The present disclosure relates generally to additive manufacturing, and more specifically to techniques for thermal management using re-coaters in powder bed fusion-based three-dimensional printers.
Powder bed fusion (PBF)-based three-dimensional (3-D) printers generally use high-powered energy sources, such as lasers and electron beams, to selectively fuse and solidify layers of metallic powder deposited onto powder beds using re-coaters. These high energy sources can cause large thermal gradients in the powder bed during the print cycle when the fusion process occurs. These large thermal gradients, in turn, can cause stresses in the solidified material which can lead to cracks, deformations, and reduced life cycles of the printed parts. In addition, cooler temperatures of powder applied to the powder bed with respect to the fused layer can result in reduced thermal conductivity in the subsequent print cycle, which can reduce dimensional accuracy in the part and cause distortion.
Various aspects of the disclosure are set forth herein. According to one aspect of the disclosure, a re-coater for a powder bed fusion (PBF) three-dimensional (3-D) printer includes a heat source configured to heat a powder layer, the powder layer being deposited by the re-coater during a re-coat cycle.
According to another aspect of the disclosure, a powder bed fusion (PBF) three-dimensional (3-D) printer having an integrated thermal management system includes a re-coater configured to deposit a layer of powder onto a powder bed during a re-coat cycle, at least one energy beam source configured to selectively fuse the powder during a print cycle to form a build piece, and a heat source configured to heat the powder during the re-coat cycle.
According to another aspect of the disclosure, a re-coater for a powder bed fusion
(PBF) three-dimensional (3-D) printer includes a body to traverse a surface of a powder bed during a powder re-coating cycle, a leveling member coupled to the body to level a layer of powder on the powder bed, and a heat source coupled to the body to heat the powder.
Other aspects will become readily apparent to those skilled in the art from the following detailed description, wherein is shown and described only several embodiments by way of illustration. As will be realized by those skilled in the art, concepts herein are capable of other and different embodiments, and several details are capable of modification in various other respects, all without departing from the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
Powder-based-fusion (PBF) 3-D printing, a category of additive manufacturing (AM), is becoming ubiquitous in a number of industries that rely on the production of custom components. Examples include the automobile, aircraft, and transportation industries in general, among many other businesses for which AM applications have been used for producing consumer products. AM harbors this capability because manufacturers can use existing computer-aided-design (CAD) technologies to design and print structures with virtually limitless shapes and geometries. Conventionally, manufacturers have relied on expensive and project-specific tooling to produce unique parts for their product lines. This tooling often becomes obsolete when the projects have run their courses, at which time the manufacturer must often acquire expensive new tooling as a necessary prerequisite for producing new or different product designs. AM has therefore become a desirable alternative for many manufacturers to these expensive and limiting manufacturing practices.
PBF-based technologies represent a category of 3-D printers that use lasers, electron beams, or similar energy sources to produce primarily metal-based components and alloys. Examples of PBF technologies include, among many others, Direct Metal Laser Sintering (DMLS), Selective Laser Melting (SLM), Direct Metal Printing (DMP), and Direct Metal Laser Melting (DMLM). The AM process begins with a designer using a CAD program to model a 3-D representation of the part that will be printed. During a subsequent computer-aided-modeling (CAM) stage, support structures may be modeled, if needed. When a 3-D build piece is being printed, in some instances the build piece may include overhangs. The support structures are arranged under these overhangs to prevent the build piece from deforming due to gravity. In some embodiments, support structures may be incorporated into the 3-D print process, or the need for support structures may be eliminated altogether if a clever design is adopted.
