The purpose of our sponsored project is to develop an environment control system for the 3D printing chamber that can maintain a chamber temperature of 50±5°C in environmental conditions ranging from -15°C to 50°C. This will allow for the use of a wider range of military grade material in printing production. We will be accomplishing this by modeling temperature loss under various environmental conditions, developing insulation methodologies, and optimizing the chamber system. Our project deliverables will be integrated into the beta prototype for the Craitor 3D printer. 

Our Executive Summary can be accessed here.

We first conducted market research on consumer grade solutions that could assist in the development of the heater block, either as a solution to directly integrate, or to model off of. Next, we developed an analysis of the given constraints (power limitations, reasonable efficiency, and insulation specifications) to determine the current feasibility of the constraints and determine whether it is necessary to alter the goals and/or specific constraints. Next, we finalized the scope of the project once we had a better understanding of complexity of the technology and what had to be designed as opposed to integrated off the shelf solutions. Finally, we developed CADs and ran an initial proof of concept thermal simulation to present as our risk reduction.

Our current environmental control design consists of four main components:

• A Stergo PTC Fan Heater, mounted along the right interior wall near the bottom corner to heat up the interior chamber to the target temperature

• A layer of 1-inch Polyisocyanurate Insulation, along the interior walls of the printing chamber to reduce heat loss and protect electronics

• An SSRK-240D20 Solid-State Relay, to control the heater to maintain the target temperature

• A 100K Thermistor, to sense and measure the ambient temperature of the printing chamber

(A more in depth look at our components and design considerations along with assembled CAD is on our Final Design page.)

Predictions

The performance was predicted before each test by both a closed-form solution and a finite element simulation using ANSYS and Fusion 360. In either case, the assumptions made are identical, that is:

• Steady-state (time-independent)

• The insulation sheet in perfect contact with the aluminum shell

• The internal temperature not dependent on the position

• Perfect free convection (the printer is not in contact with anything other than air)

• Radiative heat loss negligible due to the reflective layer on the insulation sheet

Under such assumptions, the total heat loss from the chamber and the external shell temperature of the aluminum shell could be predicted and compared with the results from testing.

(Closed form solution and simulation results are further detailed in the final report. Files are found under the CAD and Code tab)

Performance

The initial proof of concept was tested with Aluminum foam insulation as a stand-in for the optimal insulation to reduce cost and confirm the validity of our model. The system was tested within a prototype that was lent to our team by Craitor. Because this was not the finished system, we could not test at the target temperatures to start. The first test consisted of the application of the heater and the insulation and then heating the chamber to 50◦C. After leaving the printer to reach steady-state (when the external temperature no longer increases), we measure the temperature on the inside of the chamber wall and the temperature on the outside of the chamber wall, along with the ambient temperature inside and out the chamber. The internal and external temperatures for each side were taken to be the average temperature between three locations on that side. For consistency, measurements were taken on tape using an infrared thermometer.

Temperature values are measured both with and without the insulation integrated to the chamber. Using these values plugged into the closed-form solution and the simulations developed on ANSYS and Fusion 360, we were able to verify the validity of the model. For the second test, we integrated the optimal insulation and ran the printer at the target value of 70◦C at room temperature to start to verify that the adjustments to the model, and the given values for the optimal insulation, were accurate.