Patent Description:
Additive manufacturing (AM) refers to processes of joining materials to make parts from 3D model data, usually layer upon layer. In recent years, additive technologies have been adopted in a variety of manufacturing sectors, including aerospace, automotive, medical, and consumer products.

The materials that can be used to produce workpieces in AM processes vary widely, and include plastics, metals, ceramics, and composites. These materials are typically supplied in liquid or powder form, heated during the AM process, and then bound together. For example, in molten material systems, a pre-heating chamber raises the material temperature to melting point so that the material can flow through a delivery system. When thermoplastics are used, AM processes often involve laser sintering techniques that use a laser as the power source to sinter powdered material, binding the material together to create a solid structure. When metallic parts are built, frequently used techniques include partial-melting processes and complete-melting processes. Heat treatment may be applied to reduce the thermal residual stresses or optimize the microstructure of the fabricated metallic parts.

In each of these AM processes, uncontrolled heating and cooling of different parts of the workpiece can result in inconsistent physical, thermal, mechanical, and/or chemical properties throughout the workpiece, for example, due to differing microstructures and grain sizes in the resultant workpiece. For this reason, additively manufactured parts are often distorted because of spatially variable heating and cooling. For some materials additively manufactured layer-wise, consistent anisotropic properties are important to maintain throughout the workpiece, and uncontrolled cooling can negatively affect such properties. In view of the above, a challenge exists to properly control the heating and cooling of workpieces during AM processes in order to manufacture high quality workpieces.

<CIT> states, according to its abstract, that a method of controlling an additive manufacturing machine includes: measuring a first temperature of a part being processed by the additive manufacturing machine; determining that the first measured temperature exceeds a temperature threshold; activating an auxiliary gas flow; cooling the auxiliary gas flow with a cooling system; and directing the cooled auxiliary gas flow towards the part.

<CIT> states, according to its abstract, that methods for direct writing of single crystal super alloys and metals are provided. The method can include: heating a substrate positioned on a base plate to a predetermined temperature using a first heater; using a laser to form a melt pool on a surface of the substrate; introducing a superalloy powder to the melt pool; measuring the temperature of the melt pool; receiving the temperature measured at a controller; and using an auxiliary heat source in communication with the controller to adjust the temperature of the melt pool. The predetermined temperature is below the substrate's melting point. The laser and the base plate are movable relative to each other, with the laser being used for direct metal deposition. An apparatus is also generally provided for direct writing of single crystal super alloys and metal.

<CIT> states, according to its abstract, that a controller can serve to receive temperature data that represent the temperature distribution of at least a portion of a current layer of building material, which is measured by a temperature sensor. The control can serve to determine one or more weighting factors which represent the degree of influence of each of one or more previous layers of the building material under the current layer on a property of the current layer. The control may serve to identify one or more regions in the current layer based on the one or more weighting factors and based on how the property is exhibited by each of the one or more regions. The control may serve to cause the current layer to reach a target temperature if the temperature data in the selected region of the identified one or more regions does not correspond to the target temperature.

<CIT> states, according to its abstract, that a three-dimensional object printing system comprises an ejectors configured to eject drops of material towards a platen, a heater, a sensor configured to sense temperature of the ejected material, a radiator configured to direct radiation to the ejected material, a cooler configured to cool the ejected material, and a controller operatively connected to the ejectors, heater, sensor radiator and cooler. The controller is configured to control the ejectors to form layers of material for a three-dimensional object on the surface of the platen with reference to image data of the three-dimensional object, to operate the heater to heat the surface of the platen, to compare a temperature signal received from the sensor to a predetermined threshold, to operate the radiator to radiate the object layers, and to operate the cooler to attenuate heat produced by the radiated material in response to the signal from sensor exceeding the predetermined threshold.

According to the present disclosure, a method, and a system as defined in the independent claims <NUM> and <NUM> are provided. Further embodiments of the claimed invention are defined in the dependent claims. Although the claimed invention is only defined by the claims, the below embodiments, examples, and aspects are present for aiding in understanding the background and advantages of the claimed invention.

To address the above issues, according to one aspect of the present disclosure, a method for additive manufacturing of a three-dimensional workpiece is provided. In this aspect, the method includes depositing material onto a substrate to form a shape of the workpiece in an additive manufacturing process and determining a thermal characteristic of a portion of the workpiece during the additive manufacturing process. The method further includes determining that the thermal characteristic of the portion exceeds a threshold associated with the portion and adjusting a cooling parameter of a cooling flow to be applied to the workpiece responsive to the determination. The method further includes applying the cooling flow with the adjusted cooling parameter to the portion of the workpiece, wherein the thermal characteristic is one of:temperature gradients; or peak temperature over time or within a region; or average temperature over time or within a region.

Another aspect of the present disclosure relates to an additive manufacturing apparatus with an additive manufacturing deposition head, a cooling applicator configured to apply coolant, a processor operatively coupled to the deposition head and the cooling applicator, and a memory storing instructions that, when executed by the processor, cause the apparatus to perform the method described above.

Yet another aspect of the present disclosure not falling under the scope of the claimed invention relates to a method for additive manufacturing of a three-dimensional workpiece as follows. The method in this aspect includes depositing material onto a substrate to form a shape of the workpiece in accordance with an additive manufacturing process and measuring thermal characteristics of a plurality of portions of the material. Each of the plurality of portions has a corresponding upper threshold, a corresponding lower threshold, and a corresponding threshold period of time. The method further includes determining whether a thermal characteristic of a given portion of the plurality of portions exceeds the corresponding upper threshold associated with the given portion for the corresponding threshold period of time at which the corresponding upper threshold is exceeded. The method further includes pausing the deposition of material and increasing coolant application to the given portion responsive to the determination that the thermal characteristic of the given portion exceeds the corresponding upper threshold for the corresponding threshold period of time. The method further includes applying the coolant until it is determined that the thermal characteristic of the given portion is lower than the corresponding lower threshold associated with the given portion, decreasing coolant application and resuming the deposition of material responsive to determining that the thermal characteristic of the given portion is below the corresponding lower threshold for the corresponding threshold period of time.

The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings.

