WO2023187395A1

WO2023187395A1 - Liquefier assembly

Info

Publication number: WO2023187395A1
Application number: PCT/GB2023/050843
Authority: WO
Inventors: Sanjay Mortimer; John Connor LECLAIRE; Dylan ROBERTS; Joshua Rowley
Original assignee: E3D Online Ltd
Current assignee: E3D Online Ltd
Priority date: 2022-04-01
Filing date: 2023-03-30
Publication date: 2023-10-05
Anticipated expiration: 2024-10-01
Also published as: GB202204824D0

Abstract

The invention relates to a liquefier assembly (1) for an extrusion¬ based additive manufacturing system. The assembly includes a body (31), a filament passageway (34) through the body and a heating element (7) at least partially within the filament passageway. The heating element is operatively connected to circuitry configured to supply, in use, power directly to the heating element such that build material flowing along or through the filament passageway is heated by the heating element. In some examples, the circuitry is configured to supply a current to the heating elements (7). In other examples, the circuitry is configured to heat inductively the heating elements via heating coils.

Description

LIQUEFIER ASSEMBLY

This invention relates generally to additive manufacturing systems for producing three- dimensional (3D) parts and particularly to liquefier assemblies for such systems. More specifically, although not exclusively, this invention relates to such a liquefier assembly having a replaceable nozzle.

Additive manufacturing, also called 3D printing, is a process in which a part is made by adding material, rather than subtracting material as in traditional machining. A part is manufactured from a digital model using an additive manufacturing system, commonly referred to as a 3D printer. A typical approach is to slice the digital model into a series of layers, which are used to create two-dimensional path data, and to transmit the data to a 3D printer which manufactures the part in an additive build style. There several different methods of depositing the layers, such as stereolithography, ink jetting, selective laser sintering, powder/binder jetting, electron-beam melting and material extrusion.

In a typical extrusion-based additive manufacturing system, such as a fused deposition modelling system, a part may be formed by extruding a viscous, molten thermoplastic material from a distribution head along predetermined paths at a controlled rate. The head includes a liquefier, which receives thermoplastic material, normally in the form of a filament. A drive mechanism engages the filament and feeds it into the liquefier. The filament is fed through the liquefier, where it melts to produce the flow of molten material, and into a nozzle for depositing the molten material onto a substrate. The molten material is deposited along the predetermined paths onto the substrate, where it fuses to previously deposited material and solidifies as it cools, gradually building the part in layers.

Traditionally, both the filament and the channel or passage within the liquefier section are of substantially circular cross-section. It has been observed that because of the low thermal conductivity of thermoplastic material, heat from the heater is not efficiently and quickly transferred to the centre of a circular filament. This, in turn, can have a negative impact on both the rate and quality of extrusion. For example, uneven heating across the crosssection of the filament may result in differences in viscosity, resulting in uneven flow and can be detrimental to the properties of the finished product.

It is therefore a first non-exclusive object of the invention to provide a liquefier assembly that overcomes, or at least mitigates, the drawbacks of the prior art. It is a further non-exclusive object of the invention to provide an improved liquefier assembly, additive manufacturing system and method of heating a build material as it is passed through a liquefier assembly.

Accordingly, a first aspect of the invention provides a liquefier assembly, e.g. for an extrusion-based additive manufacturing system, the assembly comprising a body, a filament passageway through the body and a heater at least partially within the filament passageway such that build material flowing, in use, along or through the filament passageway is heated by the heater.

The provision of a heater at least partially within the filament passageway introduces heat to the centre of the filament, thereby improving the speed with which the liquefier melts the filament.

The heater preferably includes a heater element or heating element, hereinafter heating element but these terms may be used interchangeably. The heating element may be at least partially within the filament passageway. The heating element may be configured to receive power directly from a power source.

Another aspect of the invention provides a liquefier assembly, e.g. for an extrusion-based additive manufacturing system, the assembly comprising a body, a filament passageway through the body and a heating element at least partially within the filament passageway which is configured to receive, in use, power directly thereto such that build material flowing along or through the filament passageway is heated by the heater.

The heating element may comprise an active heating element. The heating element may be operatively connected to circuitry, for example electrical circuitry. The liquefier assembly may comprise the circuitry. The circuitry may be configured to supply, in use, power directly to the heating element to heat the build material.

Another aspect of the invention provides a liquefier assembly, e.g. for an extrusion-based additive manufacturing system, the assembly comprising a body, a filament passageway through the body, a heating element at least partially within the filament passageway and circuitry operable to apply power directly to the heating element such that build material flowing, in use, along or through the filament passageway is heated by the heating element.

The circuitry may be configured to supply, in use, a current to the heating element.

Another aspect of the invention provides a liquefier assembly, e.g. for an extrusion-based additive manufacturing system, the assembly comprising a body, a filament passageway through the body, a heating element at least partially within the filament passageway and circuitry operable to apply a current directly to the heating element such that build material flowing, in use, along or through the filament passageway is heated by the heating element.

The circuitry may be electrically connected to the heating element. The heating element may comprise at least one electrical contact, e.g. a pair of electrical contacts. The heater may comprise at least one electrical contact, e.g. a pair of electrical contacts, which may be operatively or electrically connected to the heating element. The electrical contact(s) may be operable or configured to receive a current. The electrical contact(s) may be electrically connected to the circuitry.

The heating element may be a joule heating element or a resistive heating element. The heating element may comprise a wire, e.g. a resistive wire. The liquefier may be configured such that the flow of build material around the heating element heats the build material, e.g. by resistive heat. The liquefier may be configured such that heat, e.g. resistive heat, is induced by the heating element as the build material flows therearound.

The circuitry may comprise one or more wires or wired connections. The circuitry may connect, or be configured to connect, the liquefier assembly and/or heating element to a source of electrical power or current.

The heating element may have a positive temperature coefficient of resistance. The circuitry may be operable to determine, in use, the flow rate and/or temperature of the build material, e.g. as it contacts or flows around and/or over the heating element.

The circuitry may be operable to determine, in use, the flow rate and/or temperature of the build material, e.g. as it contacts or flows around and/or over the heating element. The circuitry may be operable to determine, in use, the flow rate and/or temperature of the build material in dependence on a change in electrical resistance of the heating element.

The liquefier assembly and/or circuitry may comprise a current sensor. The current sensor may be connected, e.g. operatively, to the liquefier assembly and/or circuitry. The current sensor may be for measuring or operable to measure or determine, in use, a current across the heating element, e.g. as build material flows therearound.

The liquefier assembly and/or circuitry may comprise a voltage sensor configured to determine a change in voltage across the heating element.

The liquefier assembly may comprise a controller. The controller may comprise or be operatively connected to the circuitry. The controller may comprise or be operatively connected to the current sensor. The controller may comprise or be operatively connected to the voltage sensor.

The controller or circuitry may be configured to determine the electrical resistance of the heating element, e.g. in dependence on voltage supplied thereto and/or a current measured by the current sensor. The controller or circuitry may be configured to determine a change in current, e.g. using a current measured or determined by the current sensor. The change in current may be indicative or representative of flow rate and/or temperature of the build material. The controller or circuitry may be configured to determine a change in voltage, e.g. using a voltage measured or determined by the voltage sensor.

The controller or circuitry may be configured to determine the temperature of the build material and/or heating element, e.g. in dependence on the electrical resistance. The controller or circuitry may comprise a memory. The temperature of the build material and/or heating element may be determined using one or more look-up tables, which may be stored on the memory. The one or more look-up tables may correlate temperature and resistance of the material of the heating element.

The temperature of the build material and/or heating element may be determined using the following equation:

Where T is the current temperature, R is the measured resistance, Ro is the resistance measured at a reference temperature To and a is the temperature coefficient of resistance for the material of the heater or heating element.

The liquefier assembly and/or controller or circuitry may comprise or describe a feedback loop. The controller or circuitry may be configured to adjust the current supplied to the heating element, e.g. in dependence on the temperature of the build material and/or heating element.

The liquefier assembly and/or controller or circuitry may comprise a measurement bridge. The measurement bridge may be connected, e.g. operatively connected, to the liquefier assembly and/or circuitry. The measurement bridge may comprise a Wheatstone bridge.

