BACKGROUND

[0001] In some examples, a seal is to seal part of an environment against a fluid.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Examples will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

[0003] Figure 1 is a flowchart of an example of a method;

[0004] Figure 2 is a flowchart of an example of a method;

[0005] Figures 3A-3D are schematic diagrams of an example process that may be performed according to the method of Figure 1 and 2;

[0006] Figure 4 is a simplified schematic diagram of an example machine- readable medium in association with a processor;

[0007] Figure 5 is a schematic diagram of an example seal; and

[0008] Figure 6 is a schematic diagram of an example seal.

DETAILED DESCRIPTION

[0009] Examples herein relate to designing and generating a seal according to the design. In some examples, a seal geometry may be designed considering a type of fluid to be sealed and an operating condition to which the seal is to be subjected. The operating condition may comprise an environmental condition (such as temperature or a climate or a humidity etc.) or a force to which the seal is subject during use (e.g. a static or dynamic force, a compressive or tensile force etc.). Given that the seal may be subject to different operating conditions (e.g. a particular force applied to a particular area, with other areas of the seal having no, or different, applied forces), some examples herein relate to determining a differential elastic profile of the seal along a geometry of the seal and to generating the seal having the differential elastic profile. In this way, a seal may be designed having a bespoke profile, which may comprise a complicated profile, having areas of different elastic behaviour. Some examples herein relate to methods for designing, and testing, such a seal and modifying the design of the seal depending on the testing, which in some examples comprises a simulation.

[0010] The seal may be generated in an additive manufacturing process. Additive manufacturing techniques may generate a three-dimensional object through the solidification of a build material. In some examples, the build material may be a powder-like granular material, which may for example be a plastic, ceramic or metal powder. 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 layer by layer, for example within a fabrication chamber. According to one example, a suitable build material may comprise polymeric (e.g., polyamide, polypropylene, TPU, TPA), ceramic or metallic (e.g., stainless steel) particles.

[0011] In some examples, selective solidification is achieved through directional application of energy, for example using a laser or electron beam which results in solidification of build material where the directional energy is applied. In other examples, at least one print agent may be selectively applied to the build material, and may be liquid when applied. For example, a ‘coalescence agent’ or ‘coalescing agent’ (for example, a fusing agent in examples where the build material comprises a plastics powder, or a binder agent in examples where the build material comprises a metal powder, or, in other examples, a plastics powder) may be selectively distributed onto portions of a layer of build material in a pattern derived from data representing a slice of a three-dimensional object to be generated (which may for example be generated from structural design data). The fusing agent may have a composition which absorbs energy such that, when energy (for example, heat) is applied to the layer, the plastic build material coalesces and solidifies to form a slice of the three-dimensional object in accordance with the pattern. The binder agent may have a composition that, when heated or when UV energy is applied, causes the metal particles of build material to which binder agent is applied to adhere to one another. In other examples, coalescence may be achieved in some other manner.

[0012] According to one example, a suitable fusing agent may be an ink-type formulation comprising carbon black. In one example such a fusing agent may additionally comprise an infra-red light absorber. In one example such a fusing agent may additionally comprise a near infra-red light absorber. In one example such a fusing agent may additionally comprise a visible light absorber. In one example such a fusing agent may additionally comprise a UV light absorber. Examples of print agents comprising visible light enhancers are dye based colored ink and pigment based colored ink.

[0013] As noted above, additive manufacturing systems may generate objects based on structural design data. This may involve a designer generating a three- dimensional model of 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 generate slices of 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.

[0014] As also noted above, additive manufacturing systems may generate objects through the selective solidification of a build material comprising plastic particles or metal particles (for example a stainless steel powder). This may involve depositing build material in layers on a print bed, or build platform and selectively depositing a fusing agent (in examples where the build material comprises plastic particles) or a binder agent (in examples where the build material comprises metal particles or other suitable types of material), for example using printheads to jet the agent, onto portions of a layer of build material in a pattern derived from data representing a slice of a three-dimensional object to be generated (which may, for example, be generated from structural design data). When heat is applied to a layer of build material, those portions of build material to which a thermal fusing agent has applied will heat and coalesce. When a binder agent is applied to the build material, when heat is applied to the build material (either on a layer-by-layer basis or to a set of layers as a whole, e.g. a volume of build material) this creates a binder matrix that comprises the build material.

[0015] In the example of a plastics build material, the portions of build material treated with fusing agent absorb energy (e.g. heat energy), coalesce, and solidify to form a slice of the three-dimensional object in accordance with the pattern. Following the application of energy therefore, the portions of build material to which fusing agent was applied heat up, coalesce, and then solidify upon cooling to form the three- dimensional object. Any build material to which fusing agent was not applied (un coalesced, “loose” build material, or build material remnant), e.g. those parts of the build material that will not form part of the generated object, will not solidify and remain as un-coalesced, loose, excess, build material. Following the application of energy, therefore, the three-dimensional object may therefore be embedded and/or at least partially surrounded by un-coalesced, loose, build material which will need to be separated from the object prior to any subsequent operations (e.g. a post-processing operation such as dyeing).

