Three Dimensional Printing Apparatus And A Method

Abstract

A three dimensional printing apparatus (100; 200) is disclosed. The 3D printing apparatus comprises a primary and a secondary set of material dispensing units (1; 10) which each have a nozzle (3) for depositing particulate material (5; 220a, 220b; 224; 226) on a build surface (7), where the nozzle defines a through passage (9) for the material. The through passage has an inlet end (11) for receiving the material and an outlet end (15) for dispensing the material. A valve (21) is provided at least one of at, within or in fluid communication with the through passage for controlling flow of the material via the through passage, the valve being operable between open and closed positions. Flow of said material into the through passage is blocked when in the closed position and, when in the open position, flow of the material into the through passage is allowed. The 3D printing apparatus also comprises an enclosure (137) for containing the material dispensed by the dispensing units and one or more heating elements (210, 212) for heating the material contained in the enclosure to a first predetermined temperature. A method of forming a three dimensional object (31) is also disclosed.

Claims

1-52. (canceled)

53. A three dimensional printing apparatus comprising: one or more primary particulate material dispensing units for dispensing a first particulate material; one or more secondary particulate material dispensing units for dispensing a second particulate material; an enclosure for containing the material dispensed by the one or more primary and one or more secondary particulate material dispensing units; wherein the enclosure comprises a build chamber having a build plate and walls surrounding the build plate, the build plate including a build surface on which the particulate material is deposited layer by layer, wherein the one or more primary and one or more secondary dispensing units are arranged to lay a layer of particulate material on top of an immediately lower layer of particulate material without requiring sintering of each individual layer prior to the laying of the next layer above; wherein each of the said particulate material dispensing units comprise: a nozzle for depositing particulate material on the build surface; the nozzle defining a through passage for said particulate material, the through passage having an inlet end for receiving said particulate material and an outlet end for dispensing said particulate material; a valve provided at least one of at, within or in fluid communication with the through passage for controlling flow of said particulate material via the through passage, the valve being operable between open and closed positions, wherein, in the closed position, flow of said particulate material into the through passage is blocked and, in the open position, flow of said particulate material into the through passage is allowed, wherein the particulate material dispensing unit further comprises a controllable actuator arrangement adapted for actuating the valve to open or close; wherein the through passage has a width in a cross section substantially perpendicular to the direction of flow of said particulate material through said passage and said width is sufficient to allow only a single particle of a predetermined diameter of the particulate material to pass through the cross section widthwise at a time such that only one particle of the predetermined diameter of the particulate material is allowed to exit through passage widthwise and be deposited on the build surface at a time; wherein the through passage has a length in the cross section of the through passage substantially perpendicular to the direction of flow of said particulate material through the passage, the length extending substantially perpendicular to the width; and wherein the length is sufficient to allow a predetermined number of particles of a predetermined diameter of the particulate material to pass through the cross section lengthwise at a time such that the trail of particles deposited on the build surface during relative movement of the particulate material dispensing unit across the build surface, with the valve open, takes the form of a band one particle high and the predetermined number of particles wide in the direction across the band to thereby form a layer one particle high; and the three dimensional printing apparatus further comprising: a control mechanism to provide a predetermined spacing between the build surface and the outlet end of the nozzle of the particulate material dispensing unit so that the distance between the outlet end and the build surface is sufficient to allow each layer to only consist of a single particle high of particulate material to be accommodated between the outlet opening and the build surface; wherein the enclosure further includes one or more heating elements for heating the material contained in the enclosure to a first predetermined temperature; wherein one or more of the heating elements are provided in the walls and the build plate includes one or more of the heating elements and are arranged to pre-heat the material being deposited in the enclosure as well as to bring the temperature of the material to the first predetermined temperature; wherein the respective heating elements are provided within or are arranged in close conductive contact with the walls and the build plate, such that when the respective heating elements are heated in use, that heat is firstly conducted to the walls and build plate and then conducted on to the particulate material deposited therein; wherein the first predetermined temperature is a sintering temperature of the first particulate material and wherein the first particulate material has a melting point lower than that of the second particulate material such that upon being heated by the heating element to the sintering temperature, the first material becomes sintered into a finished article whereas the second material remains unchanged; and wherein the said one or more heating elements provided in the walls and the build plate are capable of heating the entire volume of the material that has been deposited in the enclosure to the first predetermined temperature such that intermediate steps of sintering layer by layer are avoided.

54. A three dimensional printing apparatus according to claim 53, wherein the upper surface of the build plate serves as a build surface for a first layer of the article to be printed.

55. A three dimensional printing apparatus according to claim 53, wherein the width of the through passage in a cross section substantially perpendicular to the direction of flow of said particulate material through the passage is one of constant or varied along the through passage between the inlet and outlet ends as long as there is at least one cross section substantially perpendicular to the direction of flow of said particulate material through the passage whose width is sufficient to allow only a single particle of a predetermined diameter of the particulate material to pass through the cross section widthwise at a time.

56. A three dimensional printing apparatus according to claim 53, wherein the length is sufficient to allow only a single particle of a predetermined diameter of the particulate material to pass through the cross section lengthwise at a time such that the trail of particles deposited on the build surface during relative movement of the dispensing unit across the build surface, with the valve open, takes the form of a line one particle high and one particle wide.

