Additive manufacturing systems and methods

Abstract

To deliver an arbitrarily large amount of laser power to the build surface in a controllable profile that can be scanned as a single entity.SOLUTION: An additive manufacturing system may comprise two or more laser energy sources, and associated optical fibers. An optics assembly may be constructed and arranged to form a rectangular laser energy pixel associated with each laser energy source. Each pixel may have a substantially uniform power density, and the pixels may be arranged to form a linear array of laser energy pixels on a build surface with no spacing between the pixels. Exposure of a portion of a layer of material on the build surface to the linear array of laser energy pixels may melt the portion of the layer.SELECTED DRAWING: Figure 26

Description

Technical Field

[0001] Field

[0001] The disclosed embodiments relate to systems and methods for additive manufacturing.

Background Art

[0002] Background

[0002] At present, in the market, many metal additive manufacturing methods are available. These methods can be classified by the form of the material source (powder, wire, thin film, etc.) and the form of additional energy for obtaining melting / bonding (laser melting, e-beam melting, welding arc, sintering, etc.). The resolution, accuracy, and achievable feature size of the end portion in a given process are based on the form of the initial material and the ability to control the energy distribution for metal fusion. The effective rate of a given process is usually limited by the ability to supply energy into the build surface in a controlled manner.

[0003]

[0003] In a selective laser melting process for metal additive manufacturing, usually, the laser spot is scanned over a thin layer of metal powder. The metal powder scanned by the laser spot is melted and fused into a solid metal structure. Once the layer is completed, the structure is indexed, a new layer of metal powder is placed, and the process is repeated. When an area on a new layer located on a previously scanned area on a previous layer is scanned by the laser spot, the powder is melted and fused onto the individual material of the previous layer. This process can be repeated many times to build almost any form of three-dimensional shape.

Summary of the Invention

Means for Solving the Problems

[0004] Summary

[0004] In one embodiment, the additive manufacturing system includes a build surface, two or more laser energy sources, and two or more optical fibers. Each optical fiber is configured to transmit laser energy from a first end coupled to a related laser energy source among the two or more laser energy sources and from a second end outward, and the second ends of the two or more optical fibers are arranged along a single line. The additive manufacturing system further includes an optics assembly constructed and configured to shape the laser energy output from each optical fiber to form rectangular laser energy pixels associated with each laser energy source. Each rectangular laser energy pixel has a substantially uniform power density, and the rectangular laser energy pixels are configured to form a linear array of laser energy pixels on the build surface without spacing between adjacent laser energy pixels, and exposure of the layer of material on the build surface to the linear array of laser energy pixels melts at least a portion of the layer of material.

[0005]

[0005] In another embodiment, the additive manufacturing method includes exposing a layer of material on a build surface to a linear array of laser energy pixels. Each laser energy pixel has a rectangular shape and a substantially uniform power density, and in this case, there is no spacing between adjacent laser energy pixels. The method further includes melting a portion of the layer of material as a result of the partial exposure of the laser energy pixels to the linear array.

[0006]

[0006] The concepts described above and any further concepts described below can be made up in any suitable combination, as this disclosure is not limited in this respect. Furthermore, other advantageous and novel features of this disclosure will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the attached drawings.

[0007] Brief explanation of the drawing

[0007] The attached drawings are not intended to be drawn to an exact scale. In the drawings, identical or nearly identical components shown in different figures may be represented by the same reference numerals. For clarity, not all components are labeled in all drawings. The drawings are as follows: [Brief explanation of the drawing]

[0008] [Figure 1]

[0008] This is a schematic representation of a circular beam having a Gaussian power density. [Figure 2]

[0009] This is a schematic representation showing the power density of two adjacent circular beams having a Gaussian power density. [Figure 3]

[0010] This is a schematic representation of the power density at different locations in a circular beam with Gaussian power density. [Figure 4]

[0011] This is a schematic representation of a rectangular beam with uniform power density. [Figure 5]

[0012] This is a schematic representation of the power density at different locations in a rectangular beam with uniform power density. [Figure 6]

[0013] A schematic diagram of the incident energy profile of a linear array of rectangular pixels with uniform power density is drawn. [Figure 7]

[0013] A schematic diagram of the incident energy profile of a linear array of rectangular pixels having a uniform power density is drawn. [Figure 8]

[0014] A schematic diagram of the incident energy profile of a linear array of circular pixels with Gaussian power density is drawn. [Figure 9]

[0014] A schematic diagram of the incident energy profile of a linear array of circular pixels having a Gaussian power density is drawn. [Figure 10]

[0015] Depict a schematic representation of the power density of a linear pixel array according to some embodiments. [Figure 11]

[0016] Depict a schematic representation of the power density of a linear pixel array and a fixed spot array. [Figure 12]

[0017] Depict a schematic representation of the power density output of a linear pixel array according to some embodiments. [Figure 13]

[0018] Depict a schematic representation of the power density output of a linear pixel array according to some embodiments. [Figure 14]

[0019] It is a schematic representation of a linear pixel array at the focus. [Figure 15]

[0020] It is a schematic representation of a linear pixel array away from the focus. [Figure 16]

[0021] It is a schematic representation of the pattern of pixels generated by rotationally misaligned square fibers. [Figure 17]

[0022] Depict a schematic representation of a rectangular beam profile formed from a circular beam profile according to some embodiments. [Figure 18]

[0022] Depict a schematic representation of a rectangular beam profile formed from a circular beam profile according to some embodiments. [Figure 19]

[0023] It is a schematic representation of an embodiment of an additive manufacturing system. [Figure 20]

[0024] It is a schematic representation of an embodiment of an optics assembly. [Figure 21]

[0025] It is a schematic representation of an embodiment of a fiber mount. <00000X7><000009X>It is a schematic representation of an embodiment of a lens array. [Figure 23]

[0027] It is a schematic representation of another embodiment of an optics assembly. [Figure 24]

[0028] This is a schematic representation of one embodiment of an additive manufacturing system including a galvanometer. [Figure 25]

[0029] This is a schematic representation of one embodiment of an additive manufacturing system including a fixed mirror assembly. [Figure 26]

[0030] This is a schematic representation of a linear pixel array formed on the surface of a powder bed according to several embodiments. [Figure 27]

[0031] This is a schematic representation of one embodiment of an additive manufacturing system. [Figure 28]

[0032] This is a schematic representation of another embodiment of the additive manufacturing system. [Modes for carrying out the invention]

[0009] Detailed explanation

[0033] The inventors have recognized and understood that the thickness of the powder layer, the size of the laser spot, and the precision of the laser spot motion can all be combined to affect the dimensional accuracy and precision of the final part produced by the selective laser melting process. Furthermore, the size and power of the laser spot can also affect the rate limits of a given mechanical process. For example, for a given laser spot size, there exists a minimum spot power required to enable the melting of the powder layer. Laser power below this point cannot supply sufficient energy to melt and fuse the powder below the laser spot, even when the laser spot is stationary on the powder surface. This minimum energy depends on the material (e.g., the type of metal powder), the thermal properties of the powder bed, and the absorption properties of the powder surface with respect to a given laser wavelength. Consequently, when the laser spot is scanned on the powder surface, this minimum laser power must be increased so that, at the scanning speed, the laser beam can supply sufficient energy to the powder for a given period of time to melt and fuse the powder while a given point is below the laser beam spot profile. The higher the scanning speed, the greater the minimum power required to maintain a continuous molten pool below the scanning spot.