[0016] In the example of a metal build material (or, in one example of a plastics build material), the binder agent may comprise an adhesive element (for example a polymeric concentrate) suspended within a liquid carrier that will cause portions of build material to which binder agent was applied to coalesce during a curing process. For example, following the layer-wise deposition of the metal build material and the selective deposition of the binder agent thereon the build platform and/or the powder contain therein may undergo a curing process during which the build material (including the layers of build material with the binder agent applied and surrounding build material to which no binder agent has been applied) is subjected to energy to cure the build material (for example, using UV light or heat to layer-by-layer cure the build material or using heat to cure a volume (e.g. a set of layers) of build material). During the curing process, the binder agent, applied to portions of the build material, is thermally activated when subject to the curing temperatures, causing adhesive particles (e.g. polymeric particles) to separate from the liquid carrier and adhere to particles of the build material while the liquid carrier evaporates, leaving the portions of build material to which binder agent was applied solidifying and effectively being glued together. Postcuring, any build material to which binder agent was not applied (“loose” build material, or build material remnant), e.g. those parts of the build material that will not form part of the generated object, will not solidify and remain as generally loose, excess, build material. Curing may be performed on a plurality of layers of build material, in other words a whole volume of build material may be subject to heat to cure the whole volume of build material at substantially the same time. For the curing process, the build platform may be moved to a separate curing station comprising a curing oven or similar.

[0017] After curing, the solidified build material (those portions of the build material to which binder agent was applied and have adhered during curing due to the activation of the adhesive) may be referred to as a “green part”, being unfinished but substantially resembling the final part, and being a loosely bound part having a relatively low density. Once cured, to form the final object to be generated from the metal build material, the green part is transferred to a sintering oven in which the green part undergoes a sintering process. During sintering, the green part is exposed to elevated temperatures to sinter the build material particles (of the green part) into the final, solid, three-dimensional object (which will have a higher density than the green part).

[0018] In examples where a target environment is to be sealed, for example fluidly sealed (to avoid leakages of liquids or gases or build material) or acoustically sealed (to restrict or impede the transmission of sound), or thermally sealed, etc. seals may be manufactured from elastomers and formed by an injection moulding process or an extruded elastomer process. Although, in these processes, it may be possible to design and form different shapes, the available shapes are usually non-complex (e.g. having substantially linear profiles) since they are formed from moulds and therefore the design of a seal having a bespoke profile to seal a complex geometry may be difficult, or even not possible, via injection moulding (by complex geometry it is meant to comprise complicated seal profiles such as having 360-degree closure or having undercuts in different axes, etc.). If the seal is to have a more complex profile, e.g. having a 360-degree closure (or a loop), then these parts of the seal may be formed by cutting and then gluing or welding moulded seal segments together to form the final seal. However, in these examples the resulting seal may comprise welding points or parting lines (the juncture between two seal portions that have been joined together). Such welding points or parting lines can reduce the life of the seal as they can present localised points of structural weakness or can even lead to unexpected leakages.

[0019] Some examples herein relate to generating a seal using an additive manufacturing process, meaning that seals having bespoke, and potentially complicated, geometrical profiles, such as including bends, twists, loops, etc. may be made, including profiles that may not be considered possible to manufacture through injection moulding or extrusion, and such profiles may be produced without any welding points or parting lines that could damage the sealings and/or generate leakages. Moreover, some examples herein relate to a three-dimensional seal having a differential elastic profile, or elastic behaviour, or elasticity, or hardness along the geometry of the seal. Example ways of producing such a differential elastic profile will be discussed below but, according to some examples herein, a seal may be generated having different portions of a different parameter value, the parameter being a measure of elastic behaviour, such that a single, one-piece, seal can have different properties along its geometry. In turn, this can mean that the seal responds differently to forces depending on where the forces are applied. For example, the seal may comprise different resonance, or vibration, frequencies along its geometry, or different hardnesses, or a different response to an applied force (e.g. a different compressive or tensile strength). The seal may also have different vibration transmission frequencies, or attenuation properties, along its geometry such that different parts of the seal can have different acoustic properties (e.g. acoustic transmission or isolation properties). There is therefore re-usability, a short lead time, and low costs associated with manufacturing such a seal, in addition to a great amount of design freedom allowing bespoke seals to be easily, cost-effectively, and quickly manufactured.

[0020] Figure 1 shows an example method 100 which may comprise a computer-implemented method and which may comprise a method of generating a representation of a seal.

[0021] At block 102 the method comprises operating, e.g. by a processor, on data describing an area of an environment to be sealed against a fluid, or a fluid type such as a first fluid type. Hereinafter, the terms “fluid”, “fluid type”, and “first fluid type” should be regarded as interchangeable. At block 104 the method comprises operating, e.g. by a processor, on data describing an operating condition to which the seal is to be subjected. At block 106, the method comprises determining, e.g. by a processor, based on the operating condition, a differential elastic profile of the seal. At block 108 the method comprises generating, e.g. by a processor, a representation of a seal to seal a representation of the area to be sealed against the first fluid type. The environment to be sealed, in one example, may comprise a pen pocket of an additive manufacturing apparatus and the fluid type to be sealed may comprise a build material such as a powder, e.g. a plastics or metal build material.

[0022] The elastic profile may comprise a parameter that comprises a measure of elastic behaviour and/or elasticity and/or compressive strength and/or resilience and/or density and/or tensile strength and/or an ability to withstand, or react to, an applied force and/or an ability to recover its original shape after a force causing deformation has been removed and/or an acoustic property, such as acoustic transmission and/or acoustic isolation and/or attenuation and/or impedance and/or absorption and/or resistance and/or hardness and/or softness and/or brittleness and/or rigidity and/or ductility and/or stiffness and/or flexibility and/or firmness and/or an elastic modulus. The parameter may comprise a “compression set” by which it is meant to comprise a material’s capacity, or ability to recover its original shape following the removal of an applied force causing deformation. Determining, based on the operating condition, a differential elastic profile of the seal may comprise determining a value of one of the parameters as discussed above. As will be discussed below, to achieve a particular elastic behaviour, the seal may be made having a particular internal structure (such as a lattice or mesh structure, or a structure comprising voids absent material). In some examples, determining the elastic profile of the seal may comprise determining a seal material from which the seal is to be made. For example, the operating condition may describe a temperature of the environment (e.g. hundreds of degrees) and so a seal material may be chosen comprising metal particles (e.g. a metal build material) to confer on the seal a particular thermal behaviour (e.g. thermal expansion).

