Bi-material Die Inserts for High Temperature Metal Forming
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Solution Overview
Problem
Conventional high temperature forming dies made of materials with low thermal expansion coefficients, such as carbon/graphite, face issues with metal parts locking onto features due to differential shrinkage rates, leading to damage and reduced usability for complex shapes.
Innovation Solution
A bi-material die apparatus with die segments of low thermal expansion and inserts of higher thermal expansion metal, such as stainless steel, to ensure the inserts shrink more than the formed metal parts, preventing locking and allowing easy part removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional low CTE die materials (carbon/graphite) are used, then the die maintains dimensional stability during forming, but the metal part locks onto die features during cooling due to differential shrinkage
Solution Approach 1:
The die is segmented into two distinct material components: a base die structure made of low CTE material (carbon/graphite) and inserts made of high CTE material. This segmentation allows each component to perform its specific function - the base die provides overall dimensional stability while the inserts manage the shrinkage differential to prevent part locking.
Solution Approach 2:
Instead of making the entire die from high CTE material, the invention applies high CTE material locally through inserts positioned at specific features where part release is critical. This local quality approach ensures that only the necessary regions have the shrinkage characteristics needed to prevent locking, while the rest of the die maintains dimensional stability.
2Ease of operation
If high CTE insert materials are used, then the metal part releases easily from the die, but the insert material must be selected from a limited range of high CTE metals
Solution Approach 1:
The invention changes the thermal expansion parameter by selecting insert materials with CTE specifically higher than both the base die material and the workpiece metal. This parameter change ensures that during cooling, the insert shrinks more than both other components, creating clearance that facilitates easy part removal while maintaining compatibility with various metal workpieces.
3Ease of manufacture
If simple die shapes are formed, then the basic low CTE die technique works adequately, but complex shapes with indentations cause binding and locking of the part onto die features
Solution Approach 1:
The die structure is segmented by adding removable inserts to the basic low CTE die. This segmentation allows the die to handle complex shapes with indentations and projections that would otherwise cause locking, while the base die structure remains simple and easy to manufacture.
Solution Approach 2:
The high CTE insert acts as an intermediary between the low CTE base die and the metal workpiece. It mediates the thermal expansion differences and prevents direct binding between the workpiece and the base die features, enabling the formation of complex shapes without locking.
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 the formation of complex metal parts without damaging the die, as the inserts with higher thermal expansion shrink more than the sheet metal, preventing locking and ensuring easy part removal and die integrity.
Implementation Method 1
The sheet metal blank is heated in the die and expanded by blowing gas into the space between the sheets, so that the heat-softened sheets superplastically expand outward and conform to the interior surface of the die
Implementation Method 2
The sheet metal to be formed has a relatively high coefficient of thermal expansion (CTE). As the temperature is increased, the sheet metal will expand and take the form of the forming die. Upon completion of the forming, when the assembly is cooled, the sheet metal will shrink more than the die, due to the difference in CTE between the two materials
Data Source
AI summary
A bi-material die apparatus for high temperature forming of metal parts has at least two opposing die segments having inner surfaces together forming a hollow mold chamber for receiving a mold blank between the die segments. The die segments are of a first material having a first coefficient of thermal expansion CTE1. At least one insert of a second material is associated with the inner surface of at least one of the die segments so as to project into the mold chamber, the second material having a second coefficient of thermal expansion CTE2 higher than CTE1 and higher than the coefficient of thermal expansion of the metal product to be formed in the cavity.