Patent Description:
Additive manufacturing techniques have been proposed in several fields of manufacturing. Specifically, additive manufacturing has been suggested for producing annular or cylindrical components of turbomachines, such as for instance flanges and casings of compressor and turbine sections. These are thick and large pieces of machinery, which must withstand high internal pressure and high temperature conditions, and which shall also be sufficiently strong to resist the impact of any rotating blade that may break inside the turbomachine. <CIT> discloses methods for producing parts of turbomachines using hybrid additive manufacturing techniques. <CIT> discloses producing by additive manufacturing a plurality of separate segments of a turbomachine component.

Additive manufacturing is advantageous for manufacturing thick outer annular components, of turbomachines, in that additive manufacturing techniques offer high geometric flexibility when compared to subtractive manufacturing techniques or casting techniques. Additive manufacturing further may offer cost savings and flexibility in enabling changes to be made during the production process without re-tooling.

However, additive manufacturing suffers from limitations in manufacturing thin-walled components, mainly due to the high thermally induced stresses and consequent deformations caused by the additive manufacturing process.

Thin-walled components, such as turbomachine components having wall thickness about or below <NUM>, e.g. about or below <NUM> are usually manufactured by forging, metal spinning or welding of pre-formed sheets. Shape tolerance control represents the main issue to date.

A need therefore exists to improve the manufacturing of think-walled, large diameter components, typically parts of turbomachines.

Disclosed herein is a method of making a hollow turbomachine component, comprising the step of sequentially producing by additive manufacturing on a substrate: a first terminal portion of a semi-finished component, said first terminal portion adhering to the substrate; an intermediate portion adjoining the first terminal portion; and a second terminal portion adjoining the intermediate portion. The method further comprises the step of removing at least one of said first terminal portion and second terminal portion. The removed terminal portion may include a feature, not forming part of the final component to be manufactured, but which is aimed at reducing thermally induced stresses and deformations in the final component. In some embodiments, the removed terminal portion can include a stiffening feature, for instance a stiffening flange. In other embodiments, the removed terminal portion includes an add-on portion of metallic material, in which thermally induced deformations concentrate, such that the actual final component, obtained once the terminal portion has been removed, is free or substantially free of deformations.

Further features and embodiments of the method according to the present disclosure are described in the following detailed description and are set forth in the appended claims.

In order to reduce manufacturing costs and manufacturing time, as well as to achieve enhanced manufacturing flexibility of large, thin-walled turbomachine components, the method disclosed herein provides for steps aimed at reducing or avoiding thermally induced deformations, such as buckling, of the final component, such that a net shape or near net shape component can be obtained at the end of the additive manufacturing procedure.

Since thermally induced deformations concentrate at one or both terminal portions of the component produced by additive manufacturing, the method disclosed herein provides for producing a semi-finished component, which includes at least one terminal portion that will be removed therefrom. Such sacrificial terminal portion can be designed so that inadmissible deformations, i.e. those deformations which would not be acceptable in the finished product, are located entirely in the sacrificial terminal portion, which is removed upon cooling of the component. In some embodiments, the sacrificial terminal portion is configured to stiffen the component such that thermally induced deformations are prevented or substantially reduced.

For this purpose, a three-dimensional model of the final component can be provided, which includes additional features, to be removed from the final component. In a nutshell, a computer aided design 3D-model (CAD model) can be created, which includes additional removable features at one or both ends thereof. The additive manufacturing apparatus runs under the control of a computer based on the CAD model, such that the final product obtained by additive manufacturing includes one or more removable features, where deformations, such as buckling, shrinkage or other thermally induced deformations concentrate. By removing those portions a net shape or near net shape component is obtained.

By concentrating deformations or artifacts provoked by thermally induced stresses in sacrificial terminal features, large and thin-walled components can be produced by additive manufacturing.

Components, which according to the current art are manufactured by pre-formed sheet welding, or direct machining from semi-finished workpieces produced by forging or metal spinning, can thus be produced by additive manufacturing with beneficial effects in terms of cost reduction, reduced lead time, reduced time to test new components, and also in terms of reduced component thickness.

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> disclose 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. In general, the abovementioned processes are performed on a reusable or sacrificial substrate. In the abovementioned processes, conventionally, the build platform is removed from the component formed after a component build is complete.

