- freely available
Metals 2019, 9(8), 859; https://doi.org/10.3390/met9080859
2. Four-Point Air Bending for JCO Forming Process of LSAW Pipes
3. Establishment and Analysis of the Mechanical Model
3.1. Static Analysis (Bending Moment)
3.2. Elastic–Plastic Analysis
3.2.1. Basic Assumptions
- Pure bending assumption: the static bending process is considered to be a pure bending process, which means to ignore the influence of normal stress causes and to consider the bending strains only.
- Neutral layer coinciding assumption: the strain neutral layer, stress neutral layer, and geometric neutral layer always coincide during the deforming process.
- Bilinear hardening material model assumption: Effects of initial strain and change of material properties are neglected. The relationship between strain and stress is
- Plane section assumption: any plane section remains plane after deforming and no aberrance occurs, so the strain distribution on any section is linear. The strain is expressed as
- Uniaxial stress state assumption: any particle on the sheet is uniaxially stretched or compressed when a deformation occurs.
3.2.2. Bending Process and Springback Analysis
4. Finite Element Simulation and Parameters Formulation
4.1. Finite Element Model
4.2. Analysis of Simulation Results
4.2.1. Radius Error Analysis
4.2.2. Residual Straight Segment Length Analysis
4.2.3. Dimension Analysis
4.3. Formulation of Process Parameters
5. Contour Detection Method Based on Machine Vision
5.1. Formulation of Process Parameters
5.2. Splicing Algorithm for the Overall Contour
6. Experiment Design
7. Experimental Results Analysis
- The bending moment in the four-point bending process is evenly distributed between punch points, producing an arc with uniform curvature for the LSAW pipes.
- The steel sheet does not need to crimp the edge before JCO forming process, which improves efficiency and reduces cost.
- The pressure and reduction can be calculated based on the mechanical model of the four-point bending process, the material properties and process parameters.
- The simulation results show that there is a limit to the relative spacing of punch for the pipe with certain geometrical dimensions and mechanical properties; based on this, the other process parameters are further determined.
- The contour detection method based on the CCD camera can be used to detect the forming status of single pass, and the contour splicing method is proposed at the same time to obtain the overall contour of the formed part. These new methods take less time and have higher accuracy than previous detection methods.
- Aiming at the four-point bending JCO forming process and the new contour detection method, the experiments were carried out. The two pipes required 13 and 15 passes, respectively, and the roundness of pipes are less than 1.1%, which is significantly less than the three-point bending JCO forming process. In addition, the contour detection system seems to run stably and accurately.
Conflicts of Interest
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|Material||Yield Strength||Young’s Modulus |
|Diameter of Pipe|
|Radius of punch|
|Radius of die|
|Punch Radius||Die Radius||Limit Relative Spacing of Punch|
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