Methods for monitoring and controlling additive manufacturing processes

Abstract

A method for monitoring and controlling an additive manufacturing process in which selective fusion of powder material in successively formed layers to manufacture a three-dimensional product is performed comprises the steps of delivering to a working space, for example in a vacuum chamber (12) of an electron beam additive manufacturing apparatus (10), an amount of powder material that exceeds the amount required to form a layer of a given volume in a build zone of the space, and spreading the powder material in the working space by a spreader (17) to form a layer in the build zone and also to form an accumulation of excess powder material in an accumulation zone adjacent to the build zone. The spreading step is repeated to form a series of said layers and accumulations, the volume of each accumulation being determined by imaging along an optical path (B) of a structured light pattern projected along an optical path (A) onto each accumulation from an imaging direction different from the projection direction, resulting in a distortion of the pattern by the accumulation. The imaged pattern can then be evaluated to derive the volume of the accumulation from the distortion, and the determined volume of the accumulation is utilized to control the additive manufacturing process.

Description

Technical Field

[0001] The present invention relates to a method for monitoring and controlling an additive manufacturing process, particularly a method for monitoring the consumption of powder material used in this process.

Background Art

[0002] Additive manufacturing is a well-established technique for manufacturing three-dimensional products. In this technique, a product is produced by selectively melting a fusible powder material by irradiation with an energy beam such as, for example, an electron beam or a laser beam. The irradiation and fusion are carried out in relation to a layer of this powder material which is continuously formed such that the material in each layer is melted according to a defined pattern and not only fuses in itself but also welds to the pre-fused material of the base layer, whereby the product shape is produced layer by layer, i.e., on an additive manufacturing basis. An important equipment element for carrying out this procedure is a powder material feeding and distribution system. This powder material feeding and distribution system typically comprises a powder material source, a spreader for spreading a series of powder material layers within the manufacturing space, and a mechanism for lowering the manufacturing space after the spreading of each layer and the selective fusion of the hard powder material. For reasons of product quality, it is important that the powder material forming each layer is evenly distributed across the area of this manufacturing space and that the layer thickness is clearly defined and matches a predetermined value. Furthermore, it is desirable to form each layer rapidly in order to maintain the manufacturing speed as high as possible.

[0003] To ensure uniform distribution of powder material within each layer, it is usually necessary to supply the spreader with a quantity of material exceeding the amount consumed in each layer. However, since powder raw materials are generally expensive, it is highly desirable to reuse any available surplus powder from each layer. As a result of operations using surplus powder material, the amount of surplus material present tends to be variable as product manufacturing progresses, and this can further constitute a variable in the product manufacturing cycle, potentially impairing the precise control and management of the additive manufacturing process.

[0004] Known methods for powder material measurement, such as those described in U.S. Patent No. 10406599B2, capture an image of the shape of a portion or more of a large amount of powder material that has not yet been distributed, i.e., unfolded to contribute to layer formation, in front of the spreader of an additive manufacturing apparatus. One or more dimensions of this portion are derived from the image and compared to desired parameter values ​​related to the amount of powder material. These comparison results are used to assist in achieving uniform powder material distribution, including changes in the amount of material supplied. While the described method can identify the presence of excess powder material after distribution, it does not disclose a method for specifically determining the amount of such excess material, nor does it disclose a measurement method capable of making such a determination. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent No. 10406599B2 [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the main objective of the present invention is to enable monitoring and control of the additive manufacturing process, specifically the process in which the amount of powder material exceeds the amount required for each layer, thereby eliminating or at least reducing the importance of variables that negatively affect process control, and thus enabling the process to be carried out more accurately.

[0007] A secondary objective is to enable monitoring so that data on powder material consumption during layer formation can be obtained using a simple yet effective method, and so that this data can be used to prepare the supply and replenishment of powder materials in order to realize the economics of the process, particularly in the use of powder materials.