In view of the considerations discussed above, systems and methods are provided to cool portions of a workpiece that is additively manufactured. When a thermal characteristic, such as temperature or time-at-temperature which are both not falling under the scope of the claimed invention, of the workpiece is determined, through measurement or computational simulation, to exceed a threshold, cooling of the workpiece is adjusted to properly cool the workpiece. As a result, target mechanical and dimensional properties can be more reliably achieved. Thermal history data about the thermal characteristics exhibited by the workpiece and cooling performed on the workpiece during the AM process are recorded and outputted for later reference, as discussed in detail below. This thermal history information is used for a variety of purposes, including for example, to detect anomalies in manufactured workpieces and to modify downstream manufacturing operations to improve quality.

Referring initially to <FIG>, an AM system <NUM> is provided comprising a deposition subsystem <NUM> including an AM deposition head <NUM> configured to deposit a material M, a cooling subsystem <NUM> including a cooling applicator <NUM> configured to apply coolant C, a controller <NUM> including a processor <NUM> operatively coupled to the deposition head <NUM> and the cooling applicator <NUM>, and a memory <NUM> storing instructions <NUM> that, when executed by a processor <NUM>, cause the processor <NUM> to control the system <NUM> to perform operations of the AM processes described herein.

The processor <NUM> is a microprocessor that include one or more of a central processing unit (CPU), a graphical processing unit (GPU), an application specific integrated circuit (ASIC), a system on chip (SOC), a field-programmable gate array (FPGA), a logic circuit, or other suitable type of microprocessor configured to perform the functions recited herein. The memory typically includes non-volatile memory that retains stored data even in the absence of externally applied power, such as FLASH memory, a hard disk, read only memory (ROM), electrically erasable programmable memory (EEPROM), etc., and volatile memory such as random access memory (RAM), static random access memory (SRAM), dynamic random access memory (DRAM), etc., which temporarily stores data only for so long as power is applied during execution of programs. The instructions <NUM> include one or more programs and data used by such programs sufficient to perform the operations described herein.

The processor <NUM> of controller <NUM> is configured to cause the AM manufacturing system <NUM> to perform an AM process that includes depositing material M onto a substrate <NUM> to form a shape of a workpiece <NUM>. The shape of the workpiece <NUM> is typically defined in a Computer Aided Drafting (CAD) model <NUM>, which may be in a variety of formats such as Standard Tessellation Language (STL) or Additive Manufacturing Format (AMF). The workpiece <NUM> may take a virtually limitless variety of forms and sizes, including gears, shafts, tubes, frames, and housings that span several millimeters, centimeters, or even meters in length. The CAD model <NUM> is interpreted by a control program <NUM> which then creates a manufacturing plan including a plurality of deposition paths stacked in layers to form the workpiece additively. Each deposition path occurs within a layer by relative movement of the deposition head <NUM> and the workpiece during deposition of the layer. The control program <NUM> causes the processor <NUM> to send deposition commands <NUM> to the deposition subsystem <NUM> which cause the deposition head <NUM> to be moved to an appropriate position along the deposition paths and to deposit material M drawn from the material supply source <NUM> via material feed line <NUM> in accordance with the manufacturing plan.

During the AM process, the processor <NUM> is configured to determine a thermal characteristic <NUM> of at least a portion of the workpiece <NUM>, such as first portion <NUM> or second portion <NUM>. In the paragraphs that follow, the determination of the thermal characteristic and subsequent cooling with be described with reference to first portion <NUM>, although it will be appreciated that this description is equally applicable to second portion <NUM>. A variety of thermal characteristics of first portion <NUM> may be determined. For example but not falling under the scope of the claimed invention, the thermal characteristic <NUM> may be time at temperature, that is, a cumulative time period that a portion of the workpiece has spent at a threshold temperature. Example thermal characteristics <NUM> that are determined include temperature gradients, peak temperature over time or within a region, and average temperature over time or within a region.

The thermal characteristic <NUM> of the portion may be determined by measuring a surface temperature of the portion, for example. The surface temperature of the first portion <NUM> may be measured by a thermal sensor <NUM>. Examples of suitable thermal sensors include a pyrometer 46A, an infrared camera 46B, and a thermometer 46C, although other types of thermal sensors may alternatively be used. In one specific example, a non-contact infrared pyrometer 46A may be used. As an alternative to direct measurement of the workpiece, the thermal characteristic <NUM> may be determined based on a computer simulation using a thermal model <NUM> of the AM process for the workpiece, so that both internal and external temperatures of the first portion <NUM> can be estimated. The computer simulation includes a finite element analysis of the heat transfer caused by deposition of the material during the AM process. Thus, in this example the thermal model <NUM> includes a finite element model (FEM) based on the CAD model <NUM>, which includes a representation of the workpiece <NUM> at each stage of manufacture as additional deposition elements are added in each layer of the workpiece <NUM>.

The processor <NUM> is configured to determine that the thermal characteristic <NUM> of at least the portion <NUM> exceeds a threshold <NUM> associated with the first portion <NUM>. In one example, when the thermal characteristic <NUM> is time at temperature, the threshold <NUM> includes a threshold period of time at which a threshold temperature is exceeded. When a computer simulation is used to estimate a temperature of the workpiece, the threshold <NUM> may be a threshold temperature, temperature gradient, average temperature, time at temperature, etc., of a finite element or region of such elements in the FEM model, for example.

The processor <NUM> is further configured to issue a cooling command <NUM> to the cooling subsystem <NUM> to adjust a cooling parameter of the cooling flow of the coolant C to be applied to the workpiece <NUM> responsive to determining that the thermal characteristic <NUM> of at least the first portion <NUM> exceeds the threshold <NUM> associated with the first portion <NUM>. The processor <NUM> is also configured to apply the cooling flow of the coolant C with the adjusted cooling parameter to at least the first portion <NUM> of the workpiece <NUM>, via the cooling subsystem <NUM>. The cooling flow of the coolant C proceeds from cooling tank <NUM>, via cooling line <NUM> and valve V5, through a compressor <NUM> and cooler <NUM> to be emitted by applicator <NUM> toward the workpiece <NUM>. The determined thermal characteristic <NUM> of the first portion <NUM> of the workpiece <NUM> may be stored in memory <NUM> as part of a thermal history <NUM> of the workpiece <NUM>. A more detailed description of thermal history <NUM> is presented below in reference to <FIG>. The thermal history <NUM> may be outputted by the processor <NUM> as output data <NUM>, which may be a data file or collection that is stored on media or is transmitted over a computer network to a receiving computing device. The thermal history <NUM> may enable downstream examination of the actual conditions of the workpiece during manufacture, for example, during an inspection prior to the part being placed into service, or during an inspection after the part has spent time in service. As another example, the thermal histories <NUM> of a set of workpieces <NUM> may be compared to determine a distribution of quality characteristics among the set.