After a 3-D representation of the component is modeled using a suitable CAD program, the 3-D model is “sliced” during a slice stage. In particular, a 3-D representation of the model is partitioned into a plurality of individual layers by a software application known as a slicer to thereby produce a set of instructions for 3-D printing the object. Slicer programs convert the 3-D component model into a series of individual layers representing thin slices (e.g., about 100 microns thick) of the object be printed. The sliced representation of the 3-D model is then compiled, and printer-specific instructions for 3-D printing the model are produced. These software components are uploaded as necessary to electronic storage components in the 3-D printer for access by a print controller to initiate and enable the print process. As explained below, during this process, each layer is individually deposited into a powder bed during a re-coat cycle. Thereafter, the re-coater device moves off the powder bed surface and a print cycle occurs. During the ensuing print cycle, one or more primary energy beam sources use deflectors to selectively fuse and solidify designated portions of the layer that constitute sections of the printed component, also called the build piece. After the print cycle, a re-coat cycle occurs in which the 3-D printer deposits a fresh layer of powder material into the powder bed to ready the printer for the next print cycle. Another print cycle occurs, followed by another re-coat cycle, and so on. In this way, the build piece is constructed layer-by-layer in a vertical fashion until it is complete.
A wide variety of PBF 3-D printers with different attributes and controller implementations are available, and many are customizable based on user preferences. The foregoing is intended to describe non-limiting embodiments of one such examples. The principle of operation of PBF 3-D printer 100 lies in reproducing the 3-D model by depositing and then selectively fusing, or solidifying through an energy beam source 103 (or plurality thereof), layers of a suitable powder 192 to form build piece 109 as described below. Powder 192 can be a metallic powder or an alloy, and serves as the print material for PBF 3-D printer 100.
During a current re-coat cycle as illustrated, a re-coater 102 traverses a horizontal axis of motion to deposit a powder layer 194 over a previously-deposited powder layer. During preceding re-coat cycles, the powder layers were deposited by re-coater 102 one over the other, beginning originally with a first powder layer deposited on a substrate such as a build plate 107. In
Following a re-coat cycle in which the powder layer is deposited, a print cycle may occur to solidify portions of that powder layer. Energy beam source 103 can be collimated to produce the precise energy beam needed to selectively melt and then solidify selected cross-sectional regions of the deposited powder layers during the ensuing print cycle. In particular, energy beam source 103 melts selected regions of the powder layer by emitting an energy beam (e.g., a laser, electron beam, etc.) at a deflector 105. The deflector can dynamically be oriented at various predetermined angles as controlled by instructions from print controller 183. The resulting energy beam emitted by energy beam source 103 and reflected from deflector 105 strikes and thereby melts the selected regions of the powder layer. After the temperature cools, the melted portions cool and solidify. The remaining unfused powder 192a can be removed later for recycling.
During this time, re-coater 102 has moved away from the print area to avoid interfering with the print cycle. For example, re-coater 102 may position itself at the far right just above a right powder bed receptacle wall 112b, if during its immediately prior re-coat cycle the re-coater moved from left to right. Likewise, if the last re-coat cycle caused the re-coater to end on the left side, the re-coater can position itself at the far left above a left powder bed receptacle wall 112a.
Referring back to the print cycle, in
PBF 3-D printer 100 may include a chamber 113 in which the basic print elements are arranged. The chamber may be pre-filled with an inert gas, such as argon. The chamber advantageously isolates the print elements from unwanted particles or other elements in the air. Further, because argon is inert, the print material in chamber 113 is not likely to perform unwanted chemical reactions. For example, absent the isolating chamber, powder 192 would likely engage in unwanted oxidation reactions due to the oxygen in the air. Other undesirable chemical reactions result. Sealing the print elements and housing them in chamber 113 with an appropriate inert substance, as shown in
Build plate 107 is arranged at a horizontal base of 3-D printer 100 adjacent a build floor 111. The build plate is also adjacent powder bed receptacle walls 112a-b on each side to collectively form powder bed 121. Build floor 111 may include a piston 141 configured to successively move build plate 107 downward in a vertical manner after each print cycle. Piston 141 may move build floor 111 vertically downward for a distance after each print cycle that coincides with a thickness of powder layer 194. In this manner, piston 141 can keep the surface of powder bed 121 and build piece 109 at a fixed distance from energy beam source 103, enabling piston 141 to help ensure print uniformity. In short, piston 141 operates to periodically move build floor 111 downward to prevent the powder layers from accumulating at the top of powder bed 121, which in turn provides a substantially fixed distance for enabling PBF 3-D printer 100 to complete build piece 109 of any size that otherwise fits within chamber 113, governed by the printer's specifications.
