Patent Application
20190099942
This invention relates generally to additive manufacturing, and more particularly to methods for applying and selectively curing a binder in an additive manufacturing process.
Additive manufacturing is a process in which material is built up layer-by-layer to form a component, as opposed to conventional manufacturing in which material is machined away from a piece of stock to form a component. Additive manufacturing is also referred to by terms such as “layered manufacturing,” “rapid manufacturing,” “freeform manufacturing,”, and “3D printing”. Such terms are treated as synonyms for purposes of the present invention.
One category of prior art additive manufacturing process works by selectively binding a powder by depositing a liquid binder onto a build area in a pattern that defines the boundaries of the finished component. The binder is applied, for example, by a moving print head having a plurality of very fine nozzles. The binder is cured non-selectively, by inputting energy into the entire build area.
One problem with these types of prior art additive manufacturing processes is that they can be slow, because the binder is applied from a linear source (a print head) that is moved across a planar surface and the binder must be cured between layers. In addition, these types of prior art additive manufacturing processes tend to have relatively poor precision because the pattern is defined by the binder droplets from the print head. A faster moving print head is likely to have less precise placement of the binder. Larger volumes of binder required are likely to have larger pixel sizes. In addition, the spread of the binder (pixel size) is hard to control because it is influenced by how the binder soaks into the material.
At least one of these problems is addressed by a method of additive manufacturing in which the binder is selectively cured.
According to one aspect of the technology described herein, a method for producing a component layer-by-layer include the steps of: depositing a layer of particulate material having a first area over a build platform; applying a radiant-energy-curable binder to the layer so that a selected portion of the first area is uniformly coated with binder; selectively curing a second area of the layer smaller than the selected portion of first area, using an application of radiant energy in a specific pattern that defines the geometry of a cross-sectional layer of the component; and repeating the steps of depositing, applying, and curing for a plurality of layers until the component is complete.
According to another aspect of the technology described herein, a method for producing a component layer-by-layer includes the steps of: depositing a layer of particulate material premixed with a radiant-energy-curable binder over a build platform, the layer covering a first area; selectively curing a selected portion of the layer smaller than the first area, using an application of radiant energy in a specific pattern that defines the geometry of a cross-sectional layer of the component; and repeating the steps of depositing and curing for a plurality of layers until the component is complete.
According to another aspect of the technology described herein a method for producing a component layer-by-layer includes: depositing a layer including a particulate material, a first binder curable at a first radiant energy wavelength, and a second binder curable at a second radiant energy wavelength over a build platform, the layer covering a first area; wherein at least one of the binders of the layer is deposited so that a selected portion of the first area is uniformly coated with the at least one binder; curing the first and second binders by application of radiant energy at the first and second wavelengths, wherein at least one of the binders is selectively cured in a second area of the layer smaller than first area, using radiant energy in a specific pattern that defines the geometry of a cross-sectional layer of the component; and repeating the steps of depositing, and curing for a plurality of layers until the component is complete.
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
The table 12 is a rigid structure defining a planar worksurface 30. The worksurface 30 is coplanar with and defines a virtual workplane. In the illustrated example, it includes a build opening 32 communicating with the build chamber 16 and exposing the build platform 14 and a supply opening 34 communicating with the particulate material supply 18.
For purposes of convenient description, the plane of the worksurface 30 may be considered to be oriented parallel to an X-Y plane of the apparatus 10, and a direction perpendicular to the X-Y plane is denoted as a Z-direction (X, Y, and Z being three mutually perpendicular directions).
Means may be provided for moving the build platform 14 parallel to the Z-direction. In
The particulate material supply 18 may be any device or combination of devices which is operable to apply a layer of particulate material “P” to the worksurface and to level the particulate material P. In the example shown in
In the illustrated example, the particulate material supply 18 includes a recoater 44 which is a rigid, laterally-elongated structure that lies on the worksurface 30. It is connected to an actuator 46 (shown schematically) operable to selectively move the recoater 44 along the worksurface 30, to move particulate material P from the supply container 38 and to level it in the build chamber 16. It is noted that there are known configurations for particulate material supply in which a build chamber is not used or required; for example, the build chamber may be simply eliminated, or the apparatus 10 may be used to build sacrificial chamber walls as part of the build process.
