Method of printing a layer of a 3D object from a first material and a second material

Abstract

A method of printing a layer of a three-dimensional object formed from a first material and from a second material, wherein the method comprises during a printing pass depositing the first material, the first material being provided up to a predetermined border, wherein the deposited first material comprises a wall portion located at the predetermined border; and during a subsequent printing pass depositing the second material, the second material being provided up to the predetermined border wherein the deposited second material includes a wall portion located at the predetermined border; wherein the during the first printing pass the second material is also deposited as a bulk portion but as a lower proportion of the layer than the deposited wall portion, and / or during the second printing pass the first material is also deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion; and wherein the deposited bulk portion is separated from the predetermined border by a gap

Description

METHOD OF PRINTING A LAYER OF A 3D OBJECT FROM A FIRST MATERIAL AND A SECOND MATERIALFIELD

[0001] The present application relates to a method of printing a layer of a three-dimensional object. The method may for example be a material jetting 3D printing method.BACKGROUND

[0002] Forming a three-dimensional object by printing layers of the object is known as 3D printing or additive manufacturing. Material jetting 3D printing is an advanced fabrication technique that builds three-dimensional objects layer by layer using inkjet printing technology.

[0003] When using Material jetting 3D printing to print an object, multiple printing passes are used for a given layer. A printing pass refers to a single traversal of a printer's print head system over an object area which is being printed (or a single traversal of an object supporting platform beneath a print head system). Material that has been deposited during the printing pass is cured before the next printing pass. In some cases, in order to avoid undesirable coalescence of deposited droplets of material, four or more printing passes of the print head system are needed in order to form a layer. This means that a considerable time is required to form the layer. Because the object is formed from many layers, this may mean that material jetting 3D printing of some objects is slow, and that the objects are expensive.

[0004] It is an object of the present invention to provide a method of printing a layer of a three- dimensional object which addresses a problem associated with known printing methods.SUMMARY

[0005] According to a first aspect of the invention there is provided a method of printing a layer of a three-dimensional object formed from a first material and from a second material, wherein the method comprises during a printing pass depositing the first material, the first material being provided up to a predetermined border, wherein the deposited first material comprises a wall portion located at the predetermined border; and during a subsequent printing pass depositing the second material, the second material being provided up to the predetermined border wherein the deposited second material includes a wall portion located at the predetermined border; wherein during the first printing pass the second material is also deposited as a bulk portion but as a lower proportion of the layer than the deposited wall portion of the first material, the deposited bulk portion being separated from the predetermined border by a gap; and / or during the second printing pass the first material is also deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion of the second material, the deposited bulk portion being separated from the predetermined border by a gap.

[0006] Advantageously, the method can provide a layer using less printing passes and / or with a higher accuracy than conventional methods.

[0007] In an embodiment, the first and second materials are provided on opposite sides of the predetermined border.

[0008] In an embodiment, the term “wall portion located at the predetermined border” may be interpreted as meaning a wall portion which has an outer surface which lies at the predetermined border. Thus, the wall portion of the first material meets the wall portion of the second material at the predetermined border. The first material is on one side of the predetermined border and the second material is on the other side of the predetermined border.

[0009] During the printing pass which deposits the first material, the first material may also be deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion. During the subsequent printing pass which deposits the second material, the second material may also be deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion.

[0010] During the first printing pass all locations in the first material wall portion may receive the first material. During the subsequent printing pass all locations in the second material wall portion may receive the second material.

[0011] Two printing passes may be performed to form the layer (the subsequent printing pass being the second printing pass). During the first printing pass the first material may be deposited as the wall portion and the bulk portion. The second material may be deposited as the bulk portion separated from the predetermined border by the gap. During the subsequent printing pass the second material may be deposited as the wall portion and the bulk portion. The first material may be deposited as the bulk portion separated from the predetermined border by the gap.

[0012] Three printing passes may be performed to form the layer

[0013] Four printing passes may be performed to form the layer. During the first printing pass and a second printing pass the first material may be deposited as the wall portion and the bulk portion. The second material may be deposited as the bulk portion separated from the predetermined border by the gap. The first printing pass and second printing pass may both taking place before the subsequent printing pass. During the subsequent printing pass and a further subsequent printing pass the second material may be deposited as the wall portion and the bulk portion. The first material may be deposited as the bulk portion separated from the predetermined border by the gap.

[0014] The object may be formed from an object material and a support material, the support material being configured for subsequent removal from the object material to form a finished object. The first material may be the support material and the second material may be theobject material. Alternatively, the first material may be the object material and the second material may be the support material.

[0015] The first and second materials may both be object materials. Providing the first and second materials as object materials may be used when it is desired to have a well-defined border between two object materials.

[0016] The wall portion may have a width of at least 100 pm.

[0017] The gap may have a width of at least 100 pm.

[0018] The object layer may be a layer of a dental aid.

[0019] According to a second aspect of the invention there is provided a method of printing an object, wherein the method comprises printing multiple layers of the object using the method of the first aspect until the object has been completed, and then removing the support material to obtain a finished object

[0020] The method may be a material jetting 3D printing method.

[0021] According to a third aspect of the invention there is provided a computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control a material jetting 3D printing process to perform the method of any preceding aspect.

[0022] According to a fourth aspect of the invention there is provided a material jetting 3D printer comprising a substrate table and a print head system having an array of nozzles, wherein the material jetting 3D printer further comprises a controller programmed to cause the material jetting 3D printer to perform the method of the first or second aspect of the invention.

