Ceramic Friction Stir Welding Tool Geometry to Prevent Shoulder Chipping
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Solution Overview
Problem
Conventional friction stir welding tool members made of silicon nitride sintered bodies with high volumes of cBN, SiC, and TiN additives face challenges in sinterability and wear resistance, leading to insufficient performance and longevity due to the shape of the shoulder portion, which is prone to chipping during the welding process.
Innovation Solution
A friction stir welding tool member with a ceramic body featuring a shoulder and probe portion integrally formed with curved surfaces, a specific curvature ratio (R1/D) between 0.02 and 0.20, and an inclined surface from the shoulder to the probe, utilizing a silicon nitride sintered body with controlled additive components and surface roughness to enhance strength and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cBN, SiC, and TiN are added in a content as large as 20 vol% to improve wear resistance, then wear resistance is improved to a certain degree, but sinterability becomes difficult and dense sintered body cannot be obtained
Solution Approach 1:
The patent changes the chemical composition parameters by limiting sintering aid content to 15% by mass or less and specifying a particular combination of sintering aids (Y2O3, Al2O3, SiO2, SiC, TiO2, MgO, and/or AlN). This parameter optimization enables achieving both high wear resistance and good sinterability, resolving the contradiction between adding wear-resistant particles and maintaining sinterability.
2Ease of manufacture
If a rectangular cross-section shape is used for the shoulder portion, then manufacturing is simple, but the shoulder portion is chipped during welding and welding function is lost
Solution Approach 1:
The patent applies curvature to the shoulder portion by forming a curved surface between the probe portion and the end surface of the shoulder portion, with a curvature radius R1 satisfying 0.02 ≤ R1/D ≤ 0.20. This curved geometry eliminates stress concentration at sharp corners, preventing chipping during welding while maintaining manufacturing feasibility through standard ceramic forming and sintering processes.
3Reliability
If the curvature radius of the shoulder portion end is increased to prevent chipping, then durability is improved, but the shoulder portion becomes excessive in size and welding precision is affected
Solution Approach 1:
The patent optimizes the curvature radius parameter by defining the ratio R1/D (curvature radius to outer diameter) within the specific range of 0.02 to 0.20. This parameter control ensures the shoulder portion has sufficient curvature to prevent chipping and improve durability, while maintaining appropriate size proportions to preserve welding precision and avoid excessive dimensions.
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 tool member exhibits improved strength, reduced breakage, and enhanced durability, allowing for stable and efficient friction stir welding with increased longevity and reduced wear, even under high-temperature and high-speed conditions.
Implementation Method 1
pressing a welding tool member called a probe against the plural members while the welding tool member is being rotated at a high speed... softened by the frictional heat
Implementation Method 2
the periphery of the welding portion is subjected to plastic flow by the rotation torque of the probe... capable of withstanding the frictional heat
Data Source
Figure 1
Figure 2
AI summary
The friction stir welding tool member according to the present invention is characterized by comprising a ceramic member in which a shoulder part and a probe are integrally formed, wherein a base section of the probe part and the end of the shoulder part both have a curved surface shape, and when a curvature radius of the end of the shoulder part is defined as R1 (mm) and the outer diameter of the shoulder is defined as D (mm), R1/D is 0.02-0.20. In addition, the ceramic member is preferably made of a silicon nitride sintered compact having a Vickers hardness of at least 1400HV1. According to this configuration, the present invention is able to provide a friction stir welding tool member that has excellent durability.