Method for producing a vehicle part consisting of a polymer material

A method for obtaining a motor vehicle part having at least one visible surface extending up to a portion of an edge of the part, the part being formed by a skin of a polymer material, the thickness of which is significantly smaller than other dimensions of the skin, the method comprising the steps of:

• injecting the polymer material into a mould comprising a cavity in at least two contiguous sections, the at least two contiguous sections comprising a main section for forming the part and at least one additional section for forming an add-on for the part, the additional section extending over a length ranging from 10 mm to 30 mm, the thickness of the at least one additional section at a junction with the main section being at most equal to the thickness at the junction of the main section and at least equal to the thickness at the junction of the main section decreased by 0.5 mm, and the at least one additional section being arranged between an entry point of the polymer material into the cavity and the main section;
• separating the part and the add-on by cutting to form said portion of an edge of the part, wherein cutting is carried out with a position tolerance with respect to the junction of less than 0.5 mm and a cut obtained has no bead and no roughness;
• creating an incipient break at the junction between the part and the add-on and reducing the temperature of the junction to a temperature less than or equal to the embrittlement point of the polymer material;
• and then
• once the temperature of the junction between the part and the add-on is less than or equal to the embrittlement point of the polymer material, mechanically breaking at the junction,
• wherein the step of creating an incipient break at the junction between the part and the add-on consists of forming a sharp angle at the surface of the junction, and
• wherein the sharp angle is formed by creating, at the junction between the part and the add-on, a groove using a blade after ejecting the part and the add-on from the mould.