WO2020226605A1

WO2020226605A1 - Temperature values in additive manufacturing

Info

Publication number: WO2020226605A1
Application number: PCT/US2019/030681
Authority: WO
Inventors: Theodore ROBINSON; Jacob Wright; David RAMIREZ MUELA; Sergio GONZALEZ MARTIN
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2019-05-03
Filing date: 2019-05-03
Publication date: 2020-11-12

Abstract

In an example, a method includes acquiring, by at least one processor, a voxelised model of at least part of an intended content of a fabrication chamber to be formed using additive manufacturing. An initial temperature value may be associated with each voxel of the voxelised model, wherein the initial temperature value is a first temperature value if the voxel models a solid part of the intended content, and otherwise the initial temperature value is a second temperature value. The voxelised model may be convolved with at least one convolution kernel in three dimensions to estimate a temperature value of each voxel after a time period.

Description

TEMPERATURE VALUES IN ADDITIVE MANUFACTURING

BACKGROUND

[0001] Additive manufacturing techniques may generate a three-dimensional object through the solidification of a build material, for example on a layer-by-layer basis. In examples of such techniques, build material may be supplied in a layer-wise manner and the solidification method may include heating the layers of build material to cause melting in selected regions. In other techniques, chemical solidification methods may be used.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Non-limiting examples will now be described with reference to the accompanying drawings, in which:

[0003] Figure 1 is a flowchart of an example method of processing data for use in additive manufacturing;

[0004] Figure 2 is a flowchart of an example method for generating at least a layer of an object;

[0005] Figure 3A shows an example object;

[0006] Figures 3B and 3C show, respectively graphs of example temperature values and print agent amounts associated with object voxels;

[0007] Figures 4 and 5 are simplified schematic drawings of example apparatus for use in additive manufacturing; and

[0008] Figure 6 is a simplified schematic drawing of an example machine readable medium associated with a processor. DETAILED DESCRIPTION

[0009] Additive manufacturing techniques may generate a three-dimensional object through the solidification of a build material. In some examples, the build material is a powder-like granular material, which may for example be a plastic, ceramic or metal powder and the properties of generated objects may depend on the type of build material and the type of solidification mechanism used. In some examples the powder may be formed from, or may include, short fibres that may, for example, have been cut into short lengths from long strands or threads of material. Build material may be deposited, for example on a print bed and processed layer by layer, for example within a fabrication chamber. According to one example, a suitable build material may be PA12 build material commercially referred to as V1 R10A“HP PA12” available from HP Inc.

[0010] In some examples, selective solidification is achieved through directional application of energy, for example using a laser or electron beam which results in solidification of build material where the directional energy is applied. In other examples, at least one print agent may be selectively applied to the build material, and may be liquid when applied. For example, a fusing agent (also termed a ‘coalescence agent’ or ‘coalescing agent’) may be selectively distributed onto portions of a layer of build material in a pattern derived from data representing a slice of a three-dimensional object to be generated (which may for example be generated from structural design data). The fusing agent may have a composition which absorbs energy such that, when energy (for example, heat) is applied to the layer, the build material coalesces and solidifies to form a slice of the three-dimensional object in accordance with the pattern. In other examples, coalescence may be achieved in some other manner.

[0011] According to one example, a suitable fusing agent may be an ink-type formulation comprising carbon black, such as, for example, the fusing agent formulation commercially referred to as V1 Q60Q“HP fusing agent” available from HP Inc. In one example such a fusing agent may comprise an infra-red light absorber. In one example such a fusing agent may comprise any or any combination of a near infra-red light absorber, a visible light absorber, and a UV light absorber. Examples of print agents comprising visible light absorption enhancers are dye based colored ink and pigment based colored ink, such as inks commercially referred to as CE039A and CE042A available from HP Inc. [0012] In addition to a fusing agent, in some examples, a print agent may comprise a coalescence modifier agent, which acts to modify the effects of a fusing agent for example by reducing or increasing coalescence or to assist in producing a particular finish or appearance to an object, and such agents may therefore be termed detailing agents. In some examples, a coalescence modifier agent may have a cooling effect, and thus be termed ‘cooling agent’. While a cooling action may assist in reducing coalescence by reducing the temperature of the build material to prevent it from reaching its melting point, in some examples, other processes, such as increasing a separation between build agent particles may also contribute to decreasing coalescence. In some examples, the detailing agent may be used in particular near edge surfaces of an object being printed, although it may also be used in other regions, and may for example be distributed according to a distribution map or pattern, which may be derived from data representing a slice of a three-dimensional object to be generated. According to one example, a suitable detailing agent may be a formulation commercially referred to as V1 Q61A“HP detailing agent” available from HP Inc. In some examples, the detailing agent is an aqueous composition (comprising a high percentage of water) which undergoes evaporation when heated, resulting in a cooling effect.

