Patent Application
20180264598
The disclosure relates to an improved method of producing components using an additive manufacturing technique. The disclosure provides an improved method of producing components, some of examples of which comprise: improved microstructure, decreased manufacturing time, decreased cost, decreased waste of materials. In particular, the disclosure relates to a process of scanning a laser during an additive manufacturing build process.
Additive manufacturing (AM) techniques may include electron beam freeform fabrication, laser metal deposition (LMD), laser wire metal deposition (LMD-w), gas metal arc-welding, laser engineered net shaping (LENS), laser sintering (SLS), direct metal laser sintering (DMLS), electron beam melting (EBM), powder-fed directed-energy deposition (DED), and three dimensional printing (3DP), as examples. AM processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), AM encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. AM techniques are capable of fabricating complex components from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer aided design (CAD) model. As an example, a particular type of AM process uses an energy beam, for example, an electron beam or electromagnetic radiation such as a laser beam, to sinter or melt a powder material and/or wire-stock, creating a solid three-dimensional object in which a material is bonded together.
Selective laser sintering, direct laser sintering, selective laser melting, and direct laser melting are common industry terms used to refer to producing three-dimensional (3D) objects by using a laser beam to sinter or melt a fine powder. For example, U.S. Pat. No. 4,863,538 and U.S. Pat. No. 5,460,758 describe conventional laser sintering techniques. More specifically, sintering entails fusing (agglomerating) particles of a powder at a temperature below the melting point of the powder material, whereas melting entails fully melting particles of a powder to form a solid homogeneous mass. The physical processes associated with laser sintering or laser melting include heat transfer to a powder material and then either sintering or melting the powder material. Electron beam melting (EBM) utilizes a focused electron beam to melt powder. These processes involve melting layers of powder successively to build an object in a metal powder.
AM techniques, examples of which are discussed above and throughout the disclosure, may be characterized by using a laser or an energy source to generate heat in the powder to at least partially melt the material. Accordingly, high concentrations of heat are generated in the fine powder over a short period of time. The high temperature gradients within the powder during buildup of the component may have a significant impact on the microstructure of the completed component. Rapid heating and solidification may cause high thermal stress and cause localized non-equilibrium phases throughout the solidified material. Further, since the orientation of the grains in a completed AM component may be controlled by the direction of heat conduction in the material, the scanning strategy of the laser in an AM apparatus and technique becomes an important method of controlling microstructure of the AM built component. Controlling the scanning strategy in an AM apparatus is further crucial for developing a component free of material defects, examples of defects may include lack of fusion porosity and/or boiling porosity.
The abovementioned AM processes is controlled by a computer executing a control program. For example, the apparatus 110 includes a processor (e.g., a microprocessor) executing firmware, an operating system, or other software that provides an interface between the apparatus 110 and an operator. The computer receives, as input, a three dimensional model of the object to be formed. For example, the three dimensional model is generated using a computer aided design (CAD) program. The computer analyzes the model and proposes a tool path for each object within the model. The operator may define or adjust various parameters of the scan pattern such as power, speed, and spacing, but generally does not program the tool path directly. One having ordinary skill in the art would fully appreciate the abovementioned control program may be applicable to any of the abovementioned AM processes. Further, the abovementioned computer control may be applicable to any subtractive manufacturing or any pre or post processing techniques employed in any post processing or hybrid process.
The above additive manufacturing techniques may be used to form a component from stainless steel, aluminum, titanium, Inconel 625, Inconel 718, Inconel 188, cobalt chrome, among other metal materials or any alloy. For example, the above alloys may include materials with trade names, Haynes 188®, Haynes 625®, Super Alloy Inconel 625™, Chronin® 625, Altemp® 625, Nickelvac 625, Nicrofer® 6020, Inconel 188, and any other material having material properties attractive for the formation of components using the abovementioned techniques.
In the abovementioned example, a laser and/or energy source is generally controlled to form a series of solidification lines (hereinafter interchangeably referred to as hatch lines, solidification lines and raster lines) in a layer of powder based on a pattern. A pattern may be selected to decrease build time, to improve or control the material properties of the solidified material, to reduce stresses in the completed material, and/or to reduce wear on the laser, and/or galvanometer scanner and/or electron-beam. Various scanning strategies have been contemplated in the past, and include, for example, chessboard patters and/or stripe patterns.
