Steel Sheet Surface Roughness for Cold Pressing Die Life
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Solution Overview
Problem
Existing high strength steel sheets used in automobile bodies face challenges in reducing die damage during cold pressing, leading to a shorter die life, which hinders the weight reduction and safety enhancement goals.
Innovation Solution
A steel sheet with increased surface roughness is developed by modifying the hot rolling and annealing processes, incorporating specific chemical compositions and microstructures, allowing for improved lubrication and reduced die damage, thereby extending die life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength steel sheet is used to increase strength and reduce weight, then the strength level is improved, but the surface pressure during cold pressing rises causing increased die damage and reduced die life
Solution Approach 1:
The invention applies local quality by creating specific surface roughness features (protrusions and recesses) only on the sheet surface while maintaining the bulk material's high strength properties. The surface roughness is controlled to have protrusions of 5-20 μm and recesses of 3-15 μm, providing localized lubrication areas without affecting the overall strength level of 1300 MPa or more.
Solution Approach 2:
The surface roughness structure acts as an intermediary between the high strength steel sheet and the die during cold pressing. The protrusions and recesses create a lubrication layer that mediates the contact between the sheet and die, reducing direct friction and die damage while allowing the high strength material to be formed.
2Manufacturing precision
If cold pressing is performed to form automobile parts, then the parts can be formed with high precision, but the surface pressure causes increased die damage and reduced die life
Solution Approach 1:
The invention creates local surface roughness features (protrusions of 5-20 μm and recesses of 3-15 μm) that provide lubrication specifically at the contact areas during forming, enabling high precision forming without causing excessive die damage from surface pressure.
Solution Approach 2:
The surface roughness is created during the hot rolling process before the final cold forming operation. This preliminary action prepares the sheet surface with lubrication features that will act during subsequent cold pressing, preventing die damage before the forming process begins.
3Duration of action of stationary object
If the steel sheet surface is made rougher to improve lubrication and reduce die damage, then die life is extended, but the manufacturing process becomes more complex
Solution Approach 1:
The invention merges the surface roughening operation with the existing hot rolling process. By controlling the hot rolling conditions (using lubricant, controlling reduction ratio of 30-70% at one stand before final stand), the surface roughness is created during standard manufacturing rather than requiring separate equipment or processes.
Solution Approach 2:
The invention changes specific parameters of the hot rolling process (applying lubricant, controlling rolling reduction ratio at specific stands, controlling temperature) to create the desired surface roughness. These parameter changes are implemented within existing manufacturing capabilities without requiring new equipment.
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
The solution effectively reduces die damage and increases die life by enhancing lubrication during cold pressing, enabling the production of high strength steel sheets suitable for lightweight and safe automobile bodies.
Implementation Method 1
hot rolling a steel slab having a chemical composition according to (1) or (2) to obtain a hot rolled steel sheet, wherein the hot rolling includes supplying a lubricant between a rolling mill and sheet while rolling the sheet
Implementation Method 2
annealing the hot rolled steel sheet without cold rolling or annealing it after cold rolling
Data Source
AI summary
Steel sheet able to reduce die damage at the time of cold pressing, that is, steel sheet having a predetermined chemical composition and steel microstructure which has on the sheet surface a plurality of step differences having height differences of more than 5.0 μm at intervals of 2.0 mm or less.