[0008] Other objectives and advantages of the present invention will become apparent from the following description. [Means for solving the problem]

[0009] The present invention provides a method for monitoring and controlling an additive manufacturing process in which selective fusion of powder materials in layers formed in a continuous manner for manufacturing a three-dimensional product is carried out. The method includes the steps of: delivering an amount of powder material into a workspace that exceeds the amount required to form a layer of a given volume within a construction zone of space; deploying the powder material into the workspace to form a layer within the construction zone and to additionally form a deposit of excess powder material in a deposit zone adjacent to the construction zone; repeating the steps of deploying to form a series of layers and deposits; determining the at least rough volume of each deposit by imaging a structured light pattern projected onto each deposit from a direction different from the direction of projection so that distortion of the projected pattern by the deposits is generated in the imaged pattern; and evaluating the imaged pattern to derive at least the rough volume of the deposits involved in the distortion from the distortion of the pattern; and controlling the additive manufacturing process based on the determined volumes of the deposits.

[0010] The formation of each powder material layer, based on the surplus material required for the layer and the resulting deposit of surplus material in a dedicated storage zone, establishes essential conditions for forming layers with a desired constant thickness by mitigating the risk of voids, thinning of the layer, or other depletion, and for reusing surplus material available to contribute to the formation of at least one subsequent layer. Such reuse or recycling of powder material can accelerate the production rate and reduce material waste. Under these conditions, it is a significant advantage to be able to monitor the product manufacturing cycle using the recognition of the approximate or actual volume of each such deposit of surplus powder. This approximate or actual volume of each such deposit of surplus powder corresponds to a parameter of powder material consumption by each layer, and recognizing this parameter makes it possible to control various aspects of the ongoing layer formation, among other things. By utilizing a projected and imaged structured light pattern such that the target powder material deposit causes distortion of the pattern in the pattern image, and then analyzing the distortion of the pattern in this image, a simple non-contact means is provided to achieve volumetric measurement of shape, particularly height and base area, which would otherwise be difficult to perform accurately. The approximate volume of each deposit can be mathematically determined without difficulty from the direction and degree of distortion of the structured light pattern, in combination with known parameters such as the direction of light projection.

[0011] Preferably, the control step is carried out in relation to the powder material used or intended for use in the additive manufacturing process. This allows for correction of volumetric measurements using points directly related to the additive manufacturing process. In this case, the control step may include controlling at least one of the powder material delivery control to the workspace and the deployment of the powder material within the workspace. If this control step is applied to the powder material delivery, the material supply for layer formation may be set or adjusted taking into account the volume of each accumulation of excess material. If the control step is applied to the deployment of the powder material, the deployment parameters may similarly be set or adjusted based on volumetric measurements. As a result, in a preferred example of this method, the control step includes adjusting the parameters of powder layer formation within the build zone, thereby allowing the additive manufacturing process, as applied to each product, to be carried out layer by layer with adjustments based on recognition of the volume of excess material remaining after the formation of each layer. In processes using an inherently passive system for automated powder material distribution, the monitoring achieved by this method can enable, for example, the recognition of changes in the system and, in particular, the resulting control in the sense of adjusting the system during single-product or multi-product construction to compensate for long-term drift. These parameters can be, for example, the powder material distribution rate for layer formation, the position or time at which the spreader finishes unfolding for layer formation, or other factors that control layer formation.

[0012] In a more direct or dynamic use of volumetric measurement, this method includes the step of comparing a given volume of a layer with the determined, at least rough, volume of each accumulation in order to obtain a measured powder material consumption by each layer, and then the additive manufacturing process is controlled in accordance with the obtained measured powder material consumption. This provides room for precise control of the ongoing additive manufacturing process based on the powder material consumption by each layer. Such consumption is determined not by direct measurement of the volume of each layer, but by a simple indirect measurement related to the remaining powder material from each layer. The determined volume of the remaining material, i.e., the accumulation of excess material, can be simply correlated with a volume calculation, for example, on a weight basis, of the material supplied for layer formation, in order to obtain data related to the actual volume of material in the layer once formed.