[0010]

[0034] In addition, the inventors have understood that there is a limit to the amount of energy that can be supplied under a given laser spot size. The incident laser energy is usually absorbed in a very narrow layer on the surface of the powder. This energy is converted into thermal energy within this thin layer, and then conduction and convection allow this absorbed energy to diffuse further downward into the powder layer. Conduction is limited by the minute contact points between individual powder particles, and convection occurs through the gaps between the particles. If excessive energy is incident on the layer surface, the energy cannot diffuse sufficiently fast throughout the powder layer, and the powder surface temperature will reach a temperature high enough to evaporate each part of the metal powder surface. This rapid evaporation on the layer surface results in the powder particles being released from the powder surface.

[0011]

[0035] High incident energy can cause surface evaporation on the powder surface, as well as evaporation of the metal within the molten pool. The molten pool is a predetermined amount of molten metal generated by laser heating of the metal powder while the laser spot is scanning the powder surface. Alternatively, the molten pool can be described as a certain amount of metal powder remaining after it has melted and before the molten metal has cooled sufficiently to become solid again. If a portion of the metal from the molten pool evaporates due to excess energy from the laser spot, the rapid expansion of the metal during the evaporation process can cause the molten metal to be ejected from the molten pool. These ejected particles can deform the powder surface within the area still to be scanned, potentially leading to further molten pool instability due to the uneven surface.

[0012]

[0036] In addition, due to their large surface area, elevated temperature, and exposure to ambient gases during the release process, the particles released from the molten metal may tend to form oxides and / or other compounds. These particles may eventually remain in the area being scanned and melted during the ongoing scanning process, potentially affecting the microstructure and mechanical properties of the final product.

[0013]

[0037] If the incident laser spot energy is excessively high, and the scanning speed is increased to compensate for the resulting metal evaporation issues, the thermal energy may not propagate through the powder layer at a speed fast enough to sufficiently melt and fuse all the metal powder. Consequently, the final product may contain voids of unmelted metal powder, which can impair the properties of the final product.

[0014]

[0038] In some cases, the aforementioned challenges can be addressed by reducing the thickness of the powder layer to ensure sufficient dissolution of all metal powders at a given laser spot energy and scan speed. However, this approach reduces the effective rate of the process because a large number of relatively thin layers are required to construct a given portion. Furthermore, there are limitations on the layer thickness, as it cannot be less than the average powder particle size (typically in the range of 15-45 μm).

[0015]

[0039] As laser spot power and speed increase, another challenge arises. When the incident power and scanning speed are sufficiently increased, the molten pool may still become unstable, while still ensuring sufficient melting of all metal powder below the scan track. Instead of generating a continuous molten pool that is subsequently cooled into a continuous solid metal track, the molten pool becomes unstable and begins to break into individual molten droplets, which then cool into fragmented balls on the surface of the processed area. This phenomenon, often referred to as "balling," is a mechanism for forming fragmented droplets due to Rayleigh instability. This instability is observed when the length-to-width ratio of the molten pool reaches a certain critical value. As a result, a high surface tension gradient can lead to the formation of voids within the tail of the molten pool. The length-to-width ratio increases with increasing laser spot scanning speed, as the length of the molten pool grows significantly more rapidly than its width. Further factors contributing to this molten pool instability phenomenon include the local composition of specific powder particles, wetting, Marangoni flow, and gravity.

[0016]

[0040] In addition to the above, another possible method for increasing the rate of the laser-based powder bed fusion / melting process is to increase the spot size. As the spot size increases, the total spot power increases while the average power density of the spot remains constant, thereby increasing the effective machine rate. However, the inventors have recognized that the ability to increase the spot size is limited, as at certain sizes, the added power results in metal evaporation rather than an increase in the net effective powder processing rate. Furthermore, as the spot size increases, the spatial resolution of the final finished portion also decreases. If the resolution of the feature size decreases sufficiently, the benefits of the selective laser melting process are lost, as the resulting portion will require intensive post-machining and processing to obtain the final desired and useful state.

[0017]

[0041] In light of the above, the selective laser melting process in current machines is constrained by the physical limitations of the process. It is not possible to achieve a relatively large net processing rate while maintaining a high-quality process state. One attempt to address these limitations is to add multiple laser beams to a single machine, with each beam being scanned completely independently using a rotating mirror. For example, a machine with two, or in some cases four, beams is available with a total power in the range of 2-4 kW. This method can allow for a relatively large effective machine rate by increasing the number of beam spots, although each spot is still constrained by the energy limits outlined above. Furthermore, the positional accuracy between each spot location on the powder layer can make single-point multi-spot processing difficult without partial accuracy and a reduction in resolution.

[0018]

[0042] Multi-spot laser systems can be useful for generating multiple independent parts within a single powder bed, and while they may have sufficiently independent laser spot control, the effective rate for each part / spot combination is still limited by the process power combination. Furthermore, while it is possible to use multiple independent spots on a single part, in this case, the spatial accuracy between spots becomes extremely important and difficult to control. Partial accuracy and resolution may be reduced, and care must be taken to avoid interference between the beam and beam positioning mechanics. As machine size increases to accommodate relatively larger build volumes, maintaining spatial accuracy between multiple independent spots becomes even more difficult.

