Filament for fused deposit modeling

A method for producing an object by an additive process, comprising the steps of:

• selecting a feedstock comprising an elongated filament having a series of irregularities along the length of the filament;
• feeding the feedstock to a device operable to melt the filament to form a stream of melted material;
• and
• controlling the stream of melted material to build a series of layers to form an object by an additive process.

A method for forming polymer filament for use in an apparatus for producing an object by an additive process, wherein the method for forming the polymer filament comprises the steps of:

• melting a polymer;
• selecting an extrusion characteristic calculated to induce a polymer flow instability;
• extruding the melted polymer using the selected extrusion characteristic to produce an elongated substantially solid extrusion, wherein the polymer flow instability creates distortions on the surface of the extrusion;
• pulling the elongated extrusion;
• automatically measuring the cross-sectional characteristic of the elongated extrusion during the step of pulling;
• and
• varying either the step of extruding or the step of pulling in response to the step of measuring.