[0013] As a result, in such a dynamic method, which involves the delivery of additional powder material to the workspace for use in forming a series of layers, the controlling step may include adjusting the delivery in accordance with the acquired powder material consumption measurements. In this case, the additive manufacturing process may be carried out based on periodic powder material replenishment, taking into account the actual and ongoing material requirements for these layers, rather than evaluations made before the process. This dynamic method is particularly advantageous with respect to possible needs for adaptation during the product manufacturing cycle, for example, when powder materials with various characteristics such as particle size, weight, and fluidity are introduced in the middle of the cycle. The adjustment of delivery can take various forms, for example, with respect to the timing of delivery and / or the amount of additional powder material in the delivery. Both of these adjustment forms, whether undertaken as alternatives or in combination, provide room for very precise control of the additive manufacturing process. Thus, advantageously, the method includes a step of determining from the powder material consumption measurements the amount of additional powder material required to form further such layers. In this case, the determined amount of additional powder material preferably further includes the amount required to form further such accumulations.

[0014] While the method for monitoring the additive manufacturing process can be implemented as a completely independent technique within the context of this process, the operational economy can be enhanced if, in combination with the execution of the steps of this method, a structured light pattern is simultaneously projected onto both the surface of the formed layer of powder material and the adjacent deposit of excess powder material remaining after the formation of this layer, generating an image of the pattern on both the layer surface and the deposit, and the distortion of the pattern in the image is evaluated not only to determine the volume of the excess powder deposit but also to identify defects in the layer surface. Therefore, the projection of a structured light pattern onto the deposit and the imaging of the resulting distortion pattern from the deposit can be used in simultaneous processing for two different tasks, namely defect detection on the layer surface and volume measurement of the deposit. The acquired images undergo different processing and analysis to yield different desired results. While separate projection and imaging devices can be used for these two tasks, it is advantageous that the pattern is projected onto the layer surface and the deposit by a common projection system, and the projected pattern onto the layer surface and the deposit is imaged by a common imaging system.

[0015] One method of this kind is particularly suitable for execution by an additive manufacturing apparatus having a liftable support for a material bed formed from continuous layers of powder material. This support has an area corresponding to a construction zone into which energy is introduced to selectively melt and fuse the layer material. A spreader is movable within the support to spread the powder material within the construction zone for the formation of a series of layers of a specified depth, and to guide the excess powder material from each layer into a storage zone adjacent to the construction zone. The support can be lowered to allow the spreader to move over the storage zone without colliding with the excess powder material collected inside, and then raised to allow the spreader to move back and forth over the storage zone and the return of the excess powder material by the spreader to the construction zone, thus enabling the recirculation of the excess powder material. The area of ​​the storage zone can be large enough to allow for the collection of sufficient excess powder material to form a layer of a given area and a given specified depth during the return of excess powder material to the construction zone, and thus the storage zone area can be large enough to accommodate a volume of excess powder material larger than the two-dimensional area of ​​the construction zone and a given depth of product for each layer. The layer depth in additive manufacturing is usually about 20 to 100 microns, in which case the area of ​​the storage zone does not need to be particularly large to accommodate the required volume. Therefore, the storage of returnable excess powder material can be sufficient for the formation of an entire layer, or even multiple layers, or even just a part of a layer. In the last example, the addition of powder material can be performed before or during the formation of the layer.

[0016] A preferred example of a method according to the present invention will be described in more detail below, with reference to the attached drawings, in combination with an apparatus capable of carrying out this method. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic elevation view of an additive manufacturing apparatus capable of carrying out one method illustrating the present invention. [Figure 2A] It is a schematic diagram showing one of a series of steps in the layered manufacturing of a product by this device. [Figure 2B] It is a schematic diagram showing one of a series of steps in the layered manufacturing of a product by this device. [Figure 2C] It is a schematic diagram showing one of a series of steps in the layered manufacturing of a product by this device. [Figure 2D] It is a schematic diagram showing one of a series of steps in the layered manufacturing of a product by this device. [Figure 2E] It is a schematic diagram showing one of a series of steps in the layered manufacturing of a product by this device. [Figure 3A] It is a schematic diagram showing a variant of one aspect of the method for exemplifying the present invention. [Figure 3B] It is a schematic diagram showing a variant of one aspect of the method for exemplifying the present invention. [Figure 3C] It is a schematic diagram showing a variant of one aspect of the method for exemplifying the present invention.