Threshold <NUM> may vary based on the location of the first portion <NUM> within the workpiece <NUM>, and also may vary depending on the material M being deposited to form the workpiece <NUM>. Further, the threshold <NUM> may vary based on a current stage of the AM process. The threshold <NUM> may be set to an operating temperature that has an effect on the material properties of the solidified workpiece. In one specific example, titanium alloys have two main phases, alpha and beta. A titanium alloy's beta transus temperature is around <NUM> (<NUM>°F) or higher. Aging temperatures are approximately <NUM>-<NUM> (<NUM>-<NUM>°F). Microstructure and the subsequent material properties of the fabricated workpiece <NUM> can vary significantly depending on time at temperature above or just below the beta transus, cooling rate from these elevated temperatures, and time at or around aging temperature. Heat treatment affects the size, shape, and proportion of these phases and subsequent material properties. By controlling the thermal conditions of the workpiece <NUM> during manufacture, the microstructure of the final workpiece <NUM> can be controlled. To achieve this control, for example, the threshold <NUM> may be set to the beta transus temperature of the material M, which in one specific example may be <NUM> (<NUM>°F), or to a predetermined value below the beta transus temperature, or to a temperature that is within the aging temperature range, such as <NUM> (<NUM>°F).

The cooling parameter may be at least one of a coolant flow rate and a coolant temperature. The coolant C may be at least one of a liquid and a gas such as argon. The cooling flow may be applied until the processor <NUM> determines that the thermal characteristic <NUM> of at least the first portion <NUM> is below the threshold <NUM> associated with the first portion <NUM>. At this point, coolant application may be decreased and the deposition of material M continued.

The adjustment of the cooling parameter may be performed by adjusting the coolant temperature and/or adjusting the cooling flow. Coolant temperature may be adjusted by altering the temperature of the coolant gas or liquid. Cooling flow may be adjusted by varying the flow rate of the emitted coolant. The variation of flow rate of the coolant may be achieved by adjusting the coolant compressor <NUM>, which regulates the pressure of the coolant C. The first portion <NUM> may be rapidly cooled or cooled at a more moderate pace depending on the temperature of the coolant C. The cooling application may proceed intermittently, or continuously in conjunction with the AM process.

Accordingly, the controlled cooling application prevents the first portion <NUM> from becoming too hot. Benefits of such a controlled cooling application include tailored mechanical properties and microstructure, consistent deposition layer heights, reduced defect counts, reduced grain growth, reduced residual stress, and providing a predictable starting stock. Such benefits can be linked to savings on inspection, programming, and machining of the final workpiece <NUM>, potentially reducing or eliminating post-deposition treatment. Thresholds <NUM> for thermal characteristics <NUM> and coolant flow rates and coolant temperatures can be set based on the material used and the desired mechanical properties.

In certain embodiments, the portion of the workpiece may be a first portion <NUM> as described above, and the threshold <NUM> may be a first threshold, the coolant parameter may be a first cooling parameter, and the workpiece <NUM> may further include a second portion <NUM>. The AM process may further include determining whether a thermal characteristic of the second portion <NUM> exceeds a second threshold associated with the second portion <NUM>, the second threshold configured to be different from the first threshold, adjust a second cooling parameter of a cooling flow to be applied to the workpiece <NUM> responsive to determining that the thermal characteristic of the second portion <NUM> exceeds the second threshold associated with the second portion <NUM>, the second cooling parameter configured to be different from the first cooling parameter, apply the cooling flow with the second cooling parameter to the second portion <NUM> of the workpiece <NUM>, and decreasing coolant application and continuing the deposition of material responsive to determining that the thermal characteristic of the second portion <NUM> is below the second threshold associated with the second portion <NUM>. In this way, the cooling of the workpiece <NUM> may be tailored based on a spatial configuration of the workpiece, such that different thresholds are applied, and thus different cooling commands are generated for the first portion <NUM> and second portion <NUM>.

<FIG> illustrates one example configuration for the deposition head <NUM> and cooling applicator <NUM> of the AM system <NUM> of <FIG>. As shown, material M may be supplied to the deposition head <NUM> from a material supply source <NUM> via material feed lines <NUM>, thereby allowing the deposition head <NUM> to deposit the material M as a series of deposits to build the 3D workpiece <NUM> in a piece-by-piece, layer-by-layer manner. The material supply source <NUM> may be a powder supply container, for example. In other examples, a filament spool or cassette may be used. The deposition head <NUM> may be a nozzle with a fixed or variable nozzle diameter for ejecting powdered material M, for example. In other configurations, an extrusion nozzle may be used. Further two or more of the depicted nozzles may alternatively be included in the deposition head <NUM>. In other words, the nozzle diameters and number of nozzles may vary between machines. In some configurations, the nozzle <NUM> may be configured as a co-axial head with a tapered cone design that provides powdered material a full <NUM> degrees around a melt pool created by a laser, directing powdered material to the melt pool created by the laser.

