Development of Measurement Equipment and Experimental and Numerical Simulation Studies for Warm Forming Limits of High-Strength Steel
Abstract
:1. Introduction
2. Design of Warm-Forming-Limit Measurement Equipment
2.1. Structural Design of the Part for Warm Forming
2.2. Design of the Digital Image Measurement Part
2.3. Working Procedures
- Camera calibration: Adjust the direction of the two LED light sources to ensure that the light can pass through the glass above the host and that there is light on the specimen. Use the two cameras to shoot the calibration board from different directions to acquire images, identify the three-dimensional coordinates of the calibration points, and obtain the accurate inner parameters and external position parameters of the cameras through calculations, thus preparing for the acquisition of images in the experimental process.
- Argon gas is injected through the air inlet to exhaust the oxygen so as to reach the preset values of pressure.
- Heat the internal space environment of the chamber to the preset temperature and keep the temperature constant.
- The specimen is pushed with the electric drive pusher to the preset position on the blank holder along the guide rail. The specimen gradually rises to the same temperature as the space environment inside the closed cabinet. If the specimen needs to be heated rapidly, according to the specific experimental parameters, it is quickly heated to the preset temperature with a rapid heating coil, and then moved along the guide rail to the preset position on the blank holder with the electric drive pusher.
- Start the hydraulic system and control the displacement to make the blank holder move upward until the lifted specimen is under the plane joint with the die. The blank holder will then continuously and tightly press the specimen with the preset force. The punch will move upward according to the forming speed in the settings, and the bulging experiment process is started after making contact with the specimen. Serial images of the specimen will be collected over the whole forming process. If quenching is required for the specimen in the process, the water-cooling unit can be opened and the corresponding cooling rate can be set. In terms of experiments without any phase changes in the specimen, the water-cooling unit may also be started after the forming of the specimen to cool down the specimen and die in the heating furnace in order to facilitate the removal of the specimen.
- Use the forming-limit measurement software developed to carry out procedures such as “define the computing area and conduct the digital speckle matching and computing”, “calculate the surface strain field”, and “generate cross section in the obtained strain field to acquire the limiting strain” to obtain the maximum and minimum strain limits of the specimen. The specific information can be found in our previously published literature [16].
3. Materials and Methods
3.1. Specimen
3.2. Warm-Forming and Room-Temperature-Forming Experiments
3.3. Numerical Simulation
4. Results and Discussion
4.1. Experimental Results
4.2. Numerical Simulation Results
- Select the ultimate strain moment of the grid, find the point where the maximum principal strain is located, connect it with the central point of the specimen to make a cross line, and obtain the maximum principal strain and minimum principal strain of the node on each grid of the cross line, as well as the length of the arc line from each node to the central point of the specimen. The above values should then be imported into the quadratic function polynomial , where x represents the length of the arc line from the strain measurement node to the center of the specimen, and represents the value of the maximum principal strain, or . This method is adopted to select and obtain the or values of m nodes on both sides of the distorted grid, except for the No. 6 and No. 7 nodes (refer to Figure 10). The values of a total of 2 m nodes are obtained (m = 2,3,4,5…, and the number of nodes taken is symmetrically distributed on both sides of the distorted grid).
- In the smooth data area, the quadratic parabolic function of any 2 m continuous strain measurement points , , ……, , on the cross-sectional line is obtained by interpolation.
- Use to perform least squares fitting for 2 m consecutive points on the same cross-sectional line to obtain the corresponding extreme value of , which is the limit value of the major strain, and determine the value of x’ for x that corresponds with the time when the value is obtained. Apply the same method to perform quadratic function fitting for , and take the that corresponds with the value of x’ as the limit value of minor strain.
- Use the above method to calculate the forming limit values of the specimens at each width to obtain the forming limits under nine width conditions.
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Abbreviations
Abbreviations, acronyms, and symbols | |
FLC | Forming limit curve |
FLD | Forming limit diagram |
PLC | Programmable logic controller |
LED | Light-emitting diode |
CCD | Charge-coupled device |
ε1 | Maximum principal strain |
ε2 | Minimum principal strain |
m | The number of nodes |
n | Hardening exponent |
t | Thickness |
DSA | Dynamic strain aging |
Appendix A
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Indicator | Parameter |
---|---|
Maximum stamping force (KN) | 600 |
Forming speed (mm/min) | 0–750 |
Maximum clamping force (KN) | 600 |
Stamping stroke (mm) | 0–150 |
Sheet material thickness range (mm) | 0.2~4.0 |
Sheet material width range (mm) | 0~220 |
Specimen heating temperature (°C) | Up to 900 |
Cupping punch diameter (mm) | 100 |
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Yu, Q.; Liang, J.; Li, Q.; Li, C. Development of Measurement Equipment and Experimental and Numerical Simulation Studies for Warm Forming Limits of High-Strength Steel. Materials 2021, 14, 2373. https://doi.org/10.3390/ma14092373
Yu Q, Liang J, Li Q, Li C. Development of Measurement Equipment and Experimental and Numerical Simulation Studies for Warm Forming Limits of High-Strength Steel. Materials. 2021; 14(9):2373. https://doi.org/10.3390/ma14092373
Chicago/Turabian StyleYu, Qiang, Jin Liang, Qiu Li, and Chengyao Li. 2021. "Development of Measurement Equipment and Experimental and Numerical Simulation Studies for Warm Forming Limits of High-Strength Steel" Materials 14, no. 9: 2373. https://doi.org/10.3390/ma14092373