CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Serial No. 62/668,741, filed May 8, 2018. TECHNICAL FIELD

This specification relates to additive manufacturing, also known as 3D printing.

BACKGROUND

Additive manufacturing (AM), also known as solid freeform fabrication or 3D printing, refers to a manufacturing process where three-dimensional objects are built up from successive dispensing of raw material (e.g., powders, liquids, suspensions, or molten solids) into two- dimensional layers. In contrast, traditional machining techniques involve subtractive processes in which objects are cut out from a stock material (e.g., a block of wood, plastic or metal).

A variety of additive processes can be used in additive manufacturing. Some methods melt or soften material to produce layers, e.g., selective laser melting (SLM) or direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM), while others cure liquid materials using different technologies, e.g., stereolithography (SLA). These processes can differ in the way layers are formed to create the finished objects and in the materials that are compatible for use in the processes.

Conventional systems use an energy source for sintering or melting a powdered material. Once all the selected locations on the first layer are sintered or melted and then re- solidified, a new layer of powdered material is deposited on top of the completed layer, and the process is repeated layer by layer until the desired object is produced.

SUMMARY

An additive manufacturing apparatus for forming an object includes a platen to support the object being formed, a dispenser to deliver a plurality of layers of a powder to the platen, an inductive heater configured to generate eddy currents in a region of the powder, and an energy source to apply energy to the powder to form a fused portion of the powder.

Implementations may include one or more of the following features. The inductive heater may be positioned and configured to heat the region of the powder before the region of powder is fused by the energy source. A controller may be configured to cause the inductive heater to heat the region of the powder from an initial temperature to an elevated temperature that is less than a temperature at which the powder fuses.

The inductive heater may be positioned and configured to heat the region of the powder before the region of powder is fused by the energy source. A controller may be configured to cause the inductive heater to cause the region of the powder to cool at a predetermined rate.

The inductive heater may include a coil and a power source to apply an AC voltage to the coil. The coil may be wound around a magnetic core.

The inductive heater may be movable along a first direction relative to the platen. The inductive heater may have a plurality of coils configured to heat a plurality of regions positioned along a second direction that is perpendicular to the first direction. The plurality of regions may be arranged in a line along the second direction. A power source may apply an AC voltage to each coil of the plurality of coils, and the power source may be configured such that power to each coil is independently controllable.

The energy source may include a light source to generate a light beam and a beam scanner to reflect the light beam. The inductive heater may include a coil, and the coil and the beam scanner may be secured to a common movable support such that the coil and beam scanner inductive move in conjunction along a first direction. The beam scanner may include a polygon mirror scanner to reflect the light beam and scan the light beam along a second direction perpendicular to the first direction.

A housing may enclose the platen and dispenser in a sealed chamber.

Advantages of the foregoing may include, but are not limited to, the following. Powder can be heated either in bulk or in a localized region before and/or after fusing. Heating can be performed rapidly, precisely and repeatedly. More than 2000 F in 1 Sec may be possible. The heating can be performed at high efficiency. 99% efficiency may be possible. The heating works with most metal powder when coupled with a fully fused lower layer of metal. There is no flame, and thus heating is safer. There is a high coupling efficiency, e.g., in the range of 10 ~ 25MM. There may be precise and localized heating.

The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other potential features, aspects, and advantages will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an example additive manufacturing apparatus.

FIG. 2A is a schematic side view of an example of a printhead for an example additive manufacturing apparatus.

FIG. 2B is a schematic top view of the printhead of FIG. 2 A.

Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION

Additive manufacturing (AM) apparatuses can form an object by dispensing and fusing successive layers of a powder on a build platform. This powder, in the case of metal powders, needs to be melted and then resolidified to form the desired part. In techniques such as selective laser sintering (SLS) and selective laser melting (SLM), a laser is selectively applied to the powder to sinter or melt the powder.

It is often desirable to pre-heat or heat-treat the powder (or solidified material) before the material is fused, e.g., by a laser. This permits a lower thermal fluctuation, which can avoid creating voids or internal stresses in the fabricated part. One technique to heat the powder is to apply infrared heaters. However, the emissivity and thermal conductivity of metal powder could cause this technique could be inefficient. Another technique to heat the powder is to scan the powder with a laser. However, this technique could result in poor temperature uniformity and could also be inefficient. An inductive heater can be used to heat to the powder. An inductive heater could avoid the problems noted above.