A laser source <NUM> or other light source may be provided within the deposition head <NUM> to use as a power source to emit a laser beam L that sinters the ejected powdered material M, binding the material M together to create a solid structure of sintered material. As the deposition head <NUM> is moved by the robotic arm of the robot <NUM> in the deposition direction relative to the workpiece <NUM>, powdered material M is caused to bind by the laser beam L, and a line of solidified material M is formed. The material M deposited onto the substrate <NUM> is not particularly limited and may be a metal such as steel and its alloys, titanium and its alloys, nickel, aluminum, copper, magnesium, cobalt-chrome, or tungsten. Further, the material M may be a polymer or composite material. In the depicted embodiment, the deposition head <NUM> and the coolant applicator <NUM> are attached to the tip of an articulated robotic arm of a robot <NUM>. However, it will be appreciated that deposition head <NUM> and coolant applicator <NUM> may alternatively be provided on separate robotic arms. The movement of the deposition head <NUM> is also not limited to being moved by a robotic arm of a robot, and the deposition head <NUM> may alternatively be moved via a gantry or platform, for example. In other embodiments, the deposition head <NUM> the coolant applicator <NUM> may be fixed in set locations, while a mobile platform moves the workpiece <NUM> on the substrate <NUM> to facilitate the AM process. The thermal sensor <NUM> is illustrated as mounted to the robotic arm in <FIG>. Alternatively, it will be appreciated that the thermal sensor may be mounted to a separate robotic arm than the coolant applicator <NUM> and deposition head <NUM>, or may be mounted to another surface, such as a wall of a manufacturing enclosure, for example. The thermal sensor <NUM> is positioned such that a range of measurement <NUM> for the thermal sensor <NUM> encompasses at least the first portion <NUM> and the second portion <NUM> of the workpiece <NUM>.

<FIG> illustrates a section of the deposition head <NUM> and cooling applicator <NUM> of the example embodiment of <FIG> and <FIG>. As shown, powdered material M is carried through internal passages <NUM> in the deposition head <NUM>, and flows to a melt zone <NUM> at the deposition site, at which location the laser beam L provides energy that melts and sinters the powdered material M, causing it to bind (upon heating) and solidify (upon cooling) into solidified material M. It will be appreciated that deposition head <NUM> moves in a deposition direction relative to the workpiece <NUM> during deposition, with movement of either deposition head <NUM> or workpiece <NUM> or both being possible to accomplish this relative movement. The cooling of the deposited material occurs after the deposited material M is moved out of the melt zone <NUM> of the laser beam L, and/or after the laser beam L is turned off. Coolant C flows through the cooling applicator <NUM> and is directed to cool the deposited material M. As in <FIG>, the thermal sensor <NUM> is illustrated as having a range of measurement <NUM> that includes at least a portion of the deposited material M, and therefore can measure the thermal characteristic <NUM> of the deposited material M of a portion of the workpiece <NUM>. Feedback control of the cooling flow based on the measured thermal characteristic <NUM> will be described below.

<FIG> illustrates one possible cooling flow path of the example embodiment of <FIG>. As shown, coolant C is supplied from a coolant tank <NUM>, which is contained within an enclosure <NUM>, illustrated as a laser freeform manufacturing technology (LFMT) enclosure. The enclosure <NUM> is typically substantially airtight, i.e., hermetically sealed and substantially filled with an inert gas, such as argon. In this embodiment, the coolant C is an inert gas, such as argon, which is filtered and drawn into the coolant tank <NUM> for temporary storage and cooling. In other embodiments, another gas or a liquid may be used as the coolant C. The coolant C in the coolant tank <NUM> is flows under pressure generated by compressor <NUM> out of the enclosure <NUM> into cooler <NUM> for cooling and back into the enclosure <NUM>, passing through hose couplers <NUM> at the edge of the enclosure <NUM>. The compressor <NUM> is a bootstrap compressor that is powered by shop air, which is air from the environment that has been pressured to a working pressure via an external air compressor <NUM>. Other types of compressors may alternatively be used. Shop air is fed into the enclosure <NUM> through a coupler <NUM>, passes to the compressor <NUM> via a shop air loop line <NUM>, and powers a turbine <NUM> within the compressor <NUM>. The turbine <NUM> within the compressor <NUM> is mechanically linked to and rotates an impeller <NUM> in the cooling line <NUM>, thereby pressurizing the cooling line <NUM>. Shop air is fed out of the compressor <NUM> via the shop air loop line <NUM>, passes through the enclosure <NUM> via another coupler <NUM>, and is exhausted to environment. Valves V1, V2 are provided on the inlet side and within the enclosure <NUM> on the shop air loop line <NUM> for controlling flow of the shop air to compressor <NUM>. Valves V1 and V2 may be manually adjusted or actuated under the command of the controller <NUM>.

The cooler <NUM> is depicted as a vortex cooler in <FIG>. The cooler <NUM> transfers heat from the coolant C passing through the shop air cooler line <NUM> through cooler <NUM> to shop air, and exhausts hot shop air to the environment as shown. Compressor <NUM> is powered by shop air that is flowed in from outside enclosure <NUM> through a clear bowel <NUM>, pressure regulator <NUM>, and valve V2. The pressure at which the shop air is provided in shop air loop line <NUM>, which is proportional to the pressure in the cooling line <NUM>, is set according to the pressure setting <NUM>, which is set as part of cooling command <NUM> issued by the processor <NUM> of controller <NUM>.

Cooling command <NUM> issued by controller <NUM> includes either one or both of a flow rate command <NUM> and a temperature command <NUM>. The flow rate command <NUM> includes one or more valve settings <NUM>. One particular valve setting <NUM> included in the flow rate command is a coolant applicator valve setting that is transmitted to the applicator valve <NUM>, and which controls the flow rate of coolant C supplied by cooling line <NUM> and ejected toward the workpiece <NUM>. Other valve settings <NUM> may be included in the flow rate command and transmitted to the valves V1, V2, V3 to achieve a flow rate change in the cooling line <NUM>. Temperature command TMP may be transmitted to the cooler <NUM> to set a setpoint of the cooler to a desired temperature, and/or to adjust a valve setting of valve V4. In this manner the temperature of the coolant in cooling line <NUM> may be controlled. Alternatively, a plurality of independent cooling lines <NUM> may be provided and may be cooled to different temperatures, and a mixing valve may be provided as the applicator valve AV, and the temperature command may include a valve setting for the mixing valve, to thereby mix the two coolants C of different temperatures from the different cooling lines at a desired mixing ratio to achieve a desired temperature of the coolant C emitted to the workpiece.

