Mechanical and Mechatronics Engineering
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This is the collection for the University of Waterloo's Department of Mechanical and Mechatronics Engineering.
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Browsing Mechanical and Mechatronics Engineering by Subject "22MnB5 steel"
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Item Developing and Improving a Thermometallurgical Model for 22MnB5 Steel in a Roller Hearth Furnace(University of Waterloo, 2022-04-29)Ultra-high strength steel (UHSS) such as Al-Si coated 22MnB5 are commonly used in the hot forming die quenching (HFDQ) process to produce light-weight automotive parts while maintaining good crashworthiness. The steel blank is typically austenitized in a roller hearth furnace, according to independently set heating zones and other parameters such as roller speed and part spacing. Most often these parameters are chosen heuristically based on experience, resulting in sub-optimal efficiency and part quality. To improve process efficiency and ensure complete austenitization before forming, a complete thermal-metallurgical furnace model that predicts the blank heating profile and the austenitization progress inside a roller hearth furnace is needed. This work introduces a framework for the furnace model, then evaluates three candidate austenitization submodels of different levels of complexity, including: a first order (F1) kinetics model, an Internal State Variable (ISV) model, and a phenomenological model. To address the drawbacks of conventional goodness-of-fit model derivation and evaluation method, the Bayesian model selection technique is introduced and used to evaluate the three candidates. This technique considers the uncertainties in the data, and the trade-off between model complexity and accuracy. Dilatometry data is used to calibrate the models and validate them. The selected austenitization submodel, ISV model, is integrated into the overall furnace model and its performance is validated using roller hearth furnace trials collected with instrumented blanks. The resultant coupled thermo-metallurgical furnace model provides a useful tool for researchers and industrial engineers to maximize production rate and ensure consistent part quality.Item Experimental Characterization and Numerical Modelling of the Interfacial Heat Transfer Coefficient in Hot Stamping of Al-Si Coated 22MnB5 Steel(University of Waterloo, 2023-10-18)In automotive hot stamping of Al-Si coated 22MnB5 steel, the heat transfer coefficient (HTC) between the blank and die is crucial for predicting the mechanical properties of the as-formed part. While average HTCs associated to a range of interfacial pressures are used in hot stamping operations design, in reality the HTC varies during quenching and depends on many other process parameters in addition to interfacial pressure. An improved understanding of the transient behavior of the HTC is the overarching focus here. This work involves an experimental investigation to study the effects of pressure, coating weight, and surface roughness on the HTC evolution. Flat dies were mounted on a hydraulic press to obtain the temperature history within the blank and die. The data was analyzed using an inverse heat conduction algorithm to infer the time-resolved HTC. The HTC increases in two stages with the first being attributed to press tonnage ramp-up that gradually increases interfacial pressure. The second stage is attributed to an increase in the thermal conductivity and volume of the blank as its microstructure transforms from austenite to martensite. The experimental work also highlights how seemingly subtle aspects of this experiment, like the positioning and time-constant of the thermocouples, may impact the inferred HTC. Furthermore, nonuniformity of the interfacial pressure appears to lower the target pressure at which the HTC saturates, and diminish the time-averaged HTC with increasing target pressures. This work also presents a physics-based model that explains and predicts the HTC evolution. The model simulates imperfect contact using the measured blank surface topography, an explicit finite difference scheme to solve the transient heat conduction, and a nonlinear mechanical submodel to solve the microscale displacement of the die due to uniaxial compression of surface asperities. The predicted HTC history is in fair agreement with the experimental result. The model suggests that the evolving thermal conductivity of 22MnB5 does not affect the HTC due to the shielding behavior of the resolidified Al-Fe-Si coating layer at the interface. The model also explains how all hot stamping process parameters influence the HTC and lays the groundwork for a unified model that captures the physics of the entire hot stamping process.