Patent Description:
Many components of gas turbine engines include internal cooling passages as well as small-diameter cooling holes extending through the components. For example, hollow castings, such as airfoils for a high-pressure turbine, may be laser drilled to provide cooling holes extending between an internal cooling cavity or passage and an exterior surface of the casting. However, laser drilling of such components poses the problem of back striking which can lead to damage of internal walls of the casting during laser drilling.

Conventionally, in order to prevent back striking, castings have been filled with materials such as wax, epoxy, or some other organic compound, prior to laser drilling, to attenuate the laser energy. This technique can be effective but is time consuming and requires the extra steps of filling the internal cavities of the casting with the material and subsequently burning or leaching out the material after laser drilling. Accordingly, what is needed is an improved way of preventing back striking during laser drilling of a component.

<CIT> discloses a prior art method as set forth in the preamble of claim <NUM>.

According to an aspect of the invention, there is provided a method for laser drilling a hollow component as recited in claim <NUM>.

The present disclosure, and all its aspects, embodiments and advantages associated therewith will become more readily apparent in view of the detailed description provided below, including the accompanying drawings.

It is noted that various connections are set forth between elements in the following description and in the drawings. It is noted that these connections are general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. A coupling between two or more entities may refer to a direct connection or an indirect connection. An indirect connection may incorporate one or more intervening entities. It is further noted that various method or process steps for embodiments of the present disclosure are described in the following description and drawings. The description may present the method and/or process steps as a particular sequence. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the description should not be construed as a limitation.

Referring to <FIG>, an exemplary gas turbine engine <NUM> is schematically illustrated. The gas turbine engine <NUM> is disclosed herein as a two-spool turbofan engine that generally includes a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM>, and a turbine section <NUM>. The fan section <NUM> drives air along a bypass flowpath <NUM> while the compressor section <NUM> drives air along a core flowpath <NUM> for compression and communication into the combustor section <NUM> and then expansion through the turbine section <NUM>. Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiments, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including those with three-spool architectures.

The gas turbine engine <NUM> generally includes a low-pressure spool <NUM> and a high-pressure spool <NUM> mounted for rotation about a longitudinal centerline <NUM> of the gas turbine engine <NUM> relative to an engine static structure <NUM> via one or more bearing systems <NUM>. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided.

The low-pressure spool <NUM> generally includes a first shaft <NUM> that interconnects a fan <NUM>, a low-pressure compressor <NUM>, and a low-pressure turbine <NUM>. The first shaft <NUM> is connected to the fan <NUM> through a gear assembly of a fan drive gear system <NUM> to drive the fan <NUM> at a lower speed than the low-pressure spool <NUM>. The high-pressure spool <NUM> generally includes a second shaft <NUM> that interconnects a high-pressure compressor <NUM> and a high-pressure turbine <NUM>. It is to be understood that "low pressure" and "high pressure" or variations thereof as used herein are relative terms indicating that the high pressure is greater than the low pressure. An annular combustor <NUM> is disposed between the high-pressure compressor <NUM> and the high-pressure turbine <NUM> along the longitudinal centerline <NUM>. The first shaft <NUM> and the second shaft <NUM> are concentric and rotate via the one or more bearing systems <NUM> about the longitudinal centerline <NUM> which is collinear with respective longitudinal centerlines of the first and second shafts <NUM>, <NUM>.

Airflow along the core flowpath <NUM> is compressed by the low-pressure compressor <NUM>, then the high-pressure compressor <NUM>, mixed and burned with fuel in the combustor <NUM>, and then expanded over the high-pressure turbine <NUM> and the low-pressure turbine <NUM>. The low-pressure turbine <NUM> and the high-pressure turbine <NUM> rotationally drive the low-pressure spool <NUM> and the high-pressure spool <NUM>, respectively, in response to the expansion.