One attempt at controlling the stresses within the material of the built AM component involves the rotation of stripe regions containing a plurality of adjoining parallel vectors, as solidification lines, that run perpendicular to solidification lines forming the boundaries of the stripe region. for each layer during an AM build process. Parallel solidification lines, bounded by and perpendicular to a stripe, are rotated for each layer of the AM build. One example of controlling the scanning strategy in an AM apparatus is disclosed in U.S. Pat. No. 8,034,279 B2.
As shown in
Even with the abovementioned rotating stripe strategy, the need exists to further create variance in each layer. By employing the various embodiments disclosed, build efficiency can be further increased by preventing unnecessary jumps of the energy source, preventing unnecessary on/off transitions of the laser and/or improving control and/or efficiency of heat buildup within the layer. Further the microstructure of the part can be altered by creating each solidification line as a waveform.
One challenge associated with laser based AM is producing a desired melt pattern in the powder while maintaining a desired speed of the build process. The buildup of heat within the powder and fused material during a build is a concern, as various material defects may occur if too much heat is built up in the material during an AM process and/or if insufficient heat is built up to properly fuse the powder. Since variance of the scan pattern in each build layer is generally desirable during an AM build, a waveform shaped scan pattern is used to create variance in the AM build layers, and by controlling the speed of the laser, the laser power, and the period, frequency, and amplitude of the waveform scan pattern, desirable material properties and efficiency of the build is achieved.
The disclosure relates to an improved scanning strategy, having a waveform hatch pattern for scanning a laser during an AM build process. When controlling the laser during the build process according to one embodiment, a waveform hatch pattern is formed on each layer so as to increase the variance between layers and improve the microstructure of the completed component. In one aspect, a first layer is formed by scanning a laser in a series of hatch lines formed as a smooth repetitive oscillation (e.g. as a sinusoidal wave). Each subsequent layer may have the series hatch lines formed as a differing sinusoidal and/or smooth repetitive oscillating pattern. For example, any one or a combination of the amplitude, frequency, angular frequency and/or phase of the sinusoidal pattern may be varied in each layer of the build. By varying the pattern when forming each layer, the desired variance in each layer can be achieved.
The abovementioned sinusoidal solidification patterns may be formed across the entire surface of the layer of the build. Further, the surface of the build may be divided into a series of stripe regions, and a series of sinusoidal solidification patterns may be formed within each stripe region.
Using the techniques discussed below, build efficiency and quality can be increased by preventing unnecessary jumps of the energy source, preventing unnecessary on/off transitions of the laser and/or by improving efficiency of heat buildup within the layers of the build. In the case of multiple lasers and/or energy sources being used, the disclosed scanning scheme may be used to further improve the AM build by employing various strategies for the use of multiple energy sources (e.g. lasers).
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more example aspects of the present disclosure and, together with the detailed description, serve to explain their principles and implementations.
While the aspects described herein have been described in conjunction with the example aspects outlined above, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that are or may be presently unforeseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the example aspects, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the disclosure. Therefore, the disclosure is intended to embrace all known or later-developed alternatives, modifications, variations, improvements, and/or substantial equivalents.
When using any of the abovementioned AM techniques to form a part by at least partially melting a powder, a scan or mark of the laser across the powder material, in a raster scan fashion is used to create hatch scans (hereinafter referred to interchangeably as solidification lines, hatch scans, rasters and/or scan lines). During an AM build, the abovementioned raster scans are used to form the bulk of a part cross section. Contour scans, may further be used to outline the edges of the part cross section. During a raster scan process, the energy source or laser is turned on in regions where a solid portion of the AM build is desired, and switched off, defocused and/or decreased in power where melt formation of the object's cross section in that layer is not desired. These hatch scans are repeated along adjacent lines (e.g. 213A and 213B in
When employing the scan strategy according to one embodiment at least a partially fused region may be formed on a first layer of powder. As shown in
When forming the adjacent curved solidification lines discussed above, a laser and/or energy source may adjusted to control the amount of powder melted along a solidification line; accordingly, a melting width and depth of each solidification line may be controlled. When the laser melts powder corresponding to solidification line 301, the material in the portion between solidification lines may not have cooled and the thin line of powder between curved solidification line 301 and the previous or subsequently formed adjacent curved solidification line may at least partially melt. The molten material in the curved solidification line 301 may fuse with the previously or subsequently formed curved solidification line and the molten material may fuse with the material bordering or other solidification lines formed in the powder. The energy source and/or laser may also be controlled so that the heat radiating from the curved solidification line 301 and a previously formed or subsequently formed curved solidification line may cause the thin line of powder between the adjacent solidification lines to sinter together without melting. Further, the scanning of the energy source and/or laser may be controlled to cause the thin line of powder between the solidification lines 301, and a previously or subsequently formed solidification line to remain unfused without sintering and/or melting.
