Injection Molded Screwdriver
Overview
Completed Spring 2024
This project was part of my fixturing and tool design class at Cal Poly. The goal was to design and manufacture a cost effective and functional screwdriver handle utilizing injection molding. The project included design of the handle for effective injection molding, as well as complete design and machining of an aluminum injection mold. The handle is Vydyne 41H black nylon that is over molded onto a #2 Philips head screwdriver blade.
Design
Both the mold and handle were designed in Solidworks. For the handle I used a skeletonized design that shows off the screwdriver blade through the middle of the handle. I kept all of the walls the same thickness to allow for even part cooling after the mold, with the one exception being the area where the back of the blade is contained with the handle since I did not want the screwdriver to break free during use. All edges and corners are rounded off to make the handle comfortable and to prevent excessive stress from building up during molding. All vertical walls have a 3 degree draft to allow the part to be removed after molding
To make the mold I started by scaling up the handle part to account for the shrinkage of the plastic during cooling. The scale factor was calculated using the data sheet for the Vyndyne 41H nylon. The scaled handle was arranged inside the mold blank, and subtracted to create the mold cavity. After the main cavity was made I added in a sprue and runner system for the liquid plastic, as well as alignment pins to locate to mold halve to one another. I also added sketches for the Cal Poly “CP” logo as well as my initials to be used for an engraving toolpath during machining.
Manufacturing
Each half of the mold was cut out of aluminum using a HAAS VF2 CNC mill. The toolpaths were programed in HSM works which isn’t my favorite CAM software but it is what we were using for the class. Once the mold was cut we used the slots on the bottom to clamp the mold in place on the machine. There is a bore on the bottom face of the mold that locates it in the center of the injection molder’s mounting plate to ensure correct position of our setup. Since the screwdriver blade was not fully contained within the mold we added two screws to the mounting plate to keep the blades in place under the pressure of the injection. Each injection cycle yields two screwdrivers, and the runners are designed to easily break away without the need for any extra tools.