[0013] A coloring agent, for example comprising a dye or colorant, may in some examples be used as a fusing agent or a coalescence modifier agent, and/or as a print agent to provide a particular color for the object.

[0014] As noted above, additive manufacturing systems may generate objects based on structural design data. This may involve a designer generating a three-dimensional model of at least one object to be generated, for example using a computer aided design (CAD) application. The model may define the solid portions of the object(s). To generate three-dimensional object(s) from the model using an additive manufacturing system, model data can be processed to generate slices of parallel planes or slices of the model. Each slice may define a portion of a respective layer of build material that is to be solidified or caused to coalesce by the additive manufacturing system.

[0015] During object generation, a particular layer of build material may be heated. However, over time, the build material of that layer may receive additional energy from previously and subsequently processed layers. This additional energy may cause overheating, potentially resulting in fusion of build material which was intended to remain unfused, or object defects. Conversely, if excess detailing agent is used to prevent such overheating, this can result in increased use of materials, and in some cases under heating and associated object defects. Over and/or under heating, and/or over use of detailing agent (i.e. using more detailing agent than needed to ensure that unintended fusing does not occur) can be associated with effects such as thermal bleed (which may cause fusion where none was intended), wrinkled surface textures (known as‘elephant skin’), hole filling (e.g. intended voids in an object closing up), bubbles, small feature erosion, lower than intended mechanical properties, poor dimensional accuracy and the like.

[0016] Figure 1 is an example of a method, which may comprise a computer implemented method for determining set point temperatures within a fabrication chamber, which may compensate for changes in the temperature of locations within previous printed,‘buried’ layers of the fabrication chamber content. As is further set out below, this can be used in determining an amount of print agent (e.g. cooling agent) to apply to a layer of build material to compensate for thermal conduction within processed portions of a fabrication chamber content.

[0017] The method comprises, in block 102, acquiring, by at least one processor, a voxelised model of at least part of an intended content of a fabrication chamber to be formed using additive manufacturing. The voxelised model may for example be acquired from a memory, or received over a network or the like. The model may be thought of as a ‘virtual’ fabrication chamber, or virtual build volume, which is rasterised into print addressable locations, or sub-volumes referred to as voxels herein, i.e. three- dimensional pixels, wherein each voxel occupies or represents a discrete volume.

[0018] In some examples of additive manufacturing, three-dimensional space may be characterised in terms of such voxels. In some examples, the voxels are determined based on the print resolution of an object generation apparatus, such that each voxel represents a region (or voxel location) which may be uniquely addressed when applying print agents, and therefore the properties of one voxel may vary from those of neighbouring voxels. In other words, a voxel may correspond to a volume, or voxel location, which can be individually addressed by an object generation apparatus (which may be a particular object generation apparatus, or a class of object generation apparatus, or the like) such that the properties thereof can be determined at least substantially independently of the properties of other voxels. For example, the‘height’ of a voxel may correspond to the height of a layer of build material. In some examples, the resolution of an object generation apparatus may exceed the resolution of a voxel. In general, the voxels of an object model may each have the same shape (for example, cuboid or tetrahedral), but they may in principle differ in shape. In some examples, voxels are cuboids, for example based on the height of a layer of build material. In some examples, in processing data representing an object, each voxel may be associated with properties, and/or with object generation instructions, which apply to the voxel as a whole. In examples herein, each voxel of the voxelised model may be associated with an indication of whether a region of build material corresponding to that voxel is intended to fuse, or is not intended to fuse, in an additive manufacturing operation. In some examples, each voxel may be associated with other attributes. When considered in terms of a particular slice of a model, voxels may be referred to as pixel locations, or simply pixels.

[0019] The voxels may for example be defined with a resolution corresponding to 300 dots per inch (dpi), having the height of a layer of build material. In some examples, the voxels may be combined (i.e. downscaled) to a resolution such as 300dpi or lower to ease processing resources utilised in the methods set out herein (and may subsequently be upscaled, or divided to a higher print resolution).

