How material selection influenced the design of Tesla’s head-turning new electric vehicle
18 December 2019
To say that the Cybertruck is different is an understatement. Since its launch, people have talked about its high towing and payload capability, longer driving range, increased battery capacity and reasonably tiered pricing. However, most of the discussion pertains to Tesla’s bold aesthetic design. Here, Ben Smye, head of growth at materials search engine Matmatch, examines the influence of material selection in the design and aesthetic of the vehicle.
The Cybertruck sports a radical, futuristic look and does not follow the conventional pickup truck form, which is precisely one of the things pointed out by Elon Musk that hasn’t changed much for a hundred years, since the early 1900s. Looking at the conceptualisation of the Cybertruck, is the planar design just a whimsical decision or a result of material choice and manufacturing considerations? Let’s take a look at these factors.
The Cybertruck exoskeleton steel grade
The Cybertruck exoskeleton is made from Tesla’s own stainless steel alloy, referred to as the “Ultra-hard 30X Cold-rolled Stainless Steel”. While the blend is proprietary, Elon mentioned during the product launch that the exoskeleton material of the vehicle is the same as the SpaceX Starship shell. If that is indeed the case, Musk has previously confirmed in an interview regarding the use of high quality 300 series stainless steel for the Starship as the material of choice instead of the advanced carbon fiber that his team was initially working with.
Stainless steel was decided to be utilised for the Starship due to the following factors:
• Stainless steel costs half of the advanced carbon fiber material
• It can withstand cryogenic temperatures for ascending
• It has a high melting point for spaceship reentry.
The initial material for the Cybertruck skins was supposed to be titanium but, with this, it can be deduced that the stainless steel “30X” is a kind of steel grade under the 300 series code.
The AISI 300 Stainless Steel Series
The 300 stainless steel series is a subcategory of alloy that belongs to the austenitic stainless steel family. Austenites have a face-centered cubic crystal structure. The 300 steel series, particularly, has a typical chromium content of 18 per cent, 8 per cent nickel and 0.1 per cent carbon.
Austenites perform in a wide range of temperatures, are non-magnetic and have excellent corrosion and oxidation resistance. They can withstand scratches and have attractive surface finish properties.
There are many steel types under the 300 series, the most common of which are 304 and 316, mostly used for chemical processing equipment, home and commercial applications, aircraft as well as some industrial machinery. Type 301, the steel mentioned by Musk for the Starship, is a stainless steel type that has excellent corrosion resistance and possesses a high strength to density ratio after hardening. Also, this type of stainless steel can only be hardened through cold working.
The combination of these properties makes the 300 steel series grade a compelling choice as the Cybertruck exoskeleton material. It is also likely that Tesla has re-engineered and enhanced its properties further to create the dent-free, bullet-proof Cybertruck exterior.
What is cold-rolled stainless steel?
Another known aspect of the Cybertruck shell is how it was processed. Cold rolling is a type of work hardening and finishing process that compresses hot rolled steel in between a series of power rollers in order to make harder and thinner steel sheets.
Cold rolling, implemented at room temperature, is done after the hot rolling process to achieve dimensional accuracy, improve strength and enhance surface finish. Hot rolled steel is prone to shrinkage as it cools down and has a scaled feel as a result of cooling from extreme temperatures of over 1700 °F (927 °C), above the steel recrystallisation temperature.
In a stress-strain curve, cold rolling applies stress beyond the material’s elastic deformation limit or its yield strength, into the plastic range in order to permanently change the material structure plastically. As pressure is applied to the hot rolled steel in the cold rolling process, the granular and crystalline structure is elongated and dislocated along the direction of the roll, which increases the yield strength of the material than its prior state.
It also produces steel that has high-tension breaking resistance and increased resistance to deformation. Since cold rolling is a further process of hot rolling, cold-worked stainless steel comes at a higher cost. Cold rolled stainless steel is right for applications where high precision, high strength and better surface characteristics are required, just like the paint-free Cybertruck.
New automotive manufacturing process
Besides the material used in the Cybertruck, Musk clarified that Tesla went with the planar design as a result of the cold-rolled 30X stainless steel’s capability to break a stamping press. Whether that statement is said in layman’s terms or the material is indeed too hard for pressing, the key implication is that Tesla would have to devise a new body manufacturing method that does not apply standard automotive manufacturing techniques.
Musk has shared that the body panels will be laser cut and that standard stamping was not implemented in the Cybertruck prototype. Besides the impact on aesthetics, this new body manufacturing method will provide Tesla the flexibility to adjust, reduce cost and improve manufacturing time with its simple flat panel design.
Cybertruck and Tesla’s mission
In conclusion, it is apparent that the material selection and the manufacturing considerations played a key part and influence in the design and aesthetic of the vehicle. Tesla’s priority is to deliver an excellent, environmentally sound product at a reasonable cost to make the technology available to the mass market.
The choices implemented in the Cybertruck might be polarising and divisive as some may perceive, but its popularity and growing demand is in alignment with Tesla’s mission; that is to accelerate the use of sustainable transport to the masses as soon as possible.
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