Mode for Carrying Out the Invention

[0018] Referring to the figure, Figure 1 illustrates in a highly schematic form an additive manufacturing apparatus 10 for producing three-dimensional products of a specified shape by selectively melting and fusing powder materials, particularly metallic materials, in continuously deposited layers within a construction zone. The configuration of this apparatus allows one method illustrating the present invention to be carried out by this apparatus during the product manufacturing process. In the case of apparatus 10, melting is performed by the action of an electron beam, although the energy can also be supplied by, for example, a laser or other suitable energy source. The powder material can also be a plastic or other soluble material. The environment for electron beam operation is provided by a housing 11 that defines a vacuum chamber 12, within which a vacuum can be established as an essential condition for the propagation of the electron beam 13. The beam 13 is generated by an electron gun 14, which is located at the top of the housing 11 and oriented to send the generated beam downward toward the target region along the vertical neutral axis. The beam 13 can be deflected in the X and Y directions by means of an electromagnetic deflector (not shown), for example, as illustrated by the dashed arrow at the opposite end of the deflection range in the X direction in Figure 2D. Appropriately controlled beam deflection allows the beam to move its incident point on the target, thereby corresponding to areas of a predetermined shape that correspond to individual cross-sectional layers of the product being manufactured.

[0019] Within the gap in the vacuum chamber 12 below the electron gun 14 and within the target area of the generated beam, a liftable support 15 for a bed formed from a series of powder material deposition layers is provided, and thus a support that is movable in the Z direction as indicated by the double arrows associated in FIG. 1 and the individual arrows in FIGS. 2C and 2D. This support 15 has the form of a table that is mounted on a post and guided to move vertically within a shaft 16, and the wall of this shaft 16 substantially defines this material bed when the material bed is present. Above these walls, the table is surrounded by a peripheral portion having a flat surface, and the top of the table or the top of the material bed on the table can be substantially aligned to be located within the common plane with this flat surface. The movement of the support 15 is realized by a drive unit (not shown), and this drive unit can be a piston cylinder unit, a spindle drive, a rack and pinion drive, a linear motor, or any other suitable means that provides periodic reciprocating linear movement.

[0020] The movement cycle of the support 15 in the context of additive manufacturing in the conventional approach starts with positioning the top of the table below the surface of the peripheral portion to a defined depth or thickness of the powder material layer, spreading the powder material on the table to form a layer having a top surface substantially within the plane of the surface of the peripheral portion, and selectively melting and thus fusing the powder material within this layer. Thereafter, this approach continues by lowering the support 15 to a defined layer depth so that another such layer can be formed, again spreading the powder material on the table to form the next layer having a top surface within the plane of the surface of the peripheral portion, selectively melting the powder material within this layer, not only fusing the materials together within this layer but also welding the powder material to the pre-fused material of the layer located below the powder material. This approach is repeated such that a series of selective melting of powder material layers by scanning the material bed with the electron beam 13 is combined with the stepwise descent of the support 15 to form successive cross-sectional layers of a product of a desired shape in the X, Y, and Z directions.

[0021] The spreading of the powder material to form each layer is performed by a spreader 17, which is movable on a support base 15 to distribute the powder material flatly so as to be substantially coplanar with the surface of the surrounding area. The movement of the spreader 17 for reciprocating movement in the X direction on the support base, as indicated by the accompanying arrows in Figures 2A and 2E, is achieved by a drive (not shown). This drive is controlled by a control unit 18 and can be, for example, a cogged belt and pinion drive, a spindle drive, a rack and pinion drive, a linear motor, or any other suitable means that provides periodic reciprocating linear movement. The control unit 18 is shown as an independent unit in a purely symbolic sense, but in practice it may be an integral part of the overall control system or higher-level control system of the apparatus, such as a system to which appropriate commands are issued by software involved in controlling the operation of the apparatus to perform a manufacturing cycle. Such types of spreaders are used in various structural forms in prior art apparatuses.

