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Senior Design: TECS

This capstone engineering project aimed to work on a team to control the core thermal energy of a printed workpiece throughout the additive manufacturing process.

Senior Design is a semester-long course that serves as the capstone of Notre Dame's mechanical engineering curriculum.  Groups are randomly assigned and the class is presented with a comprehensive project that draws upon four years of engineering education.  Throughout the project, each team member was assigned roles, communicated with vendors, wrote technical memos, built the system in the workshop, and presented design reviews to faculty members.  This semester, the objective was to control the thermal energy of a printed workpiece throughout the additive manufacturing process.  The designed Thermal Energy Control System (TECS) controls the core temperature of the workpiece to limit stress, warping, and other distortions due to thermal variance that may occur in the workpiece during the AM process.  A workpiece was used in place of an actual built part.  The goal of the TECS was to heat, dwell, and cool the workpiece to predetermined temperatures within predetermined times.  Emphasis was placed on the capacity of the subsystems to be controlled effectively to heat and cool in designated times.  The temperature of the workpiece itself could not be used in the control system.  At the end of the semester, the system would be tested against a variety of temperature profiles to test for robustness and accuracy.

Initial research into additive manufacturing processes revealed a few possible solutions for both heating and cooling such as radiative, conductive, and current-based.  Each student conducted a trade study to gain an expertise on one aspect and understand specific requirements for that element.  The heating mechanisms used were a heat lamp and a peltier thermoelectric control module.  My individual trade study below was for selection of the radiative heating element and resulted in the selection of the specific model of heat lamp.  See the PDF below for the full report and the various options studied.  Calculations for heat output, convection fan speed, and internal temperature were all performed in this study.

One breakthrough for our group was discovering the possibility of using the peltier thermoelectric control module  as the cooling mechanism for the system through the use of an H-bridge that allowed the module to both heat and cool through this switching mechanism.  A duty cycle was calculated to control the heat lamp to run based off various input data.  The peltier device was essential to the design as it could easily be switched back and forth between heating and cooling making the  dwell periods much easier to control.  Proportional control from the feedback of the external surface thermistor was used to calculate the voltage and the direction of the current sent to the peltier module as well as the duty cycle for the heat lamp.  The controller required many slight adjustments as we ran tests in the weeks leading up to the final performance evaluation.  Our runs from the evaluation can be found in the gallery above.  Using the proportional controller, the internal temperature of the workpiece was able to follow the desired temperature profile.  The control system used MatLab and Arduino software.

Team Members: Jack Gallagher, Will Gaynord, Ellen Londergan


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