Friction Stir Weld End Geometry for Leak-Resistant Battery Packs

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Solution Overview

Problem

Existing friction stir welding methods face challenges in achieving strong welding strength at the terminal end of the welding line, particularly in battery packs where water pressure can cause leakage due to weak welding.

Innovation Solution

A friction stir welding method that forms a closed space at the terminal end of the welding line by moving the welding tool in a circular manner around the target pulling-out position, ensuring the probe hole portion is positioned inside the closed space, thereby enhancing the welding strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the welding tool is pulled out at a terminal end of the welding line, then the welding process is completed, but a probe hole portion is formed and welding strength is weak

Engineering Contradiction:

Improvewelding process completionVSAvoidwelding strength at terminal end

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The method performs preliminary action by forming a closed space at the terminal end of the welding line before pulling out the welding tool. This closed space is created by moving the welding tool in a circular or arc-shaped path, which prepares the region to contain and support the probe hole portion, preventing water leakage and maintaining welding strength.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The welding terminal end is segmented into two distinct regions: a closed space region formed by circular/arc-shaped movement, and a probe hole portion formed when the tool is pulled out. This segmentation allows the closed space to provide structural support and sealing function, while the probe hole portion accommodates the tool extraction, thereby resolving the contradiction between completing the welding process and maintaining welding strength.

Inventive Principle:

Principle #1Segmentation

2Ease of operation

If a probe hole portion is formed at the welding end, then the welding tool can be pulled out, but water leakage occurs under water pressure

Engineering Contradiction:

Improvetool extractionVSAvoidsealing performance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The method applies beforehand cushioning by creating a closed space structure at the terminal end before the welding tool is pulled out. This closed space acts as a cushioning structure that supports the probe hole portion and prevents water from penetrating through the weak welding region, thereby maintaining sealing performance while allowing tool extraction.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The probe hole portion, which initially causes harm by creating a weak point for water leakage, is converted into a beneficial feature. By positioning the probe hole within a closed space formed by circular/arc-shaped movement, the hole becomes a controlled feature that does not compromise sealing, as the closed space structure prevents water penetration.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Device complexity

If the welding tool moves linearly, then the welding process is simple, but welding strength at the terminal end is weak

Engineering Contradiction:

Improvewelding path complexityVSAvoidwelding strength at terminal end

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The method applies spheroidality by replacing the linear welding path with a circular or arc-shaped path at the terminal end. This curved movement creates a closed space that provides structural support and enhances welding strength, while adding minimal complexity to the overall welding process.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 method effectively improves the welding strength at the terminal end of the welding line, preventing water leakage even under water pressure, and ensures a robust seal in battery packs.

Implementation Method 1

one metal member is softened by frictional heat and penetrated by pressing a welding tool against the one metal member while rotating

Methodology Applied

Scientific EffectFrictional heat: Friction

Implementation Method 2

Friction stir welding (FSW) is known as a method of welding metal members

Methodology Applied

Scientific EffectFriction welding: Friction Welding

Implementation Method 3

a plastically flowing material rapidly loses the frictional heat and is cooled and solidified

Methodology Applied

Scientific EffectRapid cooling and solidification: Freezing

Data Source

PatentUS20250140970A1Friction stir welding method and battery pack

Publication Date: 2025.05.01 HONDA MOTOR CO LTD

AI summary

A friction stir welding method welds at least two members to be welded by overlapping the members to be welded and moving a welding tool. The friction stir welding method has a step of forming a closed space at a terminal end of a welding line which is a movement track of the welding tool, and a step of moving the welding tool to inside the closed space and pulling out the welding tool from the members to be welded.