WO2023146547A1

WO2023146547A1 - Assistance structure for additive manufacturing

Info

Publication number: WO2023146547A1
Application number: PCT/US2022/014536
Authority: WO
Inventors: Daniel MOSHER; Gabriela GRIFFIN
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2022-01-31
Filing date: 2022-01-31
Publication date: 2023-08-03

Abstract

Example implementations relate to compensating for distortions in 3D printing processes. One example implementation determines a geometry and a spatial arrangement of an object model within a virtual build volume, the object model representing an object to be generated within a build volume of a powder-based additive manufacturing system using a thermally curable binder agent. An assistance structure model is generated within the virtual build volume, the assistance structure model representing an assistance structure to be generated within the build volume to assist during a printing phase when the object to be generated is defined using the thermally curable binder agent and to assist during a curing phase when the thermally curable binder agent is cured to generate the object. The assistance structure model has a geometry and spatial arrangement within the virtual build volume that is dependent on the geometry and spatial arrangement of the object model within the virtual build volume.

Description

ASSISTANCE STRUCTURE FOR ADDITIVE MANUFACTURING

BACKGROUND

[0001] When an object is formed by powder-bed 3D printing, geometric differences may arise between the formed object and the 3D object model used in the object formation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figure 1 illustrates a 3D printing system according to an example;

[0003] Figure 2 illustrates application of thermally curable binder agent layer-by-layer for objects and assistance structures according to an example;

[0004] Figure 3 is a plan view of an assistance structure according to an example;

[0005] Figure 4 is a section view of the assistance structure of Figure 3;

[0006] Figure 5 illustrates objects and assistance structures in a build volume and according to an example;

[0007] Figure 6 illustrates objects and assistance structures in a build volume and according to another example;

[0008] Figure 7 illustrates a method of generating an assistance structure model for generating assistance structures together with objects according to an example; and

[0009] Figure 8 is a block diagram of a controller for a 3D printer according to an example.

DETAILED DESCRIPTION

[0010] In some 3D powder-bed binder jet printing systems, an object is generated according to an object model using a printing process and a curing process. The object model is associated with a geometry and spatial arrangement of the object model within a virtual build volume. The object model represents an object to be generated within a corresponding build volume of a powder-based additive manufacturing system using a thermally curable binder. In the printing process successive layers of a particulate build material or powder are distributed within a build volume. Each layer of powder is distributed across the surface of the previous layer, or a build platform of the printing system for the first layer. Thermally curable binder agent is selectively applied to a number of layers of powder according to the object model. Once the thermally curable binder agent has been applied to a layer of powder, a subsequent layer of powder is distributed and thermally curable binder agent is then selectively applied to the new layer. In this way, an object is defined within the build volume by the presence of thermally curable binder agent within the powder. A build bed is formed as layers of powder are distributed and thermally curable binder agent applied to each layer. When the build bed is completed a curing process is applied. During the curing process heat is applied to the build bed to solidify components of the thermally curable binder agent to solidify the defined object.

[0011] In one example, a thermally curable binder agent may be used, which combines with some of the powder to form a composite powder-binder material having powder onto which thermally curable binder agent has been applied or has penetrated. The curing process comprises heating the build bed to cure components, such as latex components, of the thermally curable binder agent. The curing process may also comprise generating an airflow through the build bed to extract binder agent solvents therefrom. Loose powder which has not been penetrated by the thermally curable binder agent may be removed after completion of the curing process to leave the solidified or generated object.

[0012] In an example, the powder may comprise powder particles of various materials such as ceramics and/or metals. The composite material may be subject to densification or compaction of the respective powder particles. This compaction of powder within the build bed can affect the geometric or other properties of the generated object. For instance, the action of applying the thermally curable binder agent on powder may cause local changes in the density and permeability of the composite material. This may change its characteristics, such as mechanical and thermal characteristics, when compared with the surrounding loose powder. These changes may affect the distribution of powder in subsequent layers further exacerbating these changes. Different consolidation behavior between loose powder and composite material can lead to dimensional inconsistencies and defects such as bending and cracking of the generated object. These distortions and weaknesses may be exacerbated for object geometries which include certain features, such as overhangs and fine detail. Such fine details may include features below a predetermined threshold size dependent on the properties of the powder and the resolution and drop size at which binder agent is deposited.