Methods disclosed herein preferably use powder laser metal deposition, which may result in a more accurate net shape component, such that in some embodiments, high surface quality and low surface roughness can be achieved without the need to resort to surface polishing treatments, or other costly and time consuming finishing steps.

Turning now to the drawings, <FIG> is a schematic diagram showing an exemplary powder laser metal deposition apparatus <NUM> for additive manufacturing. The apparatus <NUM> comprises a table <NUM> and a head <NUM>. The table <NUM> can be configured to rotate around a rotation axis A-A, for instance under the control of a motor <NUM>. In some embodiments, the table <NUM> can also be controlled to tilt around tilting axes, e.g. a horizontal axis, according to arrow B. The tilting axis B can be a numerically controlled axis.

The head <NUM> comprises an energy source <NUM>, for instance an electron beam gun, a plasma source, or preferably an electromagnetic radiation source. Particularly advantageous embodiments of the methods disclosed herein use lasers as power sources. The head <NUM> further comprises a nozzle <NUM> connected to a powder feed source <NUM> and a source of shield gas <NUM>. Powder material <NUM> is fed though the nozzle <NUM> by powder feed source <NUM>. Powder P from the powder feed source <NUM> is fed along with shield gas G from shield gas source <NUM> through the nozzle <NUM>. As the powder is fed through nozzle <NUM>, the powder is melted into a melt pool M by energy from source <NUM>, for example a laser beam LB.

Manufacturing of a component <NUM> can start from a substrate <NUM>, which can be attached to table <NUM>, such as to move integrally therewith during the manufacturing process.

Starting from the substrate <NUM>, metal powder P is melted in pool M and subsequently solidified. By moving the head <NUM> and the table <NUM> one with respect to the other, layers of melted powder can be superposed on the substrate or on previously solidified parts.

Either the head <NUM>, the table <NUM> and substrate <NUM>, or both may be lowered and/or moved, to melt the powder P on any portion of the substrate <NUM> and/or on the previously solidified portion of component <NUM>, until the component <NUM> is completely built up from a plurality deposited layers built from melted powder P. Specifically, for manufacturing axially symmetrical components <NUM>, the table <NUM> and the substrate <NUM> are kept into rotation around the vertical axis A-A and the head <NUM> and table <NUM> are moved according to three mutually orthogonal, numerically controlled axes X, Y, Z. Tilting around the numerically controlled tilting axis, i.e. rotation axis, B may be useful to produce flanged sections of the component <NUM>. In some embodiments more numerically controlled rotation axes can be provided.

The method disclosed herein can be particularly useful for the manufacturing of thin-walled, axially symmetrical turbomachine components. However, several turbomachine thin-walled components may have a hollow non-symmetrical shape. This is particularly the case of so-called transition pieces of canned combustors of gas turbine engines, as will be described later on. The method disclosed herein attains several advantages also in the manufacturing of such asymmetrical components. In such case, manufacturing will be through more complex mutual movements of the table <NUM> and the head <NUM> of the additive manufacturing apparatus <NUM>.

The energy source <NUM> and the numerically controlled axes X, Y, Z, B as well as the motor <NUM> may be controlled by a computer system schematically shown at <NUM>, including a processor and a memory. The computer system <NUM> may determine a predetermined path for each melt pool and subsequently solidified bead to be formed, and energy source <NUM> to irradiate the powder material according to a pre-programmed path.

The abovementioned additive manufacturing process may be controlled by the computer system <NUM> executing a control program. The computer system <NUM> can receive, as input, a three-dimensional model <NUM> of the component <NUM> to be formed. For example, the three-dimensional model is generated using a computer aided design (CAD) program. The computer system <NUM> analyzes the model <NUM> and generates movements according to numerically controlled axes X, Y, Z, B according to the model <NUM> to manufacture the component <NUM>.

The above described additive manufacturing process involves concentration of energy and high temperature gradients within the component <NUM> being formed. Subsequent solidification of the superposed layers generates thermally induced stresses in the solidified component. Stress release processes and post processing procedures are usually required. The geometry of the component <NUM> must be such that thermally induced stresses do not generate deformations of the component, which would result in the shape of the component <NUM> being inconsistent with the 3D model. Thermally induced stresses and consequent deformations of the component after solidification represent a major obstacle in the manufacturing of large, thin-walled components, which are unable to withstand high thermally induced stresses and would be subject to buckling or deformation.