Additive Manufacturing Apparatuses

FIG. 1 illustrates a schematic side view of an example additive manufacturing (AM) apparatus 100 that includes a printhead 102 and a build platform 104 (e.g., a build stage). The printhead 102 dispenses a powder 106 and, optionally, fuses the powder 106 dispensed on the platform 104. Optionally, as described below, the printhead 102 can also dispense and/or fuse a second powder 108 on the platform 104. The printhead 102 and a build platform 104 can both be enclosed in a housing 180 that forms a sealed chamber 186, e.g., a vacuum chamber, that provides a controlled operating environment. The chamber 180 can include an inlet 182 coupled to a gas source and an outlet 184 coupled to an exhaust system, e.g., a pump. The gas source can provide an inert gas, e.g. Ar, or a gas that is non-reactive at the temperatures reached by the powder for melting or sintering, e.g., N _2. This permits the pressure and oxygen content of the interior of the housing 180 to be controlled. For example, oxygen gas can be maintained at a partial pressure below 0.01 atmospheres.

The chamber 186 may be maintained at atmospheric pressure (but at less than 1% oxygen) to avoid the cost and complexity of building a fully vacuum compatible system.

Oxygen content can be below 50 ppm when the pressure is at 1 atmosphere, e.g., when dealing with Ti powder particles. A load lock chamber accessible through a valve 188, e.g., a slit valve, can be used to separate the chamber 186 from the external environment while permitting parts, e.g., the build platform with the fabricated object, to be removed from the chamber. For example, the build platform 104 can be movable on a track 189, e.g., a rail.

Referring to FIGS. 1 and 2B, the printhead 102 is configured to traverse the platform 104. For example, the apparatus 100 can include a support, e.g., a linear rail or pair of linear rails 119, along which the printhead can be moved by a linear actuator and/or motor. This permits the printhead 102 to move across the platform 104 along a first horizontal axis. In some

implementations, the printhead 102 can also move along a second horizontal axis perpendicular to the first axis.

The printhead 102 can also be movable along a vertical axis. In particular, after each layer is fused, the printhead 102 can be lifted by an amount equal to the thickness of the deposited layer of powder. This can maintain a constant height difference between the dispenser on the printhead 102 and the top of the powder on the platform 104. A drive mechanism, e.g., a piston or linear actuator, can be connected to the printhead or support holding the printhead to control the height of the printhead. Alternatively, the printhead 102 can be held in a fixed vertical position, and the platform 104 can be lowered after each layer is deposited.

Referring to FIGS. 1, and 2 A, the printhead 102 includes at least a first dispensing system 116 to selectively dispense powder 106 on the build platform 104. Referring to FIGS. 1 and 2A, the first dispensing system 116 includes a hopper 131 to receive the powder 106. The powder 106 can travel through a channel 132 having a controllable aperture, e.g., a valve, that controls whether the powder is dispensed onto the platform 104.

Returning to FIGS. 2A and 2B, the apparatus 100 also includes an energy source 114 to selectively add energy to the layer of powder on the build platform 104. The energy source 114 can be incorporated into the printhead 102 (as shown in FIGS. 2 A and 2B), be mounted on a support that holds the printhead, or be mounted separately, e.g., on a separate support is independently movable relative to the printhead 102, or on a frame supporting the build platform 104 or on the housing 180 that surrounds the build platform 104.

In some implementations, the energy source 114 generates a light beam 115 that increases a temperature of a small area of the layer of the powder. For example, the energy source 114 can be a laser and the light beam 115 can be a laser beam. The energy source 114 can fuse the powder by using, for example, a sintering process, a melting process, or other process to cause the powder to form a solid mass of material.

The energy source 114 can be positioned on the printhead 102 such that, as the printhead 102 advances in a forward first direction, the energy source can selectively heat regions of powder dispensed by the dispensing system 116. The light beam 115 can be scanned, e.g., by a rotating polygon, across the powder in a second direction perpendicular to the first direction.

This permits the light beam 115 to perform a raster scan across the layer of powder. Selective activation of the light beam 115 permits selective voxels to be fused.

Referring to FIGS. 1 and 2A, the apparatus 100 includes a heater 112 to raise the temperature of the deposited powder. The heater 112 can heat the deposited powder to a temperature that is below its sintering or melting temperature. The heater 112 can include at least one inductive heater.

The heater 112 can include a first inductive heater 1 l2a that is configured to pre-heat the deposited powder, i.e., heat a portion of the powder prior to that portion of the powder being fused by the light beam 115. In this case, the first inductive heater 1 l2a can be located, relative to the forward moving direction of the printhead 102, behind the first dispensing system 116 and in front of the energy source 114. As the printhead 102 moves in the forward direction, the first inductive heat source 1 l2a moves across the area where the first dispensing system 116 was previously located. Pre-heating the powder raises the temperature of the powder from an initial temperature to an elevated temperature, but still below the sintering or melting temperature of the powder. This permits fusing by the light beam 115 to be performed with a smaller temperature excursion, which can improve uniformity, reduce likelihood of keyholing, and improve part quality.