[0022] The powder material for the layer forming the powder material bed is supplied by a feeder or dispenser 19 appropriately positioned relative to the support base 15, for example, on one side of the support base table 15. The dispenser is known in various forms in the prior art and may include, for example, a hopper that holds a sufficient amount of powder material to produce individual products or a given number of products. The spreader 17 itself may also include a dispenser, which is supplied from such a hopper or periodically from a powder reserve outside the housing 11. The supply of powder material from the dispenser 19 is carried out under the control of a control unit 20, which determines the amount and duration of powder material supplied for dispersion. In a similar manner to the control unit 18, the control unit 20 is shown as an independent unit in a symbolic sense, but may also be an integral part of the overall control system.

[0023] The movement of the support base 15 and spreader 17 during the manufacturing cycle, i.e., during the creation of each cross-sectional layer of the product, is correlated, as will be evident from the foregoing and as will be explained below with reference to Figures 2A to 2E. Specifically, the drive of the support base and the drive of the spreader are controlled to move the support base and spreader at specific points in time and in specific directions during each cycle, and such control is realized by control means symbolically represented by control units 18 and 20.

[0024] One feature of this apparatus, as described in the introduction, is the operation of deploying more powder material than actually required for each layer, and therefore a powder material supply volume exceeding the volume of the layer, during the formation of each layer. The concentrated oversupply of powder material ensures that the spreader 17 forms layers that are free from voids, depressions, or other defects caused by powder shortages as much as possible. The oversupply results in a surplus of powder material at the end of each layer's formation, which in turn necessitates returning this surplus for reuse, particularly for economic reasons. This return is achieved by deploying the surplus powder onto the most recently formed layer by the return movement of the spreader 17 to form some or all of the subsequent layers after exposure to the thermal effect of the electron beam. Powder recirculation can be achieved in various ways, including operations such as moving the spreader from one side of the surplus powder accumulation to the other side. Another possibility utilized in the apparatus 10 described and illustrated herein is achieved by limiting the excess powder material to the support base 15 and returning the powder by correlated movement of the support base 15 and the spreader 17, as will be discussed later in relation to Figures 2A to 2E.

[0025] To limit excess powder material to the support base 15, the support base defines not only an area for the construction zone where product manufacturing is carried out by electron beam action, but also an adjacent, specifically continuous area for an excess powder material storage zone where excess powder material from each powder material layer is collected and forms a deposit. For this purpose, the top of the support base table is conceptually divided into two areas that form two volume bottoms of variable height. These volume bottoms are defined by two projections perpendicular to the surface of the top of the table, corresponding to the construction zone and the storage zone, respectively. These zones move upward relative to the support base 15 as the support base 15 is gradually lowered during the formation of the powder material bed, and as the height of this bed is gradually increased. Thus, at the start of manufacturing, these zones overlap directly on the top of the table, and subsequently overlap on each preceding layer at the top of the material bed. The majority of the total surface area at the top of the table is occupied by the area associated with the construction zone, while a relatively small strip-shaped area is reserved as the area associated with the excess powder material accumulation zone. The latter area extends along the boundary of the table and has the form of a strip that extends in the transverse direction with respect to the reciprocating movement direction of the spreader 17, as indicated by the accompanying arrows in Figures 2A and 2E, and thus a strip that extends in the Y-axis direction.

[0026] The operating range of the electron beam 13 is specifically limited to the construction zone. This limitation of the beam's operating range is achieved simply by controlling the beam deflection range made possible by the beam deflector described above.

[0027] The action sequence associated with the formation of each powder material layer and the recycling of excess material will be described below in combination with Figures 2A to 2E. These figures show in cross-section a support base 15 consisting of a table and posts, a shaft 16 with a portion of the perimeter, and a spreader 17, respectively. Each figure shows a stage in the production of product 21, surrounded by partially molten or unmolten powder material and supported on the top of the table. The production of the product by powder material melting and fusing is carried out within the construction zone, at a maximum small distance from the perimeter, to avoid the risk of the product adhering to the surrounding material, particularly the walls of the shaft 16. Note that, aside from the highly schematic nature of Figures 2A to 2E, the powder material layer depths and excess powder material accumulations are illustrated in greatly exaggerated sizes for the sake of understanding.