[0023] According to a fifth aspect of the invention there is provided a computer readable medium, the computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable controller, computer or processor, the controller, computer or processor is caused to perform the method according to the first or second aspect of the invention.

[0024] Features of different aspects of the invention may be combined together.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in whichFigure 1A schematically illustrates a material jetting 3D printer at an initial stage of operation;Figure 1 B schematically illustrates the material jetting 3D printer shown in Figure 1 A at a subsequent stage of operation;Figure 1C schematically illustrates the material jetting 3D printer shown in Figures 1A and 1 B at another subsequent stage of operation;Figure 1 D schematically illustrates the material jetting 3D printer shown in Figures 1A, 1 B and 1C at a another subsequent stage of operation;Figure 2 depicts a first printing pass of a dental nightguard according to an embodiment of the invention;Figure 3 depicts a second printing pass of the dental nightguard according to an embodiment of the invention; andFigure 4 depicts a layer of the dental nightguard formed using the first and second printing passes according to an embodiment of the invention.DETAILED DESCRIPTION

[0026] In the following description an embodiment will be described with reference to a set of Cartesian axes, which are shown in the figures.

[0027] Figures 1A-D schematically illustrate a material jetting 3D printer 1 (hereafter referred to as ‘the printer T) in various stages of operation.

[0028] The printer 1 comprises a support material printhead 2, a first object material printhead 4, a second object material printhead 6, a moveable substrate table 8 and a UV source 10. The support material printhead 2, the first object material printhead 4, and the second object material printhead 6 may be collectively referred to as the printheads. The printheads 2, 4, 6 are offset from the UV source 10 such that the UV light is not incident upon nozzles of the printheads. The substrate table is disposed below the printheads 2, 4, 6 and the UV source 10 (i.e. in located in the negative z-direction). The print heads 2, 4, 6 may collectively be referred to as a printhead system.

[0029] The support material printhead 2 is configured to eject droplets of a support material toward the substrate table 8. The first object material printhead 4 is configured to eject droplets of a first material toward the substrate table 8. The second object material printhead 6 is configured to eject droplets of a second material toward the substrate table 8. Each of the printheads 2, 4, 6 comprises a plurality of nozzles, each configured to eject droplets. The plurality of nozzles of may be arranged in a linear array, disposed in the y-direction. Each of the plurality of nozzles in the printhead 2,4,6 defines a y-position.

[0030] The first and second materials may have different compositions.

[0031] The substrate table 8 (which may also be referred to as a build platform) is configured to be translatable in at least the z and x-axes. In an alternative, the substrate table 8 may be rotatable or translatable in the x, y, and z-axes.

[0032] In general, the printheads and substrate table move relative to each other. In some embodiments, dynamic printheads may move relative to a static substrate table. In other embodiments, both the printhead and the substrate table may move.

[0033] The UV source 10 may have a variable intensity output.

[0034] Figure 1A shows a first layer of droplets being deposited on the substrate table 8. As the substrate table moves past the printheads 2,4,6 in the positive x-direction, the ejected droplets are received on the substrate table 8. A selected number of droplets are ejected and deposited at each x-y position in a layer. The number of droplets deposited for each x-y position may be expressed as droplets per dot (DPD). Where multiple droplets are ejected by the printhead for each x-y position, the droplets may coalesce. The ejected droplets may coalesce in flight, before being received on the substrate table 8. The coalesced droplet may be referred to as a deposited droplet 12. The deposited droplets 12 have a specified pattern or distribution in the x-y plane.

[0035] Each x-y position in a layer corresponds to a voxel in an input model. The input model may comprise data indicative of the physical configuration of the object to be printed. Data indicative of the physical configuration may include object composition and object geometry.

[0036] To determine which nozzle (corresponding to a y-position) of which print head (corresponding to a composition) should eject a droplet, and to compute the specific timing of jetting this droplet (corresponding to an x-position), an output model with information on a voxel level is sent to the printer. The output model may comprise one or more bitmap files.

[0037] Turning now to Figure 1 B, the deposited droplets 12 flow to form a layer 14 having a generally uniform layer thickness 5. The layer thickness 5 is a geometric parameter of the printing process. Translation of the substrate table 8 places printed layer 14 under the UV source 10. The U source 10 emits U radiation which is incident on the printed layer 14, curing the printed layer.

[0038] The first and second object materials may be referred to as first and second object inks respectively. Typically, the first and second object inks are UV-curable inks. UV light triggers polymerisation of the (liquid) first and second object inks into a rigid solid form via photochemical reactions. The solidification of the first and second object inks is referred to as curing. The first and second object inks will form a finished object (once support material has been removed, as explained below) and may be collectively referred to as object inks.

[0039] The support material is used to reduce flow effects that might cause inaccuracy of printed objects and to support hollow or overhanging parts. The support material forms a support structure which supports the object inks during printing. Typically, the support material is a UV-curing material. The support material may be a soluble material that can be washed away after printing of the object has been completed. In an alternative, the support material may also be removed from an object by melting or (mechanical) breaking.