[0013] In an example, one or more assistance structures may be useful to mitigate the effects on generated objects caused by local changes to composite material density within the build bed that may occur before the thermally curable binder agent has been cured. Example assistance structures may include additional features formed within the build bed. These assistance structures may be sized, shaped and located within the build bed to compensate for the effects of compaction or densification within the build bed caused by application of the thermally curable binder agent. In an example the assistance structures may help to stabilize powder within the build volume or build bed which helps prevent problems with the quality of the eventually generated object, for example by reducing dimensional or geometric differences between the generated object and the object model from which it was generated. In another example, the assistance structures may additionally or alternatively modify or guide airflows during the curing process to improve the quality of the object being generated. The wetting action of applied agent to the powder of the assistance structures changes the way air flows through the powder compared with loose powder. Appropriate location and geometry of assistance structures within the build bed can be used to modify airflows through the build bed in desired ways, for example to improve airflow in corners of the build bed or between defined objects. The assistance structures may also be useful for controlling air flow around solidifying objects to assist with the removal of solvents during the curing process. Airflows may be applied during the curing process using vacuum holes in a screen or base plate on which the build bed rests. Without the assistance structures, the airflow would be dependent on the relative location of the vacuum holes and the objects solidifying in the build bed. This may result in parts of the build bed not being subject to sufficient airflow which may result in object quality issues in those parts of the build bed. By adding assistance structures, airflow to those parts of the build bed may be improved, for example by directing some airflow away from the locations of vacuum holes to other areas of the build bed.

[0014] One or more assistance structure models may be generated in a virtual build volume with one or more object models with an assistance structure model representing an assistance structure to be generated within the build volume to assist during a printing process when the object to be generated is defined using the thermally curable binder agent and to assist during a curing process when the thermally curable binder agent is cured to generate the object. In an example, the assistance structure model has a geometry and spatial arrangement within the virtual build volume that is dependent on the geometry and spatial arrangement of an object within the virtual build model.

[0015] Example assistance structures may include cubes, spheres and other 3D shapes including longitudinally extending or planar members with or without holes therethrough. A planar member may extend horizontally in one or more of the lower layers. The assistance structure or structures may depend on an object generating property such as the location, size and shape of one or more object models within the virtual build bed, and/or the location, size and shape of other assistance structures. The object generation property may be a property associated with the materials used to generate the object such as the type of powder and/or thermally curable binding agent and/or a characteristic of the object generation system such as the position of vacuum holes relative to a build bed, a curing temperature or level of applied air flow. In an example, the one of more assistance structures may be defined through application of the same thermally curable binder agent used for defining the objects in the build volume. Alternatively, a different thermally curable binder agent may be employed to define the assistance structures. In another example, the assistance structures may be defined using a non-binder agent such as water.

[0016] The irregularities of heating and/or airflows experienced within the build bed in subsequent processes such as curing may be mitigated by the assistance structures. The completed build bed comprises loose powder and the composite material (i.e. powder on which a thermally curable binder agent has been applied). In an example, a curing process applies heat and vacuum pressure in order to solidify the composite material defining the object and to remove excess binder agent solvent. The addition of heat and airflows, or heated airflows, may be used to reduce the production cycle time of the object(s). However, the heating may be experienced unevenly within the build bed, for example due to solidifying objects acting as heat sinks which may cause dimensions of generated objects to be outside of intended tolerances. The airflows may also be experienced unevenly within the build bed, for example due to application of vacuum pressure through large gaps in a screen underneath the build bed. There may also be varying stiffness across the build bed in the XY (horizontal) plane due to varying density of loose powder underneath (Z axis) composite material, as well as proximity of other defined objects. As noted above, this may be due to the application of thermally curable binder agent to powder causing local densification of the powder.