[0020] Block 104 comprises associating, by at least one processor, (which may be the same processor(s) as used in block 102) an initial temperature value with each voxel of the voxelised model, wherein if the voxel models a solid part of the intended fabrication chamber content, the initial temperature value associated with that voxel is a first temperature value, and otherwise the initial temperature value associated with that voxel is a second temperature value. The first temperature value may be higher than the second temperature value.

[0021] In one example, the first temperature value is a target temperature value of build material which is intended to fuse and the second temperature value is a target temperature of build material which is not intended to fuse. In some examples, the first temperature value may be associated with voxels corresponding to locations to which fusing agent is to be applied and/or, in some examples, the second temperature value may be associated with voxels corresponding to locations to which no fusing agent is to be applied. In some examples, the first temperature value may be greater or higher than the second temperature value. In some examples, the first temperature value may be a value which is greater than the melting temperature of build material whereas the second temperature value may be a value which is less than the melting temperature of build material. For example, in the case of polypropylene (which is the build material under consideration in relation to the data of Figure 3A-C), which has a melting point of around 140°C the first temperature may be around 154°C and the second temperature may be around 123°C, although these temperatures will vary depending on the materials used. In other examples, the first temperature may not be above the melting temperature, or may be close thereto. For example, for semi-crystalline build materials, the first temperature may be close to- within a few degrees of- the melting temperature. In addition, the target temperature may vary throughout a thermal cycle and at some points temperature may be below the melting point. In some examples, as the target temperature may be the temperature after fusing as occurred (e.g. the now-coalesced powder is cooling), the target temperature may be below the melting point as it represents a‘solidified’ or‘post-melting’ state.

[0022] Block 106 comprises convolving, by at least one processor (which may be the same processor(s) as used in block 102 and/or block 104), the voxelised model with at least one convolution kernel in three dimensions to estimate a temperature of each voxel after a time period. This may for example simulate how the temperature of each voxel may impact the temperature of the voxels around it. In other words, this convolution may be applied to predict a future temperature for build material represented by each voxel, assuming that, at the start of the process, the voxel was associated with one of the first and second temperature values. The voxel array following convolution may therefore comprise a 3D modelled thermal distribution map, which shows how a thermal distribution may have evolved during the time period, it the voxels were to have the first and second temperature values at the start of the time period.

[0023] It may be noted that, as will be discussed in greater detail below, this does not model or predict an expected thermal evolution during a particular additive manufacturing build operation to generate the intended content described in relation to block 102 but instead provides a result which can be used to determine or modify set points, or target temperatures, for the voxels. In other words, while the kernel(s) may model how voxels having the first and second temperature values at the start of the time period may change in temperature over the time period, a corresponding additive manufacturing operation may in examples be intended to behave such that the intended one of the first or second temperature values are reached (at least approximately) at the end of the time period. The convolution allows a compensation for heat transfer within the time period to be derived to achieve (or at least approach) this result.

[0024] Print agent amounts may be determined by considering a difference between a predicted temperature without a print agent, or with a predetermined amount of a print agent, and the determined or modified set point or target temperature, wherein the print agent amount is determined so as to adjust the predicted temperature towards the set point.

[0025] In some examples, the convolution kernel(s) may comprise three 1 D kernels, which may effectively act as a 3D convolution kernel. In other examples, a 3D kernel may be used, or a combination of a 2D and a 1 D kernel may be used.

[0026] In some examples the convolution kernel(s) is/are sized so as to encompass a plurality of layers in object generation. For example, a convolution kernel may be sized to cover voxels corresponding to at least ten, or even tens of layers in additive manufacturing. In some examples, it has been found that a good result may be obtained by modelling around 15 voxels in each direction while not utilising processing resources unduly, however, in some examples, a central voxel may be convolved with voxels within a neighbourhood which extends 32 voxels in one direction, and 31 in another (so that, in three dimensions, the kernel(s) covers 64 layers, and has a footprint of 64 by 64 voxels within a layer. In some examples, the footprint may be 128 by 128. Such a kernel size may be stored as 64bit integers, which is compatible with computing systems. In some examples, a smaller kernel may be effectively provided having such a standard size by having some values set to null. This therefore may be used to model the thermal behaviour, for example, over a time period comprising tens of seconds, in some examples up to a number of minutes, and in three dimensions.

[0027] In some examples, the edges of the voxel array modelling the intended fabrication chamber may be processed by adding ‘virtual’ voxels associated with a temperature value which is the temperature value of the edge voxel. For example, edge columns of voxels, and/or bottom or top voxel slices, may be replicated to provide as many columns of such‘virtual’ voxels as are needed to fill the kernel. In other examples, other values may be used for such virtual voxels, for example modelling thermal losses to the environment.

