Titanium Stretch Forming with Resistance Heating and Insulated Dies
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Solution Overview
Problem
Stretch forming titanium components is challenging due to their yield point being close to ultimate tensile strength, making traditional methods like bump forming and machining expensive and time-consuming.
Innovation Solution
A method and apparatus for stretch forming and creep forming titanium at elevated temperatures using a thermally-insulating enclosure and electrical resistance heating, with a ceramic die and moveable swing arms to control temperature and shape the workpiece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If titanium is stretch-formed at room temperature, then the process is simple, but the yield point is very close to ultimate tensile strength resulting in minimal percent elongation and forming difficulty
Solution Approach 1:
The patent applies parameter changes by heating the titanium workpiece to elevated temperatures (typically 500-900°C) before forming. This temperature increase fundamentally changes the material's mechanical properties, reducing the yield point relative to ultimate tensile strength and increasing percent elongation, thereby enabling successful stretch forming that would be impossible at room temperature.
2Ease of manufacture
If titanium components are bump formed and machined from large billets, then forming is possible, but the process is expensive and time-consuming
Solution Approach 1:
By changing the temperature parameter to elevated levels, the patent enables direct stretch forming of titanium components, replacing the multi-step bump forming and machining process with a single forming operation, thereby significantly improving productivity.
Solution Approach 2:
The patent extracts the machining step from the manufacturing process by enabling direct forming of near-net-shape components through hot stretch forming, eliminating the time-consuming machining operation that was previously necessary.
3Use of energy by moving object
If electrical current is passed through the workpiece for resistance heating, then heating is efficient, but the jaws and workpiece must be electrically connected
Solution Approach 1:
The patent uses electrically conductive jaws as an intermediary to transfer electrical current to the workpiece. The jaws serve dual functions: mechanically gripping the workpiece and electrically heating it through resistance heating, thereby simplifying the overall system by combining gripping and heating functions in a single component.
4Temperature
If the workpiece is heated to elevated temperatures for forming, then forming becomes feasible, but heat loss to the environment increases energy requirements
Solution Approach 1:
The patent employs an inert or controlled atmosphere environment during hot stretch forming to prevent oxidation of the titanium workpiece at elevated temperatures. This atmospheric control is essential for maintaining material integrity while enabling the temperature parameter change needed for successful forming.
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
Enables efficient and cost-effective formation of titanium components with reduced tooling costs and energy requirements, improving the repeatability and safety of the process.
Implementation Method 1
passing the electrical current to the workpiece through the jaws
Implementation Method 2
surrounding the die and a first portion of the workpiece with a thermally-insulating enclosure
Implementation Method 3
moving the swing arms to wrap the workpiece around the working face
Implementation Method 4
creep-forming of the workpiece by maintaining the workpiece formed against the working face and at a controlled temperature for a selected dwell time
Data Source
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AI summary
A stretch-forming apparatus includes a main frame which carries a die enclosure between jaw assemblies. An insulated die is mounted in the enclosure. A method of forming a component includes placing a workpiece in the enclosure, heating the workpiece to a working temperature using electrical resistance heating, and then stretching the workpiece against the die. The method is particularly useful for titanium workpieces.