INTRODUCTION TO CAD
Fall 2018
For her final project in the Boston University College of Engineering's ME 359 Introduction to Computer Aided Design (CAD) course, students were tasked with the project of dissembling at Black&Decker Li2000 Screwdriver. Using the dissembled screwdriver, students had to model the gearbox in Creo, analyze how the gearbox worked mathematically and create engineering drawings of the parts modeled. The students also had to analyze different parts of the screwdriver to determine how they work and even had to do a little bit of basic circuits to show how the forward/reverse button in the screwdriver worked. This large project was to showcase the cumulative skills that Amy had learned throughout the semester, and the portfolio below is her interpretation of this project.
BLACK&DECKER LI2000 SCREWDRIVER
Computer-Aided Design Functional Models of the Multi-Stage Epicyclic Gear Train
PRODUCT STRUCTURE
This image is a graphical representation of the complete product structure of the Black&Decker Li2000 Screwdriver.
GEAR BOX ANALYSIS
Why would Black&Decker choose to use an epicyclic gear train for their screwdriver?
While although there are many types of gear trains that can be utilized on the market, the reason that Black&Decker chose to use an epicyclic gear train for their Li2000 screwdriver is for two main reasons: design flexibility and power output. The design of the epicyclic gear train found in the Li2000 screwdriver allows for a multi-stage gear train setup in a relatively small and compact battery pack easily. Likewise, the design of this epicyclic gear train allows for the planetary pinions to share the same axis which distributes the load among the other components of the gear train which means less wear and tear of the gear teeth and then subsequently, a longer life span. The large number of planetary pinions in the gear train also increases the amount of power the gear train can handle, increasing the marketability of the screwdriver.
DMFA: ASSEMBLY MISTAKE-PROOFING
MOTOR CASING DEISGN
An example of the usage of DMFA in the Black&Decker Li2000 screwdriver is how the motor casing was designed. The outer and inner diameters of the motor casing have designed indentations that insure that the only way to assemble the screwdriver is to have the motor and gearbox aligned precisely so that both components join perfectly.
U-SHAPED PIN DESIGN
Another example of the usage of DMFA in the Black&Decker Li2000 screwdriver is how this U-shaped pin was designed. The pin and the casing of the screwdriver were designed so that the U-shaped pin can only enter in one direction, making sure that the screwdriver is only assembled in one way, lowering chance of injury due to mistake in the assembly of the screwdriver.
GEAR SHAPED DESIGN FEATURE
Lastly, a third example of the usage of DMFA in the Black&Decker Li2000 screwdriver is how the orange plastic casing and the black battery handle have been designed to join together like a gear. An interesting design feature is how both gears on each casing are missing one tooth of gear. The reason for this design feature is to make sure the two parts are placed back together the same way each time.
HOW DO THESE PARTS WORK?
HOW DOES THE FORWARD/REVERSE SWITCH WORK?
The forward/reverse switch on the Black&Decker Li2000 screwdriver is essentially a small circular ring underneath the plastic casing that is attached to a circuit in the battery pack. When the switch is pressed forward, the movement of the ring causes the switch to activate the motor, causing the current to flow in one direction. When the switch is pressed backwards, the ring rotates backward, causing the switch to activate and change the flow of the direction of current.
HOW DOES THE TOOL HANDLE PIVOT LOCK WORK?
The tool handle pivot lock on the Black&Decker Li2000 screwdriver gives the user of the product the choice between choosing an automatic or manual option for using the product. By pressing downwards on the cap of the pin, a gear underneath the cap is compressed and allows the handle to move positions.
HOW DOES THE POWER/MANUAL OPTION WORK?
The power/manual option of the Black&Decker Li2000 screwdriver works by allowing the user of the product the choice between choosing an automatic power option or a manual power option. By choosing the automatic power option, the planetary carrier and ring gear work separately within the gear box. However, when the user chooses the manual power option, the ring gear separates below from the carrier to prevent it from moving, locking the two gears in place.
REFLECTING: WHAT I LEARNED FROM THIS PROJECT
Though this final project was a means of testing my understanding of the material covered in the course this semester, the most useful skill I learned from this assignment was not anything CAD related, but more on the professional development side. Before this project, I did not know what an engineering portfolio was, nor even had one. Now though, mainly because creating an online portfolio was a recruitment of the project, I have both the knowledge of what a portfolio is and my very first one as well! Though it was excruciatingly work to create my first portfolio, I know that is incredibly beneficial for myself as an engineer and as engineer who wants a job. I cannot wait to expand on my portfolio in the future and compile my future projects within it.