Patent Application
20250001508
The present invention relates to a machining device for producing at least one orifice in a workpiece, such as an aircraft turbomachine workpiece. The invention also concerns a method for producing an orifice in a workpiece using such a machining device.
The prior art comprises documents U.S. Pat. Nos. 2,339,324, 2,794,353 and 5,033,917.
Some turbomachines, in particular double-flow turbomachines with a longitudinal axis, are equipped with one or more acoustic panels allowing to reduce noise. These acoustic panels are sandwich structures consisting of an acoustic skin (usually a multi-perforated skin), a honeycomb core and a solid skin. The acoustic skin is generally in contact with the air flow passing through the turbomachine so as to attenuate the noise generated by the air flow. The presence of the acoustic orifices increases the roughness of the wall of the duct and the pressure drop in the duct.
Each orifice is drilled using a drill bit, for example. The drill bit generally has a diameter of between 1.4 and 2.6 mm. The drilling may be carried out manually, using a numerical control system or by a multispindle drilling robot.
The pressure drops induced by the presence of the acoustic orifices depends in particular on the diameter of the orifices and of the porosity (density of orifices) of the acoustic skin. All other things being equal, increasing the diameter of the orifices leads to an increase in pressure drop and porosity. However, the porosity of the acoustic skin is dictated by acoustic performance. Reducing the porosity of the acoustic skin may not really reduce the pressure drops.
On the other hand, the pressure drops may be limited by reducing the diameter of the orifices. The reduced diameter may be 0.3 mm, for example. This diameter is much smaller than that currently used for the acoustic panels mounted in the turbomachine or aircraft nacelles. A drill bit with such a small diameter may be very sensitive to the angle at which it strikes the acoustic panel, and may break at the slightest deviation due to its orientation or its slipping. A “rebound” effect that occurs after the drill bit has passed through the acoustic panel may also cause the drill bit to break. In particular, once the orifice has been drilled, the acoustic panel, stressed during the drilling phase, returns to its initial position, which may create a lateral force on the drill bit and cause the latter to break. Mechanical clamping elements installed around the perimeter of the acoustic panel may allow to minimize the bounce of the acoustic panel. In the case of a large workpiece, the disadvantage of the mechanical clamping elements is that they are not very effective when faced with the numerous areas to be drilled and their locations. The same type of disadvantage occurs with a vacuum clamping table. Another type of clamping is to apply an adhesive tape to the panel to be drilled. However, the adhesive tape tends to stick to the drill bit and cause it to break.
There is a need to resolve some or all of the above disadvantages.
The aim of the present invention is to provide a simple, economical and robust solution that improves the performance of a machining device while allowing to reduce the pressure drops on a workpiece drilled with such a device.
This objective is achieved in accordance with the invention by means of a machining device for producing at least one orifice in a workpiece made of composite material, the machining device comprising a tool holder and at least one drill bit mounted on the tool holder, the drill bit being configured to be driven in rotation about an axis of rotation, the machining device comprising a cylindrical guide body coaxial with the axis of rotation, mounted on the tool holder, and surrounding the drill bit, the guide body being configured to bear on the workpiece during the production of the orifice and the drill bit projecting from the guide body.
Thus, this solution allows to achieve the above-mentioned objective. In particular, the guide body allows, on the one hand, to hold and guide the drill bit in position and, on the other hand, to limit or even cancel the rebound effect that occurs when the workpiece has been drilled. The guide body allows a force to be applied to the workpiece while making an orifice. This allows to drill small-diameter orifices to allow to reduce the pressure drops. This solution is also more economical, as there is less drill bit breakage, and it saves time by reducing maintenance. Added to this is the fact that the guide body is a simple and economical solution; it is easy to make and does not involve any substantial modifications to the tool holder or other members of the machining device.
The machining device also comprises one or more of the following characteristics, taken alone or in combination:
The invention also relates to a method for machining a workpiece made of composite material, comprising the following steps:
According to the method, the composite material comprises carbon fibers and an epoxy-based resin.
The invention will be better understood, and other purposes, details, characteristics and advantages thereof will become clearer upon reading the following detailed explanatory description of embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the appended schematic drawings in which:
In the following description, identical or substantially identical elements and/or elements with the same functions are represented by the same numerical references.
The composite material comprises reinforcing fibers densified in a matrix. The fibrous reinforcement is made by weaving, superimposing sheets with fibers oriented in different directions, or is made from several plies of fibers pre-impregnated with a resin. The reinforcing fibers may be carbon, glass, ceramic, Kevlar®, polyamide, etc. or a mixture of these fibers. Advantageously, but without limitation, the fibers are made of carbon.