The controller or circuitry may be operable to measure or determine, in use, a change in voltage across the measurement bridge, e.g. as build material flows around and/or over the heating element. The change in voltage may represent a change in balance of the measurement bridge. The change in voltage may be indicative or representative of flow rate and/or temperature of the build material.

The measurement bridge may comprise the heating element. The heating element may be a resistor or resistive element of the measurement bridge or Wheatstone bridge. The measurement bridge may comprise a variable resistor.

The controller may be operatively connected to the circuitry and/or measurement bridge. The controller may be configured to maintain, in use, a substantially constant current or substantially constant temperature in or through the heating element, e.g. as build material flows therearound.

The circuitry, measurement bridge or controller may comprise an amplifier, e.g. a servo amplifier. The circuitry, measurement bridge or controller may comprise a feedback loop, e.g. configured to feedback input current or voltage into the measurement bridge. The amplifier and/or feedback loop may be configured to feedback into the measurement bridge in the event that there is a change in voltage across the measurement bridge. The amplifier and/or feedback loop may be configured to re-balance the measurement bridge, e.g. by adjusting the voltage and/or current input to the measurement bridge. The amplifier may be or form part of the feedback loop.

The liquefier assembly or body may comprise two or more, e.g. a plurality of heating elements. The or each heating element may comprise a wire, film, ribbon or a metal-ceramic heater, at least one of which may span the filament passageway. The plurality of heating elements may comprise a combination of a wire, film, ribbon or metal-ceramic heater. The or each heating element may comprise one or more of nickel, nickel-iron alloy, nickelchrome alloy, iron-chromium-aluminium alloy, stainless steel or titanium.

At least one or all or each heating element may be located or received within the body or filament passageway, e.g. located or received entirely within the body or filament passageway.

The liquefier assembly or body may comprise a fin or blade. The fin or blade may span the filament passageway. The fin or blade may extend along at least part of the filament passageway. The heating element(s) may be received or embedded within the fin or blade. The fin or blade may be one of a plurality of fins or blades, each of which may span at least part of the filament passageway. The fins or blades may intersect, e.g. at a centre of the filament passageway. Each fin or blade may comprise one or more heating elements, e.g. received or embedded therewithin. The heating element(s) may comprise glass insulated nichrome.

The fin or blade may comprise or be formed of or by a metal-ceramic heater. The metal ceramic heater may comprise a printed metal-ceramic heater.

The circuitry may be operable or configured to heat, in use, the heating element(s) by electromagnetic induction.

Another aspect of the invention provides a liquefier assembly, e.g. for an extrusion-based additive manufacturing system, the assembly comprising a body, a filament passageway through the body, a heating element at least partially within the filament passageway and circuitry operable to heat, in use, the heating element by electromagnetic induction such that build material flowing along or through the filament passageway is heated by the heating element. The inductive heating element may comprise two or more, e.g. a plurality of, heating elements. The circuitry or controller may comprise an inductive heating coil. The inductive heating coil may surround at least part of the heating element(s). The inductive heating coil may be operable or configured to heat, in use, the heating element(s) by electromagnetic induction. The heating element(s) may comprise an electrically conductive material. The heating element(s) may comprise one or more of steel, copper, brass, graphite, gold, silver, aluminum, and carbide.

The liquefier assembly or body may comprise a liquefier tube. The liquefier tube may comprise the heater or heating element. The liquefier tube may be partially received at least partially within the body or may comprise or provide the body. The liquefier tube may be received at least partially within and/or describe at least part of the filament passageway.

At least part of the heating element(s) may be formed of a first material. At least part of the body, e.g. the liquefier tube, may be formed of a second material. The first material may have a higher magnetic permeability than the second material. The first material may be more susceptible to inductive heating than the second material.

The magnetic permeability and/or susceptibility to inductive heating of each of the first and second materials may be selected such that heating power is divided and/or balanced between the body or liquefier tube and the heating element(s). The first material may comprise a mild steel or some other material having a high or higher magnetic permeability and/or susceptibility to inductive heating. The second material may comprise stainless steel or some other material having a low or lower magnetic permeability and/or susceptibility to inductive heating.

The circuitry may be configured or operable to approximate the temperature of the build material passing therethrough, e.g. based at least in part on the curie temperature of the first and second materials.

At least part of the heating element(s) may be shaped and/or configured so as to absorb more inductive heating energy than at least part of the body or liquefier tube. Alternatively, at least part of the body may be shaped so as to absorb more inductive heating energy than at least part of the heating element(s). The shape and/or configuration of at least part of the heating element(s) and the shape and/or configuration at least part of the body or liquefier tube may be selected such that heating power is divided and/or balanced between the body or liquefier tube and the heating element(s).

The inductive heating coil may be configured to emit, in use, a frequency configured to heat the heating element(s) more than the body, e.g. during one mode of operation, for example a first mode of operation. Additionally or alternatively, the inductive heating coil may be configured to emit, in use, a frequency configured to heat the body more than the heating element(s), e.g. during one mode of operation, for example another mode of operation or a second mode of operation. The inductive heating coil may be configured to emit, in use, a frequency configured such that heating power is divided and/or balanced between the body or liquefier tube and the heating element(s).

The liquefier assembly or body may comprise magnetic shielding. The magnetic shielding may be configured to shield, in use, a magnetic field emitted by the inductive heating coil, e.g. from a conductive and/or ferrous build bed upon which the liquefier assembly is depositing build material.

The liquefier assembly or body may comprise an insert. The insert may comprise or provide the heater or heating element, or at least one of the heating elements. The insert may be received at least partially within the body, e.g. at least partially within the filament passageway. The insert may be received within the body or filament passageway, e.g. received entirely within the body or filament passageway. The insert may be at least partially received within and/or describe at least part of the filament passageway. The insert may describe the entire filament passageway.

In some examples, at least part of the filament passageway, or at least part of the body describing the passageway, comprises or provides a heating element, e.g. a further heating element. The body may comprise a coating or layer of material, which may be susceptible to inductive heating. The coating or layer may be on an external side or surface of the body and/or on an internal side or surface of the body. The coating or layer may be included, located, deposited or plated on an internal, or even external, surface of the body. The coating or layer of material may be on or within the liquefier tube, e.g. included, located, deposited or plated on an internal, or even external, surface thereof. The coating or layer of material which may be more susceptible to inductive heating than the material from which the body or tube is formed. The liquefier tube may comprise a ceramic material, for example upon or within which the coating or layer of material may be included, located, deposited or plated.

For example, at least part of the surface describing at least part of the filament passageway may comprise the coating or layer of material. The coating or layer may comprise the first material.

Additionally or alternatively, the liquefier tube may be divided in two or more components, one of which components may be non-conductive or the components may be connected to one another by a non-conductive element.

The liquefier assembly may comprise a nozzle, which may include the body and/or the liquefier tube. The liquefier assembly or body or nozzle may comprise a nozzle tip, which may be connected to one end, e.g. a first end, of the liquefier tube. At least part of the nozzle tip may be received within the liquefier tube. Alternatively, at least part of the liquefier tube may be received within the nozzle tip.

The liquefier assembly or body may comprise a connection sleeve or heat sink, which may be connected to one end, e.g. the other end or a second end, of the liquefier tube. At least part of the connection sleeve or heat sink may be received within the liquefier tube. Alternatively, at least part of the liquefier tube may be received within the connection sleeve or heat sink.

The liquefier assembly may be arranged such that build material flowing, in use, through the filament passageway contacts the heating element. The heating element may project from a wall of the body, insert or liquefier tube into the filament passageway. The heating element may project from a wall of the body, insert or liquefier tube to another portion of the wall.

The heating element may, but need not, be connected to the body, insert, liquefier tube or wall at one or more points or locations. The heating element may be connected to the body, insert, liquefier tube or wall at a first point or location and/or at a second point or location. The heating element may comprise a first end, which may be connected to the body, insert, liquefier tube or wall at the first point or location. The heating element may comprise a second end, which may be connected to the body, insert, liquefier tube or wall at the second point or location.

The second point or location may be opposite the first point or location. The second point or location may be diametrically opposite the first point or location. Additionally or alternatively, the first point or location may be upstream or downstream of the second point or location. Additionally or alternatively, the first point or location and the second point or location may be on the same plane.

