First, we disassembled the wrench and used multiple tools including an optical comparator to precisely measure each part. We also performed a six sigma analysis on the “jaw” component to learn about the inconsistencies in manufacturing processes and how properly tolerancing your parts to account for tolerance stack up. We also determined areas of each part that required tighter or looser tolerances depending on the functional requirements of each part. Using this knowledge, we designed fixtures to hold the wrench during the assembly process that would allow us to consistently assemble quality wrenches.

Gaining Understanding

During the project, I designed the fixtures for my team. I observed that there were three riveting stages that needed to be accomplished in a specific order. The three stages were the assembly of the inner plates, then the assembly of the outer plates onto the inner plates, and then the assembly of the jaws onto the head of the wrench. My goal was to create fixtures that would assist in riveting the wrenches in the fastest, most efficient manner. The jaw assembly stage appeared to take the most time as it had the largest number of individual components involved. This led me to design one fixture specifically for this jaw assembly step. I decided to combine the other two steps to save on material and improve manufacturability since some of the locating pins could be used for both steps.

Main Fixture Design

While observing the wrench parts and manipulating them in different scenarios to simulate potential manufacturing processes, I found that using a sliding motion to move the part from point A to point B was faster than picking up the wrench and putting it down again. This led to the problem of being able to accurately slide from one riveting location to another. I realized that since our CAD model was highly accurate, I could create a pattern for riveting by connecting the rivet locations on our CAD model of the wrench assembly. This led to our final fixture design which consisted of two plates- one was made from high-strength steel that the wrench and rivets were placed directly on. This allowed for a strong surface that would not deform easily when subjected to the force of the riveter. This main plate had steel pins that held the parts accurately in place and two locating pins that fit into the transition plate. The second plate was this transition plate- it was laser cut from acrylic for easy manufacturing and consisted of the pattern I created, which was repeated for locating accuracy and the locating pins from the main plate would fit into. This transition plate also located the entire assembly on the riveter.

Jaw Fixture Design

In addition to the main fixtures, I also created the jaw fixtures. When looking at the jaw rivets, I saw they were organized in a hexagonal pattern. Experimenting with this configuration led to my final design- a hexagonal base that supported the wrench head and could freely move around in the hexagonal pattern provided by the transition plate. Due to time constraints of the class, we found that the fastest, most accurate, and most precise way to create our final prototype would be to laser cut the main body of the plate and then drill holes and insert steel pins to have a hard surface to rivet on.

Production System Design

These fixtures then informed the design of our standard operating procedure. After performing multiple trials with this procedure, which involved laying out the components spatially similar to the desired workstations and then using our fixtures and the riveter to completely assemble a wrench, we had a rough time estimate of how long each step of the manufacturing process would take. This allowed us to create our value stream map and design work stations that were as similar in time as possible to minimize inefficiencies.

I learned about the importance of the assembly-line worker when designing for manufacturing. The assembly-line worker is the one who will ultimately bring your design to fruition. Therefore, it is important to consider their needs to help create a safe, efficient environment that will allow them to excel at their job. I also successfully completed the time trial for our team and produced the most wrenches in 30 minutes out of the entire class.