[0028] It may be a characteristic of the kernel that it extends upward and/or downwards from a nominal voxel being processed. In some examples, the nominal voxel may be a central voxel and/or the kernel may be symmetrical in one, two or three dimensions. The kernel may be, for example, a blurring or Gaussian kernel. Gaussian kernels act as spatial filters which‘blur’ images, and may in effect operate as a moving window which is scanned across the voxel array modelling the intended fabrication chamber. The characteristics of the kernel may be determined or derived for example experimentally, empirically or through application of theory to result in a kernel which produces an intended result based on the thermal characteristics of the material(s) being used. For example, different kernels may be used for different build material and/or for different apparatus, or the like. In this case, the binary choice of the first or second temperature value will be blurred such that the effect of heat conduction from build material which is conducted into surrounding build material may be modelled.

[0029] It may be noted that reference has been made to conducted heat: once a region of build material is buried under several other layers, conduction may be the main source of heat transfer as heat diffusion and radiation in plastic powder build materials may be low, and therefore in some examples, these sources of heat transfer need not be considered. However, in other examples, the kernel may be modelled to include consideration of such effects.

[0030] In an example, the kernel(s) may be determined to match the estimated temperature profile for voxels approximately after about 10 minutes to predict how such a temperature may have changed from the initially assigned temperature values during the time period. In this time, according to an example thermal model represented by the kernel(s), a virtual slice of an object will be buried by a number of subsequent slices (as would happen in a corresponding real additive manufacturing process). Therefore, it may be appropriate to consider the effects of conduction alone in some examples.

[0031] In some examples, temperature evolution due to conduction (and no other heat transfer mechanism) is modelled thereby. In an example apparatus, 10 minutes may correspond to the amount of time to print about 80 layers, or around 6mm of material, and therefore, the slice may be considered to be buried by around 80 other slices. At this point the radiation and convection effects may be considered to be negligible- while radiation is known to affect about 5-6 layers of the fabrication chamber, but that effect is considered to be diluted in the global effect of 80 layers. While kernels which model other thermal behaviours could be used, this would increase the complexity thereof.

[0032] To consider the effect of such a kernel in some particular examples, a small object which is surrounded by a relatively large amount of unfused build material may be expected to lose heat to the surrounding build material. Therefore, the temperature values for voxels representing such an object may be expected to decrease over time. Conversely, if a small strip of unfused build material separates two relatively large objects, the temperature of such a strip may be expected to increase over time, and therefore the temperature values of voxels modelling such a strip may be greater after convolution than before. The kernel(s) is/are intended to model this thermal behaviour.

[0033] Figure 2 comprises a method for determining a print agent amount based on the convolved voxelised model generated using the method of Figure 1 , and for generating layer(s) of object(s) in a fabrication chamber

[0034] Block 202 comprises determining, for each of a plurality of voxels, a difference between the estimated temperature value of the voxel determined in block 106 and the initial temperature value of the voxel. For example, this may indicate that a region of build material corresponding to a voxel is likely to become hotter or cooler over time.

[0035] Block 204 comprises using the determined difference to determine a temperature set point for processing that voxel during object generation. For example, the temperature difference for a particular voxel may be determined as:

TmodellecT T initial ^— T diff

[0036] Where T_modeiied is the temperature value of the voxel following convolution and T i_nitial is the temperature value of a voxel associated therewith in block 104 (i.e. one of the first or second temperature values). T _diff will be negative if the voxel is associated with a decrease in temperature value and positive if the voxel is associated with an increase in temperature value. The negative of the temperature change T _diff may be added to a temperature set point (i.e. a target temperature for that voxel). In other words, the temperature set point may be increased for a voxel which is associated with a decrease in temperature over time, and decreased for a voxel which is associated with an increase in temperature over time. This effectively compensates for the evolution of the temperature: by virtue of the adjustment, voxels associated with a region of build material which is likely to lose heat over time are associated with a higher set point temperature than they would otherwise be, and voxels associated with a region of build material which is likely to gain heat over time are associated with a lower set point temperature.