Other types of particulate material supplies may be used; for example, one or more rollers (not shown) may be provided to move and level the particulate material P. Alternatively, the particulate material may be leveled by vibrating the build chamber 16. Alternatively, particulate material P may be applied by dropping it into the build chamber 16 by an overhead device (not shown). Depending on the type of particulate material supply used, it may be provided with means for movement parallel to the Z-axis, and the build platform 14 may remain stationary during the build process.
The binder applicator 22 may be any device or combination of devices which is operable to apply a layer of binder B over the particulate material P in the build chamber 16. In contrast to prior art hardware and methods, the boundaries of the applied binder do not define the boundaries of the completed component, therefore the binder applicator 22 need not be capable of applying the binder with any specific level of accuracy. The binder applicator 22 may be configured to apply binder B over the entire exposed surface area of the particulate material P, or it may be configured to apply binder B over a smaller, predetermined area, as described in more detail below. In either case, the binder B is generally applied such that there is more surface area of binder applied than there will be surface area of cured binder.
Nonlimiting examples of suitable binder application devices include chutes, hoppers, pumps, spray nozzles, spraybars, or precision spraying devices such as inkjet printheads.
The spraybar 48 is mounted to an actuator 54 permitting selective motion along an axis perpendicular to the long axis of the spraybar 48 and parallel to the worksurface 30 (e.g. the Y-axis). Coordinated operation of the spray nozzles 50 and the actuator 54 will permit the application of binder over the build chamber 16 in arbitrary patterns.
The radiant energy apparatus 24 may comprise any device or combination of devices operable to generate and project radiant energy on the particulate material P in a suitable pattern and with a suitable energy level and other operating characteristics to cure the binder B during the build process, described in more detail below.
In one exemplary embodiment as shown in
The radiant energy source 58 may comprise any device operable to generate a beam of suitable energy level and frequency characteristics to cure the binder B. In the illustrated example, the radiant energy source 58 comprises a UV flash lamp.
The image forming apparatus 60 may include one or more mirrors, prisms, and/or lenses and is provided with suitable actuators, and arranged so that the source beam 62 from the radiant energy source 58 can be transformed into a pixelated image in an X-Y plane coincident with the worksurface 30. In the illustrated example, the image forming apparatus 60 may be a digital micromirror device. For example, the projector 56 may be a commercially-available DLP projector.
In another exemplary embodiment as shown in
The radiant energy source 68 may comprise any device operable to generate a beam of suitable power and other operating characteristics to cure the binder. Nonlimiting examples of suitable radiant energy sources include lasers or electron beam guns.
The beam steering apparatus 70 may include one or more mirrors, prisms, and/or lenses and provided with suitable actuators, and arranged so that a beam 72 from the radiant energy source 68 can be focused to a desired spot size and steered to a desired position in plane coincident with the worksurface 30. The beam 72 may be referred to herein as a “build beam”. Other types of scanned beam apparatus may be used. For example, scanned beam sources using multiple build beams are known, as are scanned beam sources in which the radiant energy source itself is movable by way of one or more actuators.
The apparatus 10 may include a controller 74. The controller 74 in
The particulate material P literally comprises particles, which are conventionally defined as “a very small bit of matter”. The particulate material P may comprise any material which can be laid down in a substantially flat layer and which is chemically and physically compatible with the selected binder. In general, the term “powder”, conventionally defined as “dry material made up of fine particles”, may be considered a synonym for the term particulate material.
It will be understood that the resolution of the apparatus and the process, that is, the smallest feature size that may be created, is related to the particle size of the particulate material P. The particles may be regular or irregular in shape, may be uniform or non-uniform in size, and may have variable aspect ratios. For example, the particles may take the form of small spheres or granules, or may be shaped like small rods or fibers.
The composition of the particulate material P, including its chemistry and microstructure, may be selected as desired to suit a particular application. For example, the particulate material P may be metallic, ceramic, polymeric, and/or organic. Mixtures of different compositions may be used.
The particulate material may be “fusible”, meaning it is capable of consolidation into a mass upon further processing, such as sintering via application of heat and/or pressure. For example, fusibility is a characteristic of many available ceramic and metallic powders.
The binder B comprises a material which is radiant-energy curable and which is capable of adhering or binding together the particulate material P in the cured state. As used herein, the term “radiant-energy curable” refers to any material which solidifies in response to the application of radiant energy of a particular frequency and energy level. For example, the binder B may comprise a known type of photopolymer resin containing photo-initiator compounds functioning to trigger a polymerization reaction, causing the resin to change from a liquid state to a solid state. Alternatively, the binder B may comprise a material which contains a solvent that may be evaporated out by the application of radiant energy. The uncured binder B may be provided in solid, liquid, or vapor form.
