Pressed Roof Rail Forming to Control Spring-Back and Twisting
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Solution Overview
Problem
The manufacturing of automotive structural members with complex lateral cross-section profiles, such as roof rails, faces challenges with shape fixability due to spring-back during cold pressing, leading to issues like twisting and residual stress, which affects the desired shape and strength of the components.
Innovation Solution
A manufacturing method involving a two-step process using a press apparatus with specific die and punch configurations to form an intermediate component with a step projection along the length direction of the top plate, followed by narrowing the step width and adjusting the angle of the curved wall to reduce residual stress and prevent bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high tensile sheet steel blank is cold pressed to manufacture curved configuration elements, then manufacturing cost is suppressed and strength is increased, but spring-back occurs during press mold release causing twisting and poor shape fixability
Solution Approach 1:
The patent divides the pressing process into two distinct stages: a first pressing process that forms the basic configuration element, and a second pressing process that corrects shape deviations. This segmentation allows each process to have optimized parameters - the first process achieves basic forming while the second process specifically addresses spring-back and shape precision, thereby resolving the contradiction between strength (achieved through cold pressing of high tensile steel) and shape fixability (achieved through the two-stage pressing approach).
Solution Approach 2:
The first pressing process performs preliminary forming of the configuration element with anticipated spring-back in mind. By pre-forming the basic shape and anticipating the spring-back deformation, the second pressing process can then focus on correcting the shape deviations. This preliminary action allows the final pressing to achieve precise shape control while maintaining the strength benefits of cold pressing high tensile steel.
2Manufacturing precision
If a step is formed in the curved wall during first pressing, then shape fixability is improved, but bending occurs in curved walls due to spring-back after mold removal
Solution Approach 1:
The second pressing process acts as a feedback mechanism that detects and corrects the bending and shape deviations caused by spring-back in the first pressing process. By using the outcome of the first pressing (including its defects) as the input for the second pressing, the system continuously adjusts and corrects the shape, thereby improving curved wall integrity while maintaining the shape fixability benefits of the step formation.
3Manufacturing precision
If flange is bent back in second process to reduce residual stress, then shape fixability is improved, but deviatoric residual stress arises at inner faces of vertical walls and top plate causing bending
Solution Approach 1:
The patent changes the pressing parameters and sequence between the two processes. The first pressing uses parameters optimized for basic forming and step creation, while the second pressing uses different parameters specifically optimized for stress relief and shape correction. By changing parameters between processes rather than using a single set of parameters, the patent achieves shape fixability improvement while managing residual stress distribution to prevent bending.
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
The method effectively suppresses bending and residual stress in the pressed components, ensuring better shape fixability and strength, particularly in components with curved profiles, thereby improving the manufacturing efficiency and quality of automotive structural members.
Implementation Method 1
pressing a blank to form an intermediate formed component
Implementation Method 2
spring-back occurs during press mold release, leading to concerns of twisting in the top plate
Data Source
AI summary
A process of pressing a blank to form an intermediate formed component configured including a top plate, the ridge lines at short direction ends of the top plate, and vertical walls facing each other in a state extending from the respective ridge lines and at least one of the vertical walls configuring a curved wall curving as viewed from an upper side of the top plate, such that a step projecting toward an opposite side to a side on which the vertical walls face each other is formed to the curved wall so as to run along a length direction of the top plate. The method includes pressing the intermediate formed component to narrow a projection width of the step, or to move a portion of the curved wall where the vertical walls face each other.