[0037] Determining the temperature set point may comprise subtracting T_diff from the initial temperature value T _inmai for that voxel (i.e. one of the first and second temperature values). Thus, the temperature set point may be less than T_inmai for voxels which are expected to gain heat and/or more than T_mm_ai for voxels which are expected to lose heat (for example, such that those voxels may be at or near the associated one of the first and second temperature T_inmai at the end of the time period modelled by the kernel(s)) [0038] Block 206 comprises using the adjusted temperature set point to determine a print agent amount to apply to each voxel. In this example the print agent is a cooling agent, such as a water-based detailing agent. In some examples, the adjusted set point may be compared to a predicted temperature, and the difference may be mapped to a fusing agent amount by an algorithm, a look up table or the like. The relationship may be predetermined, for example having been determined through experimentation and/or theoretical analysis. In some examples, determining the amount of fusing agent comprises comparing a predicted temperature for a location corresponding to a voxel without that agent being applied (e.g. from a thermal model of a layer to be processed) to the determined set point. For example, a fusing agent amount may be low or nil and/or a cooling agent amount may be relatively high if the set point is lower than the predicted temperature (the location is likely to need cooling to avoid overheating once the location is buried by subsequent layers), or a fusing agent amount may be relatively high and/or a cooling agent amount may be relatively low or nil if set point is higher than the predicted temperature (the location is likely to lose heat to its surroundings). The amounts may depend on the magnitude of the difference.

[0039] For example, the amount of cooling agent may depend on the difference between a predicted temperature without cooling agent, and the set point temperature. Therefore when a voxel is associated with a predicted temperature which is considerably higher than the set point, the amount of cooling agent specified may be higher than when the difference is smaller. In some examples, the amount of cooling agent may be specified as a contone level or a volume or the like. In some examples, the amount of cooling agent may be specified as a ‘correction’ amount to add or subtract from an amount of cooling agent specified by another model (which cooling agent amounts may have been assumed when determining the predicted temperatures of the layer). The cooling agent amounts may provide or specify a print agent distribution, or a print agent distribution function.

[0040] Block 208 comprises determining object generation instructions for generating at least a layer of fabrication chamber content based on the determined print agent amounts.

[0041] In general, the object generation instructions in some examples may specify an amount of print agent to be applied to each of a plurality of locations corresponding to voxels on a layer of build material. For example, determining object generation instructions may comprise determining‘slices’ of a virtual build volume comprising virtual object(s) rasterised into voxels. An amount of print agent (or no print agent) may be associated with each of the voxels. For example, if a voxel relates to a region of a build volume which is intended to solidify, the object generation instructions may be determined to specify that fusing agent should be applied to a corresponding region of build material in object generation. If however a voxel relates to a region of the build volume which is intended to remain unsolidified, then object generation instructions may be determined to specify that no agent, or a coalescence modifying agent such as a detailing agent, may be applied thereto, for example to cool the build material.

[0042] The amounts of detailing agent may be specified as set out in relation to block 206 and the amount of fusing agent may be determined based on thermal considerations or the like. In other examples, object generation instructions may specify how to direct directed energy, or temperatures of heat lamps, drop size, printhead speed, layer thickness, or any other object generation parameter may also be specified. In some examples, techniques such as halftoning may be used to determine where drops of print agents are placed within a layer.

[0043] Block 210 comprises generating at least a layer of fabrication chamber content based on the object generation instructions. Generating the layer (or a plurality of layers) may comprise generating the objects based on object generation instructions (or‘print instructions’). For example, at least one object may be generated layer by layer. For example, this may comprise forming a layer of build material, applying print agents, for example through use of ‘inkjet’ liquid distribution technologies in locations specified in the object generation instructions for an object model slice corresponding to that layer using at least one print agent applicator, and applying energy, for example heat, to the layer. Some techniques allow for accurate placement of print agent on a build material, for example by using print heads operated according to inkjet principles of two- dimensional printing to apply print agents, which in some examples may be controlled to apply print agents (e.g. detailing agent and/or fusing agent) with a resolution of around 300dpi, 600dpi, or 1200dpi. A further layer of build material may then be formed and the process repeated, for example with the object generation instructions for the next slice. In other examples, objects may be generated using directed energy, or through use of chemical binding or curing, or in some other way.

[0044] Block 212 comprises monitoring temperatures during additive manufacturing and, if the temperatures are outside a predetermined range, using the monitored temperatures to determine object generation instructions for subsequent layers. This may for example result in changing the initial set points (i.e. the first and second temperature values) for subsequent layer(s) if the temperatures seen do not conform to those anticipated.

[0045] Figure 3A-C demonstrates how set points may be derived and used to determine amounts of print agent.

