Two-Pass Arc Spot Welding High Strength Steel
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Solution Overview
Problem
High strength steel sheets with carbon content above 0.3% by mass or greater pose challenges in achieving high cross tensile strength and tensile shear strength during arc spot welding due to weld metal sag and difficulty in forming specific reinforcement portions, leading to reduced joint strength.
Innovation Solution
Implementing a two-pass welding process where the first pass forms a reinforcement portion on the back face of one steel sheet and the second pass forms a reinforcement portion on the front face of the other, with specific heat input control to achieve the desired bead diameter and reinforcement height, thereby stabilizing the weld joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength steel sheets with tensile strength of 980 MPa or greater are arc spot welded, then the joint strength should be high, but the cross tensile strength reduces due to weld metal sag and inability to form proper reinforcement portions
Solution Approach 1:
The welding process is divided into two separate passes: a first pass that forms a reinforcement portion on the back face, and a second pass that forms a reinforcement portion on the front face. This segmentation allows each pass to be optimized independently, preventing weld metal sag in the first pass and ensuring proper reinforcement formation in the second pass, thereby achieving high cross tensile strength for high strength steel sheets.
Solution Approach 2:
The first welding pass performs a preliminary action by forming a reinforcement portion on the back face before the second pass. This preliminary reinforcement structure prevents weld metal sag during the subsequent second pass and provides a stable foundation for forming the front face reinforcement portion, enabling proper joint formation in high strength steel sheets.
2Strength
If high pressure is applied during spot welding to improve joint strength, then the tensile shear strength increases, but the steel sheet thickness reduces and stress concentration increases, reducing cross tensile strength
Solution Approach 1:
The welding process is divided into two separate passes: a first pass that forms a reinforcement portion on the back face, and a second pass that forms a reinforcement portion on the front face. This segmentation allows each pass to be optimized independently, preventing weld metal sag in the first pass and ensuring proper reinforcement formation in the second pass, thereby achieving high cross tensile strength for high strength steel sheets.
Solution Approach 2:
The invention changes the welding parameters by specifying different heat input ranges for the first and second passes. The first pass uses a heat input of 1.0 to 3.0 kJ to form the back face reinforcement, while the second pass uses a heat input of 0.5 to 2.0 kJ to form the front face reinforcement. This parameter optimization prevents excessive melting and thickness reduction while ensuring proper reinforcement formation, maintaining both tensile shear strength and cross tensile strength.
3Ease of manufacture
If single pass arc spot welding is used to simplify the process, then the manufacturing complexity is reduced, but the reinforcement portions cannot be properly formed on both faces, reducing joint strength
Solution Approach 1:
The welding process is divided into two separate passes: a first pass that forms a reinforcement portion on the back face, and a second pass that forms a reinforcement portion on the front face. This segmentation allows each pass to be optimized independently, preventing weld metal sag in the first pass and ensuring proper reinforcement formation in the second pass, thereby achieving high cross tensile strength for high strength steel sheets.
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 ensures high cross tensile strength and tensile shear strength while preventing burn-through and excessive deformation, enabling the use of high strength steel sheets in automotive applications with improved collision safety and reduced vehicle weight.
Implementation Method 1
employing the electric arc as the heating and fusing medium
Implementation Method 2
resistance welding
Data Source
Figure 1A~1D
Figure 2
Figure 3
AI summary
In an arc spot welded joint manufacturing method in which two steel sheets configured by high strength steel having a component carbon content of 0.07% by mass or greater are overlapped, and the steel sheets are lap welded together in a spot pattern by gas metal arc welding, with at least one of the overlapped steel sheets having a component carbon content of 0.3% by mass or greater. The arc spot welded joint manufacturing method includes a first welding pass in which a second steel sheet 12 on the lower side is melted up to a back face 12b side, and first weld metal 31 is formed including a first reinforcement portion 41 protruding out on the back face 12b side, and a second welding pass in which a second weld metal 32 including a second reinforcement portion 42 protruding out from a front face of the first steel sheet is formed over the first weld metal 31, such that a reinforcement height h of the heights h1, h2 of the first reinforcement portion 41 and the second reinforcement portion 42 is formed at t/5 or greater with respect to the sheet thickness t of the steel sheets, and the average weld bead diameter is formed at from 3t to 10t.