[0017] In one example, the geometry and spatial arrangement of an object model in a virtual build volume is used to determine an assistance structure model in the virtual build volume. The assistance structure model is then used to define a corresponding assistance structure in a build volume together with defined objects in order to reduce the above noted issues. The object model may comprise information about the geometry and spatial arrangement of the object model within a virtual build volume. The assistance structure model may comprise information about the geometry and spatial arrangement of the assistance structure model within the virtual build volume and is dependent on the geometry and spatial arrangement of the object within the build volume. The one or more assistance structure models represent assistance structures to be defined in a build volume to better define objects within the same build volume during the printing process and to better distribute airflows and/or heat within the completed build bed during the curing process. Additionally, the assistance structure or structures may modify the stiffness of the build bed to induce a more uniform mechanical response to any combination of physical conditions on the build volume such as the application of heat or vacuum pressure. Reducing the effects of local consolidation of the powder within or near the location of a defined object within the build bed as well as uneven thermal gradients within the build bed may produce more consistent generated object dimensions, including in the z-axis or dimension (height), as well as reduce defects in generated objects like cracking and bending.

[0018] Figure 1 illustrates a powder-based additive manufacturing system 100 using a thermally curable binder agent in which build data 105 is received at a computing function or controller 110 which may be part of a 3D printer or a preprocessing station which forwards data to a 3D printer. The build data 105 may be received from a source such as a user library or object design station 115 and comprises the geometry and spatial arrangement of one or more object models 140m within a virtual build model 135m and representing one or more objects 140g to be generated using a build volume 135v. The object models define wanted characteristics or properties for each object such as their size, dimensions in different axes, type, shape, geometry, and location within the build volume. The spatial arrangement information may comprise a specific range of coordinates in different axes, a centroid of the object model together with coordinates of the centroid, as well as other object model related data.

[0019] The controller 110 is arranged to use the build data 105 to generate assistance structure data 120 comprising one or more assistance structure models 145m. and which is dependent on one or more object generation properties such as characteristics of the object models(s), other assistance structures models and/or the printing system. The assistance structure data may be experimentally derived based on experimentation with printing and curing different objects and locations within a build bed, or it may be determined using the object model size and height within the virtual build volume. For example, an assistance structure model 145m may be generated below an object model 140m within the virtual build volume 135m, with the thickness of the assistance structure model dependent on the height and/or size of the object model within the virtual build volume. Various other characteristics of the object model may be used to determine one or more assistance structure models.

[0020] In some examples, a predetermined assistance structure model corresponding to a horizontal planar member with through-holes and within the lower portion of the virtual build volume may be generated. This assistance structure model may be modified depending on object generation parameters such as the location of vacuum holes in a base plate and/or the location of object models above it in the virtual build volume. For example, the thickness of a horizontal planar member assistance structure model may be adjusted across the horizontal plane depending on the location of object models above it. The horizontal planar member assistance structure model may also comprise through holes in specific locations and of specific dimensions. The through hole locations and sizes may be generated depending on characteristics of the object models such as location within the virtual build volume, size and distance above the planar member assistance structure model. In another example, the assistance structure models may comprise longitudinally extending members such as vertically extending structures rising below, between and/or around object models. These longitudinally extending members may have solid or hollow crosssections.

[0021] The generation of corresponding assistance structures in the build volume may increase uniformity of the thermal gradient within the completed build volume or build bed as the build bed is heated during a curing phase. They may also be provided to improve the distribution of airflow generated within the build bed during the curing phase to facilitate the removal of binder agent solvent. The use of hollow-section members may be used to further control uniformity of the thermal gradient as such members do not require the application of binder agent throughout the whole structure. The assistance structures may also increase uniformity of the stiffness gradient across the build bed, which again is beneficial during the curing phase.

[0022] The controller uses the build data 105 together with the assistance structure data 120 to generate print data 122 which is forwarded to control a binder agent dispensing apparatus 125. The binder agent dispensing apparatus may comprise a thermal or piezo type printhead. The remaining powder on which no binder agent is present remains loose and does not correspond to a defined object or assistance structure. [0023] Once the build volume 135v has been completed to form a build bed, a curing process may be performed thereon. This may be performed within the 3D printer, or may be performed by a separate curing apparatus as illustrated. The curing apparatus 150 applies heat 155 and vacuum pressure 160 to the build bed in order to complete generation of the object 140g. Thermal curing of the thermal curing binder agent causes components of the binder agent to bind together, thereby solidifying powder particles together in a matrix to form the generated object 140g.

