The Aptera Forum
Thanks, fixed it!
What are the embedded (into the composite structure) parts made of?
Marine environment: northeast US, the rust belt.
I have a neighbor with a 2002 Focus with 75000 miles with a completely rusted out rear subframe. A little galvanizing would have avoided that.
Are there any renderings or drawings of the various components?
Northeast US: Oh, right. Some states still use salt, so ya, that's virtually a marine environment! I'm pretty sure one Aptera co-founder actually has a boat company, so that could be a good influence, & the car does seem easier than most to hose down the metal parts. Too bad about your neighbor's Ford, because now I guess you need to ask about corrosion control on every vehicle you buy! Sorry I can't help you more, but I've seen some computer images that others may be able to send.
@philsfcs and @kiteboarder.. My team is in the middle of researching the total life cycle costs of mid-sized metal parts* out of 316 stainless steel vs anodized aluminum vs powder coated steel. My prediction is that stainless will win out when advanced 3D printing is used to minimize the amount of the stronger metal is needed.🧐
I promise to post the results as soon as available.
*This would include parts like Aptera‘s front a-arms and rear swing arm. Maybe even the entire front tubular sub frame made in one piece.
Aptera is going to pursue a material that has a high specific modulus and strength, meaning aluminum or possibly titanium. Stainless steel isn't the best choice. My guess is that they are 3D printing wax parts, coating them in plaster of paris, doing a lost wax casting of aluminum, machine the precision joints, them zincate, electroless copper, heavy electroplated nickel, followed by multiple layers of powder coating. A similar finish is used on fake chrome wheels. In fact, maybe Aptera should put a fake chrome finish on their chassis parts just for the cool factor.
@Jeff Petsinger I really appreciate your comment. This is an extremely interesting metal exercise due to all the variables involved.
Note that if you add all the costs associated with the processes you creatively lay out, and then add in the time, labor, and equipment needed to do these multiple processes, the "specific modulus per unit dollar"* for aluminum plummets. Titanium fairs better but is still low due to material and machining costs.
In the upper A-arm example, 3D printed stainless steel could be about 18% lighter in weight as it can be made hollow. Therefore, a straight specific modulus comparison does not reflect this coring capability not available with casting. Furthermore, stainless is neither brittle nor require any secondary coating for corrosion resistance, the subject of this thread.
*"Specific modulus per unit dollar", where the unit dollar variable contains ALL life cycle costs, is what I am comparing.
As promised, here are some initial comparative numbers for "Unit lifecycle cost per Specific Modulus (tm)"* for a theoretical front upper A arm:
316 Stainless built using DED Additive Manufacturing, no coating: $99
Steel Stampings, welded together, then powder coated: $162
CNC Aluminum milled from billet, then anodized: $270
Aluminum casting, anodized: $351
Aluminum laser sintered Additive Manufacturing, then anodized: $1,361
* A quantitative measure of the relative cost of making a strong, lightweight part.
From my salt water experience, like pictured above, powder-coating will bubble, peel & rusts about as fast as any other paint. Anodized aluminum lasts pretty well, but still eventually corrodes, & is more subject to fatigue failure than any kind of steel. Stainless steel is ideal for longevity, & as you note, when optimized it can be cost-effective and also pretty light.
I'm pretty sure the metal parts are aluminum. Ideally hard-anodized, but even just paint would be fine for non-marine environments.
Garaged all its life!
Yikes! That's a little scary.
It doesn't look like any of the discussion mentions the embedded parts (embedded in the composite body structure)...the parts that cannot be repaired/replaced...what the subframes are attached to. those have to be strong and absolutely not allowed to corrode.
SAAB used galvanized subframes and they have performed very well around here.
My verdict on powder coating: nope. The least defect on the coating traps moisture below and the cancer grows almost faster than bare metal!