According to the method disclosed herein, a novel approach to additive manufacturing is suggested, which overcomes the limitations of the current art techniques and allows using additive manufacturing also for the production of thin-walled, large diameter components of axially symmetrical or non-symmetrical shape, such as combustor liners, annular combustion chamber components, transition pieces, or other thin-walled components of turbomachinery, in particular turbomachinery components arranged inside or around the hot combustion gas path.

In general terms, the 3D-model used to control the additive manufacturing apparatus <NUM> includes portions or features, which are not intended to be part of the final component <NUM>. These portions or features, therefore, generate sacrificial parts of the component <NUM>, i.e. parts intended to be removed from the final component, and are designed such that thermally induced deformations concentrate therein and are moved away from the remainder of the component. In so doing, thermally induced deformations will localize in the sacrificial parts, rather than in the actual final component to be manufactured.

In some embodiments, the sacrificial feature may include a portion of larger thickness, which does not deform under thermally induced stresses, or a portion, the shape whereof is such as to increase stiffness and thus reduce the thermally induced deformations of the component, or limit the deformations to a removable part of the semi-finished component generated by the additive manufacturing apparatus <NUM>.

In some embodiments, the sacrificial part adds a variation of the transverse dimension of a hollow component. The variation of the transverse dimension has a stiffening effect on the thin-walled structure of the component. For instance, an axially symmetrical piece of machinery having a substantially constant diameter is prone to thermally induced deformation. The addition thereon of an end portion of conical shape, having a variable diameter dimension, or in general a portion of non-constant diameter, stiffens the structure against buckling or other thermally induced deformations. Upon cooling of the component, the conical end portion can be removed. A similar effect can be achieved also if the component is non-symmetrical. In general terms, the rigidity of the wall against buckling or other deformations can be increased by forming thereon a transitional piece, which introduces a dimensional discontinuity.

The position and dimension of the sacrificial parts or features are such that residual deformations in the final component are negligible, i.e. within the dimension and shape tolerances. Upon solidification of the semi-finished component, the sacrificial features or parts thereof are removed along with the thermally induced deformations, which concentrate therein.

<FIG> shows a cross-sectional view of a large, thin-walled component <NUM>, for instance an axially symmetrical component of a combustor for a gas turbine. The component <NUM> of <FIG> is illustrated by way of example only. Those of ordinary skill in the art will understand that the design approach described below with respect to the exemplary component17 of <FIG> can be used for manufacturing a variety of different axially symmetrical or non-symmetrical components.

The component <NUM> of <FIG> is obtained by additive manufacturing of a semi-finished component having sacrificial portions at both ends thereof, and by subsequently removing said sacrificial portions. By way of example, the component <NUM> of <FIG> has a main body of axially symmetrical shape. The longitudinal axis of the component <NUM> is indicated as X-X. The component <NUM> in <FIG> has a first end 17A and a second end 17B. More specifically, the first end 17A comprises a flange facing radially inwardly towards the axis X-X, and the second end 17B terminates a substantially cylindrical portion of the component <NUM>, i.e. a portion of constant diameter.

The finished component <NUM> is obtained starting from a CAD 3D-model of the component, which is used by the additive manufacturing apparatus <NUM> to generate a semi-finished article of manufacture, including end sacrificial portions, which are removed after cooling. The semi-finished component <NUM> is shown in <FIG>.

Since <FIG> represents the semi-finished component <NUM> generated by the additive manufacturing apparatus <NUM> under the control of the computer system <NUM> using the 3D-model <NUM>, the shape of the virtual 3D-model is the same as the shape of the semi-finished component <NUM> obtained at the end of the additive manufacturing process, except for thermally induced deformations which will appear in the solidified semi-finished component. Thus, the following description of the shape of the semi-finished component <NUM> applies to both the virtual 3D-model of the component and to the solidified semi-finished component <NUM> generated by the additive manufacturing apparatus <NUM>.

