Method to control additive manufacturing builds using laser angle of incidence

Abstract

The present disclosure generally relates to methods of additive manufacturing with control of the energy beam incidence angle that allows for aligning the laser beam angle to directly oppose the building direction of an angled wall. The method includes building an object in an additive manufacturing powder bed where the object includes a surface that is defined by a build vector projecting outward relative to the build plate center at an angle Φ relative to normal of the build plate such that 90°>Φ>0° and the directed energy beam forms an angle θ.sub.L2 relative to normal of the build plate such that 270°>θ.sub.L2>180°, wherein θ.sub.L2−Φ=180°±Δ, and Δ<45°. The present methods provide finished objects having overhanging regions with more consistent surface finish and resistance to mechanical strain or stress.

Claims

1. A method of fabricating an object, the method comprising: (a) fusing a first portion of a given layer of build material with a first directed energy beam from a first galvo scanner and a second portion of the given layer of build material with a second directed energy beam from a second galvo scanner to form at least one fused region on or over a build plate by irradiation; (b) providing a subsequent layer of build material; and (c) repeating steps (a) and (b) until the object is formed; the object comprising a surface that is defined by a build vector projecting outward relative to the build plate center at an angle Φ relative to normal of the build plate such that 90°>Φ>0° and the directed energy beam forms an angle θ.sub.L2 relative to normal of the build plate such that 270°>θ.sub.L2>180°, wherein θ.sub.L2−Φ=180°±Δ, and Δ<45°.

2. The method of claim 1, wherein Δ<30°.

3. The method of claim 1, wherein Δ<20°.

4. The method of claim 1, wherein Δ<10°.

5. The method of claim 1, wherein each of the first and second directed energy beams is a laser beam.

6. The method of claim 1, wherein each of the first and second directed energy beams is an electron beam.

7. The method of claim 1, wherein the build material is a metal powder.

8. The method of claim 1, wherein during the fabricating, Φ varies between subsequent layers.

9. A method of fabricating an object, the method comprising: (a) fusing a first portion of a given layer of metal powder with a first directed energy beam from a first galvo scanner and a second portion of the given layer of metal powder with a second directed energy beam from a second galvo scanner to form at least one fused region on or over a build plate by irradiation; (b) providing a subsequent layer of metal powder; and (c) repeating steps (a) and (b) until the object is formed; the object comprising a surface that is defined by a build vector projecting outward relative to the build plate center at an angle Φ relative to normal of the build plate such that 90°>Φ>0° and the laser beam forms an angle θ.sub.L2 relative to normal of the build plate such that 270°>θ.sub.L2>180°, wherein θ.sub.L2−Φ=180°±Δ, and Δ<45°.

10. The method of claim 9, wherein Δ<30°.

11. The method of claim 9, wherein Δ<20°.

12. The method of claim 9, wherein Δ<10°.

13. The method of claim 9, wherein the metal powder is cobalt chrome.

14. The method of claim 9, wherein during the fabricating, Φ varies between subsequent layers.

15. A method of fabricating an object within an additive powder bed system comprising a build platform, a powder bed defined over the build platform, an energy source configured to produce a directed energy beam, and a galvo scanner provided above the powder bed, the method comprising: directing an energy beam from the galvo scanner to fuse a portion of a layer of build material within the powder bed to form an object, wherein the object comprises a surface that is defined by a build vector projecting outward relative to the build plate center at an angle Φ relative to normal of the build plate such that 90°>Φ>0° and the directed energy beam forms an angle θ.sub.L2 relative to normal of the build plate such that 270°>θ.sub.L2>180°, wherein θ.sub.L2−Φ=180°±Δ, and Δ<45°, wherein the energy source comprises a first energy source configured to produce a first directed energy beam toward a first galvo scanner and a second energy source configured to produce a second directed energy beam toward a second galvo scanner.

16. The method of claim 15, wherein the energy source is a laser source.

17. The method of claim 15, wherein the directed energy beam is an electron beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic diagram of an example of an apparatus for AM according to conventional methods.

(2) FIG. 2 shows a schematic diagram of energy beam angles of incidence during AM according to a first embodiment of the present disclosure.

(3) FIG. 3 shows a perspective view of an alternative shape of objects manufactured according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

(4) The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known components are shown in block diagram form in order to avoid obscuring such concepts.