57. A three dimensional printing apparatus according to claim 53, wherein in use, the dispensing unit is positioned in the three dimensional printing apparatus such that during deposition of the particulate material from the nozzle of said dispensing unit, the width of the cross section of the through passage is substantially parallel to the direction of relative movement of the dispensing unit across the build surface and the length of the cross section of the through passage is substantially perpendicular to the direction of relative movement of the dispensing unit across the build surface in a plane substantially parallel to the build surface.

58. three dimensional printing apparatus according to claim 53, wherein the nozzle includes a planar surface surrounding the outlet opening of the through passage and lying in a plane substantially perpendicular to the direction of flow of said particulate material through the passage.

59. A three dimensional printing apparatus according to claim 53, wherein the valve comprises a body movable relative to the through passage of the nozzle between a first position in which the body blocks the through passage and the valve is closed and a second position in which the through passage is unblocked and the valve is open.

60. A three dimensional printing apparatus according to claim 53, wherein the actuator arrangement is controlled by a control unit.

61. A three dimensional printing apparatus according to claim 53, wherein the actuator arrangement comprises a cam pair comprising a cam member and a follower member wherein the follower member is linked with the valve body to move the valve body to open and close the through channel and the cam member is coupled to the follower member, such that movement of the cam member is translated into the movement of the follower member and that of the valve body.

62. A three dimensional printing apparatus according to claim 53, wherein the actuator arrangement is adapted for moving the valve body between the first and second positions thereby opening and closing the through passage.

63. A three dimensional printing apparatus according to claim 53, wherein the actuator arrangement comprises a drive unit for providing motive force for moving the valve.

64. A three dimensional printing apparatus according to claim 53, wherein the body comprises a through channel, wherein in the open position of the valve, the through channel is in alignment with the through passage of the nozzle, and in the closed position of the valve, the through channel is out of alignment with the through passage of the nozzle such that the body blocks the through passage.

65. A three dimensional printing apparatus according to claim 61, wherein the cam member is arranged to move in the dispensing unit along a first path and the follower member is linked with the valve body to move the valve body along a second path for opening and closing the through channel.

66. A three dimensional printing apparatus according to claim 61, wherein the follower member is formed integrally with the valve body and the cam member is coupled with the follower member such that movement of the cam member along the first path is translated into the movement of the follower member and that of the valve body along the second path.

67. A three dimensional printing apparatus according to claim 61, wherein the cam pair comprises a predetermined translation ratio which is the correlation of the distance travelled by the cam member and the distance travelled by the follower member as a result, wherein the predetermined ratio is selected such that for a given distance travelled by the cam member the follower member travels a known smaller distance.

68. A three dimensional printing apparatus according to claim 61, wherein the cam member comprises a piston rod and the follower member comprises a portion of the valve body and a bore is defined in the follower member for receiving the piston rod, wherein the bore has internal walls bevelled in relation to each of the first and second paths and the piston rod is in engagement with the bevelled walls such that during movement of the piston rod to and fro along the first path, force is applied to the bevelled walls of the bore to move the follower member respectively to and fro along the second path with the applicable translation ratio thereby moving the valve body between the open and closed positions.

69. A three dimensional printing apparatus according to claim 61, wherein the cam member is moved by the drive unit of the actuator arrangement.

70. A three dimensional printing apparatus according to claim 53, wherein the dispensing unit comprises a housing incorporating the nozzle, the housing also defining a cavity for accommodating the valve and a seat for mounting the actuator arrangement.

71. A three dimensional printing apparatus according to claim 53, wherein the dispensing unit comprises a delivery arrangement for delivering said particulate material into the through passage and wherein the delivery arrangement is arranged in communication with a storage vessel for containing the particulate material and feeding the particulate material into the delivery arrangement.

72. A three dimensional printing apparatus according to claim 53, wherein a plurality of particulate material dispensing units are arranged in an array to form an assembly of dispensing units.

73. A three dimensional printing apparatus according to claim 60, wherein the control unit is configured for controlling the speed of relative movement of the one or more dispensing unit across the build surface taking into account the predetermined diameter of the particles of the particulate material so that the particles are deposited on the build surface in a one particle thick trail adjacent to each other and, in some instances, in abutment with each other.

74. A three dimensional printing apparatus according to claim 60, wherein the control unit is configured for controlling the actuator arrangement to open and close the respective valve in each dispensing unit independently, such that a three dimensional article can be created which includes parts composed from different particulate materials.

75. A method of forming a three dimensional object, the method comprising the steps of: providing a three dimensional printing apparatus in accordance with claim 53; and printing a three dimensional article using the three dimensional printing apparatus.

76. A method of forming a three dimensional object according to claim 75, wherein the method comprises the step of controlling the valve of the one or more dispensing units to open and close and in the open position of the valve allowing only a single particle of a predetermined diameter of the particulate material to pass through the cross section of the through passage of the nozzle of the one or more dispensing units widthwise at a time.

77. A method of forming a three dimensional object according to claim 75, wherein the method comprises the step of moving the one or more dispensing units relative to the build surface in plane substantially parallel to the build surface and depositing a one particle high trail of particulate material on the build surface.

78. A method of forming a three dimensional object according to claim 75, wherein the method further comprises the step of creating one particle high layer of particulate material of a plurality of trails of particles deposited on the build surface during relative movement of the one or more dispensing units across the build surface, each trail being laid in the form of a band one particle high and a predetermined number of particles wide in the direction across the band or a line one particle high and one particle wide.