Between the inbound coupler <NUM> on the cooling line <NUM> after the cooler <NUM>, sufficient flexible hose is provided in the cooling line <NUM> to accommodate movement of the coolant applicator <NUM> by robot <NUM> along a X power track, Y power track, and Z power track, in this order. In the depicted embodiments, the coolant applicator <NUM>, deposition head <NUM>, and thermal sensor <NUM> are co-mounted to one articulated robotic arm. Alternatively, a plurality of robotic arms may be provided and these components each may be independently mounted on a respective robotic arm. Further, other types of mechanisms besides an articulated robotic arm may be utilized to achieve the relative movement between the workpiece and the deposition head <NUM>, cooling applicator <NUM>, and thermal sensor <NUM>. For example, these three components may be mounted to a trunnion-style machine or a rotate swivel type machine, similar to a vertical axis or horizontal axis milling machine. With any of these configurations, the coolant applicator can realize a full range of motion in three dimensions to operate on the three-dimensional workpiece <NUM>, while still being supplied with coolant C.

<FIG> illustrates an example thermal history <NUM> for a portion of the three-dimensional workpiece <NUM>. The thermal history <NUM> includes a measured temperature for the portion of the workpiece, graphed in a solid line. The thermal history <NUM> also includes a first threshold temperature, illustrated by a dot-dash line, at which a flow rate of the coolant to the portion of the workpiece is adjusted, and a second threshold temperature, illustrated by a double dot dash line, at which a temperature of the coolant is adjusted. For the time at which the temperature exceeds the first temperature threshold, the coolant flow rate, indicated as a dotted line, is raised. This interval is referred to as the time above temperature for the first threshold temperature. The coolant flow rate drops back down once the temperature falls below the first threshold temperature. Further, when the temperature falls below the second threshold temperature, the coolant temperature, shows in a dash line, is reduced. Data regarding each of these parameters can be stored in thermal history <NUM> for later reference and comparison.

Turning now to <FIG>, another example of the thermal history <NUM> outputted in output data <NUM> is illustrated. As illustrated, the workpiece <NUM> may be divided into a plurality of three-dimensional voxels, roughly corresponding to the minimum deposition size, i.e., deposition resolution, of the additive manufacturing process. The illustrated thermal history <NUM> includes thermal data that has been measured on a voxel-by-voxel basis. Alternatively, the thermal history <NUM> may include thermal data for a range of voxels or for the workpiece in its entirety. It will be appreciated that the first portion <NUM> and second portion <NUM> illustrated in <FIG> may be respective voxels or respective ranges of voxels within the workpiece <NUM>. The illustrated thermal history <NUM> includes, for each voxel, a measure of time above temperature during the manufacturing process, and a coolant flow rate. As the cooling flow is applied, a temperature, flow rate, pressure, etc. of the cooling flow may be measured.

As shown in <FIG>, system <NUM> may implement a machine learning algorithm using a processor and associated memory of a training computing device to learn when cooling operations performed on workpieces <NUM> are potentially inadequate, and take appropriate measures using during the manufacturing process to ensure cooling operation adequacy. For example, a machine learning model <NUM> such as a convolutional neural network may be trained based on a training data set <NUM> to produce a trained classifier <NUM> that may be employed in additive manufacturing system <NUM> at run time to identify potential cooling inadequacies. The training data set <NUM> includes thermal history <NUM> of output data <NUM>, CAD model <NUM>, and test data <NUM>. The thermal history <NUM> includes, for each workpiece, the cooling settings <NUM> used during manufacture, the cooling commands <NUM> issued during manufacture, and the thermal measurements <NUM> of the thermal characteristics <NUM> of the workpiece <NUM> taken during manufacture. The CAD model <NUM> includes, for each workpiece <NUM>, the workpiece geometry. The CAD model <NUM> may also include the deposition path data used to manufacture the workpiece <NUM>. In the depicted example, the training data set <NUM> includes test data <NUM>, which in turn includes, for each workpiece <NUM>, the test results <NUM> of a predetermined quality test of post-manufacture quality testing. These results can be expressed as pass or fail, or may be other categories such as high quality, medium quality, low quality, etc. The test results <NUM> serve as ground truth in training the machine learning model <NUM>. The thermal measurements <NUM> of the thermal characteristics <NUM> taken with sensor <NUM> during manufacture of each workpiece may also be used as ground truth. To train the machine learning model <NUM>, in the case of a convolutional neural network, an input vector is formed including the cooling settings <NUM> and commands <NUM>, and the output classifications are set to be the results of the testing. In one embodiment, the thermal measurements <NUM> may be filtered and used as the ground truth output classifications. For example, the thermal measurements <NUM> may be filtered to two classifications, namely, "exceeded permitted time at temperature" and "did not exceed permitted time at temperature" for the workpiece. Using the thermal measurements <NUM> as the test data can greatly reduce training time of the neural network, by cutting down on the time necessary to prepare the training data set <NUM> for consumption by the convolutional neural network. By examining a training data set <NUM> for a large number of workpieces <NUM>, a trained classifier <NUM> can be produced that can be used to predict when a potential failure might occur for a workpiece <NUM> that is about to be manufactured. Specifically, the machine learning model <NUM> is trained using the training computing device at training time on the training data set <NUM> including the thermal history <NUM> for a plurality of workpieces, to thereby generate a trained classifier <NUM> executed by the processor <NUM> that predicts, at runtime, whether runtime input <NUM> of a set of cooling commands <NUM> and/or cooling settings <NUM> for use during manufacturing a current workpiece will result in a current workpiece that passes or fails the predetermined quality test.

To this end, at runtime, a runtime input <NUM> is received by the processor <NUM> of the AM system <NUM>. The runtime input <NUM> includes an input vector that can be inputted into the trained classifier <NUM>, which is loaded into memory <NUM> and executed by processor <NUM> at runtime. The input vector includes aspects of the geometry <NUM> of current workpiece <NUM> to be manufactured from the CAD model <NUM> for the current workpiece <NUM>, as well as cooling settings <NUM> (such as the valve settings <NUM> and pressure settings <NUM> for flow rate command <NUM>, and temperature setting for temperature command <NUM>) and cooling commands <NUM> from the thermal model <NUM> for the current workpiece. It will be appreciated that features may be identified in the geometry <NUM> of the workpiece <NUM>, and those features may be stored in a feature vector. The runtime input vector may be formed by concatenating the feature vector with a vector for the cooling settings <NUM> described above and a vector for the cooling commands <NUM> for the current workpiece <NUM>. Upon receiving the runtime input <NUM>, the trained classifier <NUM> is configured to output a classification result <NUM>. The classification result <NUM> is depicted indicate a pass <NUM> or a potential failure <NUM>, and each result typically has a confidence value associated with it, which is typically expressed in percentage form (e.g., potential failure (<NUM>%), pass (<NUM>%), etc.).

