Press Forming of Curved Frame Components Without Stretch Flange Cracking
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Solution Overview
Problem
Existing methods for manufacturing vehicle body frame components with curved shapes, such as L or T shapes, using high tensile strength steel sheets face challenges with sporadic stretch flange cracking and increased costs due to die wear and surface defects from bead formations.
Innovation Solution
A method involving a press forming process where a metal sheet is bent with a pad and lower die, using ridgelines on the die and pad to control material movement and apply out-of-plane deformations, reducing sporadic stretch flange cracking and costs by stabilizing material movement during bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pad bending-based method is used to manufacture high tensile strength steel sheet components, then cracking is avoided, but stretch flange cracking still occurs at the flange end of the curved portion
Solution Approach 1:
The method applies preliminary bending to the metal sheet before final forming, creating a pre-formed shape that prevents stretch flange cracking during subsequent pressing operations. This preliminary action prepares the material in advance to avoid cracking issues.
Solution Approach 2:
The invention introduces a movable die that can move in the pressing direction during the forming process. This dynamic element allows the die to adapt to material flow and stress distribution changes, preventing crack formation while maintaining forming quality.
2Productivity
If mass production is performed by the method in PTL 1, then production efficiency is maintained, but the moving amount fluctuates due to die wear and oil coat changes, causing sporadic stretch flange cracking
Solution Approach 1:
The movable die is positioned in advance at an optimal location before pressing begins, establishing a predetermined material flow path. This preliminary positioning ensures consistent material movement even as the die wears during mass production, maintaining reliability.
Solution Approach 2:
The movable die design inherently provides feedback through its ability to move in response to material flow resistance. As the die moves during pressing, it automatically compensates for variations in material properties and die surface conditions, maintaining stable forming results.
3Reliability
If bead and steps are formed on the blank material prior to main forming, then stretch flange cracking is avoided, but manufacturing cost increases and surface defects occur
Solution Approach 1:
The forming process is segmented into multiple stages: preliminary bending followed by final pressing. This segmentation allows each stage to address specific forming requirements, preventing cracks without requiring additional beads or steps that would increase cost and surface defects.
Solution Approach 2:
The movable die enables dynamic adjustment during the forming process, allowing the material to flow naturally without requiring pre-formed beads or steps. This eliminates the need for additional manufacturing steps and avoids the surface defects associated with bead formation.
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 suppresses sporadic stretch flange cracking and reduces production costs by stabilizing material movement and minimizing surface defects during the formation of L or T-shaped components from high tensile strength steel sheets.
Implementation Method 1
as the material moves, out-of-plane bending and unbending deformations are continuously applied to the metal sheet region sandwiched by the lower die and the pad at a position of a bend portion
Implementation Method 2
the moving amount and the moving rate of a portion sandwiched by the die (lower die) and the pad during the forming are governed by a frictional force between the die (the pad or the punch) and the blank material
Data Source
AI summary
A material is press formed into a component shape including a top sheet portion including a curved outer peripheral edge portion curved in such a manner as to be recessed inward, a vertical wall portion, and a flange portion. When a lower die and a pad sandwich a sandwiching region that is a region including at least a part of a region corresponding to the top sheet portion, an upper die is moved in a pressing direction to perform bending while moving the sandwiched material to the vertical wall portion side. A surface of the lower die that sandwiches the sandwiching region is provided with one or more ridgelines for forming bends. The ridgelines are set at positions such that, when the bending is complete, the position of the top sheet portion is located on the vertical wall portion side rather than the positions of the ridgelines.