[0023] Therefore, the seal having a differential elastic profile may comprise a first portion having a first elastic profile (e.g. comprising a first value of an elastic parameter) and a second portion having a second elastic profile (e.g. comprising a second value of the elastic parameter. As stated in the preceding paragraph, the parameter may comprise a measure of elastic behaviour and/or elasticity and/or compressive strength and/or resilience and/or density and/or tensile strength and/or an ability to withstand, or react to, an applied force and/or an ability to recover its original shape after a force causing deformation has been removed and/or an acoustic property, such as acoustic transmission and/or acoustic isolation and/or attenuation and/or impedance and/or absorption and/or resistance and/or hardness and/or softness and/or brittleness and/or rigidity and/or ductility and/or stiffness and/or flexibility and/or firmness and/or an elastic modulus. In one example, the parameter comprises hardness (or a measure of hardness). Hardness may be measured according to a hardness scale such as Shore hardness or Brinell hardness and may comprise a measure of an ability to react to an applied force. Therefore, in one example, the differential elastic profile of the seal may comprise a differential hardness, e.g. a first portion having a first hardness and a second portion having a second hardness.

[0024] The operating condition may comprise an environmental condition such as a climate, for example, a thermal condition (e.g. the temperature of the environment, or a saturation condition for example, a level of wetness and/or moisture etc. and may comprise a pressure of an environment. In this way, according to the operating condition it may be determined that the environment and seal are to be operated in a hot environment and/or a pressurized environment and/or in an underwater environment etc. The operating condition may comprise a dynamic or a static condition. The operating condition may comprise a condition to which the seal is to be subject during use (or performance of the seal) and may therefore be considered to be a performance condition. The operating condition may comprise a force (e.g. a static or dynamic force), for example a force to which the seal is subject during use, such as a compressive and/or tensile and/or torque force. By ‘environment’ in environmental condition it is meant to comprise both the environment to be sealed (e.g. in the example of temperature, whether the seal is to seal an area that is at an extreme temperature, e.g. hot metal) in addition to the wider surrounding environment (e.g. whether the seal is to seal an area in room etc. that is at an extreme temperature). The operating condition may comprise any condition that affects the lifespan (or usable life) of the seal.

[0025] The first fluid type may comprise a liquid or a gas or sound (e.g. acoustic pressure waves) or a build material (e.g. a powder, for example comprising metal or plastic particles). Therefore, the seal may comprise a fluid seal (such as a fluid-tight) seal or a hermetic seal or an acoustic seal etc. In examples where the seal comprises an acoustic seal, the differential elastic profile of the seal may be formed by different structures of the seal (for example an internal or external structure or internal and/or external portions of the seal having a different profile) and may be such that acoustic pressure waves incident on a first external surface of the seal are impeded from being transmitted through the seal or attenuated etc. In other words, the seal 100 may comprise a portion having an internal structure comprising an irregular mesh (or lattice) which means that when incident soundwaves propagate through the seal they are caused to break, or collapse, thereby minimising, or eliminating, the soundwaves able to pass through the seal, which thereby functions as an acoustic isolator. In this way, a first portion of the seal may comprise a first acoustic impedance and/or resistance and/or vibration and/or absorption and a second portion of the seal may comprise a second, different, acoustic impedance and/or resistance and/or vibration and/or absorption such that the seal in this example comprises a differential acoustic property. In other examples, the seal may comprise a thermal seal such that different portions of the seal are to have different thermal properties (the operating condition in these examples comprise a thermal condition such as the temperature of the environment).

[0026] Therefore, according to the Figure 1 example, a seal may be designed taking into account conditions in which the seal is to operate in use (such as forces and/or extreme temperatures etc.) and a seal may be created having a differential elastic profile to respond to these conditions, which may mean that the elastic behaviour changes along a geometry of the seal. For instance, if the operating condition describes a particular compressive force that is to be applied onto a first area of the seal then the representation of the seal corresponding to that first area may be determined such that it has a lower hardness/greater ability to deform in response to the force such that the seal may deform around the impulse and still function as a seal. In this way, the differential elastic profile of the seal may be determined, having regard to the operating condition, such that the seal is able to properly function as a seal when it is subject to the operating condition. In other words, a seal may be designed that is rigid but when subject to a dynamic force (such as a dynamic torque) may twist away from the environment to be sealed such that fluid may leak and by determining a differential elastic profile the seal can have an improved reaction to such a force such that the seal doesn’t produce any leaks. For example, the effects of static and dynamic forces may be different such that, in response to a dynamic force, the seal profile may be determined such that it has a lower hardness, in order to be able to adapt its shape quicker, to the dynamic force in the portion of the seal that is to be subject to the force. In one example, the seal designed according to the method 100, or any other method described herein, or any of the other seals described herein, may comprise a gasket.

[0027] As will be discussed below, generating the representation of the seal may comprise generating a set of mesh points defining a portion of the seal such that the representation may be generated using finite-element analysis. Portions of the seal that are to have different elastic profiles may, in some examples, be formed at the level of the seal mesh (e.g. individual mesh points may be removed to create differing elastic behaviours), creating portions having different internal or external structures. Determining the elastic profile of the seal (e.g. block 106) may comprise determining a seal geometry such that the seal representation seals the environment to be sealed, e.g. such that there are no gaps between the seal representation and the representation of the area of the environment to be sealed. The term “no gap” may comprise a gap but having a geometry that is less than a threshold based on a particle of the type of fluid to be sealed (e.g. the threshold may be based on an average particle diameter and may be substantially equal to the average particle diameter). In this way, a gap that is small enough such that no fluid can pass through the gap may also be considered to be the absence of a gap.

