ME359 CAD AND MACHINE COMPONENTS
"Modeling and technical drawing in two- and three-dimensions is covered in detail using advanced computer aided-design (CAD) tools. CAD-based assembly, mechanism creation, and finite element analysis (FEA) are introduced. Geometrical dimensioning and tolerancing methods are applied to a variety of tasks and a course project. Other topics include design for manufacturing and assembly, specification and analysis of basic machine components, including gears, bearings, cams and the relationship of those components to modern manufacturing processes."
SCREWDRIVER DECONSTRUCTION PROJECT
Assignment is as follows:
Disassemble the B&D Li2000 Screwdriver
Measure and use CAD to model the driver gearbox
Analyze the gearbox to determine the output torque and RPM as a function of the motor torque and RPM.
Apply the Mechanisms tool in CREO to animate the CAD gearbox.
Create and assembly drawing of the gearbox (with exploded view) and associated part drawings.
Tehcnical Drawings
Created using Creo Parametric 5.0
Gearbox Analysis and Product Structure
DFMA
DFMA was incorporated when B&D designed this screwdriver with a minimal amount of parts. On top of the small amount of parts used, there are very few variety of parts and each part in each category has the same dimensions which means that there is no need for a wide variety of machines to produce those parts (i.e. the screws used). In other words, each part is easily mass produced. Another way is that everything is made from materials that are cheap, abundant, and easily manipulated with which makes decreases the load during the manufacturing process. The screwdriver in general was made to be easily assembled and disassembled. For example, the parts can be laid all on one side of the casing and then it only takes 4 screws to fasten everything in place which cuts down assembly time and complexity. In conclusion, this screwdriver was designed for manufacturing by using only a few variety of parts, readily available material, and by being easily assembled.
Forward/Reverse Switch
This switch controls the direction of the spin of this screwdriver. As shown in the pictures, this switch is connected to the positive and negative terminals of the battery through a metal ring fixed and insulated on a plastic plate. As the user turns the switch, they are completing one of two circuits (one that rotates the screwdriver forward/clockwise and one that rotates the screwdriver in reverse/counterclockwise). Please refer to the circuit diagram for more information (click to enlarge).
Handle Pivot Lock
This lock operates through two pins with gear pitches and one spring. There are two sets of teeth on the longer pin which also are also present on the housing of the screwdriver. The force from the spring would continually push outward which means that the outer teeth are in phase with the teeth on the housing which holds the handle in place. Only when the pivot lock is pressed, do the teeth release and allow the handle to pivot.
Power/Manual Option
The Power/Manual option works by locking and unlocking the front carrier gear in the gearbox. When the screwdriver is in “Manual Mode,” the output gear is locked in place which allows the user to use the screwdriver through manual motion. When the screwdriver is put back into “Power Mode,” the fastener holding the gear in place releases so that the gearbox can once again be rotated by the motor.
The most interesting thing that I have learned from this project is how beautiful CAD can be when planning and constructing gearboxes. My confidence in my ability to take apart and create gearboxes have significantly grown because of this project. I also have a newfound appreciation for how something so simple as a screwdriver can have so much complexity and thought behind it.