One of the most challenging, yet practical courses I took at the University of Maryland was ENME 371: Product Engineering and Manufacturing. In this course, the product we analyzed was a DEWALT DCD701 brushless power drill. Each week, we were tasked with completing tests on DEWALT, Makita, and Bosch drills. We collected data and compared each drill’s performance by compiling the data into lab reports. The final project for this class was simply to use the data that we had collected during the semester to re-design the DEWALT drill, making it more efficient. This project was presented to research and development engineers at DEWALT.
One week, we performed thermal testing on each drill. In this lab, we wired and programmed thermistors to an Arduino Uno to process our data. We then disassembled each drill, attached the thermistors to the drills’ motor stator, battery housing, air inlet, air outlet, and housing grip, and re-assembled the drills. Then, we held the trigger down until failure.
When analyzing our data, we noticed that the DEWALT drill overheated sooner than the Bosch or Makita models. In addition, we noticed that the battery housing saw the most intense thermal loads. Before overheating, the housing reached a maximum temperature of 67 degrees Celsius (153 degrees Fahrenheit).
For our final project, our goal was to prolong the battery life of the drill, by decreasing the thermal load on the battery housing. Our solution was to create a removable heat sink attachment.
Of course, a user is typically not going to use a power drill until it overheats for every application. By making our attachment removable, we were able to allow the user to decide when it is necessary to use it.
Using SolidWorks, we modeled a 6063-T6 Aluminum alloy heat sink. We selected this material due to its high thermal conductivity value of 209 W/(m*K). Performing Finite Element Analysis via SolidWorks, we determined that the attachment could decrease thermal loads from 67 degrees Celsius to 40 degrees Celsius. As the optimal temperature range of a lithium-ion battery is between 20 and 50 degrees Celsius, this project was a success.
This assignment was one of my favorite school projects, and it is definitely the project I am most proud of, as our group received the highest grade in the class for our presentation.
The graph to the right shows the data collected from a thermistor at the battery housing. Notice that the maximum temperature occurs at 67 degrees Celsius. After hitting this maximum, the drill became noticeably less efficient, and eventually overheated.
This image shows the SolidWorks model for the heat sink attachment, dimensioned to attach to the bottom of the battery housing.
This image shows the Finite Element Analysis results of the heat sink. Notice that the bottom of the heat sink is royal blue, and under worst-case load conditions, it stays at a temperature of 293 K, which is roughly room temperature. Though this addition adds mass, it is an important safety feature, as the user’s hand should not contact any area at an intense temperature.