[0028] Figure 2 shows an example method 200 which may comprise a computer-implemented method and which may comprise a method of generating a representation of a seal. The method 200 may comprise a method of simulating a seal and/or simulating the performance of a seal. The method 200 may comprise the method 100.

[0029] Figure 2 relates to a method whereby the quality of a generated seal may be tested and, in some examples, refined by generating a seal representation and then modifying the seal representation. According to the Figure 2 example, the seal may be determined by generating a seal representation and then simulating its performance, e.g. in a virtual environment, when subject to the operating condition. For example, the virtual environment may simulate an environment at a temperature, or moisture etc. as described by the operating condition and as described above, or may simulate a type of force being applied to the seal representation during use, the force being described by the operating condition as described above. During, or after, the simulation it may be determined whether the seal has properly, or adequately, functioned as a seal, in other words, whether it properly sealed the environment against the first fluid type/whether it a perfect seal. This may be determined by determining if a gap existed during, or after, the simulation between the seal representation and the representation of the area of the environment to be sealed that was big enough to prevent the passage of a fluid of the first type. Determining the gap may comprise comparing the distance between a part of the seal representation and a part of the representation of the area of the environment and determining whether this distance is greater than (or less than) a threshold (e.g. a predetermined threshold) that is based on the diameter of a particle of the fluid type to be sealed.

[0030] At blocks 202 and 204 of the method 200, the method respectively comprises operating, e.g. by a processor, on data describing an area of an environment to be sealed against a first fluid type and operating, e.g. by a processor, on data describing an operating condition to which the seal is to be subjected, for example as described above with respect to blocks 102 and 104 of the method 100.

[0031] At block 206, the method comprises generating a first representation of a seal to seal a representation of an environment to be sealed against a first fluid type and, at block 210, the method comprises simulating the response of the representation of the seal when sealing against the representation of the environment to the first fluid type when the environment is subject to the operating condition. At block 212, the method comprises determining whether, during or after the simulation, a gap exists between the representation of the seal and the representation of the environment that can allow passage therethrough of a fluid of the first fluid type. If it is determined that a gap exists then, at block 214, the method comprises generating a modified representation of the seal, where the seal according to the modified representation comprises a different seal profile than the seal according to the first representation in a portion of the representation of the seal proximate the gap. The modified representation of the seal may comprise the representation of the seal generated at block 108 of the method 100 or the first representation of the seal (generated at block 206 of the method 200) may comprise the representation of the seal generated at block 108 of the method 100.

[0032] Therefore, blocks 210-214 of the method 200 represent a test as to the quality of the seal according to the first representation when it is subject to the operating condition. As stated above, these blocks may comprise subjecting the seal representation to an environmental condition (such as a thermal condition) described by the operating condition or to a static or dynamic force as described by the operating condition and, therefore, at block 212 it may be determined if, at any point during the simulation, or after the simulation, a gap existed meaning that the seal according to the first representation could not adequately function as a seal in use. If so, at block 214 the first representation of the seal is modified.

[0033] Generating the modified representation at block 214 may, in some examples, comprise modifying the first representation (generated at block 206) and may comprise changing any parameter that affects the elastic profile. For example, the seal according to the first representation may comprise a uniform elastic profile and the seal according to the modified representation may comprise a differential elastic profile. In one example, the seal according to the first representation comprises a first differential elastic profile and the seal according to the modified representation may comprise a second differential elastic profile, the second being different to the first. In this latter example, according to the first differential elastic profile the seal representation may comprise a portion having a first value of an elastic parameter (e.g. a first material, compressive strength, hardness etc. as described above). Then, generating the modified representation may comprise modifying the portion such that the elastic parameter takes a different value, or such that a different elastic parameter takes a different value or modifying the seal representation such that a different portion of the seal representation has a different elastic parameter value. In this way, any part of the seal representation may be modified to improve the performance of the seal representation.

[0034] As indicated at blocks 216 and 218, determining whether a gap exists may comprise comparing, at block 216, the distance between boundary portions of the representation of the seal and the representation of the environment is less than a threshold that is based on the diameter of a particle of the first fluid type, and if it is determined, at block 218, that the gap is not less than the threshold, it may be determined, at block 212, that the gap exists. [0035] For example, the threshold may comprise a predetermined threshold. The predetermined threshold may be based on an average particle diameter of a fluid of the first fluid type. In some examples, the predetermined threshold may be substantially equal to or equal to the average diameter of a particle of a fluid of the first fluid type. In this way, it is tested whether the seal representation forms a tight enough seal during or after the simulation such that average particles of the first fluid type are not permitted to pass through. The distance between boundary portions of the seal representation and representation of the environment may be compared since the seal and environment will be in contact at their boundaries.

[0036] In some examples, the representation of the seal and/or environment may be generated using finite element analysis whereby the seal and/or environment are represented by a set of finite elements. The finite elements may comprise mesh points and may be triangular in shape, although other shapes may be used. In one example, the representation of the environment comprises a first set of mesh points defining the environment to be sealed and, as indicated by block 208, generating, at block 206, the first representation of the seal may comprise generating a second set of mesh points defining a portion of the representation of the seal, wherein a boundary subset of the second set of mesh points defines a boundary of the representation of the seal corresponding to a boundary of the seal, the boundary being a region of the seal that is to seal against the environment to be sealed, wherein the seal is generated such that the distance between opposing portions of representation of the environment to be sealed as defined by the first set of mesh points and the boundary of the representation of the seal as defined by the boundary subset of the second set of mesh points is less than a threshold that is based on the diameter of a particle of the first fluid type.

