WO2023195981A1

WO2023195981A1 - Print agents in additive manufacturing

Info

Publication number: WO2023195981A1
Application number: PCT/US2022/023661
Authority: WO
Inventors: Sergio GONZALEZ MARTIN; Tomas CUATRECASAS ARAGAY; Jordi BAUTISTA BALLESTER
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2022-04-06
Filing date: 2022-04-06
Publication date: 2023-10-12

Abstract

In an example, a method includes, using processing circuitry identifying, in a candidate data model of an object to be generated in additive manufacturing, at least one object region. The identified at least one region may be assessed to determine if a location is to be solidified in a first layer and a corresponding location is to remain unsolidified and is to be printed with a cooling agent in a second layer which is adjacent to the first layer. An output may be provided based on the assessment.

Description

PRINT AGENTS 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 and/or binding methods may be used and/or objects may be formed using ‘fused deposit’ modelling or the like.

BRIEF DESCRIPTION OF DRAWINGS

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

[0003] Fig. 1 is an example method of identifying corresponding locations to be solidified in a first layer and printed with cooling agent in an adjacent layer;

[0004] Fig. 2A and 2B show respectively, an example of an object having a beam lattice structure and an example cell of a beam lattice structure;

[0005] Fig. 3 illustrates an example of how print agent may be applied over multiple layers of build material;

[0006] Fig. 4 is an example method of identifying overprinting of different print agents;

[0007] Fig. 5 shows an example of how overprinting may depend on angle of inclination;

[0008] Fig. 6 is an example of an apparatus; and

[0009] Fig. 7 is an example machine-readable medium associated with a processor.

DETAILED DESCRIPTION

[0010] 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. Build material may be deposited, for example on a print bed and processed in a layer by layer manner, for example within a fabrication chamber. According to some examples, suitable build material may include Polyamides (e.g., PA11 , PA12), Thermoplastic Polyurethane (TPU) materials, Thermoplastic Polyamide materials (TPA), Polypropylene materials, and the like.

[0011] In examples herein, print agents are to be selectively applied to layers of 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 determined from structural design data). In addition, a cooling agent (also termed a detailing agent), which acts to reduce or inhibit coalescence may be printed. A cooling agent may be used near edge surfaces of an object being printed, for example extending in a perimeter about the surface of an object in a layer, to assist in defining the edge of an object and/or to assist in creating certain surface effects. Additionally, in some examples, cooling agent may be selectively applied within the surfaces of the object being printed for temperature control purposes.

[0012] 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 to which it has been applied heats up, coalesces and solidifies, upon cooling, to form a slice of the three-dimensional object in accordance with the pattern. According to one example, a suitable fusing agent may be an ink-type formulation comprising, for example, carbon black. Such a fusing agent may comprise any or any combination of an infra-red light absorber, a near infra-red light absorber, a visible light absorber and a UV light absorber. Examples of fusing agents comprising visible light absorption enhancers are dye based colored inks and pigment based colored inks.

[0013] In some examples, the cooling agent may for example comprise an aqueous liquid or solution, for example comprising water, or water with additives such as surfactants and/or salts added thereto. [0014] 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.

[0015] As noted above, additive manufacturing systems may generate objects based on structural design data. This may involve a designer determining a data model of an object to be generated, for example using a computer aided design (CAD) application. The model may define the solid portions of the object. To generate a three-dimensional object from the model using an additive manufacturing system, the model data can be processed to define slices or parallel planes 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. In some examples, each slice may be divided into pixels, which may be associated with a print instruction to print an amount of at least one print agent, and/or an instruction that the pixel should remain untreated, or unprinted, with print agent. Each pixel (or voxel, as they may also be termed to designate a ‘volumetric pixel’) may be thought of as an (x, y) location in a layer, wherein the layers may be associated with a z dimension. Moreover, as mentioned above, it may be noted that in some examples, cooling agent and fusing agent may be printed to the same location, wherein that location is intended to fuse to form part of the object, for example to control overheating.