The heating element may span the filament passageway, e.g. such that power supplied by the circuitry is received, in use, directly by the heating element across the filament passageway. The heating element may divide the filament passageway. The heating element may pass through a centre of the filament passageway.

The heating elements may all span the filament passageway. The heating elements may be rotationally offset from or relative to one another. The heating elements may be skewed relative to one another.

The heating elements may be spaced from one another along the filament passageway and/or a portion of the length of the body, insert or liquefier tube. The heating elements may be adjacent to one another along the filament passageway and/or a portion of the length of the body, insert or liquefier tube. Additionally or alternatively, the heating elements may be spaced from one another along the filament passageway and/or a portion of the length of the body, insert or liquefier tube.

The heating elements may together describe a crossed-spoke pattern, e.g. when viewed along the filament passageway.

Each of the heating elements may bisect one another when viewed along the filament passageway. Each of the heating elements may intersect one another at or toward a centre of the filament passageway when viewed along the filament passageway.

Each heating element may pass through a, or proximate a, centre of the filament passageway. The heating elements may be configured such that, in use, the heat induced by the heating elements at or toward the centre of the filament passageway is greater than the heat induced thereby at or toward a periphery of the filament passageway.

One or more of the plurality of heating elements may extend into and/or along, e.g. axially along, the filament passageway.

Two or more heating elements may be or lie adjacent and/or in contact with one another.

The insert may be received at least partially within a downstream end of the body. The body may include a receptacle, e.g. within which the insert may be received, such as by a press- fit or interference fit. Alternatively, the insert may be secured to or within the body by some other means, for example it may be welded, soldered or brazed. In some embodiments, the insert may be secured by mechanical means. The insert may be threadedly connected or mounted to or within the body, or connected to or within the body by a bayonet, snap fit or any other mechanical means.

The insert may comprise a cylindrical portion, which may be press-fit into the receptacle. The insert may comprise a downstream end, which may describe an outlet or outlet passage of the body or liquefier assembly. The heating element may project from an upstream side of the cylindrical portion.

The filament passageway may have a dimension or diameter, e.g. an outer dimension or diameter. The dimension or diameter may comprise a major dimension or diameter or a minor dimension or diameter. The dimension or diameter may change or vary, for example it may increase and/or decrease, along at least part of its length. The dimension or diameter may change or vary to accommodate the heating element, for example to maintain a similar or substantially the same flow area. The filament passageway may comprise a substantially constant hydraulic dimension or diameter, for example along its length or at least part or all of its length.

The dimension or diameter of the filament passageway may increase, for example from the inlet to a region surrounding the heating element ,e.g. a primary heating zone or region. The dimension or diameter may increase from a first, e.g. inlet, dimension or diameter to a second, e.g. primary heating zone or region, dimension or diameter. The filament passageway may comprise a transition or transition zone or region, for example along which the dimension or diameter increases, e.g. from the first dimension or diameter to the second dimension or diameter.

The body may comprise the transition or transition zone or region. In some examples, the connection sleeve or heat sink comprises the transition or transition zone or region. In other examples, the liquefier tube comprises the transition or transition zone or region.

The dimension or diameter of the filament passageway may decrease, for example from the region surrounding the heating element ,e.g. a primary heating zone or region, to or toward an outlet or outlet zone or region. The dimension or diameter may decrease from the second dimension or diameter to a third, e.g. outlet or outlet zone or region, dimension or diameter. The filament passageway may comprise a taper or taper zone or region, for example along which the dimension or diameter decreases, e.g. from the second dimension or diameter to the third dimension or diameter.

The body may comprise the taper or taper zone or region. In some examples, the nozzle tip comprises the taper or taper zone or region. In other examples, the liquefier tube comprises the taper or taper zone or region.

At least part of the heating element may be in or within or at a centre, e.g. located in or within or at a centre, of the filament passageway. The filament passageway may comprise an inlet.

The heating element may comprise a rod or elongate member. The heating element may comprise a heating core, e.g. an elongate heating core. The heating element may be downstream and/or coaxial with the inlet or filament passageway. The heating element may extend along the filament passageway. The heating element may be spaced from a wall of the body, e.g. to describe therewith an annular portion of the filament passageway.

The heating element may be downstream of and/or parallel to and/or coaxial with the inlet or the filament passageway. The heating element may extend along the filament passageway. At least part of the heating element may be spaced from a wall of the body, e.g. to describe therewith at least a portion of the filament passageway. The heating element, e.g. the rod or elongate member or heating core, may describe an inner part of an annular or tubular portion of the filament passageway. The heating element may describe with the body the or an annular or tubular portion of the filament passageway.

The heating element, e.g. the heating core, may comprise a central hole. The central hole may be along at least part of the length of the heating element. The central hole may describe a central flow path. The central flow path may be coaxial with and/or surrounded by the annular portion of the filament passageway.

The heating element, e.g. the heating core, may be spaced from the wall of the body by one or more spacers. The spacer(s) may comprise one or more ribs, spokes, bars or balls. The spacer(s) may comprise one or more projecting portions of the body or liquefier tube. The liquefier tube may be deformed or have deformed regions, e.g. to provide or for providing the spacers or projecting portions. The heating element may be supported by the spacers or by one or more ribs, spokes, bars or balls.

The spacers, ribs, spokes, bars or balls may be formed integrally with the heating core. Alternatively, the spacers, ribs, spokes, bars or balls may be formed integrally with the body. The body may comprise a tube, e.g. the liquefier tube, which may have a substantially constant cross-section, for example along at least part of its length. The tube may comprise a substantially constant cross-section surrounding at least part of the heating element. The tube may comprise localised regions which are deformed to provide or for providing the spacers.

The tube or liquefier tube may comprise a radial wall thickness. The radial wall thickness may be substantially constant. The radial wall thickness may be substantially less than the radius of at least part of the filament passageway. The radial wall thickness may be less or more than or substantially the same or similar to the width or thickness of the heating element.

The radial wall thickness of the liquefier tube may be selected such that heating power is divided and/or balanced between the body or liquefier tube and the heating element(s).

The insert may comprise one or more holes, slots or channels, which may surround or circumscribe the heating element. The slot(s) or channel(s) may be curved or arcuate, e.g. may have a curved or arcuate section. The hole(s), slot(s) or channel(s) may join or connect, e.g. fluidly connect, the annular portion of the filament passageway to the outlet passage. The hole(s), slot(s) or channel(s) may extend at an angle, e.g. relative to the axis of the insert or heating element or nozzle or filament passageway.

The inductive heating coil may surround at least part of the heating element of the insert. The inductive heating coil may be operable or configured to heat, in use, the entire heating element by electromagnetic induction. The inductive heating coil may be operable or configured to heat, in use, the entire insert, or at least the heating element thereof, by electromagnetic induction. The insert or at least the heating element thereof may comprise an electrically conductive material, such as steel, copper, brass, graphite, gold, silver, aluminum, and carbide.

The liquefier assembly or heater or a further heater may comprise a heating element, e.g. a further heating element, which may be at least partially external of the filament passageway or body. The heating element or further heating element may at least partially surround the filament passageway or body. Alternatively, the heating element or further heating element may be received within the body, e.g. within a hole or pocket or recess or slot in the body.

According to another aspect of the invention, there is provided a method of heating a build material as it is advanced through a liquefier assembly, e.g. of an extrusion-based additive manufacturing system, the method comprising advancing a build material along a filament passageway through a body such that the build material is heated by a heater at least partially within the filament passageway.

The method may comprise supplying power to, e.g. directly to, a heating element of the heater, for example to heat the build material.

Another aspect of the invention provides a method of heating a build material as it is advanced through a liquefier assembly, e.g. of an extrusion-based additive manufacturing system, the method comprising supplying power to a heating element projecting or extending into a filament passageway of a body and advancing a build material along the filament passageway such that the build material flows around and is heated by the heating element. The heating element may receive power directly from circuitry. The method may comprise advancing a build material along a filament passageway through a body such that the build material is heated by a heating element at least partially within the filament passageway, which receives power directly from circuitry

The method may comprise supplying a current to the heating element, e.g. so as to heat the build material as it flows around the heating element.

