Sensor Element Joining Structure for Stable Resistance Welding
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Solution Overview
Problem
The existing methods for joining lead wires and stranded wires in sensor elements, such as those used in temperature sensors, face challenges in achieving high and stable joining strength due to the sublimation of tin plating during resistance welding, which affects the electrical resistance and corrosion resistance of the core wires.
Innovation Solution
A joining structure is developed with a main joining region and sub-joining regions, where compacting is performed on the sub-joining regions to expose copper core wires and concentrate heat generation in the main joining region, promoting high joining strength by maintaining tin plating in this area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If resistance welding is performed to join lead wire and stranded wire, then joining strength is improved, but tin plating sublimates due to heat exceeding melting point
Solution Approach 1:
The joining structure is divided into multiple regions: a first region with tin plating for stable resistance welding, a second region (main joining region) for concentrated heat generation and welding, and a third region for additional support. This segmentation allows different regions to serve different functions, preventing tin plating loss while achieving high joining strength.
Solution Approach 2:
Different regions of the stranded wire are given different properties: the first region maintains tin plating for electrical resistance and welding stability, while the second region is designed as the main joining region with concentrated heat generation. This local differentiation solves the contradiction by protecting tin plating in areas where it's needed while concentrating welding heat where it's most effective.
2Reliability
If tin plating is applied to core wires for corrosion resistance, then corrosion resistance is improved, but electrical resistance increases making resistance welding difficult
Solution Approach 1:
The stranded wire is segmented into regions with different plating conditions. The first region retains tin plating for corrosion resistance, while the second region is designed as the main joining region where welding occurs. This segmentation allows tin plating to provide corrosion resistance where needed while concentrating welding activity in a controlled region.
Solution Approach 2:
The tin plating acts as an intermediary layer that provides both corrosion resistance and controlled electrical resistance. By concentrating the welding current and heat generation in the main joining region, the tin plating's higher electrical resistance becomes advantageous for generating the heat needed for welding while still protecting the core wires from corrosion.
3Ease of manufacture
If two-stage welding is performed to join lead wire and stranded wire, then joining process is simplified, but tin contributing to welding is lacked in second welding
Solution Approach 1:
The welding process is segmented into a first welding stage that joins the lead wire to the stranded wire in the first region with tin plating, and a second welding stage that concentrates heat in the main joining region (second region). This segmentation ensures tin plating is available for welding in both stages, with the second stage achieving concentrated heat generation for strong joining.
Solution Approach 2:
The first welding stage performs preliminary joining of the lead wire to the stranded wire, establishing initial contact and positioning. This preliminary action prepares the structure for the second welding stage, which then concentrates heat in the main joining region to achieve high joining strength. The preliminary welding ensures tin plating is positioned correctly for the subsequent concentrated heating.
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 stabilizes the joining strength of lead wires and stranded wires, achieving twice the joining strength of conventional methods without compacting, while preventing the lead wire from sinking between core wires, thus ensuring consistent joining quality.
Implementation Method 1
tin is higher in electrical resistance than copper configuring each of the core wires. Accordingly, when the lead wire and the stranded wire are joined through resistance welding, a tin-plated part mainly generates heat by Joule heat to achieve welding.
Implementation Method 2
tin configuring the plating is sublimated because tin has a low melting point of about 232°C and heat exceeding the melting point of tin is applied to tin configuring the plating.
Data Source
Figure 1A~1D
Figure 2A~2C
Figure 3A~3D
AI summary
A sensor element 10 according to the present invention includes: an element body (11) including, for example, a thermistor; paired lead wires (15 and 15) drawn out from the element body (11); and stranded wires (19) that are each obtained by twisting a plurality of core wires (21) and are joined to the respective paired lead wires (15 and 15) in a welding region. The welding region includes a main joining region (31) provided in a predetermined region in an axis direction, and sub-joining regions (33 and 35) adjacent to the main joining region (31), and joining strength of each of the lead wires (15) and the corresponding stranded wire (19) is higher in the main joining region (31) than in the sub-joining region (33).