Resistance Spot Welding of Galvanized Sheets With Crack-Safe Nugget Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Resistance spot welding of galvanized steel sheets is prone to cracking, particularly at the shoulder of the welded portion, due to liquid metal embrittlement, and securing a stable nugget diameter is challenging, especially when the thickness ratio of the surface layer steel sheet is large or disturbances occur.
Innovation Solution
Control the shoulder angles of the steel sheets and divide the current passing process into two stages to form an intermediate nugget, minimizing deformation and cracking, while ensuring a desired nugget diameter through controlled heat input and current patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If resistance spot welding is applied to galvanized steel sheets, then joining of overlapped steel sheets is achieved, but cracking occurs in the welded portion due to liquid metal embrittlement
Solution Approach 1:
The welding process is divided into multiple stages with different current values. The first stage uses a higher current value to quickly form a nugget, while the second stage uses a lower current value to complete the welding without excessive heat input. This segmentation of the welding process prevents liquid metal embrittlement cracking while ensuring adequate joint strength.
Solution Approach 2:
The welding current is applied in a periodic manner with distinct phases - an initial high-current phase followed by a lower-current phase. This periodic application of current allows the welding process to achieve nugget formation while controlling heat input to prevent cracking in galvanized steel sheets.
2Length of stationary object
If the thickness ratio of the surface layer steel sheet is large, then joining of thick steel sheets is achieved, but securing a stable nugget diameter becomes challenging
Solution Approach 1:
The welding current value is dynamically adjusted during the welding process. The current starts at a higher value to penetrate through thick steel sheets and form a nugget, then transitions to a lower value to complete the welding. This dynamic current adjustment ensures stable nugget diameter even when joining steel sheets with large thickness ratios.
3Strength
If high current value is applied to form a large nugget, then nugget diameter is increased, but deformation and cracking at the shoulder increase
Solution Approach 1:
The welding process applies current in two stages: the first stage applies a higher current value that would normally cause excessive heat input, but this is immediately followed by the second stage with lower current. The combination achieves adequate nugget formation while the controlled transition prevents excessive shoulder deformation and cracking.
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
The method effectively suppresses cracking and maintains a stable nugget diameter, suitable for galvanized steel sheets, even with large thickness ratios or disturbances, enhancing joint strength and corrosion resistance.
Implementation Method 1
Pressure is applied from the welding electrodes 3, 4 from above and below while a welding current is passed between the welding electrodes 3, 4 to join the sheet combination 2. In this welding method, a point-like welded portion is obtained by using resistance heat generated by the welding current.
Implementation Method 2
Pressure is applied from the welding electrodes 3, 4 from above and below while a welding current is passed between the welding electrodes 3, 4
Data Source
AI summary
Provided is a welded joint for which cracking of the welded portion is suppressed and nugget diameter is a desired size, even when at least one of the surface layer steel sheets of a sheet combination is a galvanized steel sheet and the thickness ratio of a surface layer steel sheet is large or a disturbance has a large effect. At least one of Expressions (1) or (2) is satisfied for a shoulder angle a of the first steel sheet of the sheet combination and a shoulder angle b of the nth steel sheet of the sheet combination.