Another aspect of the invention provides a method of heating a build material as it is advanced through a liquefier assembly, e.g. of an extrusion-based additive manufacturing system, the method comprising supplying a current to a heating element projecting or extending into a filament passageway of a body and advancing a build material along the filament passageway such that the build material flows around and is heated by the heating element.

The liquefier assembly may comprise circuitry operatively connected to the heating element. The method may comprise supplying a current to the heating element via the circuitry, so as to conduct heat to the build material as it flows around the heating element.

The heating element may have a positive temperature coefficient of resistance. The liquefier assembly may comprise a measurement bridge operatively connected to the circuitry and a controller operatively connected to the circuitry and/or measurement bridge. The method may comprise maintaining a substantially constant current or substantially constant temperature in the heating element.

The method may comprise measuring a change in the voltage across a measurement bridge as the build material flows around the heating element. The method may comprise determining, e.g. in dependence on the change in the voltage across the measurement bridge, the flow rate and/or temperature of the build material, e.g. as it flows around and/or over the heating element.

The method may comprise heating the heating element by electromagnetic induction.

Another aspect of the invention provides a method of heating a build material as it is advanced through a liquefier assembly, e.g. of an extrusion-based additive manufacturing system, the method comprising heating by electromagnetic induction a heating element projecting or extending into a filament passageway of a body and advancing a build material along the filament passageway such that the build material flows around and is heated by the heating element.

The method may additionally comprise heating the body externally, e.g. as the build material is heated by the heating element.

The method may comprise heating the build material with a heating element, or a further heating element, which is at least partially external of the filament passageway or body. The method may comprise heating the build material with a heating element, or a further heating element, which at least partially surrounds the filament passageway or body. Alternatively, the method may comprise heating the build material with a heating element, or a further heating element, received within the body, e.g. within a hole or pocket or recess or slot in the body.

The method may comprise the use of a liquefier as described above.

Another aspect of the invention provides an additive manufacturing system comprising a liquefier assembly as described above and/or operable to carry out a method as described above.

For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention. For example, the liquefier assembly may comprise any one or more features of the method relevant to the liquefier assembly and/or the method may comprise any one or more features or steps relevant to one or more features of the liquefier assembly or the additive manufacturing system.

Another aspect of the invention provides a computer program element comprising and/or describing and/or defining a three-dimensional design, e.g. of one or more components of the liquefier assembly described above or an embodiment thereof. The three-dimensional design may be for use with a simulation means or an additive or subtractive manufacturing means, system or device. The computer program element may be for causing, or operable or configured to cause, an additive or subtractive manufacturing means, system or device to manufacture one or more components of the liquefier assembly described above or an embodiment thereof. The computer program element may comprise computer readable program code means for causing an additive or subtractive manufacturing means, system or device to execute a procedure to manufacture one or more components of the liquefier assembly described above or an embodiment thereof.

A yet further aspect of the invention provides the computer program element embodied on a computer readable medium.

A yet further aspect of the invention provides a computer readable medium having a program stored thereon, where the program is arranged to make a computer execute a procedure to implement one or more steps of the aforementioned method.

A yet further aspect of the invention provides a control means or control system or controller comprising the aforementioned computer program element or computer readable medium.

For purposes of this disclosure, and notwithstanding the above, it is to be understood that any controller(s), control units and/or control modules described herein may each comprise a control unit or computational device having one or more electronic processors. The controller may comprise a single control unit or electronic controller or alternatively different functions of the control of the system or apparatus may be embodied in, or hosted in, different control units or controllers or control modules. As used herein, the terms “control unit” and “controller” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide the required control functionality.

A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) or control module(s) to implement the control techniques described herein (including the method(s) described herein). The set of instructions may be embedded in one or more electronic processors, or alternatively, may be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on or more electronic processors, optionally the same one or more processors as the first controller.

It will be appreciated, however, that other arrangements are also useful, and therefore, the present invention is not intended to be limited to any particular arrangement. In any event, the set of instructions described herein may be embedded in a computer-readable storage medium (e.g., a non-transitory storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

For the avoidance of doubt, the terms “may”, “and/or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so- described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a side view of a liquefier assembly; Figure 2 is a cross-sectional view of the liquefier assembly of Figure 1 with a nozzle body within which is received an insert incorporating a heating element;

Figure 3 is an end view of the insert of the liquefier assembly of Figure 2;

Figure 4 is a cross-sectional view taken along line A-A of Figure 3;

Figure 5 is an end view of an alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 6 is a cross-sectional view taken along line B-B of Figure 5;

Figure 7 is an end view of another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 8 is a cross-sectional view taken along line C-C of Figure 7;

Figure 9 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 10 is a cross-sectional view taken along line D-D of Figure 9;

Figure 11 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 12 is a cross-sectional view taken along line E-E of Figure 11 ;

Figure 13 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 14 is a cross-sectional view taken along line F-F of Figure 13;

Figure 15 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2; Figure 16 is a cross-sectional view taken along line G-G of Figure 15;

Figure 17 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 18 is a cross-sectional view taken along line H-H of Figure 17;

Figure 19 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 20 is a cross-sectional view taken along line l-l of Figure 19;

Figure 21 is an end view of yet another alternative insert, which can also be received within the liquefier assembly of Figures 1 and 2;

Figure 22 is a cross-sectional view taken along line J-J of Figure 21 ;

Figure 23 is a perspective view of another heater, which can be incorporated within the nozzle of the liquefier of Figures 1 and 2;

Figure 24 is a perspective cross-sectional view of the nozzle of Figure 23, taken across a fin thereof;

Figure 25 is a perspective cross-sectional view of the nozzle of Figure 23, taken along the fin;

Figure 26 is a perspective view of another heater, which can be incorporated within the nozzle of the liquefier of Figures 1 and 2;

Figure 27 is a perspective cross-sectional view of the nozzle of Figure 26, taken across a heating plate thereof;

Figure 28 is a cross-sectional view of an alternative liquefier assembly with a liquefier tube incorporating a pair of heating elements; Figure 29 is a view of the liquefier tube of the liquefier assembly of Figure 28, taken adjacent the heating elements;

Figure 30 is a cross-sectional view of a portion of the liquefier tube taken along line K-K of Figure 29;

Figure 31 is a view of an alternative liquefier tube, which can also be used in the liquefier assembly of Figure 28;

Figure 32 is a cross-sectional view taken along line L-L of Figure 31 ;

Figure 33 is a schematic of a control system for use in a liquefier assembly;

Figure 34 is a schematic, cross-sectional view of an alternative liquefier assembly in which a tip insert provides an inductive heating element;

Figure 35 is a perspective view of the tip insert of the liquefier assembly of Figure 34;

Figure 36 is a perspective view of another liquefier assembly incorporating an inductive heating assembly;

Figure 37 is a cross-sectional view of the liquefier assembly of Figure 36;

Figure 38 is a view similar to that of Figure 37, but with the inductive heating sleeve omitted;

Figure 39 is a perspective view of the inductive core and nozzle tip of the liquefier assembly of Figures 37 and 38;

Figure 40 is a cross-sectional view of another liquefier assembly incorporating an inductive heating assembly; and

Figure 41 is a cross-sectional view of yet another liquefier assembly incorporating an inductive heating assembly. Referring now to Figures 1 and 2, there is shown a liquefier assembly 1 according to a first example, which includes a heat sink 2, a nozzle 3 releasably connected to the heat sink 2, a ring heater 4 biased against the nozzle 3 by a coil spring 5, a fan assembly 6 mounted to the heat sink 2 and an embedded heater 7 within the nozzle 3. The liquefier assembly 1 includes a connector 10 at a first end of the heat sink 2 for connection with a filament feed mechanism (not shown) of an additive manufacturing system (not shown), and is configured to facilitate replacement of the nozzle 3 in an unheated state. The connector 10 is in the form of a head 11 having a necked portion 12.

The heat sink 2 includes a substantially cylindrical core 20 with a plurality of disc-shaped fins 21 projecting radially from the core 20 and a filament passageway 22 extending axially through the centre of the core 20 between its ends for receiving a filament from the filament feed mechanism (not shown). The passageway 22 includes an upstream portion 23 that is smooth, with a diameter that is slightly larger than the diameter of the filament (not shown) to be fed therethrough. The passageway 22 also includes a connection feature 24 extending along a downstream portion of the passageway 22. In this example, the connection feature 24 is in the form of internal threads. The heat sink 2 also includes an engaging ring 25 surrounding the downstream end of the passageway 22 and projecting axially from the core 20. The coil spring 5 is retained on the engaging ring 25 at the downstream end of the passageway 22.