[0019]

[0043] Furthermore, multi-spot laser systems can be constructed to have fixed final supply optics in relation to each other. While this approach can help solve the problem of positional accuracy between spot locations, the layout of the spot locations may not be optimal due to the size of the supply optics. For example, in order to keep the output spots in close proximity to each other, the supply optics, due to their size, may have to be positioned considerably further away than the spot size. In some cases, the beams can be focused into one by positioning the optics at predetermined angles to each other so that the beam converges in the incident area on the powder surface or at another point before the final reflecting mirror or Garbo scanner assembly. However, a challenge with this approach is that the incident angles of multiple spots result in different melting behavior below each laser spot. Also, the different incident angles limit the proximity to which each spot can be positioned and maintained adjacent to each other. To obtain a uniform melting front from two adjacent circular spots, the energy density within each spot must be uniform, which can be very difficult to achieve with different incident angles and separate supply optics. For this reason, fixed relative position multi-spot laser systems are typically configured to operate with individual, separate spots, each generating its own distinct molten pool. As a result, the scanning pattern is designed to be incrementally stepped in the gaps between spots on a continuous scan canvas. Furthermore, the challenges associated with arranging multiple fixed optics heads adjacent to one another impose practical limitations on the number of laser units that can be used simultaneously with this scheme; therefore, fixed independent laser optics head systems are typically limited to 4-5 individual laser spots.

[0020]

[0044] Another approach used to address the aforementioned power density limitations in single or multi-spot selective melting systems involves scanning spots very rapidly in a reciprocating direction along a linear path to generate a heated area with an average line shape. However, even with very high scanning speeds, the resulting average line shape is still limited by the power input due to the heat transfer characteristics of the powdered metal layer, as described above. For example, excessive power still leads to metal evaporation and metal pool instability.

[0021]

[0045] In view of the above, the inventors have recognized and understood numerous advantages associated with selective laser melting systems utilizing a line-shaped incident energy source. For example, such a system may offer an increased effective material processing rate compared to the methods described above. In some embodiments, the instantaneous shape of the incident energy is a line having a first dimension (e.g., line length) that is greater than a second dimension (e.g., line width). The power density profile across and along the line may be controlled to be substantially uniform, and the line may be scann in at least two directions, with the primary scanning direction perpendicular to the longer dimension of the line. In some embodiments, the power density profile of the line may be modulated over time.

[0022]

[0046] The embodiments described herein address many of the aforementioned challenges by increasing the effective laser power supply limits described, while maintaining partial resolution and accuracy over relatively large build volumes in powder bed metal additive manufacturing. The systems and methods described herein can supply any large amount of laser power to the build surface in a controllable profile that can be scanned as a single entity. In some embodiments, the ideal shape of this incident laser power is a line having long and short dimensions, in which case the primary scanning direction is perpendicular to the long dimension of the line. The power density in the long direction of the line can be made substantially uniform.

[0023]

[0047] In some embodiments, the incident laser energy line consists of a plurality of individual laser energy pixels arranged adjacent to each other, each of which can be individually controlled in terms of its power level. Each laser energy pixel can be independently turned on or turned off, and the power of each pixel can be independently controlled. The power density across any single pixel can be substantially uniform such that the pixel has a top-hat energy profile when the pixel is turned on. In some embodiments, the power densities of two adjacent pixels can generate a uniform power density along the length of the resulting line when both pixels are turned on and set to the same power density.

[0024]

[0048] The resulting pixel-based lines are primarily scanned perpendicular to the long axis of the line, and therefore the forward velocity and pixel power density are still constrained by nearly the same power and velocity limits as in conventional single-spot laser selective melting processes. However, because multiple spots are directly adjacent to each other, the effective process rate can be approximately N times the single-pixel rate, where N is the number of available pixels. Furthermore, since each pixel can be turned on and off individually, the effective partial resolution and accuracy remain comparable to that of a single-spot system. The system can operate as a single-spot system by turning on only a single pixel, in which case the effective system rate becomes substantially the same as that of a single-spot system.

[0025]

[0049] In some embodiments, the additive manufacturing system includes an optical path configured within an optics assembly (e.g., an optics box) for generating a line, which includes a set of lenses arranged in series. Alternatively, or in addition to this, one or more mirrors may be added to the beam path for beam rotation or bending, and / or a Garbo scanner may be added to the beam path for uniaxial powder bed scanning.

[0026]

[0050] In some embodiments, the laser energy of each laser energy pixel is generated by an independently controllable laser energy source and supplied to the optics assembly through individual optical fibers associated with each laser energy source. In some examples, each individual optical fiber may include fiber segments joined together to form a single optical fiber. Alternatively, or in addition to this, a single optical fiber path can also be created by using an optical connector to join the ends of two fibers into one. All optical fibers from multiple (e.g., two or more) independent laser energy sources are routed to the optics assembly. Within the optics assembly, the ends of the optical fibers are received in mounting fixtures (e.g., fiber holders) that ensure the ends of the optical fibers are parallel and aligned. The ends of multiple optical fiber cables can be cut and polished to ensure a clear and uniform optical path at the exit from each optical fiber. The ends of multiple optical fiber cables can also be coated with an anti-reflective coating. From these fiber ends, all individual laser beams pass through a single set of optical lenses and mirrors within the optics assembly. This configuration maintains the optical paths of all laser energy sources in the same state, and ensures that individual pixels from each laser energy source remain adjacent to each other, while keeping the size of the optical system to a minimum.

[0027]

[0051] With all optics following the same optical path through the same lens array, the resulting laser energy line maintains its shape, can be reflected by a single mirror assembly, and can be scanned using a mirror mounted on a single-axis Garbo scanner. As a result, any number of laser systems can be combined into a pixel-based line to generate a high-rate selective laser melting process.

[0028]

[0052] As will be described in more detail later, in some embodiments, the output from the optics assembly can be guided toward the powder layer using a Garbo scanner, and then passed through a lens or lens assembly, such as an f-θ or telecentric lens, to minimize beam shape distortion at non-normal incidence on the powder layer.

[0029]

[0053] In some embodiments, the output of the optics assembly may be scanned in the primary direction using a Garbo scanner, while the entire optics assembly is scanned in a secondary direction perpendicular to the primary direction using a motorized stage actuator. Alternatively, the output of the optics assembly may be scanned in high-speed motion using a Garbo scanner in the primary direction, while the optics box is scanned in relatively low-speed motion in both the primary and secondary directions perpendicular to the primary direction using a motorized stage mounted orthogonally. In other embodiments, the output from the optics assembly may be scanned using only motorized stage motion without any Garbo scanner stage. In further embodiments, the optics assembly can be mounted such that the pixel array line output from the optics assembly is oriented at a fixed angle relative to the motion stage, so that both stages are actuated to move a line perpendicular to the long axis of the pixel line. Alternatively, this can also be achieved by scanning the output from the optics assembly using a Garbo scanner. In other embodiments, the output from the optics assembly can be dynamically rotated in relation to the motion stage during motion. Alternatively, the dynamic rotation of the optics box can be coupled with a Garbo scanner fixed in relation to the optics box.