[0024] The binder agent dispensing apparatus 125 prints thermally curable binder agent according to an object model 140m of the build data 105 to generate a defined object 140d in the build volume and prints thermally curable binder agent or another print agent according to the assistance structure model 145m of the assistance structure data 120 to generate an assistance structure 145d in the build volume 135v. This leaves some loose powder between the defined object 140d and assistance structure 145d. Once completed, the build volume 135v is subject to the curing process to solidify a generated object 140g and may also generate a solidified assistance structure 145g. In an example, the assistance structure data is arranged such that the assistance structure 145d does not contact the defined object 140d which ensures that a solidified assistance structure 145g is not bound or joined with the generated object 140g. This enables simple separation of the generated object from the build bed whilst still increasing accuracy of the geometric rendering of the generated object. The solid assistance structure 145g may be discarded or recycled following completion of the curing process.

[0025] In some examples, a non-binder agent may be applied to the powder to print the assistance structures. This second agent may be water or a non-water solvent for example. In such an example, the curing process does not result in the generation of a solid assistance structure 145g comprised of cured binder agent and powder. However, an assistance structure 145d printed using such a second agent may still be used to improve the defining and curing of the object to be generated, during both the printing and the curing processes as previously described. [0026] Figure 2 shows a 3D printer according to an example and illustrates the application of thermally curable binder agent for the defined object and assistance structure in more detail. The 3D printer 200 comprises a build chamber having build chamber walls 205 and a build platform 210. The build platform 210 supports a plurality of layers of powder 235, and is movable in direction D during operation to accommodate each new layer of powder. The build chamber provides a build volume 250 which is defined by the build chamber walls and the build platform when in its lowest operational position. In this example, the build volume 250 will therefore be at or below the top of the build chamber walls 205 when the last layer of powder has been added

[0027] A layering apparatus 215 is arranged to spread a layer of powder, such as a metal powder, at the top of the build chamber walls 205, along the line 220. An agent dispensing apparatus such as a printhead 225 with a number of nozzles is arranged to selectively direct or print a thermally curable binder agent or another printing agent 230 to the top or new layer of powder material. A thermally curable binder agent is a material that, when combined with powder, causes the powder to bind together upon the application of heat. The combined thermally curable binder agent and powder or composite material defines one or more defined objects 240 within the build volume 250. Upon the application of heat in a curing process, these defined objects are solidified to generate corresponding generated objects. In some examples, additional agents may also be applied to the layers, for example using a different printhead.

[0028] The printer 200 may also comprise a controller 270 arranged to control operation of the various parts of the printer. This may include the locations of each layer to which thermally curable binder agent is to be applied in order to generate the defined objects 240 as well as any agents used to generate assistance structures 245p, 245v. Once all layers of the build volume have agent applied, the completed build bed has to be cured to finish generating the objects. Where thermally curable binder agent is used for generating the defined objects 240 and the assistance structures 245p, 245v, this may be the same type of thermally curable binder agent or different agents for the defined object and assistance structures. In some examples, non-binder agents may be used to generate the assistance structures, for example water or non-water solvents and/or surfactants.

[0029] Two types of assistance structures are illustrated. First, a horizontally extending planar member assistance structure 245p is located with a first set of layers of powder at or towards the bottom of the build volume 235. This planar member assistance structure 245p may be located in a lower portion of the build bed and located below the layers used for the defined objects. The planar member assistance structure 245p may extend fully across the XY plane or partially, for example below defined objects 240. Second, one or more longitudinally extending members 245v extend vertically in the Z-axis above the XY plane and may be located about the defined objects. However, many assistance structure configurations may be employed including for example one or more of the following: a vertically extending member having agent applied throughout the cross section or around the periphery of the member in order to generate a member having a hollow cross-section; a longitudinally extending member corresponding to a physical member having a solid or hollow crosssection oriented at a pre-determined angle to the defined object; cubes, spheres or pyramids; a planar member located below a defined object, with or without through holes.

[0030] Figure 3 illustrates a top view of a planar member assistance structure 345p which may be employed in the arrangement of Figure 2. The planar member assistance structure 345p comprises a number of voids or depressions 360 which have a thinner cross-sectional area than other parts of the planar member assistance structure 345p. The depressions 360 may also comprise through holes 365 which pass though the planar member assistance structure 345p from one side to the other. A defined object 340 is illustrated in dashed outline to indicate it at a different (higher) layer. The depressions 360 and holes 365 may be located according to defined object location and size. The through holes facilitate the air flow around formed (or forming) objects during curing.