Referring to <FIG> and <FIG>, the gas turbine engine <NUM> may include one or more components <NUM> which may be configured as hollow castings. For example, as illustrated in <FIG>, the component <NUM> may be an airfoil configured for use in the compressor section <NUM> and/or the turbine section <NUM> of the gas turbine engine. However, as will be understood from the present disclosure, the component <NUM> may be any suitable gas turbine engine <NUM> component requiring the drilling of holes therethrough, such as, but not limited to, airfoils, vanes, combustor wall assembly components, etc..

The component <NUM> includes a component body <NUM> defining one or more internal cavities <NUM>. The component body <NUM> includes an external wall <NUM> having an external surface <NUM> and an internal surface <NUM>. A plurality of holes <NUM> (e.g., air cooling holes) are formed through the component body <NUM> of the component <NUM> between the internal cavity <NUM> and the external surface <NUM>. The plurality of holes <NUM> may be formed through the component body <NUM>, for example, by drilling subsequent to formation of the component body <NUM>. For example, laser drilling of the plurality of holes <NUM> may be used to quickly produce hundreds or thousands of holes with a high degree of accuracy. However, the component body <NUM> may be susceptible to damage from back strikes during laser drilling of the plurality of holes <NUM>. A back strike is an event which occurs when, for example, a drill bit, laser, EDM electrode, machining process/component, etc. passes through the component body <NUM> from the external surface <NUM>, into the internal cavity <NUM>, and contacts an internal wall <NUM> of the component <NUM> or an internal surface <NUM> of the external wall <NUM> of the component <NUM>, opposite the hole being drilled, potentially causing damage to the internal wall <NUM> or the internal surface <NUM> of the external wall <NUM> (see, e.g., <FIG> illustrating exemplary back strike locations <NUM> caused by, for example, a laser beam <NUM>).

Referring to <FIG> and <FIG>, a block diagram of a drilling apparatus <NUM> is illustrated. The drilling apparatus <NUM> includes a laser generator <NUM> configured to apply the laser beam <NUM> to the component <NUM> for drilling the plurality of holes <NUM> through the component body <NUM> from the external surface <NUM> to the internal cavity <NUM>. In various embodiments, the laser generator <NUM> is configured to move in one or more of an x-, a y-, and a z-direction, rotate, and/or tilt relative to the component <NUM> so as to form each hole of the plurality of holes <NUM> in the desired location and with the desired orientation.

The drilling apparatus <NUM> includes a fluid source <NUM> configured to contain a fluid <NUM>. A pump <NUM> is in fluid communication with the fluid source <NUM> and the internal cavity <NUM> of the component <NUM> via one or more conduits <NUM>. The pump <NUM> is configured to inject the fluid <NUM> into the internal cavity <NUM> of the component <NUM> so as to achieve a pressure of the fluid <NUM> within the internal cavity <NUM> that is greater than an ambient pressure (i.e., a pressure external to the component <NUM>, e.g., atmospheric pressure). As a result of the pressure of the fluid <NUM> within the internal cavity <NUM> being greater than ambient pressure, the fluid <NUM> may directed from the internal cavity <NUM> and through the plurality of holes <NUM>, as the plurality of holes <NUM> are formed, so as to exit the component <NUM> via the plurality of holes <NUM>. In various embodiments, a seal <NUM> may be used to fluidly couple the fluid source <NUM>, pump <NUM>, and conduits <NUM> to the internal cavity <NUM> of the component <NUM> and to minimize or eliminate any leakage of fluid <NUM>.

The drilling apparatus <NUM> may include one or more sensors <NUM> disposed in the conduit <NUM> between the component <NUM> and the pump <NUM>. The one or more sensors <NUM> may include, for example, fluid pressure sensors, fluid flow sensors, fluid temperature sensors, etc. The one or more sensors <NUM> may be in signal communication with the pump <NUM>. Accordingly, the pump <NUM> may be, for example, a variable flow pump configured to control a flow rate of the fluid <NUM> injected into the internal cavity <NUM> of the component <NUM> based on an output of the one or more sensors <NUM>. In various embodiments, the pump <NUM> may include one or more valves configured to control the flow rate of the fluid <NUM> injected into the internal cavity <NUM> of the component <NUM>.