When forming a subsequent layer of the AM build (e.g. as shown in
When forming either of adjacent series of solidification lines as shown in
It may be desirable to control the melt characteristics as described above, the varying distance between adjacent solidification lines may need to be compensated for to achieve a uniform effect on the material between the solidification lines (e.g. 314) and/or on the next or subsequent solidification line (e.g. 315). For example, since a distance is greater between solidification lines 310 and 315 at a portion of the pattern 314B, it may be necessary to impart an increase amount of energy to the powder while forming a solidification line in a region of the pattern corresponding with 314B. Further, since a distance is less between solidification lines 310 and 315 at a portion of the pattern 314A, it may be necessary to impart a decreased amount of energy to the powder while forming a solidification line in a region of the pattern corresponding with 314A. The amount of energy imparted when forming a solidification line may adjusted by controlling any on one of or the combination of a speed at which the solidification line is formed (i.e. speed at which the energy source is scanned along the powder), the power of the energy beam, and/or the focus of the energy beam. For example, it may be desirable to increase the speed at which the energy source is scanned along the powder at portions 303 and 313 where the distance (e.g. as represented by 314A) between solidification lines is smaller and decrease the speed when forming portions 302, 304, 311, and/or 312 where the distance (e.g. as represented by 314B) between solidification lines is greater. As another example, it may be desirable to decrease the power of the energy source and/or slightly de-focus the energy source in a portions 303 and 313 where the distance 314A between the solidification lines is smaller and increase the power of the energy source and/or re-focus the energy source at portions 302, 304, 311, and/or 312 where the distance 314B between solidification lines is greater. Further, a combination of the two abovementioned methods may also be employed (e.g. a decrease in speed and power). In each of the abovementioned examples, the irradiation energy received by the powder may be varied as a function of distance from the axis about which the pattern oscillates. By using the abovementioned methods, it is possible to control the uniformity of the heat distribution across the layer, or to control the stresses, variance in the build, crystal growth, and/or control/improve microstructure within the material during a build process and/or to improve efficiency of the build process.
When forming a second layer 417, a layer of powder is provided over the first layer 418. The second layer 418 may be at least partially fused as a series of curved adjacent solidification lines 457. The energy source follows at least a second path, wherein the second path is shaped as a second pattern that oscillates about an axis. The second series of solidification lines 417 may be varied in geometry with respect to the first series of solidification lines 418. As an example, when forming the curved solidification lines along a pattern that is a sinusoidal pattern, any one or a combination of the direction, amplitude, frequency, angular frequency and/or phase of the sinusoidal pattern may be varied with respect to the solidification lines 458 of the first layer of the build. It is also noted that either as an alternative or in combination with the abovementioned variations, the axis about which the oscillating pattern is formed when forming the second series of curved solidification lines 457 may be rotated with respect to the previously formed solidification lines 458.