[0030]

[0054] In certain embodiments, the optics assembly may also be mounted on a motorized stage that allows for upward and downward motion perpendicular to the powder layer on the build surface, in combination with motorized motion in other axes. This can allow for improved focusing of the output beam as the beam is scanned in the reciprocating direction by the Garvo scanner. Alternatively, the optical path within the optics assembly may include an autofocus array to enable rapid dynamic focal length adjustment. This can allow for relatively large focal length adjustments to accommodate a relatively wide Garvo scanning range.

[0031]

[0055] Depending on the embodiment, a linear array of laser energy pixels (i.e., a line array) can have a uniform power density along the length of the line array. In some examples, a line output pixel array can have a non-uniform power density along the length of the line array by setting different power output levels for each associated laser energy source of each pixel. Furthermore, individual pixels on the ends of a linear array can be selectively turned off or on to generate line arrays with relatively short or relatively long lengths in the length direction. In some embodiments, all pixels except a single pixel can be selectively turned off to obtain a single point pixel for fine feature profiling. In certain embodiments, a linear array can be divided into a plurality of relatively small linear arrays, each having the same power density along the respective relatively small linear array. Alternatively, or in addition to this, the plurality of relatively small linear arrays may have different power densities, uniform within each of the relative small arrays but different from array to array. In some examples, multiple relatively small linear arrays can have different power densities among the small arrays themselves, as well as different power densities across each of the relatively small arrays.

[0032]

[0056] Furthermore, in some embodiments, the power levels of various pixels within a linear array of laser energy can be independently controlled throughout the additive manufacturing process. For example, the various pixels may be selectively turned on, turned off, or operated at intermediate power levels to provide a desired power density along the length of the linear array.

[0033]

[0057] According to some aspects of this disclosure, the optical path of the incident laser beam after it leaves the optical fiber may be important for obtaining a uniform line shape on the powder surface. In some embodiments, the optical path of the additive manufacturing system includes a lens array, which includes one or more microlenses (e.g., one or more microlens arrays) followed by one or more objective lenses. All beams from independent laser energy sources pass through the same set of lenses in the lens array and the same objective lens in the optics assembly. As will be described in more detail later, the lens array (including one or more microlenses) may be configured to collimate the laser energy output from each optical fiber source and to transform the beam shape from a circular beam profile with a Gaussian power distribution to a rectangular beam profile with a uniform power distribution on both axes (e.g., a top-hat power distribution). In this way, the lens array can transform the laser energy output into an array of rectangular laser energy pixels. The objective lenses may be configured to define the focal length of the combined line array and to function to reduce the output from the lens array. This reduction involves changing the pixel spacing from an initial spacing determined by the distance between adjacent fibers in the fiber holder to a desired pixel spacing on the powder surface. For example, an objective lens can be configured to reduce the array so that there is no spacing between adjacent pixels.

[0034]

[0058] In some embodiments, the laser line output from the optics assembly may be a linear array having two or more rectangular pixels, in which case the line is longer than its width when all pixels are turned on. For example, in a system with two laser energy sources, if both lasers are controlled to output the same laser power, the power density along the length of the line is substantially uniform. Alternatively, the power levels of these two pixels can be controlled to have different levels, resulting in a line output with a power density that varies along the length of the line. In other embodiments, more than two pixels can be used to realize a relatively long laser line. In some such embodiments, the power density along the length of the line can be kept uniform by controlling each pixel to have the same power output. Alternatively, any combination of power densities along the line can be obtained by independently controlling the pixels to have different power levels.

[0035]

[0059] The inventors have understood that the conversion of the beam output from each laser energy source from a circular Gaussian profile to a square top-hat profile is crucial for enabling multi-track single-pass melt pool stability on a powder surface. For example, Figure 1 shows a circular beam with a Gaussian power density around its centerline. As shown in Figure 2, when two circular Gaussian beams are placed adjacent to each other, the power densities are combined according to their exact beam power densities. The sum of the combined power densities along the line through the centers of both circular profiles is shown in the graph on the right of Figure 2. The combined power density defines peaks and valleys and is not uniform. As shown in Figure 3, when these two spots move in a direction perpendicular to their stacking direction, different tracks on the powder surface will be exposed to different power profiles depending on the position of the track relative to the centerline of the incident beam. Tracks directly located on the center of individual circular beams (Track A in Figure 3) correspond to relatively wider beam shapes with relatively larger peak intensities compared to tracks offset from the centerlines of individual circular beams (Track B in Figure 3). The greatest difference between the different tracks lies between the tracks on the individual beam centerlines and the tracks at the intersection of two adjacent circular beams. The differences in effective incident beam width and peak power density between the different tracks under this moving line result in different melting rates and melt pool instabilities, as described above.

[0036]

[0060] In contrast to the circular Gaussian beam shape described above, when the output from each independent laser energy source is shaped (for example, using one or more microlenses) into a rectangular beam shape (i.e., a top-hat profile) with uniform power density, the resulting beam shape and power density are shown in Figure 4. The power profile of the resulting rectangular beam shape is substantially uniform in both the X and Y directions. As a result, when two rectangular profiles are placed adjacent to each other and moved perpendicular to their stacked length in the longitudinal direction, the power profiles of the adjacent beam profiles are combined to provide a substantially uniform profile not only along the length of the line projection but also across the short width of the line. This means that each track line (tracks C, D, and E in Figure 5) corresponds to the same effective beam width and peak power as all the other tracks as the line is scanned on the powder surface.

[0037]

[0061] Furthermore, the inventors have understood that the uniformity of the net power exposure of the incident laser energy line on the powder surface is crucial for generating high-quality fused material tracks. As shown in Figures 6-9, a line composed of multiple adjacent rectangular top-hat profile pixels (Figures 6-7) generates a relatively uniform incident energy profile at all points within the scanned beam, compared to a similar line composed of adjacent circular Gaussian pixels (Figures 8-9). With a rectangular top-hat profile, not only is the centerline power density relatively uniform across the width of the line, but the off-center power density across the width of the line is also relatively uniform. Even when a circular Gaussian profile is converted to a circular top-hat profile (i.e., a circular beam shape with uniform power density), the centerline power density profiles between the rectangular and circular beam shapes remain the same, while the off-center power density of the rectangular beam shape is significantly more relatively uniform than the off-center power density of the top-hat circular beam shape. Therefore, in all cases, the rectangular top-hat beam shape for each pixel generates a relatively uniform power density at all points within the multi-pixel line compared to a similar multi-pixel line composed of circular beam shapes of Gaussian or top-hat profiles. Furthermore, this relatively uniform power density can generate relatively small melt pool instability, while also allowing for relatively high processing speeds, relatively high power densities, and a relatively wide process window.