The nozzle 3 in this example includes a connection sleeve 30, a nozzle body 31 , a liquefier tube 32 between the connection sleeve 30 and nozzle body 31 and a tip cover 33 mounted over a head 35 the nozzle body 31. The connection sleeve 30 is threaded externally and has a radial flange 30a at a downstream end. The liquefier tube 32 has a substantially constant diameter and thickness and is received in an interference fit within the downstream end of the connection sleeve 30 and the upstream end of the nozzle body 31. The connection sleeve 30, nozzle body 31 and liquefier tube 32 collectively describe a filament passageway 34 through which a filament (not shown) is fed.

In this example, the embedded heater 7 that is within the nozzle 3 is a wire extending through the side wall of the nozzle body 31 and across the filament passageway 34. The heater 7, shown more clearly in Figures 3 and 4, includes a resistive heating element 72 within the nozzle body 31. The resistive heating element 72 spans across the nozzle body 31 from diametrically opposite sides thereof, and intersects the centre of the filament passageway 34. The ends of the heating element 72 are connected to a pair of electrical leads 74.

The ring heater 4 includes a cylindrical cover 40 that surrounds a heating sleeve 41. The heating sleeve 41 includes electrical leads 42 for providing electrical power thereto, and an engaging ring 43 over which the coil spring 5 is retained, thereby connecting the ring heater 4 to the heat sink 2. This connection between the ring heater 4 and heat sink 2 enables the ring heater 4 to move freely relative to the heat sink 2, such that the nozzle 3 may be misaligned when inserted into the heating sleeve 41 of the ring heater 4, and manipulated into engagement and proper alignment with the heat sink 2 to enable the threads of the connection sleeve 30 to mesh with the threads of the connection feature 24 in the downstream portion of the passageway 22.

In use, an electrical current applied to the electrical leads 42 heats the ring heater 4, which in turn heats the nozzle body 31 . Heat from the nozzle body 31 is transmitted via conduction to the filament passageway 34 to heat the outside of the build material (not shown) as it advances therethrough in a manner that is similar to known liquefiers.

However, in this liquefier assembly 1 , an electrical current is also applied to the electrical leads 74 of the embedded heater 7, which heats the resistive heating element 72 directly. Heat from the resistive heating element 72 is transmitted to the centre of the filament passageway 34 and therefore into a central region of the build material (not shown) as it flows around the resistive heating element 72. This has been found to improve drastically the speed and effectiveness with which the build material melts and is able to transit through the liquefier assembly 1 .

This arrangement has also been found to improve drastically the homogeneity of heating throughout the build material as it flows through the filament passageway 34, without increasing substantially the pressure drop caused by the resistive heating element 72.

Figures 5 and 6 show an embedded heater 107 incorporated within the nozzle body 31 according to another example. The embedded heater 107 according to this example is similar to that of Figures 3 and 4, but it includes three heating elements 172. Each of the heating elements 172 extends into, and along a portion of, the filament passageway 34, rather than spanning the filament passageway 34 as in the previous example. More particularly, the heating elements 172 are each connected to the nozzle body 31 at two points spaced along its length. The heating elements 172 fall short of the centre of the filament passageway 34 in this example. The ends of each heating element 172 are electrically connected to the electrical leads 74.

The heating elements 172 are rotationally offset from one another, when viewed along the filament passageway 34. In particular, the heating elements 172 are rotationally offset by 120 degrees in this example.

As with the embedded heater 7 described above, an electrical current is applied to the electrical leads 74 of this heater 107, which heats the resistive heating elements 172 directly. Heat from the resistive heating elements 172 is transmitted toward the centre of the filament passageway 34 and therefore toward a central region of the build material (not shown) as it flows around the resistive heating elements 172.

Figures 7 and 8 show an embedded heater 207 incorporated within the nozzle body 31 according to another example. The embedded heater 207 according to this example is similar to that of Figures 3 and 4, except that it includes a second heating element 272, which also spans across the nozzle body 31 from diametrically opposite sides thereof, and intersects the centre of the filament passageway 34.

The heating elements 272 are also orthogonal to one another, and bisect one another when viewed along the filament passageway 34. The heating elements 272 are spaced along the length of the nozzle body 31 such that they are out of contact with one another. The ends of each heating element 272 are electrically connected to the electrical leads 74.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 207, which heats the resistive heating elements 272 directly. Heat from the resistive heating elements 272 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 272. Figures 9 and 10 show an embedded heater 307 incorporated within the nozzle body 31 according to another example. The embedded heater 307 according to this example is similar to that of Figures 3 and 4, but it includes four rotationally offset heating elements 372 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another.

The heating elements 372 extend through the centre of the filament passageway 34 and are each connected at diametrically opposing sides of the nozzle body 31. The ends of each heating element 372 are electrically connected to the electrical leads 74.

A first pair of the heating elements 372 are orthogonal to one another, and bisect one another when viewed along the filament passageway 34. Likewise, a second pair of the heating elements 372 are orthogonal to one another, are rotationally offset from the first pair by 45 degrees and bisect one another when viewed along the filament passageway 34. Together, the heating elements 372 describe a crossed spoke pattern. The heating elements 372 are spaced along the length of the nozzle body 31 such that they are out of contact with one another.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 307, which heats the resistive heating elements 372 directly. Heat from the resistive heating elements 372 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 372.

Figures 11 and 12 show an embedded heater 407 incorporated within the nozzle body 31 according to another example. The embedded heater 407 according to this example is similar to that of Figures 3 and 4, but includes four heating elements 472 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another. A first two of the heating elements 472 lie parallel with one another, but are located on opposite sides of a longitudinal axis of the nozzle body 31. A second two of the heating elements 472 lie parallel with one another, but are also located on opposite sides of the longitudinal axis of the nozzle body 31. The heating elements 472 are spaced along the length of the nozzle body 31 , and a first two of the heating elements 472 also lie orthogonal to the second two. The ends of each heating element 472 are electrically connected to the electrical leads 74. As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 407, which heats the resistive heating elements 472 directly. Heat from the resistive heating elements 472 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 472.

Figures 13 and 14 show an embedded heater 507 incorporated within the nozzle body 31 according to another example, for use in the liquefier assembly 1 of Figures 1 and 2. The embedded heater 507 according to this example is similar to that of Figures 3 and 4, but includes four heating elements 572 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another.

A first two of the heating elements 572 lie parallel, adjacent and out of contact with one another. The first two of the heating elements 572 are located on opposite sides of a longitudinal axis of the nozzle body 31 and are at a first longitudinal position. A second two of the heating elements 572 lie parallel, adjacent and out of contact with one another. The second two of the heating elements 572 are located on opposite sides of the longitudinal axis of the nozzle body 31 and are at a second longitudinal position, spaced from the first longitudinal position. The first two heating elements 572 lie orthogonal to the second two heating elements 572. The ends of each heating element 572 are electrically connected to the electrical leads 74.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 507, which heats the resistive heating elements 572 directly. Heat from the resistive heating elements 572 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 572.

Figures 15 and 16 show an embedded heater 607 incorporated within the nozzle body 31 according to another example. The embedded heater 607 according to this example is similar to that of Figures 3 and 4, but includes three heating elements 672 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another. A first two of the heating elements 672 lie parallel, adjacent and out of contact with one another. The first two heating elements 672 are located on opposite sides of a longitudinal axis of the nozzle body 31 and are at different longitudinal positions. A third heating element 672 lies orthogonal to, and bisects, the first two heating elements 672 when viewed along the filament passageway 34. The third heating element 672 also extends through a space described between the heating elements 672 and passes through the centre of the filament passageway 34. The third heating element 672 extends diagonally along a portion of the length of the filament passageway 34, such that it is connected to the nozzle body 31 at two points spaced along the length thereof. The ends of each heating element 672 are electrically connected to the electrical leads 74.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 607, which heats the resistive heating elements 672 directly. Heat from the resistive heating elements 672 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 672.