[0037] In these examples, determining, at block 212, whether a gap exists may comprise comparing the distance between opposing portions of the representation of the environment to be sealed as defined by the first set of mesh points and the boundary of the representation of the seal as defined by the boundary subset of the second set of mesh points to the threshold based on the diameter of a particle of the first fluid type and, if it is determined that the distance between opposing portions of the representation of the environment to be sealed as defined by the first set of mesh points and the boundary of the representation of the seal as defined by the boundary subset of the second set of mesh points is greater than the threshold based on the diameter of a particle of the first fluid type at any given opposing portion of the representation of the environment to be sealed and an opposing portion of the boundary of the representation of the seal, then it is determined that a gap exists between the representation of the seal and the representation of the environment.

[0038] As indicated by blocks 228, 220 and 230, generating, at block 214, the modified representation of the seal may comprise determining, block 228, whether the hardness of a portion of the first representation of the seal proximate the gap is below a predetermined threshold. If it is determined that the hardness of a portion of the first representation of the seal proximate the gap is not below the predetermined threshold then the method comprises, at block 214, generating the modified representation of the seal, wherein the portion of the representation of the seal proximate the gap according to the modified representation has a lower hardness than the portion of the representation of the seal proximate the gap according to the first representation of the seal. If it is determined that the hardness of a portion of the first representation of the seal proximate the gap is below the predetermined threshold then the method comprises, at block 230, generating the modified representation of the seal, wherein the portion of the representation of the seal proximate the gap according to the modified representation has a greater volume of seal material than the portion of the first representation of the seal proximate the gap.

[0039] In some examples, if it is determined, at block 228, that the hardness of a portion of the first representation of the seal proximate the gap is not below the predetermined threshold then generating the modified representation of the seal comprises, at block 220, reducing the amount of seal material in the first portion of the first representation seal to thereby lower the hardness of the first portion of the representation of the seal.

[0040] In these examples, the predetermined threshold may comprise a measure of the minimum hardness of the seal and, if it is determined that the seal is not below that threshold, e.g. not below the minimum, then the amount of seal material may be reduced. This may increase the number of voids (a void being a part of the seal absent seal material) in the representation and will therefore change the internal structure of the seal, for example by increasing the number of voids in an internal lattice or mesh structure of the seal. Doing so may decrease the hardness of the seal, moving the hardness closer toward the minimum threshold. On the other hand, if it is determined that the seal is below the threshold then reducing the seal volume any further (to reduce the hardness) could compromise the integrity of the seal and so, in these examples, a greater amount of seal volume may be added to the seal, for example by adding finite elements (e.g. mesh points) to increase the volume of the seal representation to change its hardness in that way. In summary, in the example shown in blocks 228, 230, and 220, if it is determined that the hardness of the seal may be decreased or reduced without compromising the seal integrity then this may be done and, if not, additional seal material may be added to the seal representation. Decreasing the seal volume to change the internal seal structure, or external seal profile, to include more voids may cause the seal to be more reactive to applied force, e.g. increase the seal’s ability to deform around an object applying the force, or change its shape etc.

[0041] Although hardness is depicted in blocks 228, 230 and 220, in other examples a different parameter indicative of elastic behaviour may be used.

[0042] In some examples, reducing the seal volume (at block 220) comprises removing portions of the seal representation to which no force was subject during the simulation. For example, if during the simulation individual (e.g. internal) finite elements (e.g. mesh points) then a subset of these portions may be removed to thereby reduce the portion of the seal to which the force according to the operating condition was applied. In some examples, portions of the seal which reacted to the forces at a level less than surrounding portions may be removed. For example, a predetermined threshold level of reaction to an applied force may be established and a subset of those portions of the seal representation whose reaction to the applied force is less than the predetermined threshold may be removed. As indicated by the looping arrow 226, blocks 210-214 (including, in some examples, blocks 208, 216, 218, 228, 220, and 230) may be repeated for the modified representation and the quality of the seal according to the modified representation may be tested. If the modified representation still results in a gap then the modified representation may be further modified (e.g. in the manner described in blocks 228, 230, and 220) to produce a further modified representation. Put another way, once the modified representation, at block 214, is generated and the method proceeds back to block 210 as indicated by the looping arrow 226, block 210 comprises simulating the response of the representation of the seal according to the modified representation when sealing against the representation of the environment to the first fluid type when the environment is subject to the operating condition, and block 212 comprises determining whether, during or after the simulation, a gap exists between the modified representation of the seal and the representation of the environment that can allow passage therethrough of a fluid of the first fluid type. Then, if, at block 212, it is determined that a gap exists, then the method further comprises generating, at block 214, a further modified representation of the seal, where the seal according to the further modified representation comprises a different seal profile than the modified representation of the seal in a portion proximate the gap.

[0043] Blocks 210-214 may be repeated until, at block 212, it is determined that no gap exists. For example, determining that the gap exists between the first representation may comprise determining that a gap of a first size exists that is larger than an average diameter of a particle of the first fluid type. If, following the generation of the modified representation there exists a gap of a second size, smaller than the first size, but still larger than the average diameter of the particle, then blocks 210-214 may be repeated to generate a further modified representation. If a gap remains between the further modified representation and the environment, then blocks 210-214 may be repeated yet again and, at the repetition of block 214, modify the further modified representation. The repetition may continue until it is determined that no gaps exist between the generated representation at block 214 and the environment.