[0038]

[0062] In some embodiments, it may be important to operate the additive manufacturing process with a powder surface positioned within the focal point. For example, this can ensure the maximum possible power density as the incident beam area is minimized on the powder surface. This also allows for minimizing the size of each pixel and consequently allows for the highest possible resolution of the resulting molten pool and fused partial features. Operating out of focus may result in a lower effective power density of the incident beam, which may necessitate a relatively slow scanning speed and thus a slower net processing rate. Alternatively, a relatively high-power laser energy source may be required to operate at the same speed and achieve a similar processing rate. These large net powers may lead to molten pool instability, as mentioned above, which will also consequently require a relatively small processing speed to operate within a stable set of process parameters. Operating within the focal point can also help maintain a substantially uniform power density profile across the width of the multi-pixel line. Due to out-of-focus operation, pixels may overlap, and the power density profile along the line length may have undesirable peaks and valleys. Depending on the particular embodiment, the type, number, and spacing of the objective lenses depend on the desired degree of reduction, the desired focal length, and the desired focal size.

[0039]

[0063] Referring to Figures 10-13, another example of the effect of power distribution within a linear array of laser energy pixels is described. Specifically, Figure 10 depicts a linear array 200 that can be projected onto a surface (e.g., a powder bed surface), and the linear array includes a series of adjacent rectangular laser energy pixels 201-205. As described above, the power density across the width of individual pixels can have different distributions, and the interaction of the different power density distributions of adjacent pixels will determine the uniformity of the power density of the linear array 200. When the power density distribution for individual pixels takes a Gaussian form 210, and multiple adjacent pixels are set to the same power level, the individual pixels 220, 221, and 222 are combined to form a single output line 230, which has an output power density distribution that is the spatial sum of the individual pixels. The variation in density on this single output line 230 is due not only to the variation within each pixel but also to the sum of the overlap areas between the pixels. When the power density distribution for each individual pixel is uniform (i.e., a top-hat shape) 215, and adjacent pixels in the linear array 200 are set to the same power level, the individual pixels 225, 226, and 227 are combined to form a single output line 235. Compared to Gaussian pixels, the output line 235 has a relatively uniform power density distribution because there is relatively little variation across the width of each individual pixel, and there is relatively little overlap area between adjacent pixels. The same applies to the power distribution across the width of a single output line. The top-hat profile 215 across the width of a pixel results in a relatively uniform power density distribution than the Gaussian distribution 210 across the width.

[0040]

[0064] As shown in Figure 11, the use of a single-output linear array 250, including independently controllable laser energy pixels 251–255, has advantages over the use of individual fixed-spot arrays 270, where the individual laser energy inputs must be tilted relative to each other to accommodate the size of their optical arrays. In the single-output linear array 250, each individual pixel is incident on the surface (e.g., the powder bed surface) at the same angle. This angle can be perpendicular to the surface (280), or it can be a sharp angle with respect to the surface, either away from the primary scan direction (281) or toward the primary scan direction (282). All pixels always maintain the same angle. In the case of having a top-hat power density profile across the width of this line, the power density for sharp angles (283, 284) has a relatively wide width but a low peak value depending on the actual incident angle. In contrast, in the case of a Gaussian distribution, the power density across the width of the line shows an elongated lead-in 286 or elongated tail 288 with a sharp incidence angle, compared to a normally incident pixel 287.

[0041]

[0065] Furthermore, depending on the individual spot array 270, due to the size limitations of its optical array, the incident beam will always consist of a combination of sharp incident angles in both the direction toward the primary scan direction (301) and the direction away from it (302), and may also include a perpendicular incident spot (300). For individual spots with a top-hat power density distribution, spots with the same incident angles 303, 305 from different directions will result in similar power distributions, but the perpendicular spot 304 will result in a different power density. In the case of a Gaussian power distribution, different incident angles will result in several spots being scanned simultaneously by elongated lead-ins 306 and elongated tails 308, as well as potential perpendicular spot incidents 307 without lead-ins or tails. This hinders the optimization of scan speeds for different incident beams. As the incident angle increases, the difficulty of managing different scan power density profiles increases.

[0042]

[0066] Figure 12 shows a line array with different possible outputs. The top plot shows a potential array of eight pixels forming a line. Each pixel in this line can be set to the same power density to produce a full-width line with uniform power density along the length of the line, as shown in the top plot of Figure 12. In some examples, individual pixels can be turned off to produce relatively short individual lines, as shown in the middle plot of Figure 12. Alternatively, the power level of each pixel can be set individually along the length of the line, or along multiple relatively small lines, to produce lines of almost any power density. As the total line width and pixel count increase, the ability to set non-uniform power densities along the length of the line can be useful for adapting the process to address edge effects. Pixels on the powder bed surface, adjacent to other pixels on both sides, may require relatively less total incident power to obtain a stable molten pool state than pixels on the edge of the line. This is due to convection and conduction heat losses at the edge of the line, which must be addressed with relatively more power. Furthermore, the presence or absence of fusion material beneath individual pixels from previous scan layers can affect the local thermal properties of the molten pool of a given pixel. One solution to these edge and previous scan effects is to set a custom power density along the length of the line, depending on the boundary conditions of that pixel at that point during the scan. The lower plot in Figure 12 shows the line power density with relatively high power at two edges and the stepped profile across the remaining pixels of the line.

[0043]

[0067] Figure 13 illustrates another example of the ability to turn off individual pixels within a linear array. Similar to the configuration described above in relation to Figure 12, this can also allow the use of multiple relatively short segments as well as line segments of different lengths. As shown in the upper plot of Figure 13, the linear array can be divided down to the resolution of individual pixels. The ultimate resolution of the 3D features formed from the powder bed fusion process by turning on or off individual pixels at various points during the scanning motion of the optics assembly is that of a single pixel. The line length can also be formed from multiple pixels shown in the two central plots of Figure 13 to a single plot shown in the lower plot of Figure 13. Single-pixel resolution can be generated from any pixel in the linear array. As a result, by activating any single pixel at any point, fine-resolution features can be generated at any point in the scanning motion of the linear array. Furthermore, single-pixel resolution can be obtained from a single scan of a line array, which has the characteristic of having a predetermined angle with respect to the direction of scanning motion by turning on and off consecutive adjacent pixels in an optics unit moving on the powder bed surface.