[0046] In Figure 3A, an object 300 to be generated is shown in cross section, with the solid sections thereof cross-hatched and the graphs of Figures 3B and 3C relate to the temperatures and cooling agent for a line of voxels in a slice corresponding to a layer of the object 300, as indicated by dotted line 302. The graphs are scaled to the horizontal size of the object as shown- in other words, a vertical line extending through the object and down the page links (at least approximately) the location associated with a voxel along line 302 to the temperature values and detailing agent amount for that voxel.

[0047] As can be seen, the object 300 comprises a first region with a cross section formed with linked rings of fused material which will be formed with surrounding portions of unfused powder and a second region which is mainly fused, with holes which, as the object is being formed, will contain unfused material.

[0048] Figure 3B shows temperature values associated with voxels along line 302 of Figure 1A.

[0049] Line 304 indicates the initial temperature values assigned to the voxels prior to convolution. Voxels which are not intended to fuse have been assigned the second temperature value, whereas voxels which are intended to fuse have been assigned the first temperature value. Thus, it can be seen that holes in the object 300 are aligned with dips in line 304. In this example, the first temperature value is 154°C and the second temperature value is 123°C.

[0050] Line 306 indicates the resulting temperature values following convolution.

According to the model, which corresponds in this example to how heat would be transferred if the voxels did have the initial temperature values, the temperature values associated with object voxels which are near unfused voxels have decreased and the temperature values associated with unfused voxels which are near object voxels have increased.

[0051] Line 308 indicates the set points: where voxels are expected to lose heat, the set point for a voxel is determined by adding the magnitude of the temperature difference between line 304 and 306 to the initial temperature value for that voxel and where voxels are expected to gain heat, the set-point for the voxel is determined by subtracting the magnitude of the temperature difference between line 304 and 306 from the initial temperature value for that voxel.

[0052] Line 310 indicates the predicted temperature of the voxels without cooling agent being applied, for example based on a predicted heat map of the layer containing the locations modelled by the voxels as it is being processed in additive manufacturing, for example after fusing agent has been applied regions corresponding to the solid portions of the object in that layer and/or energy has been supplied.

[0053] Turning to Figure 3C, line 312 indicates example detailing, or cooling, agent amounts. The amount is determined to have effect such that the predicted temperatures (line 310) are reduced to the set point temperatures (line 308). As can be seen, the amount of cooling agent is highest for voxels which border a bulk portion of the object, and lowest for voxels at an object surface. The units on the vertical axis are contone units specifies coverage of a given voxel in a 8 bit per pixel (voxel) scale (0-255), which specifies an amount of cooling agent relative to a maximum amount (assigned a value of 255) to be delivered by a given apparatus. In one particular example, a contone unit is equivalent

drops per inch), where a drop may be in the range of 4-16

nanograms (ng), for example around 9 ng.

[0054] In general, the methods set out herein may result in a more accurate determination of the amount of cooling agent, with cooling agent being delivered where it is most likely that thermal bleed will be significant, and reduced in other areas. This may assist in reducing the use of cooling agent.

[0055] Figure 4 shows an apparatus 400 comprising processing circuitry 402. The processing circuitry 402 comprises a print instruction module 404, which in turn comprises a print agent module 406.

[0056] In use of the apparatus 400, the print instruction module 404 determines a distribution of at least one print agent to be applied to a layer of build material in a layer by layer additive manufacturing process. The print agent module 406 convolves an array modelling print locations with at least one kernel modelling thermal behaviour in three dimensions, wherein the print locations of the array are initially associated with a first temperature value if they are intended to fuse and are otherwise associated with a second temperature value. The print agent module 406 further determines an amount of print agent to be applied to each of a plurality of print locations based on the temperature associated with print locations following the convolution.

[0057] As described above, this may comprise the print agent module 406 determining a difference between the determined temperature for a print location with the associated one of the first and second temperature and to determine or modify a target temperature for that print location based on the difference (wherein the first and second temperatures may be the target temperatures for particular voxels). The print agent amount may be determined based on a difference between that target temperature and a predicted temperature of the location without fusing agent being applied, or with a default amount of print agent applied. The amounts of print agent determined may be used to provide the distribution of that print agent.

