Patent Application
20230193772
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-pressure and temperature exhaust gas flow. The high-pressure and temperature exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section may include low and high pressure compressors, and the turbine section may also include low and high pressure turbines.
Airfoils in the turbine section and components in other hot sections of the engine are typically formed of a superalloy and may include thermal barrier coatings to extend temperature capability and lifetime. Ceramic materials (e.g., monolithic and ceramic matrix composites) are also being considered for these components. Among other attractive properties, ceramics have high temperature resistance. It has been a challenge, however, to develop efficient processes to machine features, such as cooling holes, into ceramic components.
A method of machining cooling holes according to an example of the present disclosure includes providing a workpiece in which a cooling hole is to be formed. The cooling hole, once formed, defines distinct first and second sections. The workpiece is secured in a fixture that is mounted in a first machine and a laser is used to drill a through-hole in a wall of the workpiece. The through-hole is spatially common to the first and second sections of the cooling hole. After drilling the through-hole, the fixture is removed with the workpiece secured therein from the first machine and mounted in a second machine. The second machine uses ultrasonic machining to expand a portion of the through-hole to form the second section. An abrasive slurry used in the process is drained through the through-hole during the ultrasonic machining.
In a further embodiment of any of the foregoing embodiments, the through-hole is of constant cross-section along a longitudinal central axis of the through-hole.
In a further embodiment of any of the foregoing embodiments, the second section is of non-uniform cross-section along the longitudinal central axis.
A further embodiment of any of the foregoing embodiments includes providing a first computerized 3-dimensional model representing the cooling hole, and extracting from the first computerized 3-dimensional model a second computerized 3-dimensional model representing the through-hole.
In a further embodiment of any of the foregoing embodiments, the use of the laser includes scanning the laser across the workpiece in accordance with the second computerized 3-dimensional model to cause removal of material of the workpiece layer-by-layer.
In a further embodiment of any of the foregoing embodiments, the first machine and the second machine have a common type of chuck configured to receive the fixture.
A further embodiment of any of the foregoing embodiments includes determining compensated linear and rotational positions of the through-hole and using the compensated linear and rotational positions in the ultrasonic machining.
In a further embodiment of any of the foregoing embodiments, the laser is a water-jet guided laser.
In a further embodiment of any of the foregoing embodiments, the workpiece is ceramic.
A method of machining cooling holes according to an example of the present disclosure includes providing a ceramic airfoil in which cooling holes are to be formed. The cooling holes, once formed, each define distinct first and second sections. The ceramic airfoil is secured in a fixture that is mounted in a first machine and a laser is used to drill through-holes in the ceramic airfoil. Each of the through-holes is spatially common to the first and second sections of a respective one of the cooling holes. After drilling the through-holes, the fixture is removed from the first machine with the ceramic airfoil secured therein and mounted in a second machine. The second machine uses ultrasonic machining to expand a portion of each of the through-holes to form the second sections. An abrasive slurry used in the process is drained through the through-holes during the ultrasonic machining.
In a further embodiment of any of the foregoing embodiments, each of the through-holes is of constant cross-section along a longitudinal central axis of the through-hole.
In a further embodiment of any of the foregoing embodiments, the second section is of non-uniform cross-section along the longitudinal central axis.
A further embodiment of any of the foregoing embodiments includes providing a first computerized 3-dimensional model representing the cooling holes, and extracting from the first computerized 3-dimensional model a second computerized 3-dimensional model representing the through-holes.
In a further embodiment of any of the foregoing embodiments, the use of the laser includes scanning the laser across the ceramic airfoil in accordance with the second computerized 3-dimensional model to cause removal of material of the ceramic airfoil layer-by-layer.
In a further embodiment of any of the foregoing embodiments, the first machine and the second machine have a common type of chuck configured to receive the fixture.
A further embodiment of any of the foregoing embodiments includes determining compensated linear and rotational positions of the through-holes and using the compensated linear and rotational positions in the ultrasonic machining.
In a further embodiment of any of the foregoing embodiments, the laser is a water-jet guided laser.
The present disclosure may include any one or more of the individual features disclosed above and/or below alone or in any combination thereof.
The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.
The low speed spool 30 generally includes an inner shaft 40 that interconnects, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive a fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in the exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 may be arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.
The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded through the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of the low pressure compressor, or aft of the combustor section 26 or even aft of turbine section 28, and fan 42 may be positioned forward or aft of the location of gear system 48.
The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), and can be less than or equal to about 18.0, or more narrowly can be less than or equal to 16.0. The geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3. The gear reduction ratio may be less than or equal to 4.0. The low pressure turbine 46 has a pressure ratio that is greater than about five. The low pressure turbine pressure ratio can be less than or equal to 13.0, or more narrowly less than or equal to 12.0. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to an inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1 and less than about 5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.
