Molybdenum Brazed Joint Formation With Constant-Voltage Pulses
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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, and additional pulses ensure a predetermined thickness of the interface liquid layer, while removing the Mo oxide layer enhances joint strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional resistance brazing processes are used to join Mo component and non-Mo component, then the joining process can be completed, but the bending or torsional strength of the joint 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 constant voltage resistance brazing. This parameter change in the electrical input controls the heat generation more effectively, ensuring consistent melting of the non-Mo component and formation of a uniform liquid layer. The constant voltage parameter maintains stable current density despite contact area variations, resulting in consistent joint strength that meets quality requirements.
Solution Approach 2:
The patent implements feedback control through the constant voltage mechanism that automatically adjusts current based on contact area changes. As the non-Mo component melts and contact area increases, the constant voltage system naturally reduces current density to maintain consistent heating. This self-regulating feedback ensures reliable and consistent joint strength without manual intervention.
2Ease of operation
If constant current is used in resistance brazing, then the process is simpler to control, but the current density varies as contact area changes causing inconsistent heating and liquefaction
Solution Approach 1:
The patent changes the controlling electrical parameter from constant current to constant voltage. This parameter change ensures that current density remains consistent despite variations in contact area during the brazing process. The constant voltage approach automatically compensates for contact area changes, producing consistent liquid layer thickness and reliable joint quality.
3Object-affected harmful factors
If Mo oxide layer is present on the Mo component surface, then the component is protected from oxidation, but the brazed joint strength is reduced and joint failures are more likely
Solution Approach 1:
The patent applies preliminary action by removing the Mo oxide layer before the resistance brazing process. Through surface preparation techniques such as mechanical polishing, chemical etching, or plasma treatment, the oxide layer is eliminated in advance. This preliminary removal ensures that when brazing occurs, clean Mo surfaces contact the liquid non-Mo material, creating strong metallurgical bonds and preventing joint failures.
4Area of stationary object
If the contact area between components increases during liquefaction, then more material can be joined, but the current density decreases causing inconsistent heating
Solution Approach 1:
The patent changes the electrical control parameter from constant current to constant voltage, which automatically compensates for contact area increases. As contact area grows during liquefaction, the constant voltage system naturally reduces current to maintain consistent current density. This ensures uniform heating rates and consistent temperature distribution regardless of contact area variations.
Solution Approach 2:
The constant voltage mechanism provides automatic feedback control where the system responds to contact area changes by adjusting current density. As the non-Mo component melts and contact area increases, the voltage-controlled system naturally reduces current flow to maintain consistent heating, ensuring reliable and consistent temperature distribution throughout the 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
The method consistently produces brazed joints with improved mechanical strength, reduced likelihood of failures, and adherence to quality standards by maintaining current density and controlling heat distribution, thus meeting the design requirements for medical implants.
Implementation Method 1
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.
Implementation Method 2
The localized heating causes the adjacent parent material, which begins in a solid state, to soften and liquefy. As the parent material liquefies, welding electrodes push the components together.
Implementation Method 3
The interface liquid layer is cooled to form a brazed joint between the non-Mo component and the Mo component. The interface liquid layer can have a predetermined thickness, and thus, the brazed joint can be strong and have a reduced likelihood of joint failures.
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.