Alternatively or in addition, the heater 112 can include a second inductive heater 1 l2b that is configured to heat-treat the layer, i.e., apply heat to a portion of the powder after the light beam 115 has fused that portion. In this case, the second inductive heater 1 l2b can be located, relative to the forward moving direction of the printhead 102, behind the energy source 114. Heat-treating permits the powder and/or fused material to undergo cool-down at a controlled rate, treatment and/or control of the cooldown of the powder and/or fused material.

The inductive heaters 1 l2a, 1 l2b can be secured to the same support as the energy source

114, e.g., support 102, or to a separate support that is independently movable (e.g., along the second direction) relative to the support 102.

An inductive heater 1 l2a, 1 l2b includes one or more conductive coils 140. For example, the first inductive heater 112a can include one or more conductive coils l40a, and the second inductive heater 1 l2b can include one or more conductive coils l40b. Each coil can optionally be wound around a magnetic core 142, e.g., a material having a high magnetic permeability, e.g., iron or an iron-nickel alloy.

The coils 140 are electrically coupled to a power source 144 (see FIG. 2B) that applies a voltage, e.g., an AC voltage to the coils 140. Application of the AC voltage to a coil 140 generates a magnetic field 146 (see FIG. 2 A) that extends from the coil toward the layer of powder or fused material. The magnetic field can induce eddy currents in the layer of powder or fused material, and resistance to the eddy currents in the material heats the layer in regions where the magnetic field is applied. The power source 144 can control the power supplied to the coil and/or the frequency of the AC voltage, and thereby control the amount of heat generated in the layer.

As shown in FIG. 2B, in some implementations an inductive heater, e.g., the first inductive heater 1 l2a and/or the second inductive heater 1 l2b, can include an array of coils, e.g., coils l40a, l40b respectively. The array of coils can be a linear array, e.g., the coils can be positioned in a line. The line of coils can extend along the second direction, e.g., perpendicular direction of travel of the support 102. Similarly, the individual coils within an array can be spaced apart in the second direction. In some implementations, the array of coils extends across the width of the build platform 104.

In some implementations, the power source 144 can independently control the power applied to each coil 140, thereby permitting independent control of heating to different regions, e.g., different regions along the second direction where the inductive heater includes an array of coils arranged along the second direction. By independently controlling heating, the layer of powder can be raised to a more uniform temperature, or to a temperature that more closely matches a desired temperature profile along the second direction.

Optionally, the printhead 102 can also include a first spreader 118, e.g., a roller or blade, that cooperates with first the dispensing system 116 to compact and spread powder dispensed by the dispensing system 116. The spreader 118 can provide the layer with a substantially uniform thickness. In some cases, the first spreader 118 can press on the layer of powder to compact the powder.

The printhead 102 can also optionally include a first sensing system 120 and/or a second sensing system 122 to detect properties of the apparatus 100 as well as powder dispensed by the dispensing system 116.

In some implementations, the printhead 102 includes a second dispensing system 124 to dispense a second powder 108. The second dispensing system 116, if present, can be constructed similarly with a hopper 133 and channel 134. A second spreader 126 can operate with the second dispensing system 124 to spread and compact the second powder 108.

The first powder particles 106 can have a larger mean diameter than the second particle particles 108, e.g., by a factor of two or more. When the second powder particles 108 are dispensed on a layer of the first powder particles 106, the second powder particles 108 infiltrate the layer of first powder particles 106 to fill voids between the first powder particles 106. The second powder particles 108, being smaller than the first powder particles 106, can achieve a higher resolution, higher pre-sintering density, and/or a higher compaction rate.

Alternatively or in addition, if the apparatus 100 includes two types of powders, the first powder particles 106 can have a different sintering temperature than the second particle particles. For example, the first powder can have a lower sintering temperature than the second powder. In such implementations, the energy source 114 can be used to heat the entire layer of powder to a temperature such that the first particles fuse but the second powder does not fuse. In implementations when multiples types of powders are used, the first and second dispensing systems 116, 124 can deliver the first and the second powder particles 106, 108 each into different selected areas, depending on the resolution requirement of the portion of the object to be formed.

Examples of metallic particles include metals, alloys and intermetallic alloys. Examples of materials for the metallic particles include titanium, stainless steel, nickel, cobalt, chromium, vanadium, and various alloys or intermetallic alloys of these metals. Examples of ceramic materials include metal oxide, such as ceria, alumina, silica, aluminum nitride, silicon nitride, silicon carbide, or a combination of these materials.

