Patent Description:
Additive manufacturing 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), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing 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. A particular type of additive manufacturing 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, creating a solid three-dimensional object in which particles of the powder material are bonded together. Different material systems, for example, engineering plastics, thermoplastic elastomers, metals, and ceramics are in use. Laser sintering or melting is a notable additive manufacturing process for rapid fabrication of functional prototypes and tools. Applications include direct manufacturing of complex workpieces, patterns for investment casting, metal molds for injection molding and die casting, and molds and cores for sand casting. Fabrication of prototype objects to enhance communication and testing of concepts during the design cycle are other common usages of additive manufacturing processes.

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, <CIT> and <CIT> describe conventional laser sintering techniques. More accurately, 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. Although the laser sintering and melting processes can be applied to a broad range of powder materials, the scientific and technical aspects of the production route, for example, sintering or melting rate and the effects of processing parameters on the microstructural evolution during the layer manufacturing process have not been well understood. This method of fabrication is accompanied by multiple modes of heat, mass and momentum transfer, and chemical reactions that make the process very complex.

<FIG> is a diagram showing a cross-sectional view of an exemplary conventional system <NUM> for direct metal laser sintering ("DMLS") or direct metal laser melting (DMLM). The apparatus <NUM> builds objects, for example, the part <NUM>, in a layer-by-layer manner by sintering or melting a powder material (not shown) using an energy beam <NUM> generated by a source <NUM>, which can be, for example, a laser for producing a laser beam, or a filament that emits electrons when a current flows through it. The powder to be melted by the energy beam is supplied by reservoir <NUM> and spread evenly over a powder bed <NUM> using a recoater arm <NUM> travelling in direction <NUM> to maintain the powder at a level <NUM> and remove excess powder material extending above the powder level <NUM> to waste container <NUM>. The energy beam <NUM> sinters or melts a cross sectional layer of the object being built under control of an irradiation emission directing device, such as a galvo scanner <NUM>. The galvo scanner <NUM> may include, for example, a plurality of movable mirrors or scanning lenses. The speed at which the laser is scanned is a critical controllable process parameter, impacting how long the laser power is applied to a particular spot. Typical laser scan speeds are on the order of <NUM> to <NUM> millimeters per second. The build platform <NUM> is lowered and another layer of powder is spread over the powder bed and object being built, followed by successive melting/sintering of the powder by the laser <NUM>. The powder layer is typically, for example, <NUM> to <NUM> microns. The process is repeated until the part <NUM> is completely built up from the melted/sintered powder material.

The laser <NUM> may be controlled by a computer system including a processor and a memory. The computer system may determine a scan pattern for each layer and control laser <NUM> to irradiate the powder material according to the scan pattern. After fabrication of the part <NUM> is complete, various post-processing procedures may be applied to the part <NUM>. Post processing procedures include removal of excess powder by, for example, blowing or vacuuming. Other post processing procedures include a stress release process. Additionally, thermal and chemical post processing procedures can be used to finish the part <NUM>.

Additive manufacturing, by way of irradiation of a material through a translucent window upon which the build material rests, is typically referred to as processes such as, for example, constrained stereolithography when the radiation source is a laser or digital light processing (DLP) when the radiation source is a digital light projector. These processes have an advantage over conventional powder bed processes in that the irradiated material is formed against a window often eliminating the need for certain support structures. Constrained stereolithography and DLP are often limited, however, and do not work well with metal powders, coated metal powders, and metal slurries.

<CIT> discloses an apparatus for additively manufacturing three-dimensional objects comprising a translucent window on which a layer of build material can be applied and an irradiation of the applied layer of build material from below the translucent window with energy beams emitted from an energy source can be performed.

Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

The foregoing and/or aspects of the present invention may be achieved by a method of repairing a damaged tip portion of a turbine blade or a stator vane by additive manufacturing according to appended claim <NUM>. In an aspect, the method includes (a) lowering a build platform having a given layer of build material to powder provided on a window; (b) irradiating the powder to form a subsequent layer corresponding to the given layer; (c) solidifying the subsequent layer; (d) raising the build platform and the solidified subsequent layer away from the window; and (e) repeating steps (a)-(d) until the object is formed.

The foregoing and/or aspects of the present invention may be achieved by an apparatus for additively repairing a turbine blade or a stator vane according to appended claim <NUM>. In an aspect, the apparatus includes a powder dispenser, a window, and a platform on which the object is built. The apparatus also includes a recoater providing layers of powder over the window and an irradiation source positioned below the window.

The scope of the present invention is set forth in the appended claims.

The present invention relates to additive manufacturing and utilizes, but is not limited to, additive technology of metal powders in a layer by layer manner. In one aspect, powdered metal may be melted to form each part layer. It may be appreciated by those skilled in the art that the present invention is not limited to melted powders but may also be applicable to polymer coated metal powders and metal powder containing slurries.

The present invention provides an apparatus capable of continuously extracting a part from loose powder or powder slurry irradiating a 2D cross section from below the powder/slurry and continuously fusing the 2D sections until the part is completed and separate from the powder source.

<FIG> illustrate an apparatus for additive manufacturing according to exemplary embodiments of the present invention. In <FIG>, the apparatus includes a build plate <NUM> horizontally oriented and configured to be vertically lowered and raised to build an object <NUM>. The build plate <NUM> may be made of a heat resistant material that may adhere to the object <NUM> being built. For example, the build plate <NUM> may be lowered to position the object <NUM> being built into a metal powder <NUM>.

