Asymmetrical Mandrel Ball Geometry for Thin-Walled Tube Bending
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Solution Overview
Problem
Current rotary draw bending methods for producing bent tubes often result in ruptures, flattening, and buckling, especially when aiming for thin-walled tubes with high strength and small radii of curvature, making it difficult to achieve tubes suitable for industrial applications without secondary operations.
Innovation Solution
The use of an asymmetrical mandrel ball with a specific cross-sectional shape and positioning during rotary draw bending to control the gap between the mandrel and the tube, preventing ruptures and buckling while maintaining a satisfactory flattening and thickness reduction ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rotary draw bending is performed to efficiently produce bent tubes with fast machining speed, then productivity is improved, but large local distortions and ruptures arise in the bent tube
Solution Approach 1:
The mandrel ball is designed with asymmetrical geometry where the dimension facing the outside of bend (L1) is smaller than the dimension facing the inside of bend (L2), creating a ratio L1/L2 of 0.95 or less. This local variation in geometry allows the mandrel to provide different levels of support at different locations, preventing ruptures at the outside of bend while controlling flattening at the inside of bend, thus resolving the contradiction between productivity and manufacturing precision
Solution Approach 2:
The mandrel ball employs asymmetrical design with unequal dimensions in different directions. Specifically, the cross-sectional shape has L1 (dimension facing outside of bend) smaller than L2 (dimension facing inside of bend), creating an asymmetrical support profile that adapts to the different stress conditions at inside and outside of the bend, enabling high-speed bending without ruptures or excessive distortions
2Reliability
If the tensile strain amount at the outside of bend is reduced by adjusting bending conditions, then ruptures are prevented, but the bending efficiency and productivity decrease
Solution Approach 1:
The mandrel ball acts as an intermediary element inserted inside the tube during bending. It provides internal support to counterbalance the tensile stresses at the outside of bend, preventing ruptures without requiring reduction of bending speed or tensile force. This allows the bending process to maintain high productivity while ensuring reliability through the mandrel's mechanical support
3Shape
If a conventional symmetrical mandrel is used to prevent flattening, then the cross-sectional shape is maintained, but tensile strain increases causing ruptures at the outside of bend
Solution Approach 1:
The mandrel ball uses asymmetrical geometry with L1 < L2 to create differential support. The smaller L1 dimension facing the outside of bend allows greater clearance to prevent tensile strain and ruptures, while the larger L2 dimension facing the inside of bend provides sufficient support to control flattening. This asymmetrical design simultaneously addresses both shape maintenance and rupture resistance
Solution Approach 2:
Different regions of the mandrel ball are designed with different dimensions to address local requirements: the region facing the outside of bend has smaller dimension L1 to prevent rupture, while the region facing the inside of bend has larger dimension L2 to control flattening. This local differentiation resolves the contradiction between maintaining cross-sectional shape and preventing ruptures
4Manufacturing precision
If the mandrel gap is reduced to prevent buckling and maintain shape, then manufacturing precision is improved, but the complexity of positioning and controlling the mandrel increases
Solution Approach 1:
The asymmetrical mandrel ball design enables self-positioning during the bending process. The asymmetrical geometry naturally orients the mandrel ball such that the smaller L1 dimension faces the outside of bend and the larger L2 dimension faces the inside of bend, eliminating the need for complex external positioning mechanisms. This self-service capability maintains manufacturing precision while reducing device complexity
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 approach allows for the production of bent tubes with high strength, appropriate flattening, and thickness reduction, preventing ruptures and buckling, enabling their use as starting materials or further processing without additional operations.
Implementation Method 1
The mandrel has only one set of a combination of the connection mechanism and the mandrel ball; and in a cross-section orthogonal to an axial direction of the mandrel ball at a central position in the axial direction of the mandrel ball, the mandrel ball has a first position and a second position at which a first straight line that passes through a mandrel ball center meets an outer periphery of the mandrel ball, and a ratio (L1/L2) between a dimension L1 from the mandrel ball center to the first position and a dimension L2 from the mandrel ball center to the second position is in a range of 0.915 or more to 0.976 or less.
Data Source
AI summary
A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L1/L2) between a dimension L1 from the mandrel ball center 17 to the first position 19 and a dimension L2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.