Figures 17 and 18 show an embedded heater 707 incorporated within the nozzle body 31 according to another example. The embedded heater 707 according to this example is similar to that of Figures 3 and 4, but includes a single heating element 772 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another, passing through the centre thereof.

The heating element 772 extends diagonally along a portion of the length of the filament passageway 34, such that it is connected to the nozzle body 31 at two points spaced along the length thereof. The ends of the heating element 772 are electrically connected to the electrical leads 74.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 707, which heats the resistive heating element 772 directly. Heat from the resistive heating element 772 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating element 772. Figures 19 and 20 show an embedded heater 807 incorporated within the nozzle body 31 according to another example. The embedded heater 807 according to this example is similar to that of Figures 3 and 4, but includes a pair of heating elements 872 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another.

The heating elements 872 lie parallel with one another, but are located on opposite sides of a longitudinal axis of the nozzle body 31. Each of the heating elements 872 is positioned at a different longitudinal position along the nozzle body 31 . The ends of each heating element 872 are electrically connected to the electrical leads 74.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 807, which heats the resistive heating elements 872 directly. Heat from the resistive heating elements 872 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 872.

Figures 21 and 22 show an embedded heater 907 incorporated within the nozzle body 31 according to another example. The embedded heater 907 according to this example is similar to that of Figures 3 and 4, but includes a pair of heating elements 972 extending into and spanning across the filament passageway 34 from one side of the nozzle body 31 to another.

The heating elements 972 lie parallel, adjacent and out of contact with one another. The heating elements 972 are located on opposite sides of a longitudinal axis of the nozzle body 31 and are at substantially the same longitudinal position. The ends of each heating element 972 are electrically connected to the electrical leads 74.

As with the previous examples, an electrical current is applied to the electrical leads 74 of this heater 907, which heats the resistive heating elements 972 directly. Heat from the resistive heating elements 972 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 972. Figures 23 to 25 show an embedded heater 1007 incorporated within the nozzle body 31 according to another example. The embedded heater 1007 according to this example is similar to that of Figures 3 and 4, but includes a fin or blade 1075, hereinafter fin 1075, spanning across a modified filament passageway 1034 from one side of the nozzle body 31 to another, and includes a heating element 1072 received therein.

The fin 1075 has a tapered upstream end 1075a and a tapered downstream end 1075b to gradually separate and reunite a build material flowing through the filament passageway. The fin 1075 also has a series of spaced holes 1076 across its width. The heating element 1072 in this example is a resistive wire, which is coiled around the nozzle body 31 and extends through each of the holes 1076. As a result, the heating element 1072 heats both the portion of the nozzle body 31 that describes the filament passageway 1034 and the fin 1075, Thus, the ring heater 4 may be omitted from the liquefier assembly 1 in this case.

The heater 1007 also includes a temperature sensor 1077 received within a pocket 1078 in the fin 1075. The temperature sensor 1077 includes a pair of leads 1079 for connection with control means for measuring the temperature of the fin 1075. However, the skilled person will appreciate that the temperature sensor 1077 may be omitted, particularly given the disclosure below in relation to the control system 8 of Figure 33.

The filament passageway 1034 has an inlet region 1034a, a transition region 1034b, a primary heating region 1034c, a tapering region 1034d and an outlet region 1034e. The inlet region 1034a has a first diameter, the primary heating region 1034c has a second diameter greater than the first diameter and the outlet region 1034e has a third diameter smaller than both the first and second diameters. The diameter of the filament passageway 1034 increases along the transition region 1034b, from the first diameter to the second diameter, and decreases along the tapering region 1034d, from the second diameter to the third diameter.

In this example the variation of the diameter of the filament passageway 1034 is configured to accommodate the change in flow area that would otherwise result from the presence of the fin 1075. More specifically, the filament passageway 1034 is configured to provide a substantially constant hydraulic diameter along the length of the inlet, transition and primary heating regions 1034a, 1034b, 1034c. The skilled person will appreciate that multiple fins 1075 may be included, which could be parallel to one another or perpendicular to one another (e.g. and intersecting). The heating element 1072 or multiple heating elements 1072 could be embedded within each of the fins 1075.

Figures 26 and 27 show an embedded heater 1107 incorporated within the nozzle body 31 according to another example. The embedded heater 1107 according to this example is similar to that of Figures 23 to 25, wherein like references depict like features, which are incremented by ‘100’. The embedded heater 1107 according to this example differs from that of Figures 23 to 25 in that the fin or blade 1175 is formed of a metal-ceramic heater 1172, such that no separate heating element 1072 is required.

In this example, the metal-ceramic heater 1172 is received within a slot in the side of the nozzle body 31 , protrudes out of the nozzle body 31 and includes exposed electrical leads 1174 for connection with a source to resistively heat the metal-ceramic heater 1172.

Referring now to Figure 28, there is shown a liquefier assembly 1201 according to a second example, which is similar to that of Figures 1 and 2, wherein the same features share the same references, but similar but different features denoted by like references incremented by ‘1200’. This liquefier assembly 1201 differs from the liquefier assembly 1 of Figures 1 and 2 in that the embedded heater 1207 is incorporated within the liquefier tube 1232, which is also longer and the nozzle 1203 is shorter to accommodate the embedded heater 1207.

Figures 29 and 30 show more clearly the embedded heater 1207, which includes an oval cross-section in this example. This can be obtained by localised crushing of the liquefier tube 1232 before the heating elements 1272 are incorporated therein. However, the skilled person will appreciate that the liquefier tube 1232 may have a round cross-section.

In this example, the heater 1207 includes a pair of heating elements 1272, which are wires in this example, extending through the liquefier tube 1232 into and spanning across the filament passageway 34 from one side of the liquefier tube 1232 to the other side. The ends of each heating element 1272 are electrically connected to the electrical leads (not shown).

As with the previous examples, an electrical current is applied to the electrical leads (not shown) of this heater 1207, which heats the resistive heating elements 1272 directly. Heat from the resistive heating elements 1272 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 1272.

Figures 31 and 32 shown an embedded heater 1307 incorporated within a liquefier tube 1332 according to another example, for use in the liquefier assembly 1 of Figure 28. The embedded heater 1307 according to this example is similar to that of Figures 29 and 30, wherein like features will be denoted by like references incremented by a further ‘100’.

In this example, the portion of the liquefier tube 1332 incorporating the heater 1307 has a cruciform cross-sectional shape. This can also be obtained by localised crushing of the liquefier tube 1332 before the heating elements 1372 are incorporated therein. However, the skilled person will appreciate that the liquefier tube 1332 may have a round crosssection.

The heater 1307 includes a pair of heating elements 1372 extending into and spanning across the filament passageway 34 from one side of the liquefier tube 1332 to another. The heating elements 1372 are orthogonal to one another, within a respective pair of opposed limbs of the cruciform cross-section, and bisect one another when viewed along the filament passageway 34. The heating elements 1372 are also spaced along the length of the liquefier tube 1332 such that they are out of contact with one another.

As with the previous examples, an electrical current is applied to the electrical leads (not shown) of this heater 1307, which heats the resistive heating elements 1372 directly. Heat from the resistive heating elements 1372 is transmitted to the centre of the filament passageway 34 and therefore to a central region of the build material (not shown) as it flows around the resistive heating elements 1372.

Referring now to Figure 33, there is shown a control system 8 for use with an additive manufacturing system incorporating the liquefier assembly 1 of Figures 1 and 2 or the liquefier assembly 1001 of Figure 28, within which any of the aforementioned heaters 7, 107, 207, 307, 407, 507, 607, 707, 807, 907, 1007, 1107, 1207, 1307 is incorporated.

The control system 8 has a microcontroller 80 which receives inputs from each of a current sensor 81 and power source 82. The microcontroller 80 feeds a voltage controller 83, which is also fed by the power source 82. The voltage controller 83 sends an output to a heater 84, which in the present example represents any of the heaters 7, 107, 207, 307, 407, 507, 607, 707, 807, 907, 1007, 1107, 1207, 1307 described above, having a positive temperature coefficient of resistance and being electrically conductive. The heater 84 provides an output to the current sensor 81.

In use, the control system 8 is configured to determine the temperature of a build material as it advances along a liquefier assembly.