(5) The present application is directed to methods for fixed bed large scale additive manufacturing with control of energy beam angle of incidence. According to the present disclosure, points in a given powder layer that are on the edge of the powder bed (such as an overhang in a vertically asymmetric object) are irradiated with a separate energy beam from that which irradiates points near the horizontal center of the powder layer. By irradiating edge points with a secondary energy beam, the surface finish is improved at these overhang points, resulting in a finished object with improved object life and/or improved resistance to stress especially at these overhang points.

(6) As used herein, a directed energy beam angle of incidence is “substantially normal” to a surface if it irradiates the surface at a normal angle (i.e., 90°) or within ±45° of normal, such as within ±30° of normal, within ±15° of normal, within ±11°, within ±10°, within ±5°, within ±3°, or any integer or subrange in between. The tolerance for the deviation from normal will depend on the particular build material used and/or the particular application, and can be determined by persons of ordinary skill in the art. For example, an angle of incidence for cobalt chrome within 45° of normal may be sufficient.

(7) FIG. 2 shows an exemplary apparatus according to an embodiment of the present disclosure. In this embodiment, apparatus 200 is an additive laser powder bed system, such as used for direct metal laser melting (DMLM). The apparatus comprises a laser source 220, a galvo scanner 232, powder bed 212, and build platform 214. Some aspects of a DMLM system, such as the powder reservoir and waste container, are not shown in FIG. 2. The first galvo scanner 232 is located above and near or at the center of the powder bed 212, and second galvo scanner 242 is located above and near or at an edge of the powder bed 212.

(8) The apparatus of FIG. 2 is particularly well adapted to making objects 229 having overhanging surfaces 221. These surfaces may be described as projecting outward from the center of the build platform at an angle Φ relative to normal line 271. The surface 221 overhang is such that 0°<Φ<90°, and more usually the overhang is such that Φ<45°, and in certain preferred embodiments Φ<30°, 20°, 10°, or 5°.

(9) When irradiating a given powder layer 225, first galvo scanner 232 is used to direct the first energy beam 236 to points 223 at or near the center of the powder bed that are below the first galvo scanner 232. The first laser beam 236 has an angle of incidence Θ.sub.L1 where 90°<Θ.sub.L1<2700. More often Θ.sub.L1 is controlled within the range of about 135°<Θ.sub.L1<225°. This range of beam angles Θ.sub.L1 is typical for conventional powder bed additive systems. At point 223 at or near the center of the powder bed, first beam 236 forms an angle θ.sub.L1 relative to the build plate normal such that θ.sub.L1 is at or near 1800. As points on the powder bed are irradiated in regions away from the center, the θ.sub.L1 forms angles that are ±45° from 180°.

(10) When irradiating the given powder layer 225 at or near a point 224 proximal to the lateral edge of the powder bed, a second laser beam 246 directed by the second galvo scanner 242 is used. The second laser beam 246 has an angle of incidence Θ.sub.L2 such that 180°<Θ.sub.L2<270°. More typically, often Θ.sub.L2 is controlled within the range of about 180°<Θ.sub.L2<225°. The angle Θ.sub.L2 is ideally ±180° relative to the overhang angle Q. In this way the laser direction as it impacts the surface of the powder bed is directly opposite the direction of which the part overhang of the surface 221 is growing. Where Θ.sub.L2−Φ=180°±Δ°, the process is ideally controlled to minimize Δ. In general Δ should be below 45°, and is preferably below 30°, more preferably below 20° and most preferably below 10°, or any subrange within these ranges. As will be evident to those of ordinary skill in the art, the actual value of A will depend on a variety of factors, including but not limited to, one or more of the size of the powder bed, and the lateral dimensions of the object relative to the powder bed, and/or the placement of second galvo scanner 242 relative to the powder bed 212.

(11) Preliminary testing showed a 60% improvement in surface finish of the down-skin surface (i.e., surface 221) by putting the laser directly in line with the down-skin angle (i.e., Θ.sub.L2−Φ=180°), and a 25% improvement in up-skin surface finish (i.e., the horizontal surface at the top of the uppermost layer 225 of the finished object 229) by putting the laser directly in line with the up-skin angle (i.e., a 25% improvement in the finish at the upper surface of point 224).

(12) In addition, the choice of build material may influence the acceptable limits on θ.sub.L1, and the choice of when to switch between first galvo scanner 232 and the second galvo scanner 242. Switching between first galvo scanner 232 and second galvo scanner 242 (and control of the beam splitter, if used) may be controlled by any suitable means known to persons of ordinary skill in the art, such as by a manual switch or using a computer. Computer-assisted switching may be manual or automated, using methods known to those of ordinary skill in the art.