[0016] In some examples, thermal gradients within build material may cause defects in additive manufacturing. In some examples, thermal gradients may for example result in any or any combination of an appearance defect, a dimension defect (i.e., the object, once generated does not have an intended dimension) or a strength defect, where build material which is intended to fuse does not fully fuse. To ameliorate thermal gradients within a layer in additive manufacturing, in some examples, print instructions may specify that a region of build material between the fusing agent in a region of a layer of the build material which is intended to solidify and a cooling agent applied about the perimeter of the region which is to fuse is left clear of any agent to reduce thermal gradients which might otherwise cause object defects. [0017] Fig. 1 is an example of a method of assessing a candidate data model of an object to be generated in additive manufacturing. The data model is a candidate data model in the sense that it may be used in additive manufacturing but is to be assessed by the method set out herein, and may in some examples be disregarded and/or modified prior to object generation depending on the assessment. The candidate data model may be assessed to determine if a location is to be solidified in a first layer and a corresponding, or same, location (e.g., the same (x,y) location) is to remain unsolidified and to be printed with a cooling agent in a second layer which is adjacent to the first layer, wherein the adjacent second layer is the layer immediately underlying or overlying the first layer, without any intervening layers. For example this may comprise determining if different print agent types are to be printed in the same location in consecutive layers. For example, a first print agent type may consist of a fusing agent, or a mixture of fusing agent and cooling agent, and a second, different, print agent type may consist of cooling agent (printed alone, i.e. , in the absence of fusing agent). In some examples, the method may comprise determining if at least some fusing agent is to be printed in a location in a first layer and cooling agent is to be printed without any fusing agent in a corresponding location in an adjacent layer. In some examples, the method comprises determining if a location in a first layer is to be printed with at least some fusing agent and a corresponding location in a second layer is to be printed with a cooling agent and no fusing agent. In this example the method is carried out by processing circuitry, which may comprise at least one processor.

[0018] Where a location is to be printed with a fusing agent in one layer and is to remain unsolidified and printed with a cooling agent in an adjacent layer, this may cause thermal gradients between the layers, which may result in defects as outlined above. Thus, assessing a candidate data model may allow a likelihood of such defects to be identified, and in some examples, as outlined below, actions may be taken to reduce the number or likelihood of such defects, and/or to prevent generation of an object in which defects are likely.

[0019] The method comprises, in block 102, identifying, in a candidate data model of an object to be generated in additive manufacturing, a region of the object. The region may in principle comprise any region of the object, as set out below. For example, the region may comprise adjacent layers. However, in some examples, the region may comprise a surface region of an object. Locations which are to be solidified in a first layer and remain unsolidified in an adjacent layer may be found in such surface regions and not in interior portions of the object, and therefore identifying surface regions may identify locations which are more likely to be solidified in a first layer and remain unsolidified in an adjacent layer. In some examples, block 102 may comprise identifying a region of the object represented by the data model which falls within a predetermined distance of a surface of the object.

[0020] The data model may for example represent the surfaces of an object using a polygon mesh (e.g., an STL model), or may comprise a voxel model of the object in which a volumetric space occupied by the object is divided into small regions and the individual regions may be labelled to indicate whether that region comprises an interior portion of the object, or is exterior thereto. In other examples, other model types may be used.

[0021] In some examples, block 102 may comprise identifying at least one beam feature of the object. A beam feature may be any feature which spans between two end points, for example comprising a structural element (or strut) of an open mesh or lattice structure (for example a mesh or lattice comprising at least 30% empty space, or at least 50% empty space), or at least one beam linking two otherwise substantially separate object portions. In some examples, the beams may have a prismatic shape. A beam feature may for example be identified by the ratio of its length to its cross section (for example being at least as long, or at least twice as long, as the largest cross-sectional dimension), the ratio of surface area to its volume, and/or may be identified in a candidate data model by being ‘tagged’ by a user or the like.

[0022] In some examples, block 102 comprises identifying at least one beam feature which has a cross sectional dimension of less than a threshold size. This therefore may identify relatively narrow beams. In some examples, the beams may be of less than a threshold dimension, e.g., less than 1cm in cross section, or less than 5mm in cross section, or less than 2mm in cross section. [0023] In some examples, the object modelled by the candidate data model may be intended to comprise a beam lattice portion. In other words, the object may be intended to comprise at least a portion which is intended to comprise beams formed around (and/or defining) a plurality of voids. In some examples, identifying the object region, or the beam feature, in block 102 may comprise identifying any region of the object which is part of the beam lattice portion. Such beam lattice structures may be used in additive manufacturing to provide an infill region without undue use of material. For example, portions or regions of an object which may not be seen may be generated with a sparse lattice form, for example in which at least 30% or at least 50% of the space occupied by the lattice is empty space. In some such objects, build material which is not fused can be recycled. Moreover, beam lattices may be used to provide properties to the generated object. For example, such lattices may provide a flexible and/or compressible structure. In other examples, the distribution of solid material throughout an object may be controlled so as to provide a particular centre of mass, density or the like. Examples of beam lattice structures are described in greater detail below.