The composition of the binder B may be selected as desired to suit a particular application. Mixtures of different compositions may be used.
The binder B may be selected to have the ability to out-gas or burn off during further processing, such as the sintering process described above.
Examples of the operation of the apparatus 10 will now be described in detail with reference to
To begin the build process, the apparatus 10 is positioned to define a selected layer increment. For example, the build platform 14 may be positioned below the worksurface 30 by a selected layer increment. The layer increment affects the speed of the additive manufacturing process and the resolution of the component 76. The layer increment can be variable, with a larger layer increment being used to speed the process in portions of a component 76 not requiring high accuracy, and a smaller layer increment being used where higher accuracy is required, at the expense of process speed.
In one exemplary embodiment, the particulate material supply 18 is used to deposit particulate material P, without binder, over the build platform 14. For example, the elevator 40 of the supply container 38 may be raised to push particulate material P through the supply opening 34, exposing it above the worksurface 30. The recoater 44 is moved across the worksurface 30 to spread the raised particulate material P horizontally over the build platform 14 and to form a level surface. Any excess particulate material P drops into the overflow container 20 as the recoater 44 passes from left to right. Subsequently, the recoater 44 may be moved back to a starting position. The leveled particulate material P may be referred to as a “build layer” and the exposed upper surface thereof may be referred to as a “build surface”. Other known types of particulate material supply utilize a recoater arm which moves above the build platform, not relying on a worksurface to ride upon.
Optionally, different layers may comprise two or more particulate materials. For example, one layer may comprise particulate material of a first composition, and a second layer may comprise particulate material of a second composition. The different particulate materials may be provided, for example, by providing one or more additional particulate material supply containers 78, as seen in
Optionally, any of the layers may comprise two or more particulate materials.
Next, binder B is applied over the particulate material P, using the binder applicator 22. For example, if a liquid binder B is used, it may be discharged from the spray nozzles 50 of the spraybar 48 as the spraybar is traversed across the build surface.
Two options are possible in the application of the binder B. For either option, the surface area of the binder B applied is larger than the surface area of the cross-section that will eventually be cured. In the first option, binder B is applied over the surface of the exposed particulate material P in a selected area 88 (
In a second option, binder B would be applied over the surface of the exposed particulate material P in a selected area 90 tailored to the cross-section of the component 76 being built, for the specific layer under consideration. For example, the selected area 90 may be a regular shape such as a polygon having minimum dimensions slightly larger than the maximum dimensions of the component cross-sectional area in each axis. In another example, the selected area 90 may be an arbitrary or irregular shape generally following the outermost perimeter of the component cross-section, with an additional marginal boundary 92. This shape may be described as roughly approximating the shape of the component cross-section.
The second option may be referred to as a “gross” or “rough” or “coarse” application of binder, these terms referring to the level of accuracy achieved. It will be understood that this gross, rough, or coarse application of binder may be achievable using a simple spraybar apparatus as described above and need not require the use of a conventional printhead apparatus. Alternatively, this gross, rough, or coarse application of binder may be achieved using a conventional printhead apparatus (not shown).
Optionally, different layers may comprise two or more binders of different compositions. For example, one layer may comprise a binder of a first composition, and a second layer may comprise a binder of a second composition. The different binders may be provided, for example, by providing one or more additional binder reservoirs 94 coupled to the spraybar 48, as seen in
In another exemplary embodiment, the particulate material P would be pre-mixed with binder B, then loaded into the particulate material supply 18, and the particulate material supply 18 would be used to deposit the mixture of the particulate material and the binder B over the build platform 14. As used herein, the term “pre-mixed” refers to a mechanical mixture of particulate material and binder, as well as to particulate material in which the constituent particles have been coated with a layer of a binder. As noted above, different layers may have different particulate material compositions, or individual layers may include multiple sections with different particulate material compositions.
Once the particulate material P and binder B have been applied, the radiant energy apparatus 24 is used to cure a two-dimensional cross-section or layer of the component 76 being built.
Where a projector 56 is used as shown in
Where a scanned beam apparatus is used instead of a projector, the radiant energy source 68 emits a beam 72 and the beam steering apparatus 70 is used to selectively cure the binder B by steering a focal spot of the build beam 72 over the exposed particulate material P and binder B in an appropriate pattern. Exposure to the radiant energy cures and solidifies the pattern in the binder B.
