Offset-Rotated Needle Peening for Weld Toe Fatigue Improvement
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Solution Overview
Problem
Existing needle-peening methods for weld toes of welded joints in automotive suspension parts often cause overlapping defects due to the mismatch in radius of curvature between the peening pin and the weld toe, leading to inadequate stress relief and fatigue improvement, especially when using pins with larger radii, which require expensive equipment and result in reduced fatigue properties.
Innovation Solution
A needle-peening method using a peening pin with a radius of curvature between 0.05 mm and 1.00 mm, where the pin is rotated about an offset axis while vibrating and moving along the welding direction, to relieve stress concentration and prevent overlapping defects by flattening the welding ripple at the weld toe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a peening pin with a large distal end radius (≥1.0 mm) is used to relieve stress concentration at the weld toe, then the compressive residual stress is increased, but overlapping defects are caused due to plastic flow of the material, leading to reduced fatigue properties
Solution Approach 1:
The invention changes the critical parameter of distal end radius from the conventional ≥1.0 mm to a smaller range of 0.05-1.00 mm. This parameter change allows the peening pin to effectively introduce compressive residual stress while avoiding the plastic flow that causes overlapping defects, thereby resolving the contradiction between stress relief and fatigue property preservation
Solution Approach 2:
The invention applies local quality by creating a specific geometric configuration where the distal end radius is precisely controlled within 0.05-1.00 mm to match the local curvature requirements of the weld toe. This localized geometric optimization ensures effective stress relief without causing material flow defects at the critical weld toe region
2Reliability
If a peening pin with a small distal end radius (<0.05 mm) is used to avoid overlapping defects, then the fatigue properties are improved by preventing defects, but the compressive residual stress introduced is insufficient
Solution Approach 1:
The invention identifies and optimizes the critical parameter range of 0.05-1.00 mm for distal end radius, which represents the optimal balance point where sufficient compressive residual stress is introduced while avoiding overlapping defects. This optimized parameter range resolves the contradiction by finding the precise threshold where both requirements are satisfied
3Stress or pressure
If the distal end radius of the peening pin is made equal to or larger than the radius of curvature of the weld toe, then stress concentration is relieved, but overlapping defects are caused due to plastic flow of the material
Solution Approach 1:
The invention changes the critical parameter relationship by specifying that the distal end radius should be equal to or larger than 0.05 mm but smaller than 1.00 mm, which is specifically designed to be smaller than typical weld toe radii. This parameter change allows effective stress concentration relief while preventing the plastic flow that causes overlapping defects
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 effectively prevents overlapping defects, improves fatigue properties, and reduces the need for large, expensive equipment, allowing for efficient stress relief and enhanced durability of welded joints.
Implementation Method 1
vibrating one or a plurality of the peening pins in a center axis direction
Implementation Method 2
peening the weld toe by a vibrating hammer tip or peening pin
Implementation Method 3
giving a compressive residual stress by plastic deformation
Implementation Method 4
rotating the one peening pin about a single rotation axis parallel to the center axis while the center axis of the one peening pin is offset from the rotation axis
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A needle-peening method according to the present invention is a needle-peening method of peening a weld toe 19 of a welded joint 11 for welding and joining two pieces of sheet metal 13 and 15 by using a peening pin 1. A radius of curvature of a cross section perpendicular to a welding direction at a distal end part 1a of the peening pin 1 is equal to or larger than 0.05 mm and smaller than 1.00 mm, and one or a plurality of the peening pins 1 are vibrated in a center axis direction, and the one peening pin 1 is rotated about one rotation axis parallel to the center axis while the center axis of the peening pin 1 is offset from the rotation axis, or the peening pins 1 are rotated about the rotation axis and moved along the welding direction to peen the weld toe 19.