process controls described above can be used to identify portions of welds that are most likely to contain weld discontinuities, and therefore constitute the best use of our NDE resources. The output of sensor has the potential of “pointing fingers” to suspect welds.
6) As data is collected, it is probable that the need for new sensors will be identified that would further reduce the need for after-the-fact NDE.
7) Closed loop system could be developed to adjust welding output real time so as to eliminate conditions that result in weld flaws. Currently, seam tracking and joint volume measurement tool are being used to adjust robotic welding conditions to eliminate underfill and incomplete fusion problems.