[0024] In some examples, block 102 may comprise identifying each instance of a beam feature in an object model, and/or each instance of a beam feature meeting predetermined criteria, for example having a predetermined ratio of length to cross section, and/or ratio of surface area to volume, and/or cross section dimension below a threshold size.

[0025] The method continues in block 104 by assessing if a location is to be solidified in a first layer and a corresponding location in a second layer, adjacent to the first layer, is to remain unsolidified and is to be printed with a cooling agent. [0026] In some examples, block 104 may comprise identifying a number of such locations. This may comprise assessing if different print agent types or combinations of print agent types are to be printed in the same location on consecutive layers in additive manufacturing. For example, pairs of pixels in a data model associated with a location to be solidified in a first layer and a corresponding location in an adjacent layer which is to remain unsolidified and is to be printed with a cooling agent may be identified, and the number of such pixel pairs may be determined. In some examples, block 104 may comprise determining the proportion of such pixels or pixel pairs compared to the total number of pixels.

[0027] In some examples, block 104 may comprise determining an angle of generation of identified beam feature(s), as this angle may imply the extent to which a beam may be associated with location(s) to be solidified in a first layer where corresponding location(s) in a second layer, adjacent to the first layer, are to remain unsolidified and printed with a cooling agent. This is described in greater detail below. The angle may be determined directly from the object model (e.g., an angle of a medial axis may be determined) or may be implied, for example by determining a pixel offset between the content of a first layer and an adjacent layer. Further examples in relation to determining the angles are set out in relation to Fig. 4 below.

[0028] Block 106 comprises providing an output based on the assessment. In some examples, the output may comprise a parameter, or score, associated with the candidate object model, or a portion thereof, wherein the score may be indicative of an amount of overprinting expected in generation of an object based on the candidate data model (wherein the term ‘overprinting’ is used herein to describe printing a location in one layer of build material with at least some fusing agent such that it is intended to fuse and printing a corresponding or same location in an adjacent layer of build material with cooling agent such that it is intended to remain un-solidified).

[0029] In some examples, providing an output may comprise providing a notification that an amount of overprinting (for example a number of locations, or a number/proportion of beam features extending at an angle associated with overprinting, identified in block 104, or a score associated therewith) exceeds a predetermined level. The predetermined level may be determined empirically (for example based on a level of overprinting which has resulted in objects showing defects as determined by a user) or theoretically, and/or may be based an intended level of print quality, as in some print operations a higher level of defects may be acceptable than in other print operations. This may allow a user to determine whether to proceed with the object generation process, for example given that there is a significant possibility of defects. In some examples, object generation may be prevented from proceeding if the amount of predicted overprinting exceeds a threshold, wherein threshold may in some examples depend on an intended print quality and/or a build material type (as some build materials may be more prone to defects associated with thermal gradients than others).

[0030] In another example, providing an output may comprise determining an orientation for the model to reduce the number of locations to be solidified in a first layer where a corresponding location of an adjacent layer is to remain unsolidified and is to be printed with a cooling agent. The output may comprise the determined orientation. The output may further comprise a rotated data model of the object, wherein the rotation is determined to provide the determined orientation. Further examples in relation to how modifying the angle of object generation may reduce the amount of overprinting are discussed in greater detail below.

[0031] In still further examples, modifications may be made to the candidate data model. For example, where the candidate data model comprises a lattice beam structure in at least a portion thereof, an alternative lattice beam structure may be identified. For example, a first lattice beam structure of a candidate data model may include a first number of locations to be solidified in a first layer where a corresponding location in an adjacent layer is to remain unsolidified and is to be printed with a cooling agent. The alternative lattice beam structure may include a second number of locations to be solidified in a first layer where a corresponding location in an adjacent layer is to remain unsolidified and is to be printed with a cooling agent. The second number may be less than the first number. In such examples, the output may comprise a modified data model incorporating the alternative beam lattice structure in place of the first beam lattice structure, and/or a notification to a user that such an alternative beam lattice structure exists.