[0040] The process of printing another layer is schematically illustrated in Figures 1C. The substrate table 8 is translated in the negative z-direction by a single layer thickness 5 (ensuring a constant gap between the printheads 2, 4, 6 and a deposition surface). A second set of deposited droplets 16 is then deposited on top of the first printed layer 14 in substantially the same manner as the previously deposited droplets 12 (as described with reference to Figure 1A). The second set of deposited droplets 16 flow to form a second printed layer of uniform layer thickness 5.

[0041] Figure 1 D shows the curing of the second printed layer 18 by the UV source 10. This provides a printed object having a height of 2b.

[0042] The process described with reference to Figures 1A-D may be repeated until an object of the desired height and geometry is created by cumulative addition of printed layers.

[0043] In an embodiment, an object that is printed by the material jetting 3D printer 1 may be a dental night-guard. Figure 4 depicts a layer of a dental night-guard 22 formed using a printing method according to an embodiment of the invention. A dental night-guard is a protective device which is worn by a user when they sleep. The night-guard has a series of recesses with shapes that are matched to the teeth of the user. The user presses the night-guard onto their teeth (typically the teeth of the upper jaw) such that the teeth fill the recesses. The night-guard is held in place by friction arising from contact between the teeth and the night-guard. The night-guard protects the user’s teeth whilst the user is sleeping.

[0044] In embodiments of the invention the night-guard is formed by printing a series of layers, in the manner described above in connection with Figures 1A-1 D. In one example around 750 layers are printed to form a night-guard. In one example, a typical layer thickness is 20pm. Each layer is printed by depositing an array of droplets of material and curing the droplets so that they solidify.

[0045] The layer of the night-guard 22 depicted in Figure 4 comprises three different materials, each material being illustrated by a different darkness of shading. The materials are a first object material 24, a second object material 26, and a support material 28. The first object material 24 and second object material 26 together form a finished night-guard (in combination with other layers of the first and second object materials). The first object material 24 and second object material 26 may have the same physical properties but may have different colours. That is, they may be the same material but containing different pigment (or containing no pigment). In this example, the first object material 24 is harder than the second object material 26. The harder first object material 24 provides the night-guard with overall rigidity, whilst the softer second object material 26 grips the user’s teeth more effectively than a harder material.

[0046] In one example, the first object material 24 may be transparent, and the second object material 26 may be coloured. In the depicted example, a portion of the second object materialcorresponds with a user’s incisor teeth (excluding canine teeth) and other portions of the second object material correspond with the user’s molar teeth (excluding wisdom teeth). This is merely one example of an arrangement of two object materials, and other colour arrangements may be used.

[0047] The use of materials with two different colours may provide the night-guard with an attractive appearance. More object materials may be used to provide additional colours. Alternatively, a single object material may be used. The object material(s) may be UV curable ink.

[0048] The support material 28 provides support to the first and second object materials 24, 26 during fabrication of the night-guard 22. Support material 28 is desirable when forming a complex geometry such as a night-guard recess shaped to receive a user’s tooth. This is because the support material helps to ensure that the object material retains a desired shape at the surface of the recess (which may be referred to as a wall of the recess). If the support material 28 was not present then the object material would be at risk of deforming into empty space adjacent to the object material, thereby deforming the wall of the recess. This is undesirable because then the night-guard 22 will not fit correctly to the teeth of the user.

[0049] The support material 28 may for example be a UV curable and water soluble ink.

[0050] A surface of the object material 24, 26 where the object material meets the support material 28 may be referred to as a border of the object material. The border may be referred to as a predetermined border (meaning that the position of the border has previously been set). The predetermined border is a perimeter of the object material 24, 26 when the layer of the night-guard has been formed.

[0051] In Figure 4 support material 28 is provided at locations where recesses will be located in the night-guard to receive users teeth. In addition, support material 28 is provided around an outer periphery of the first object material 24. The support material provided at the outer periphery may ensure that outer walls of the night-guard 22 are correctly formed. In some embodiments support material 28 may be omitted from at least part of the outer periphery of the night-guard.

[0052] As noted further above, Figure 4 depicts a layer of a night-guard 22. The layer is made up of two passes of a print head system. The second pass of the print head system prints material that is complementary to the first pass of the print head system. That is the second pass of the print head system prints material to locations that did not receive material during the first pass of the print head system. The first and second passes of the print head system together print material to all locations of the night-guard layer 22. Figure 2 depicts material deposited by the first pass of the print head system, and Figure 3 depicts material deposited by the second pass of the print head system.

[0053] Multiple printing passes are desirable because printing the night-guard layer in a single printing pass would generate significant errors. As noted further above, each of the printheads 2, 4, 6 of the printer 1 comprises a plurality of nozzles, each configured to eject droplets. Errors may arise for example because one or more nozzles are blocked, or one or more nozzles are partially blocked such that less material is deposited from those nozzles. In addition, errors may arise from coalescence effects. That is, adjacent droplets of material may be so close to each other that they flow into each other in an undesirable and inconsistent manner. All of these errors reduce the accuracy with which the night-guard layer 22 would be formed, and are reduced or eliminated by printing the night-guard layer using multiple printing passes.

[0054] In an embodiment of the invention first and second printing passes are used, the first and second printing passes being arranged to form the night-guard layer 22 with improved accuracy (compared with a method in which the layer is printed in a single pass).

