Spark Plug Ground Electrode Welding Strength via Hardness Control
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Solution Overview
Problem
Spark plugs for internal combustion engines face challenges in achieving sufficient welding strength between the ground electrode and the metal shell due to high hardness regions caused by thermal residual stress, leading to potential breakage or damage during use.
Innovation Solution
Forming a high hardness region in the metal shell with a Vickers hardness of 3×10^2 to 5×10^2 Hv and a length of 0.3 to 0.8 mm, containing an acicular martensite structure, and using a specific electrode material with a specific resistance range to ensure strong electrical resistance welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ground electrode is made of high Ni content alloy to improve spark wear resistance, then spark wear resistance is improved, but welding difficulty increases and welding strength decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the ground electrode material (Ni: 93-98 mass%, Cu: 0.5-5 mass%, Mn: 0.01-1 mass%, C: 0.01-0.5 mass%, Cr: 0.01-1 mass%, Si: 0.01-0.5 mass%, Al: 0.01-0.5 mass%, and impurities: 0.01-1 mass%) to achieve optimal balance between spark wear resistance and weldability. This compositional parameter optimization allows the high Ni content alloy to maintain both reliability in spark wear resistance and sufficient welding strength.
2Strength
If a large electric current is supplied during resistance welding to improve welding strength, then welding strength is improved, but thermal residual stress increases causing breakage
Solution Approach 1:
The patent applies parameter changes by optimizing the composition parameters of the ground electrode material to improve electrical conductivity and heat distribution characteristics. The controlled addition of Cu (0.5-5 mass%) enhances electrical conductivity, allowing for more efficient current distribution during welding. This reduces the need for excessively high current densities that would generate excessive thermal residual stress, thereby preventing breakage while maintaining welding strength.
Solution Approach 2:
The patent applies local quality by creating a specific compositional gradient and microstructure distribution in the ground electrode. The controlled presence of Mn, C, Cr, Si, and Al creates localized phases that improve both weldability and mechanical properties. This local compositional optimization ensures that the welding zone has appropriate properties for strong bonding while the overall structure maintains resistance to thermal stress-induced breakage.
3Ease of operation
If the ground electrode is bent before welding to improve bending workability, then bending workability is improved, but welding strength decreases due to separation at welding interface
Solution Approach 1:
The patent applies parameter changes by optimizing the compositional parameters of the ground electrode material to achieve appropriate hardness and ductility balance. The controlled addition of Mn (0.01-1 mass%), C (0.01-0.5 mass%), and other alloying elements creates a microstructure that provides sufficient bending workability for adjustment operations while maintaining high welding strength. This eliminates the need to bend the electrode before welding, as the material can be directly welded in its original state.
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 approach securely joins the ground electrode to the metal shell with high welding strength, reducing the risk of breakage and maintaining joint integrity under high-temperature conditions.
Implementation Method 1
a high hardness region is formed with a Vickers hardness of 3×10^2 to 5×10^2 Hv in the metal shell, and the high hardness region contains an acicular martensite structure
Implementation Method 2
the ground electrode is joined to an end portion of the metal shell by resistance welding
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4~5
AI summary
It is an object of the present invention to provide a spark plug (1) having a ground electrode (6) joined securely by electric resistance welding. The spark plug (1) includes a cylindrical metal shell (4) and a ground electrode (6) joined by electric resistance welding to an end portion of the metal shell (4). The metal shell (4) has a high hardness region (42) formed with a Vickers hardness of 3×102 to 5×102 Hv in the end portion thereof in such a manner that the high hardness region (42), when viewed in cross section along a plane including an axis of the spark plug (1) and an axis of the ground electrode (6), has a length d of 0.3 to 0.8 mm from a ground electrode (6) side welding boundary to a metal shell (4) side welding boundary in a direction of load applied during the electric resistance welding.