[0028] Figure 2A illustrates the components referred to in the previous paragraph in a stage in which the support base 15 is positioned within the shaft 16 such that the top of the table is located below the surface of the periphery by an amount preferably equal to a predetermined depth of the powder material layer to be formed, for example, 0.07 millimeters. In the position of this support base described and illustrated, the spreader 17, moving to the right, spreads the powder material supplied from the dispenser 19 onto the table, thereby forming a flat and uniform first layer 22 that is substantially coplanar with the surface of the periphery and as a result of the desired depth. Figure 2A shows the partially formed layer 22. The powder material, dragged by the spreader 17 and not yet spread, exists as a gradually decreasing-in-size mass in front of the spreader in the direction of movement to the right.

[0029] Figure 2B shows the final formation of the first layer 22, which here completely covers the top of the table within the construction zone. A key aspect of layer formation in terms of achieving consistent layer depth and a flat surface is, as previously mentioned, the supply of excess powder material in the amount actually needed for the formation of each layer. Excess powder, which may be enough for, for example, part of the next layer, all of the next layer, or multiple subsequent layers, is guided to the accumulation zone by the spreader 17.

[0030] Subsequently, as shown in Figure 2C, the support base 15 is lowered under the control of the control unit 18 until the collected excess powder material is separated from the spreader and positioned at a distance below the surface of the surrounding area. During this time, the excess material, which is no longer enclosed by the spreader 17 on the left side and enclosed by the wall of the shaft 16 on the right side, is redistributed under gravity over a wider base area but still within the accumulation zone to form a roughly ridge-shaped accumulation 23. For an accumulation zone with a width of 300 mm in the Y direction, this accumulation is typically 3 mm high and has a base dimension of 17 mm in the X direction. Under the control of the control unit 18, the spreader 17 is moved further to the right, then across the accumulation zone, without colliding with the accumulation 23, until it is positioned above the surrounding area.

[0031] At this stage, with a fully formed layer 22 within the construction zone and the support base 15 preferably raised as shown in Figure 2D, the electron gun 14 is energized to emit an electron beam 13 in the direction of the layer 22. The emitted beam is deflected as shown by the dashed arrow in Figure 2D, which indicates the maximum range of deflection, and scans a predetermined area of ​​the layer to be melted, which is an area dependent on the specific shape characteristics of the product, thereby fusing the powder of the layer together and forming a first cross-section of the product 21.

[0032] In the next step, and as shown in Figure 2E, with the support base 15 positioned such that the top of the newly formed cross-section of the product 21 and the residual powder of the first layer 22 is again positioned below the surface of the surrounding area by a predetermined depth of the powder material layer, the spreader 17 is then moved to the left in the reverse direction, dragging the accumulation of excess powder material 23 and spreading this material to form part or all of the next (second) layer 24. The cycle of steps described with reference to Figures 2A to 2E is repeated, except that all subsequent layers are always partially spread over the partially manufactured product and the top of the residual powder away from the center in the construction zone until the product achieves a predetermined shape and is fully manufactured. During these cycles, and therefore during the additive manufacturing process, the action of the electron beam 13 not only fuses the target powder material of the top layer together, but also welds this powder material to the already fused material located below.

[0033] The previously described exemplary dimensions of the layer thickness and the previously described exemplary dimensions of the excess powder material accumulation 23 after layer formation may be sufficient when forming two or more continuous layers, for example, when the layer area is approximately 300 mm wide in each of the X and Y axes. However, the actual volume of the excess powder material accumulation remaining after each layer formation is usually variable. The information that can be obtained about this volume is one of several parameters useful for monitoring progress and adjusting the additive manufacturing process, and therefore the apparatus 10 is provided to enable determination of each accumulation volume by a simple non-contact method, and is therefore provided to carry out one method illustrating the present invention.

[0034] To this end, the apparatus incorporates a non-contact measurement system, which firstly comprises an optical projector 25 for projecting structured light onto an optical projection path A, shown by a dashed line in Figures 1 and 2C, passing through a vacuum chamber 12 via a window (not shown), in order to define a fringe pattern on the opposing surface of each accumulation 23 of excess powder material in the accumulation zone. This pattern is formed along the entire length of the accumulation 23 in the transverse axis or transverse direction with respect to the reciprocating direction of the spreader 17. Optionally, the structured light defining the fringe pattern may be further projected onto a larger optical path (defined from the left by an additional dashed line in Figure 1) within the construction zones on the respective formed powder material layers 22, 24. The projection is performed before or after beaming the layers to melt the constituent powder materials, but in either case, before the spreader 17 returns to unfold the material constituting the accumulation. The fringe patterns generated by computer software can take on various shapes, but for convenience they are composed of an array of strips 26 spaced at regular intervals with contrasting tones (fringes). Some examples of such projected fringe patterns are shown in Figures 3A to 3C, which will be discussed further below.

