Reverse Engineering of RYOBI Circular Saw

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The objective of the project was to perform reverse engineering of the RYOBI circular saw and redesign the saw based on Design for Assembly (DFA) and Design for Manufacturing (DFM) analysis. The analysis conducted was based on the Boothroyd and Dewhurst methods. The project also involved developing function model,requirement list, bill of materials, connectivity graphs and FMEA of the circular saw. Further, based on the DFA and DFM analysis design changes were implemented to reduce the manufacturing and assembly cost. In the end all the findings were compiled into a technical report.

RYOBI Circular Saw

Design for Assembly (DFA) Analysis

Design for Assembly analysis was conducted based on Boothroyd and Dewhurst method, it was determined that three design changes are required to reduce the assembly time. The first design change was to integrate the Back-light Housing into the Back-light Ring. The light was originally held within a plastic housing that was clipped onto a plastic ring concentric to and within the motor housing. In order to improve the assembly time, the plastic housing was integrated with the ring. This saved one assembly operation accounting for 3.13 seconds. The second design was to combine the two springs on the Lower Blade Guard into one spring with pins on its ends. The retractable Lower Blade Guard was originally held in place on its spindle by two springs-one with pins on its ends and one without. These springs also made it a retractable part. This redesign change saved 9 seconds of assembly time. The third redesign implementation involved the dust nozzle subassembly. The dust nozzle in the original design was made up of two parts, clipped onto each other to make one nozzle and then fastened to the blade guard using a screw. These two halves become one part. Additionally, the screw fastening process was eliminated by adding a cantilevered ‘hook’ to one surface of the dust nozzle so that it would snap-fit onto the blade guard, thus saving a screwing operation. Overall, these changes for the dust nozzle subassembly saved about 15 seconds in assembly time.

Injection Molding Design for Manufacturing (DFM) Analysis

After performing a design for manufacturing analysis on all injection molded parts, it was determined that two design changes should be implemented. The first change, as previously mentioned in the DFA analysis, was to combine the Dust Nozzle Outer End and Inner End into one part. This change resulted in decreased of 59 percent in the relative mold cost . The second design changes was to combine the Back-light Ring and the Back-light Ring Housing into one part. The change resulted in a decrease of 61 percent in relative mold cost.

Die Casting Design for Manufacturing (DFM) Analysis

Four parts were analyzed using the Design for Manufacturing methods for die casting. These parts include the Upper Guard, Lower Blade Guard, Base, and Rotor Housing. Two redesign changes suggested for all of these parts were to decrease the cavity details and to remove all cast-in inserts. The cavity detail was decreased on all of the parts; however, only in the Lower Blade Guard did it decrease the subsidiary complexity rating. In regard to the cast-in inserts, it was assumed that all internal threads in hollow bosses were cast-in inserts for the analysis. Therefore, it was being suggested that these threads be machined after the casting is completed, and not to be made by using cast-in inserts. This change decreased the relative cycle time for each part and therefore its processing cost. One redesign suggestion specific to the Lower Blade Guard was to reduce the wall thickness to the point where it is uniform throughout the part. In the original Lower Blade Guard design, the wall thickness increased greatly towards the center of the part; however, it was suggested that the wall thickness remain uniform throughout. This improved the basic relative cycle time and therefore the processing cost. In regard to the Base, it was suggested that gussets be added to support the rib wall, as this would reduce its basic relative cycle time and processing cost. The design changes resulted in the part cost reduction, involving 11 percent for Upper Guard, 2 percent for Lower Blade Guard, 1 percent for Base, 6 percent for Rotor Housing.

Some of the design changes implemented are: