Steel Sheet Double Cutting for Delayed Fracture Suppression
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Solution Overview
Problem
The occurrence of delayed fractures in high-strength steel sheets, particularly those with a tensile strength of 1180 MPa or more, is a significant issue in press forming, especially at the sheared end surfaces, which is not effectively addressed by existing methods like temperature elevation or punch design, and these methods are not suitable for mass production.
Innovation Solution
A method involving double cutting processing is employed, where a partial beam-shaped projection portion is formed at the location prone to delayed fracture in the first cutting, followed by a second cutting to shape the end, reducing tensile residual stress and preventing end cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heating the steel sheet is used to reduce tensile residual stress, then delayed fracture resistance is improved, but production time increases and mass production becomes difficult
Solution Approach 1:
The patent replaces the thermal field (heating) with a mechanical field (double cutting processing). Instead of applying heat to reduce residual stress, the invention uses mechanical cutting actions - first creating a projection portion and then removing it - to achieve stress reduction through plastic deformation and material removal, enabling mass production without heating time
Solution Approach 2:
The patent changes the physical state and geometric parameters of the material through double cutting. The first cutting creates a projection portion that plastically deforms the material, and the second cutting removes this projection, fundamentally altering the stress distribution state without changing temperature parameters
2Reliability
If stepped punch is used in punching work to reduce tensile residual stress, then delayed fracture resistance is slightly improved, but the improvement effect is insufficient
Solution Approach 1:
The patent divides the single punching operation into two separate cutting operations. The first cutting creates a projection portion with specific geometry, and the second cutting removes this projection. This segmentation allows each cutting to serve a specific function, achieving superior stress reduction compared to the single-step stepped punch method
3Reliability
If shaving method is used to reduce tensile residual stress, then delayed fracture resistance is improved, but clearance management becomes difficult
Solution Approach 1:
The patent extracts the problematic projection portion created in the first cutting through a second cutting operation. This approach avoids the clearance management issues of shaving by completely removing the projection rather than attempting to control and manage it through precise clearance settings
4Productivity
If double punching cut-off method is used, then punching work efficiency is improved, but it cannot be applied to outer peripheral portions
Solution Approach 1:
The patent creates a universal cutting method that can be applied to any location on the steel sheet - inner peripheral portions, outer peripheral portions, and intermediate areas. The double cutting process with projection portion creation and removal is location-independent, providing multi-functional applicability that punching methods lack
Data Source
AI summary
A technology capable of suppressing end cracking due to a delayed fracture without restrictions on the target pressed component shape. When it is estimated that the end cracking due to the delayed fracture in an end of a material to be pressed is concerned, double cutting processing including performing cutting processing of the end containing at least a place where the end cracking is concerned twice is provided as preprocessing for the press forming causing the concern about the end cracking. The double cutting processing includes performing, in first cutting, cutting to form a partial beam-shaped projection portion at a position containing the place where the end cracking is concerned, and cutting the projection portion in second cutting.