The matrix is preferably an organic matrix and may be a thermoplastic resin or a thermosetting resin. The resin may advantageously be an epoxy-based resin. In this description, the terms “resin” and “matrix” are equivalent.
The composite material workpiece 2 may be a turbomachine workpiece, which is not shown. The turbomachine is configured to be mounted on an aircraft, such as an aeroplane. The turbomachine may be a turbojet engine such as a turbofan, a turboprop equipped with at least one unducted propeller (also referred to as open rotor) or a turboshaft engine.
An example of a composite material workpiece 2 for a turbomachine is an acoustic panel centered around a longitudinal axis of the turbomachine. The acoustic panel may be equipped to a fan casing or a nacelle of a turbomachine.
Of course, the composite material workpiece 2 with through orifices obtained by drilling may be another turbomachine workpiece or may be applicable to other types of field, for example automotive.
With reference to
The tool holder 4 has a generally cylindrical shape with an axis of revolution 6. The tool holder 4 comprises an external cylindrical surface 7 which is connected to a receiving surface 8. The latter is defined in a plane perpendicular to the axis of revolution 6 of the tool holder 4. The receiving surface 8 is advantageously delimited by an annular shoulder 9 centered on the axis of revolution 6. Advantageously, but without limitation, the tool holder 4 moves in translation away from or towards the workpiece 2 to be drilled. Advantageously, the tool holder 4 may be equipped with a mechanical slide system to allow this movement.
The drill bit 5 extends along an axis of rotation 10. The drill bit 5 is mounted in rotation on the tool holder 4 along the axis of rotation 10. In this case, the tool holder 4 is attached relative to the drill bit 5.
To this end, the machining device 1 comprises a system 11 for driving the drill bit 5 in rotation. The drive system 11 comprises a motor 12 which is shown schematically in
Alternatively, the drive system 11 with the motor 12 may be integrated into the tool holder 4 as shown in
Advantageously, the tool holder 4 is equipped with detection means 16 which are configured to detect and transmit information relating to the position of the tool holder 4 or of the drill bit 5. The detection means 16 may be a presence sensor, a position sensor, a contact sensor or a combination of these sensors. The detection means 16 are connected to an electronic control unit 17 shown schematically. The latter is equipped with calculation, memory and information processing means allowing the machining device 1 to act and/or react according to the information received from the detection means 16. The electronic control unit 17 may be mounted in the tool holder 4 or in the robotic arm. The motor 12 may be connected to the electronic control unit 17.
The drill bit 5 extends in particular between a proximal end 5a and a distal end 5b. The drill bit 5 has a cross-section transverse to the axis of rotation 10 which is circular or generally circular.
Generally speaking, the drill bit 5 comprises a first part 13 which is smooth and a second part 14 which comprises cutting edges or lips 15. In
Advantageously, the drill bit 5 projects from the receiving surface 8. The drive shaft and the drill bit 5 are preferably coaxial. We understand that there is a single motor 12 and a single drill bit 5 in this embodiment.
The distal end 5b is configured to come into contact with a leading surface 18 of the workpiece 2 and to pass through the workpiece 2 while the orifice 3 is being drilled. Advantageously, but without limitation, the orifice 3 passes through the thickness of the wall of the workpiece 2 on both sides.
In this example, the drill bit 5 is made from a metallic material or metallic alloy. An example of a metallic material is steel. Alternatively, the drill bit 5 is made from a ceramic material. The ceramic may be alumina (Al2O3) or zirconia (Zr02) or a mixture of at least one of these two compounds.
As shown in
In particular, the guide body 20 advantageously extends between a first end 20a and a second end 20b along the axis of revolution 21. The guide body 20 has a constant circular cross-section along its axis of revolution 21. Of course, the guide body 20 may have a different cross-section. Advantageously, as may be seen in
In the present example of embodiment, the guide body 20 has an external diameter D1 equal to or less than the external dimensions (here diameter D2) of the tool holder 4. This means that the dimensions of the machining device 1 are not affected and the latter is not bulky.
Advantageously, the guide body 20 is hollow and has a longitudinal cavity 22 which opens out at the first end 20a and at the second end 20b. The guide body 20 is arranged so as to surround the drill bit 5 preferably over a major part of the length of the drill bit. In other words, the drill bit 5 is engaged inside the longitudinal cavity 22 of the guide body 20 and passes through it on either side along the axis of revolution 21. Advantageously, but without limitation, the longitudinal cavity 22 has a circular cross-section. In this example of embodiment, the longitudinal cavity 22 has different diameters.
Still referring to
The second end 20b has a flat surface in complementary contact with the leading surface 18 of the workpiece to be drilled. Alternatively, the second end 20b has a curved surface complementary to the leading surface 18 of the workpiece 2.