[0032] As a further example, an output may comprise determining a modified separation distance between different print agents in the same layer. The output may comprise the modified separation, which may for example be used in generating print instructions. As noted above, in some examples, a region of build material may be left unprinted between a region which is printed at least with fusing agent and a region which is printed with a cooling agent. In some examples, the size of the separation distance (i.e., the width of the unprinted region) may be increased, as will be discussed in greater detail below.

[0033] In still further examples, if the assessment in block 104 suggests that the amount of overprinting will be low, for example being below a predetermined threshold or level (where, as outlined above, this may be based on an empirical or theoretical assessment of whether an object generated will be likely to meet an intended print quality level), the output may comprise any or any combination of an indication that generation of the object may proceed, generation of print instructions and printing of the object as described by the candidate data model. [0034] Such print instructions may be derived from the candidate data model of the object. For example, an object data model may be ‘voxelised’ and each voxel (or pixel within a surface of a layer) may be associated with an instruction to print a fusing agent, a cooling agent, a combination of a fusing agent and a cooling agent, or by instruction or default due to the absence of an instruction, may be left clear of print agent. Generation of print instructions may be intensive in terms of computing resource, so determining whether the object model is likely to result in an object with defects associated with thermal gradients between layers may avoid the resource intensive step of instruction generation in some examples.

[0035] In generating the object in a layer-wise manner, fusing and cooling agents may be selectively applied, for example through use of ‘inkjet’ liquid distribution technologies, and energy, for example heat, may be applied to each layer using one or more energy source. Generation of objects consumes materials and energy, and therefore determining whether the object model is likely to result in an object with defects may avoid the resource intensive step of object generation in some examples.

[0036] Fig. 2A shows an example of a beam lattice 200, of the type which may be formed using additive manufacturing, for example to provide a sparse infill section (e.g., at least 20% empty space, at least 30% empty space or at least 50% empty space) of an object and/or to provide intended object properties, for example flexibility, compressibility, density, buoyancy and the like. While the example of Fig. 2A shows a regular cubic lattice comprising a number of diagonally slanted beams, there are many variations of such lattices that may be provided. For example, lattices may be regular, or made up of biomimicry forms such as branchlike or veinlike structures. In some examples, Voronoi structures may be used. In other examples, beams may be curved, for example forming springlike structures which may be joined together.

[0037] Fig. 2B shows an enlarged version of a portion of the lattice 200 shown in Fig. 2A. In particular, Fig. 2B shows a structure of a single ‘cell’ 202 of the lattice 200 (albeit with somewhat narrower beams), formed by beams 204 (only some of which are labelled to avoid overcomplicating the Figure). In this example, each lattice cell 202 is made up of six faces, each of which is formed by perimeter beams and diagonal cross beams. Moreover, beams extend through the interior of the cell 202, linking diametrically opposed comers. Thus, the beams provide a number of cross linkages between nodes at the corners of the cell 202, so providing a structure which in this example is self-supporting but may be compressible. As can be seen from Fig. 2A and 2B, in this example, the beams extend at various angles (for example, vertically (90°) and at 45° in the orientation illustrated). In other examples, an angle at which a beam extends may be different to those shown.

[0038] Fig. 3 illustrates how print agent may be applied in order to print, or generate, a beam feature in additive manufacturing, and shows an example of how print instructions may be assigned to pixels or voxels 302 (herein after, pixels 302), only some of which are labelled to avoid overcomplicating the Figure. In particular, Fig. 3 illustrates the print instructions relating to a vertical slice through the centre of a beam rising from left to right. Each row of pixels is associated with a different layer in additive manufacturing and in this example, each column is associated with a different X coordinate and the same Y coordinate within the layers. The black pixels indicate pixels to which fusing agent is to be applied whereas the shaded pixels indicate pixels to which cooling agent is to be applied. In this example, it is specified that there is a one pixel space, or separation, between the application of fusing agent and cooling agent within each layer, for example in order to reduce a thermal gradient in object generation between the regions of build material corresponding to pixels of a layer. In other examples, there may be no such space, or the space may be a greater number of pixels, for example on the order of 5, 10, 15 or 20 pixels. It will be appreciated that whilst, in this example, this space is shown in the X dimension, there may be a similar spacing or separation in the Y dimension. As can be seen, given the angle with which the beam extends, and the one pixel separation, there are four pixels, highlighted with a bold border, in which detailing agent is to be printed on a pixel which is directly above a pixel which is to be solidified and on which fusing agent is to be printed. As build material which is to be fused becomes hot and build material to which cooling agent is applied tends to be cool, this may create a thermal gradient between the layers during object generation which may in turn result in defects in the generated object. Beam features, in particular narrow beams, may be particularly susceptible to adverse impacts associated with such thermal gradients, which may be due to their relatively large surface area to volume ratio.

