Hot Press Forming of Metal Sheet Without Quenching Hold Time
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Solution Overview
Problem
The hot press-forming method for manufacturing automobile components faces low productivity due to the need for prolonged holding times at the forming bottom dead center for quenching, resulting in inefficient forming tool operation and increased forming time, while indirect methods increase the number of processes, extending forming time.
Innovation Solution
A method where the metal sheet is heated, cooled to a predetermined temperature, and then subjected to press-forming, with the process ending at the martensite transformation start temperature or more, allowing for rapid cooling outside the forming tool, enhancing forming tool efficiency and productivity by using a mechanical or hydraulic press with high-speed forming capabilities and integrated cooling units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the metal sheet is heated and formed using the hot press-forming method to achieve high strength (1500 MPa), then the tensile strength is improved, but the forming time is prolonged due to the need for holding at the forming bottom dead center for quenching
Solution Approach 1:
The metal sheet is preliminarily cooled to 600°C or lower before the press-forming process begins. This preliminary cooling action allows the forming process to be completed quickly without requiring prolonged holding time for quenching, as the temperature condition for martensite transformation is already established before forming starts
Solution Approach 2:
Instead of the conventional sequence of heating → forming → quenching, the patent inverts the temperature control sequence by cooling the metal sheet to the martensite transformation temperature range before forming, then maintaining that temperature during forming. This inversion eliminates the need for post-forming quenching holding time while still achieving the desired microstructure and strength
2Manufacturing precision
If the forming process is performed with prolonged holding time for quenching to ensure proper cooling, then the microstructure control is improved, but the forming tool operation efficiency decreases
Solution Approach 1:
The cooling to 600°C or lower is performed preliminarily before forming, so the metal sheet is already in the optimal temperature range for martensite transformation when forming begins. This preliminary temperature preparation ensures proper microstructure control during the brief forming process without requiring prolonged holding time that would reduce tool efficiency
Solution Approach 2:
The patent skips the conventional prolonged quenching holding step by performing the essential cooling action before forming. The forming process itself is rushed through quickly at the predetermined temperature, achieving both microstructure control and high tool efficiency by eliminating unnecessary time delays
3Strength
If the metal sheet strength is improved to decrease automobile weight, then the fuel efficiency is improved, but the press-formability is degraded due to decreased elongation and Lankford value
Solution Approach 1:
The patent changes the temperature parameter of the metal sheet from ambient temperature to 600°C or lower (martensite transformation temperature range) before forming. This parameter change transforms the material properties, enabling high strength formation while maintaining press-formability through controlled phase transformation during the forming process
Solution Approach 2:
The patent utilizes the martensite phase transition by cooling the metal sheet to the martensite transformation start temperature or lower before forming. The phase transition occurs during or after forming, allowing the material to achieve high strength through martensitic transformation while maintaining formability during the forming operation itself
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 significantly improves productivity by reducing forming tool operation time, maintaining formability, and preventing breakages or cracks, while achieving the desired strength and reducing manufacturing costs.
Implementation Method 1
a metal sheet (blank) is heated to a predetermined temperature (for example, an austenite-phase temperature) so as to decrease the strength
Implementation Method 2
the punch and the die are respectively provided with passageways 1a and 2a through which a cooling medium (for example, water) may pass, and these members are cooled when the cooling medium passes through the passageways
Implementation Method 3
a metal sheet (blank) is heated to a predetermined temperature (for example, an austenite-phase temperature)... and is formed by a forming tool having a low temperature... thereby performing a shaping process and a supper-cooling heat treatment (quenching)
Data Source
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AI summary
Provided is a press-forming product manufacturing method of manufacturing a forming product having satisfactory formability for a drawing process by press-forming a metal sheet using a press-forming tool with high productivity, including: heating the metal sheet to a transformation temperature Ac1 or more; cooling the metal sheet to 600°C or lower; forming the metal sheet by a forming tool; ending the forming process at a martensite transformation start temperature Ms or more; taking out the metal sheet from the forming tool; and cooling the metal sheet.