If the result <NUM> indicates a pass, then unmodified settings <NUM> are used for the comparison by the control program, similar to the process described with respect to <FIG>. If the result <NUM> indicates potential failure <NUM> with at least a threshold confidence value, such as <NUM>%, then the cooling settings (such as the threshold <NUM>, or first and second thresholds depicted in <FIG>) described above may be modified prior to comparison with the thermal characteristic <NUM> used to generate the cooling command <NUM>. The modification may be performed manually by an operator of the system <NUM> or may be performed programmatically according to preset rules or according to the results of a generative neural network or other model that is trained to generate cooling settings that do not lead to failure under test conditions, for example. If modified settings <NUM> are used, the control program <NUM> is configured to compare the thermal characteristic <NUM> to the modified threshold 50A, and if the modified threshold 50A is exceeded to adjust the cooling flow based on a modified cooling parameter such as a modified cooling temperature or a modified flow rate, at <NUM>. The control program <NUM> outputs the cooling command <NUM> based on the modified cooling parameter, to thereby cool the workpiece with coolant appropriately.

In another aspect, system <NUM> may be used to compare the cooling operations performed on two different workpieces <NUM>. For example, the processor <NUM> may output a flow rate command to set the flow rate of the coolant C, and a time duration of the coolant application. After the cooling flow is applied, the amount of cooling flow may be stored in memory <NUM>. The amount of cooling flow may be stored in thermal history <NUM> of a first workpiece, for example, to inform the setting of cooling parameters in future AM processes. Accordingly, when a second workpiece is manufactured using the same AM process as the first workpiece, the thermal histories <NUM> of the first workpiece and the second workpiece may be compared to verify that the material properties of the first workpiece and the second workpiece are similar. In addition to the data described elsewhere herein as being included within the thermal history <NUM>, in this aspect the thermal history <NUM> may include a time stamp and location stamp indicating when cooling flow was applied during the AM process, where the cooling flow was applied on the workpiece, and how much cooling flow was applied on the workpiece each time the cooling flow was applied. In addition, the thermal history <NUM> may include a time stamp and location stamp indicating the thermal characteristic of the portion at each point in time of the AM process. When multiple thermal histories are collected in this manner, a neural network such as that described in relation to <FIG> may be applied to the thermal histories to develop a machine learning model that is trained to predict which portions of the workpiece will require cooling, and how much cooling flow each portion of the workpiece will require.

<FIG> illustrates a flow chart of an example configuration of a first method <NUM> according to one aspect of the present disclosure. The following description of method <NUM> is provided with reference to the software and hardware components described above and shown in <FIG>. It will be appreciated that method <NUM> also may be performed in other contexts using other suitable hardware and software components.

At step <NUM>, the method includes depositing material onto a substrate to form a shape of the workpiece in accordance with an AM process. At step <NUM>, the method includes determining a thermal characteristic of at least a portion of the workpiece during the AM process. At step <NUM>, the method includes storing the determined thermal characteristic of the portion of the workpiece in memory as part of a thermal history of the workpiece. The thermal characteristic may be continuously monitored during this determination. At step <NUM>, it is determined whether the thermal characteristic of at least the portion exceeds a threshold associated with the portion. At step <NUM>, responsive to determining that the thermal characteristic of at least the portion does not exceed a threshold associated with the portion, the cooling application is decreased or turned off. At step <NUM>, the deposition of material is continued.

At step <NUM>, responsive to determining that the thermal characteristic of at least the portion exceeds the threshold associated with the portion, a cooling parameter of a cooling flow to be applied to the workpiece is adjusted. At step <NUM>, the cooling flow is applied with the adjusted cooling parameter to at least the portion of the workpiece. At step <NUM>, the amount of cooling flow may also be tracked or measured. At step <NUM>, a thermal characteristic is again determined of at least a portion of the workpiece. The threshold of step <NUM> may be different from the threshold of step <NUM>, or the thresholds may be configured differently from each other. It will be appreciated that, when continuous monitoring is performed, the determination of the thermal characteristic may be continuously performed during all steps of the method <NUM>. An amount of the cooling flow may be tracked or measured. After the cooling flow is applied, the amount of cooling flow may be stored in memory at step <NUM>. The amount of cooling flow may be stored as a thermal history of the workpiece to inform the setting of cooling parameters in future manufacturing processes. The thermal history may include a time stamp and location stamp indicating when cooling flow was applied during the AM process, where the cooling flow was applied on the workpiece, and how much cooling flow was applied on the workpiece each time the cooling flow was applied. In addition, the thermal history may include a time stamp and location stamp indicating the thermal characteristic of the portion at each point in time of the AM process. Accordingly, when a second workpiece is manufactured using the same AM process as a first workpiece, the thermal histories of the first workpiece and the second workpiece may be compared to verify that the material properties of the first workpiece and the second workpiece are similar.

At step <NUM>, it is determined whether the thermal characteristic of at least the portion exceeds a threshold associated with the portion. Responsive to determining that thermal characteristic of at least the portion exceeds the threshold associated with the portion, the method <NUM> returns to step <NUM> to adjust the cooling parameter of the cooling flow. Responsive to determining that the thermal characteristic of at least the portion does not exceed the threshold associated with the portion, the method <NUM> returns to step <NUM> to continue the deposition of material. However, in another embodiment, responsive to determining that thermal characteristic of at least the portion does not exceed the threshold associated with the portion, the method <NUM> may proceed to step <NUM>, determining whether the portion is finished, or no further deposition of the portion is necessary. When the determination is negative, the method <NUM> may continue to step <NUM> to continue the deposition of material at the portion. When the determination is positive, the method may continue to step 702A shown in <FIG>.

