Multi-Sheet Metall Connection via Spot Welding and Soldering
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Solution Overview
Problem
Existing methods for producing three-sheet connections from dissimilar sheet metals, particularly in lightweight motor vehicle bodies, result in weld nuggets that do not adequately cover the thickness of softer steel sheets, leading to insufficient and fluctuating strength.
Innovation Solution
Combining spot welding with spot soldering for high-strength sheet metal parts and using spot soldering for softer parts, allowing for simultaneous fusion joints adapted to each material's strength, with a solder depot forming a local brazing layer between them, and employing a conventional spot welding machine with electrodes matched to the materials' strengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If spot welding is used to join high-strength sheet metal parts with a softer sheet metal part, then the weld nugget only melts the surface of the soft sheet, but the connection strength becomes insufficient and strongly fluctuating
Solution Approach 1:
A solder depot made of low-melting-point material is introduced as an intermediary between the high-strength sheet metal parts and the softer sheet metal part. During resistance welding, the solder depot melts first and creates a reliable soldered connection with the softer sheet, while the electrode continues to weld the high-strength parts together. This intermediary solves the problem of insufficient weld nugget penetration into the soft sheet while maintaining connection strength and reducing fluctuations.
Solution Approach 2:
The invention changes the thermal and melting parameters by introducing a material with significantly lower melting point than the sheet metals. The solder depot's melting point is chosen to be between the melting points of the high-strength and soft sheet metals, allowing selective melting and bonding. This parameter change enables the weld nugget to cover approximately 50% of the soft sheet thickness through the solder medium, achieving reliable connection strength.
2Manufacturing precision
If different connection methods are used for high-strength and soft sheet metal parts, then connection quality improves, but production complexity increases
Solution Approach 1:
The invention merges spot welding and spot soldering operations into a single resistance welding process. The solder depot is pre-applied to the softer sheet metal part before assembly, and during the resistance welding operation, both the welding of high-strength parts and the soldering to the soft part occur simultaneously. This eliminates the need for separate welding and soldering steps, reducing production complexity while maintaining high connection quality.
Solution Approach 2:
The solder depot is prepared and positioned on the softer sheet metal part in advance, before the resistance welding operation begins. This preliminary action ensures that when the welding current is applied, the solder is already in position to melt and bond with the soft sheet, enabling simultaneous welding and soldering in one step and simplifying the production process.
3Strength
If electrode pressure is increased to improve weld nugget coverage, then connection strength improves, but surface deformation of the soft sheet increases
Solution Approach 1:
The solder depot acts as a protective intermediary layer between the electrode and the softer sheet metal part. During resistance welding, the solder melts and creates a cushioning effect that distributes the electrode pressure more evenly. This allows sufficient pressure to be applied to achieve adequate weld nugget coverage (approximately 50% of sheet thickness) while the solder layer prevents excessive surface deformation and electrode impressions on the visible soft sheet surface.
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 method produces multi-layer connections with stable breaking loads and low production effort, using conventional equipment, effectively addressing the strength fluctuations in three-sheet connections by creating joints that cover 50% of the softer sheet's thickness and maintaining minimal surface deformation.
Implementation Method 1
under the heat generated in the process - and pressure effect is melted and connects the sheet metal parts to each other
Implementation Method 2
is melted and connects the sheet metal parts to each other as a thin, local brazing layer
Implementation Method 3
under the heat generated in the process
Data Source
Figure 1~3b
AI summary
In a multi-sheet connection between at least three sheet metal and, in particular, steel sheet metal parts (1, 2, 4), of which two directly superimposed sheet metal parts (1, 2) have a lower thermal conductivity than a third sheet metal part (4) resting on them, the sheet metal parts are, according to the invention, connected to each other in a manufacturingly simple and process-reliable manner with a high joining strength dependent on the sheet metal material, despite their different physical properties, such that they are welded together by means of spot-shaped resistance heating on the sheet metal parts (1, 2) of lower thermal conductivity and at the same time soldered together on the side of the sheet metal part (4) of higher thermal conductivity in the area of a previously applied solder deposit (9).