79. A method of forming a three dimensional object according to claim 75, wherein the method comprises controlling the speed of relative movement of the dispensing unit across the build surface taking into account the predetermined diameter of the particles of the particulate material being deposited so that the particles are deposited on the build surface adjacent to each other.

80. A method of forming a three dimensional object according to claim 75, wherein the method includes controlling relative movement of the one or more dispensing units in relation to the build surface along an axis substantially perpendicular to the build surface so as to provide a predetermined spacing between the build surface and the outlet end of the through passage of nozzle of the dispensing unit.

81. A method of forming a three dimensional object according to claim 75, wherein the method includes controlling said relative movement so that a distance between said outlet end and the build surface is sufficient to allow only a single particle of a predetermined diameter of the particulate material to be accommodated between the outlet opening of the nozzle and the build surface in the direction substantially perpendicular to the build surface.

82. A method of forming a three dimensional object according to claim 75, wherein once a new layer has been created, the dispensing unit is spaced from the new layer by the same distance.

83. A method of forming a three dimensional object according to claim 75, wherein the build volume is pre-heated via heating elements provided in the build plate and surrounding walls to bring the temperature of the powder to just under the temperature required for sintering.

84. A method of forming a three dimensional object, the method comprising the steps of: providing a three dimensional printing apparatus in accordance with claim 53; wherein the method includes dispensing a first particulate material and a second particulate material into the enclosure, wherein the first predetermined temperature is a sintering temperature of the first particulate material and wherein the first particulate material has a melting point lower than that of the second particulate material and the method further includes heating the first material by the heating element to the first predetermined temperature so that the first material becomes sintered into a finished article whereas the second material remains unchanged; wherein the method includes depositing all the particulate material required to form an article into the enclosure and heating the entire volume of the material that has been deposited in the enclosure such that intermediate steps of sintering layer by layer are avoided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Embodiments of the present invention are described hereinafter with reference to the accompanying drawings in which:

[0102] FIG. 1 is a cross-sectional side view of a material dispensing unit in accordance with the invention showing a valve of the dispensing unit in a closed position; and a close-up view of the valve;

[0103] FIG. 2 is a cross-sectional side view of the dispensing unit of FIG. 1 showing the valve of the dispensing unit in an open position; and a close-up view of the valve;

[0104] FIG. 3 is a quarter-sectional perspective view of a dispensing unit similar to that of FIG. 2 showing the valve of the dispensing unit in an open position and a line of material particles being deposited by the dispensing unit; and a close-up view of the valve;

[0105] FIG. 4 is a quarter-sectional perspective view of a dispensing unit similar to that of FIG. 2 showing the valve of the dispensing unit in an open position and a band of material particles being deposited by the dispensing unit; and a close-up view of the valve;

[0106] FIGS. 5, 6 and 7 are, respectively, a front view, a bottom view and a perspective view of a primary assembly of dispensing units of FIG. 1;

[0107] FIG. 8 is a partial perspective view of the assembly of FIGS. 5 to 7;

[0108] FIG. 9 is a partial cross-sectional end view of the assembly of FIGS. 5 to 7;

[0109] FIGS. 10, 11 and 12 are perspective views showing variations of a through channel in a valve body of the valve of the dispensing unit;

[0110] FIGS. 13, 14, 15 and 16 are, respectively, a perspective view, a front view, a bottom view and an enlarged partial bottom views of an ancillary assembly of dispensing units of FIG. 1;

[0111] FIG. 17 is a perspective view of a housing of the primary assembly of FIGS. 5, 6 and 7;

[0112] FIG. 18 is a transparent perspective view of the housing of FIG. 17;

[0113] FIG. 19 is a perspective view of a housing of the ancillary assembly of FIGS. 13, 14, 15 and 16;

[0114] FIG. 20 is a transparent perspective view of the housing of FIG. 19;

[0115] FIGS. 21 and 22 are, respectively, a perspective view and a plan view of a 3D printing apparatus in accordance with the invention, prior to printing a 3D article;

[0116] FIGS. 23 and 24 are, respectively, a perspective view and a front cross-sectional view of a 3D printing apparatus in accordance with the invention, after printing a 3D article;

[0117] FIG. 25 is a front cross-sectional view of another embodiment of a 3D printing apparatus in accordance with the invention;

[0118] FIG. 26 is a front cross-sectional view of the embodiment of 3D printing apparatus of FIG. 25 but in more detail; and

[0119] FIG. 27 is a perspective part (quarter) cross-sectional view of the embodiment of 3D printing apparatus of FIG. 26.

DETAILED DESCRIPTION OF THE INVENTION

[0120] Referring to FIGS. 1 to 25, a three dimensional (3D) printing apparatus for forming three dimensional objects, a material dispensing unit therefor and a corresponding method of three dimensional printing will now be jointly described. The material dispensing unit of the invention is indicated generally using reference numerals 1 and 10 in the Figures. The 3D printing apparatus of the invention is indicated generally by reference numerals 100 and 200 in the Figures.