In an embodiment, PBF 3-D printer 100 includes a hopper 115, which is a storage structure primarily used to store powder 192 that will be used during the re-coat cycles. In other embodiments, the powder storage mechanism may be in a reservoir adjacent one of powder bed receptacle walls 112a-b, in some cases using a mechanism similar to piston 141 to push the powder in the reservoir upward for easier acquisition as more layers 194 are formed and more powder 192 is needed. In the embodiment shown, hopper 115 is connected to re-coater 102. The re-coater 102 can receive powder 192 from hopper 115 (or, in other embodiments, from a separate source) before traversing the surface of powder bed 121 to successively deposit the thin and uniform layers of powder 192 as described above. Hopper 115 may, but need not, be permanently connected to re-coater 102. In an embodiment, hopper 115 may use one or more apertures or channels, or tubes (collectively represented by the small black member in between hopper 115 and re-coater 102) to fill an open cavity present in the re-coater 102 with powder 192 as needed, so that the re-coater 102 can refill its stock of powder 192 when running low. In this embodiment, re-coater 102 can periodically reconnect with hopper 115 above left powder bed receptacle wall 112a to receive refills as needed. In other embodiments, hopper 115 is permanently attached to re-coater 102 and moves along with re-coater 102 during a re-coat cycle.
Referring still to
Alternatively, the re-coater 102 can be bi-directional. In this case, re-coater 102 can move in both left and right directions in the printer shown and may, for example, return from right powder receptacle wall 112b after the print cycle, during which time the re-coater and leveler deposit another layer. After this re-coat cycle, re-coater may then move to left powder bed receptacle wall 112a and out of the way before the next print cycle begins.
In an aspect of the disclosure, heat source 175 is coupled to re-coater 102. Heat source 175 will be described further below.
As described above with reference to
As the temperatures reduce and the energy beam moves on to fuse other portions of the layer, the weld pool quickly reduces in temperature and causes the local portion of the layer to solidify into the general shape intended by the energy beam source. The energy beam source 103 activity continues during this print cycle until the remaining selected portions of the layer has been fused. The powder 192 not fused during the layer falls into powder bed 121 as shown. The print cycle is complete, and the re-coater 102 readies itself for deposition of the next successive layer. This downward shift ensures that the powder bed remains between powder bed receptacle walls 112a-b and that re-coater 102 and energy beam source 103 remain at the same relative distance from a surface of powder bed 121 during the printing of each layer. at the end of the build job, the build piece 109 can be extracted and PBF 3-D printer 100 can be readied for the next component as determined by the next 3-D model.
The above description of a PBF printer is exemplary in nature. As described above, a number of specific PBF designs and products are available, and these known designs and products are intended to fall within the scope of the present disclosure. Other PBF systems are similar in functionality in terms of the techniques relevant to this disclosure, and therefore the concepts herein apply with equal force to other such PBF printers.
A deficiency noted above with all such PBF printers is that the thermal gradients introduced to the different layers can be large. These gradients can crack the build piece, or cause deformation over time. More precisely, during the print cycle, the metallic powder material that is deposited at room temperature to form a given layer can be suddenly exposed to very high temperatures when struck by the energy beam from deflector 105 and energy beam source 103. In some cases, the selectively fused powder goes from room temperature to a very high temperature in a very small amount of time. Thereafter, the fused powder in the layer is left to solidify as the temperature again drops quickly from a very high value back toward room temperature. In addition, immediately after the print cycle, there may be a number of warm or hot areas of the layer adjacent the remainder of the layer, the latter of which may be comparatively cooler.