[0044] Once no gap exists the method proceeds to blocks 222 and 224. At block 222, the method comprises determining object model data describing the seal according to the generated representation, at block 214, (which may comprise the first representation or a modified representation, or even a further modified representation etc. depending on the outcome of the simulation) and, at block 224, the method comprises generating, in an additive manufacturing process, the seal according to the object model data. The object model data, determined at block 222, may comprise data representing at least a portion of the seal to be generated by an additive manufacturing apparatus by fusing, or binding, a plastics or metal build material. The object model data may for example comprise a Computer Aided Design (CAD) model, and/or may for example comprise a STereoLithographic (STL) data file, and/or may be derived therefrom. In some examples, the data may be received over a network, or received from a local memory or the like. In some examples, the data may define the shape of the part of an object, i.e. its geometry. In some examples the data may define the seal’s elastic profile and/or behaviour, e.g. at least one mechanical property, for example strength, density, resilience or the like and as described above. Generating the seal, at block 224, may comprise forming a layer of build material, applying print agents, such as fusing agent or binder agent, in locations specified in the object generation instructions for an object model slice corresponding to that layer, and applying energy, for example heat, to the layer. Some techniques allow for accurate placement of print agent on a build material, for example by using print heads operated according to inkjet principles of two-dimensional printing to apply print agents, which in some examples may be controlled to apply print agents with a resolution of around 600dpi, or 1200dpi. A further layer of build material may then be formed and the process repeated, with the object generation instructions for the next slice.

[0045] According to the Figure 2 example, the seal may be generated in an additive manufacturing process but, in other examples, the seal may be generated by processes other than additive manufacturing.

[0046] Figures 3A-3D show one example of a process that may be performed according to the method 200. Figure 3A shows a representation 300, e.g. a virtual representation, of an area of an environment to be sealed. More specifically, the area 300 of the environment is to be sealed to seal off the passage 301 through the area 300. For example, the area may comprise an end of a pipe and the representation 300 may be generated accordingly, the passage 301 representing, in this example, the pipe interior. In this example the representation of the area is formed as a plurality of finite elements, indicated in this example as a triangular mesh. The area of the environment to be sealed and/or the seal itself may be subject to an operating condition describing a torque force that the seal is to be subjected in use. In Figure 3B a first representation 302 of the seal is generated to seal the representation 300 of the area of the environment. In Figure 3C the performance of the representation 302 is simulated when it is subject to the operating condition. More specifically, the response of the representation 302 of the seal may be simulated in Figure 3C when the seal representation 302 seals the representation 300 of the environment, during or after a simulation when the environment representation 302 is subject to the torque force. In this example, a gap 303 is present between the first representation 302 and the representation 300 such that, a passage through one the seal representation 302 from one side to another is possible for a fluid of a first fluid type to be sealed. In this example, Figure 3D shows a modified representation 304 that is generated having a modified internal structure in an area 305 proximate the gap. In this case, the representation of the seal has been modified to remove seal material in the representation, thereby creating a number of voids 307. In this way, the internal structure of the representation is modified, the internal structure comprising a lattice, or mesh, structure. According to the modified representation, the density and/or volume of the seal material may be different (e.g. reduced), for example to lower the elastic behaviour (such as hardness) of the seal representation. In this example the modified seal 304, having its lower hardness, may when subject to the simulation, exhibit no gaps and so a seal may be generated (e.g. in an additive manufacturing process) based on object model data describing the seal according to the modified representation. In this way, the seal representation may comprise a reduced hardness in those areas that experience greater forces, so that the seal may deform and/or adapt to the applied force, while in other areas the seal may comprise a higher hardness.

[0047] Figure 4 shows an example non-transitory and machine-readable medium (which may comprise a computer-readable medium) 400 associated with a processor 402. The medium 400 comprising a set of instructions 404 stored thereon which, when executed by a processor 402, may the cause the processor 402 to perform the method 100 or 200 as described above (e.g. any one or combination of the blocks thereof). For example, the instructions 404 are to cause the processor 402 to operate on environment data describing an area of an environment to be sealed against a first fluid type (e.g. to perform block 102 of the method 100), operate on operating data describing a condition to which the seal is to be subjected (block 104), determine, based on the operating data, a differential elastic behaviour of the seal along a geometry of the seal (block 106), and generate a representation of a seal to seal a representation of the area to be sealed against the first fluid type (block 108).

[0048] The representation of the seal may comprise a modified representation, and the instructions 404 that are to cause the processor 402 to determine a differential elastic profile of the seal may be to cause the processor to generate a first representation of a seal to seal a representation of an environment to be sealed against a first fluid type (see block 206 of the method 200), simulate the response of the representation of the seal when sealing against the representation of the environment to the first fluid type when the environment is subject to the operating condition (block 210), determine (block 212) whether, during or after the simulation, a gap exists between the representation of the seal and the representation of the environment that can allow passage therethrough of a fluid of the first fluid type and, if it is determined that a gap exists, then the instructions to generate the representation of the seal comprise instructions 404 that are to cause the processor 402 to generate (block 214) the modified representation of the seal, where the seal according to the modified representation comprises a different seal profile than the seal according to the first representation in a portion of the representation of the seal proximate the gap.

[0049] The instructions 404 that are to cause the processor 402 to generate the modified representation of the seal may be to cause the processor to determine (block 228) whether the hardness of a portion of the first representation of the seal proximate the gap is below a predetermined threshold. If it is determined that the hardness of a portion of the first representation of the seal proximate the gap is not below the predetermined threshold then the instructions 404 may be to cause the processor 402 to generate the modified representation of the seal, wherein the portion of the representation of the seal proximate the gap according to the modified representation has a lower hardness than the portion of the representation of the seal proximate the gap according to the first representation of the seal, for example by causing the processor 402 to reduce the amount of seal material in the first portion of the first representation seal to thereby lower the hardness of the first portion of the representation of the seal (e.g. block 220). If it is determined that the hardness of a portion of the first representation of the seal proximate the gap is below the predetermined threshold then the instructions 404 may be to cause the processor 402 to generate the modified representation of the seal, wherein the portion of the representation of the seal proximate the gap according to the modified representation has a greater volume of seal material than the portion of the first representation of the seal proximate the gap (e.g. block 230). In other examples, the parameter may be an elastic parameter other than hardness.