As each subsequent layer is built (e.g. 416 and 415), the energy source may follow a path that varies from the previous or any subsequently formed layer. For example solidification lines 456 and 455 in subsequent layers 416 and 415 may be formed as a sinusoidal pattern, that may vary in any one or a combination of the direction, amplitude, frequency, angular frequency and/or phase of the pattern of solidification lines formed in any immediate subsequent or previous layer. It is also noted that either as an alternative or in combination with the abovementioned variations, the axis about which the oscillating pattern is formed when forming the curved solidification lines 456 and 455 may be rotated with respect to the previously formed solidification lines. When forming each of the individual curved solidification lines 455, 456, 457, 458, the energy source may be scanned along a path as shown in
As shown in
As shown in
While the abovementioned exemplary scan patterns are formed across the surface of the layer being formed, depending on the desired properties of the completed build and/or time constraints of the build process, it may be desirable to divide up each layer to be built into stripe regions bounded by stripe boundaries. Further examples of stripe regions and boundaries are further disclosed in U.S. patent application Ser. No. 15/451108, titled “Triangle Hatch Pattern for Additive Manufacturing,” with attorney docket number 037216.00070, and filed Mar. 6, 2017 and U.S. patent application Ser. No. 15/451043, titled “Leg Elimination Strategy for Hatch Pattern,” with attorney docket number 037216.00078, and filed Mar. 6, 2017, which are incorporated herein in their entirety.
When forming a second layer 616, a layer of powder is provided over the first layer 616. The second layer 616 may be at least partially fused as a series of curved adjacent solidification lines 656 formed within a stripe region bounded by stripe boundaries 670 and 671. The energy source follows at least a second path, wherein the second path is shaped as a second pattern that oscillates about an axis. The second series of solidification lines 656 may be varied in geometry with respect to the first series of solidification lines 667. As an example, when forming the curved solidification lines along a pattern that is a sinusoidal pattern, any one or a combination of the direction, amplitude, frequency, angular frequency and/or phase of the sinusoidal pattern may be varied with respect to the solidification lines 667 of the first layer of the build. It is also noted that either as an alternative or in combination with the abovementioned variations, the axis about which the oscillating pattern is formed when forming the second series of curved solidification lines 656 may be rotated with respect to the previously formed solidification lines 667. Further, a stripe width may also be varied in the subsequent layer. For example, a stripe width 615B of layer 616 may be narrower or wider than the stripe width 615C of layer 617.
As each subsequent layer is built (e.g. 615), the energy source may follow a path that varies from the previous or any subsequently formed layer. For example solidification lines 655 in subsequent layer 615 may be formed as a sinusoidal pattern, that may vary in any one or a combination of the direction, amplitude, frequency, angular frequency and/or phase of the pattern of solidification lines formed in any immediate subsequent or previous layer. It is also noted that either as an alternative or in combination with the abovementioned variations, the axis about which the oscillating pattern is formed when forming the curved solidification lines 655 may be rotated with respect to the previously formed solidification lines. Further, a stripe width may also be varied in the subsequent layer as discussed above. Further, each of the abovementioned embodiments and scan methods may be used in combination with one another. For instance a layer of the build may be formed using curved solidification lines that span across the entire layer of the build, and a subsequent layer may be formed with curved solidification lines formed within stripe regions.
In an aspect, the present invention relates to the curved solidification pattern used in additive manufacturing techniques which may be of the present invention incorporated or combined with features of other powder bed additive manufacturing methods and systems. The following patent applications include disclosure of these various aspects and their use:
U.S. patent application Ser. No. 15/406,467, titled “Additive Manufacturing Using a Mobile Build Volume,” with attorney docket number 037216.00059, and filed Jan. 13, 2017;
U.S. patent application Ser. No. 15/406,454, titled “Additive Manufacturing Using a Mobile Scan Area,” with attorney docket number 037216.00060, and filed Jan. 13, 2017;
U.S. patent application Ser. No. 15/406,444, titled “Additive Manufacturing Using a Dynamically Grown Build Envelope,” with attorney docket number 037216.00061, and filed Jan. 13, 2017;
U.S. patent application Ser. No. 15/406,461, titled “Additive Manufacturing Using a Selective Recoater,” with attorney docket number 037216.00062, and filed Jan. 13, 2017;
U.S. patent application Ser. No. 15/406,471, titled “Large Scale Additive Machine,” with attorney docket number 037216.00071, and filed Jan. 13, 2017.
The disclosures of the above listed applications are incorporated herein in their entirety to the extent that they disclose additional aspects of powder bed additive manufacturing methods and systems that can be used in conjunction with those disclosed herein.
This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspect, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.