[0039] As described above, method of Fig. 1 may identify where ‘overprinting’ will occur and may allow an object generation operation to be aborted, and/or action taken to ameliorate this possible source of defects before object generation occurs and/or before the determination of print instructions.

[0040] Fig. 4 is an example of how the assessment of block 104 of Fig. 1 may be carried out, in an example in which block 102 comprises identifying a region comprising at least one beam feature.

[0041] In this example, the method comprises, in block 402, determining an angle of generation of the at least one identified beam feature. This may be the angle relative to the plane of a layer in additive manufacturing (i.e. , the XY plane as discussed above). The angle may be determined explicitly or implicitly. For example, determining the angle may comprise determining a medial axis (i.e., a centre line of the beam feature), wherein the determined angle is the angle of the medial axis. In some examples, the beams may be placed into categories based on the angle. For example, bins may be defined classifying angles from 0° to the XY plane to 90° to the XY plane. For example, there may be 18 such bins or subranges defined, each of them with a 5° spread. [0042] The method further comprises, in block 404, determining a thickness of a layer of build material to be used in additive manufacturing. This may for example comprise determining the settings of the print apparatus which is intended to generate the object from the candidate data model. In other examples, a default thickness may be used.

[0043] Block 406 comprises determining a separation between the different print agents in the same layer (or a width of untreated build material). For example, this may comprise determining if there is a separation specified in a number of pixels (for example, in the case of Fig. 3, one pixel), or specified as a geometrical distance or the like.

[0044] It will be appreciated that, in terms of geometry, and with reference to the example of Fig. 3, the thickness of the layer determined in block 404 and the separation determined in block 406 will have an impact on the angles which will result in overprinting in adjacent layers. For example, if the separation in Fig. 3 was two pixels, then at least two of the highlighted pixels would no longer be highlighted.

[0045] In a particular example, and as noted above, the angles may be categorised based on subranges, i.e., the beams may be placed into bins categorising their angle of generation. A weighting may be associated with each of the subranges. For example, a higher weighting may be associated with a subrange associated with a higher amount of overprinting than a subrange associated with a lower amount of overprinting (or vice versa in some examples). This weighting may be based on a number of factors. For example, a factor may comprise the type build material which is to be used in object generation. Some materials may be more prone to defects associated with overprinting in consecutive layers and such build materials may be associated with a higher weight than other materials. A further factor may comprise a printing profile, or an intended print quality level. For example, this may be associated with an intended level of print quality. In some examples, a print quality specification may allow a higher number of defects than in other examples. Where a high quality printed output is specified, a higher weight may be given to subranges associated with overprinting. Moreover, the thickness of the layer determined in block 404 and/or the separation determined in block 406 may be used as parameters in determining such weightings.

[0046] Once a weighting has been assigned to each subrange and the number of beams in each subrange has been determined, an overall parameter, or score, for the object may be determined. For example, this may be determined by multiplying the associated weight of a subrange with a percentage of the total beams which are within that range, and summing this over the subranges.

[0047] In other examples, a parameter or score for the object model indicative of the amount of predicted overprinting may be determined in some other way. For example, the score may be determined based on the number or proportion of beams which have an angle of inclination to the XY plane which is below a threshold angle, wherein this number or proportion may be compared to at least one threshold parameter to determine if the amount of predicted overprinting meets a predetermined standard. The threshold angle and/or the threshold parameter may be based on, for example, any or any combination of the build material type, the layer thickness, the separation between different print agents in a layer, a specified intended print quality or the like, and may be determined empirically or theoretically. In other examples, a voxelised model may be considered and the number of voxels or pixels which are to be overprinted with different agents in successive layers may be determined.

