Adaptive Drawn-Arc Fastener Welding Control
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Solution Overview
Problem
Drawn arc fastener welding faces challenges such as rapid cooling rates leading to brittle welds, excessive heat input causing instability, and issues with zinc coatings on workpieces, which result in poor weld quality and increased porosity, especially in underwater environments and when welding thicker materials or coated metals.
Innovation Solution
A process that dynamically senses arc voltage and calculates its derivative to control the position and motion of the fastener relative to the weld pool, allowing for cyclic redrawing of the arc and short circuiting with reduced current, thereby slowing the cooling rate and maintaining a stable welding process, even with lower power sources, and vaporizing zinc coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the main arc current and time are increased to slow down the cooling rate, then the cooling rate is reduced and more ductile microstructure is achieved, but process instability occurs resulting in excessive stud burn off, base metal melt through, and lateral expulsion
Solution Approach 1:
The patent implements periodic action by cycling between drawn arc and short circuit modes during the welding process. This allows the system to deliver heat in controlled intervals rather than continuously, enabling the cooling rate to be slowed down while maintaining process stability. The cyclic operation prevents excessive heat accumulation that would cause stud burn off and base metal melt through, while still achieving sufficient heat input for ductile microstructure formation.
Solution Approach 2:
The patent applies dynamics by making the welding process adaptive and variable rather than static. The system dynamically adjusts between different welding modes (drawn arc and short circuit) based on real-time conditions, allowing optimization of heat input throughout the welding cycle. This dynamic control enables precise management of the cooling rate without sacrificing process reliability.
2Reliability
If extreme lift or extreme arc length is used to avoid accumulated liquid bridging to the molten puddle, then arc extinction is avoided, but susceptibility to arc blow and uneven melting of the stud increases
Solution Approach 1:
The patent uses periodic action by implementing cyclic transitions between drawn arc and short circuit modes. During the short circuit phase, the fastener contacts the workpiece, allowing accumulated liquid to be safely discharged. This periodic discharge mechanism eliminates the need for extreme lift or arc length to prevent bridging, as the system proactively manages liquid accumulation through controlled short circuits. Consequently, arc stability is maintained without compromising melting uniformity.
3Productivity
If conventional drawn arc welding is performed quickly in less than 1 second, then productivity is high, but the cooling rate is very fast resulting in brittle microstructure and poor ductility
Solution Approach 1:
The patent resolves this contradiction by implementing periodic action with multiple cycles of drawn arc and short circuit modes. This cyclic approach extends the effective welding time beyond the conventional sub-1-second duration, allowing heat to be delivered more slowly to achieve ductile microstructure. The periodic operation maintains high productivity by efficiently utilizing each cycle to advance the welding process, while the extended total time enables controlled cooling rate for improved metallurgy.
4Reliability
If zinc coating is present on the workpiece or fastener, then corrosion resistance is improved, but weld quality deteriorates due to contamination and porosity
Solution Approach 1:
The patent addresses this contradiction through periodic action by implementing repeated cycles of drawn arc and short circuit modes. The drawn arc phase generates sufficient heat to vaporize zinc coating and other contaminants from the weld zone, while the subsequent short circuit phase allows these vaporized materials to be expelled. This cyclic process effectively removes zinc contamination that would otherwise cause weld porosity and quality issues, while preserving the corrosion resistance benefits of zinc coating on the non-welded portions of the components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a more ductile weld with improved mechanical properties, reduced porosity, and the ability to weld thicker materials and coated metals effectively, while reducing the risk of arc blow and uneven melting, and allows for longer welding times with lower current inputs.
Implementation Method 1
drawing a pilot arc plasma. Next, the arc current is increased to a higher main arc current melting the weld end of the fastener and the work piece
Implementation Method 2
plunging of the fastener into the work piece forming a weld
Data Source
AI summary
In one aspect, there is disclosed a drawn arc fastener welding process that includes the steps of providing a fastener positioned in a welding tool, providing a weld control, providing a work piece, contacting the fastener against the work piece, energizing a pilot current, lifting the fastener from the work piece and drawing a pilot arc, energizing a main arc for a predetermined duration, short circuiting the fastener relative to the work piece, cyclically redrawing an arc and short circuiting the fastener relative to the work piece at least one additional cycle, dynamically sensing an arc voltage and calculating a derivative signal of the voltage over time for each drawn arc and short circuit of the cycle wherein a position and motion of the fastener relative to the work piece is controlled and the energizing of the arc is controlled, and plunging the fastener into the work piece forming a weld.