Spark Plug Noble Metal Tip Joining via Laser Welding
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Solution Overview
Problem
Conventional spark plugs with a noble metal tip and relieving layer tip joined by resistance welding face issues with joint strength and oxidation, leading to potential separation of the noble metal tip from the ground electrode due to thermal expansion differences and oxidation scale progression.
Innovation Solution
A spark plug design featuring a platinum alloy noble metal tip and relieving layer tip with a smaller area of contact, where the noble metal tip is joined to both the relieving layer tip and ground electrode using resistance and laser welding, respectively, to form a molten portion that covers the joint, reducing thermal stress and preventing oxygen penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a noble metal tip and ground electrode are directly joined by resistance welding, then manufacturing is simple, but joint strength is insufficient and cracks occur due to thermal expansion difference
Solution Approach 1:
The patent introduces a relieving layer tip as an intermediary component between the noble metal tip and ground electrode. This relieving layer tip has a linear expansion coefficient intermediate between the noble metal tip and ground electrode, serving as a thermal expansion mediator that reduces stress concentration at the joint interface and prevents crack formation while maintaining joint strength.
2Stability of the object's composition
If a relieving layer tip is added between noble metal tip and ground electrode, then thermal expansion stress is reduced, but joint strength between noble metal tip and relieving layer tip is insufficient due to resistance welding limitations
Solution Approach 1:
The patent replaces the conventional resistance welding method with laser welding for joining the noble metal tip to the relieving layer tip. Laser welding provides deeper penetration, higher joint strength, and better control over the welding process, overcoming the limitations of resistance welding while maintaining the thermal expansion stress relief function of the relieving layer tip.
3Ease of manufacture
If resistance welding is used to join noble metal tip and relieving layer tip, then manufacturing is straightforward, but oxidized scale progresses in joint portions due to minute cracks
Solution Approach 1:
The patent replaces resistance welding with laser welding to eliminate minute cracks in the joint portions. Laser welding creates a more complete fusion with fewer defects, preventing oxygen penetration and oxidized scale progression, while still maintaining manufacturing feasibility through automated laser welding processes.
4Stability of the object's composition
If the relieving layer tip has the same area as the noble metal tip, then stress distribution is uniform, but manufacturing precision requirements increase
Solution Approach 1:
The patent intentionally designs the relieving layer tip with an asymmetric area relationship to the noble metal tip, where the relieving layer tip has a larger area. This asymmetric design provides sufficient overlap area for strong laser welding while ensuring complete coverage of the noble metal tip, achieving both uniform stress distribution and relaxed manufacturing precision requirements.
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 design ensures secure joining of the noble metal tip to the ground electrode, prevents crack formation, and effectively inhibits the progression of oxidized scale, thereby preventing separation and improving the spark plug's durability and performance.
Implementation Method 1
a molten portion formed by melting at least the noble metal tip and the ground electrode by laser welding is provided on an entire outer circumference of a boundary portion between the ground electrode and the noble metal tip
Implementation Method 2
a plate-like relieving layer tip embedded in and joined to a front end portion of the ground electrode by resistance welding
Implementation Method 3
The relieving layer tip is made of a platinum alloy having a linear expansion coefficient between that of the platinum alloy constituting the noble metal tip and a metal material constituting the ground electrode
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
To firmly join a noble metal tip to a ground electrode, and by means of controlling a progress of oxidized scale in a joint portion, a separation of the noble metal tip from the ground electrode is prevented. A spark plug 1 is provided with a ground electrode 27, a noble metal tip 33 made of a Pt alloy, and a relieving layer tip 32 made of a Pt alloy which has a linear expansion coefficient between that of the ground electrode 27 and that of the noble metal tip 33. The relieving layer tip 32 is joined to the ground electrode 27 by resistance welding, while the noble metal tip 33 is joined to the ground electrode 27 and the relieving layer tip 32 by resistance welding. A portion of the relieving layer tip 32 to which the noble metal tip 33 is joined has a smaller area than that of one end of the noble metal tip 33. A molten portion 36 is formed in a boundary between the ground electrode 27 and the noble metal tip 33. The molten portion 36 is comprised of a Pt alloy constituting the noble metal tip 33 and a Ni alloy constituting the ground electrode 27 both of which are melted by laser welding.