Additive manufacturing to the wider public more commonly known as 3D-printing technology or "3D printing" is a production technology where the material is added layer by layer. Several methods of additive production have been developed. They differ in the technology for layer creation and the materials used. One of the most widespread technologies is the Fused Filament Fabrication (FFF). FFF is a technology in which the deposited thermoplastic material filaments are applied to the working surface, layer by layer, by means of a mobile nozzle. In order to obtain a quality finished product, it is very important to prepare the filaments of an appropriate diameter. In this paper the process of PE-HD filaments extrusion was optimized. The experiment was carried out in the Tin 1.1 single screw extruder, which has the ability to regulate the temperature, engine power and speed of the puller. The optimization was carried out in the Design-Expert computer program and optimal conditions were obtained for obtaining an ideal diameter of 1.75 mm and a minimum standard deviation. Eight different combinations of conditions were found in which the desired diameter values and small standard deviations were obtained. The first combination, with the highest likelihood, gives a diameter of 1.76 mm, has the smallest standard deviation of 0.07 mm and is achieved at a temperature of 190 °C, a power of 45 % and a puller speed of 9 mm/s. In order to gain insight into the speed of filament production, a second analysis was carried out with the given criteria: the maximum speed of the pullers as the most important response, the temperature and engine power as the least important responses, and diameter of 1.75 mm and minimum standard deviation as the medium-important response. By optimization, only one combination of conditions giving a 1.75 mm diameter has been obtained, it has a small standard deviation of 0.08 mm, and is achieved at a temperature of 170 °C, a power of 78 % and a pull speed of 21 mm/s.