In implementations with two different types of powders, in some cases, the first and second powder particles 106, 108 can be formed of different materials, while, in other cases, the first and second powder particles 106, 108 have the same material composition. In an example in which the apparatus 100 is operated to form a metal object and dispenses two types of powder, the first and second powder particles 106, 108 can have compositions that combine to form a metal alloy or intermetallic material.

The processing conditions for additive manufacturing of metals and ceramics are significantly different than those for plastics. For example, in general, metals and ceramics require significantly higher processing temperatures. Thus 3D printing techniques for plastic may not be applicable to metal or ceramic processing and equipment may not be equivalent. However, some techniques described here could be applicable to polymer powders, e.g. nylon, ABS, polyetheretherketone (PEEK), polyetherketoneketone (PEKK) and polystyrene.

If the apparatus 100 dispenses two different types of powders having different sintering temperatures, the first and second heat sources 112, 125 can have different temperature or heating set points. For example, if the first powder 106 can be sintered at a lower temperature than the second powder 108, the first heat source 112 may have a lower temperature set point than the second heat source 125.

A controller 128 controls the operations of the apparatus 100, including the operations of the printhead 102 and its subsystems, such as the heater 112, the energy source 114, and the first dispensing system 116. The controller 128 can also control, if present, the first spreader 118, the first sensing system 120, the second sensing system 122, the second dispensing system 124, and the second spreader 126. The controller 128 can also receive signals from, for example, user input on a user interface of the apparatus or sensing signals from sensors of the apparatus 100. The controller 128 can operate the dispensing system 116 to dispense the powder 106 and can operate the energy source 114 and the heat source 112 to fuse the powder 106 to form a workpiece 130 that becomes the object to be formed.

The controller 128 can include a computer aided design (CAD) system that receives and/or generates CAD data. The CAD data is indicative of the object to be formed, and, as described herein, can be used to determine properties of the structures formed during additive manufacturing processes. Based on the CAD data, the controller 128 can generate instructions usable by each of the systems operable with the controller 128, for example, to dispense the powder 106, to fuse the powder 106, to move various systems of the apparatus 100, and to sense properties of the systems, powder, and/or the workpiece 130. In some implementations, the controller 128 can control the first and second dispensing systems 116, 124 to selectively deliver the first and the second powder particles 106, 108 to different regions.

The controller 128, for example, can transmit control signals to drive mechanisms that move various components of the apparatus. In some implementations, the drive mechanisms can cause translation and/or rotation of these different systems, including dispensers, rollers, support plates, energy sources, heat sources, sensing systems, sensors, dispenser assemblies, dispensers, and other components of the apparatus 100. Each of the drive mechanisms can include one or more actuators, linkages, and other mechanical or electromechanical parts to enable movement of the components of the apparatus.

For a controller to be configured to perform particular operations or actions means that the controller has it software, firmware, hardware, or a combination of them that in operation cause the system to perform the operations or actions. For one or more computer programs to be configured to perform particular operations or actions means that the one or more programs include instructions that, when executed by data processing apparatus, cause the apparatus to perform the operations or actions.

Conclusion

The controller and other computing devices in the systems described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware. For example, the controller can include a processor to execute a computer program as stored in a computer program product, e.g., in a non-transitory machine readable storage medium. Such a computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

While this document contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple

embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example:

• Other techniques can be used for dispensing the powder. For example, powder could be dispensed in a carrier fluid, e.g., a quickly evaporating liquid such as Isopropyl Alcohol (IP A), ethanol, or N-Methyl-2-pyrrolidone (NMP), and/or ejected from a piezoelectric printhead.

Alternatively, the powder could be pushed by a blade from a powder reservoir adjacent the build platform.

• Other techniques can be used for addressing the layer of powder with a light beam. For example, the light beam can be directed by a pair of mirror galvos so as to trace a path in an X-Y plane. In this case, the mirror galvos need not be attached to the support 102, but can stationary, e.g., on the housing 180.

• For some powders, an electron beam could be used instead of a laser beam to fuse the powder.

• The apparatus 100 can include other heating systems in addition to the inductive heater. For example, the apparatus 100 could also include heat lamps, e.g., IR lamps, a resistive heater in the platform 104, and/or a light beam, e.g., a laser, that scans across the layer of powder.

• Although FIGS. 1, 2A and 2B illustrate the apparatus as including an inductive heater both before and after the energy source 114, the apparatus could include only the inductive heater before the energy source, or only the inductive heater after the energy source.

Accordingly, other implementations are within the scope of the claims.