[0055] Referring first to Figure 2, a first printing pass is depicted in which the first object material 24, second object material 26, and support material 28 are deposited. Around half of the material used to make the layer is deposited during the first pass (although more than half or less than half may be deposited). The positions at which the material is deposited are generally distributed across the layer (for example using a random mask). Figure 2 includes an enlarged view of part of the night-guard layer 22. In the enlarged view it may be seen that the materials 24, 26, 28 have a dappled or spotty appearance. This is because the first pass comprises locations which receive material 24, 26, 28 and locations which do not receive material. Areas made up of locations which receive material and locations which do not receive material may be referred as a bulk portion.

[0056] Referring to Figure 3, a second printing pass is depicted in which the first object material 24, second object material 26, and support material 28 are again deposited. Again, around half of the material used makes up the layer is deposited during the first pass. More than half or less than half may be deposited - this depends upon the proportion that was deposited during the first printing pass (the two printing passes should together deposit a full layer). The positions at which the material is deposited are again generally distributed across the layer (for example using a random mask which is an inverse of the mask used for the first printing pass). Figure 3 includes an enlarged view of part of the night-guard layer 22. Again, the materials 24, 26, 28 have a dappled or spotty appearance, indicating that the second pass comprises locations which receive material 24, 26, 28 and locations which do not receive material. Again, areas made up of locations which receive material and locations which do not receive material may be referred as a bulk portion.

[0057] Referring to Figure 4, the result of the first and second printing passes is shown. The materials 24, 26, 28 now have solid shading rather than dappled or spotted shading. This is because locations which did not receive material 24, 26, 28 during the first printing passreceived that material during the second printing pass. As a result all locations of the nightguard layer 22 have received material.

[0058] Referring again to Figure 2, the object material 24, 26 is deposited as a bulk portion. It may be seen that the object material 24, 26 is not printed up to a border 30. The border is a perimeter which will correspond with a wall of a recess in the finished night-guard. The border may be referred to as a predetermined border. Areas which do not receive object material 24, 26 (and which receive no material) may be most easily seen in the enlarged view of Figure 2. Although only two borders 30 are labelled in Figure 2, borders are present around each area of support material 28. Some of the borders correspond with recess perimeters, and other borders correspond with an outer peripheral wall of the night-guard 22.

[0059] Because the object material 24, 26 is not provided up to the borders 30, a gap 32 is present between the object material 24, 26 and the support material 28. The gap 32 is depicted in Figure 2 by a white line. The gap 32 defines an area of the night-guard layer 22 which does not receive any material during the first printing pass.

[0060] The gap 32 may for example have a width of at least 100 pm. A larger gap 32, e.g. having a width of 200 pm or more may be desirable. The gap may be sufficiently large that there is no interaction (e.g. coalescence) between the object material 24, 26 and the support material 28. The gap 32 may for example have a width of up to 400 pm, e.g. up to 500 pm. The size of the gap 32 used when forming a layer of an object may be selected based upon properties of the material being deposited. For example, when depositing relatively large droplets of material a larger gap may be used. When depositing relatively small droplets of material a smaller gap may be used.

[0061] A typical material droplet size may for example be 30-40pL. A small material droplet may be as small as 5 pL. A large material droplet may be up to 100 pL (or more). An associated voxel size for a given material droplet size may be determined. The voxel size may be mapped to the material droplet size using a cubed relationship (e.g. (17 pmA3) = 4.9 pL, (33 um)A3 = 36 pL, (46 um)A3 = 97 pL).

[0062] A voxel is a three-dimensional volume. A voxel may correspond with a two dimensional pixel combined with a material thickness (which provides the third dimension). The layer of the night-guard which is being formed may be represented in data as a set of pixels along with a thickness (thereby defining a set of voxels). When a droplet of material is delivered to a location, this may be considered to be delivery of the material to a pixel location. The droplet of material may be considered to fill or substantially fill the voxel associated with the pixel. In practice the droplet of material will not have a cube shape, and so will not precisely fill a voxel. More than one droplet of material may be delivered to a pixel during a printing pass.

[0063] The support material 28 is deposited up to the border 30 (which as noted above will correspond with a wall of a recess in the finished night-guard). A wall portion 34 of the supportmaterial 28 is defined as a portion of the support material which is located at the border 30 (i.e. has an edge which corresponds with the border). In this embodiment, all support material 28 which is needed to form a wall portion 34 of the support material is deposited. In Figure 2 this is illustrated by the wall portions 34 having solid shading rather than dappled or spotted shading. The wall portions 34 of the support material 28 may for example have a width of at least 100 pm, e.g. 200 pm or more. The wall portions 34 may for example have a width of up to 400 pm, e.g. up to 500 pm. A wall portion 34 of the support material 28 may be considered to be a portion of the support material having an outer surface which corresponds to a border where the support material will meet the object material 24, 26 when the night-guard layer 22 has been fully printed.

[0064] All locations in the wall portion 34 receive the support material. Other locations at which the support material 28 is deposited may be referred to as a bulk portion. Support material 28 which is deposited as a bulk portion may be referred to as bulk material. Deposited bulk support material 28 is distributed across locations so that some locations receive the bulk material and other locations do not receive the bulk material. As noted above, in Figure 3 deposited bulk support material 28 is dappled or spotted, indicating that some locations receive bulk support material 28 and other locations do not receive bulk support material. Similarly, the object material 24, 26 is bulk material in Figure 3, and is also distributed such that some locations receive the object material and other locations do not receive the object material. Where the context allows, the term “locations” may be considered to be synonymous with pixels or voxels. Bulk material deposited during a printing pass may for example provide 20% or more (e.g. up to 80%) of material required by the area to which the bulk material is deposited. The remaining required bulk material is deposited during one or more subsequent printing passes.