[0031] Figure 4 illustrates a section view through the planar member assistance structure 345p of Figure 3. The section of the planar member assistance structure 435p comprises the voids or depressions 460 and through holes 465. In this example it can be seen that the defined object 440 is located above a depression 460 with though holes 465. Also illustrated is an assistance structure in the form of a vertical column 470. In this example, the vertical column 470 extends above an area of the planar member assistance structure 445p which does not correspond with a depression 460. The vertical column also extends next to the defined object 440, both above and below the defined object. The use of variations in thickness of the planar member assistance structure 445p, through holes 465 and vertical columns depends on the defined objects to be printed and are used to facilitate the object generation process for example by increasing the uniformity of heating of and/or air flow around solidifying objects. [0032] The planar member assistance structure 345p, 445p may add stiffness to at least a portion of the build bed and/or result in other changes to the build bed which increase the accuracy of generated objects. For example, the use of assistance structures may compact powder which helps prevent layers of powder above the assistance structures from moving when they are used to form portions of defined objects during the printing process. In addition, spaced rectangular depressions 360, 460 in the planar member assistance structure 345p, 445p allows for more controlled and evenly distributed air flow about the solidifying objects during the curing process. Features of the planar member assistance structure, like the spacing between depressions, size of depressions or holes 365, 465, distribution of the depressions and holes, minimum and maximum thickness of the planar member assistance structure, distance between the lowest level of defined objects 340, 440 and the planar member assistance structure 345p, 445p, and distance between the planar member assistance structure and the base of the build bed can be varied depending on the defined objects to be generated. Some other example arrangements are shown in Figures 5 and 6.

[0033] For example, in Figure 5, the thickness of the planar member assistance structure 545p varies based on the z-height of the respective centroid of each defined object 540. The centroid height from an origin or base of the planar member assistance structure 545p is illustrated at 580 and a defined object height within the build bed 535 is illustrated at 585. The planar member assistance structure also comprises a series of through holes which may be uniformly distributed as shown or may be distributed according to defined objects located above them. Tuning of the parameters of the planar member assistance structure 545p may be based on the results of curing the build bed from experimentation or from derived equations. These may be evaluated using stereovision camera systems, and through green part and sintered part metrology data.

[0034] In the example of Figure 6, the thickness of a planar member assistance structure 635 is uniform but the through holes 665 are distributed below defined objects 640 (shown hashed). Additional assistance structures in the form of vertically extending columns 670 are printed about the defined objects 640. As shown, the columns 670b, 670a, 670s may be located beneath (670b), above (670a) and beside (670s) the defined objects 640. The use of these assistance structures may provide improved curing performance as previously described.

[0035] A higher density of columns 670 may be employed for some defined objects, such as those having overhangs (middle and far right objects) and/or for defined objects using these for additional support around fine features (far right defined object). In some examples, a planar member assistance structure may be absent or extend across part of the build bed. In some examples, the planar member assistance structure may extend partially vertically as well as horizontally. In some examples the columns may extend partly horizontally, have triangular or other sectional shapes and may be solid, hollow or partially hollow. Apart from planar and longitudinally extending columns, other shapes of assistance structures may be employed such as cubes and spheres.

[0036] Figure 7 illustrates a method of determining assistance structure data for generating assistance structures together with objects in a 3D printing system and according to an example. The method 700 may be implemented in the controller 110 of Figure 1 or the control module of Figure 2, and may be used to generate assistance structures such as those illustrated in Figures 3-6 as well as many others. [0037] At 710, the method receives build data to generate an object in a build volume of the 3D printing system. The build data may comprise an object model having characteristics corresponding to a defined or generated object such as size, shape, type, orientation, location within the build volume. The build data may be processed to derive instructions to apply binder agent layer-by-layer to powder within the build volume of the 3D printing system in order to generate a corresponding object.

[0038] At 720, the method determines a geometry and spatial arrangement of the object model within a virtual build volume. This may include size, shape and other properties of the object model as well as a location and orientation within the virtual build volume which is a digital analog of a build volume to be used to generate an object using the object model. The object model represents an object to be generated within a build volume of a powder-based additive manufacturing system using a thermally curable binder agent.

