Ultrasonic Joining of Nitinol to Stainless Steel Without Heat Damage
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Solution Overview
Problem
Current medical instruments made of either non-shape-memory metals like stainless steel or shape-memory metals like Nitinol face limitations due to single material constraints, with existing joining methods failing to create high-strength, defect-free joints that preserve the mechanical and shape memory properties of shape-memory metals.
Innovation Solution
The method involves using ultrasonic additive manufacturing to join non-shape-memory metals with shape-memory metals, embedding the shape-memory metal portions within the non-shape-memory metal portions to form a strong, gapless joint, allowing for the retention of both materials' beneficial properties without degrading their properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional welding methods (fusion welding, laser welding, micro-resistance welding) are used to join shape-memory metals, then joining strength is improved, but the material properties are degraded due to heat damage and brittle intermetallic formation
Solution Approach 1:
The patent replaces thermal welding processes with ultrasonic welding, which uses mechanical vibration energy instead of heat to join metals. The ultrasonic vibrations create friction and plastic deformation at the interface, forming a metallurgical bond without significant heat input, thereby preserving the shape-memory properties of Nitinol while achieving strong joints.
Solution Approach 2:
The patent changes the fundamental parameter of the joining process from thermal energy input to mechanical vibration energy input. By using ultrasonic frequencies (typically 20-40 kHz) and controlling the amplitude and duration of vibration, the process achieves bonding through mechanical means rather than thermal means, avoiding the harmful effects of heat on shape-memory alloys.
2Ease of manufacture
If crimping is used to join actuators, then ease of manufacture is improved, but pull-out force is reduced and design freedom is limited
Solution Approach 1:
The patent replaces the crimping mechanical fastening system with ultrasonic welding, which creates a metallurgical bond. This substitution maintains manufacturing simplicity while dramatically improving the joint strength and pull-out force, as the ultrasonic weld creates a permanent metallurgical connection rather than relying on mechanical interlocking.
3Ease of manufacture
If stainless steel is used for the entire instrument including the tip, then ease of manufacture is improved, but shape retention and safety are reduced due to plastic deformation
Solution Approach 1:
The patent creates a composite structure by joining stainless steel (for the shaft) with Nitinol (for the tip). This composite construction allows each material to perform its optimal function: stainless steel provides structural support and ease of manufacture, while Nitinol provides shape retention and safety through its shape-memory properties, preventing permanent deformation at the critical tip area.
4Reliability
If Nitinol is used for the entire instrument including the shaft, then shape retention is improved, but ease of operation is reduced due to compliance
Solution Approach 1:
The patent creates a composite structure with stainless steel shaft and Nitinol tip, where the stainless steel shaft provides stiffness and controlability for easy manipulation by the operator, while the Nitinol tip maintains shape retention and safety. This composite design allows each material to optimize its functional contribution to the overall instrument performance.
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 enables the creation of medical instruments that combine the stiffness of stainless steel with the shape retention and high strain recovery of Nitinol, providing better control and maintaining the smart properties of shape-memory metals, while avoiding the brittleness and heat damage associated with traditional welding methods.
Implementation Method 1
joining at least a first layer of the non-shape-memory metal to the base portion using ultrasonic additive manufacturing
Data Source
AI summary
Various implementations include a method of manufacturing one or more devices. The method includes obtaining a base portion of a non-shape-memory metal, disposing one or more shape-memory metal portions along the base portion, and joining at least a first layer of the non-shape-memory metal to the base portion using ultrasonic additive manufacturing. The shape-memory metal portions are disposed along a first base surface of the base portion. The shape-memory metal portions have a first portion contacting the base portion and a second portion spaced apart from the first portion and extending from the base portion. The first layer is joined to the base portion using ultrasonic additive manufacturing and has a first layer surface that is joined to the first base surface. The first layer surface contacts the shape-memory metal portions when the first layer is joined to the base portion.