Metal Plate Burring Gap Control to Prevent Flat-Hole Cracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional burring methods for metal plates, such as header plates in heat exchangers, often result in stress concentration and cracking at the apical portions of flat holes, leading to unstable brazing and durability issues, particularly when forming large or high-burring holes.
Innovation Solution
A burring method where the gaps between the punch's vertical outer surfaces and the die's inner surfaces at both ends are set smaller in the longitudinal direction, allowing for controlled burring height and reducing stress concentration, without the need for pre-formed holes, enabling flexible and wide-range applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If press machining is performed with uniform gaps between punch and die, then the burring process is simple, but stress concentration occurs at apical portions causing cracks
Solution Approach 1:
The patent applies local quality by setting different gap sizes at different locations of the punch-die interface. Specifically, the gap is made smaller at the apical portions (ends in the major axis direction) where stress concentration occurs, and larger at other portions. This localized variation in gap size reduces stress concentration at critical areas while maintaining overall burring functionality, thereby preventing cracks without complicating the entire process.
2Reliability
If prepared holes are formed in advance to reduce stress, then crack prevention improves, but the process becomes more complex and metal is removed
Solution Approach 1:
The patent applies preliminary action by pre-forming holes at the apical portions of the metal plate before the main burring operation. These prepared holes are positioned at locations where stress concentration would occur during burring. By creating these holes in advance, the metal structure is modified to reduce stress concentration during the subsequent press machining, thereby preventing cracks without requiring complex process changes.
3Reliability
If gap at both ends is made smaller to reduce burring height and stress, then crack prevention improves, but the solution is limited for large or high-burring applications
Solution Approach 1:
The patent applies local quality by making the gap smaller only at the apical portions (ends in the major axis direction) while maintaining larger gaps at other portions of the punch-die interface. This localized approach reduces stress concentration and burring height specifically where cracks occur, while preserving adequate burring height in other areas. This allows the method to be applicable to both small and large flat holes, as well as high-burring applications, thereby improving versatility.
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 reduces stress concentration and prevents cracking, enhancing brazing stability and joining strength, while simplifying the process and allowing for accurate formation of large or high-burring holes.
Implementation Method 1
pressing a flat burring punch from the other surface of the metal plate toward the cavity portion, the burring punch having a vertical outer circumferential surface relative to the planar face of the die, wherein: the punch has a flat cross-section parallel to the planar face; and in a state in which the punch is pressed toward the cavity portion with the metal plate therebetween
Data Source
AI summary
Respective gaps between a pair of vertical outer surfaces parallel to a pressing direction of a punch and inner surfaces of a cavity portion of a die facing the same, at positions at both ends in a longitudinal direction of the cross-section of the punch, are set smaller than respective gaps between outer surfaces parallel to the pressing direction of the punch and inner surfaces of the cavity portion of the die facing the same, at positions at both ends in a width direction of the cross-section. Burring height formed by pressing a punch for burring toward the cavity portion to insert the punch into the same is generally proportional to these gap values, and therefore the burring height at ends in the major axis direction becomes lower than that in the minor axis direction.