Lap-Fillet Weld Toe Geometry for Fatigue Crack Prevention
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Solution Overview
Problem
Lap-fillet arc welding joints in automotive parts tend to generate fatigue cracks at the weld toe due to stress concentration, particularly at the start and termination portions of the weld bead, where existing techniques fail to adequately reduce stress concentration and improve fatigue strength without increasing welding costs or processes.
Innovation Solution
The lap-fillet arc welding joint design includes a projecting portion on one sheet that extends along the weld bead, with the weld toe located on a slope surface portion of this projection, reducing stress concentration and improving fatigue strength by increasing the flank angle and curvature radius of the weld toe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lap-fillet arc welding is performed on overlapped sheets, then the welding process is simple and cost-effective, but stress concentration occurs at the weld toe particularly at start and termination portions leading to fatigue cracks
Solution Approach 1:
A projecting portion is formed on one of the sheets before welding takes place. This projecting portion creates a slope surface that modifies the weld toe geometry, increasing the flank angle and curvature radius to reduce stress concentration and prevent fatigue crack initiation at the weld start and termination portions.
Solution Approach 2:
The projecting portion is specifically located at the start and termination portions of the weld bead where stress concentration is most severe. This localized modification creates different geometries at different locations along the weld, with the slope surface portion providing enhanced fatigue resistance where needed most while maintaining the simplicity of the overall welding process.
2Manufacturing precision
If existing techniques form a slope portion higher toward the root of weld, then welding can be performed, but the weld toe projects to the slope portion rather than following it, failing to reduce stress concentration effectively
Solution Approach 1:
The projecting portion with its slope surface is formed on the sheet before welding begins. This pre-formed geometry guides the weld metal to flow along the slope surface, ensuring the weld toe follows the slope and achieves proper positioning that reduces stress concentration, unlike techniques where the slope is formed after welding or where surface tension causes the weld toe to project outward.
3Ease of manufacture
If conventional fillet arc welding is performed on flat overlapped sheets, then the welding process is straightforward, but weld toes at start and termination portions are located in regions without stress-reducing geometry
Solution Approach 1:
The projecting portion is strategically positioned at the start and termination portions of the weld bead where stress concentration is most severe. This creates a localized geometry modification that increases the flank angle and curvature radius specifically where needed, while the middle portion of the weld maintains conventional geometry. This selective application strengthens the weld toe at critical locations without complicating the overall welding process.
Data Source
AI summary
A lap-fillet arc welding joint includes a weld bead, the weld bead being formed on an end portion of one sheet of overlapped two sheets and a surface of other sheet along the end portion. The other sheet includes a projecting portion projecting from the surface at a side of a weld toe of at least one of a start portion and a termination portion of the weld bead. The weld toe is located on a slope surface portion of the projecting portion at a side of the end portion of the one sheet.