(13) In some aspects, apparatus 200 may contain a second energy source from which second galvo scanner 242 receives an energy beam 256. In some aspects, both first and second energy sources are laser sources. In some aspects, both first and second energy sources are electron beam sources. In aspects where the first and second energy source are electron beam sources, one or more deflector coils (not shown) may be used to modulate the first and second energy beams, (i.e., instead of first galvo scanner 232 and second galvo scanner 242).

(14) Although object 229 is shown in FIG. 2 as containing a surface 221 projecting from base 227 at a constant angle Φ outward relative to build platform 214, it is to be understood that object 229 is not limited to objects containing solid walls projecting outward relative to build platform 214 at a constant angle Φ toward point 224. FIG. 3 depicts an object that has an overhanging edge that includes an angle Φ defined as tangent to the surface that varies as the object is built up within the powder bed. Object 229 may have any shape with an overhang, including a shape that does not contain a wall connecting base 227 to point 224 in a straight line. As shown in FIG. 3, angle Φ varies with each given and subsequent layer of object 229 resulting in curved overhang. Suitable objects 229 may also be thin-walled, with outer surface 282 and inner surface 283 as shown in FIG. 3. In addition, the methods of the present disclosure are not limited to manufacture of objects that are laterally symmetric (i.e., objects having an axis of symmetry in the z-direction).

(15) In addition, according to the methods of the present disclosure, 0°<Φ<90° and 180°<θ.sub.L2<270°, and the values of Φ and θ.sub.L2 may be independent of each other. In some aspects, 90°>Φ>0° and 270°>θ.sub.L2>180°, such as 255°>θ.sub.L2>195°, 240°>θ.sub.L2>210°, or 230°>θ.sub.L2>220°, or any integer or subrange in between. In some aspects, 75°>Φ>15° and 270°>θ.sub.L2>180°, such as 255°>θ.sub.L2>195°, or 240°>θ.sub.L2>210°, or 230°>θ.sub.L2>220°, or any integer or subrange in between. In some aspects, 60°>Φ>30° and 270°>θ.sub.L2>180°, such as 255°>θ.sub.L2>195°, or 240°>θ.sub.L2>210°, or 230°>θ.sub.L2>220°, or any integer or subrange in between. In some aspects, 50°>Φ>40° and 270°>θ.sub.L2>180°, such as 255°>θ.sub.L2>195°, or 240°>θ.sub.L2>210°, or 230°>θ.sub.L2>220°, or any integer or subrange in between. In some aspects, 270°>θ.sub.L2>180° and 90°>Φ>0°, such as 75°>Φ>15°, or 60°>Φ>30°, or 50°>Φ>40°, or any integer or subrange in between. In some aspects, 255°>θ.sub.L2>195° and 90°>Φ>0°, such as 75°>Φ>15°, or 60°>Φ>30°, or 50°>Φ>40°, or any integer or subrange in between. In some aspects, 240°>θ.sub.L2>210° and 90°>Φ>0°, such as 75°>Φ>15°, or 60°>Φ>30°, or 50°>Φ>40°, or any integer or subrange in between. In some aspects, 230°>θ.sub.L2>220° and 90°>Φ>0°, such as 75°>Φ>15°, or 60°>Φ>30°, or 50°>Φ>40°, or any integer or subrange in between.

(16) The methods and systems described herein may be used with any build material suitable for use in additive printing, as will be known to those of ordinary skill in the art. In some aspects, the build material is a metal powder. In some aspects, the build material is cobalt chrome, stainless steels, tooling steel, maraging steel, aluminum alloys, nickel alloys, copper alloys, or titanium alloys. In some aspects, the build material is cobalt chrome. In some aspects, the build material is a polymer, a ceramic slurry, a metallic slurry, or a metal powder. In some aspects, the polymer is a powdered polymer. Tolerance for angles θ.sub.L1 other than 180° will depend on the specific build material used and can be determined by those of ordinary skill in the art (i.e., the definition of “generally opposing” for a given build material will depend on the build material).

(17) The methods of the present disclosure may be used in conjunction with additive printing methods known in the art, including, but not limited to direct metal laser melting (DMLM), stereolithography (SLA), selective laser melting (SLM), and other powder-based processes. In some aspects, the present disclosure is related to a method of fabricating an object using DMLM. In other aspects, the present invention may be used in connection with powder bed e-beam systems where a first and second e-beam are provided over a single powder bed.

(18) 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.