Galvanized Steel Spot Welds With Two-Stage Current Crack Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Resistance spot welding of galvanized steel sheets is prone to cracking due to liquid metal embrittlement, especially at the shoulder of the welded portion, and securing a stable nugget diameter is challenging, particularly when the thickness ratio of the surface layer steel sheet is large or disturbances occur.
Innovation Solution
A two-stage current process is employed, with controlled heat input in the first current process to minimize deformation and a subsequent current process with repeated cooling and current passing to enlarge the nugget, accompanied by a pressure hold process to suppress cracking and ensure a desired nugget diameter, while controlling the shoulder indentation ratio and nugget diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If resistance spot welding is applied to galvanized steel sheets, then joint strength is achieved, but cracking occurs due to liquid metal embrittlement
Solution Approach 1:
The welding current is divided into multiple stages (first current process and second current process) with different parameters. The first process uses higher current for a shorter duration to form the nugget, while the second process uses lower current for a longer duration to suppress cracking, thereby segmenting the welding process to simultaneously achieve joint strength and cracking resistance
Solution Approach 2:
The welding process employs periodic current application with distinct phases - an initial high-current phase followed by a lower-current phase. This periodic variation in current intensity allows the nugget to form and grow while controlling thermal cycles to prevent liquid metal embrittlement cracking
2Adaptability or versatility
If the thickness ratio of the surface layer steel sheet is large, then manufacturing flexibility is improved, but securing a stable nugget diameter becomes difficult
Solution Approach 1:
The welding process dynamically adjusts current parameters between two stages. The first current process uses higher intensity to rapidly form the nugget core, while the second current process applies lower intensity for an extended period to allow the nugget to grow to the desired diameter. This dynamic parameter adjustment compensates for variations in sheet thickness ratio, maintaining nugget diameter stability across different manufacturing conditions
3Manufacturing precision
If high current is applied to enlarge the nugget, then nugget diameter increases, but deformation and cracking increase
Solution Approach 1:
The welding current is applied periodically in two distinct phases: a first phase with high current to rapidly generate heat and form the nugget core, followed by a second phase with lower current that continues heating more gradually to enlarge the nugget diameter. This periodic current application allows the nugget to grow to the required size while the lower current in the second phase reduces thermal stress and deformation, preventing 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 ensures a stable nugget diameter, suitable for galvanized steel sheets, even with large thickness ratios or disturbances, maintaining joint integrity 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 to join the sheet combination 2.
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. An indentation ratio b/T of shoulders of the sheet combination satisfies at least one of the following Expressions (1) or (2).b/T≤0.6/(T/tU)0.5×(980/SU)0.5 (1)b/T≤0.6/(T/tL)0.5×(980/SL)0.5 (2)