Projection-Welded Nut Joints With Cancellation Stress Against Delayed Fracture
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Solution Overview
Problem
Delayed fracture in welded portions resulting from projection welding due to residual stress is a persistent issue, especially when using standard welding nuts without special shapes, as it can lead to structural failures.
Innovation Solution
Applying a cancellation stress to the welded member after projection welding by directly loading the welding nut or workpiece to counteract the stress generated during cooling, thereby reducing the residual stress that causes delayed fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If projection welding is performed to join workpiece and welding nut, then welding strength is improved, but residual stress causes delayed fracture
Solution Approach 1:
The patent applies preliminary anti-action by generating a cancellation stress in the opposite direction to the residual stress before delayed fracture can occur. The stress generating device applies a load to create compressive stress that counteracts the tensile residual stress from welding, preventing delayed fracture initiation
Solution Approach 2:
The patent changes the stress state parameter by transitioning from a purely tensile residual stress state to a combined stress state where compressive cancellation stress offsets the tensile component. This parameter change reduces the net tensile stress that would otherwise cause delayed fracture
2Reliability
If welding nut with depressions is used to reduce residual stress, then delayed fracture resistance is improved, but manufacturing complexity increases
Solution Approach 1:
Instead of modifying the welding nut geometry (which would require creating depressions), the patent copies the stress-reducing effect by applying an external cancellation stress that mimics the desired stress state, achieving the same protective effect without geometric modification
Solution Approach 2:
The patent replaces the mechanical geometry modification approach (creating depressions in the welding nut) with a mechanical stress application approach (applying cancellation stress through a stress generating device), substituting one mechanical solution with another that is easier to manufacture
3Reliability
If cancellation stress is applied after projection welding, then delayed fracture resistance is improved, but additional processing time is required
Solution Approach 1:
The patent applies preliminary action by implementing the cancellation stress application as an integrated step within the welding process flow. The stress generating device operates immediately after welding while the workpiece is still in the fixture, utilizing the existing setup rather than requiring separate post-processing time
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 method effectively reduces the occurrence of delayed fracture in welded portions without the need to consider complex heat quantity requirements, as the cancellation stress is applied post-welding, ensuring the stability of the welded structure.
Implementation Method 1
The projections are melted by electric current applied by the projection welding to form the welded portion between the workpiece and the welding nut
Implementation Method 2
a stress is generated due to cooling after the welding. Due to the stress that remains, delayed fracture may tend to occur in the welded portion
Data Source
AI summary
Disclosed is a method for manufacturing a welded member in which a workpiece made of a high tensile material and a welding object are welded. The method includes welding the workpiece and the welding object such that welded portions are formed between the workpiece and the welding object by performing projection welding. The method also includes applying a cancellation stress to the welded member after the projection welding, so that a stress that is generated in the welded portions after the projection welding and acts in a direction to pull the welded portions close to each other is canceled.