The guide body 20 has a length L1 that is less than the effective length L2 of the drill bit 5. The length L1 of the guide body 20 is measured between the first end 20a and the second end 20b. The effective length L2 of the drill bit 5 is measured between the receiving surface 8 and the distal end of the drill bit 5.
Advantageously, the guide body 20 is removably mounted. This allows the guide body 20 to be replaced if damaged, or the drill bit 5 to be replaced with another drill bit of a different diameter, for example.
The guide body 20 is made of a “hard” or “soft” material. The material of the guide body 20 is hard or soft compared to the material of the drill bit. The material of drill bit 5 in the present invention is considered canonical. In particular, the guide body 20 is made of a metallic, ceramic and/or carbide material. An example of metallic material is steel, aluminum, bronze and brass. The hard materials are steel and carbide, while soft materials are aluminum, bronze and brass.
Referring to
The guide body 20 also comprises a suction portion 24 which allows chips or dust from the material of the workpiece 2 to be removed during machining, for example. This also prevents clogging of the drill bit 5 and an increase in the temperature of the drill material.
The suction portion 24 is located towards the first end 20a of the guide body 20. The suction portion 24 and the guide portion 23 are arranged along the axis of revolution 21 of the guide body 20. In particular, the suction portion 24 opens into the first end 20a, while the guide portion 23 opens into the second end 20b. In other words, the suction portion 24 surrounds a portion of the drill bit. Advantageously, the suction portion opens onto the receiving surface 8.
Advantageously, but without limitation, the guide portion 23 has an internal diameter which is smaller than the internal diameter of the suction portion 24. The internal diameter of the guide portion 23 allows the drill bit 5 to be guided more effectively, while the internal diameter of the suction portion 24 allows chips or dust to be removed efficiently from the leading surface 18 of the workpiece 2.
In addition, a resilient return member 32 is configured so as to keep the second end 20b of the guide body 20 in contact or under pressure with the leading surface 18 of the workpiece 2. The elastic return member 32 is preferably arranged between the guide body 20 and the tool holder 4. Advantageously, but without limitation, the elastic return member 32 is a compression spring 36. To this end, the guide body 20 comprises at least one groove 33 wherein the compression spring 36 is housed. In the present embodiment, the groove 33 is annular and centered on the axis of revolution 21 of the guide body. A single compression spring 36, centered on the axis of revolution 21, is housed in the groove 33. The compression spring 36 extends between a first end 36a and a second end 36b. The first end 36a is in contact with the bottom of the slot 34 provided in the tool holder 4 and the second end 36b is in contact with the bottom of the groove 33 made in the guide body 20. The leading surface 18 is flat but could have one or more curvatures as explained above.
With reference to
The passages 25 could also be formed in the guide portion of the guide body 20, which comprises a single suction portion.
This embodiment also differs from the previous one in that the guide device 1 comprises several drill bits 5. In this example, the drill bits 5 are spaced apart. The proximal end 5a of each drill bit 5 is received in a housing in the tool holder 4. Each drill bit 5 is encased or surrounded by a guide body 20. The first end 20a of each guide body 20 is secured to the tool holder 4 and the second end 20b rests against the workpiece 2. In this way, a pressure is applied to the workpiece 2 so as to prevent it bouncing back. The smaller external diameter D1 of each guide body 20 compared to the external diameter D2 of the tool holder 4 allows several guide bodies 20 to be arranged side by side.
Here, each drill bit 5 has different diameters. In particular, each drill bit 5 comprises at its proximal end 5a a first diameter D3 which is greater than a second diameter D4 of the drill bit 5 at its distal end 5b. The first diameter D3 extends over the entire height of the first part 13, which is smooth and serves to guide the drill bit 5. The second diameter D4 is applied to the second cutting part 14. As the diameter of the drill bit 5 at its proximal end 5a is larger, the rigidity of each drill bit 5 remains greater. Of course, at least one of the drill bits 5 could have a single diameter along its entire length.
An advantageous but non-limiting characteristic of this embodiment is that at least one of the drill bits 5 slides along the axis of rotation 10. Advantageously, each drill bit 5 slides along the axis of rotation 10 independently of the other drill bits 5. This configuration allows the drill bits 5 to adapt to the leading surface 18, which may be convex or concave or have different curvatures.
Advantageously, but without limitation, the system 11 for driving the drill bits 5 comprises at least one motor 12. In this case, it is a single motor 12. Each drill bit 5 may be coupled directly to the drive shaft via the collet/nut system. Alternatively, the collet/nut system may be provided at the output of a gearbox (not shown). The gearbox would comprise an input connected to the single motor and several outputs rotated by gear sets. Alternatively, the drive system comprises several motors 12, each of which drives a drill bit 5.