In various embodiments, the drilling apparatus <NUM> may include a collector <NUM> configured to collect the fluid <NUM> which exits the component <NUM> via the plurality of holes <NUM>. For example, the collector <NUM> may be disposed underneath the component <NUM> such that fluid <NUM> exiting the component <NUM> via the plurality of holes <NUM> may fall into the collector <NUM>. The collector <NUM> may be in fluid communication with the fluid source <NUM> via one or more conduits <NUM>. Accordingly, fluid <NUM> which exits the component <NUM> via the plurality of holes <NUM> may be returned to the fluid source <NUM> and again injected into the internal cavity <NUM> of the component <NUM> by the pump <NUM>. In various embodiments, the drilling apparatus may include a filter <NUM> disposed between and in fluid communication with the collector <NUM> and the fluid source <NUM> to filter impurities (e.g., recast material formed during laser drilling of the component <NUM>) from the fluid <NUM>. In various embodiments,.

Referring to <FIG>, a method <NUM> for forming a hollow component (e.g., the component <NUM>) is disclosed. In Step <NUM>, the pump <NUM> injects the fluid <NUM> from the fluid source <NUM> into the internal cavity <NUM> of the component <NUM> to achieve a pressure of the fluid <NUM> within the internal cavity <NUM> that is greater than the ambient pressure external to the component <NUM>.

In Step <NUM>, the laser generator <NUM> drills the plurality of holes <NUM> through the component <NUM> from the external surface <NUM> of the component <NUM> to the internal cavity <NUM> by applying the laser beam <NUM> to the component <NUM>. The fluid <NUM> present in the internal cavity <NUM> may attenuate the laser beam <NUM> as it enters the internal cavity <NUM>, thereby preventing or reducing damage to the internal wall <NUM> of the component <NUM> by preventing the back strike or reducing the energy density or concentration of the laser beam <NUM> such that the laser beam <NUM> does not damage the internal wall <NUM>.

In Step <NUM>, the fluid <NUM> is directed from the internal cavity <NUM> of the component <NUM> through the plurality of holes <NUM>, as a result of the pressure of the fluid <NUM> in the internal cavity <NUM> greater than the ambient pressure, so as to exit the component <NUM> via the plurality of holes <NUM>. As a result of the positive pressure of the fluid <NUM> within the internal cavity <NUM> relative to ambient pressure, flow of the fluid <NUM> through a hole of the plurality of holes <NUM> may begin immediately upon completion of the hole from the external surface <NUM> to the internal cavity <NUM>. The fluid <NUM> may, therefore, immediately provide cooling to the material of the component body <NUM> surrounding the hole and may cause molten material of the component body <NUM>, formed during laser drilling, to solidify. Continued flow of the fluid <NUM> through the plurality of holes <NUM> and, in various embodiments, down the external surface <NUM> of the component <NUM>, during drilling, may additionally provide cooling to the component body <NUM> such that the component body <NUM> can accommodate a faster rate of laser drilling without experiencing an adverse increase in temperature. Directing the fluid <NUM> out of the internal cavity <NUM> through the plurality of holes <NUM> may allow recast material (e.g., loose material of the component body <NUM> formed during laser drilling) and other debris to be flushed from the component <NUM>. Directing the fluid <NUM> out of the internal cavity <NUM> through the plurality of holes <NUM> may also cause any air trapped within the internal cavity <NUM> to be flushed from the component <NUM> via the plurality of holes <NUM>. Air trapped within the internal cavity <NUM> may prevent attenuation of a laser beam <NUM> entering the internal cavity <NUM> by causing the fluid <NUM> to be locally displaced. Accordingly, flushing trapped air from the internal cavity <NUM> by directing the fluid <NUM> to exit the internal cavity <NUM> via the plurality of holes <NUM> may further reduce the likelihood of damage to the internal wall <NUM> as a result of a back strike.