[0048] Fig. 5 shows how angle of inclination and other factors may have an impact on the number of pixels which are associated with overprinting in consecutive layers. The graph shows the number of pixels in which either cooling agent is printed in the absence of fusing agent in a layer following a layer in which fusing agent is applied, or vice versa, for a given angle of beam extension, wherein overprinting is indicated by a negative number of pixels (i.e., values below 0 on the vertical axis). A positive number of pixels indicates that there is at least one intervening pixel between a pixel to be solidified and a pixel to be treated with cooling agent, for example being associated with an instruction to be left clear of fusing agent.

[0049] A first example, shown with the solid line 500, shows the number of pixels overprinted in adjacent layers when the layer thickness is 200 pm, the XY resolution is 600 dots per inch (dpi) and the separation between fusing agent and cooling agent in a single layer is 380 pm. A second example, shown with the dotted line 502, shows the number of pixels overprinted when the layer thickness is 80 pm, the XY resolution is 1200 dpi and the separation between fusing agent and cooling agent in a single layer is 500 pm.

[0050] For example, based on the conditions associated with the solid line 500, it may be determined if any beam has an angle which is between 3° and 20° (meaning between around 5 and 50 pixels may be overprinted in pairs of consecutive layers) and, if such a beam exists, an alert may be generated and/or the object model data may be modified to remove such beams, for example by rotation of the orientation of the object model for object generation, or replacement of a portion of the object model associated with beams extending at such angles. In other examples, the number of or proportion of beams falling into this range may be assessed to determine if it is below a threshold acceptable value, wherein the threshold acceptable value may be determined empirically or theoretically. In a further example, the number of beams in each 5° range, or some other range may be considered. A ‘score’ may be determined wherein beams which are for example between 5° and 10° are given a higher weighting than beams between 10° and 5° due to the higher number of pixels associated with overprinted, and beams which have an angle of or above may be given a weighting of 0, or a negative weighting as they are not associated with overprinting. The score may comprise a weighted sum of a count of the beams. In other examples, a ‘score’ may be determined in some other way, for example comprising a count, or proportion, of pixels associated with overprinting or the like.

[0051] It may be noted that, in general, reducing the layer thickness and/or increasing the separation between fusing agent and cooling agent may reduce the number of pixels which are associated with overprinting. Moreover, steeper beams may experience less overprinting than beams that extend out of the XY plane at a shallower angle. The dpi value is relevant to the pixel count as a higher dpi is indicative of smaller pixels, so the number of pixels associated with overprinting also depends on the dpi (although the length of the overprinted portion, measured in microns or the like, may be more consistent for a given angle). For example, at 1200dpi, a pixel may have a dimension of around 21 urn whereas at 600dpi a pixel may have a dimension of 42um.

[0052] As noted above, there may be a threshold angle (which may depend on layer thickness and separation between fusing agent and cooling agent within a layer) at which overprinting no longer occurs. Thus, in some examples, in an output as mentioned in block 106, a candidate object model may be rotated in an attempt to reduce or minimise the number of beams which are to be printed at an angle at which overprinting is predicted to occur (i.e., the orientation of object generation may be modified). As another example of an output, a beam lattice structure of a portion of an object to be generated may be replaced with an alternative structure, which may be more suited to a set of object generation parameters. For example, while a given beam lattice structure may be suitable for generation when the separation distance between fusing agent and cooling agent within a layer is relatively large, it may not be suitable when that separation is relatively small. The lattice beam structure could therefore be replaced with another structure with steeper beams given an intention to generate the object with a relatively small separation between fusing agent and cooling agent (wherein a small separation distance may assist in defining a sharp edge to a generated object, or the like).

[0053] Fig. 6 is an example of an apparatus 600, which may be used in some additive manufacturing operations. The apparatus 600 comprises processing circuitry 602, the processing circuitry 602 comprising a model analysis module 604 and a model assessment module 606.