The apparatus also includes a powder recoater mechanism <NUM> to provide a layer of the metallic powder <NUM> over a translucent window <NUM>. The powder <NUM> may be supplied from reservoir <NUM> by powder feeder <NUM>. The layer of powder <NUM> may be thin or thick depending on a subsequent layer of powder for the part being built. Generally, the layer thickness may be kept constant throughout the build process. The recoater mechanism <NUM> moves horizontally and sweeps a uniform layer of powder <NUM> over the window <NUM> each time the object <NUM> is lifted from the powder <NUM>. The recoater mechanism <NUM> may include a recoater blade (not shown) to provide control of the powder <NUM> over the window <NUM>, and may also be configured, for example, as a hopper where powder may be dropped onto the window <NUM>.

The window <NUM> may define a length and width of an area for building the object <NUM>. A size of the window <NUM> may vary dependent upon the size of the part being built. The window <NUM> may be made of a material that may withstand energy emitted thereon from an energy source. It may also be made of a material in which the melted metal powder <NUM> may not adhere. Exemplary materials for the window <NUM> may include translucent materials capable of withstanding high heat such as, for example, quartz and glass. The melting point of the metal powder <NUM> may be lower than that of the translucent window <NUM>. In the case of high melting point metals, however, an embodiment of the present invention may work by coating the metal powder <NUM> with a radiation curable polymer that fuses when exposed to laser or other light sources. The object <NUM> may then be further heat treated to drive off the polymer and/or fuse the metallic powder <NUM> into a solid object.

The apparatus may include an energy source <NUM> positioned below the translucent window <NUM>, as shown in <FIG>. The energy source <NUM> may be, for example, a laser or laser galvo or a digital light projector capable of projecting light through the translucent window <NUM> and either melting or fusing the metal powder <NUM> placed above the window <NUM>. Where the energy source <NUM> is a digital light projector, for example, the energy source <NUM> may be capable of projecting 2D patterns of light through the window <NUM>.

As shown in <FIG>, the build plate <NUM> may be lowered such that a last layer of the object <NUM> being built contacts the metal powder <NUM>. A laser beam or light pattern <NUM> emitted from the energy source <NUM> melts or fuses a select 2D area of the metal powder <NUM> (see <FIG>). Upon re-solidification, the fused layer forms the next layer <NUM> of the object <NUM>, as shown in <FIG>. In <FIG>, the build plate <NUM> may be raised and a new layer of powder <NUM> may then be provided over the translucent window <NUM> to continue building the object <NUM>. The process may be repeated until the desired metal part is formed. As mentioned above, the new layer of powder may be thinner or thicker depending on the part being built, although the layer thickness is generally consistent throughout the process. Unused powder may be collected in a receptacle <NUM> to be recycled and reused, as shown in <FIG>.

Metallic powder materials for building the object <NUM> may be, for example, stainless steel alloys, aluminum alloys, titanium alloys, nickel based superalloys, and cobalt based superalloys. Where the metal powder <NUM> is utilized, the energy source <NUM> must be capable of melting the powder <NUM> without damaging the translucent window <NUM>. Low melting point powders or fusable alloys may be more suitable for use and include, for example, known eutectic and non-eutectic alloys having a melting point below <NUM>.

<FIG> is a diagram of an additive manufacturing process, according to an embodiment of the present invention. A first step, for example, may involve fastening the workpiece/object <NUM> to the build plate <NUM> and lowering the workpiece <NUM> to the layer of metal powder <NUM>. In step <NUM>, the metal powder <NUM> may be irradiated through the window <NUM> contacting the metal powder <NUM>. The metal powder <NUM> may then be melted to the workpiece <NUM> to form the new layer <NUM>. In step <NUM>, the workpiece <NUM> with the new layer <NUM> may then be lifted from the metal powder <NUM>. In step <NUM>, a new layer of the metal powder <NUM> may be spread across the window <NUM>. The process may be repeated until the desired part is repaired.

The above-described manufacturing methods according to the present invention are used to repair a damaged tip portion of a turbine blade or a stator vane, such as a high pressure turbine blade. Methods for repairing an turbine blade tip using metal powder additive techniques are disclosed in<CIT>. These methods, however, require placing the turbine blade into a traditional powder bed manufacturing apparatus similar to that of <FIG>. A disadvantage of such an approach is that a powder bed must be created around at least the portion to be repaired or built.

The methods in accordance with exemplary embodiments of the present invention are particularly advantageous for tip repair because the turbine blade may be attached to the build platform and lowered toward the window such that only the tip portion to be repaired need come into contact with the metal powder. As such, unnecessary powder use may be eliminated. Using the present techniques, the damaged turbine blade tip is ground to a flat surface, attached to the build plate such that the flat surface faces toward the window, and the partial turbine blade lowered into the metal powder above the window where the build may take place. Additionally, the above-described process, in accordance with the present exemplary embodiments, may be used to create entirely new turbine blades or stator vanes, or other desired metal objects (not part of the invention).

Claim 1:
A method of repairing a damaged tip portion of a turbine blade or a stator vane, by additive manufacturing, comprising:
(a) fastening the turbine blade or the stator vane with the damaged tip portion ground to a flat surface to a build platform such that the flat surface faces a window (<NUM>) and lowering the build platform (<NUM>) having a given layer of build material to powder
(<NUM>) provided on the window (<NUM>) to position the flat surface of the damaged tip portion to come in contact with the powder (<NUM>);
(b) irradiating the powder (<NUM>) to form a subsequent layer corresponding to the given layer;
(c) solidifying the subsequent layer;
(d) raising the build platform (<NUM>) and the solidified subsequent layer away from the window (<NUM>); and
(e) repeating steps (a)-(d) until the damaged tip portion is repaired.