[0121] Referring initially to FIGS. 1 to 4, the material dispensing unit 1 for the three dimensional printing apparatus 100 comprises a housing 2 incorporating a nozzle 3 for depositing particulate material 5 on a build surface 7. It will be appreciated that in the present specification, for brevity, the term “build surface”, unless otherwise specified, includes an upper surface of a newly created layer onto which a subsequent layer is to be deposited as well as an upper surface of a build plate (to be described below) of the three dimensional printing apparatus. Typically, the upper surface of the build plate serves as a build surface for a first layer of the article to be printed. The nozzle 3 defines a through passage 9 for the material 5 and has an inlet end 11 for receiving the material 5 and an outlet end 15 for dispensing the material 5. The housing 2 incorporates a delivery arrangement provided in the form of a delivery duct 17 for delivering the material 5 into the through passage 9. The housing 2 also defines a cavity 19 for accommodating a valve 21 provided between the delivery duct 17 and the through passage 9 for controlling flow of the material 5 between the delivery duct 17 and the through passage 9. The valve 21 is operable between open and closed positions, wherein, in the closed position (FIG. 1), flow of the material 5 into the through passage 9 is blocked and, in the open position (FIGS. 2, 3 and 4), flow of the material 5 into the through passage 9 is allowed. The valve comprises a body 23 movable relative to the through passage 9 of the nozzle 3 between a first position (FIG. 1) in which the body 23 blocks the through passage 9 and the valve 21 is closed and a second position (FIGS. 2, 3 and 4) in which the through passage 9 is unblocked and the valve 21 is open. The body 23 comprises a through channel 25, wherein in the open position of the valve 21, the through channel 25 is in alignment with the through passage 9 of the nozzle 3 and with the delivery duct 17, and in the closed position of the valve 21, the through channel 25 is out of alignment with the through passage 9 of the nozzle 3 such that the body 23 blocks the through passage 9.

[0122] The through passage 9 has a longitudinal axis 33 (FIG. 1) extending between the inlet end 11 and the outlet end 13 substantially in the direction X (FIGS. 1 and 2) of flow of the material 5 through the passage 9. The through passage 9 has a width W in a cross section Z (FIGS. 1 to 4) substantially perpendicular to the longitudinal axis 33. In the presently described embodiment, the width W is sufficient to allow only a single particle 27 of a predetermined diameter of the particulate material 5 to pass through the cross section Z widthwise at a time. Accordingly, only one particle 27 of the predetermined diameter of the particulate material 5 is allowed to exit the through passage 9 widthwise and be deposited on the build surface 7 at a time. This allows a one particle high trail 29 of particles 27 of the predetermined diameter to be deposited on the build surface 7 during relative movement of the dispensing unit 1 across the build surface 7 with the valve 21 open. This in turn increases accuracy of a finished printed 3D article 31 (FIGS. 23 and 24). The speed of relative movement of the dispensing unit 1 across the build surface 7 is selected taking into account the predetermined diameter of the particles 27 so that the particles of the trail 29 are deposited on the build surface 7 adjacent to each other and, in some instances, in abutment with each other. Other widths W may be selected however, as appropriate.

[0123] Preferably, the predetermined diameter is the maximum particle diameter specified for a given batch of the particulate material.

[0124] In the presently described embodiment, the width W of the through passage 9 between the inlet and outlet ends 11, 13 in any given cross section Z substantially perpendicular to the direction X is constant. It will be appreciated, however, that the width W can vary along the direction of flow of the material through the passage 9 between the inlet and outlet ends 11, 13 as long as there is at least one cross section Z substantially perpendicular to the direction of flow of the material through the passage 9 whose width W is sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material 5 to pass through the cross section Z widthwise at a time. In the presently described embodiment, the width W is provided by the cross sectional dimension of the through passage 9 itself. In other instances, the width W may be provided differently, for example, by obstructing the through passage 9 by another object, such as, for example, but not limited thereto, by a relevant portion of the valve 21.

[0125] The through passage 9 has a length L (not visible in FIGS. 1 to 4, but shown in FIGS. 6, 15 and 18) in the cross section Z of the through passage 9 substantially perpendicular to the direction of flow of the material through the passage 9. The length L extends substantially perpendicular to the width W.

[0126] In the variation shown in FIG. 3, the length L is sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material 5 to pass through the cross section Z lengthwise at a time. In other words, the cross section Z of the through passage 9 takes the form of an aperture 35 (see FIG. 15) having a width W and a length L, in other words, a diameter, sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material 5 to pass through the cross section Z at a time. In this variation, the trail 29 of particles 27 deposited on the build surface 7 during relative movement of the dispensing unit 1 across the build surface 7, with the valve 21 open, takes the form of a line 37 (see FIG. 3) one particle 27 high and one particle 27 wide. In one particular variation, the aperture may be 0.1 mm in diameter.

[0127] In the variation shown in FIG. 4, the length L is sufficient to allow a predetermined number of particles 27 of the predetermined diameter of the particulate material 5 to pass through the cross section Z lengthwise at a time. In other words, the cross section Z of the through passage 9 takes the form of a slit 39 (see FIG. 15) having a width W sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material 5 to pass through the cross section Z widthwise at a time and a length L sufficient to allow a predetermined number of particles 27 of the predetermined diameter of the particulate material 5 to pass through the cross section Z lengthwise at a time. In this variation, the trail 29 of particles 27 deposited on the build surface 7 during relative movement of the dispensing unit 1 across the build surface 7, with the valve 21 open, takes the form of a band 41 (see FIG. 4) one particle 27 high and the predetermined number of particles 27 wide in the direction Y across the band 41. In one particular variation, the slit 39 may be 0.1 mm wide and 4 mm long.