Although method <NUM> is described as adjusting the cooling parameter of the cooling flow based on the thermal characteristic of the portion, alternatively the cooling parameter of the cooling flow may be adjusted based on a subsequent value for the thermal characteristic is determined at a later point in time. Therefore, at steps <NUM> and <NUM>, instead of determining the thermal characteristic of the portion, a subsequent value for the thermal characteristic may be determined at a later point in time. At steps <NUM> and <NUM>, instead of determining whether the thermal characteristic of the portion exceeds a threshold associated with the portion, it may be determined whether the subsequent value of the thermal characteristic is lower than the threshold associated with the portion. At step <NUM>, alternatively, the adjusted cooling parameter of the cooling flow that is applied to at least the portion of the workpiece may be reduced, responsive to determining that the subsequent value for the thermal characteristic is lower than the threshold.

<FIG> illustrates a flow chart of operations performed in continuation of the method <NUM> of <FIG>. The following description of method <NUM> is provided with reference to the software and hardware components described above and shown in <FIG>. It will be appreciated that method <NUM> also may be performed in other contexts using other suitable hardware and software components. Method <NUM> continues from step <NUM> responsive to determining that thermal characteristic of at least the portion does not exceed the threshold associated with the portion.

At step 702A, method includes depositing material onto the substrate to form a shape of the workpiece in accordance with an AM process. The material may be the same or different from the material used in the operations of <FIG>. The deposition of material occurs at a second portion of the workpiece. At step 704A, the thermal characteristic is determined of the second portion of the workpiece. At step 720A, the determined thermal characteristic of the second portion of the workpiece may be stored in memory as part of a thermal history of the workpiece. The thermal characteristic may be continuously monitored during this determination. At step 706A, it is determined whether a thermal characteristic of the second portion exceeds a second threshold associated with the second portion, the second threshold configured to be different from the first threshold. In this embodiment, the portion, the threshold, and the cooling parameter discussed in relation to <FIG> are the first portion, the first threshold, and the first cooling parameter, respectively. At step 708A, responsive to determining that the thermal characteristic of at least the portion does not exceed a threshold associated with the portion, the cooling application is decreased or turned off. At step 702A, the deposition of material is continued.

At step 710A, responsive to determining that the thermal characteristic of the second portion exceeds the second threshold associated with the second portion, a second cooling parameter of a cooling flow to be applied to the workpiece is adjusted, the second cooling parameter configured to be different from the first cooling parameter. At step 712A, cooling flow is applied with the second cooling parameter to the second portion of the workpiece. At step 712A, the amount of cooling flow may also be tracked or measured. At step 714A, a thermal characteristic is again determined of the second portion of the workpiece. It will be appreciated that, when continuous monitoring is performed, the determination of the thermal characteristic may be continuously performed during all steps of the method <NUM>. After the cooling flow is applied, the amount of cooling flow may be stored in memory at step 720A. The amount of cooling flow may be stored as a thermal history of the workpiece to inform the setting of cooling parameters in future manufacturing processes. The thermal history may include a time stamp and location stamp indicating when cooling flow was applied during the AM process, where the cooling flow was applied on the workpiece, and how much cooling flow was applied on the workpiece each time the cooling flow was applied. In addition, the thermal history may include a time stamp and location stamp indicating the thermal characteristic of the portion at each point in time of the AM process. The threshold of step 706A may be different from the threshold of step 716A, or the thresholds may be configured differently from each other.

At step 716A, it is determined whether the thermal characteristic of the second portion exceeds the second threshold associated with the second portion. Responsive to determining that thermal characteristic of the second portion exceeds the second threshold associated with the second portion, the method returns to step 710A to adjust the second cooling parameter of the cooling flow. At step 718A, responsive to determining that the thermal characteristic of the second portion does not exceed the second threshold associated with the second portion, it is determined whether the second portion is finished, or no further deposition of the second portion is necessary. When the determination is negative, the method <NUM> may continue to step 702A to continue the deposition of material at the second portion. When the determination is positive, the method <NUM> may terminate.

Although only a first portion <NUM> and a second portion <NUM> are depicted in the Figures, it will be appreciated that the thermal characteristics of a plurality of portions, or more than two portions, may be measured, each of the plurality of portions having a corresponding upper threshold, a corresponding lower threshold, and a corresponding threshold period of time. Subsequent to determining whether a thermal characteristic of a given portion of the plurality of portions exceeds the corresponding upper threshold associated with the given portion for the corresponding threshold period of time at which the corresponding upper threshold is exceeded, and responsive to determining that the thermal characteristic of the given portion exceeds the corresponding upper threshold associated with the given portion for the corresponding threshold period of time associated with the given portion, the deposition of material may be paused and coolant application increased to the given portion. Coolant may be applied until it is determined that the thermal characteristic of the given portion is lower than the corresponding lower threshold associated with the given portion. Coolant application may be decreased, and the deposition of material resumed responsive to determining that the thermal characteristic of the given portion is below the corresponding lower threshold associated with the given portion for the corresponding threshold period of time associated with the given portion.

Through active, in-process thermal cooling of AM components cooling rates, microstructure, mechanical properties, distortion, build geometry and stability can be further refined or controlled. The in-process cooling, in some applications, can inhibit a portion from becoming too hot and during processing. By controlling the cooling of an AM component, and the thermal profile subjected to the part during processing, the resultant microstructure can be altered to achieve desired mechanical properties. Establishing an in-process cooling method can have the potential benefit of balancing the effects from differences in thermal mass of a component geometry.

The systems and processes describe herein have the potential benefit of significantly reducing cycle times for AM components by eliminating stress relief or heat treatment processes typically required, allowing for tailored microstructures of AM components, increasing mechanical properties to desired needs.

Further, the disclosure comprises:
There is disclosed a method for use in additive manufacturing of a three-dimensional workpiece not falling under the scope of the claimed invention, comprising: depositing material onto a substrate to form a shape of the workpiece in accordance with an additive manufacturing process; determining a thermal characteristic of at least a portion of the workpiece during the additive manufacturing process; determining that the thermal characteristic of at least the portion exceeds a threshold associated with the portion; adjusting a cooling parameter of a cooling flow to be applied to the workpiece responsive to determining that the thermal characteristic of at least the portion exceeds the threshold associated with the portion; and applying the cooling flow with the adjusted cooling parameter to at least the portion of the workpiece.

Preferably, the cooling parameter is at least one of a coolant flow rate and a coolant temperature.

Preferably, the thermal characteristic of the portion is determined by measuring a surface temperature of the portion.