[0054] In use of the apparatus 600, the model analysis module 604 analyses an intended content of pairs of layers to be generated in object generation to determine a predicted overprinting parameter indicative of an amount of overlap between a first print agent to be printed in a first layer of additive manufacturing and a second print agent to be printed in a second layer of additive manufacturing, wherein the second layer is to be formed directly on the first layer. The predicted overprinting parameter may for example be indicative of an amount of predicted overprinting as defined above, and may for example be indicative of a number or proportion of locations (e.g., pixels) associated with overprinting, a number of beams associated with overprinting and/or a weighted sum of a number of beams associated with overprinting, and/or a score determined based on such parameters as discussed above. The first print agent may comprise at least some fusing agent and the second print agent may be free of fusing agent, and may comprise a cooling agent, or these designations may be reversed (i.e., when fusing agent is to be printed on the second layer and cooling agent is to be printed to the first layer). In some examples, the model analysis module 604 is to analyse the content of layers comprising or near to object surfaces, and/or to analyse features having a dimension which is less than a threshold dimension and/or to analyse beam features as discussed above. By performing the analysis on such object regions, portions or features and not other regions, portions or features, processing resources may be conserved whilst still identifying features which are more likely to suffer from defects as a result of overprinting. In some examples, the model analysis module 604 may determine an angle associated with each beam feature, as discussed above. For example, the model analysis module 604 may carry out blocks 102 and/or block 104 of Figure 1 , and may carry out any of the blocks of Figure 4 and/or may carry out any of the methods set out in relation thereto.

[0055] In use of the apparatus 600, the model assessment module 606 determines, based on the analysis of the model analysis module 604, if an amount of overlap for the object exceeds a threshold. The threshold may be associated with an intended print quality, and may be determined empirically or theoretically, as discussed above. The threshold may depend on an intended print quality and/or a build material type. For example, the model assessment module 604 may provide an output, which may be any of the outputs described above for example in relation to block 106.

[0056] In some examples, the apparatus 600 may comprise further processing modules, such as a print instruction module to determine a distribution of fusing and cooling agents to be applied to a layer of build material in a layer by layer additive manufacturing process to generate an object. Indeed, the apparatus 600 may further comprise additive manufacturing apparatus which may be used to generate objects using additive manufacturing. The additive manufacturing apparatus may comprise at least one fusing energy source to irradiate a print bed (which may in practice comprise a removable component of the apparatus) and may generate objects in a layer-wise manner by selectively solidifying portions of layers of build material formed on the print bed. The selective solidification may be achieved by selectively applying print agents, for example through use of ‘inkjet’ liquid distribution technologies.

[0057] The additive manufacturing apparatus may comprise additional components, for example a fabrication chamber, at least one print head for distributing print agents, a build material distribution system for providing layers of build material, fusing energy source(s), carriages for sweeping fusing energy source(s) across a print bed and the like.

[0058] The apparatus 600 may, in some examples, carry out at least one of the blocks of Fig. 1 , or Fig. 4, and/or any of the methods set out in relation thereto.

[0059] Fig. 7 shows an example of a tangible machine readable medium 702 in association with a processor 704. The machine readable medium 702 stores instructions 706 which, when executed by the processor 704 cause the processor to carry out actions.

[0060] In this example, the instructions 706 comprise instructions to cause the processor 704 to determine a value based on an amount of overlap of a portion of build material to be fused and a portion of build material to be treated or printed with a cooling agent and remain unfused in consecutive layers in an object to be generated in additive manufacturing. The value may therefore be indicative of the amount of predicted ‘overprinting’ as defined herein. The value may for example comprise a number of pixels, a score, an indication of angles of beam features, an overprinting parameter, or the like as described above. The instructions 706 may further cause the processor 704 to determine an indication of whether the object, once generated, is predicted to be of a predetermined quality (e.g., meet predetermined a quality parameter or standard) based on the value. For example, the value may be compared to a threshold to determine if it will be of the predetermined quality, wherein in some examples the threshold may be associated with an intended print quality and/or a print agent type. For example, the instructions may comprise instructions for carrying out any or any combination of the blocks of Fig. 1 and/or Fig. 4, and/or any of the methods set out in relation thereto above.

[0061] In some examples, the instructions 706 comprise instructions to cause the processor 704 to identify at least a portion of a candidate data model of an object to be generated in additive manufacturing comprising a beam lattice structure, and/or identifying at least one beam feature. Further instructions may comprise instructions to cause the processor 704 to determine at least one beam angle within the structure (for example, based on a determination of the medial axis or the like) and determining the value may be based on the angle. For example, beams may be categorised into bins based on the angle, each bin having a weighting associated therewith, and a weighted sum of the number of beams in each bin may be determined to provide the value.

