Spot Welding Coated Metallic Substrates Through Native Oxide Layers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current welding methods struggle with the difficulty of joining metallic substrates coated with specific aluminum or zinc-based coatings due to the hardness and thickness of their native oxide layers, which are not effectively addressed by existing resistance spot welding techniques.
Innovation Solution
A spot welding method using an inverter direct current with a pulsation cycle and a welding cycle that applies different currents and forces, breaking the native oxide layer and allowing for a welding range equal or above 1 kA, and forming a nugget without the need for cooling between pulsation and welding steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional resistance spot welding methods are used on coated hardened parts, then the welding process is simple, but the welding is difficult to realize due to the hard and thick coating
Solution Approach 1:
The patent applies a pulsation welding process with multiple current pulses instead of continuous current. The process includes a first pulse to break the oxide layer, followed by subsequent pulses to form the weld nugget. This periodic action allows the welding current to penetrate through the hard and thick coating that would otherwise prevent welding, thereby improving weldability without compromising coating strength.
2Reliability
If the coating thickness is increased to improve corrosion resistance, then the protective function is improved, but the welding difficulty increases
Solution Approach 1:
The welding process is segmented into multiple distinct phases: a first pulse phase dedicated to breaking the oxide layer, and subsequent pulse phases dedicated to nugget formation. This segmentation allows each phase to be optimized independently - the first pulse uses higher current to penetrate the thick coating for corrosion protection, while subsequent pulses use controlled current to form the weld, thereby reconciling the conflict between coating thickness and weldability.
3Ease of manufacture
If a pulsation process with multiple current pulses is used, then the welding of coated parts is enabled, but the process complexity increases
Solution Approach 1:
The patent utilizes an inverter direct current power source that can dynamically change current parameters (amplitude, duration, frequency) between different pulses. The first pulse uses higher current amplitude to break the oxide layer, while subsequent pulses use adjusted parameters for nugget formation. This parameter changing capability enables the complex welding task to be achieved through controlled electrical parameter variation rather than mechanical or chemical process changes.
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 enables easy and effective welding of hardened steel parts with specific coatings by breaking the native oxide layer, improving weldability and reducing coating splashing, with a localized current flow that forms a strong nugget at the interface between the substrates.
Implementation Method 1
The welding electrodes (1, 1') and a spot welding power source (2) applying an inverter direct current... performing a pulsation having a pulsation current (Cp) applied through said at least two metallic substrates... and a welding step having a welding current (Cw)
Data Source
AI summary
A method is provided for the manufacture of an assembly of at least two metallic substrates spot welded together through at least one spot welded joint, such method including two steps, the assembly obtainable according to this method and the use of this assembly for the manufacture of automotive vehicle.