[0050] The instructions 404, when executed by the processor 402, may be to cause the processor 402 to simulate the response of the representation of the seal according to the modified representation when sealing against the representation of the environment to the first fluid type when the environment is subject to the operating condition, determine whether, during or after the simulation, a gap exists between the modified representation of the seal and the representation of the environment that can allow passage therethrough of a fluid of the first fluid type, and if it is determined that a gap exists, then the instructions may be to cause the processor to generate a further modified representation of the seal, where the seal according to the further modified representation comprises a different seal profile than the modified representation of the seal in a portion proximate the gap (see the looping arrow 226 indicating the repetition of blocks 210-214).

[0051] In one example, the representation of the environment comprises a first set of mesh points defining the environment to be sealed. In this example, the instructions that are to cause the processor to generate the first representation of the seal are to cause the processor to generate a second set of mesh points defining a portion of the representation of the seal, wherein a boundary subset of the second set of mesh points defines a boundary of the representation of the seal corresponding to a boundary of the seal, the boundary being a region of the seal that is to seal against the environment to be sealed (see block 208), wherein the seal is generated such that the distance between opposing portions of representation of the environment to be sealed as defined by the first set of mesh points and the boundary of the representation of the seal as defined by the boundary subset of the second set of mesh points is less than a threshold that is based on the diameter of a particle of the first fluid type, and wherein the instructions that are to cause the processor to determine whether a gap exists comprises instructions that are to compare the distance between opposing portions of the representation of the environment to be sealed as defined by the first set of mesh points and the boundary of the representation of the seal as defined by the boundary subset of the second set of mesh points to the threshold based on the diameter of a particle of the first fluid type (see block 216) and if it is determined that the distance between opposing portions of the representation of the environment to be sealed as defined by the first set of mesh points and the boundary of the representation of the seal as defined by the boundary subset of the second set of mesh points is greater than the threshold based on the diameter of a particle of the first fluid type at any given opposing portion of the representation of the environment to be sealed (block 218) and an opposing portion of the boundary of the representation of the seal, then it is determined that a gap exists between the representation of the seal and the representation of the environment.

[0052] Figures 5 and 6 show example seals 500 and 600, each of which comprise a three-dimensional printed seal. Each seal 500, 600 comprises a first portion 501 , 601 of a layer of fused build material having a first elastic behavior and a second portion 502, 602 of a layer of fused build material having a second elastic behavior. The first and second portions 501 , 502, 601 , 602 of the layers are schematically indicated in exploded view. The first and second elastic behaviors are different such that the three-dimensional printed seal 500, 600 has a differential elastic profile, as is schematically indicated by the different shading in the exploded views of Figures 5 and 6. The seals 500 ad 600 therefore comprises asymmetric elastic properties, or asymmetric elastic behaviour. The internal structure of the seal 600 is shown more schematically in Figure 6. [0053] Each one of the first portions 501 , 502 may comprise a portion of a first layer of build material and each second portion 502, 602 many comprise a portion of a second layer of build material, the first and second layers being different, or the first and second portions 501, 502, 601 , 602 may each comprise portions of the same layer of build material. The build material, fused to generate the portions of the layers, may comprise the same build material (or type of build material) such that the seals 500 600 comprise a substantially identical material composition along its geometry. The first portion 501 , 601 and/or the second portion 502, 602 may each comprise a portion of the internal volume of the seal 500 and/or a portion of an external surface of the seal.

[0054] Each of the seals 500, 600 may have been generated as part of an additive manufacturing process comprising operating on (e.g. determining or receiving) object model data describing the seal and operating on object generation instructions to generate the seal based on object model data, as will be described with reference to later figures, where the layers of build material may correspond to a slice as defined by the object model data. One or each of the first and second portions may be formed by fusing a layer of a build material using a fusing agent, or binder agent, and each portion may comprise fused build material and a fusing, or binder, agent remnant following evaporation from a solvent from an applied fusing or binder agent. One or each of the first and second portions may also comprise voids, being a portion of the seal absent any (fused) building material (the voids having the same or a different size), as will be explained below.

[0055] Although not depicted in the figures, the seal may comprise a tortuous section, or a section with complex geometry, the seal nevertheless comprising a smooth outer profile, indicating how additive manufacturing can produce a seal having a complex geometry without weld points or parting lines resulting from piecing together seal segments, since the seal may be formed as one single piece. The seal therefore may therefore comprise a continuous (or smooth) external geometrical profile.

[0056] The first portion 501 , 601 comprises a first elastic profile and the second portion 502, 602 comprises a second elastic profile. The elastic profile may comprise a parameter that comprises a measure of elastic behaviour and/or elasticity and/or compressive strength and/or resilient and/or density and/or tensile strength and/or an ability to withstand, or react to, an applied force and/or an ability to recover its original shape after a force causing deformation has been removed and/or an acoustic property, such as acoustic transmission and/or acoustic isolation and/or attenuation and/or impedance and/or absorption and/or resistance and/or hardness and/or softness and/or brittleness and/or rigidity and/or ductility and/or stiffness and/or flexibility and/or firmness and/or an elastic modulus. The parameter may comprise a “compression set” by which it is meant to comprise a material’s capacity, or ability to recover its original shape following the removal of an applied force causing deformation. The two portions 501 , 502, 601 , 602 of the seal 500 or 600 may therefore comprise different elasticity and/or compressive strengths and/or tensile strengths and/or resiliences and/or densities and/or abilities to withstand, or react to, an applied force and/or abilities to recover their original shape after a force causing deformation has been removed and/or an acoustic property, such as acoustic transmission and/or acoustic isolation and/or attenuation and/or impedance and/or absorption and/or resistance and/or hardness and/or softness and/or brittleness and/or rigidity and/or ductility and/or stiffness and/or flexibility and/or firmness and/or an elastic modulus. In one example, the parameter comprises hardness (or a measure of hardness). Hardness may be measured according to a hardness scale such as Shore hardness or Brinell hardness and may comprise a measure of an ability to react to an applied force. Therefore, in one example, the differential elastic profile of the seal may comprise a differential hardness, e.g. a first portion having a first hardness and a second portion having a second hardness.