[0128] In use, the dispensing unit 1 is positioned in the three dimensional printing apparatus 100 such that during deposition of the particulate material 5 from the nozzle 3, the width W of the cross section Z of the through passage 9 is substantially parallel to the direction D of relative movement of the dispensing unit 1 across the build surface 7 and the length L of the cross section Z of the through passage 9 is substantially perpendicular to the direction of relative movement of the dispensing unit 1 across the build surface 7 in a plane substantially parallel to the build surface 7.

[0129] The nozzle 3 includes a planar surface 43 (FIGS. 1 and 2) surrounding the outlet opening 13 of the through passage 9 and lying a plane substantially perpendicular to the direction of flow of the material through the passage 9. The provision of the planar surface 43 helps to ensure that a one particle high layer of particles 27 is deposited on the build surface 7 and to hold down the already deposited particles 27.

[0130] As shown in FIGS. 10 to 12, the through channel 25 of the valve body 23 may be shaped to conform to the shape of the through passage 9 of the nozzle 3. For example, if the through passage 9 takes the form of an aperture 35, the through channel 25 may also be provided as an aperture 45 (FIG. 10). If the through passage 9 takes the form of a slit 39, the through channel 25 may also be provided as a slit 47 (FIGS. 11 and 12).

[0131] The dispensing unit 1 comprises a controllable actuator arrangement 49, hereinafter referred to as actuator 49 for brevity, adapted for actuating the valve 21 to open or close. The actuator is located in a seat 18 provided in the housing 2. The actuator 49 is controlled by a control unit (not shown) of the 3D printing apparatus 100. The actuator 49 is adapted to move the valve body 23 between the first and second positions thereby opening and closing the through passage 9 as will be described in more detail below. The actuator 49 comprises a drive unit 51 for providing motive force for moving the valve 21. The drive unit 51 may be provided, for example, in the form of a stepper motor. An example of a suitable stepper motor is Haydon Kerk™ L15000 but other suitable models will be apparent to a person skilled in the art. It will be appreciated that the drive unit 51 may also be provided in any suitable form apparent to a person skilled in the art, such as for example, a different type of motor, a piezoelectric transducer, a hydraulic or pneumatic cylinder or other suitable means. The control unit is preferably an electronic control unit, preferably, a programmable electronic control unit.

[0132] The actuator 49 further comprises a cam pair comprising a cam member provided in the form of a piston rod 53 and a follower member 55 defined by a portion of the valve body 23. The piston rod 53 is moved by the drive unit 51 and is linked to the drive unit 51 by an actuator rod 57. The follower member 55 is integrally formed with the valve body 23 to move the valve body 23 to open and close the through channel 9 and the piston rod 53 is coupled with the follower member 55, such that movement of the piston rod 53 is translated into the movement of the follower member 55 and that of the valve body 21. The piston rod 53 is preferably arranged to move in the dispensing unit 1 along a first path P1. The follower member 55 moves the valve body 21 along a second path P2 for opening and closing the through channel 9. The piston rod 53 is coupled with the follower member 55 such that movement of the piston rod 53 along the first path P1 is translated into the movement of the follower member 55 and that of the valve body 21 along the second path P2. In the presently described embodiment, the first and second paths P1, P2 are provided perpendicular to each other. A bore 59 is defined in the follower member 55 for receiving the piston rod 53. The bore 59 has internal walls 61 bevelled in relation to each of the first and second paths P1, P2 and the piston rod 53 has complementary bevelled surfaces 63 in engagement with the bevelled walls 61 such that during movement of the piston rod 53 to and fro along the first path P1, force is applied to the bevelled walls 61 of the bore 59 to move the follower member 55 respectively to and fro along the second path P2. The cam pair has a predetermined translation ratio, i.e. the correlation of the distance travelled by the piston rod 53 along the first path P1 and the distance travelled by the follower member 55 along the second path P2 as a result. The predetermined ratio is selected such that for a given distance travelled by the piston rod 53 the follower member 55 travels a known smaller distance. Such an arrangement provides for a greater precision of the movement of the follower member 55 and as a result, that of the valve body 23. For example, if the ratio of the cam pair is 5:1, for any 5 given units of distance travelled by the piston rod 53 the follower member 55 travels 1 unit of distance. Other suitable ratios may be selected as necessary. Other variations of the cam member 53 and the follower member 55 will be apparent to a person skilled in the art.

[0133] It will be appreciated that the present invention is not limited to a particular type the actuator 49 and other types of actuator 49 will be apparent to a person skilled in the art. For example, but not limited thereto, the actuator 49 may be provided by a gear box, a worm box, a gear and a plank or another suitable mechanical or electromechanical actuation mechanism.

[0134] As shown in FIGS. 17 to 20, the housing 2 comprises one or more interlocking members or portions 65 for being connected with one or more housings 2 of further such dispensing units 1 in order to form an assembly comprising a plurality of dispensing units 1 as will be described below. Alternatively or additionally, as shown in FIGS. 8, 9 and 13, 14, the housing 2 may incorporate a plurality of nozzles 3, a plurality of cavities 19 for accommodating respective valves 21 and a plurality of seats 18 for mounting respective actuators 49.

