Numerical and Experimental Analysis of Hardening Distortions of Drawpieces Produced in Hot Stamping Process
Abstract
:1. Introduction
- Flexure—flexure of the drawpiece after removal from the stamping die belongs to dominant form of the distortion;
- Torsion (skewing)—torsion of the drawpiece around imaginable axis of the drawpiece, after removal from the stamping die also belongs to dominant form of the distortion.
2. Hardening Distortions—Source of Origin
3. Torsional Form of the Hardening Distortions
3.1. FEA Models and Materials
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- Stamping speed 80 mm/s,
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- Ambient temperature 20 °C,
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- Thermal conductivity coefficient from the blank to the stamping die 3.5 , this coefficient was scaled depending on value of the pressure between the punch, the stamping die, and the blank,
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- Thermal conductivity coefficient from the blank, the punch, and the stamping die to the environment, linearly variable and dependent on temperature of the blank and the stamping die (for 20 °C equal to 0.02 ), for 950 °C equal to 0.075 ),
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- Temperature of the stamping die—150 °C,
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- Pressure force to the drawpiece during quenching 1500 kN,
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- Quenching time 8 s.
3.2. Analysis Results
4. Hardening Distortions Having Form of Flexure
5. Experimental Verification of Results of the Analysis and Discussion
5.1. Testing of the Shape-Dimensional Accuracy
5.2. Testing of the Mechanical Parameters
- From the measurement points in each, the material of the both drawpieces has reached its required hardness, which was within assumed range from 400 to 550 HV;
- The yield strength in each from the measurement points has the required values, from 950 to 1200 MPa;
- The tensile strength has also reached the required value in range of 1300–1650 MPa in each from the measurement points.
5.3. Testing of the Mechanical Parameters
6. Conclusions
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- The defining requirements for the dimensional and shape tolerances of the analyzed drawpieces;
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- Verifying if the shape of the drawpiece is technologically feasible—i.e., is possible to be produced in process of the hot stamping;
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- Developing a plan of technological process to produce the drawpiece, considering all requirements and restrictions of integrated processes of plastic forming and heat treatment;
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- Developing a method how to set datum positions of the drawpiece in the tool;
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- Constructing superficial CAD models of the working tools (stamping dies, die clamps, punches);
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- Elaborating technical assumptions of the hot stamping technology (temperature of the blank, time of transfer of the blank from furnace to press, time of stamping operation, course of speed motion of ram of the press, time of hardening, temperature of the tools, required hardness of the drawpiece, model of the material for specified thickness of drawpiece);
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- Defining the shape of the blank, which assures obtaining finished drawpiece in required manufacturing tolerance of external outline of the blank;
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- Constructing FEM models of the blank and working surfaces of stamping die, defining all its components, kinetic and thermal parameters;
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- Carrying out simulation and analyzing results of the simulation in view of the characteristic, which would ensure correct plastic working (FLD diagrams and thinning) and the heat treatment (distribution of the hardness and martensite);
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- Analyzing the results of the simulation in view of the values of the hardening distortions in the drawpiece, in relation to the requirements of the shape-dimensional tolerances specified in the technical documentation.
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- Creating a model to calculate the compensation of the hardening distortions and executing analysis of the hardening compensation at assumed parameters of the compensator;
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- Analyzing the obtained compensation results of the tool in view of the hardening distortions of the drawpiece; in the case when the hardening distortions are still too high, carrying out the next loop of the calculations. The loops are repeated till obtaining the drawpieces having the hardening distortions within the assumed field of the tolerances;
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- Memorizing compensated superficial CAD models of the tools, which in the course of the next steps are to be used by tool design engineers as the base surfaces to develop the manufacturing tools.
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Inner Panel of B Pillar | Door Beam | |||||
---|---|---|---|---|---|---|
Tolerance field | −0.5 +0.5 | −0.7 +0.7 | −0.2 −0.7 | −0.3 +0.3 | −0.5 +0.5 | −0.2 −0.5 |
Maximal value | +0.42 | +0.55 | −0.11 | 0.15 | 0.42 | −0.14 |
Minimal value | −0.40 | −0.55 | −0.62 | −0.25 | −0.21 | −0.45 |
Standard deviation | 0.027 | 0.031 | 0.024 | 0.021 | 0.036 | 0.054 |
Max | Min | Average | Std Deviation | |||||
---|---|---|---|---|---|---|---|---|
Beam | B Pillar | Beam | B Pillar | Beam | B Pillar | Beam | B Pillar | |
hardness HV | 546 | 533 | 464 | 450 | 510.6 | 492.2 | 10.2 | 12.5 |
Ra MPa | 1151 | 1142 | 984 | 953 | 1087.4 | 1076.7 | 10.8 | 18.7 |
Rm MPa | 1559 | 1616 | 1372 | 1296 | 1504.8 | 1495.1 | 9.4 | 10.2 |
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Wróbel, I. Numerical and Experimental Analysis of Hardening Distortions of Drawpieces Produced in Hot Stamping Process. Metals 2021, 11, 457. https://doi.org/10.3390/met11030457
Wróbel I. Numerical and Experimental Analysis of Hardening Distortions of Drawpieces Produced in Hot Stamping Process. Metals. 2021; 11(3):457. https://doi.org/10.3390/met11030457
Chicago/Turabian StyleWróbel, Ireneusz. 2021. "Numerical and Experimental Analysis of Hardening Distortions of Drawpieces Produced in Hot Stamping Process" Metals 11, no. 3: 457. https://doi.org/10.3390/met11030457