Drilling the plurality of holes <NUM>, as discussed above with respect to Step <NUM>, includes sequentially drilling each hole of the plurality of holes <NUM> progressively from a first position of the component <NUM> to a second position of the component <NUM> which is higher than the first position, relative to a gravitational field. As a result, fluid <NUM> exiting the plurality of holes <NUM> or fluid <NUM> disposed on the external surface <NUM> of the component <NUM> may not interfere with the laser drilling of subsequent holes of the plurality of holes which may be formed at a higher position relative to previously drilled holes.

In various embodiments, injecting the fluid <NUM> into the internal cavity <NUM> of the component <NUM>, as discussed above with respect to Step <NUM>, may include controlling a flow rate of the fluid <NUM>, with the pump <NUM>, from the fluid source <NUM> to the component <NUM>. For example, the pump <NUM>, may maintain a predetermined pressure of the fluid <NUM> within the internal cavity <NUM> of the component <NUM> as the plurality of holes <NUM> are sequentially drilled. The pump <NUM> may maintain the predetermined pressure of the fluid <NUM> within the internal cavity <NUM> based on, for example, the output of the one or more sensors <NUM>. For example, the pump <NUM> may maintain a predetermined pressure of the fluid <NUM> within the internal cavity <NUM> which is greater than ambient pressure. In various embodiments, the pump <NUM> may maintain a predetermined pressure of the fluid <NUM> within the internal cavity which is at least one pound per square inch (psi) (<NUM> kPa) greater than the ambient pressure. Accordingly, as the number of holes in the plurality of holes <NUM> increases, the pump <NUM> may increase the rate of flow of the fluid <NUM> injected into the internal cavity <NUM> in order to maintain the predetermined pressure of the fluid <NUM> within the cavity (e.g., to compensate for the increasing number of holes of the plurality of holes <NUM>). The predetermined pressure may be determined based on one or more factors, for example, a height of the component <NUM>, a desired amount of cooling or flushing to be provided to the component <NUM>, or a velocity of the fluid <NUM> exiting the component <NUM> via the plurality of holes <NUM>.

In various embodiments, the method <NUM> may include collecting the fluid <NUM> exiting the component <NUM> via the plurality of holes <NUM> with the collector <NUM> in Step <NUM>. In Step <NUM>, the fluid <NUM> collected by the collector <NUM> may be returned to the fluid source <NUM> for reuse by the pump <NUM> in Step <NUM>. In various embodiments, returning the collected fluid to the fluid source <NUM> may include passing the fluid <NUM> through the filter <NUM> to remove any recast material or other debris from the component <NUM> prior to reintroducing the fluid <NUM> to the fluid source <NUM>.

The fluid <NUM> may be, for example, a liquid configured to absorb or scatter the laser beam <NUM> upon entry of the laser beam <NUM> into the internal cavity <NUM> of the component <NUM>. For example, in various embodiments, the fluid <NUM> may be water. In various other embodiments, the fluid <NUM> may include one or more dyes configured to improve the laser energy attenuation effectiveness of the fluid <NUM>. The dye may be an opaque dye and may be organic/carbon based (e.g., carbon black) such that the dye can be removed from the component <NUM> during a burnout cycle.

Claim 1:
A method for laser drilling a hollow component (<NUM>), the method comprising:
injecting a fluid (<NUM>) into an internal cavity (<NUM>) of the hollow component (<NUM>) to achieve a pressure of the fluid (<NUM>) within the internal cavity (<NUM>) that is greater than an ambient pressure;
drilling a plurality of holes (<NUM>) through the hollow component (<NUM>) from an external surface (<NUM>) of the hollow component (<NUM>) to the internal cavity (<NUM>) by applying a laser beam (<NUM>) to the hollow component (<NUM>) with a laser generator (<NUM>); and
directing the fluid (<NUM>) from the internal cavity (<NUM>) and through the plurality of holes (<NUM>) so as to exit the hollow component (<NUM>) via the plurality of holes (<NUM>),
characterised in that
drilling the plurality of holes (<NUM>) through the hollow component (<NUM>) comprises sequentially drilling each hole (<NUM>) of the plurality of holes (<NUM>) progressively from a first position of the hollow component (<NUM>) to a second position of the hollow component (<NUM>), the second position is higher than the first position.