[0039] At 730, the method generates an assistance structure model within the virtual build volume which represents an assistance structure to be generated within the build volume to assist during a printing process when the object to be generated is defined using the thermally curable binder agent and to assist during a curing process when the thermally curable binder agent is cured to generate the object. The assistance structure model has a geometry and a spatial arrangement within the build volume that is dependent on the geometry and spatial arrangement of the object model within the virtual building model. The assistance structure may be generated using thermally curable binder agent or a different agent used to define the object

[0040] The assistance structure model may also be dependent on other object generating properties such as characteristics or properties of more than one object model and/or any other assistance structure models, including for example location and size as well as properties of the printing process such as locations and/or sizes of vacuum holes in a base plate in a curing apparatus. The curing apparatus may be provided in the printer, for example in the agent dispensing area with the implementation of additional functions including applying heat and/or vacuum pressure. In another example, the curing apparatus may be separate from the agent applying part of a printer.

[0041] In one example, as previously described, the assistance structure model may comprise a planar member a lower portion of the virtual build volume. The thickness of the assistance structure model and the presence of features such as through holes or depressions may be dependent on the location and/or size of objects models above. Longitudinally extending assistance structure models may be located between, above or below object models depending on characteristics such as having an overhang or fine features, z-height and/or the presence of a plane member assistance structure. Predetermined or standard assistance structures may be used, with object models located about these. In other examples, assistance structure models may be located between objects in order to increase some property of the build bed such as the ratio of composite material to loose powder or to increase stiffness uniformity.

[0042] Object generation properties of the object model or assistance structure may include one or more of the following: size; location within the virtual build volume; centroid; height of centroid; center of mass; height of center of mass; geometry; composition of the thermally curable binder agent to be used for generating the object and assistance structure; composition of the powder to be used. Object generation properties of a 3D printer system may include one or more of the following: the heat applied during curing and the air flow applied during curing; location and/or size of vacuum holes in a base plate through which the air flow is applied.

[0043] At 740, a printing process is performed by the method where it applies thermally curable binder agent to powder in the build volume using the object model and the assistance structure model. This may be implemented by a different processor to that used for 710, 720, 730 or the same processor may be employed for example in a 3D printer which pre-processes received build data before applying the thermally curable binder agent. The thermally curable binder agent is applied layer-by-layer so that one layer of powder is formed, thermally curable binder agent is applied for that layer to areas and according to the object model, and a new layer is then formed and the process repeated. In this way the printing process defines objects as well as generating assistance structures in the build volume.

[0044] At 750, a curing process is performed by the method which cures the powder in the completed build volume or build bed generate one or more objects. One or more solid assistance structures may also be generated where thermally curable binder agent is used to generate these in the build volume. The curing process includes the application of heat. Pressure (e.g. vacuum pressure) and pressure differentials may subsequently be applied to the build bed to help remove binder agent solvents. These applications promote desired chemical and physical reactions such as polymerization and evaporation.

[0045] In some examples, the use of the assistance structures facilitates air flow through the build volume thereby facilitating removal of solvents. The assistance structures may also increase the uniformity of heating during the curing process.

[0046] In some examples, the use of assistance structures reduces powder disturbance in the build volume by the application of thermally curable binder agent. This in turn increases the accuracy of generated objects.

[0047] Support for challenging object geometries and layouts may also be provided.

[0048] In some examples, the use of assistance structures increases the stiffness of the build volume or build bed.

[0049] In some examples, assistance structures may be used to change the distribution of powder and curing temperature to achieve effects other than increased rendering accuracy.

[0050] The example methods described above may be performed partly by a computing device, such as that shown in Figure 8. For example, the controller 110 of Figure 1 or the control module 270 of Figure 2 comprise a computing device of the type shown in Figure 8. The computing device 800 of Figure 8 comprises a processor 810, a non-transitory storage medium 820, and an input/output interface 830. The processor 810 is responsible for controlling the operation of the computing device 800 and executes an instruction set 840 stored in the storage medium 820. When executed by the processor 810, the instruction set 840 causes the computing device 800 to perform part of the example methods described above.

[0051] The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with any features of any other of the examples, or any combination of any other of the examples.

