I don't buy that the only disadvantage is the increase repair cost of the car in case if accident.
Automotive companies utilize a myriad of frame designs for their vehicles - each one a collection of different alloys, structural shapes and castings depending on the design goals for not only the vehicle of today, but changes that they foresee in future vehicles that would utilize the same basic BIW lines (to conserve capital expenditures, training procedures and inspection methodologies).
There are some automotive companies that rely on some cast product of various sizes in their frame designs. That is not really new.
Tesla is obviously taking some more extreme measures than other automakers, but electric vehicles do inherently put more frame design freedom on the table given that there is not an engine compartment per se to consider in terms of passenger safety.
That said, generally, the disadvantages of large castings in automotive applications are:
1. Poor reparability, and
2. Porosity risks (which can unexpectedly yield structural issues), and
3. Wide tolerances, and
4. Need for a post-cast finished machining process (application dependent), and
5. Long cycle times, and
6. Design space difficulty in managing the weight/strength tradeoff and crumble zone development (application dependent).
Keep in mind that while a casting process may seem simpler that "traditional" BIW lines, those traditional lines are highly optimized and generally very efficient and flexible (often running multiple different kind of frames over a single line) - typically employing above 95% automation. I know Tesla has struggled with their BIW lines in the past in terms of quality. I am not sure of Tesla's current situation having not really followed Tesla's process for a number of months.
The advantage, I suppose, that Tesla is seeing is that they can radically simplify their BIW line.
These kinds of castings are relatively new, and car companies are surprisingly unwilling to spende more than low millions on moonshot tech. It was not an insignificant gamble by Tesla.
Teslas RD budget is tiny, given for much stuff they do in-house - designing cars, autopilot, seats, batteries, robots, solar panel, solar roof, and many others. Their RD is roughly on the level of Mazda, which does much less stuff in-house.
> None of the carmakers do R+D on basic materials and are limited by the commercially available alloy formulas
You really believe that companies that spend billions of dollars per year on basic materials, that are some of the most important for their products, just look at the prodcut catalogue from suppliers and order from there?
That is pretty close to what they do. Modern car companies mostly do integration and final assembly along with some marketing and finance. Vertical integration in the American auto industry died with Henry Ford until Tesla revived it. You could argue that Toyota is somewhat vertically integrated with the cross holdings they have in some of their Japanese suppliers.
Citation needed. What has Tesla been able to accomplish with its inhouse R&D that nobody else has? Other than battery design (using cells developed and manufactured by Panasonic), pretty much everything Tesla does is subpar compared to automobile industry standards.
May I know what is the basis for those claims? As someone who works in the field, I feel very curious to know where you got such a wrong impression.
Materials research has been constantly reducing car weight for decades, at the same time that safety was improved and production costs reduced. New aluminum and steels are developed every day.
For example, the development of high strength steels have been driven by the automotive industry. The contribution of Tesla is merely anecdotic at this point.
If you believe that I have a bridge to sell you...
Pretty much every traditional automaker spent more on R&D last year than Tesla made.
Carmakers have tried unibody frames in the past, and they abandoned them pretty quickly because they're expensive to repair in the event of even minor accidents. (This is also why nobody else does shell cars like the Cybertruck anymore; because any damage to the shell can cause a structural weakness that would require the entire shell be replaced to make the car legally roadworthy.)
With multi-part frames, individual parts of the frame can be made of different materials and stiffnesses based on the physics or safety requirements imposed on that part of the frame. This means that the overall frame can be both stronger and lighter. With a unibody frame, you have to use the same material through the frame, and the only way to adjust stiffness in any part is to control the amount of material used.