[0062] In some examples, the instructions 706 comprise instructions to cause the processor 704 to determine the value based on at least one of a width of untreated build material separating a region to be fused from a region which is to remain unfused in a layer, a build material type, and an intended layer height.

[0063] In some examples, the instructions 706 may cause the processor 704 to act as any part of the processing circuitry 602 of Fig. 6. In some examples, the instructions 706 may cause the processor 704 to carry out at least one of the blocks of Fig. 1 , or Fig. 4.

[0064] 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.

[0065] 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 at least some blocks 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.

[0066] 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 and devices (such as the processing circuitry 602, model analysis module 604 or model assessment module 606) 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.

[0067] 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.

[0068] Such 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 block diagrams.

[0069] 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. [0070] 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 only 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.

[0071] 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.

[0072] 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, using processing circuitry: identifying, in a candidate data model of an object to be generated in additive manufacturing, at least one object region; assessing, for the identified at least one region, if a location is to be solidified in a first layer and a corresponding location is to remain unsolidified and is to be printed with a cooling agent in a second layer which is adjacent to the first layer; and providing an output based on the assessment.

2. A method according to claim 1 wherein identifying the region comprises identifying at least one beam feature.

3. A method according to claim 2 wherein the assessing is based on determining an angle of generation of the at least one identified beam feature.

4. A method according to claim 3 wherein the assessing is further based on a thickness of a layer of build material to be used in additive manufacturing.

5. A method according to claim 3 wherein the assessing is further based on a separation between different print agents in the same layer.

6. A method according to claim 1 wherein providing an output based on the assessment comprises providing a notification to a user that a number of locations to be solidified in a first layer wherein a corresponding location is to remain unsolidified and is to be printed with a cooling agent in a second layer which is adjacent to the first layer exceeds a predetermined level.

7. A method according to claim 1 wherein providing an output comprises determining an orientation for the candidate data model to reduce the number of locations to be solidified in a first layer wherein a corresponding location is to remain unsolidified and is to be printed with a cooling agent in a second layer which is adjacent to the first layer.

8. A method according to claim 1 wherein providing an output comprises determining a modified separation between different print agents in the same layer.

9. A method according to claim 1 wherein the candidate data model comprises a first lattice beam structure in at least a portion thereof and wherein providing an output comprises identifying an alternative lattice beam structure in which the number of locations to be solidified in a first layer wherein a corresponding location is to remain unsolidified and is to be printed with a cooling agent in a second layer which is adjacent to the first layer is reduced compared to the first lattice beam structure.

10. A method according to claim 1 wherein providing the output comprises generating an object based on the candidate data model.

11. Apparatus comprising processing circuitry, the processing circuitry comprising: a model analysis module to analyse an intended content of pairs of layers in object generation to determine a predicted overprinting parameter indicative of an amount of overlap between a first print agent to be printed in a first layer of additive manufacturing and a second print agent to be printed in a second layer of additive manufacturing, wherein the second layer is to be formed directly on the first layer; and a model assessment module to determine, based on the analysis, if an amount of overlap for the object exceeds a threshold.

12. Apparatus according to claim 11 wherein the model analysis module is to analyse the content of layers comprising features having a dimension which is less than a threshold dimension.

13. A machine-readable medium comprising instructions which, when executed by a processor, cause the processor to: determine a value based on an amount of overlap of a portion of build material to be fused and a portion of build material to be treated with a cooling agent and remain unfused in consecutive layers in an object to be generated in additive manufacturing; determine an indication of whether the object, once generated, is predicted to be of a predetermined quality based on the value.

14. The machine-readable medium of claim 13 further comprising instructions which, when executed by the processor, cause the processor to: identify at least a portion of a candidate data model of an object to be generated in additive manufacturing comprising a beam lattice structure; determine at least one beam angle within the structure; and wherein determining the value is based on the angle.

15. The machine-readable medium of claim 13 further comprising instructions which, when executed by the processor, cause the processor to determine the value based on at least one of: a width of untreated build material separating a region to be fused from a region which is to remain unfused in a layer; a build material type; and an intended layer height.