Claims

CLAIMS What is claimed is:

1 . A method comprising: determining a geometry and a spatial arrangement of an object model within a virtual build volume, the object model representing an object to be generated within a build volume of a powder-based additive manufacturing system using a thermally curable binder agent; generating an assistance structure model within the virtual build volume, the assistance structure model representing an assistance structure to be generated within the build volume to assist during a printing process when the object to be generated is defined using the thermally curable binder agent and to assist during a curing process when the thermally curable binder agent is cured to generate the object; the assistance structure model having a geometry and spatial arrangement within the virtual build volume that is dependent on the geometry and spatial arrangement of the object model within the virtual build volume.

2. The method of claim 1 , wherein the assistance structure to assist during the printing process to stabilize powder within the build volume of the powderbased additive manufacturing system.

3. The method of claim 1 , wherein the assistance structure to assist during the curing process to modify an airflow.

4. The method of claim 1 , wherein determining the geometry and spatial arrangement of the object model within the virtual build volume comprises determining one or more of the following: a centroid of the object model within the virtual build volume; a height of a centroid of the object model within the virtual build volume; a center of mass of the object model; a height of a center of mass of the object model within the virtual build volume.

5. The method of claim 1 , comprising determining the geometry and spatial arrangement of a second object model within the virtual build volume; and the geometry and spatial arrangement of the assistance structure within the virtual build model is dependent on the geometry and spatial arrangement of the second object model within the virtual build volume.

6. The method of claim 1 , wherein the assistance structure comprises one or more of the following: a planar member; a planar member comprising a number of holes therethrough; a longitudinally extending member having a solid or hollow cross-section.

7. The method of claim 1 , wherein the assistance structure model is spaced apart from the object model within the virtual build volume.

8. The method of claim 1 , comprising determining an object generating property associated with generating the object, and using the object generating property to generate the assistance parameter.

9. The method of claim 8, wherein the object generating property comprises a property of one or more of the following: a type of powder to be used to generate the object; a type of thermally curable binder agent to be used to generate the object; a type of thermally curable binder agent to be used to generate the assistance structure; a non-binder agent to be used to generate the assistance structure; a curing heat to be used to generate the object; an airflow to be used to generate the object.

10. The method of claim 1 , comprising generating the object in a build volume using the virtual build volume by: applying an agent layer-by-layer to powder in the build volume accordance with the object model and the assistance structure model to generate a build bed.

11 . The method of claim 10, comprising applying the thermally curable binder agent in accordance with the object model and applying one of the thermally curable binder agent or a non-binder agent in accordance with the assistance structure model.

12. The method of claim 10, comprising applying heat to the build bed to generate the object.

13. An apparatus comprising: a memory and a processor to: determine a geometry and a spatial arrangement of an object model within a virtual build volume, the object model representing an object to be generated within a build volume of a powder-based additive manufacturing system using a thermally curable binder agent; generate an assistance structure model within the virtual build model, the assistance structure model representing an assistance structure to be generated within the build volume during a printing process when the object is defined using the thermally curable binder agent and to assist during a curing process when the thermally curable binder is cured to generate the object; the assistance structure model having a geometry and spatial arrangement within the virtual build model that is dependent on the geometry and spatial arrangement of the object model within the virtual build volume.

14. The apparatus of claim 13, comprising an agent dispensing apparatus to apply an agent layer-by-layer to powder within the build volume; the processor to control the agent dispensing apparatus to: apply agent layer-by-layer to powder in accordance with the object model and the assistance structure model to generate a build bed.

15. A non-transitory computer-readable storage medium comprising a set of computer-readable instructions that, when executed by a processor, cause the processor to: determine a geometry and a spatial arrangement of an object model within a virtual build volume, the object model representing an object to be generated within a build volume of a powder-based additive manufacturing system using a thermally curable binder agent; generate an assistance structure model within the virtual build model, the assistance structure model representing an assistance structure to be generated within the build volume to assist during a printing process when the object to be generated is defined using the thermally curable binder agent and to assist during a curing process when the thermally curable binder agent is cured to generate the object; the assistance structure model having a geometry and spatial arrangement within the virtual build model that is dependent on the geometry and spatial arrangement of the object model within the virtual build volume.