In addition to the thermal gradients directly experienced by the fused regions in each layer, local thermal gradients are also present between the hot fused powder regions (e.g., fused powder region 163) and the non-printed regions of unfused powder 192a. This latter class of local thermal gradients can also abruptly introduce high temperatures and can result in additional thermal stresses to the material as a result. That is to say, the hot, fused regions cool faster than the adjacent unfused regions. These temperature differentials can often cause structural problems.
More precisely, the thermal gradients introduced during the print cycle are often higher than the powder material can reasonably withstand. The fast temperature changes can result in thermal stresses (whether or not visible), cracks, dimensional inaccuracies, structural deformations and other problems that occur during the process or after a shortened lifetime when the manufacturers have extracted the build piece 109 and have inserted it, for example, as a component in a vehicle or other mechanical structure.
Practitioners in the art have recognized the problems associated with significant temperature transients in the powder, but unfortunately few if any viable solutions have been proposed. The attempts to reduce this problem to date have included generally heating the entire chamber of the PBF 3-D printer 100, or attempting to heat the entire powder bed by heating the build plate 107. Heating temperatures in these cases may be from 200 to 400° or greater. These prior approaches generally rely on non-local, continuous heating mechanisms that consume a large amount of energy and that are not directed at the problem areas, i.e. the thermal gradients produced at the top layer of each system. More specifically, globally heating the entire print chamber fails to target the problem areas, as does heating the build plate, which, as the build job progresses, may eventually be dozens or hundreds of layers away from the site of the thermal gradients. These conventional approaches instead place potentially unnecessary heating stresses on unaffected portions of the PBF 3-D printer 100. Moreover, such global heating represents a grossly inefficient and expensive solution in terms of the energy expenditure.
In contrast to these prior approaches, direct heating of the powder as described in this disclosure helps to maintain a constant powder bed temperature, in contrast to simply increasing the temperature of the chamber or the build plate as in conventional proposals. In particular, in one aspect of the disclosure, heat source 175 (
Unlike in prior approaches, one advantageous aspect of the present disclosure is that re-coater 102 is capable of both pre-heating and reheating the affected areas as described. This technique can more efficiently improve the printing of particularly crack-sensitive metals and alloys, given that crack sensitivity can be highly dependent on the thermal stress characteristics of the build piece 109.
In the center of re-coater 102, powder 192 is received via a channel from hopper 115 as described above. Hopper 115 is illustrated with a different texture than re-coater 102 to enable a viewer to more easily distinguish these structures. Re-coater 102 may have additional channels at a posterior surface adjacent the leveling member (see
As powder 192 exits the re-coater during the re-coat cycle and the re-coater 102 traverses the powder bed 121 at a fixed height above the surface of the powder, heat source 175 emits a heat flow 119 in the gap defined by the distance between a posterior surface of the heat source 175 and the surface of powder bed 121 where the next layer is being deposited. Adjacent leveling member 167 where powder 192 is smoothened after exiting re-coater 102, heat source 175 emits heat flow 119 to pre-heat the powder to a predesignated temperature, which may be set by print controller 183. The lines of heat, representing radiation in the form of photons or the like, can be emitted from the heating elements on heat source 175. In the embodiment shown, heat source 175 is configured to heat both the surface layers in front of and behind leveling member 167 as re-coater 102 moves to the right. Once the re-coater 102 reaches the far side of powder bed, the re-coater 102 may move out of the path of the powder layer and above right powder bed receptacle wall 112b in order to allow the print cycle to commence on the recently deposited layer.
As the print cycle is conducted, the areas on the layer corresponding to the software 3-D model are fused under the command of print controller 183. Because the powder is, immediately prior to the print cycle, warmer than it would have been due to the application of heat source 175 during the re-coat cycle, the heating caused by energy beam source 103 during the print cycle results in a less dramatic thermal gradient. That is, when the fused powder begins to cool and solidify, it already was heated, and therefore the heating transient over a short time t is reduced. Thermal stresses are therefore immediately and locally reduced without the necessity of pre-heating the entire chamber or the entire print bed.
