Wall Hooks
by Caroline Carbo, Jessica Gimbel, Elisabeth Han, and Colin Rockwell
Product Realization Course Project- Spring 2019
Objectives:
-Design and manufacture 10 identical products using low-volume manufacturing methods
-Document the entire process through 7 distinct phases
-Plan for a scale up to mass production of the final design
My responsibilities on the team:
-Updating CAD
-Updating RASCI, schedule, and risk management
-Specifications document
-Tolerance analysis of critical fit and functions
-Control plan
-Quality test plan
-Updating CAD drawings
-Tooling plan
-Act as Project Manager for the concept development phase
1. Idea Proposal
This is the slide that I made as an idea proposal. The other members of what became the team individually chose this idea as the one they wanted to work on for the semester.
2. Down-Selected Concept
After a brainstorming session where we sketched out many different ideas for wall hooks, we settled on the general concept for hooks that rotate around a vertical shaft. The design was chosen because it was the most compact design, seemed inexpensive to make, and marketable to people living in small apartments and dorms. The drawing to the left was the first iteration of the design. Risk factors in manufacturing were identified, team roles and responsibilities were assigned, and a schedule was created. The design also met the course requirements in the following checklist:
3. Initial Concept
A few changes were made to the design to create a suitable parting line and draft angle for each piece since we had decided to mold them. The idea was that these features would also be needed for injection molding if the design was to be mass produced in the end. The design was 3D printed, needed changes were identified, and a tooling plan was created. I have chosen to highlight the tooling plan for the low-volume molds here since I worked the most on this part of the assignment.
In order to go from the hook pattern created in the tooling plan on the right to the finished hook shown in this drawing, the sprues were sawed off by hand; the bottom of the hook was sanded on the belt sander; and the hole was drilled with the drill press. Notice in the pattern that there is a mark so that the drill could be lined up.
After the first half of the mold set, he whole thing was flipped upside down in the box and the parting line pattern was removed. The second half of the mold was poured over the pattern. The image to the right shows this.
The image at the left shows the box with the hook pattern (that includes the sprues) and the parting line pattern (that includes the bumps for alignment). The first half of the two-part mold was poured over this assembly.
The image to the left shows both halves of the mold interlocked. The plastic was poured at the lowest level of the mold and the air was released out of the highest level of the mold.
**The brackets had similar plans but aren't shown here for simplicity.**
4. Engineering Validation Test (EVT)
This validation test was supposed to be us successfully creating one model using the methods that we had designed in the previous phase. Instead we had numerous failed attempts, one of which is pictured here. Unfortunately, we now believe that we were using expired materials, which caused the plastic to be really flexible and never harden. Either way, we never successfully poured this design for the brackets, but the hooks came out relatively okay. We had tried to create a thinner bracket but reverted back to a thicker design for the next iteration since the thicker hooks came out better than the brackets. We also noticed a lot of air bubbles in the parts and decided to degas the plastic in the next iteration. This stage was where we learned the most.
5. Design Validation Test (DVT)
In this validation test, we successfully created two sets of wall hooks.
The standard operating procedures (SOPs) were finalized.
Design flaws were identified.
The following lists changes to be made in the following iteration:
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Replace the plastic rod that had been part of the bracket with a purchased aluminum rod.
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Add black dye to the plastic in hopes of minimizing the visibility of the air bubbles.
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Revert back to using four screw holes so that the brackets would be more secure on the wall.
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6. Production Validation Test (PVT)
For this validation test, we successfully created 10 sets of wall hooks, one of which hangs towels in my bathroom. The main takeaway from having to create so many wall hooks was how difficult it is to create identical parts using low-volume production methods. Looking back, we probably should have used a CNC to achieve better results. The measurement variations can be seen in the below graph and in the photo. We were able to implement all of our design changes. The only change that did not achieve better results was using black dye- it actually made the air bubbles more visible when after belt sanding.
7. Mass Production Plan
The deliverables for scaling up for mass production included the following:
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Cash Flow
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Capital Requirements
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Mass Production BOM and Costs
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Distribution and Reverse Logistics
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DFM Guide
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Final CAD Drawings
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Tooling Plan
The final CAD drawings for the wall hooks assembly and the hook piece are shown to the left.