[0058] In some examples, the print agent module 406 is to use a predetermined relationship (e.g. a lookup table and/or an algorithm) associating temperatures with cooling agent amounts to determine the amount of cooling agent to apply to each location, and may use the difference between a predicted temperature of a region of a layer of build material with fusing agent applied during an additive manufacturing process (e.g. following irradiation with energy), and the target temperature as an input thereto. In another example, the determined set point temperature and/or the difference may be used as an input to a conversion algorithm or the like. In some examples, the amount of cooling agent may be a correction to an amount (e.g. a default amount) to be applied to the location.

[0059] Figure 5 shows an apparatus 500 comprising processing circuitry 402 which comprises the print instruction module 404 and the print agent module 406 as described above in relation to Figure 4.

[0060] In this example, the apparatus 500 further comprises additive manufacturing apparatus 502.

[0061] In use of the apparatus 500, in this example, the print instruction module 404 generates control data to generate each of a plurality of layers of at least one object. This may for example comprise specifying area coverage(s) for print agents such as fusing agents, colorants, detailing/cooling agents and the like across each of a plurality of object layers (i.e. the amounts of print agents as specified in a print agent distribution). In some examples, object generation parameters are associated with object model voxels. In some examples, other parameters, such as any, or any combination of heating temperatures, build material choices, a number of printing passes, an intent of the print mode, and the like, may be specified. In some examples, halftoning may be applied to determine where to place print agent.

[0062] The additive manufacturing apparatus 502, in use of the apparatus 500, generates at least one object in a plurality of layers (which may correspond to respective slices of a virtual build volume/fabrication chamber) according to the generated control data. The additive manufacturing apparatus 502 may for example generate an object in a layer-wise manner by selectively solidifying portions of layers of build material. The selective solidification may in some examples be achieved by selectively applying print agents, for example through use of‘inkjet’ liquid distribution technologies, and applying energy, for example heat, to the layer. The additive manufacturing apparatus 502 may comprise additional components not shown herein, for example any or any combination of a fabrication chamber, a print bed, print head(s) for distributing print agents, a build material distribution system for providing layers of build material, energy sources such as heat lamps and the like, which are not described in detail herein.

[0063] The processing circuitry 402 or the modules thereof may carry out any of the blocks of Figure 1 or Figure 2.

[0064] Figure 6 shows a machine-readable medium 600 associated with a processor 602. The machine-readable medium 600 comprises instructions 604 which, when executed by the processor 602, cause the processor 602 to carry out processes. The instructions 604 comprise instructions 606 to cause the processor 602 to determine a modelled thermal distribution map by convolving a virtual fabrication chamber representing at least a portion of a fabrication chamber content to be generated in an additive manufacturing process with a kernel representing thermal conduction (and, in some examples, other thermal behaviours) in three dimensions within a fabrication chamber. Portions of the virtual fabrication chamber which are to be solidified are initially associated with a first temperature value and portions of the virtual fabrication chamber which are not to be solidified are initially associated with a second temperature value. The virtual fabrication chamber representing at least a portion of a fabrication chamber content may be a voxelised representation thereof. The instructions 604 further comprise instructions 608 to cause the processor 602 to determine a cooling agent distribution function based on the modelled thermal distribution map, wherein the cooling agent distribution function is to compensate for thermal conduction in processed layers of the additive manufacturing process. In some examples, the cooling agent distribution function is to determine a correction factor for an amount of print agent to be applied at each of a plurality of locations across the layer. The cooling agent distribution function may specify an amount of cooling agents to apply to each of a plurality of print addressable locations.

[0065] In some examples, the modelled thermal distribution map is used to determine a temperature correction factor for determining or adjusting a target temperature of at least one location within the fabrication chamber. The target temperature may in turn be used to determine cooling agent amounts.

[0066] In some examples, at least one kernel has a spatial width spanning a region of the virtual fabrication chamber corresponding to at least ten layers, or at least twenty layers in an additive manufacturing process. In other examples, three 1 D kernels may be used, or a combination of 1 D and 2D kernels may be used. The kernels may have any of the attributes discussed above in relation to kernels. In some examples, at least one kernel is a Gaussian kernel, and in one example, three 1 D Gaussian kernels are used.

[0067] In examples, the machine-readable medium 600 may comprise instructions to carry out any, or any combination, of the blocks of Figures 1 or 2 or to act as part of the processing circuitry 402 of Figures 4 or 5.

[0068] Examples in the present disclosure can be provided as methods, systems or machine readable instructions, such as any combination of software, hardware, firmware or the like. Such machine readable instructions may be included on a computer readable storage medium (including but not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0069] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that each block in the flow charts and/or block diagrams, as well as combinations of the blocks in the flow charts and/or block diagrams can be realized by machine readable instructions.