In an embodiment, a reheating procedure immediately follows the print cycle. The purpose of the reheating procedure is to further reduce thermal transients, and therefore reduce thermal stresses that can otherwise cause part failures down the line. Re-coater 102 may be bi-directional and may return from the right side back to the left side of PBF 3-D printer 100. During the trip from right to left, heat source 175 again emits thermal radiation over the cooling powder bed (e.g., using a raster scan) to further ensure that thermal gradients are minimized. After the print cycle, re-coater 102 may engage in the next re-coat cycle, whereby it travels over the powder bed from left to right to deposit a next layer and pre-heat the layer. The print cycle repeats in the manner described above, and so on until the build is complete.
In an alternative embodiment, re-coater 102 is further bi-directional in that it includes posterior apertures (see
At the bottom of the re-coater 102, a generally rectangular heat source 175 is coupled to the lower or posterior surface of re-coater 102. Mechanical elements such as screws 110 may be used to connect the heat source 175 to the re-coater 102. The heat source 175 in this embodiment is shaped such that, unlike conventional approaches, it can bi-directionally apply heat locally to the deposited powder as it traverses the powder bed above the pre-determined gap. In particular, heat source 175 includes edge 104a on one side of re-coater 102, and edge 104b on the other side of re-coater 102. Thus, in this embodiment, heat source 175 is symmetrically positioned on both sides of re-coater and is optimized for heating the powder bed in either direction based on bi-directional movement of re-coater 102. While the leveling member 167 deposits and levels the layers during the re-coat cycles (
In the example shown, the dashed elements represent an arrangement of heating elements 173, such as light emitting diodes, that are positioned on a posterior surface of heat source 175. To increase the maximum heat exposure to the surface of powder bed 121, the heating elements extend from the posterior surface at edge 104a across the posterior surface to edge 104b, interrupted only by the portion of re-coater 102 used for depositing powder (e.g., blade 338 and the aperture described below). As is evident from the illustration, the rectangular shape of heat source 175 is configured to cover the edges on each side of powder bed 121 such that heat can be applied to the entire powder bed as the re-coater 102 moves from side to side during re-coat cycles. In other embodiments, heating elements 173 are confined to the posterior surface of heat source 175 (obscured from view), where they are distributed across the posterior surface from edge 104a to edge 104b on both sides of re-coater 102.
In an embodiment, heat source 175 includes electronic solid-state circuitry to control the temperature and activation/deactivation of heating elements 173, and also to interface with print controller 183 as needed. These electronics may alternatively be included in re-coater 102. The re-coater may have an internal plug that leads to a power source in PBF 3-D printer 100 for controlling the heating elements.
As blade 338 deposits and levels powder 328, a series of heating elements such as LED lights emit photons across the plane of the lower member of the heat source 175 in gap 361 to heat the deposited powder to a temperature designated by the print controller. As the re-coater 102 moves from left to right, a first set of heating elements (conceptually shown by photons 333) heats the powder bed 324 that has yet to receive the new layer. After the topmost layer of layers 370 is deposited, heat source 175 has additional heating elements (conceptually shown by photons 334) that apply a designated amount of heat to the deposited layer. The re-coater traverses powder bed 324 until it reaches the other side. Thereupon, in one embodiment, the print cycle begins as re-coater 102 remains out of the way of powder bed 324. In another embodiment following arrival at the right of the printer, re-coater 102 can return left back to a position out of the way of the powder bed while applying additional heat (333 and 334) but without disturbing the new layer 334. In this alternative embodiment, the print cycle begins right after the re-coater 102 arrives on the left side of the 3-D printer.
In either case, the print cycle can begin after the re-coat cycle. Heat source 175 selectively fuses the layer based on the data model provided by the CAD program and the corresponding print instructions. Thereafter, re-coater 102 can reheat the powder bed as the new components are solidified by traversing the powder bed again and applying heat 333/334 via gap 361.