[0065] The first printing pass of the night-guard layer 22 thus comprises around half (or some other proportion) of the object material 24, 26 and support material 28 distributed across the layer, except that object material 24, 26 is separated from the borders 30 by a gap 32. The wall portion 34 of the support material 28 is provided in full. There are substantially no locations in the wall portion 34 of the support which receive no material.

[0066] Referring to Figure 3, during the second printing pass the remainder of the support material 28 which is needed to complete the support material layer is provided. As depicted, in the second printing pass the support material 28 is not provided up to the borders 30. Instead during the second printing pass there is a gap 36 between the support material 28 and the object material 24, 26. There is no need to provide support material 28 at the location of the gap 36 because the wall portion 34 of the support material has already been deposited during the first printing pass. The support material 28 is deposited as a bulk portion.

[0067] The gap 36 may for example have a width of at least 100 pm. A larger gap 36, e.g. having a width of 200 pm or more may be desirable. The gap 36 may be sufficiently large thatthere is no interaction (e.g. coalescence) between the support material 28 and the already deposited (and cured) object material 24, 26. The gap 36 may for example have a width of up to 400 pm, e.g. up to 500 pm. The size of the gap 36 corresponds with the width of the support material wall portion 34 deposited during the first printing pass.

[0068] During the second pass, the object material 24, 26 is deposited up to the border 30. A wall portion 38 of the object material 24, 26 is defined as a portion of the object material which is located at the border 30 (i.e. has an edge which corresponds with the border). In this embodiment, all object material 24, 26 which is needed to form a wall portion 38 of the object material is deposited. In Figure 3 this is illustrated by the wall portions 38 having solid shading rather than dappled or spotted shading. The wall portions 38 of the object material 24, 26 may for example have a width of at least 100 pm, e.g. 200 pm or more. The wall portions 38 may for example have a width of up to 400 pm, e.g. up to 500 pm. The wall portion 38 of the object material 24, 26 may be considered to be a portion of the object material having an outer surface which corresponds to a border where the object material will meet the support material 28 when the night-guard layer 22 has been fully printed. The wall portion 38 of the object material 24, 26 may have a different width to the wall portion 34 of the support material 28. Object material 24, 26 is also deposited as a bulk portion during the second pass.

[0069] The second printing pass of the night-guard layer 22 thus comprises around half (or some other proportion) of the object material 24, 26 and support material 28 distributed across the layer, except that support material 28 is separated from the borders 30 by a gap 36. The wall portion 38 of the object material 24, 26 is provided in full. There are substantially no locations in the wall portion 38 of the object material 24, 26 which receive no material.

[0070] Other locations at which the object material 24, 26 is deposited (i.e. locations which are not the wall portion 38) may be referred to as a bulk portion. Object material 24, 26 which is deposited as a bulk portion may be referred to as bulk material. Deposited bulk object material 24, 26 is distributed across locations so that some locations receive the bulk material and other locations do not receive the bulk material. As noted above, in Figure 4 deposited bulk object material 24, 26 is dappled or spotted, indicating that some locations receive object material 24, 26 and other locations do not receive bulk support material. Similarly, some of the support material 28 is bulk material in Figure 3, and is also distributed such that some locations receive the support material and other locations do not receive the support material. Where the context allows, the term “locations” may be considered to be synonymous with pixels or voxels. Bulk material deposited during a printing pass may for example provide 20% or more (e.g. up to 80%) of material required by the area to which the bulk material is deposited. The remaining required bulk material is deposited during one or more subsequent printing passes.

[0071] Once the first printing pass of Figure 2 and the second printing pass of Figure 3 have been performed, the layer of the night-guard 22 (including support material) is fully formed as depicted in Figure 4.

[0072] As explained further above, the depicted layer of the night-guard 22 is printed onto a previously formed layer of the night-guard (not depicted). The previously formed layer is cured before the depicted layer of the nightguard is printed. The depicted layer of the night-guard 22 adheres to a previously printed layer onto which depicted layer is provided.

[0073] The order of the first and second printing passes may be reversed (i.e. the printing pass depicted in Figure 3 may take place before the printing pass depicted in Figure 2). However, it is preferred that the order of printing passes is as depicted. This is because the wall portion of support material is deposited before the wall portion of the object material, and thereby provides support for the object material (so that the object is formed more accurately compared with depositing the object material before the support material). In general, a support material and an object material are deposited during a printing pass. In some embodiments the first material may be the support material and the second material may be the object material. In other embodiments the first material may be the object material and the second material may be the support material. In general, it is preferable that the wall portion of support material is deposited before the wall portion of the object material.

[0074] During a given printing pass object material may be deposited before support material. For example, with reference to Figure 2, a printing pass may move from left to right. In some embodiments a night-guard (or other object) may be formed without providing support material on the left hand outer side. Where this is the case, object material is deposited before support material during the left to right printing pass. In this case, bulk material may be deposited before wall material is deposited. In general, in some printing passes bulk material may be deposited before wall portion material.

[0075] Multiple layers of the night-guard are deposited until the complete night-guard (including support material) has been printed. One or more layers may be printed without using the method of an embodiment of the invention (e.g. a layer which does not include support material).