[0044]

[0068] As will be described in more detail later, one or more objective lenses following a lens array containing one or more microlenses can define the focal length and focus of the combined beam (e.g., a linear array of laser energy pixels). The focal length of the beam is the distance from the last objective lens of the optical assembly to the focus. At the focus, each beam or pixel has its minimum dimensions, and each beam is directly adjacent to an adjacent beam. For example, there may not be any gap between adjacent beams such that the edges of adjacent laser energy pixels are in contact with each other. Figure 14 schematically shows the state at this focus. As the beam moves away from the focus (in any direction along the beam path), the beam dimensions increase, and the beams may begin to overlap each other, as shown in Figure 15. The focus is usually defined as a region along the beam path where the beam size is within a defined range. In this example, it can be defined as a region in the beam path where the rectangular profile dimensions are less than a predetermined value. In some examples, the focus can be defined not as an actual single point, but as a length along the beam path, and is defined to begin when the size of individual beams (e.g., pixel dimensions) decreases to less than a defined focus size, and to end when the beam expands back to exceed the defined focus size.

[0045]

[0069] In some cases, a rectangular top-hat beam shape can be obtained without the use of a lens array including microlenses. For example, when a square optical fiber is used to supply power from an independent laser energy source, the output from the fiber in the fiber holder already has a square top-hat shape with uniform power density in both directions of the square. The independent output from the square optical fiber mounted in the fiber mount can be directed straight into the objective lens stack for reduction and focusing on the fiber surface.

[0046]

[0070] However, the inventors have understood that the use of square fibers may impose further requirements regarding the alignment and mounting of the fibers within the fiber mount. Specifically, with square fibers in which the square top-hat shape is established by the fiber itself, the fiber mount must establish not only the spacing and axial alignment, but also the rotational alignment between the square shapes. If the square fibers are not rotationally aligned, the resulting pixel pattern will also be misaligned, as shown in Figure 16. In contrast, with lens arrays including circular fibers and one or more microlenses to shape a circular beam into a rectangular beam, as shown in Figures 17-18, the orientation of the fiber around its axis is not a critical parameter. The orientation of the circular fiber is acceptable, as the ultimate rectangular shape and pixel orientation of the pixels are established and maintained by the lens array. Since each microlens in the lens array can be manufactured as a single monolithic part, maintaining the alignment between the rectangular beam shapes is specific to the manufacturing of each lens and can be controlled. Therefore, after the rectangular pixels pass through the objective lens, the output from the fiber optic assembly generates a uniform pixel array on the powder surface without the need to rotationally align the fibers.

[0047]

[0071] Next, with reference to Figures 19 to 28, specific non-limiting embodiments of the additive manufacturing systems described herein will be described in further detail. Since this disclosure is not limited to the specific embodiments described herein, it should be understood that the various systems, components, features, and methods described in relation to these embodiments may be used individually and / or in any desired combination.

[0048]

[0072] Figure 19 illustrates one embodiment of an additive manufacturing system 10. The system includes two or more independent laser energy sources 1 coupled to associated optical fibers 2. For example, an independent laser energy source 1 may be an Nd:Yag fiber laser having a maximum power output of 10 to 2000 W. In some examples, the maximum power output of each laser energy source may be 200 to 1000 W. In other embodiments, the laser source may include a fiber-coupled diode laser. Each independent optical fiber 2 for each independent laser energy source 1 is routed to an optics assembly 3 such that the first end of each optical fiber is coupled to the associated energy source, and the second end of each optical fiber is received within the optics assembly. As will be described in more detail later, the optics assembly 3 generates a combined optical output 6 that is directed onto the powder bed surface 7 located on the build surface.

[0049]

[0073] Each independent laser energy source 1 is connected to a central control unit 4 using a control cable 5. The central control unit 4 is configured to control each laser energy source 1 independently. For example, the central control unit can provide on / off signals and power output signals to each independent laser energy source. The power output signals to each independent laser energy source 1 can control the output power of the laser energy source from a minimum power level to a maximum output power level. For example, the output power range may be 10% to 100% of the maximum power output of each independent laser energy source 1.

[0050]

[0074] Figure 20 illustrates one embodiment of the optics assembly 3. Within the optics assembly 3, the ends of each optical fiber 2 are received in a fiber mount 20 (see Figure 21). The fiber mount 20 fixes the spacing between adjacent optical fibers 2, ensuring that the axes of the optical fibers 2 are parallel and aligned. On the output side of the fiber mount 20, the ends of the optical fibers 2 are cut, cleaned, and polished to ensure that a uniform and consistent beam emanates from each individual optical fiber 2. The combined laser output 34 from the individual optical fibers 2 is directed toward a series of optical lenses 21-29. The combined laser output 34 forms a single line from the projections of adjacent independent laser sources 1 through the individual optical fibers 2 linearly arranged within the fiber mount 20.

[0051]

[0075] As best illustrated in Figure 21, when all independent laser sources 1 are turned on, the combined laser output 34 forms a continuous line 55 having individual pixels 50-54. At points along the optical path within this optics assembly, adjacent pixels 50-54 may overlap, or the pixels may be separated from each other. The degree of overlap of pixels 50-54 in the combined laser energy output 34 may depend on the optical path from when the laser energy output leaves the fiber 2 in the fiber mount 20 until it passes through pixels 50-54. As a result, any suitable number of independent laser energy sources 1 can be combined into a single combined laser output 34. For example, in some embodiments, the number of independent laser energy sources 1 is in the range of 2-20, 5-50, or 10-100.

[0052]

[0076] The combined laser output 34 within the optics assembly 3 passes through a series of lenses 21-29. The number and type of lenses 21-29 depend on the desired output shape and focal length of the combined optical output 6 from the optics assembly. As shown in Figure 22, the first lens 21 is a high-speed axial collimator followed by a low-speed axial collimator 22, which are used to form the combined laser output 34 into a line shape with controlled overlap between adjacent pixels 60, 61, and 62, in which case each pixel is generated by the output of an independent laser energy source 1. The high-speed and low-speed axial collimators 21 and 22 are also used to modify the beam shape of each independent laser source 1, for example, to convert a circular beam profile from an optical fiber into rectangular laser energy pixels. The resulting pixel shapes 60, 61, and 62 form a continuous output line 63 when all independent laser sources 1 are turned on. Next, this continuous output line 63 passes through a further series of lenses 23-29 (see Figure 20), which shape and focus the output line within the optics assembly 3 to form a controlled and combined optical output 6.