The semi-finished component <NUM> generated by the 3D-model <NUM> and the virtual component defined by such model both include a first terminal portion <NUM>, an intermediate portion <NUM> and a second terminal portion <NUM>. Manufacturing starts by producing the first terminal portion <NUM> on the substrate <NUM>. In the exemplary embodiment of <FIG>, the first terminal portion <NUM> has the shape of a sacrificial flange. As better shown in the enlargement of <FIG>, the first terminal portion <NUM> is in the form of a flange with an L-shaped cross section. As will be clarified later on, the flange will be machined to generate an end flange-shaped portion of the final component. In some embodiments, the thicknesses Th1, Th2 of the several flange portions are larger than the thickness Th3 of the intermediate portion <NUM> of the component <NUM>.

The second terminal portion <NUM> of the semi-finished component <NUM> is better shown in the enlargement of <FIG>. In the exemplary embodiment of <FIG>, the second terminal portion <NUM> includes a stiffening feature, i.e. a sacrificial portion of the semi-finished component, which has the purpose of increase the overall stiffness and resistance against thermally induced deformations of the thin-walled component. In the embodiment of <FIG> the stiffening feature includes a conical stiffening flange <NUM>, having a smaller diameter adjoining the intermediate portion <NUM> of the component <NUM> and a larger diameter facing away from the intermediate portion <NUM> and forming the free end of the semi-finished component <NUM> generated by additive manufacturing on apparatus <NUM>.

In general terms, a stiffening feature may include a portion of the wall of the semi-finished component exhibiting a smooth or preferably stepped variation of the cross-sectional dimension of the component.

Both terminal portions <NUM> and <NUM> include or represent sacrificial features, i.e. parts which are removed from the semi-finished component <NUM> of <FIG> to obtain the finished component <NUM> as shown in <FIG>.

More specifically, after solidification and cooling the semi-finished component <NUM> can be removed from the substrate <NUM> by cutting. Cutting can be performed along a plane C1 through the first terminal portion <NUM>, for instance at a distance d1 from the substrate <NUM> and parallel thereto, i.e. orthogonal to the longitudinal axis X-X of the component <NUM>. Since the final component <NUM> includes a thin flange <NUM> at a first end 17A thereof, as shown in <FIG>, a part of the first terminal portion <NUM>, which remains after cutting away from the substrate <NUM>, is removed by machining, until the final thin flange <NUM> is obtained.

Thermal stresses generated during additive manufacturing of the first section of the component <NUM> will concentrate in the thicker, first end portion <NUM>, which is removed by cutting and machining. The thin wall of component <NUM> projecting from the thicker, first terminal portion <NUM> is free or substantially free of thermally induced deformations and thus represents a net shape portion of the final component <NUM>. As used herein, a portion "substantially free of thermally induced deformations" can be understood as one where any residual deformation is within admitted manufacturing tolerances.

The free second terminal portion <NUM> may be subject to buckling caused by the thermally induced stresses which, generate during cooling of the semi-finished component <NUM>. This may be specifically the case if the diameter, or more generally speaking the shape of the cross-section of the component, is constant in the area adjoining the second end of the component. Buckling may alter the shape of the final component with respect to the desired shape to such an extent that the finished component must be discarded. To prevent buckling deformations from altering the shape of the final component, the 3D-model and thus the semi-finished component may include an additional portion represented by the second terminal portion <NUM>, which is removed by cutting along a plane C2. The sacrificial second terminal portion <NUM>, which is removed from the intermediate body <NUM> of component <NUM>, includes the conical stiffening flange <NUM>, or other sacrificial stiffening feature, and may further include an annular metal part <NUM> (<FIG>) between the conical stiffening flange <NUM> and the intermediate body <NUM> of the component <NUM>.

The stiffening flange <NUM> reduces the thermally induced buckling deformation of the free end of the component <NUM>, such that the axial length of the side wall of the component subject to buckling is smaller than would be if no stiffening flange <NUM> were provided. The deformed annular portion is located between the conical stiffening flange <NUM> and the cutting plane C2, along which the semi-finished component <NUM> is cut to remove the second sacrificial part <NUM> and produce the second free end 17B (<FIG>) of the final component <NUM>. Thus, the deformed part of the semi-finished component <NUM> is removed by cutting along plane C2, along with the remaining sacrificial part, including the stiffening flange <NUM> or other stiffening feature.

