The invention concerns an additive manufacturing process by extrusion for forming a three-dimensional part with an additive manufacturing machine comprising a nozzle, the process comprising:



i) providing a pseudo-amorphous composition having a glass temperature Tg;
ii) softening the composition at a softening temperature above Tg and below 300° C. to form a softened composition which is fluid enough to flow and, extruding the softened composition from the nozzle to form an extruded part section; and,
iii) solidifying the extruded part section;


wherein the composition is based on a homopolymer or a copolymer of poly-ether-ketone-ketone, consisting of: at least an isophthalic (I) repeating unit, having the formula:






and, in the case of the copolymer, a terephthalic (T) repeating unit, having the formula:






wherein the molar proportion of T units relative to the sum of the T and I units ranges from 0% to 45% or from 55% to 65%.