[0035] Furthermore, the measurement system includes, secondly, an optical imaging camera 27 for imaging the fringe pattern projected on an optical imaging path B that passes through the vacuum chamber 12 via a further window (also not shown). The imaged pattern is shown in Figure 1B with a degree of inclination that increases the angle of the optical imaging path B relative to the optical projection path A, compared to Figure 1A. Similar to this projection, the imaging corresponds to the entire length of the deposit 23 in the transverse axis direction with respect to the reciprocating movement direction of the spreader. As represented by the relatively angled optical paths A and B, since this imaging is performed from a different field of view than the projection field of view, topographic features of higher morphologies, such as ridge-shaped deposits 23 of excess powder, result in distortion of individual strips 26 of the imaged fringe pattern. The magnitude and vector of this distortion depend on the slope and height of the surface of the deposit onto which the fringe pattern is projected, and furthermore, these slopes and heights are correlated elements of the geometric cross-sectional shape of the deposit, which represents the volume of the deposit in combination with the length of the deposit i.e., the layer along the Y-axis and the associated measured dimensions of the deposit. Figure 3A shows a small portion of the fringe pattern projected onto the target surface of the deposit with an optically added overlay on the top surface of the associated powder material layer. The fringe pattern strips extending along the entire length of the deposit 23 are illustrated with exaggerated width and spacing. In reality, these strips are very narrow and have small spacing, so they are densely packaged along the length of the deposit 23, allowing for the construction of a cross-sectional surface map of the deposit, i.e., the height of the deposit at each X and Y position of the deposit zone, when imaging and analysis are performed. Figures 3B and 3C show, at a greatly exaggerated scale, the different distortions of the imaged fringe pattern strips 26 as a result of the different slopes of the target surface of the deposit 23 and thus the different volumes of the deposit. These imaged distortions are processed and analyzed using appropriate algorithms in a processing unit 28 connected to an imaging camera 27 to receive digital data representing the imaged distortions and to process the input data to generate outputs for use in controlling the additive manufacturing process.This output, corresponding to a series of volume measurements of a series of deposits 23, can be used in a passive sense, such as in monitoring the additive manufacturing process to provide a reference for drift correction and for adjusting changes in powder material characteristics or other variables, or in a dynamic sense, such as in calculating the amount of powder material to be added to increase the amount of material forming deposits that will be spread by the spreader 17, for example, in periodic or regular adjustment of the parameters of powder material supply to the build zone, and in adjusting the amount of powder material supplied for layer formation by the reciprocating movement of the spreader, the movement speed of the spreader, and other factors. Figure 1 shows, as an example, the connection of the output of the processing unit 28 to the spreader control unit 18 and the dispenser control unit 20 to illustrate the possibility of direct dynamic control in important aspects of the additive manufacturing process.

[0036] In Figure 1, the positions of the projector 25 and camera 27 are shown at completely arbitrary positions, taking into account the two-dimensionality of the drawing, in order to clearly show the different orientations of optical projection path A and optical imaging path B, respectively. The projector and camera are positioned, for example, to superimpose on the electron gun 14 in a projection perpendicular to the plane of the drawing. This positioning is a known factor in all cases, and any corrections for any influence on the acquired image can be made during processing by the processing unit 28.

