heat. The stator is now complete and is inserted into a heated metal case, locking the stator inside as the case cools. A worker uses a hoisting system to insert the rotor inside the stator completing the construction of the motor. Additional drive unit components A worker then installs the differential and other sections of the gearbox, attaching it together using bolts. An air leak test is then conducted. The three phase tripole power inverter is then installed onto the top of the motor to convert direct current from the battery into alternating current for the motor to use. The motor then undergoes a series of automated tests taking 4 minutes to ensure correct function, and then is moved to the general assembly area to be installed into the car. The power inverter is constructed from metal–oxide–semiconductor (MOS) power transistors. Early Tesla vehicles used MOS-controlled insulated-gate bipolar transistors (IGBTs), which have been replaced by silicon carbide (SiC) power MOSFETs (MOS field-effect transistors) in later Tesla vehicles since 2018. Battery pack construction The Model S 85s battery pack contains 7,104 '18650' lithium-ion battery cells in 16 modules wired in series (14 in the flat section and two stacked on the front). Each module contains six groups of 74 cells wired in parallel; the six groups are then wired in series within the module. the battery pack uses modified Panasonic NCR18650A 3100 mAh cells with nickel-cobalt-aluminum cathodes. The use of commodity cells, similar to those found in laptops and mobile phones, is in contrast to every other electric vehicle manufacturer who use specialized large format Li-Ion cells. The liquid-cooled battery pack uses an intumescent gel to aid in fireproofing and even heat distribution. Body construction Aluminium coil blanking 98% of the Tesla Model S body is constructed from aluminium and is produced from between 50 and 60 separate coils of aluminium each for various components. The coils are unwound, flattened and cut in a blanking machine; additional cutting is also done using a laser cutter. The total weight of the aluminium used in the Model S is around . Tandem press lines A robot then transfers the aluminium blanks into the tandem press lines where the sheets are stamped into the various panels of the cars. The Schuler SMG hydraulic stamping press line is the largest in North America and the 6th largest in the world. The presses use up to 11,000