A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (“TSFC”)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. The engine parameters described above and those in this paragraph are measured at this condition unless otherwise specified. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45, or more narrowly greater than or equal to 1.25. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150.0 ft/second (350.5 meters/second), and can be greater than or equal to 1000.0 ft/second (304.8 meters/second).
Components in the engine 20, such as but not limited to, turbine blades, turbine vanes, blade outer air seals, and combustor panels, include cooling holes. The cooling holes are used to emit relatively cool air, such as bleed air from the compressor, to provide film cooling over the surface of the component. The cooling holes may be formed in a drilling operation. However, when the component is made of ceramic, such as monolithic ceramic or ceramic matrix composite (CMC), efficient drilling is a challenge because ceramics are extremely hard and brittle. The drilling of relatively deep, small-diameter holes is especially challenging. Ultrasonic machining and laser machining are under consideration for producing such features.
Ultrasonic machining involves the use of electrical energy to drive a transducer and produce mechanical vibrations along the axis of a tool at high frequency (e.g., 20-40 kHz). The vibration is transmitted through an energy-focusing horn to amplify the vibration amplitude and finally deliver vibration to the tool tip. An abrasive slurry (e.g., a mixture of abrasive particles, such as silicon carbide, boron carbide, etc., suspended in water or oil) is provided to the region being machined. The vibration of the tool causes the abrasive particles in the slurry between the tool and the workpiece to impact the workpiece surface and remove material by microchipping. The speed at which the workpiece can be machined depends on the vibration amplitude, abrasive particle concentration, and the size distribution of the abrasive particles. Ideally, if these parameters are kept constant, the machining speed should not vary with the penetration depth of the tool into the workpiece. In practice, however, the machining speed decreases significantly with increasing depth and, at approximately a 10 millimeter depth, may decline to close to zero. One reason for the decrease in machining speed is that the concentration of the abrasive particles in the region between the tool and the surface of the workpiece decreases. For instance, due to the depth of the hole, access to the region between the tool and the surface of the workpiece is limited and thus hinders removal of used slurry and introduction of fresh slurry. Additionally, the abrasive particles may be continuously broken down over time, and microchip debris may gradually accumulate. This decrease in machining speed may be mitigated to some extent by periodically lifting the tool and/or employing a special tool design. Nevertheless, mitigation techniques do not change the underlying nature of the dependence of machining speed on the cutting depth.
Laser machining, by comparison, involves ablation of the workpiece layer-by-layer through a series of passes to achieve material removal to a desired depth. In general, material removal can be controlled by the geometry and position of the laser tool, however, it is a challenge to determine the result of laser ablation with a high degree of accuracy. Computer simulations may be used to estimate the result, but uncertainty in laser ablation still remains and makes it difficult to generate accurate simulations and, in turn, accurate prediction of geometries for complex-geometry cooling holes.
In the above regards, each of ultrasonic machining and laser machining have drawbacks that heretofore have limited or prevented their application in ceramic workpieces. It has also been contemplated to use both of these machining techniques in attempt to realize the advantages of each while avoiding at least some of the drawbacks. In practicality, however, since these are two different processes on two different machines, there are compatibility issues that hinder harmonious use of these techniques together. As will be described below, the disclosed methodology facilitates overcoming such incompatibilities such that laser machining and ultrasonic machining may be used synergistically to produce cooling holes in ceramic components. As will also be appreciated, although the examples herein may be particularly directed ceramic components, the example may also be of benefit in the machining of metallic alloys.
The cooling hole 64 has at least two distinct sections, including a first section 66 and a second section 68. In this example, the first section 66 is a metering hole that is of uniform cross-section along central axis A1. The cross-section is circular but may alternatively be, but is not limited to, oval-shaped or funnel-shaped. The first section 66 has an inlet end 66a that opens to one of the internal cavities in the component 60 and an outlet end 66b that opens to the second section 68. The second section 68 has a non-constant cross-section that continually diverges along the axis A1 from an inlet end 68a that is coincident with the outlet end 66b of the first section 66 to an outlet end 68b that opens at the exterior surface of the component 60. The examples herein are also applicable to other geometries and, in particular, to relatively complex geometries that include two or more distinct sections of differing geometries.
At step 72 a workpiece (e.g., component 60 prior to formation of the cooling holes 64) is provided in which one or more of the cooling holes 64 are to be formed. The workpiece 60 is secured in a fixture (e.g., see fixture 82 in
At step 76, after drilling the through-hole 85, the fixture 82 with the workpiece 60 secured therein is removed from the first machine 84 and mounted in a second machine 86 (
As indicated above, there are challenges to combining laser machining and ultrasonic machining. The through-hole 64 is one aspect that facilitates making these techniques compatible. For instance, as the through-hole 64 is spatially common to the first and second sections 66/68, it in essence serves as a geometric link between the two processes.
Another challenge is accurate and efficient alignment on the two separate machines 84/86.
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.
