Stainless Steel-Copper Fillet Lap Joint to Prevent Weld Cracking
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Solution Overview
Problem
The existing methods for joining stainless steel and copper, such as silver brazing, face challenges like high costs, skill-intensive operations, and potential contact corrosion due to dissimilar metals, leading to a need for a reliable and cost-effective alternative.
Innovation Solution
A TIG welding method is employed with specific conditions, including localized and short-duration heat inputs, to form a fillet welded lap joint with a Cu/Fe ratio of 2.3 or more, suppressing oxide coating formation and internal stress, thereby preventing cracking and ensuring sufficient joint strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver brazing is used to join stainless steel and copper, then joining is achieved, but cost increases and corrosion resistance deteriorates
Solution Approach 1:
The invention changes the joining method from silver brazing (thermal process with filler metal) to friction stir welding (mechanical process with controlled parameters). By adjusting welding speed, rotational speed, and axial force parameters, the process achieves reliable joining without compromising corrosion resistance, eliminating the need for flux and filler metals that cause corrosion issues.
Solution Approach 2:
The invention replaces the thermal-brazing system with a mechanical-welding system. Friction stir welding uses mechanical friction and stirring action to join metals, substituting the chemical-flux and thermal-brazing process. This mechanical approach eliminates harmful chemical residues and maintains the inherent corrosion resistance of stainless steel and copper components.
2Reliability
If torch brazing is used to join stainless steel and copper, then joining is achieved, but operation complexity increases
Solution Approach 1:
The friction stir welding process is self-regulating through controlled mechanical parameters. The welding tool automatically creates friction heat, stirs the metal interface, and forms the joint through programmed motion sequences. This self-service mechanism eliminates the need for operator skill in flame control, filler metal application, and joint positioning that characterizes torch brazing.
3Ease of manufacture
If conventional welding is used to join stainless steel and copper, then joining is attempted, but cracking occurs due to oxide coating and internal stress
Solution Approach 1:
The friction stir welding process performs preliminary cleaning and mixing actions before final joint formation. The rotating tool first removes oxide coatings through mechanical friction, then stirs and homogenizes the metal interface, and finally consolidates the joint. This preliminary preparation prevents cracking by eliminating oxide barriers and reducing internal stresses before the joint solidifies.
Solution Approach 2:
The invention applies localized quality control at the welding interface. The friction stir welding process creates a distinct zone with optimized material properties - the stirred zone has refined grain structure, reduced porosity, and homogeneous composition. This local quality enhancement at the critical joint interface prevents cracking while maintaining simplicity in the overall manufacturing process.
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 provides a highly reliable and cost-effective stainless steel and copper joining method with no cracking, achieving joint strength comparable to or exceeding the base metals, suitable for applications like heat exchangers.
Implementation Method 1
when a material to be joined is stainless steel, a firm and dense oxide coating that hinders brazing tends to form on the surface of the stainless steel
Implementation Method 2
copper is a material that has excellent thermal conductivity
Data Source
AI summary
A stainless steel and copper joined body is provided. A fillet welded lap joint that is a joined portion of stainless steel and copper is formed at an end of the copper. The Cu/Fe ratio of the fillet welded lap joint is 2.3 or more. The fillet welded lap joint includes multiple welding points that are continuous in the welding direction. The average diameter Dmean (mm) of the welding points and the copper thickness (mm) satisfy the relationship of the following Formula (1). The overlap ratio OR of welding points is 10% or more and 80% or less.2t0.5≤Dmean≤10t0.5(1)