To heat a build material as it is advanced along the filament passageway 34, the power source 82 is configured to supply current to the heater 84. The heater 84 is a resistive heating wire in the example, and provides heat output when current is supplied. The heat output, in turn, heats the surrounding build material as it is advanced along the liquefier assembly.

The surrounding build material, having a different temperature to that of the heater 84, has an effect on the temperature of the heater 84. As the heater 84 has a positive temperature coefficient of resistance, an increase in the temperature thereof results in an increase in resistance.

The current sensor 81 measures the current across the heater 84 during operation, and provides this to the microcontroller 80. The microcontroller 80 uses the current across the heater 84, and the voltage supplied to the heater 84 to determine the resistance of the wire, for example using Ohm’s law.

The resistance can then be used to determine the temperature of the build material around the heater 84, either by comparing the resistance to a table of temperature-resistance values for the particular material of the heater 84.

Alternatively, the temperature can be determined using the equation:

Where T is the current temperature, R is the measured resistance, Ro is the resistance measured a reference temperature To and a is the temperature coefficient of resistance for the material of the heater or heating element. Figures 34 and 35 show an alternative liquefier assembly 1401 , which includes a nozzle 1403, an insert 1407, a controller 1408 and an inductive heating sleeve 1409 electrically connected to the controller 1408 for inductively heating the insert 1407. The nozzle 1403 is similar to the nozzle 3 of the liquefier Figures 1 and 2, wherein like features will be denoted by like references incremented by ‘1400’.

The nozzle 1403 in this example includes a connection sleeve 1430, a nozzle body 1431 and a liquefier tube 1432 between the connection sleeve 1430 and nozzle body 1431. The connection sleeve 1430 is threaded externally and has a radial flange 1430a at a downstream end. The liquefier tube 1432 has a substantially constant diameter and thickness and is received in an interference fit within the downstream end of the connection sleeve 1430 and the upstream end of the nozzle body 1431. The connection sleeve 1430, nozzle body 1431 and liquefier tube 1432 collectively describe a filament passageway 1434 through which a filament (not shown) is fed.

In this example, the insert 1407 is received within a head 1435 at the downstream end of the nozzle body 1431. More specifically, the head 1435 includes a receptacle within which the insert 1407 is press-fit. The insert 1407 includes a cylindrical portion 1471 that is press- fit into the receptacle in the head 1435, a tapered downstream end describing an outlet passage 1473 of the nozzle 1432 and a heating element or core 1472 projecting from an upstream side of the cylindrical portion 1471.

The heating core 1472 is in the form of a solid rod joined to the cylindrical portion 1471 of the insert 1407 by a tapering portion 1476 and terminating at a tapering tip 1477. A series of holes 1478 circumscribe the heating core 1472 and extend at an angle relative to the longitudinal axis of the nozzle 1403 to join the outlet passage 1473. With the insert 1407 received within the head 1435 of the nozzle body 1431 , the heating core 1472 extends along the centre of the filament passageway 1434, creating an annular portion of the filament passageway 1434.

The inductive heating sleeve 1409 includes an inductive heating coil 1490 which surrounds the insert 1407. The heating sleeve 1409 is operable, by the controller 1408, to heat the insert 1407 by electromagnetic induction. As such, build material fed into the filament passageway 1434 is forced around the heating core 1472 and through the annular portion of the filament passageway 1434. The build material is then forced into the holes 1478 before merging within the outlet passage 1473 to be deposited on a build bed.

Figures 36 to 39 show another alternative liquefier assembly 1501 , which is similar to that of Figures 34 and 35, wherein like references depict like features, which are incremented by ‘100’. The liquefier assembly 1501 according to this example includes a nozzle 1503, an insert 1507, a controller 1508 and an inductive heating sleeve 1509 electrically connected to the controller 1508 for inductively heating the insert 1507.

The nozzle 1503 in this example differs in that a nozzle tip 1535 and the connection sleeve 1530 are each received within a respective end of the liquefier tube 1532, such that the nozzle body 1531 is provided in part by each of them. The insert 1507 is received within the liquefier tube 1532 and is captivated between the nozzle tip 1535 and the connection sleeve 1530.

As shown more clearly in Figure 39, the insert 1507 includes a heating element or core 1572 in the form of a solid rod with a tapering tip 1576, 1577 at each of its ends. Three spacers 1571 are distributed equally about the circumference of the heating core 1572, adjacent the downstream tapering tip 1576. In this example, the insert 1507 is press fit into the liquefier tube 1532 and abuts the nozzle tip 1535.

With the insert 1507 received within the nozzle body 1531 , the heating core 1572 extends along the centre of the filament passageway 1534, creating an annular portion of the filament passageway 1534. Moreover, the filament passageway 1534 is shaped to approximate the outer surfaces of the heating core 1572, thereby to accommodate the change in flow area that would otherwise result from the presence of the insert 1507.

More specifically, the filament passageway 1534 has an inlet region 1534a, a transition region 1534b, a primary heating region 1534c, a tapering region 1534d and an outlet region 1534e. The connection sleeve 1530 describes the inlet and transition regions 1534a, 1534b. The liquefier tube 1532 describes the primary heating region 1034c. The nozzle tip 1535 describes the tapering and outlet regions 1034d, 1034e.

The inlet region 1534a has a first diameter, the primary heating region 1034c has a second diameter, greater than the first diameter, and the outlet region 1034e has a third diameter, smaller than both the first and second diameters. The diameter of the filament passageway 1534 increases along the transition region 1034b, from the first diameter to the second diameter. The diameter of the filament passageway 1534 decreases along the tapering region 1034d, from the second diameter to the third diameter.

As in the example of Figures 23 to 25, the variation of the diameter of the filament passageway 1534 is configured to provide a substantially constant hydraulic diameter along the length of the inlet, transition and primary heating regions 1534a, 1534b, 1534c.

The liquefier tube 1532 in this example has a substantially constant cross-section surrounding the heating element, and has a radial wall thickness that is substantially less than the width or diameter of the insert 1507. In addition, the insert 1507, and optionally the nozzle tip 1535, is formed of a material that has a higher magnetic permeability, and is more susceptible to inductive heating, than the material from which the liquefier tube 1532 is formed. By way of example, the insert 1507 may be formed at least in part of a mild steel, such as EN24, while at least part of the liquefier tube 1532 may be formed of stainless steel. Similarly, the nozzle tip 1535 may be formed at least in part of a mild steel, such as EN24. Additionally or alternatively, the nozzle tip 1535 may be formed at least in part of stainless steel, tool steel, ceramic or diamond or diamond-like carbon material.

This, coupled with the relatively thin wall of the liquefier tube 1532, results in the heating core 1572 drawing more energy and therefore heating the build material primarily from the inside out. This is contrary to conventional liquefier assemblies, which heat from the outside in. The material of the nozzle tip 1507 may also be configured to draw more energy than the liquefier tube 1532. It is envisaged that the build material would be at least substantially molten by the time it reaches the nozzle tip 1507, and so the nozzle tip 1507 material may be selected simply to maintain the temperature of the build material.

The skilled person will appreciate that several characteristics of the liquefier tube 1532 may be varied to control the balance of heating between it and the heating core 1572. For example, where the liquefier tube 1532 is formed of a material having a lower magnetic permeability or susceptibility to inductive heating, its wall thickness can be increased, for example to improve the rigidity of the assembly. Alternatively, the liquefier tube 1532 may be formed of a similar material to the heating core 1572, or a material having a similar magnetic permeability or susceptibility to inductive heating. In such cases, the wall thickness of the liquefier tube 1532 should be reduced to favour energy absorption by the heating core 1572.

Figures 36 to 39 show another alternative liquefier assembly 1501 , which is similar to that of Figures 34 and 25, wherein like references depict like features, which are incremented by ‘100’. The liquefier assembly 1501 according to this example includes a nozzle 1503, an insert 1507, a controller 1508 and an inductive heating sleeve 1509 electrically connected to the controller 1508 for inductively heating the insert 1507.

Figure 40 shows another alternative liquefier assembly 1601 , which is similar to that of Figures 36 to 39, wherein like references depict like features, which are incremented by ‘100’. The liquefier assembly 1601 according to this example differs from that of the previous example in that the spacers 1571 are replaced with separate spacing elements 1671 , in this case metallic balls. A first group of the spacing elements 1671 are located between the upstream tapering tip 1577 of the insert 1607 and the transition region 1634b of the filament passageway 1634, while a second group of the spacing elements 1671 are located between the downstream tapering tip 1576 of the insert 1607 and the tapering region 1534d of the filament passageway 1634.

