Molybdenum Brazed Joint Pulsing for Consistent Pin Strength
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Solution Overview
Problem
Conventional resistance brazing processes used in medical implant manufacturing often result in inconsistent bending or torsional strength of molybdenum (Mo) pin joints, failing to meet quality requirements due to variations in process parameters and material properties.
Innovation Solution
A method involving resistance brazing with controlled electrical pulses to form a brazed joint between a molybdenum component and a non-molybdenum component, where a first electrical pulse with constant voltage liquefies the non-Mo component to create a predetermined thickness of interface liquid layer, and additional pulses ensure joint formation around the Mo component, while surface preparation by removing the Mo oxide layer enhances joint strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resistance brazing processes are used to form Mo pin joints, then the joining process can be completed, but the bending or torsional strength of the joints becomes inconsistent and may not meet quality requirements
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional constant current resistance brazing to a controlled pulse electrical current process with constant voltage. This parameter change allows precise control of heating rate and liquid layer thickness, ensuring consistent joint strength that meets quality specifications while maintaining reliability across production batches.
Solution Approach 2:
The patent implements periodic action through the use of pulsed electrical current with specific pulse width and frequency parameters. This periodic heating approach enables controlled formation of the interface liquid layer, ensuring consistent brazing results and joint strength that conventional continuous heating cannot achieve.
2Temperature
If the electrical current is increased to ensure adequate heating and liquefaction of the non-Mo component, then the brazing process can proceed, but the contact area increases causing current density to decrease and heating becomes inconsistent
Solution Approach 1:
The patent applies feedback control by using constant voltage electrical pulses where the current automatically adjusts based on contact area changes. As the non-Mo component liquefies and contact area increases, the constant voltage ensures current density remains sufficient for consistent heating, while the pulse width is controlled to achieve the predetermined liquid layer thickness.
Solution Approach 2:
The patent implements dynamics by using time-varying pulsed electrical current rather than steady-state heating. The pulse width and amplitude are dynamically controlled to match the phase change requirements of the non-Mo component, ensuring consistent liquid layer formation regardless of contact area variations during the brazing process.
3Reliability
If the Mo oxide layer is removed through surface preparation to enhance joint strength, then the brazing quality improves, but the manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by removing the Mo oxide layer through surface preparation (such as sandblasting or chemical etching) before the resistance brazing process. This preliminary step ensures clean metal surfaces that promote strong, reliable joints, and the prepared surfaces can be stored until brazing, separating the surface preparation complexity from the actual joining operation.
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
The method consistently produces brazed joints with improved mechanical strength, reduced likelihood of failures, and compliance with quality standards for medical implants by maintaining current density and heat control during the brazing process, and surface preparation further enhances joint integrity.
Implementation Method 1
A first electrical pulse having a constant voltage is applied to the non-Mo component to liquefy the non-Mo component and to form an interface liquid layer at the contact point
Implementation Method 2
The process utilizes heat generated by passing a controlled electrical current through a component to weld the component to another component. The components can be forced against each other at an interface surface that the electrical current passes through. While the electrical heating occurs on all elements in the electrical loop, most of the heat is generated at the interface.
Data Source
AI summary
A method of forming a brazed joint is described. The method includes pressing a non-molybdenum component, such as a cross pin of a battery case assembly, against a molybdenum component, such as a terminal pin of the battery case assembly, and applying one or more electrical pulses to form an interface liquid layer between the components that cools to form the brazed joint. At least one of the electrical pulses has a constant voltage over a pulse time. A contact resistance between the components can decrease during the pulse time, and thus, the constant voltage can cause an uncontrolled electrical current of the electrical pulse to increase. The increasing electrical current heats the components sufficiently to form the interface liquid layer having a predetermined thickness that provides a required bend strength. Removal of surface oxides provide consistent mechanical strength for this joint. Other embodiments are also described and claimed.