Extrusion based additive manufacturing

An extrusion based additive manufacturing apparatus comprising:

• a build room adapted to be heated,
• a temperature control system to control a process temperature inside the build room,
• a build base located in the build room to support an object to be manufactured,
• a print head located in the build room, the print head comprising a nozzle for depositing crystalline or semi-crystalline thermoplastic modelling material to build the object to be manufactured, and the print head comprising a heating device to liquify the modelling material fed to the printhead in an initial solid state,
• wherein the print head and/or the base are coupled to a 3D positioning system to move the print head and/or the base relative to each other, allowing to deposit tracks of modelling material to build the object to be manufactured,
• wherein the temperature control system has a “strength mode” and an “aesthetic mode” and is adapted to toggle between said “strength mode” and said “aesthetic mode” while manufacturing the object,
• wherein:
• the control system has a setpoint for the build room temperature which corresponds to the “strength mode”, and the apparatus comprises a (precision) cooling device adapted to selectively and locally lower the temperature of the object to a temperature corresponding to the “aesthetic mode”;
• or
• the control system has a setpoint for the build room temperature which corresponds to the “aesthetic mode”, and the apparatus comprises a (precision) heating device adapted to selectively and locally raise the temperature of the object to a temperature, which corresponds to the “strength mode”.

A method for the additive manufacturing of an object of a crystalline or semi-crystalline modelling material having a melting temperature Tm, wherein tracks of modelling material are deposited in slices by means of a printhead inside the build room at an extrudate temperature Textr, wherein in each slice a plurality of tracks of the crystalline or semi-crystalline thermoplastic modelling material is deposited by the printhead on a build base or on the tracks of a previously deposited slice, wherein:

• the temperature of the build room (Tbr) ranges between 2*Tm−Textr+14 and 2*Tm−Textr+54
• wherein part of the tracks in a slice are printed in an aesthetic mode and part of the tracks are printed in a strength mode,
• wherein the temperature at a location where at least three tracks meet, in the aesthetic mode is controlled by local cooling and ranges between 2*Tm−Textr−56 and 2*Tm−Textr+4,
• wherein the temperature at a location where at least three tracks, optionally four tracks meet in the strength mode is controlled to be in the range between *Tm−Textr+14 and 2*Tm−Textr+54.

A method for determining a process temperature of a build room for additive manufacturing wherein tracks of modelling material are deposited in slices by means of a printhead inside the build room, wherein in each slice a plurality of tracks of a crystalline or semi-crystalline thermoplastic modelling material is deposited by the printhead on a build base or on the tracks of a previously deposited slice,

• wherein:
• the crystallinity of the modelling material is determined at a location where at least three tracks of the previously deposited slice and the currently deposited slice meet,
• a first process temperature (T1) is determined at which the crystallinity is less than 5% when one of said at least three tracks is deposited, and/or
• a second process temperature (T2) is determined at which the crystallinity is more than 10% when one of said at least three tracks is deposited.