Another layer increment is defined, for example by the build platform 14 being moved vertically downward by the layer increment, and another layer of particulate material P and binder B is applied in a similar thickness. The radiant energy source 68 again emits a build beam 72 and the beam steering apparatus 70 is used to steer the focal spot of the build beam 72 over the exposed particulate material P in an appropriate pattern. The exposed layer of the particulate material P is exposed to the radiant energy which cures and solidifies the pattern in the binder B and joins it to the previously-cured layer below. This cycle of incrementing a layer, applying particulate material P and binder B, and then curing the binder B is repeated until the entire workpiece W is complete.
Optionally, a scanned beam apparatus may be used in combination with a projector. For example, a scanned beam apparatus may be used to apply radiant energy (in addition to that applied by the projector) by scanning one or multiple beams over the surface of the exposed particulate material P. This may be concurrent or sequential with the use of the projector.
It will be understood that, unlike powder bed metal processes, the process described above does not involve re-melting of the previously cured layer. For some types of binders B, percentage of cure of the binder B depends upon how much radiant energy is applied. For example, the binder B may exhibit an exponential characteristic in a curing versus energy curve. Accordingly, when a multi-layer component is made using this type of binder B, the energy output of the radiant energy apparatus 24 may be carefully selected to partially cure or “under-cure” an underlying layer, with the expectation that when the subsequent layer is applied, the energy from that next layer will complete the curing of the lower layer.
The accuracy of either process, defined as the smallest component feature size which can be produced, is primarily related to the particle size of the particulate material P and the resolution of the projector 56 or scanned beam apparatus 67.
Either curing method (projector or scanned) results in a component 74 in which the particulate material P is held in a solid shape by the cured binder B. if a polymeric binder B is used, the result of the multilayer process is a cured filled polymer with a very high percentage of fill. This may be referred to as a “green” component. This green component may be usable as an end product for low-temperature conditions.
Subsequent to the curing step, the green component may be removed from the build chamber 16, and excess particulate material P and/or uncured binder B may be removed and potentially reused.
If the end product is intended to be purely ceramic or metallic, the component 76 may be treated to conventional sintering process to burn out the binder B and to consolidate the ceramic or metallic particles. Optionally, a known infiltration process may be carried out during or after the sintering process, in order to fill voids in the component with a material having a lower melting temperature than the particulate material P. The infiltration process improves component physical properties.
The build process described above may be modified by the incorporation of multiple binders of different compositions having different curing processes. As used herein, the term “different curing process” refers to differences in any aspect of a curing process, such as curing modality or the process parameters for a particular modality. For example, first and second binders may be provided, with the first being curable using a first wavelength of radiant energy, and the second binder being curable using a second wavelength of radiant energy. As another example, first and second binders may be provided, with the first being curable using a particular wavelength of radiant energy, and the second binder being curable by exposure to high temperature (e.g. in heated air). In order to selectively cure one of the binders without curing the other binder, the radiant energy apparatus 24 may be configured to apply radiant energy at different wavelengths, or more than one radiant energy apparatus 24 may be provided in the apparatus 10, or a radiant energy apparatus 24 as described above may be combined with another type of curing apparatus intended to produce nonselective or uniform curing results, such as radiant heating elements, quartz lamps, etc. These types of curing apparatus do not apply radiant energy in a pattern as described above but rather subjective the entire build chamber 16 to radiant energy.
The different binders may be incorporated as part of the binder application steps described above. Alternatively, either or both of the binders may be incorporated as part of a premix as described above.
At least one of the binders is provided by a pre-mixture or is applied before a first curing step is carried out. The remaining binders may be applied before or after curing steps are carried out.
At least one of the binders is selectively cured as described above. The remaining binders can be selectively cured or uniformly cured.
The use of two or more binders permits each binder to be tailored to a specific function. For example, the first binder may be used to help connect the particles that will form the final component, while the second binder may be used as a support structure to give the component strength through the build process.
The method described herein has several advantages over the prior art. In particular, it permits economically viable production of components with fine feature fidelity; provides freedom in the choice of materials; works at high speed; and has low cost. One specific advantage of the gross binder application process is that it should make it easier to reuse or recycle uncured particulate material in the areas that have not been sprayed with binder.
The foregoing has described a method for an additive manufacturing process. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
