Hot Wire Tool
February 2019
This project, which was completed with a group of 3 other students, was meant to introduce molding and casting processes to create components of prototypes. By creating an ergonomic hot-wire tool, the team was able to display the ability to create a functioning prototype using additive technologies as well as the previously mentioned molding and casting processes. The function of the end product was a foam-cutter in the shape of a hand gun, complete with finger forming indentations to maximize comfort during use.
Goals
By completing this project, further development of CAD skills, manufacturing skills in the form of molding, soldering, fixturing, and 3D printing, and teamwork skills will be gained. Our team will also gain experience with using simple circuitry.
The Assignment
Given 6 inches of 20 AWG nichrome wire, 16 inches of 20 AWG copper wire, and electronic components, our team will create a general hot wire tool product by controlling the current from a DC power source. Processes to be utilized to create the tool include casting, molding, 3D-printing, and fastening. The end goal of the product will be to "allow its user to shape, join, or apply finishng processes to thermoplastic materials," (E. S. Gutierrez-Wing, 2019). The final product design must be ergonomic and easy to use, and must utilize a switch to control current flow into the nichrome wire (thus heating it).
Original Design
Initial ideas for possible products all spanned creating a simple foam-cutter. Though the product's function was agreed upon by all members, initial designs varied greatly between the four of us. Such drawings are shown below.
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Final Design
The final product idea for the foam cutter consisted of an angled hand-gun shape with finger indentations on the base. In the "head" of the gun, the nichrome wire is attached in the strands of copper wire on either end, and is formed into a loop that will peak out of the gun. In order to insulate the gun from major heating, plaster is molded around the base of the nichrome wire, leaving the looped tip free to heat and the two strands of copper wire free to be manipulated from the other end.Â
Heating will be achieved by connecting the copper wire to a source of current. Current will run through the copper wires and into the nichrome wire, which will heat and therefore achieve its goal of cutting foam. A power switch will be connected to the wires to control the obstruction or otherwise of the current flowing through the circuit, thus controlling heating.Â
Outside components of the foam cutter will be 3D-printed using FDM printing in the Boston University Engineering Product Innovation Center. The solidified plaster/wiring will be placed inside the 3D-printed mold, and the switch will be inserted inside of the hole made for the switch. All wiring will be threaded through the mold and wires will peak out the end, where power will be provided. To keep the design ergonomic, finger divets were added for comfort, and the design is at an angle such that the user's hand does not get too tired during use.
Manufacturing and Assembly
Manufacture of the final design first consisted of 3D printing the CAD model. During printing, CAD modifications were made such to close the square hole on one side of the gun, since the power switch would only be visible on one side. Modifications of the 3D print were made post manufacture (via filing, hand drilling, and tapping) to account for any size inaccuracies created by the 3D printer.
The next step in manufacture was to create the plaster-covered nichrome wire. Nichrome wire was looped with copper wire, forming the exposed tip at one side and the copper-nichrome loops on the other side. The plaster was molded into the desired cylindrical shape via a syringe, and was left to harden. Once hardening was complete, the plaster was sanded in order to fit inside the 3D print.
The on/off switch was next inserted into the square hole. Copper wires extending out of the plaster were soldered to the on/off switch to form a complete circuit that would function when provided with a power source.
With soldering finished, the two sides of the 3D prints were joined using screws. The final design proved to be ergonomic as it was able to be held in multiple positions, as shown. The final design also achieved the team goal; the wire successfully heated without overheating the ABS shell, and effectively was able to cut through foam, as shown in the photos below.
Results and Discussion
The end result of the hot wire tool achieved the goal of generating enough heat to cut through foam. The end design was ergonomic and able to be held with a number of hand positions. The plastic casing also was able to resist heating for long enough as to not become too hot to hold in a given amount of time. Overall, the end result of the hot wire tool was successful, and met aesthetic and functional specifications.