Thus, can be observed by comparing <FIG> and <FIG>, the final component <NUM> (<FIG>) differs from the semi-finished component <NUM> (<FIG>) and from the 3D-model thereof, as it is devoid of the sacrificial first and second terminal portions <NUM> and <NUM>.

After removal of the sacrificial portions the resulting piece of machinery is a net shape component or near net shape component, which does not require additional chip removal machining to achieve its final shape. If required, surface machining such as sand-blasting, polishing, shot peening, or the like can be performed to improve the surface texture of the final component <NUM>.

The shape of the sacrificial terminal portions <NUM> and <NUM> shown in <FIG> is functional to the actual shape of the final component <NUM>. The sacrificial portions or features may differ depending upon the shape of the net shape component <NUM> which shall be manufactured.

A further example of thin-walled component is shown in <FIG>. More specifically, <FIG> illustrates the semi-finished component <NUM> produced with the by additive manufacturing apparatus <NUM> of <FIG>, for instance. The shape of the semi-finished component <NUM> of <FIG> corresponds to the virtual 3D-model used to control the additive manufacturing apparatus <NUM>, except for the thermally induced deformations. <FIG> illustrates the finished component <NUM> after removal of a sacrificial portion as described in more detail below.

In the exemplary embodiment of <FIG>, the semi-finished component <NUM> comprises a first terminal portion <NUM>, an intermediate portion <NUM> and a second terminal portion <NUM>. Additive manufacturing starts with the first terminal portion <NUM> which grows from the substrate <NUM>, forming the intermediate portion <NUM> and ends with the second terminal portion <NUM>. In the exemplary embodiment of <FIG>, the final component <NUM> comprises a first free end <NUM> having a larger diameter and a second free end <NUM> having a smaller diameter. The component <NUM> has therefore a tapering shape, with a smaller diameter at the second free end <NUM>.

A component <NUM> having the shape shown in <FIG> is subject to thermally induced deformations at the bottom thereof, i.e. proximate the substrate <NUM>. At a distance d3 from the substrate <NUM> the component <NUM> shrinks resulting in a reduced diameter. In order to obtain a net shape or near net shape component <NUM>, therefore, the 3D-model of the component in this case includes a sacrificial terminal portion <NUM>, which is intended to be removed after cooling of the semi-finished component <NUM>. Removal can be obtained by detaching the component <NUM> from the substrate <NUM> through cutting along a plane C3 at a distance d3 from the substrate <NUM> and parallel thereto.

<FIG> illustrates the net shape component <NUM> obtained by cutting and removing the sacrificial first terminal portion <NUM> along plane C3. The final component <NUM> has a first free end <NUM> and a second free end <NUM>, which in this specific case is formed by the second terminal portion <NUM>, which does not require to be removed, since it is substantially free of thermally induced deformations, i.e. the thermally induced deformations are within acceptable shape and dimension tolerances of the final piece of machinery.

By providing removable terminal portions, where thermally induced deformations concentrate, additive manufacturing of thin-walled components having an extensive transverse dimension become possible. By transverse dimension, the largest dimension of the cross-section of the component can be understood. In case of an axially symmetrical component, the transverse dimension can be the diameter of the section thereof along a plane orthogonal to the axis of symmetry of the component. The components <NUM> may have a maximum transverse equal to or preferably larger than about <NUM>. For instance, the largest transverse dimension can range between about <NUM> and about <NUM>, preferably between about <NUM> and about <NUM>. The wall thickness can range for instance between about <NUM> and about <NUM>, preferably between about <NUM> and about <NUM>.

Metal superalloy powder can be used for producing components intended to withstand high temperatures, such as combustor components.

The net shape component <NUM> obtained after cutting/removing the sacrificial feature(s) has its final thickness and does not require further material removing machining to achieve its final shape. However, while the component <NUM> is obtained in its net shape, additional drilling, cutting or other machining operations to produce additional elements thereon are not excluded.

During additive manufacturing the component <NUM> can be provided also with additional features such as bosses, springs, projections, tooling features, or appurtenances, which may be useful for subsequent operations and which can be removed.