Briefly referring back to
The array of heating elements of the embedded heat source of re-coater 102 helps assure reduction of thermal stresses to benefit crack-sensitive materials and to improve overall component quality while concurrently maximizing efficiency of power use by, among other attributes, applying direct heating to the layers separated by a small gap.
A series of first apertures 404 are disposed linearly across posterior surface 402 of re-coater 102 on one side to deposit powder for one of the leveling members 467 (e.g., a blade) as the re-coater 102 applies a layer in a first direction. Conversely, a series of second apertures 408 are disposed across posterior surface 402 of the re-coater on the other side to provide powder to a second leveling member 469 (e.g., a blade) as the re-coater 102 optionally applies a layer in a second direction. In an embodiment, the surface area of posterior surface 402 is as large as possible to apply a larger number of light emitting diode (LED) heating elements 429 to form LED array 452, and to ensure the leveling members 467, 469 are long enough to extend across a width of the powder bed. In other embodiments, a single blade or leveling member can be used, such as when using a uni-directional re-coater, or when the leveling member is bi-directional.
Other PBF systems use rollers to apply powder layers and to smooth the powder layers onto the powder bed. In an embodiment, the roller is coupled to or part of a re-coater for use in applying the powder. In other embodiments, the roller constitutes the re-coater itself. The roller may obtain the powder from an existing or adjacent reservoir of powder, or from a hopper. The present disclosure is intended to cover each of these embodiments.
The leveling member 502 of
In other embodiments, the heating element may be integrated with the hopper to effect fast and efficient pre-heating and reheating].
With continued reference to
Here, hopper 615 is distal from the re-coater 604. As noted above, hopper 615 includes a heat source for heating the powder to a designated temperature before sending it to the re-coater. Hopper 615 includes fasteners for stabilizing the structure to a frame of the system. In an embodiment, the fasteners are adjustable and the hopper may be replaced as necessary. In other embodiments, a user may use powder loading drum to resupply the hopper 615 with the powder it needs when the hopper is running low. Channel 606 carries pre-heated powder from the hopper 615 to a cavity in the re-coater 604 (omitted for simplicity). Re-coater 604 includes a leveling member that deposits the layers on the powder bed during re-coat cycles as before. The structure may also include the capability to reheat the powder bed immediately after fusion of structures during the print cycle.
In
In alternative embodiments, re-coater 604 may include as its heat source an embedded array of lenses that utilize the energy beam source (103) (
In other embodiments, re-coater 704 may include a leveling member of the roller type, but in this embodiment the need for a separate heating coil in the roller can be eliminated. Alternatively, the roller may have a separate heating element to enhance the preheating capability of the PBF 3-D printer. In the embodiment shown, a re-coat cycle is underway as re-coater 704 applies a layer of powder via the leveling member. On the front side of re-coater 704 is a first lens 710 (or a plurality or array thereof), and on the back side of the re-coater is a second lens 708 (or similarly a plurality or array of lenses). The lenses are specifically designed to receive energy beams 706a-b and to focus the received light onto regions of the powder beneath them to produce heat.
In the upper part of the print chamber is an energy beam source 789, such as a laser, that may be coupled to a PBF frame 777. Energy beam source 789 is ordinarily in a disabled state during the re-coat cycle. For illustrative purposes, the energy beam source 789 can be a laser. In addition to its activity during the print cycle, energy beam source 789 is activated during the re-coat cycle under command of print controller 783. One or more lasers may be involved in this process, and they may be spread out. Laser 789 applies a light ray to deflector 790, which in turn is oriented by print controller 783 to selectively apply the energy beam to one or both lenses 710/708 as the re-coater 704 and hence the coupled lenses 710/708 traverses the powder bed 702. In the embodiment shown, light rays 706a-b are multiplexed via print controller 783 to heat both sides of re-coater 704, although in other embodiments multiple energy beam sources 789 and deflectors 790 may be used for this purpose. The lenses 710/708 receive the light energy and focus the beam onto the underlying powder which is being deposited by the re-coater. The result is that the powder bed 702 is heated using the energy beam source 789. The magnitude of heating is controlled by the strength of the laser and the lenses and the duration of receipt of a laser beam as set by print controller 783. Too high a strength is unwanted, as the lens may become dangerously close to reaching the threshold of fusing the powder. Too low a strength is equally undesirable, as the powder will not become warm enough to reduce the thermal gradients by an adequate amount.
