Extrusion-based additive manufacturing

Abstract

A method of manufacturing an object. A thermoplastic matrix material is melted to transform it into liquid matrix material. The liquid matrix material is fed into a chamber via one or more matrix inlets. A fibre is also fed into the chamber via a fibre inlet. The fibre in the chamber is contacted by the liquid matrix material. A coated fibre is extruded from an extrusion outlet of the chamber onto a substrate, the coated fibre comprising the fibre with a coating of the liquid matrix material, the substrate comprising a previously extruded coated fibre. The fibre moves in and out of the chamber at the same velocity relative to the chamber. The coating fuses with the previously extruded coated fibre and solidifies after it has fused with the previously extruded coated fibre. Relative movement is generated between the extrusion outlet and the substrate as the coated fibre is extruded from the extrusion outlet.

1 . A method of manufacturing an object, the method comprising:
 melting thermoplastic matrix material to transform it into liquid matrix material;   feeding the liquid matrix material into a chamber via one or more matrix inlets;   feeding a fibre into the chamber via a fibre inlet;   contacting the fibre in the chamber with the liquid matrix material;   extruding a coated fibre from an extrusion outlet of the chamber onto a substrate, the coated fibre comprising the fibre with a coating of the liquid matrix material, and the substrate comprising a previously extruded coated fibre, wherein the coating fuses with the previously extruded coated fibre and solidifies after it has fused with the previously extruded coated fibre, and wherein the fibre moves in and out of the chamber at the same velocity relative to the chamber; and   causing relative movement between the extrusion outlet and the substrate as the coated fibre is extruded from the extrusion outlet.   
     
     
         2 . The method of  claim 1  wherein the coated fibre has a coated fibre area transverse to its length at the extrusion outlet, the fibre has a fibre area transverse to its length at the fibre inlet, and the coated fibre area is greater than the fibre area. 
     
     
         3 . The method of  claim 2  wherein each matrix inlet has a matrix inlet area, and a difference between the coated fibre area and the fibre area is less than the matrix inlet area (or the sum of the matrix inlet areas). 
     
     
         4 . The method of  claim 1  wherein the coated fibre has a coated fibre area transverse to its length at the extrusion outlet, each matrix inlet has a matrix inlet area, and the coated fibre area is less than the matrix inlet area (or the sum of the matrix inlet areas). 
     
     
         5 . The method of  claim 1  wherein the liquid matrix material has an average velocity V 2  relative to the chamber at the matrix inlet(s) as it flows into the chamber; the coated fibre is extruded at an extrusion velocity V 1  relative to the chamber at the extrusion outlet; and V 1 >V 2 . 
     
     
         6 . The method of  claim 1  further comprising:
 temporarily raising the temperature in the extrusion chamber above the melting point of the fibre to melt the fibre in the chamber after the coated fibre has been extruded onto the substrate; 
 after the fibre in the chamber has melted, causing relative movement between the extrusion outlet and the substrate to form a break in the fibre; and 
 lowering the temperature in the chamber below the melting point of the fibre after the break has been formed. 
 
     
     
         7 . The method of  claim 1  wherein the object is manufactured by extruding coated fibre onto selected parts of the substrate in a series of layers in accordance with a three-dimensional model of the object. 
     
     
         8 . The method of  claim 1  wherein the fibre is formed from a semi-crystalline polymer material. 
     
     
         9 . The method of  claim 8  wherein the semi-crystalline polymer material of the fibre has a higher melting point and a higher crystallinity than the thermoplastic matrix material after the thermoplastic matrix material has solidified. 
     
     
         10 . The method of  claim 9  wherein the difference in crystallinity by weight is greater than 5%, preferably greater than 50% and most preferably greater than 90%. 
     
     
         11 . The method of  claim 1  wherein the fibre has a crystallinity greater than 60% by weight. 
     
     
         12 . The method of  claim 1  wherein the fibre extends continuously through the chamber from the fibre inlet to the extrusion outlet. 
     
     
         13 . The method of  claim 1  wherein the fibre is pushed through the chamber. 
     
     
         14 . The method of  claim 1  wherein the fibre moves simultaneously in and out of the chamber. 
     
     
         15 . The method of  claim 1  wherein a rate of flow of the liquid matrix material into the chamber is controlled independently of a rate of flow of the fibre into the chamber. 
     
     
         16 . The method of  claim 15  wherein the rate of flow of the liquid matrix material into the chamber is controlled independently of the rate of flow of the fibre into the chamber in order to increase or decrease a pressure of the liquid matrix material in the chamber. 
     
     
         17 . The method of  claim 1  wherein the (or each) matrix inlet comprises an elongate matrix feed channel, and the thermoplastic matrix material is melted within the matrix feed channel. 
     
     
         18 . The method of  claim 17  further comprising feeding a solid matrix fibre into the elongate matrix feed channel with matrix feed rollers, wherein the solid matrix fibre has sufficient buckling strength to allow it to be driven by the matrix feed rollers into the matrix feed channel with sufficient force to apply a positive pressure. 
     
     
         19 . The method of  claim 1  wherein the object is manufactured with multiple distinct lengths of extruded coated fibres. 
     
     
         20 . The method of  claim 1  wherein the liquid matrix material in the chamber has an elevated pressure.