Metal Sheet Crystal Texture for Roughness-Resistant Deep Drawing
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Solution Overview
Problem
Conventional methods for molding metal sheets into complex shapes with deep drawing or overhang molding often result in abnormal surface roughness due to protrusions and recesses, limiting the sheet thickness decrease rate to less than 10% to avoid surface roughness issues, which restricts the production of more intricate automobile exterior sheet products.
Innovation Solution
A metal sheet with a bcc or fcc structure is treated to have specific crystal grain orientations and sizes, and subjected to plane strain tensile and biaxial tensile deformations, achieving a sheet thickness decrease rate of 10% to 30% while inhibiting surface roughness through controlled crystal texture and chemical composition, including ferrite-based steel sheets with precise chemical compositions and processing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If molding is conducted at a large machining amount (sheet thickness decrease rate of 10% or more) to achieve complicated shapes, then the shape complexity is improved, but protrusions and recesses are formed on the surface resulting in abnormal surface roughness
Solution Approach 1:
The patent changes the crystallographic parameters of the metal sheet by controlling the area fraction of crystal grains with specific orientations (15° or less relative to (001) plane) to be within 0.20 to 0.35, and controlling the average crystal grain size to be 15 μm or less. This parameter change in crystal texture allows the material to accommodate large deformations (sheet thickness decrease rate of 10% or more) without forming protrusions and recesses on the surface.
Solution Approach 2:
The patent applies preliminary action by pre-treating the metal sheet through controlled rolling and annealing processes to achieve the desired crystal grain structure before molding. The metal sheet is prepared in advance with specific crystal orientation distribution and grain size control, so that when large deformation molding is subsequently applied, the surface remains smooth without abnormal roughness.
2Manufacturing precision
If the sheet thickness decrease rate is limited to less than 10% to avoid surface roughness, then the surface finish is improved, but the ability to produce intricate designs is restricted
Solution Approach 1:
The patent fundamentally changes the material parameters by establishing specific ranges for crystal grain orientation (area fraction of 0.20 to 0.35 for grains within 15° of (001) plane) and average crystal grain size (15 μm or less). This parameter optimization enables the metal sheet to achieve both excellent surface finish and high adaptability for intricate designs with sheet thickness decrease rates of 10% or more.
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 method effectively inhibits surface roughness in molded products with complex shapes, allowing for a broader range of intricate designs in automobile exterior sheet products by maintaining a smooth surface finish even at higher sheet thickness decrease rates.
Implementation Method 1
molding the metal sheet to cause plane strain tensile deformation and biaxial tensile deformation and allowing at least a part of the metal sheet to have a sheet thickness decrease rate of from 10% to 30%
Data Source
AI summary
Provided are a metal sheet, a method of producing a metal sheet, a method of producing a molded product of a metal sheet, and a molded product of a metal sheet, in which occurrence of surface roughness is inhibited. Provided are a metal sheet satisfying conditions (a1), (b1) or (c1) at the surface and a method for producing the metal sheet. Also provided are a method for producing a molded product of a metal sheet using the metal sheet, and a molded product of the metal sheet. (a1) The area fraction of crystal grains having a crystal orientation divergent by 20° or more from a (111) plane and by 20° or more from a (001) plane is from 0.25 to 0.35, and the average crystal grain size is less than 16 μm. (b1) The area fraction of crystal grains having a crystal orientation divergent by 20° or more from a (111) plane and by 20° or more from a (001) plane is from 0.15 to 0.30, and the average crystal grain size is 16 μm or more. (c1) The area fraction of crystal grains with a Taylor Factor value from 3.0 to 3.4, when assuming plane strain tensile deformation in the transverse direction, is from 0.18 to 0.40.