[0135] The delivery duct 17 is arranged in communication with a storage vessel provided in the form of a generally upright chute 67 for containing the particulate material 5 and feeding the particulate material into the delivery duct 17. The upright chute 67 is located above the delivery duct 17 for gravity feeding the delivery duct 17.

[0136] Referring to FIGS. 5 to 7 and 13 to 16, in the presently described embodiment, a plurality of material dispensing units 1 form an assembly, indicated generally by reference numeral 70, wherein the dispensing units 1 are arranged in an array. The dispensing units 1 are connected in the assembly via the interlocking members 65 of respective housings 2. In such an assembly, individual chutes 67 may be provided for each delivery duct 17. Alternatively, as shown in FIGS. 5, 7 and 13, 14 one chute 67 may be arranged to feed a number of delivery ducts 17.

[0137] As shown in FIGS. 5 to 7, there is provided a first assembly, hereinafter referred to as the primary assembly 72 for brevity, comprising a plurality of primary dispensing units 1a arranged to form an array and adapted for dispensing first particulate material (not shown). The first particulate material may comprise one or more sub-types of the first material.

[0138] As shown in FIGS. 13 to 16, there is provided a second assembly, hereinafter referred to as the ancillary assembly 74 for brevity, comprising a plurality of ancillary dispensing units 1b arranged to form an array and adapted for dispensing second particulate material (not shown). The second particulate material may comprise one or more sub-types of the second material.

[0139] The first and second materials may be the same or different type of material. The first and second materials may be the same colour or different colours. The first and second materials may have the same or different fineness. In the presently described embodiment, the first particulate material is coarser than the second particulate material.

[0140] In the primary assembly 72, the primary dispensing units 1a have the through passages 9 that are provided as slits 39 having a width W sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material to pass through the cross section Z (see FIG. 1) widthwise at a time and a length L sufficient to allow a predetermined number of particles 27 of the predetermined diameter of the particulate material to pass through the cross section Z lengthwise at a time. The slits 39 are uniformly oriented in the primary assembly 72. The slits 39 are positioned such that an uninterrupted band (not shown) of material is deposited on the build surface 7 from the slits 39 when the respective valves 21 are open. The slits 39 may be positioned in a single line. However, as shown in FIG. 6, to ensure that there are no gaps between individual bands of material deposited between two adjacent slits 39, the slits 39 are preferably positioned along at least two parallel lines in which the slits 39 are arranged in a staggered manner.

[0141] In the ancillary assembly 74, some of the ancillary dispensing units 1b have through passages 9 that are provided as slits 39 having a width W sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material to pass through the cross section Z (see FIG. 1) widthwise at a time and a length L sufficient to allow a predetermined number of particles 27 of the predetermined diameter of the particulate material to pass through the cross section Z lengthwise at a time. As shown in FIGS. 15, 16, the assembly 74 includes four slits 39 which are positioned rotated relative to each other by 90 degrees in a plane substantially parallel to the build surface 7. The rotation between said slits allows two of the four slits 39 to deposit respective bands of material when the ancillary assembly 74 is moved in a first direction D1 substantially perpendicular to each of the two slits 39; and the other two of the four slits 39 can deposit respective bands of material when the ancillary assembly 74 is moved in a second direction D2 substantially perpendicular to each of the said other two slits 39 and to the first direction D1. Some of the ancillary dispensing units 1b have the through passages 9 that are provided as apertures 35 having cross sections Z with a width W and a length L sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material to pass through the cross section Z of the aperture 35 at a time.

[0142] Referring to FIGS. 21 to 24, the three dimensional printing apparatus 100 in accordance with the presently described embodiment of the invention comprises a primary assembly 72 of dispensing units 1a for dispensing first material and an ancillary assembly 74 of dispensing units 1b for dispensing second material. The apparatus 100 includes a build plate 107 which has an upper surface 109 serving as a build surface 7 for a first layer of the article 31 to be printed. The first layer deposited on the upper surface 109 of the build plate 107 is typically not sintered so that the printed article 31 remains unattached to the build plate 107 for ease of removal. The assemblies 72, 74 are movably arranged in the apparatus 100 to move relative to the build surface 7 in a plane substantially parallel to the build surface 7 as will be described below in more detail. Although not shown in the drawings, the apparatus 100 comprises a control arrangement configured for controlling the relative movement of the assemblies 72, 74 across the build surface 7. The control arrangement is also configured for controlling the speed of relative movement of the assemblies 72, 74 across the build surface 7 taking into account the predetermined diameter of the particles of the first and second materials so that the particles are deposited on the build surface 7 in a one particle high trail adjacent to each other and, in some instances, in abutment with each other.

[0143] A motor 103 is provided for effecting movement of the build plate 107 along an axis 111 substantially perpendicular to the build surface 7 (and which is typically the vertical axis 111) to provide spacing between the build surface 7 and the outlet ends 13 of the dispensing units 1a, 1 b. A guide structure is provided in the form of a lead screw 105 for guiding and supporting the build plate 107 during its movement along the axis 111 (typically to raise and/or lower the build platform along the vertical axis 111). The apparatus 100 also includes a control mechanism (not shown) configured for controlling the motor 103 so as to provide a predetermined spacing between the build surface 7 and the outlet ends 13 of the dispensing units 1a, 1b. Preferably, the control mechanism is configured for controlling the motor 103 so that the distance between the outlet ends 13 and the build surface 7 is sufficient to allow only a single particle 27 of the predetermined diameter of the particulate material to be accommodated between each outlet opening 13 and the build surface 7 in the direction of the axis 111. This ensures that a one particle high layer is deposited on the build surface 7 and that the already deposited particles are held in place. Once a new layer has been created and sintered, the dispensing units 1a, 1b are spaced from the new layer by the same distance to allow another new layer to be created.