Although frame 777 is shown as being coupled to print controller 783 and energy beam source 790, the structural arrangement of elements in the system may vary, and a number of such arrangements is possible.
Advantages of the lens embodiments include reduced complexity of the system, since a separate heat source is no longer needed to heat the powder layers. Also, the system can perform both pre-heat and reheat operations, since the energy beam source 789 is otherwise available for use during the re-coat cycles of 3-D printers and is conventionally only needed in PBF printers during the print cycles. In addition, the powder layers are directly heated in these embodiments, unlike the conventional warming of the print plate which invariably becomes far away from the surface of the powder bed where the thermal stress control is needed most.
In another embodiment, a PBF rotary motion system is used. PBF rotary systems differ from standard linear PBF printers in that the powder bed is circular-shaped. Also, the travel of the re-coater is circular as it moves around the rotary powder bed in a circular fashion.
Heating source 806 begins at a center 818 of the rotary system 800 and is configured to extend out to the circumference of powder bed 802. In an embodiment, heating source 806 sweeps about the center in a clockwise fashion relative to the top view, in flow direction 814 and 824. Re-coater 813 is also disposed on powder bed 802 and originates at center 818 and moves in flow direction 814 and 824, but is arranged in this example to be 180° from heating source 806. Heating source 806 can be connected to the re-coater 813 at center 818. During a re-coat cycle, re-coater 813 applies its leveling member to the powder it receives via a powder channel 874 from a hopper 813 or reservoir-based storage tank and would encircle the system to depositing the next layer. Since
Meanwhile, heating source 806 can “follow” the re-coater 813 out-of-phase by heating the circularly-deposited powder layer to a desired temperature dictated by the print controller and the capabilities of the heating source This layout of the re-coater applying a layer followed by the heating source in flow direction 814/824 can achieve a more uniform and predictable heat map.
In an embodiment, a power emitted by heating source 806 is variable across a radial direction “r” of powder bed 802. That is to say, heating source 806 may apply a constant amount of heat at the center 818, and then apply a linearly increasing amount of heat to the powder layer as a point on the heat source 806 moves farther in radial direction r towards the circumference of the circle. Conversely, in another embodiment, the application of heat by the heating source 806 may be highest in the center and may be reduced at the edge. This latter application may be more ideal in situations where the build piece is configured to be centered at the center 818 of the circular powder bed 802. In various embodiments, the radial increase or decrease in heat may be approximately linear or exponential, or it may follow another pattern.
In all of these embodiments with respect to the different printer types, using reheating to heat the area again can result in stretching out the heat application over a longer period of time, resulting in lower stresses, less or no cracks, less deformation, and a generally longer lifetime of the part.
A further benefit of pre-heating and reheating the powder bed surface is that the air gap between the powder particles of the un-melted powder and the heated powder may increase the effective thermal conductivity of the un-melted powder, further reducing distortion during printing. Dimensional accuracy of the build piece can be dramatically improved by mitigating these thermal stresses using application of heat directly onto the powder bed surface.
Next, at step 1003, the print cycle occurs for the deposited layer, and the printer's energy beam source and deflector selectively fuses the layer to create a section of the build piece. Thereupon, in some embodiments, the re-coater re-heats the powder bed by applying heat from the re-coater, as shown in step 1004.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to the exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art, and the concepts disclosed herein may be applied in other contexts and for different purposes. Thus, the claims are not intended to be limited to the exemplary embodiments presented throughout the disclosure, but are to be accorded the full scope consistent with the language claims. All structural and functional equivalents to the elements of the exemplary embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f), or analogous law in applicable jurisdictions, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”