[0053]

[0077] The optics assembly 3 may include certain mirrors 30, 31, 32 configured to bend a continuous output line 63 of laser energy. In some cases, this bending helps to maintain the dimensions of the optics assembly 3 in a limited state. In the embodiments depicted, the continuous output line 63 is bent twice within the optics assembly 3. However, since this disclosure is not limited in this respect, it should be understood that the output line 63 does not have to be bent and may be bent once, three times, or any other appropriate number of times. The optics assembly 3 further includes a frame 36 including a fiber mount 20, lenses 20-29, and mounting and alignment features for the mirrors 30-32. The optics assembly 3 may also include an adjustable focus array 37 having a set of adjustable lenses 27, 28, 29 that can adjust the focal length of the combined optical output 6.

[0054]

[0078] Depending on the particular embodiment, the combined optical output 6 of the optics assembly 3 can be detached from the assembly in any suitable orientation, such as being perpendicular to the input of each optical fiber 2, parallel to each optical fiber 2, or at any angle to the optical fiber 2.

[0055]

[0079] Figure 23 depicts another embodiment of the optics assembly 500. In this embodiment, independent optical fibers 600 enter one side of the optics assembly 500, and the ends 601 of the optical fibers are received by a fiber mount 602. The fiber mount ensures that the ends of individual fibers 601 are firmly held, aligned, and parallel within the optical assembly. Depending on the particular embodiment, the spacing between individual fibers in the fiber mount may be about 500 microns to about 10 mm. For example, in some embodiments, the spacing between adjacent fibers may be about 1 mm or about 2 mm. The ends of individual fibers 601 are cleaved, abraded, and polished at the exit of the fiber mount 602. The beam output from the ends of individual fibers 601 is then directed to a cylindrical lens 603 that collimates the beam in a first direction perpendicular to a plane passing through the center of the end of the fiber 601. Next, the beam passes through a cylindrical microlens array 604 that collimates the beam in a second direction perpendicular to the first direction. Then, the beam passes through another cylindrical lens 605 that shapes the beam from a circular Gauss into a rectangular top-hat shape in the first direction. Next, the beam passes through a cylindrical microlens array 606 that shapes the beam from a circular Gauss into a rectangular top-hat shape in the second direction. Subsequently, the beam passes through cylindrical microlenses 607 and 608, which generate Fourier transforms in the first and second directions, respectively. At this point, the beam can be bent using mirror 610, or it can be allowed to continue in a straight path. The beam passes through a set of spherical objective lenses 611-616 that reduce the beam and set the focal length and focus. The beam path can be bent by mirror 613 before, during, or after passing through the objective lenses. The reduction may be by a coefficient of 10:1, 5:1, 20:1, or any range within these.The focal length can be set to 100 mm, 200 mm, 300 mm, or any other suitable value by adjusting the type and spacing of the objective lenses. The output beam 620 from the last objective lens may be directed straight toward the powder surface, or it may be directed toward the powder surface using a mirror or a mirror controlled by a scanning galvanometer.

[0056]

[0080] While cylindrical lenses and microlenses have been described above for collimating and shaping the beam output, it should be understood that other types of lenses may also be suitable. For example, in other embodiments, any suitable combination of cylindrical, spherical, and conical lenses can be used to collimate and / or shape the beam output. Similarly, while spherical objective lenses have been described above, other lens shapes (e.g., cylindrical and / or conical lenses) can be used as objective lenses. Therefore, it should be understood that this disclosure is not limited to any particular lens shape or combination of lens shapes.

[0057]

[0081] Referring next to Figure 24, the combined optical output 6 can be directed toward a mirror 80 mounted on the galvanometer. In the embodiment depicted, the combined optical output 6 is redirected toward the powder bed surface 7 by the mirror 80 mounted on the galvanometer. Since the mirror 80 mounted on the galvanometer rotates over an angle 84, the combined optical outputs 81, 82 (after reflection by the mirror 80) are scanned over a distance on the powder bed surface 7 defined by an angle 83. The position of the mirror 80 mounted on the galvanometer is driven by a galvanometer controller 85, which is connected to a central control unit 4 via an electrical control cable 86. The angle 83 over which the combined optical outputs 81, 82 can be scanned depends on the focal length of the combined optical output 6 from the optics assembly 3. In some embodiments, the use of an adjustable focus array 37 within the optics assembly 3 (see Figure 16) allows for a relatively wide angle 83 for scanning the powder bed surface 7. In some examples, the optics box 3, which has a mirror assembly 80 attached to the galvanometer, is movable relative to the powder bed surface 7, thereby enabling multiple scanning modes.

[0058]

[0082] As shown in Figure 25, in some embodiments, the combined optical output 6 from the optics assembly 3 can be directed toward the powder bed surface 7 using a fixed mirror assembly 90 so that the optical output 91 is fixed in relation to the position of the optics assembly 3. The optics assembly 3 can then be moved in relation to the powder bed surface 7 to obtain the desired scanning pattern.

[0059]

[0083] As described above, the combined optical output from the optics assembly, directed toward the powder bed surface, takes the form of a linear array of two or more adjacent rectangular laser energy pixels formed from the outputs of independent laser energy sources, and the linear array can be scanned on the powder bed surface to selectively melt a portion of the material on the powder bed to form a desired portion.

[0060]

[0084] Figure 26 shows a schematic representation of a linear array 110 on a powder bed surface 100, including a plurality of adjacent rectangular laser energy pixels 101-105. Depending on the particular embodiment, the laser energy pixels can be formed (for example, via a lens array including one or more microlenses) to have any suitable size. For example, in some embodiments, each rectangular pixel may have a width of about 50 microns to about 200 microns. In one embodiment, each pixel may have a width of about 100 microns. Furthermore, the power level of each individual pixel 101-105 can be independently controlled by adjusting the output of each independent laser energy source. In addition, each pixel 101-105 can be independently turned on and off by controlling the associated laser energy source.

[0061]

[0085] The resulting linear array 110 can be scanned on the powder bed surface 100 not only in the primary direction 115, which is perpendicular to the longer dimension of the linear array 110, but also in the secondary direction 116, which is parallel to the longer dimension of the linear array 110. For example, scanning in the primary direction 115 can be achieved by moving the optics assembly, or by scanning the combined optical output from the optics assembly using a mirror assembly attached to a galvanometer or other suitable configuration. Furthermore, in some examples, a combination of scanning with a mirror assembly attached to a galvanometer while moving the optics assembly can be used to scan the combined optical output on the powder bed surface in the primary direction. Scanning in the secondary direction 116 can be achieved by moving the optics assembly in relation to the powder bed surface 100. It should be understood that simultaneous scanning in both the primary and secondary directions can be used to scan any desired pattern on the powder bed surface 100.