Based on the above described exemplary embodiments, those skilled in the art will understand that the method disclosed herein can be used in a variety of situations, where it may be desirable to manufacture by additive manufacturing hollow components having a thin wall, and large transverse dimensions, for example a large diameter in case of axially symmetrical components. The shape of the 3D-model will be adapted to the thermally induced stresses and consequent thermally induced deformations arising in the final component. Such stresses and deformations depend upon the component shape and dimensions. In general terms, the 3D-model will include removable features, i.e. sacrificial parts, at one or both ends of the component, such that deformations will be either prevented or reduced by removable stiffening features and/or will be confined in those sections and portions of the additively manufactured component, which will be removed after cooling.

<FIG> illustrates a flowchart summarizing an additive manufacturing method according to the present disclosure. The method includes a step of arranging a substrate in an additive manufacturing apparatus and a subsequent step of producing by additive manufacturing thereon a component starting with a first terminal portion, followed by a central or intermediate portion and ending with a second terminal portion. The method further comprises a step of detaching the component thus formed from the substrate and an additional step of removing at least one of the first terminal portion and second terminal portion. In some embodiments, both terminal portions may be removed, for instance if both said terminal portions include sacrificial feature(s). Removing may involve cutting away or machining by material removal, to change the shape and dimension of the terminal portion, for instance to produce a thin-walled flange therefrom.

<FIG> illustrates a further flowchart of another embodiment of a method according to the present disclosure. The method of <FIG> comprises producing by additive manufacturing on said substrate arranged in an additive manufacturing apparatus a first terminal portion of a semi-finished component and subsequently producing by additive manufacturing a central or intermediate portion adjoining the first terminal portion, followed by a second terminal portion adjoining the intermediate portion. The semi-finished component is then detached from the substrate and the first terminal portion thereof is machined into an end flange.

<FIG> illustrates a yet further flowchart summarizing another embodiment of a method according to the present disclosure. Once a substrate has been arranged in an additive manufacturing apparatus, the method comprises producing by additive manufacturing on said substrate a first terminal portion of a semi-finished component, said first terminal portion adhering to said substrate. The method further comprises producing by additive manufacturing a central or intermediate portion adjoining the first terminal portion as well as a second terminal portion adjoining the central or intermediate portion and comprising a stiffening feature, for instance a stiffening flange. The component is then detached from the substrate and the second terminal portion including the stiffening feature is removed from the component.

<FIG> illustrates a flowchart of another embodiment of a method according to the present disclosure, wherein a substrate is arranged in an additive manufacturing apparatus. On said substrate a first terminal portion of a semi-finished component is produced by additive manufacturing, followed by further additive manufacturing steps, including producing a central or intermediate portion adjoining the first terminal portion, and a second terminal portion adjoining the central or intermediate portion. The component thus formed is detached from the substrate and the second terminal portion is removed.

The methods of <FIG>, <FIG> include a step of removing the component produced by additive manufacturing from the substrate. This latter can be a sacrificial support. In other embodiments, the step of detaching the component from the substrate can be omitted and the substrate can become part of the final component. In some embodiments, the manufacturing method can include a further step of machining the substrate to produce a terminal portion of the component. <FIG>, <FIG> illustrate flowcharts of modified embodiments of the methods of <FIG>, <FIG>, wherein the step of detaching the component from the substrate is omitted and replaced by a step of machining the substrate to obtain an end structural feature of the final component.

In general, the methods disclosed herein may include a step of generating a 3D-model of component to be produced, which model includes one or more removable features and is loaded in a computer system of the additive manufacturing apparatus or machine <NUM>, for controlling the additive manufacturing process. <FIG> illustrates a flowchart of a method including the step of providing the 3D-model of a turbomachine component <NUM> in a computer system <NUM> adapted to control the additive manufacturing apparatus <NUM> using the 3D-model, wherein the three-dimensional model comprises at least one removable sacrificial feature. The method may then include further steps as disclosed in one or more of <FIG>, <FIG>, <FIG>, <FIG>.

In some embodiments, as shown in <FIG>, the method includes the step of producing a component <NUM> with the additive manufacturing apparatus <NUM> using the three-dimensional model, wherein the component <NUM> has a first terminal portion, a central or intermediate portion adjoining the first terminal portion, and a second terminal portion adjoining the central or intermediate portion; one of said first and second terminal portions comprising the sacrificial feature. The method includes a further step of cooling the component and causing thermally induced deformations of the component to concentrate in the sacrificial feature, such that the thermally deformed portion of the component can be removed by detaching the component from the substrate and removing said sacrificial feature from the central or intermediate portion of the component.