[0057] The first portions 501 , 601 may comprise a different volume of build material than the second portions 502, 602 which may be characterised by each portion comprising a different density, volume of build material or a different number of voids, or holes, producing different elastic behaviour. Nevertheless, the first and second portions may comprise substantially equal geometries (e.g. external geometries), for example substantially equal lengths and/or widths and/or depths. Both the first and second portions 501, 502, 601 , 602 comprise portions of fused build material and voids absent fused material and may comprise a different number of voids (see those elements designated 603 and 607 in Figure 6). The first and second portions 501, 601 , 502, 602 of the seal therefore comprise different internal structures, with the first portion comprising a first internal structure and wherein the second portion comprises a second internal structure, wherein the first and second internal structures are different. One or both internal structures may comprise a lattice structure or a mesh structure having fused build material and voids absent build material. The voids of the first portion may be of a different size to the voids of the second portion. In this way, to produce two seal portions having different elastic behaviours, one portion may have a different number of same-sized voids to the other, or one portion may have the same number of different-sized voids to the other, or one portion may have a different number of different-sized voids to the other. In any example, the size and/or number of the voids may be selected to produce a particular internal structure, such as an internal mesh or lattice, that results in the portions of the seal 500, 600 having different elastic behaviours along its geometry. One portion may therefore comprise fewer voids, or a greater number of voids, than the other. The voids of one portion may be regular and/or symmetric in structure whereas the voids of another portion may be irregular and/or asymmetric. The voids may be entirely bounded by an internal portion of the seal to define a total internal structure, or may comprise a through-hole, extending from a first exterior surface or side of the seal to a second exterior surface or side. The seal may comprise a structure having a regular mesh or lattice (e.g. see the exploded view of the portion 602 in Figure 6) and/or a structure having an irregular, mesh or lattice (e.g. see the exploded view of the portion 601 in Figure 6). Alternate terminology for the voids may comprise holes, passages, or openings etc.

[0058] In some examples, part of the first and/or second portions 501 , 502, 601 , 602 of the fused build material may comprise part of an external surface of the three- dimensional printed seal 500, 600. Therefore, in examples where the first and/or second portions comprise a void, the void may be part of the external geometry of the seal 500, 600. In other words, any part of the first and/or second portions 501 , 502, 601 , 602 may comprise part of an internal volume, or both part of an internal volume and part of an external surface.

[0059] The seal 500 or 600 may be to seal against a fluid of a first fluid type. The first fluid type may comprise a liquid or a gas or sound (e.g. acoustic pressure waves) or a build material (e.g. a powder). Therefore, the seal 500 or 600 may comprise a fluid seal (such as a fluid-tight) seal or a hermetic seal or an acoustic seal etc. In examples where the seal 500 or 600 comprises an acoustic seal, the structure of the seal 500, 600 (for example an internal or external structure) may be such that acoustic pressure waves incident on a first external surface of the seal 500, 600 are impeded from being transmitted through the seal 500, 600 or attenuated etc. In other words, the seal 500, 600 may comprise a portion having an internal structure comprising an irregular mesh (or lattice) (see for example the exploded view of portion 601) which means that when incident soundwaves propagate through the seal they are caused to break, or collapse, thereby minimising, or eliminating, the soundwaves able to pass through the seal 500, 600, which thereby functions as an acoustic isolator. In other examples, the seal 500, 600 may comprise a thermal seal such that different portions of the seal 500, 600 are to have different thermal properties, or a pressure seal. In another example the seal 500, 600 may comprise a seal to seal against vibrations such that different portions of the seal 500, 600 have different absorptive properties. The first and second portions may therefore comprise different harmonic and/or resonance properties.

[0060] In one example, seal portions may comprise a different hardness such that the seal has a differential hardness profile. In these examples, the first portion 501 , 601 of the seal 500, 600 comprises a first hardness and the second portion 502, 602 of the seal 500, 600 comprises a second hardness, the first hardness being different to the first (e.g. greater than or less than). In this way, by virtue of their different internal structures, the seals 500, 600 may comprise different hardnesses, the different hardness of the seal can mean that different areas respond differently to applied forces, in that a different hardness means a different compressive behaviour and ability to react to an applied force or recover its original shape when the force is moved etc. In this way, a portion with a lower hardness may exhibit a greater amount of elastic deformation when compared to a portion with a greater hardness, and this greater amount of elastic deformation may ensure that this portion adequately functions as a seal when it is subject to a given force during use. A representation of the seal 500 or 600 may be determined using the method 100 or 200 as described above, e.g. using the method blocks thereof, or by the processor 402 when executing the instructions 404.

[0061] 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 is not limited to disc storage, CD- ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0062] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that each flow and/or block in the flow charts and/or block diagrams, as well as combinations of the flows and/or diagrams in the flow charts and/or block diagrams can be realized by machine readable instructions. [0063] 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 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.

[0064] 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.

[0065] 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 flow(s) in the flow charts and/or block(s) in the block diagrams.

[0066] 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.

[0067] 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. [0068] 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.

[0069] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.