Preferably, the surface temperature of the portion is measured by at least one of a pyrometer, an infrared camera, and a thermometer.

Preferably, the thermal characteristic is time at temperature, and the threshold includes a threshold period of time at which a threshold temperature is exceeded.

Preferably, the thermal characteristic is determined based on a computational simulation using a thermal model of the additive manufacturing process for the workpiece.

Preferably, the thermal characteristic of the portion is determined by modeling at least one of a surface temperature or an internal temperature of the portion.

Preferably, a coolant of the cooling flow is a liquid or a gas, and the material is a metal.

Preferably, the portion is a first portion; the threshold is a first threshold; the workpiece further includes a second portion; the cooling parameter is a first cooling parameter; and the method further comprises: decreasing coolant application and continuing the deposition of material responsive to determining that the thermal characteristic of at least the first portion is below the first threshold associated with the first portion; determining whether a thermal characteristic of the second portion exceeds a second threshold associated with the second portion, the second threshold configured to be different from the first threshold; adjusting a second cooling parameter of a cooling flow to be applied to the workpiece responsive to determining that the thermal characteristic of the second portion exceeds the second threshold associated with the second portion, the second cooling parameter configured to be different from the first cooling parameter; applying the cooling flow with the second cooling parameter to the second portion of the workpiece; and decreasing coolant application and continuing the deposition of material responsive to determining that the thermal characteristic of the second portion is below the second threshold associated with the second portion.

Preferably, the method further comprises: determining a subsequent value for the thermal characteristic at a later point in time; determining that the subsequent value of the thermal characteristic is lower than the threshold associated with the portion; and reducing the adjusted cooling parameter of the cooling flow applied to at least the portion of the workpiece responsive to determining that the subsequent value for the thermal characteristic is lower than the threshold.

Also, there is disclosed an additive manufacturing system not falling under the scope of the claimed invention comprising: an additive manufacturing deposition head; a cooling applicator configured to apply coolant; a processor operatively coupled to the deposition head and the cooling applicator; and a memory storing instructions that, when executed by the processor, cause the apparatus to: deposit material onto a substrate to form a shape of a workpiece in accordance with an additive manufacturing process; determine a thermal characteristic of at least a portion of the workpiece during the additive manufacturing process; determine that the thermal characteristic of at least the portion exceeds a threshold associated with the portion; adjust a cooling parameter of a cooling flow to be applied to the workpiece responsive to determining that the thermal characteristic of at least the portion exceeds the threshold associated with the portion; and applying the cooling flow with the adjusted cooling parameter to at least the portion of the workpiece.

Preferably, the portion is a first portion; the threshold is a first threshold; the workpiece further includes a second portion; the cooling parameter is a first cooling parameter; and the memory stores instructions that, when executed by the processor, further cause the apparatus to: decrease coolant application and continue the deposition of material responsive to determining that the thermal characteristic of at least the first portion is below the first threshold associated with the first portion; determine whether a thermal characteristic of the second portion exceeds a second threshold associated with the second portion, the second threshold configured to be different from the first threshold; adjust a second cooling parameter of a cooling flow to be applied to the workpiece responsive to determining that the thermal characteristic of the second portion exceeds the second threshold associated with the second portion, the second cooling parameter configured to be different from the first cooling parameter; apply the cooling flow with the second cooling parameter to the second portion of the workpiece; and decrease coolant application and continue the deposition of material responsive to determining that the thermal characteristic of the second portion is below the second threshold associated with the second portion.

Preferably, the thermal characteristic of at least the portion is stored in memory as part of a thermal history of the workpiece.

Preferably, the thermal history includes at least one of a measured temperature for at least the portion of the workpiece, the threshold associated with the portion, cooling settings used during manufacture, and cooling commands issued during manufacture.

Preferably, the system further comprises: a machine learning model that is trained using a training computing device at training time on a training data set including the thermal history for a plurality of workpieces, to thereby generate a trained classifier implemented via the processor that predicts, at runtime, whether runtime input of a set of cooling commands and/or cooling settings for use during manufacturing a current workpiece will result in a current workpiece that passes or fails a predetermined quality test.

Still further, there is disclosed a method for additive manufacturing of a three-dimensional workpiece not falling under the scope of the claimed invention, comprising: depositing material onto a substrate to form a shape of the workpiece in accordance with an additive manufacturing process; measuring thermal characteristics of a plurality of portions of the material, each of the plurality of portions having a corresponding upper threshold, a corresponding lower threshold, and a corresponding threshold period of time; determining whether a thermal characteristic of a given portion of the plurality of portions exceeds the corresponding upper threshold associated with the given portion for the corresponding threshold period of time at which the corresponding upper threshold is exceeded; pausing the deposition of material and increasing coolant application to the given portion responsive to determining that the thermal characteristic of the given portion exceeds the corresponding upper threshold associated with the given portion for the corresponding threshold period of time associated with the given portion; applying the coolant until it is determined that the thermal characteristic of the given portion is lower than the corresponding lower threshold associated with the given portion; and decreasing coolant application and resuming the deposition of material responsive to determining that the thermal characteristic of the given portion is below the corresponding lower threshold associated with the given portion for the corresponding threshold period of time associated with the given portion.

Claim 1:
A method (<NUM>) for use in additive manufacturing of a three-dimensional workpiece (<NUM>), comprising:
depositing material (M) onto a substrate (<NUM>) to form a shape of the workpiece (<NUM>) in accordance with an additive manufacturing process;
determining a thermal characteristic (<NUM>) of a portion (<NUM>) of the workpiece (<NUM>) during the additive manufacturing process;
determining that the thermal characteristic (<NUM>) of the portion (<NUM>) exceeds a threshold (<NUM>) associated with the portion (<NUM>);
adjusting a cooling parameter of a cooling flow to be applied to the workpiece (<NUM>) responsive to determining that the thermal characteristic (<NUM>) of the portion (<NUM>) exceeds the threshold (<NUM>) associated with the portion (<NUM>); and
applying the cooling flow with the adjusted cooling parameter to the portion (<NUM>) of the workpiece (<NUM>);
characterized in that, the thermal characteristic (<NUM>) is one of:
temperature gradients; or
peak temperature over time or within a region; or
average temperature over time or within a region.