Overlapped blank for hot stamping, method of manufacturing overlapped hot stamp molded body, and overlapped hot stamp molded body
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Solution Overview
Problem
The use of aluminum-based plated steel sheets in hot stamping processes results in a difference in temperature increasing rates between overlapped and one-sheet parts, leading to inadequate corrosion resistance and potential liquid-metal embrittlement issues due to uneven alloying reactions during hot stamping.
Innovation Solution
The implementation of an overlapped blank with a first steel sheet having a higher aluminum-based plated layer coating weight and a second steel sheet with a lower coating weight, where the second steel sheet is spot-welded to the first steel sheet, and includes a carbon-based coating or ZnO/TiO2 to optimize temperature distribution and emissivity, ensuring uniform alloying and improved corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum-based plated steel sheets are used in hot stamping, then corrosion resistance is improved, but temperature distribution uniformity deteriorates due to different emissivity between overlapped and one-sheet parts
Solution Approach 1:
The patent applies local quality by differentiating the plating coating weight between overlapped parts and one-sheet parts. Specifically, the plating coating weight at overlapped parts is set to 5-20 g/m² while at one-sheet parts it is set to 20-45 g/m². This local differentiation adjusts the emissivity of each region to achieve uniform temperature distribution across the entire workpiece during hot stamping, while maintaining adequate corrosion resistance at both regions.
2Reliability
If the plating coating weight is increased to improve corrosion resistance, then alloying reaction uniformity deteriorates due to excessive aluminum content at one-sheet parts
Solution Approach 1:
The patent applies parameter changes by optimizing the plating coating weight parameter differently for overlapped and one-sheet parts. At one-sheet parts where higher corrosion resistance is needed, the plating coating weight is increased to 20-45 g/m². At overlapped parts where excessive aluminum would hinder alloying, the plating coating weight is reduced to 5-20 g/m². This parameter optimization ensures uniform alloying reactions while maintaining adequate corrosion resistance.
3Ease of manufacture
If non-plated steel sheets are used, then manufacturing cost is reduced, but oxide scale generation increases requiring additional processing
Solution Approach 1:
The patent applies local quality by providing aluminum-based plating only at specific locations (one-sheet parts and edge portions) rather than uniformly across the entire steel sheet. This selective plating approach maintains adequate corrosion resistance and prevents oxide scale generation at critical areas while reducing overall material cost compared to full plating.
4Temperature
If the plating coating weight is decreased to improve heat absorption, then corrosion resistance deteriorates
Solution Approach 1:
The patent applies local quality by differentiating plating coating weight between regions with different functional requirements. At overlapped parts where rapid heating is critical, the plating coating weight is reduced to 5-20 g/m² to improve heat absorption. At one-sheet parts where corrosion protection is prioritized, the plating coating weight is increased to 20-45 g/m². This spatial differentiation resolves the contradiction between heat absorption and corrosion resistance.
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 effectively addresses the temperature rate disparity and enhances the corrosion resistance of the overlapped parts by promoting uniform alloying reactions and emissivity, thereby improving the overall performance and reliability of the hot stamp molded body.
Implementation Method 1
the Zn-based plating becomes Zn-Fe-based plating and the Al-based plating becomes Al-Fe-based plating after the hot-stamping heating by the alloying reaction of diffusing Fe in the plating
Implementation Method 2
heating a steel sheet up to an Ac3 point or higher (for example, 800°C or higher) to make it into austenite
Implementation Method 3
rapidly cooling it down to an Ms point or lower (for example, 400°C or lower) by a metal mold during keeping it at a bottom dead center to make the material into martensite to thereby quench it
Implementation Method 4
the second steel sheet further includes a carbon-based coating having an emissivity of 0.7 or more on the surface of the aluminum-based plated layer
Data Source
Figure 1
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AI summary
To solve the problem about the difference in temperature increasing rate between an overlapped part and a one-sheet part so as to further improve the corrosion resistance of plating after hot stamping. An overlapped blank for hot stamping includes: a first steel sheet; and at least one second steel sheet connected to a surface of the first steel sheet via a welding point and smaller in area than the first steel sheet, wherein: the first steel sheet is a plated steel sheet having an aluminum-based plated layer on both faces of the first steel sheet, and the second steel sheet is a plated steel sheet having an aluminum-based plated layer on both faces of the second steel sheet; a coating weight of the aluminum-based plated layer on the first steel sheet is W1 (g/m2) in terms of an average coating weight on both the faces; a coating weight of the aluminum-based plated layer on a surface on a side not in contact with the first steel sheet in the second steel sheet is W2 (g/m2); and each of the W1 and the W2 is within a range of 20 g/m2 or more and 120 g/m2 or less, and satisfies relationships of Expression (1) and Expression (2).