[0037] As previously described, the fringe patterns manifested in structured light projection can also be projected onto the entire layer and imaged from the entire layer, in which case topographic features such as highs and depressions appear as disturbances or distortions in individual strips of the pattern. Highs are formed by waveheads of corrugated sections within the layer, agglomerations of powder material particles, and displacements resulting from protrusions from the base layer and other defects, while depressions can be formed by troughs, voids, powder defect areas of such corrugated sections, scratches resulting from particle dragging or damage by the spreader, and other consequences. Recognition of these types of defects can be achieved by analyzing each fringe pattern imaged from the layer using analytical techniques suitable for generating data characterizing defects in the powder material layer, which in turn allows for the determination of appropriate corrective actions. These actions may relate, among other things, to parameters of powder supply, deployment, and beam operation. When defect detection is performed by structured light projection and imaging, a single optical projection and imaging system can be used, particularly with the use of the same projector 25 and camera 27 used for measuring the volume of accumulated excess powder material. [Explanation of Symbols]

[0038] 10. Additive Manufacturing Equipment 11 Housing 12 Vacuum Chamber 13 Electron beam 14. Electron gun 15. Height-adjustable support stand, table 16 shafts 17 Spreader 18 Control unit, spreader control unit 19 Dispensers 20 Control units, dispenser control units 21 Products 22 First layer, powder material layer 23 Ridge-shaped deposits 24. Second layer, powder material layer 25 Optical projector 26 strips, fringe pattern strips 27 Optical imaging camera 28 Processing Units

Claims

1. A method for monitoring and controlling an additive manufacturing process in which selective fusion of powder materials in layers formed continuously for the manufacture of a three-dimensional product is performed, The steps include: delivering an amount of the powder material into the space that exceeds the amount necessary to form a layer of a given volume within the construction zone of the workspace; The steps include: spreading the powder material in the work space in order to form the layer in the construction zone and to additionally form an accumulation of excess powder material in the accumulation zone adjacent to the construction zone; A step of repeating the step of unfolding to form a series of the aforementioned layers and the aforementioned accumulation, The steps include: imaging a structured light pattern projected onto each of the deposits formed by each of the unfolding steps from a direction different from the direction of projection, such that distortion of the projected pattern due to the deposits is generated in the imaged pattern; and determining the at least rough volume of each deposit by evaluating the imaged pattern in order to derive at least the rough volume of the deposits involved in the distortion from the distortion of the pattern; A step of controlling the additive manufacturing process based on the determined volume of the accumulated material. Methods that include...

2. The method according to claim 1, wherein the control step is carried out in relation to the powder material used or for use in the additive manufacturing process.

3. The method according to claim 2, wherein the controlling step includes controlling at least one of the delivery of powder material to the workspace and the spreading of powder material within the workspace.

4. The method according to claim 3, wherein the controlling step includes adjusting the parameters of powder layer formation within the construction zone.

5. The method according to claim 4, wherein the parameter is the powder material distribution rate for forming the layer.

6. The method according to any one of claims 1 to 5, comprising the step of comparing a given volume of a layer with the determined at least rough volume of each deposit in order to obtain a powder material consumption measurement for each layer, wherein the additive manufacturing process is controlled in accordance with the obtained powder material consumption measurement.

7. The method according to claim 6, wherein the additive manufacturing process includes a step of delivering further powder material to the workspace for use in forming the series of layers, and the controlling step includes a step of adjusting the delivery step in accordance with the obtained powder material consumption measurement.

8. The method according to claim 7, wherein the step of delivering further powder material is adjusted with respect to the timing of the delivery step.

9. The method according to claim 7 or 8, wherein the step of delivering further powder material is adjusted with respect to the amount of further powder material in the delivery.

10. The method according to claim 9, further comprising the step of determining from the measured amount of powder material consumed an additional amount of powder material required to form a further layer.

11. The method according to claim 10, wherein the amount of additional powder material determined is also the amount required to form further accumulations.

12. A method for monitoring an additive manufacturing process, comprising the step of performing the steps of the method according to any one of claims 1 to 11, wherein the structured light pattern is projected simultaneously onto both the surface of the formed layer of the powder material and an adjacent deposit of excess powder material remaining after the formation of the layer, thereby generating an image of the pattern on both the layer surface and the deposit, and the distortion of the pattern in the image is evaluated not only to determine the volume of the deposit of excess powder, but also to identify defects in the layer surface.

13. The method according to claim 12, wherein the pattern is projected onto the layer surface and the accumulated material by a common projection system, and the projected pattern on the layer surface and the accumulated material is imaged by a common imaging system.

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