The project is carried out for the Group PSA company. The object of study is the helical tooth in the gearbox of an electric vehicle to understand the noise phenomenon presents during the engagement. The noise from the gearbox can be very disturbing for the driver, even if the noise level from the gearbox is lower than the total noise level. This phenomenon is linked to manufacturing process errors, from cutting process, to grinding process to thermal-treatment process. In order to proceed with the analysis of the problem therefore necessary to study the kinematics of the machines used to manufacturing the helical gear. A MATLAB code was written to simulate the hobbing process to understand the errors.