[0070] The machine readable instructions may, for example, be executed by a general purpose computer, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine readable instructions. Thus functional modules of the apparatus (such as the print instruction module 404 and/or the print agent module 406) may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term‘processor’ is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors.

[0071] Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

[0072] Machine readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer- implemented processing, thus the instructions executed on the computer or other programmable devices realize functions specified by block(s) in the flow charts and/or in the block diagrams.

[0073] Further, the teachings herein may be implemented in the form of a computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disclosure.

[0074] While the method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. It is intended, therefore, that the method, apparatus and related aspects be limited by the scope of the following claims and their equivalents. It should be noted that the above- mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims. Features described in relation to one example may be combined with features of another example.

[0075] The word“comprising” does not exclude the presence of elements other than those listed in a claim,“a” or“an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims. Based on means based at least in part on. [0076] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.

Claims

1. A method comprising:

acquiring, by at least one processor, a voxelised model of at least part of an intended content of a fabrication chamber to be formed using additive manufacturing;

associating, by at least one processor, an initial temperature value with each voxel of the voxelised model, wherein the initial temperature value is a first temperature value if the voxel models a solid part of the intended content, and otherwise the initial temperature value is a second temperature value; and

convolving, by at least one processor, the voxelised model with at least one convolution kernel in three dimensions to estimate a temperature value of each voxel after a time period.

2. A method according to claim 1 further comprising:

determining a difference between the estimated temperature value of the voxel and the initial temperature value of the voxel; and

using the determined difference to determine a temperature set point for processing that voxel during object generation.

3. A method according to claim 2 further comprising using the determined temperature set point to determine a print agent amount to apply to a location corresponding to that voxel.

4. A method according to claim 3 in which the print agent amount is an amount of cooling agent.

5. A method according to claim 3 further comprising determining object generation instructions for generating at least a layer of fabrication chamber content based on the determined cooling agent amounts.

6. A method according to claim 5 further comprising generating at least a layer of fabrication chamber content based on the object generation instructions.

7. A method according to claim 6 further comprising monitoring temperatures during additive manufacturing and, if the monitored temperatures are outside a predetermined range, using the monitored temperatures to determine object generation instructions for subsequent layers.

8. A method according to claim 1 wherein the at least one convolution kernel comprises three 1 D Gaussian kernels having dimensions which span a plurality of voxels.

9. Apparatus comprising processing circuitry, the processing circuitry comprising: a print instruction module to determine a distribution of at least one print agent to be applied to a layer of build material in a layer by layer additive manufacturing process by selective fusing of build material; the print instructions module comprising a print agent module to:

convolve an array modelling print locations with a kernel modelling thermal behaviour in three dimensions, wherein the print locations of the array are initially associated with a first temperature value if they are intended to fuse and are otherwise associated with a second temperature value; and

determine an amount of print agent to be applied to each of a plurality of print locations based on a modified temperature value associated with print locations following the convolution.

10. Apparatus according to claim 9 wherein the print agent module is determine a difference between the modified temperature value for a print location with the associated one of the first and second temperature value and to determine a target temperature for that print location based on the difference.

1 1. Apparatus according to claim 10 wherein the print agent module is to use a predetermined relationship associating differences between target temperatures and predicted temperatures during additive manufacturing with cooling agent amounts to determine an amount of cooling agent to apply to each location.

12. Apparatus according to claim 9 further comprising additive manufacturing apparatus to generate an object.

13. A machine-readable medium comprising instructions which, when executed by a processor, cause the processor to: determine a modelled thermal distribution map by convolving a virtual fabrication chamber representing at least a portion of a fabrication chamber content to be generated in an additive manufacturing process with at least one kernel representing thermal conduction within a fabrication chamber in three dimensions, wherein portions of the virtual fabrication chamber which are to be solidified are associated with a first temperature value and portions of the virtual fabrication chamber which are not to be solidified are associated with a second temperature value; and

determine a cooling agent distribution function based on the convolution, wherein the cooling agent distribution function is to compensate for thermal conduction in processed layers of the additive manufacturing process.

14. A machine-readable medium according to claim 13 wherein the cooling agent distribution function is to determine a temperature correction factor for determining a target temperature of at least one location within the fabrication chamber.

15. A machine-readable medium according to claim 13 wherein the at least one kernel comprises a Gaussian kernel having a width spanning at least ten layers in an additive manufacturing process.