This embodiment differs from the embodiment shown in
In this example of embodiment, the intermediate workpiece 26 comprises a damping element 27 which is arranged between the receiving surface 8 of the tool holder 4 and the first end 20a of each guide body 20. The damping element 27 may be made of an elastomer. Such a material has a high capacity for deformation, compression and/or damping. In this way, when the tool holder 4 is brought close to the workpiece 2 and the guide body 20 is in contact with the leading surface 18 of the workpiece 2, each damping element 27 compresses. The damping element 27 allows to limit the impact of the guide body 20 being abutted or pressed against the workpiece 2.
Advantageously, but without limitation, the damping element 27 has an annular shape and is arranged over the entire surface of the first end 20a. This makes it easier to fit the damping element 27.
Advantageously, the sealing member 29 is an annular seal or an O-ring centered on the axis of rotation 10. The sealing member 29 may be made of a polymer, rubber or elastomer, for example. This sealing member may withstand pressure and compression. In addition, such a sealing member 29 may be easily replaced during maintenance of the machining device 1.
Of course, the machining device 1 comprising a single drill bit 5 and/or a guide body 20 with a single suction portion 24 may be equipped with an intermediate workpiece 26 as described in the various embodiments above.
With reference to
Alternatively, the guide elements 30 comprise balls (for example three in number) (not shown) each mounted on a spring attached to the radially internal surface 23 of the guide portion. The balls are positioned at 120° to each other around the axis of revolution 21.
In one variant embodiment, which is shown on one of the drill bits 5 in
In another variant of embodiment shown on one of the drill bits 5 in
Of course, the machining device 1 comprising a single drill bit and/or a guide body 20 with a single suction portion 24 may be equipped with a lubrication system 35 or guide elements 30 as described in the various embodiments above.
We will now describe a method 100 for machining a workpiece 2 made of composite material. The method is implemented using the machining device 1 and is shown in
The method 100 comprises a step 110 of supplying a workpiece 2 made of composite material to be drilled. This workpiece may be, for example, a monolithic skin or a sandwich structure (e.g., formed by two skins glued to a honeycomb).
The method comprises a step 120 of supplying the machining device 1. The drill bit or drill bits 5 are already mounted on the tool holder 4.
The supply step 120 comprises a sub-step 121 of fitting the guide body 20 onto the tool holder 4. To this end, the drill bit or bits 5 already mounted on the tool holder 4 are engaged inside the guide body 20. Once the guide body 20 has been installed, the drill bit 5 projects from it, as the length of the guide body 20 is less than that of the drill bit 5. The difference in length means that the drill bit 5 may drill through workpiece 2 without obstruction. In other words, the drill bit 5 projects from the guide body 20 before and after machining the workpiece 2.
The supply step 120 may comprise a sub-step 122 of mounting the tool holder 4 on the portable machine or the robotic arm.
The method 100 also comprises a step 130 of making at least one orifice in the workpiece using the drill bit or bits 5. During this step, the tool holder 4 is moved towards the workpiece 2 so that the distal end 5b of the drill bit 5 is in contact with the leading surface 18 of the workpiece. The drill bit 5 is driven in rotation about its axis of rotation 10 when the portable machine or robotic arm is switched on.
In the case of a robot equipped with the tool holder 4, when at least one sensor of the detection means 16 determines that the tool holder 4 is close to the workpiece 2, a command to slow down the approach of the tool holder 4 is sent to the motor 12.
The drill bit 5 begins to drill the workpiece until the first end 20b of the guide body 20 is in abutment against the leading surface 18 of the workpiece 2.
If the intermediate workpiece 26 is placed on the second end 20b of the guide body 20, the intermediate workpiece 26 is brought into contact with the leading surface 18 of the workpiece 2 and compresses to slow the approach of the tool holder 4.
In the case where the intermediate workpiece 26 is placed on the first end 20a of the guide body 20, the second end 20b of the guide body 20 is brought into contact with the leading surface 17 and then the intermediate workpiece 26 compresses to slow down the approach of the tool holder.
The guide body 20 surrounding the drill bit 5 and abutting against the workpiece 2 during machining allows to reduce the breakage rate of the drill bit or bits 5 and increases the productivity for orifices with very small diameters, i.e., diameters of less than 1 mm, preferably between 0.1 mm and 0.5 mm. In this way, the guide body 20 prevents the drill bit 5 from slipping when it starts to drill into the workpiece 2 and pressurizes the workpiece 2 to avoid the rebound effect when the drill bit 5 leaves the material after drilling. The orifices with a diameter of less than 1 mm are used to reduce pressure drops associated, for example, with acoustic treatment of the workpiece.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2306807 | Jun 2023 | FR | national |