[0062]

[0086] Figure 27 illustrates another embodiment in which the optics assembly 3 is mounted on a rotating stage that allows rotation of the optics assembly 3 around an axis. This configuration allows the linear array 110 to rotate to a new position 111 on the powder bed surface 100. In some examples, this allows subsequent passes on the powder bed surface to be performed in different directions, resulting in the molten tracks on consecutive layers 112, 113 being rotated relative to each other at a predetermined angle, while still allowing full utilization of the line array in scanning both layers. For example, in some embodiments, the rotation angle of the optics assembly 3 between consecutive layers is about 30° to about 90° (e.g., about 30°, about 45°, or about 90°). The axis of rotation of the optics assembly 3 can be aligned with an axis 130 passing through the center of the linear array 110. Alternatively, the axis of rotation of the optics assembly can be positioned away from the center of the linear array 110, such as along axis 131. In one such embodiment, the position shift of the linear array 110 can be calculated based on the displacement of the axis of rotation from the center of the linear array 110. This offset can then be addressed by applying the offset to the primary and secondary scan positions. In some embodiments, the optics assembly 3 can be moved and rotated simultaneously in the primary and secondary scan directions 115 and 116 to obtain the linear array 110 in any desired orientation on the powder bed surface 100.

[0063]

[0087] Figure 28 shows one possible layout for a multi-source powder bed laser fusion system. The build surface 510 can be indexed vertically using a vertical sliding system 560. A recoater head 570 is configured to add a layer of material (e.g., powdered metal) onto the build surface after the vertical slide has been indexed downwards. An optics assembly 500, receiving optical fibers from multiple laser sources, is mounted on another vertical slide 550, which is mounted on a cross slide 540 capable of generating lateral motion. Each end of the cross slide is mounted in a gantry style on linear slides 520, 530, which allow the cross slide to move in the other lateral dimension. As a result, the output 501 from the optics assembly can be scanned across the entire build surface as appropriate.

[0064]

[0088] While these instructions have been described in relation to various embodiments and examples, this is not intended to limit the instructions to such embodiments or examples. On the contrary, these instructions include various alternatives, modifications, and equivalents, as will be understood by those skilled in the art. Accordingly, the above description and drawings are for illustrative purposes only.

Claims

1. An additive manufacturing system, Build surface and, At least two laser energy sources, An optics assembly comprising at least two optical fibers, each optical fiber coupled to a related laser energy source and configured to guide laser energy from each laser energy source toward the build surface to form a related laser energy pixel on the build surface, and each laser energy pixel configured to melt at least a portion of the layer of material on the build surface to fuse at least a portion of the layer of material when a layer of material is deposited on the build surface, A gantry system coupled to and supporting the optics assembly, wherein the gantry system is configured to move the optics assembly in at least two lateral directions while at least one of the at least two laser energy sources is activated to scan the laser energy pixels across the build surface so that each laser energy pixel selectively forms a track of fused material in the layer of material as the layer of material is deposited on the build surface. Includes, An additive manufacturing system in which each laser energy source is independently controllable to set the power output level of the associated laser energy pixel.

2. The additive manufacturing system according to claim 1, wherein the gantry system includes a cross slide configured to move the optics assembly along a first transverse direction and a linear slide configured to move the cross slide along a second transverse direction.

3. The additive manufacturing system according to claim 1, wherein the gantry system is further configured to move the optics assembly perpendicular to the build surface.

4. The additive manufacturing system according to claim 3, wherein the gantry system includes a vertical slide configured to move the optics assembly along the vertical direction.

5. The additive manufacturing system according to claim 1, wherein the optics assembly is coupled to a rotating stage configured to rotate the optics assembly about at least one axis.

6. The additive manufacturing system according to claim 1, wherein the beams output from each of the laser energy sources have a Gaussian power density distribution, and the optics assembly is configured to convert the Gaussian power density distribution into a uniform power density distribution in the associated laser energy pixels.

7. The additive manufacturing system according to claim 1, wherein the optics assembly is configured to arrange at least two laser energy pixels on the build surface as a linear array of laser energy pixels.

8. The additive manufacturing system according to claim 7, wherein the at least two laser energy sources are configured to generate a substantially uniform power density along a linear array of laser energy pixels.

9. The additive manufacturing system according to claim 7, wherein the at least two laser energy sources are independently controllable to generate a power density that is variable along a linear array of laser energy pixels.

10. The additive manufacturing system according to claim 1, wherein the maximum power output from each laser energy source is approximately 200W to approximately 1000W.

11. The additive manufacturing system according to claim 1, further comprising a material deposition system configured to deposit a layer of the material on the build surface.

12. The additive manufacturing system according to claim 11, wherein the layer of material comprises metal powder, and the material deposition system is configured to sprinkle the metal powder on the build surface.

13. A method for additive manufacturing, To form independently controllable laser energy pixels associated with each laser energy source, the laser energy is directed along each optical fiber of the optics assembly toward the build surface, by independently controlling each of at least two laser energy sources, Exposing the layer of material on the build surface to at least one of the laser energy pixels to melt at least a portion of the layer of material, In order to selectively form a track of fused material in a portion of the layer of the material, the optics assembly is moved in at least one lateral direction relative to the build surface while at least one of the at least two laser energy sources is activated. A method that includes this.

14. The method for additive manufacturing according to claim 13, wherein moving the optics assembly includes at least one of moving the optics assembly along a cross slide in a first lateral direction and moving the optics assembly along a linear slide in a second lateral direction.

15. The additive manufacturing method according to claim 13, further comprising moving the optics assembly in a direction perpendicular to the build surface.

16. The additive manufacturing method according to claim 13, further comprising rotating the optics assembly about at least one axis.

17. The additive manufacturing method according to claim 13, wherein the beams output from each of the at least two laser energy sources have a Gaussian power density distribution, and independently controlling the at least two laser energy sources includes using the optics assembly to convert the Gaussian power density distribution into a uniform power density distribution in the associated laser energy pixels.

18. The additive manufacturing method according to claim 13, wherein independently controlling the at least two laser energy sources comprises independently controlling each of the at least two laser energy sources to form the independently controllable laser energy pixels as a linear array of independently controllable laser energy pixels.

19. The method for additive manufacturing according to claim 18, wherein independently controlling the at least two laser energy sources to form the linear array comprises independently controlling the at least two laser energy sources to generate a substantially uniform power density along the linear array of laser energy pixels.

20. The method for additive manufacturing according to claim 18, wherein independently controlling the at least two laser energy sources to form the linear array comprises independently controlling the at least two laser energy sources to generate a power density that can vary along the linear array of laser energy pixels.

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