Use

The cell holders will hold the cells in position so that there is no strain put on the spot welds. Our cell holders are made from 3/8" Acetal. Acetal was chosen mainly because of its ease of machining.

We will have 2 different cell holders in the car, one for the top of the modules and one for the bottom of the modules. The top module has holes for mounting the gusset plates to. The bottom plate has location features to allow placement in the box, and will restrain it in horizontal motion. The two acetal plates are connected with 60mm aluminum standoffs.

Relevant Specs

Acetal (not Delrin), 3/8" thick

Amount Required

We want about 30 sq feet of 3/8" acetal sheet.

Source

We will be getting our acetal from Piedmont Plastics in Kitchener. They were the cheapest source we found for 3/8" black acetal sheets. The next best option is Plasticworld.ca in Toronto. The material will come in a large sheet and will need to be cut before machining. We are getting a full 4x8 sheet of acetal cut in to 8" x 6" pieces.

Manufacturing

The acetal will be machined to shape on the HAAS VF2 in the student machine shop. Brian and Graeme have been super helpful getting set up with this.

We need to program the toolpaths in MasterCAM, and try not to throw any curveballs at them while creating them. Try and stick to the non-dynamic paths, as that is what they are used to.

Cut acetal sheets to size for the mill, keeping edges as straight and square as possible. The student shop might be getting a sled saw (that's probably not the technical term) in the next week (Nov 20?) that will help with this - we will be getting the sheets cut to 8" x 6" for us by Piedmont Plastics.
Perform a first milling operation that will drill counterbored holes. This operation will be with pieces held in the vise. The holes will allow bolting the acetal to a fixture plate for the next operations.
Second milling operation - the acetal will be bolted to the fixture plate using the holes drilled earlier. In this operation, we will do the facing and busbar pocket, as well as locating holes for the next operation
Then flip the piece over, use the location holes to position and machine the cell pocket, heat set insert holes, and aluminum standoff holes

There is a fair bit of machining (probably 2-3 days worth) that will need to be done.

After machining, we will need to do some manual deburring, especially around the 1/4" holes.

Then round off the edges on the bottom piece, and the bottom edge of the top piece to have easy module insertion and removal. Probably using a 1mm radius router bit. Doesn't have to be a perfect 1mm radius, but would be nice. A router sled and a bit for the Dremel will need to be acquired / made.

Manufacturing Files

These are the original manufacturing files sent to get quotes for machining the capture plates:

Linamar

Linamar has offered to 3D Print some parts for us. Given the quotes we received for machining and the quality of the 3D printed prototypes that we have been able to produce on our Prusa MK2.5S, we think this part would be a great candidate.
Here are the files we should send to them (Updated Jul. 14, 2020).

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