Cold Drawing Plug Tapered Geometry Reduces Residual Stress
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Solution Overview
Problem
Existing plugs for cold drawing of metal pipes do not effectively reduce tensile residual stress on the outer surface, which can lead to cracks during heat treatment due to the interaction between surface flaws and residual stresses.
Innovation Solution
A plug design featuring a first columnar portion, a second columnar portion, and a tapered portion with specific dimensions and geometry, where the outside diameters and axial length of the tapered portion are optimized to expand the metal pipe, reducing tensile residual stress through compressive strain differences between the inner and outer surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional plug is used for cold drawing, then the metal pipe can be drawn to reduce diameter and smooth outer surface, but tensile residual stress accumulates on the outer surface which may cause cracks during subsequent heat treatment
Solution Approach 1:
The plug is divided into three distinct segments: a first columnar portion with smaller diameter, a tapered portion with intermediate diameter, and a second columnar portion with larger diameter. This segmentation allows each portion to perform a specific function: the first columnar portion provides initial support, the tapered portion creates controlled expansion and compressive strain, and the second columnar portion maintains final dimensional accuracy. The segmentation resolves the contradiction by enabling stress reduction through the specialized tapered portion while maintaining drawing precision through the other portions.
Solution Approach 2:
The tapered portion is designed with specific geometric parameters (diameter between D1 and D2, length L within 0.05-0.5 times the pipe length) to create localized compressive strain only in the region where tensile residual stress needs to be counteracted. This local quality approach allows the plug to reduce tensile residual stress on the outer surface without compromising the overall dimensional accuracy and surface smoothness achieved by the other portions of the plug.
2Stress or pressure
If the plug expands the hollow shell with a tapered portion, then compressive strain is generated to reduce tensile residual stress, but the plug structure becomes more complex
Solution Approach 1:
The tapered portion is designed to create dynamic expansion during the cold drawing process. As the plug is inserted into the hollow shell, the tapered portion progressively expands the shell diameter from the initial reduced size to a slightly larger final size (expansion ratio 0.1-1.5%). This dynamic expansion generates the necessary compressive strain to counteract tensile residual stress while maintaining a relatively simple conical geometry that is easy to manufacture.
Solution Approach 2:
The invention specifies precise parameter ranges for the tapered portion: diameter D3 between D1 and D2, length L between 0.05-0.5 times the pipe length, and expansion ratio between 0.1-1.5%. By optimizing these parameters, the plug achieves effective tensile residual stress reduction while keeping the geometric complexity manageable. The parameter optimization ensures that the tapered portion is neither too short (ineffective) nor too long (excessive complexity), and neither too steep (difficult to manufacture) nor too gradual (insufficient strain generation).
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 optimized plug design effectively reduces tensile residual stress on the outer surface of metal pipes to below 0.5 times the yield stress, minimizing the risk of cracks and improving surface smoothness and fatigue characteristics.
Implementation Method 1
the compressive strain in the circumferential direction due to the elastic recovery of the metal pipe following the plug removal is greater on the inner surface side of the metal pipe than on the outer surface side thereof
Data Source
AI summary
A plug 1 includes a first columnar portion 20, a tapered portion 30, and a second columnar portion 40. The first columnar portion 20 has an outside diameter D1. The second columnar portion 40 has an outside diameter D2 which is larger than the outside diameter D1. The tapered portion 30 is formed between the first columnar portion 20 and the second columnar portion 40. The tapered portion 30 has a tapered surface 31 provided with an outside diameter which is gradually increased from the first columnar portion 20 to the second columnar portion 40, and an axial direction length L. The outside diameters D1 and D2, and the axial direction length L meet the following expressions (1) to (4):0.25≦ρ≦2.00 (1),0.06≦L/D2≦0.8 (2),L/D2≦0.3×ρ+0.575 (3), andL/D2≧0.1×ρ (4)where ρ=(D2−D1)/D1×100.Therefore, the cold drawing plug according to the present invention can reduce the tensile residual stress on the outer surface of a metal pipe after the cold drawing.