Deep-Drawing Sheet Blank Slits for Uniform Resistance Heating
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Solution Overview
Problem
Existing methods for heating steel sheet blanks for deep-drawing operations face challenges such as long heating times and inhomogeneous temperature fields due to non-uniform current density during electric resistance heating, leading to overheating in some areas and insufficient heating in others.
Innovation Solution
The modification of deep-drawing sheet blanks involves creating slits in the edges transverse to the electric current flow, oriented towards the forming zone, which act as cooling fins to reduce current intensity in overheated areas and increase heat generation in insufficient areas, resulting in a more uniform temperature field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If continuous furnaces or multi-chamber furnaces are used for heating, then the steel blank can be heated to the required temperature, but the heating time is relatively long and the conversion efficiency of electrical energy to heat input is low
Solution Approach 1:
The patent replaces the mechanical/thermal system of continuous furnaces with an electric resistance heating system. Electrical current is directly passed through the steel blank to generate heat internally via Joule heating, eliminating the need for external furnace heating. This substitution dramatically reduces heating time from minutes to seconds while significantly improving energy conversion efficiency, as electrical energy is directly converted to thermal energy within the workpiece itself.
Solution Approach 2:
The patent employs periodic or pulsed electric current application to the steel blank. By controlling the timing and duration of current pulses, the heating process can be precisely managed to achieve the required forming temperature rapidly. This periodic action allows for controlled heat generation that can be optimized for both speed and energy efficiency, further reducing heating time compared to continuous furnace operation.
2Loss of time
If electric resistance heating is used with current passing through the blank, then heating time is reduced, but the temperature field in the sheet blanks becomes inhomogeneous due to non-uniform current density
Solution Approach 1:
The patent introduces longitudinal slits that divide the steel blank into multiple segments or zones. These slits create separate current paths, forcing the electrical current to distribute more uniformly across the blank's width. By segmenting the structure, the current density becomes more evenly distributed, preventing concentration at edges and longitudinal portions, thereby achieving a more homogeneous temperature field during electric resistance heating.
Solution Approach 2:
The patent applies local modifications by creating slits at specific locations (longitudinally oriented in the blank) to address local current density issues. The slits are strategically positioned to redirect current flow in regions where non-uniform heating occurs, ensuring that each local zone receives appropriate current density. This local quality modification enables uniform temperature distribution across the entire blank while maintaining the rapid heating advantage of electric resistance heating.
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 reduces heating time, enhances the efficiency of electrical energy conversion to thermal energy, and ensures a uniform temperature field, allowing for improved formability and targeted temperature control during hot deep-drawing processes.
Implementation Method 1
A steel sheet blank can also be austenitized using electric resistance heating, where the blank is held between jaws with electric current passing through them. Conduction losses cause the blank to heat up to the temperature required for the process.
Implementation Method 2
In those locations of the sheet blank where overheating occurs, slits may be made in and perpendicularly to the edge, which modify the current density field by substantially reducing the current intensity between the slits. Thus, the slits may become cooling fins, which conduct excess heat away from potentially-overheated locations.
Data Source
AI summary
The present invention generally relates to the modification of a deep-drawing sheet blank (P) for electric resistance heating. Generally, the modified sheet blank comprises slits (Z) being made in the edges of the blank (P) transversely to the electric current flow and oriented towards the perimeter of the forming zone (T). The distances between the ends of the slits (Z) and the forming zone (T) perimeter may be equal. The ends of the slits (Z) oriented towards the forming zone perimeter (T) may also be rounded.