[0076] Once the complete night-guard has been printed, the support material is removed. This may be done for example by dissolving the support material in water or a different solvent. In general, the support material is configured for removal from the object material to form a finished object.

[0077] Although the depicted embodiment of the invention relates to a night-guard, the printing method of the invention may be used when printing other objects. For example, the printing method may be used when printing dentures. Dentures typically have complex shapes, including arches of teeth and an open space for the palate. These shapes often includeoverhanging or bridging elements to maintain the intended shape and alignment of the denture. Support material may be used to create a foundation for these features. As with the nightguard, a denture may be printed using a combination of a support material and one or more object materials. The support material and one or more object materials of a denture may be printed in the same way as described above in connection with the night-guard (i.e. in accordance with an embodiment of the invention). Night-guards and dentures are both examples of dental aids. A dental aid may be made based upon a digital scan of the user’s oral cavity. The digital scan may capture detailed information about the mouth's anatomy, including the shape of the gums, the position of the teeth, and the patient's bite alignment.

[0078] Other objects which depend upon a user’s anatomy may be printed. For example ear plugs, frames for glasses or other objects may be printed. As with dental aids, a digital scan may be used to capture information about the user so that the shape of the object may be tailored to that user. As with other objects, printing in multiple colours and / or using multiple materials with different properties, may be desirable.

[0079] Droplet sizes, pixel sizes, voxel sizes, gap sizes, wall widths etc. described above in connection with the night-guard may also apply for other objects.

[0080] Other objects printed using a support material and one or more object materials may be printed in accordance with an embodiment of the invention. An object together with support material may be referred to as an object or intermediate object. An object after support material has been removed may be referred to as a finished object.

[0081] Embodiments of the invention may use any suitable object materials. The object materials may for example be UV curable material. The object material(s) may be one or more of, thermoplastics, photopolymers, ceramics, phase change inks (e.g. waxes), or metals. The materials may be one or more of biocompatible and durable resins. Although UV curing is referred to above, other solidifying mechanisms may be used.

[0082] The support material may for example be a UV curable and water soluble ink such as WSS™150, available from Stratasys, Inc. of Rehovot, Israel. The support material may for example be a UV curable ink which is soluble using alkaline cleaning solution, an example of this ink is SUP706B™ (also available from Stratasys, Inc.). Each location to which material is provided during a printing pass may be referred to as a pixel. The term “pixel” may refer to an area in a data set which defines a location to which material is deposited during a printing pass. A voxel may correspond with a two dimensional pixel combined with a material thickness (which provides the third dimension). When a droplet of material is delivered to a location, this may be considered to be delivery of the material to a pixel location. Delivery of material to a pixel may be considered to fill or substantially fill the voxel associated with the pixel. In practice the material will not have a cube shape, and so will not precisely fill a voxel. More than one droplet of material may be delivered to a pixel during a printing pass.

[0083] The deposited material is cured before the next layer of material is printed. This helps to prevent smudging, blending, or distortion of the printed layers. In this context the term “cured” may be understood to mean sufficiently solid that material deposited during the next printing pass does not change the shape of the cured material. UV curing or a different form of curing (e.g. heat) or other solidifying mechanism (e.g. freezing or cooling) may be used.

[0084] Embodiments of the invention prevent interaction between liquid object material and liquid support material. This improves the accuracy of the printed object. That is the border between the object material and the support material is more accurately defined (compared with a printing method which allows interaction between liquid object material and liquid support material).

[0085] In the described embodiment around half of the material used to make the layer of the night-guard is deposited during the first pass. In general, when printing a layer of an object, at least 20% of material (e.g. 40% or more) which makes up the layer may be deposited during the first pass. Similarly, in general, during the second pass at least 20% (e.g. 40% or more) of material which makes up the layer may be deposited. The first and second passes may together deposit 100% of the material which makes up the layer.

[0086] In general, positions at which the material is deposited during a printing pass may be generally distributed across a layer. In this context, distributed may be understood to mean that some locations receive material and some locations do not receive material. The distribution may for example use a random mask. Other distributions may be used. The positions at which material is deposited during a second printing pass may be inverse to positions at which material is deposited during a first printing pass. That is, positions which receive material during the first printing pass do not receive material during the second printing pass, and vice versa. Proportionately more material may be printed to a wall portion than to a bulk portion. In some instances a wall portion may be fully printed during single printing pass (in which case the material is not distributed across the wall portion).

[0087] Embodiments of the invention may provide a higher throughput than for example a method in which two printing passes are used to print support material (to avoid coalescence of support material), and then two more printing passes are used to print object material (to avoid coalescence of object material).

[0088] The 3D printer 1 may be equipped with a processor (not depicted). The processor may analyse an object to be printed and determine the shape of multiple layers that can be used to make the object. The processor determines an outer perimeter of each layer of the object and determines perimeters of openings in the object (e.g. openings which will form recesses in the finished object). These perimeters may be referred to as borders or predetermined borders. The processor allocates support material to be provided in the recesses, and may allocate support material to be provided around at least part of the outerperimeter of the layer. As a result, positions at which object material and support material will be deposited to form the object layer are determined. The processor may then determine where to print material during a first printing pass and where to print material during a second printing pass, according to an embodiment of the invention.

[0089] As noted above, the processor may form part of the 3D printer. Alternatively, the processor may be separate from the 3D printer. The processor may generate data comprising instructions to be used by the 3D printer when depositing material.

