Hydroformed Rail Vehicle Tubes With Variable Wall Thickness
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Solution Overview
Problem
There is a need for weight reduction in rail vehicle interior elements such as handrails, grab handles, and luggage racks to enhance energy efficiency and economic operation while maintaining mechanical and safety requirements.
Innovation Solution
The method employs an internal high-pressure forming process (hydroforming) to adjust the wall thickness of tubular furnishing elements, reducing thickness in selected areas and maintaining or increasing it in others, allowing for a significant weight reduction with a short transition zone between thickness variations, and ensuring the elements meet mechanical and safety standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional forming processes with shaped bodies (mandrels) are used to form tubular fittings, then the inner contour of the tube can be formed, but the transition zone between different wall thickness areas becomes excessively long and the process becomes complex
Solution Approach 1:
The patent removes the shaped body (mandrel) from the forming process entirely. Instead of using a solid or shaped body inside the tube to form the inner contour, the invention uses external forming tools that apply pressure from the outside, eliminating the need for internal shaping components and thereby reducing transition zone length.
Solution Approach 2:
The patent employs hydroforming technology where a fluid (liquid or gas) is used as the forming medium. High-pressure fluid is introduced into the tube and expanded against the outer forming tools, enabling precise control of the forming process and creating smooth, short transition zones between different wall thickness areas without requiring internal mandrels.
2Weight of moving object
If multiple forming steps are performed to achieve weight optimization with variable wall thickness, then weight reduction is achieved, but work hardening becomes excessive causing dies and shaped bodies to become stuck
Solution Approach 1:
The patent replaces the mechanical contact-based forming method (using solid mandrels and dies that physically touch and grip the tube) with a fluid-pressure-based system. The hydroforming process uses distributed fluid pressure to deform the tube, eliminating excessive localized work hardening and preventing sticking between forming tools and the workpiece.
Solution Approach 2:
The patent controls the forming process by carefully managing fluid pressure parameters, applying pressure gradually and uniformly throughout the tube. This controlled parameter approach allows multiple forming steps to be performed without causing excessive work hardening, maintaining process continuity and preventing tool sticking.
3Ease of manufacture
If uniform wall thickness is maintained throughout the tubular element, then manufacturing is simpler, but weight reduction opportunities are lost in areas where thickness can be reduced
Solution Approach 1:
The patent applies different wall thicknesses to different sections of the tubular element based on local requirements. Areas requiring higher strength maintain greater wall thickness, while areas with lower load demands are formed with thinner walls. The hydroforming process enables this localized variation by using specially designed outer forming tools that create the desired thickness profile in specific zones.
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 achieves a substantial weight reduction with a minimal transition zone, enhancing the energy efficiency and economic operation of rail vehicles by applying the hydroforming process to tubular elements, ensuring they meet mechanical and safety requirements.
Implementation Method 1
an internal high-pressure forming process (hereinafter also: hydroforming process) is used in the production of a tubular furnishing element. With the hydroforming process, the material thickness or wall thickness is reduced in selected areas of a tubular furnishing element
Implementation Method 2
The process achieves a hardening of the material compared to the starting material, which occurs during cold forming due to the strain hardening that begins.
Data Source
Figure 1a~1d
Figure 2a~2c
Figure 3a~3b
AI summary
A method for producing a tubular element (1; 34; 40, 50, 51) comprising at least a first tube section (4; 31; 41) with a first wall thickness and at least a second tube section (5; 32; 42) with a second wall thickness less than the first wall thickness, and a constant or substantially constant outside diameter (A), the method comprising: a) forming (U; IHU) a tube pre-product (2) with constant wall thickness to a tube intermediate (3; 30), wherein in the tube intermediate (3; 30) in the second tube section (5; 32; 42) the wall thickness is reduced relative to the wall thickness in the first tube section (4; 31; 41) and in the second tube section (5; 32; 42) the outside diameter (A'; A") of the tube pre-product is changed, b) forming (IHU; U) of the pipe intermediate product (3; 30) such that a constant outer diameter (A) is obtained, wherein in the second pipe section (5; 32;42) the wall thickness remains reduced relative to the wall thickness in the first pipe section (4; 31; 41), with at least one forming step being carried out using internal high-pressure forming (IHPF).;