Plated Steel Sheet Surface Texture for Galling Prevention
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Solution Overview
Problem
Plated steel sheets used for automotive outer panels face issues with galling during press forming due to high sliding friction resistance, leading to increased costs and reduced surface quality, as existing methods for improving press formability either fail to effectively reduce friction or compromise weldability and adhesiveness.
Innovation Solution
A method involving a skin pass rolling process with controlled roughness skewness and oil pocket area to reduce the coefficient of repetitive friction, utilizing rolls with specific roughness skewness values and rolling forces to enhance lubrication and prevent galling, while maintaining surface roughness and peak numbers within optimal ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fine concave-convex portions are formed on the surface of plated steel sheet by conventional methods (shot blasting, electro discharge texturing, laser texturing), then surface roughness and peak number are improved, but the oil retention function is excessive and friction reduction function is insufficient
Solution Approach 1:
The invention changes the geometric parameters of surface concave-convex portions by controlling the roughness skewness (Rsk) to be -0.3 or greater and the sum of volumes of concave portions per unit area (Vc) to be within specific ranges. This parameter optimization transforms the surface morphology from one that merely retains oil to one that effectively reduces friction and prevents galling during press forming
Solution Approach 2:
The invention creates localized concave portions with specific volume characteristics on the plating layer surface. These locally optimized concave structures serve as effective oil pockets that reduce sliding friction, while the overall surface maintains appropriate roughness for lubrication retention without excessive oil accumulation
2Manufacturing precision
If plated steel sheet with fine concave-convex portions is press formed, then surface quality is improved, but galling phenomenon occurs due to high sliding friction resistance
Solution Approach 1:
The optimized concave portions on the plating layer surface act as intermediaries that retain lubricating oil and reduce direct metal-to-die contact. By controlling the volume and distribution of these concave portions, the invention creates an effective lubrication interface that prevents galling and plating layer separation during press forming while maintaining surface quality
Solution Approach 2:
The invention converts the naturally formed flat and soft plating layer surface, which causes high friction and galling, into a beneficial structured surface with controlled concave portions. These concave structures, created through optimized skin pass rolling, transform the harmful friction characteristic into a beneficial lubrication-retaining feature that prevents galling
3Productivity
If conventional texturing methods are used to form fine concave-convex portions, then press formability is partially improved, but additional expensive lubrication processes are required
Solution Approach 1:
The invention enables the plating layer surface to self-generate the necessary lubrication function through its own structural characteristics. By optimizing the roughness skewness and concave portion volume during skin pass rolling, the surface itself becomes an effective oil pocket system that reduces friction without requiring additional lubrication processes or complex equipment
Solution Approach 2:
The invention merges the surface finishing function and lubrication retention function into a single integrated process. The skin pass rolling process simultaneously creates the desired surface roughness, optimizes the concave-convex morphology, and establishes effective oil pocket characteristics, eliminating the need for separate texturing and lubrication processes
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 reduces sliding friction resistance and prevents galling, ensuring excellent surface qualities and press formability for plated steel sheets, making them suitable for automotive outer panels without compromising weldability or adhesiveness.
Implementation Method 1
performing a skin pass rolling process on the plated steel sheet by inserting the plated steel sheet into a skin pass mill
Implementation Method 2
Fine concave-convex portions formed on surfaces of plates steel sheets have a function of reducing a contact area with a die during a press forming process and function as oil pockets retaining oils such as press oil, lubricants, or rust preventive oil to reduce sliding friction resistance
Data Source
Figure 1~2
AI summary
The present invention relates to a hot-dip galvanized steel sheet used as an automobile outer panel, etc., and more specifically, to a method for manufacturing a hot-dip galvanized steel sheet having excellent surface quality and press formability.