In all methods summarized in <FIG>, <FIG>, <FIG>, <FIG> and <FIG> at least some of the steps can be re-arranged in a different sequence. For instance, the step of removing or machining the substrate can be performed after the step of removing the second terminal portion.

As described above, the component <NUM> can be a part of a turbomachine, for instance a component of a combustor of a gas turbine engine. <FIG> illustrates a schematic of an exemplary canned combustor <NUM> for a gas turbine engine. In <FIG> the final stages <NUM> of an air compressor are shown. The combustor <NUM> comprises a combustor liner <NUM> and a transition piece <NUM>, which extends from the combustor liner <NUM> to inlet nozzles of the first stage of the turbine section, not shown. The combustor liner <NUM> and the transition piece <NUM> can be produced by additive manufacturing using the above described methods.

<FIG> illustrates a sectional view of an annular combustion chamber <NUM> for a gas turbine engine. Only one half of the section is shown, above the turbine axis B-B. The annular combustion chamber can include an outer liner portion <NUM> and an inner liner portion <NUM> coaxially arranged around the axis B-B of the gas turbine engine. The annular combustion chamber ends at the high pressure turbine inlet nozzles schematically shown at <NUM>. Both liner portions <NUM> and <NUM> can be manufactured as described above.

While any laser source suitable for powder laser metal deposition can be used to perform the methods disclosed herein, laser offering a preferably constant or quasi-constant laser intensity across the laser spot are presently preferred, as they provide a more uniform melting of the powder across the laser spot and may better perform in terms of reduced thermal stresses and resulting deformations induced in the final article of manufacture.

In some embodiments, lasers having a low Beam Parameter Product (BPP) can be preferred. As known to those skilled in the art BPP is the product between the divergence angle (half angle) expressed in radian of the laser beam and the radius (expressed in mm) of the beam waist, i.e. the radius of the beam at the narrowest point thereof.

In some embodiments, lasers having a BPP ranging between about <NUM>*rad and about <NUM>*rad can be particularly advantageous in implementing the methods disclosed herein.

For additive manufacturing of thin-walled machine components, having a wall thickness of about <NUM> or below, preferably about <NUM> or below, for instance between about <NUM> and about <NUM>, a laser spot is particularly advantageous of about <NUM> micrometers or more, preferably ranging between about <NUM> micrometers and about <NUM> micrometers, more preferably between about <NUM> micrometers and about <NUM> micrometers. In presently preferred embodiments, the laser intensity within the laser spot is between about <NUM> and <NUM> kW/cm<NUM>, preferably between about <NUM> and about <NUM> kW/cm<NUM> and is substantially constant. Generally, a substantially constant laser intensity value within the laser spot is preferred in an effort to provide more uniform powder melting and reduce thermally induced stresses in the final component.

The term "substantially constant" as used herein referring to a parameter or quantity, can be understood as including a variation of +<NUM>% and preferably a variation of +<NUM>% around a fixed value of said parameter or quantity.

Unless differently specified, as used herein the term "about" when referred to a value of a parameter or quantity can be understood as including any value within + <NUM>% of the stated value. Thus, for instance, a value of "about x", includes any value within the range of (x-<NUM>. 05x) and (x + <NUM>.

Particularly efficient additive manufacturing of hollow, thin-walled components of large transversal dimensions can be achieved using fiber lasers, i.e. lasers in which energy is delivered by pumping diodes into suitably doped optical fibers which are the active gain medium of the laser.

Claim 1:
A method of making hollow turbomachine components (<NUM>) having a first end (17A), an intermediate portion (<NUM>) and a second end (17B), the method comprising:
sequentially producing by additive manufacturing on a substrate (<NUM>): a first terminal portion (<NUM>) of a semi-finished component, said first terminal portion adhering to said substrate (<NUM>); an intermediate portion (<NUM>) adjoining the first terminal portion (<NUM>); and a second terminal portion (<NUM>) adjoining the intermediate portion (<NUM>); and
removing at least one of said first terminal portion and second terminal portion;
characterized in that said at least one terminal portion comprises at least one of a removable stiffening feature (<NUM>) and a removable feature adapted to concentrate thermally induced deformations therein.