[0144] Further respective main motor 115 and ancillary motor 117 are provided for moving and positioning the assemblies 72, 74 in a plane XY substantially parallel to the build surface 7. The primary assembly 72 is mounted on a main carrier frame 119 which in turn is mounted on a main guide structure 121 and is moved by the main motor 115 along a first axis 123 substantially parallel to the build surface 7. The ancillary assembly 74 is mounted on an ancillary carrier frame 127 which in turn is mounted on an ancillary guide structure 129 and is moved by the ancillary motor 117 along a second axis 125 which is perpendicular to the first axis 123 in a plane substantially parallel to the build surface 7. The ancillary guide structure 129 is in turn mounted on the main carrier frame 119 so that the ancillary assembly 74 can be moved along both first and second axes 123, 125. Generally, the ancillary guide structure 129 is preferably arranged to give the ancillary carrier frame 127 more degrees of freedom to move across the build surface 7 than has the main carrier frame 119. In the presently described embodiment, the main guide structure 121 is provided by a pair of lead screws 121a, 121b laterally spaced apart relative to the first axis 123 and the ancillary guide structure 129 is provided by a pair of lead screws 129a, 129b laterally spaced apart relative to the second axis 125. It will be appreciated that the guide structures 121, 129 may be provided in any suitable form, as will be apparent to a person skilled in the art. Each of the main guide structure 121 and the ancillary guide structure 129 includes a synchronising mechanism, in the presently described embodiment provided in the form of respective drive belts 131, 133 coupled between the respective lead screws 121a, 121b; 129a, 129b, to synchronise rotation of the lead screws 121a, 121b; 129a, 129b. The main carrier frame 119 and the ancillary carrier frame 127 may be sliding carrier frames.

[0145] The apparatus 100 includes a build chamber 137 for containing the deposited particulate material 5. The build chamber 137 is defined by walls 139 surrounding the build plate 107 whereas the build plate 107 functions as a base of the build chamber 137. The walls 139 of the build chamber 137 may be transparent.

[0146] The apparatus 100 is preferably configured for sintering only predetermined regions in any given layer. The apparatus 100 comprises a laser sintering unit 141 provided above the build surface 7 and configured for selective sintering of the loose particulate material 5 in any given layer deposited by the dispensing units 1a, 1b to create solid regions in the layer and to bond the solid regions to the previously created layer. An electronic control system (not shown) is provided configured for controlling the operation of the laser sintering unit 141 to sinter predetermined regions 143, 145 in the layer of the deposited material. Any unsintered material 147 along with the sintered regions, becomes a support structure for the subsequent layer. The process is repeated until a solid 3D printed article 31 is obtained which can be picked up out of the unsintered material 147. Any unused loose material, including the unsintered material 147 and leftover material in the dispensing units 1a, can be re-used for the next print. The material used in the unsintered regions is preferably the material from the dispensing units 1b of the main assembly 72, i.e. the first material.

[0147] The control unit for controlling the actuators 49, is configured for controlling the actuators 49 of the main assembly 72 to selectively open and close of the valves 21 of the dispensing units 1a of the main assembly 72 in order to deposit the first material onto the predetermined regions 143 on the build surface 7. This allows the predetermined regions 147 in a layer to be left blank. The blank predetermined regions 147 can then be filled using the second material of the dispensing units 1b of the ancillary assembly 74. For this purpose, the control unit for controlling the actuators 49, is configured for controlling the actuators 49 of the ancillary assembly 74 to selectively open and close of the valves 21 of the dispensing units 1b of the ancillary assembly 74 in order to deposit the second material onto the predetermined regions 147 on the build surface 7 that have been left blank. Thus, a three dimensional article 31 can be created which includes parts 151, 153 composed from different materials. The control unit is preferably configured for controlling the actuator 49 in each dispensing unit 1a, 1b independently.

[0148] Referring to FIGS. 25 to 27, a further embodiment of the three dimensional printing apparatus of the invention is indicated generally by reference numeral 200. The apparatus 200 in the presently described embodiment is similar to the apparatus 100 described above in that it employs similar dispensing units 1a, 1b as those used in the apparatus 100 and particulate material is dispensed in a manner similar to that described above. Therefore, for brevity, the apparatus 200 will be described below in terms of its difference from the apparatus 100 and like reference numerals have used in FIGS. 25 to 27 to denote features of the apparatus 200 common with those of the apparatus 100.

[0149] The apparatus 200 comprises a primary assembly 72 comprising a plurality of primary dispensing units 1a for dispensing first particulate material 220a, 220b (which may be multiple different types of powder from respective multiple different primary dispensing units 1a simultaneously into the gaps left by the bulk or ancillary dispensing units 1b) and a second assembly 74 comprising a plurality of ancillary dispensing units 1b for dispensing second particulate material 224 (which is likely to be the bulk of the material and moreover is preferably whichever powder material that will take up the most volume in the build chamber 137). The apparatus 200 comprises an enclosure provided in the form of a build chamber 137 for containing the material dispensed by the dispensing units 1a, 1b. The build chamber 137 has a build plate 107 and walls 139 surrounding the build plate 107. The build plate 107 includes a build surface 7 on which the first layer of the material 220a, 220b, 224 is deposited, with each respective subsequent planar layer of the material 220a, 220b, 224 being deposited in turn on top of the immediately previous layer as in the apparatus 100.

