Press-Hardened B-Pillar Weld Crack Prevention
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Solution Overview
Problem
Press-hardened sheet metal components in motor vehicle construction are prone to crack formation at welded joints under high mechanical loads, particularly during accidents, due to heat-induced structural changes causing strength and hardness variations around the weld area, leading to premature failure.
Innovation Solution
Creating a localized area of reduced strength and hardness around welded connections in press-hardened sheet metal components to mitigate the notch effect and prevent crack initiation, achieved by controlling the heat input during the welding process and using specific steel materials like 22MnB5 or 16MnB5, and designing the press-hardening tool to prevent structural transformation in critical areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If press-hardening is applied to increase strength and hardness of sheet metal components, then the strength and energy absorption capacity are improved, but crack formation occurs at welded joints under high mechanical loads
Solution Approach 1:
The patent applies local quality by creating a heat-affected zone with reduced strength and hardness around the welded joint area. This localized modification allows the material to better accommodate stress concentrations at the weld, preventing crack initiation while maintaining high strength in the non-welded areas of the component.
Solution Approach 2:
The patent utilizes parameter changes by controlling the heat input during welding to induce a specific thermal process that transforms the microstructure in the heat-affected zone. By adjusting welding parameters (heat input, duration), the material undergoes structural changes that reduce hardness and strength locally, creating a gradient that prevents stress concentration and crack formation.
2Ease of manufacture
If welding is performed on press-hardened components, then assembly is achieved, but heat input causes structural transformation and creates soft areas with lower strength and hardness
Solution Approach 1:
The patent converts the harmful effect of heat-induced softening into a beneficial feature. The heat-affected zone with reduced strength and hardness acts as a stress-relief area that prevents crack initiation. The welding process, which initially causes strength reduction, is leveraged to create a protective zone that enhances overall component reliability under dynamic loads.
3Strength
If high strength and hardness are maintained uniformly across the component, then structural integrity is improved, but stress peaks occur at welded joints leading to premature failure
Solution Approach 1:
The patent implements local quality by creating a non-uniform strength distribution across the component. The heat-affected zone surrounding the welded joint has deliberately reduced strength and hardness properties, creating a gradient that eliminates stress peaks at the weld interface while maintaining high strength in the load-bearing areas of the component.
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 solution effectively reduces stress peaks and prevents crack propagation, enhancing the resilience of press-hardened sheet metal components under dynamic loads and ensuring the structural integrity of motor vehicle body structures.
Implementation Method 1
During press hardening, the strength and/or hardness of a sheet material is increased by heat treatment and subsequent cooling in a forming tool
Implementation Method 2
the cause of the formation of cracks in the area of a welded joint is the heat input during the welding process. As a result of this heat input, in a heat-affected zone around the weld joint, there is at least partial conversion and/or reconversion of the structure
Data Source
Figure 1~2b
Figure 3~4
Figure 5~6
AI summary
The method for producing a composite part (10) for a motor vehicle, comprises producing a first press-hardenable sheet metal component (20), and joining the press-hardenable sheet metal component with a second component (30) by a weld connection (40). During producing the press-hardenable sheet metal component, lower strength or hardness is locally formed in an area (21) of the weld connection than in another area of the sheet metal component to avoid a crack initiation at the composite part in the area of the weld connection during mechanical loading. The method for producing a composite part (10) for a motor vehicle, comprises producing a first press-hardenable sheet metal component (20), and joining the press-hardenable sheet metal component with a second component (30) by a weld connection (40). During producing the press-hardenable sheet metal component, lower strength or hardness is locally formed in an area (21) of the weld connection than in another area of the sheet metal component to avoid a crack initiation at the composite part in the area of the weld connection during mechanical loading. The production of the sheet metal component comprises a partial step of a press hardening in a press hardening tool, where an increase in strength and/or hardness of the sheet metal material is suppressed in the area of the weld connection by process-technical and/or tool-technical measurements. The sheet metal component is distinctly slowly cooled in the area of the weld connection during press hardening than in another area of the sheet metal component to suppress a structural transition to a solid and/or hard structure in the another area of the sheet metal component. During press-hardening, the slow cooling step takes place in the press hardening tool by targetedly controlling the cooling in the area of the weld connection. The joining step takes place by a spot welding, where during producing the press-hardened sheet metal component, lower strength and/or hardness is locally formed in the area of the spot welding than in the another area of the press-hardened sheet metal component. Independent claims are included for: (1) a motor vehicle such as a passenger car; and (2) a body structure of a motor vehicle.