[0090] In the above example embodiment, 750 layers are printed to form the night-guard. Each layer may have a thickness of around 20 pm, providing the nightguard with a height of around 15 mm (which is typical for a night-guard). In other embodiments, a different number of layers may be used to form a night-guard. For example, at least 300 layers may be printed form a night-guard. The at least 300 layers may have a layer thickness of around 50 pm, thereby providing a height of around 15 mm. In general, any number of layers, e.g. 100 layers or more, may be used to make an object (e.g. a dental aid) .

[0091] In the above example, the thickness of each layer is around 20 pm. However, other layer thicknesses may be used. For example, a layer thickness of up to around 50 pm may be used. The layer thickness may be greater than 50 pm, but this may tend to introduce inaccuracies into the object that is produced. The thickness of each layer may for example be 5 pm or more. A layer thickness of 20 pm or more may be preferred over a thinner layer thickness, because when a thinner layer thickness is used more printing passes are required to make an object (reducing the throughput of the printer). In general, each layer may have substantially the same thickness, although this is not essential.

[0092] In the above described embodiment, the night-guard layer is deposited using two printing passes. In the first printing pass the support material is deposited as a wall portion and a bulk portion, and the object material is deposited as a bulk portion. In the second printing pass the object material is deposited as a wall portion and a bulk portion, and the support material is deposited as a bulk portion. Two printing passes may also be used to form a layer of a different object.

[0093] In other embodiments more than two printing passes may be used to form a layer of an object (e.g. a night-guard). For example, three printing passes may be used. Where this is the case, in an embodiment only support material is provided in a first printing pass, the support material being provided up to a predetermined border (i.e. a wall portion and a bulk portion of the support material is provided). In a second printing pass, object material and support material are deposited, the support material being separated by a gap from the predetermined border and the object material being provided up to the predetermined border. In a third printing pass object material is provided. A wall portion of the object material may be deposited during the second printing pass or during the third printing pass. Other embodiments having threeprinting passes are possible. In one example, three printing passes may be made up of 33%- 33%-33% for the bulk portions (both object material and support material). Three printing passes may be made up of 100%-0%-0% for the wall portion support material. Three printing passes may be made up of 0%-100%-0% for the wall portion of the object material. Other proportions of materials may be used. Three printing passes may provide a higher accuracy than two printing passes. This is because smaller amounts of the bulk portion are deposited during each printing pass (compared with two printing passes), and depositing smaller amounts allows for higher accuracy. However, throughput is reduced because three printing passes are used to form a layer rather than two printing passes.

[0094] In an embodiment, four printing passes may be used. Four printing passes may provide higher accuracy than three or two printing passes, although throughput is reduced. In an example, four printing passes may be made up of 25%-25%-25%-25% for the bulk portions (both object material and support material). Four printing passes may be made up of 50%- 50%-0%-0% for the wall portion support material. Four printing passes may be made up of 0%-0%-50%-50% for the wall portion of the object material. Other proportions of materials may be used.

[0095] Irrespective of the number of printing passes, a first printing pass may deposit a wall portion of a first material, e.g. a support material wall portion.

[0096] A method according to an embodiment may be performed by one or more processors or controllers of a material jetting 3D printer. A method according to an embodiment may be performed by computing devices, processors, controllers, or other devices external to a 3D printer.

[0097] 3D ink jet additive manufacturing as used by embodiments of the invention provides advantages over traditional 3D printing methods that use additive techniques such as Fused Deposition Modelling (FDM) or Stereolithography (SLA). A print head system with an array of nozzles as used in 3D ink jet additive manufacturing can be controlled to create highly detailed and accurate 3D objects. In addition, the print head system can be used to simultaneously print different materials at different locations. This allows the use of support material in addition to object material(s), including in methods according to an embodiment of the invention.

[0098] 3D ink jet additive manufacturing as used by embodiments of the invention may fabricate objects based on three-dimensional (3D) information, for example a three- dimensional computer model (or design file), of the object.

[0099] Accordingly, examples described herein not only include objects as described herein, but also methods of manufacturing such objects via additive manufacturing and computer software, firmware or hardware for controlling the manufacture of such products via additive manufacturing.

[0100] The structure of one or more objects may be represented digitally in the form of a design file. A design file, or computer aided design (CAD) file, is a configuration file that encodes one or more of the surface or volumetric configuration of the shape of the object. That is, a design file represents the geometrical arrangement or shape of the object.

[0101] Design files can take any now known or later developed file format. For example, design files may be in the Stereolithography or “Standard Tessellation Language” (.stl) format which was created for stereolithography CAD programs of 3D Systems, or the Additive Manufacturing File (.amf) format, which is an American Society of Mechanical Engineers (ASME) standard that is an extensible markup-language (XML) based format designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be fabricated on any additive manufacturing printer.

[0102] Further examples of design file formats include AutoCAD (.dwg) files, Blender (.blend) files, Parasolid (,x_t) files, 3D Manufacturing Format (,3mf) files, Autodesk (3ds) files, Collada (.dae) files and Wavefront (. obj) files, although many other file formats exist.

[0103] Design files can be produced using modelling (e.g. CAD modelling) software and / or through scanning the surface of a product to measure the surface configuration of the product.