[0150] The apparatus 200 differs from the apparatus 100 in that instead of using a laser sintering unit to heat the required material 220a, 220b in the layer just laid (prior to the next layer being laid), the apparatus 200 comprises heating elements 210, 212 arranged in the build chamber 137 for heating the material 220a, 220b contained in the build chamber 137 to a first predetermined temperature which is a sintering temperature of the first particulate material 220a, 220b. The heating elements 210 are provided within or are arranged in close conductive contact with the walls 139 and the heating element 212 is provided within or are arranged in close conductive contact with the build plate 107, such that when the heating elements 210, 212 are heated, that heat is firstly conducted to the walls 139 and build plate 107 and then conducted on to the various powder/particulate materials 220a, 220b, 224 being used therein. Accordingly, the walls 139 and build plate 107 act as heat conductors to transfer thermal energy from the heating elements 210, 212 to the various powder/particulate materials 220a, 220b, 224 contained within the walls 139 and build plate 107. Importantly, the walls 139 and build plate 107 are formed of a heat conductive material comprising a higher melting and/or sintering temperature than all of the various powder/particulate materials 220a, 220b, 224 being used therein. It should be noted that the heating elements 210, 212 can also be initially used as pre-heaters to reduce warping and thermal stresses in the powders/particulate materials 220a, 220b, 224. However, as hereinbefore described, during the final stage the heating elements 210, 212 will raise the temperature within the build volume defined by the inner surfaces of the walls 139 and build plate 107 to just above the melting and/or sintering temperature of the powders 220a, 220b being formed into the finished product but below the temperature of the ‘refractory’ powder 224. This allows the powders 220a, 220b to be melted and/or sintered into a finished object without the need for the laser system used in the first embodiment of the three dimensional printing apparatus 100 which utilised selective laser sintering & selective laser melting. It should be noted that the heating elements 210, 212 can be simple metal or ceramic heating elements 210, 212 that use thermal conduction to transfer heat through the build chamber walls 139 and/or the build plate 107 into the build volume and such an arrangement is suitable for non-conductive powders 220a, 220b, 224. like plastics or ceramics. Alternatively, for certain metal powders, which are electrical conductors, the use of induction heat mechanisms can be utilised. Further alternatively, any other suitable form of heating can be used to raise the temperature of the build volume in a controlled manner.

[0151] Although not shown in the drawings, the build chamber 137 may be surrounded by thermal insulation to minimise heat loss and maximise the heat energy stored in the material being deposited. The first particulate material 220a, 220b has a melting point lower than that of the second particulate material 224. Upon being heated by the heating elements 210, 212 and therefore the walls 139 and build plate 107 to or just above the sintering temperature of the first material 220a, 220b, the first material 220a, 220b becomes sintered into a finished article 31 whereas the second material 224, which may also be referred to as a refractory (or crucible) material, a filler material or a bulk material, remains unchanged. Since the second material 224 retains its particulate form, the finished article 31 can be simply withdrawn from the mass of the second material 224 upon conclusion of the sintering process.

[0152] The heating elements 210, 212 are preferably arranged to pre-heat the material 220a, 220b, 224 in the build chamber 137 (in order to reduce the time taken for the overall sintering process) as well as to bring the temperature of the material 220a, 220b, 224 to the first predetermined temperature. In use, all the material 220a, 220b required to form an article 31 is deposited into the build chamber 137 and the heating elements 210, 212 are arranged to heat the entire volume of the material 220a, 220b, 224 that has been deposited in the build chamber 137. Thus, intermediate steps of sintering layer by layer are avoided and this provides the great advantage for embodiments of apparatus 200 that the time taken to produce the finished article 31 will be greatly reduced compared to the time taken for the finished article 31 produced by the first embodiment of apparatus 100.

[0153] The first particulate material 220a, 220b may comprise one or more sub-types. The sub-types of the first material 220a, 220b may be the same or different type of material, the same colour or different colours or may have the same or different fineness.

[0154] Although not shown in the drawings, the apparatus 200 may include a third dispensing unit for dispensing third particulate material 226 between the first material 220a, 220b and the second material 224. The third material may 226 be, for example, but not limited thereto, a water dissolvable plastic or a wax based particulate material. Accordingly, the second material 224 such as sand is used as the ‘refractory’ powder 224 and acts as a mould between which the ancillary powder 220 or powders 220a, 220b can be sintered and/or melted into finished parts or article 31. After sintering, a layer of the second material 224 may become adhered to outer surfaces of the finished article 31 formed from the first material 220a, 220b. Certain types of second material 224, such as for example, sand and which could be simple building sand (of approximately 80 to 100 micron size sand), can be easily removed by, for example, flushing the article with water or other suitable fluid.

[0155] Where this is not possible, the provision of the layer of third material 226 prevents contamination of the finished article 31. Alternatively, the third material 226 can be used to create a deliberate coating on the finished article 31.

[0156] Modifications are possible within the scope of the invention as will be apparent to a person skilled in the art.