Hole Widening Tool With Point-Contact Projections for Crack Control
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Solution Overview
Problem
In hole widening of high strength steel sheets, stretch flange cracks and spring-back issues occur due to the thinning of the stretched flange's front end portion, which complicates the process and reduces productivity.
Innovation Solution
A hole widening method using a forming tool with a diameter-increasing portion and line-shaped projections that come into point contact with the pilot hole's circumferential edge multiple times, allowing for controlled stress distribution and reducing distortion, while the tool can rotate to adjust contact points for enhanced efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional hole widening is performed on high strength steel sheets, then productivity is maintained through press forming, but stretch flange cracks occur at the front end portion due to excessive distortion and thinning
Solution Approach 1:
The forming tool is divided into multiple functional sections: a tip portion for initial penetration, a diameter-increasing portion for gradual hole expansion, and a line-shaped projection for controlled stress application. This segmentation allows each section to perform its specific function, preventing concentration of distortion in one area and avoiding stretch flange cracks while maintaining productivity.
Solution Approach 2:
The tip portion of the forming tool performs preliminary penetration and creates a small pilot hole before the diameter-increasing portion expands it. This preliminary action prepares the material in advance, reducing the shock load and distortion that would otherwise occur during sudden hole expansion, thereby preventing cracks in high strength steel sheets.
2Strength
If high strength steel sheets with favorable elongation are used, then material formability is improved, but hole expansibility is degraded making hole widening difficult
Solution Approach 1:
The forming tool applies different types of stress to different parts of the hole circumference. The line-shaped projection applies concentrated stress at specific contact points to initiate and control material flow, while the diameter-increasing portion provides gradual expansion. This localized quality control allows hole widening in high strength steel sheets with favorable elongation but degraded hole expansibility.
Solution Approach 2:
The forming tool is designed to rotate during the hole widening process, dynamically changing the contact points of the line-shaped projection with the hole circumference. This dynamic action distributes the forming stress uniformly around the hole, preventing localized overload and enabling successful hole expansion in high strength steel sheets that would otherwise be difficult to form.
3Productivity
If forming tool is released after hole widening, then working time is reduced for productivity, but spring-back occurs causing distortion to return
Solution Approach 1:
The line-shaped projection on the forming tool applies controlled stress ahead of the main forming action, pre-distributing the deformation energy around the hole circumference. This beforehand cushioning reduces the magnitude of spring-back that occurs when the tool is released, maintaining manufacturing precision while keeping working time short for high productivity.
4Reliability
If additional working methods like laser intercept or scraping are used to avoid stretch flange cracks, then crack prevention is improved, but productivity decreases due to additional money and work
Solution Approach 1:
The patent merges multiple functions into a single forming tool: the tip portion for penetration, the diameter-increasing portion for hole expansion, and the line-shaped projection for stress control and crack prevention. This integration combines what would otherwise require separate processes (like laser intercept or scraping) into one press forming operation, preventing stretch flange cracks while maintaining high productivity without additional work steps.
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 method effectively prevents stretch flange cracks and suppresses spring-back, improving the shape accuracy and release characteristics of the formed product, thus enabling reliable hole widening across various steel types with reduced manufacturing costs.
Implementation Method 1
pushing the forming tool into the pilot hole such that the line-shaped projection of the forming tool comes into point contact with a part of the circumferential edge portion of the pilot hole in the workpiece two times or more
Implementation Method 2
the forming tool may be pushed into the pilot hole while the forming tool rotates about a central axis thereof in a pushing direction
Implementation Method 3
while a circumferential edge portion of the pilot hole is caused to extend in a pushing direction of the forming tool, the pilot hole is radially widened
Data Source
AI summary
There is provided a hole widening method including a preparing process of preparing a forming tool which has a diameter-increasing portion increasing in diameter from a front end side toward a rear end side and a line-shaped projection formed to protrude outward from a surface of the diameter-increasing portion, and a workpiece in which a pilot hole is formed; and a hole widening process of successively widening the pilot hole by pushing the forming tool into the pilot hole such that the line-shaped projection of the forming tool comes into point contact with a part of a circumferential edge portion of the pilot hole in the workpiece two times or more, and forming a stretched flange.