Hat-Section Press-Formed Steel for Springback-Resistant Crash Loads
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Solution Overview
Problem
Existing methods fail to produce press-formed products with high tensile strength steel sheets that maintain desired shape and dimensional accuracy, leading to increased costs and man-hours due to springback and the need for post-processing like quenching or overlaying, especially when manufacturing components for automobile bodies requiring high crashing loads.
Innovation Solution
A two pad-equipped press forming apparatus is used, where a first pad supports the steel sheet from the die and a second pad supports it from the punch, allowing for controlled pressure and stroke to minimize springback, resulting in a novel work-hardening distribution that suppresses shoulder portion deflection and maintains bottom portion flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high tensile strength steel sheet is used for press-formed product, then strength is improved, but springback occurs causing shape deviation
Solution Approach 1:
The steel sheet is heated to the Ac3 transformation point or higher before press forming, which preliminary prepares the material by transforming its microstructure to austenite. This preliminary thermal action enables the subsequent forming to produce the desired shape with reduced springback, as the heated material has improved formability while maintaining final strength through controlled cooling
Solution Approach 2:
The temperature of the steel sheet is changed from ambient to the Ac3 transformation point or higher during the forming process. This parameter change (heating) temporarily alters the material properties to reduce springback during forming, while the final cooling restores the high strength characteristics
2Ease of manufacture
If conventional press forming method is used, then manufacturing process is simple, but dimensional accuracy deteriorates due to springback
Solution Approach 1:
The forming process incorporates temperature as a controlled parameter by heating the steel sheet to the Ac3 transformation point or higher before forming. This parameter change enables conventional press forming equipment to achieve improved dimensional accuracy by forming the heated material, which exhibits reduced springback characteristics compared to cold forming
3Manufacturing precision
If post-processing like quenching or overlaying is applied, then dimensional accuracy is improved, but manufacturing cost and time increase
Solution Approach 1:
The steel sheet is heated to the Ac3 transformation point or higher as a preliminary action before press forming. This preliminary heating enables the forming operation itself to achieve the desired dimensional accuracy without requiring subsequent post-processing steps like quenching or overlaying, thereby improving manufacturing efficiency while maintaining precision
Solution Approach 2:
The heating and forming operations are merged into a single integrated process flow. The steel sheet is heated and then immediately formed while hot, combining what would traditionally be separate processes into one continuous operation that achieves both dimensional accuracy and manufacturing efficiency
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 enables the production of high-strength press-formed products with improved dimensional accuracy and reduced costs, suitable for use as shock-absorbing members with high crashing loads without the need for post-processing, enhancing automobile safety and fuel efficiency by reducing weight.
Implementation Method 1
heating the steel sheet to be formed to the Ac3 transformation point or higher
Implementation Method 2
press forming the steel sheet to be formed while the temperature of the steel sheet is the transformation point Ac3 or higher
Data Source
Figure 1A~2
Figure 3~4B
Figure 5A~6B
AI summary
A press-formed product that enables inexpensively providing a shock-absorbing member having a high crashing load with respect to a three-point bending load is provided. The press-formed product is a press-formed product of a steel sheet 13, the press-formed product including a body 24 having a hat-shaped cross section and extending in a direction, the transverse cross section including a bottom portion 20a and a shoulder portion 20c that is contiguous to the bottom portion 20a through an R end 25. In the transverse cross section, a first region 27 from the R end 25 to a position a predetermined distance away in a direction in which the bottom portion 20a extends, and a second region 28 that is a part of the bottom portion 20a and is contiguous to the first region 27 have a work-hardening distribution introduced by press-forming of the body 24, the work-hardening distribution being one in which average hardness Hv1 of an area of the first region 27 from a surface of the steel sheet 13 to a position with a depth obtained by multiplying a thickness of the steel sheet 13 by 0.2 and average hardness Hv2 of an area of the second region 28 from the surface of the steel sheet 13 to the position obtained by multiplying the thickness of the steel sheet 13 by 0.2 satisfy a relationship of Hv1 > 1.05 x Hv2.