▁color ▁capabilities . ▁ ▁Pr inter s ▁that ▁work ▁directly ▁with ▁met als ▁are ▁generally ▁expensive . ▁However ▁less ▁expensive ▁printer s ▁can ▁be ▁used ▁to ▁make ▁a ▁m old , ▁which ▁is ▁then ▁used ▁to ▁make ▁metal ▁parts . ▁ ▁Material ▁extr usion ▁▁ ▁F used ▁fil ament ▁fabric ation ▁( FF F ), ▁also ▁known ▁under ▁the ▁tra dem ark ed ▁term ▁f used ▁de position ▁model ing ▁( F DM ), ▁der ives ▁from ▁automatic ▁polym er ic ▁fo il ▁hot ▁air ▁w eld ing ▁system , ▁hot - m elt ▁gl uing ▁and ▁automatic ▁g asket ▁de position . ▁Such ▁principle ▁has ▁been ▁further ▁developed ▁by ▁S . ▁Scott ▁Cr ump ▁in ▁the ▁late ▁ 1 9 8 0 s ▁and ▁was ▁commercial ized ▁in ▁ 1 9 9 0 ▁by ▁Str at as ys . ▁After ▁the ▁pat ent ▁on ▁this ▁technology ▁exp ired , ▁a ▁large ▁open - source ▁development ▁community ▁developed ▁and ▁both ▁commercial ▁and ▁DI Y ▁variants ▁util izing ▁this ▁type ▁of ▁ 3 D ▁printer ▁appeared ▁known ▁as ▁the ▁Rep R ap ▁project ▁( for ▁self - rep lic ating ▁rapid ▁pro tot y per ). ▁As ▁a ▁result , ▁the ▁price ▁of ▁this ▁technology ▁has ▁dropped ▁by ▁two ▁orders ▁of ▁magnitude ▁since ▁its ▁creation , ▁and ▁it ▁has ▁become ▁the ▁most ▁common ▁form ▁of ▁ 3 D ▁printing . ▁ ▁In ▁f used ▁de position ▁model ing , ▁the ▁model ▁or ▁part ▁is ▁produced ▁by ▁extr ud ing ▁small ▁be ads ▁or ▁streams