[0104] Once obtained, a design file may be converted into a set of computer executable instructions that, once executed by a processer, cause the processor to control an additive manufacturing apparatus to produce an object according to the geometrical arrangement specified in the design file. The conversion may convert the design file into slices or layers that are to be formed sequentially by the additive manufacturing apparatus. The instructions (otherwise known as geometric code or “G-code”) may be calibrated to the specific additive manufacturing apparatus and may specify the location and amount of material that is to be formed at each stage in the manufacturing process. The instructions may be according to an embodiment of the invention. Embodiments of the invention may comprise G-code.

[0105] The code or instructions may be translated between different formats, converted into a set of data signals and transmitted, received as a set of data signals and converted to code, stored, etc., as necessary. The instructions may be an input to the printer 1 and may come from a part designer, an intellectual property (IP) provider, a design company, the operator or owner of the additive manufacturing system, or from other sources. The printer 1 may execute the instructions to fabricate an object according to an embodiment of the invention.

[0106] Design files or computer executable instructions may be stored in a (transitory or non- transitory) computer readable storage medium (e.g., memory, storage system, etc.) storing code, or computer readable instructions, representative of the object to be produced. As noted, the code or computer readable instructions defining the object that can be used to physically generate the object, upon execution of the code or instructions by an additive manufacturing system. For example, the instructions may include a precisely defined 3D model of the objectand can be generated from any of a large variety of well-known computer aided design (CAD) software systems such as AutoCAD®, TurboCAD®, DesignCAD 3D Max, etc. Alternatively, a model or prototype of the object may be scanned to determine the three-dimensional information of the component.

[0107] Accordingly, by controlling the printer 1 according to the computer executable instructions, the printer 1 can be instructed to print the object.

[0108] In light of the above, embodiments include methods of manufacture via material jetting 3D printing. This includes the steps of obtaining a design file representing the object and instructing a printer to print the object according to the design file. The printer may include a processor that is configured to automatically convert the design file into computer executable instructions for controlling the manufacture of the object. In these embodiments, the design file itself can automatically cause the production of the object once input into the printer. Accordingly, in this embodiment, the design file itself may be considered computer executable instructions that cause the printer to manufacture the object. Alternatively, the design file may be converted into instructions by an external computing system, with the resulting computer executable instructions being provided to the printer.

[0109] Given the above, the design and manufacture of implementations of the subject matter and the operations described in this specification can be realized using digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this specification can be realized using one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer- readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

Claims

CLAIMS1 . A method of printing a layer of a three-dimensional object formed from a first material and from a second material, wherein the method comprises: during a printing pass depositing the first material, the first material being provided up to a predetermined border, wherein the deposited first material comprises a wall portion located at the predetermined border; and during a subsequent printing pass depositing the second material, the second material being provided up to the predetermined border wherein the deposited second material includes a wall portion located at the predetermined border; wherein during the first printing pass the second material is also deposited as a bulk portion but as a lower proportion of the layer than the deposited wall portion of the first material, the deposited bulk portion being separated from the predetermined border by a gap; and / or during the second printing pass the first material is also deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion of the second material, the deposited bulk portion being separated from the predetermined border by a gap.

2. The method of claim 1 , wherein during the printing pass which deposits the first material, the first material is also deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion and / or during the subsequent printing pass which deposits the second material, the second material is also deposited as a bulk portion but at a lower proportion of the layer than the deposited wall portion.

3. The method of claim 1 or claim 2, wherein during the first printing pass all locations in the first material wall portion receive the first material and / or during the subsequent printing pass all locations in the second material wall portion receive the second material.

4. The method of any preceding claim, wherein two printing passes are performed: during the first printing pass the first material is deposited as the wall portion and the bulk portion, and the second material is deposited as the bulk portion separated from the predetermined border by the gap; and during the subsequent printing pass the second material is deposited as the wall portion and the bulk portion, and the first material is deposited as the bulk portion separated from the predetermined border by the gap.

5. The method of any of claims 1 to 4, wherein four printing passes are performed:during the first printing pass and a second printing pass the first material is deposited as the wall portion and the bulk portion, and the second material is deposited as the bulk portion separated from the predetermined border by the gap, the first printing pass and second printing pass both taking place before the subsequent printing pass; and during the subsequent printing pass and a further subsequent printing pass the second material is deposited as the wall portion and the bulk portion, and the first material is deposited as the bulk portion separated from the predetermined border by the gap.

6. The method of any preceding claim, wherein the object is formed from an object material and a support material, the support material being configured for subsequent removal from the object material to form a finished object, and wherein the first material is the support material and the second material is the object material.

7. The method of any preceding claim, wherein the wall portion has a width of at least 100 pm.

8. The method of any preceding claim, wherein the gap has a width of at least 100 pm.

9. The method of any preceding claim, wherein the object layer is a layer of a dental aid.

10. A method of printing an object, wherein the method comprises printing multiple layers of the object using the method of any preceding claim until the object has been completed, and then removing the support material to obtain a finished object11. The method of any preceding claim, wherein the method is a material jetting 3D printing method.

12. A computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control a material jetting 3D printing process to perform the method of any preceding claim.13 A material jetting 3D printer comprising a substrate table and a print head system having an array of nozzles, wherein the material jetting 3D printer further comprises a controller programmed to cause the material jetting 3D printer to perform the method according to any of claims 1 to 11.

14. A computer readable medium, the computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, onexecution by a suitable controller, computer or processor, the controller, computer or processor is caused to perform the method according to any of the claims 1 to 11 .

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