Figure 41 shows yet another alternative liquefier assembly 1701 , which is similar to that of Figures 36 to 39, wherein like references depict like features, which are incremented by ‘200’. The liquefier assembly 1601 according to this example differs from that of the previous example in that the spacers 1671 are omitted. Instead, localised regions 1771 of the liquefier tube 1732 are deformed to provide the spacing function, and these localised regions 1771 are spot welded 1771a to the heating core 1772.

It is envisaged that at least part of the filament passageway 1434, 1534, 1634, 1734, or at least part of the liquefier tube 1432, 1532, 1632, 1732 or nozzle body 1431 or nozzle tip 1535, 1635, 1735 describing the filament passageway 1434, 1534, 1634, 1734, may include a coating or layer of material which is susceptible to inductive heating. The coating or layer may, but need not, include a similar material to that which forms the insert 1407, 1507, 1607, 1707. In particular, the coating or layer of material may be on or within the liquefier tube 1432, 1532, 1632, 1732, which may be formed of a ceramic material upon or within which the coating or layer of material may be included, located, deposited or plated. The nozzle tip 1535 could also include an internal coating or layer of material which is susceptible to inductive heating, whilst the majority thereof may be formed of a different material, for example stainless steel, tool steel, ceramic and/or diamond or diamond-like carbon. It is also envisaged that the liquefier tube 1432, 1532, 1632, 1732 may be divided in two or more components, one of which components may be non-conductive or the components may be connected to one another by a non-conductive element.

It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

1. A liquefier assembly for an extrusion-based additive manufacturing system, the assembly comprising a body, a filament passageway through the body and a heating element at least partially within the filament passageway that is operatively connected to circuitry configured to supply, in use, power directly to the heating element such that build material flowing along or through the filament passageway is heated by the heating element.

2. A liquefier assembly according to claim 1 , wherein the heating element projects from a wall of the body into the filament passageway.

3. A liquefier assembly according to claim 2, wherein the heating element spans the filament passageway such that power supplied by the circuitry is received, in use, directly by the heating element across the filament passageway.

4. A liquefier assembly according to claim 2 or claim 3, wherein at least part of the heating element is in a centre of the filament passageway.

5. A liquefier assembly according to claim 4, wherein the circuitry comprises an inductive heating coil which surrounds at least part of the heating element and which is operable to heat, in use, the heating element by electromagnetic induction.

6. A liquefier assembly according to claim 5, wherein at least part of the heating element is formed of a first material that has a higher magnetic permeability (is more susceptible to inductive heating) than a second material from which at least part of the body is formed.

7. A liquefier assembly according to claim 5 or claim 6, wherein the circuitry is configured to approximate the temperature of the build material passing therethrough based at least in part on the curie temperature of the first and second materials

8. A liquefier assembly according to any one of claims 5 to 7, wherein at least part of the heating element is shaped so as to absorb more inductive heating energy than at least part of the body. A liquefier assembly according to any one of claims 5 to 8, wherein the inductive heating coil is configured to emit, in use, a frequency configured to heat the heating element more than the body. A liquefier assembly according to any one of claims 5 to 9 comprising magnetic shielding configured to shield, in use, the magnetic field emitted by the inductive heating coil from a conductive and/or ferrous build bed upon which the liquefier assembly is depositing build material. A liquefier assembly according to any one of claims 5 to 10, wherein the filament passageway comprises an inlet and the heating element comprises an elongate heating core, which is downstream and coaxial with the inlet, extends along the filament passageway and is spaced from a wall of the body to describe therewith an annular portion of the filament passageway. A liquefier assembly according to claim 11 , wherein the heating core comprises a central hole along its length describing a central flow path that is coaxial with and surrounded by the annular portion of the filament passageway. A liquefier assembly according to claim 11 or claim 12, wherein the heating core is spaced from the wall of the body by one or more spacers. A liquefier assembly according to claim 13, wherein the spacers are formed integrally with the heating core. A liquefier assembly according to claim 13, wherein the spacers are formed integrally with the body. A liquefier assembly according to any one of claims 11 to 15, wherein the filament passageway has an outer diameter that increases from the inlet to a region surrounding the heating element. A liquefier assembly according to claim 16, wherein the filament passageway comprises a substantially constant hydraulic diameter along its length. A liquefier assembly according to any one of claims 5 to 17, wherein the body comprises a tube on or within which is located a coating or layer of material which is more susceptible to inductive heating than the material from which the tube is formed. A liquefier assembly according to any one of claims 2 to 4, wherein the circuitry is electrically connected to the heating element and is configured to supply, in use, a current thereto. A liquefier according to claim 19, wherein the heating element comprises a resistive heating element. A liquefier assembly according to claim 19 or claim 20, wherein the heating element has a positive temperature coefficient of resistance and the circuitry is operable to determine, in use, the flow rate and/or temperature of the build material as it flows around the heating element. A liquefier assembly according to any one of claims 19 to 21 comprising a current sensor operatively connected to the circuitry for measuring a current across the heating element as build material flows therearound. A liquefier assembly according to claim 22, wherein the circuitry is operable to determine, in use, a change in current across the heating element as build material flows therearound, the change in current being indicative of flow rate and/or temperature of the build material. A liquefier assembly according to claim 22 or claim 23, wherein the circuitry is configured to determine an electrical resistance of the heating element in dependence on a voltage supplied thereto and a current measured by the current sensor. A liquefier assembly according to any one of claims 22 to 24, wherein, the circuitry is configured to maintain, in use, a substantially constant current or substantially constant temperature in the heating element as build material flows therearound. A liquefier assembly according to any one of claims 2 to 10 and 18 to 25 comprising a plurality of heating elements at least partially within the filament passageway. A liquefier assembly according to claim 26, wherein the heating elements are rotationally offset from one another. A liquefier assembly according to claim 26 or claim 27, wherein the heating elements are spaced from one another along the filament passageway. A liquefier assembly according to any one of claims 26 to 28, wherein each of the heating elements bisect one another when viewed along the filament passageway. A liquefier assembly according to any one of claims 26 to 29, wherein each heating element passes through a centre of the filament passageway such that, in use, heat induced by the heating elements at or toward the centre of the filament passageway is greater than the heat induced thereby at or toward a periphery of the filament passageway. A liquefier assembly according to any one of claims 2 to 10 or 18 to 30, wherein the or each heating element comprises a wire, film, ribbon or a metal-ceramic heater. A liquefier assembly according to claim 31 , wherein the wire(s), film(s), ribbon(s) or metal-ceramic heater(s) span the filament passageway. A liquefier assembly according to claim 31 or claim 32, wherein the wire(s), film(s), ribbon(s) or metal-ceramic heater(s) are received or embedded within a fin spanning the filament passageway. A liquefier assembly according to claim 33, wherein the heating element comprises a metal-ceramic heater forming a fin or blade. A liquefier according to any preceding claim, wherein the heater or a further heater comprises a heating element at least partially external of the filament passageway.

36. A method of heating a build material as it is advanced through a liquefier assembly of an extrusion-based additive manufacturing system, the method comprising advancing a build material along a filament passageway through a body such that the build material is heated by a heating element at least partially within the filament passageway which receives power directly from circuitry.

37. A method according to claim 36, wherein the heating element comprises an elongate heating core which is coaxial with the filament passageway and is spaced from a wall of the body to describe therewith an annular portion of the filament passageway, the method comprising heating the heating core by electromagnetic induction.

38. A method according to claim 37, wherein the filament passageway has an outer diameter that increases from the inlet to a region surrounding the heating element.

39. A method according to claim 36 comprising supplying a current to the heating element so as to heat the build material as it flows around the heating element.

40. A method according to claim 39, wherein the heating element has a positive temperature coefficient of resistance, the method comprising maintaining a substantially constant current or substantially constant temperature in the heating element, measuring a change in the voltage across a measurement bridge as the build material flows around the heating element and determining, in dependence on the change in the voltage across the measurement bridge, the flow rate and/or temperature of the build material as it flows around the heating element.