Galvanized Steel Sheet Surface Profile for Press Formability
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Solution Overview
Problem
Galvanized steel sheets, particularly high strength ones, suffer from die galling and poor press formability due to increased sliding resistance and frictional coefficient during press forming, leading to cracking and poor surface appearance, especially in automotive applications.
Innovation Solution
Control the surface profile of the galvanized steel sheet by adjusting the arithmetic average roughness and the number and depth of valleys and convex portions to enhance press formability without a zinc phosphate-based film, using rolling techniques to achieve specified surface roughness and flattened portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a zinc phosphate-based film is formed on the surface of the galvanized steel sheet to improve press formability, then sliding resistance is reduced, but manufacturing costs increase and phosphorus emission restrictions apply
Solution Approach 1:
The invention extracts and eliminates the zinc phosphate-based film formation process from the manufacturing sequence. Instead of adding this extra coating step, the patent uses the base galvanized surface with controlled roughness parameters (Ra 0.8-2.5 μm) to achieve adequate press formability, thereby removing the source of phosphorus emissions and reducing manufacturing complexity
Solution Approach 2:
The invention changes the surface roughness parameters of the galvanized steel sheet by controlling the arithmetic average roughness (Ra) to be 0.8-2.5 μm and the maximum roughness (Rz) to be 3.0-8.0 μm. This parameter optimization allows the surface to maintain adequate lubrication during press forming without requiring additional zinc phosphate coating, thus reducing manufacturing cost and phosphorus emissions while preserving press formability
2Reliability
If the surface roughness is increased to improve slidability during press forming, then press formability is enhanced, but surface appearance deteriorates
Solution Approach 1:
The invention optimizes the surface roughness parameters within specific ranges (Ra 0.8-2.5 μm, Rz 3.0-8.0 μm) to achieve the optimal balance between slidability and surface appearance. This controlled roughness provides adequate lubrication for press forming while maintaining an acceptable surface finish for automotive applications
Solution Approach 2:
The invention creates localized flattened portions on the surface that provide lubrication reservoirs without affecting the overall surface appearance. These localized features are strategically positioned to improve slidability in critical areas while maintaining good surface finish in visible areas
3Weight of moving object
If a high strength steel sheet is used to reduce vehicle body weight, then CO2 emissions are reduced, but sliding resistance increases causing die galling
Solution Approach 1:
The invention changes the surface roughness parameters of high strength steel sheets (tensile strength 440 MPa or higher) to Ra 0.8-2.5 μm and Rz 3.0-8.0 μm. This optimized surface profile creates adequate lubrication that counteracts the increased sliding resistance inherent in high strength materials, preventing die galling while maintaining the weight reduction benefits
Solution Approach 2:
The controlled surface roughness acts as an intermediary layer between the high strength steel sheet and the die surface. This intermediate surface structure provides lubrication that mediates the interaction, preventing direct metal-to-metal contact and die galling that would otherwise occur with high strength materials
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 significantly reduces frictional coefficient, inhibiting die galling and improving press formability, especially in high strength steel sheets, while maintaining good surface appearance after painting.
Implementation Method 1
the frictional coefficient between the steel sheet and a forming die or the like is significantly decreased, so that press formability is improved
Data Source
AI summary
A galvanized steel sheet is disclosed. The galvanized steel sheet has an arithmetic average roughness Ra of a surface of the steel sheet of 0.5 μm to 2.5 μm, and has concave and convex portions on the surface thereof, in which there are flattened portions in the convex portions, in which the number of valleys between the convex portions having a valley width of 0.1 mm or more and a maximum depth of 2.0 μm or more is 50 or more and less than 100 per 25 mm on a straight line, and in which, in the flattened portions in the convex portions, the number of concave and convex portions having a height difference of 0.3 μm or more is less than 20 per 2.5 mm on a straight line.