METHOD FOR DETERMINING THE WEAR STATE OF A DRILL BIT AND CORRESPONDING DEVICE

Description

1. Scope of the invention

[0001] The field of the invention is that of drilling techniques for elements to be drilled, and that of controlling the wear of the cutting tools used for this purpose.

[0002] The invention relates in particular to methods and devices for controlling drill bit wear. 2. Prior art

[0003] Document EP 1 449 615 A1 discloses a method according to the preamble of claim 1 and a device according to the preamble of claim 11.

[0004] Various drilling devices are commonly used in industry, such as in the aerospace industry, to perform drilling of the component to be drilled.

[0005] These devices typically include an output shaft to which a cutting tool, such as a drill bit, is removably attached. Examples of these drilling devices include: Manual drills in which the thrust on the drill bit is generated manually; drills in which the drill bit feed is motorized, their body being fixed to a support during drilling and moved manually by an operator from one drilling point to another; among these drills are: automatic feed drills for which the feed speed and the rotational frequency of the drill bit are dependent, and drills with controlled cutting parameters for which the feed speed and the rotational frequency of the drill bit can vary independently of each other; drilling robots, which are similar to machine tools, in which the rotational frequency and the feed speed of the drill bit can be controlled independently of each other as for drills with controlled cutting parameters.

[0006] The present invention is more particularly intended for implementation in the context of drills with controlled cutting parameters and drilling robots. Such drilling devices, also called drilling devices with controlled cutting parameters, are connected to a control box containing, in particular, the drilling program, that is to say, all the information necessary to implement a drilling strategy automatically.

[0007] These drilling devices can be used to drill parts made of one or more layers of different materials. These materials include, in particular, aluminum alloys, titanium alloys, laminated carbon fiber, GLARE (for " Glass Laminate Aluminum Reinforced Epoxy » (in English), stainless steel, Inconel...

[0008] Each of these materials is used specifically for its mechanical, thermal, or chemical resistance characteristics and requires specific cutting parameters (particularly cutting speeds and / or feed rates) to ensure optimal drilling. These materials can be layered, in which case the drill bit will pass through different materials successively during a drilling operation.

[0009] During drilling, forces are generated on the drill bit. It therefore tends to wear down over time.

[0010] A drilling operation generally includes: a full material entry comprising a centering and stabilization phase of the drill during which the drill tip enters the material of the element to be drilled and the axis of rotation of the drill becomes stable relative to the element to be drilled; a full material drilling phase which begins after the centering and stabilization of the drill when its cutting edges have penetrated the element to be drilled.

[0011] Drill wear is accentuated by their entry into the material during the centering and stabilization phases.

[0012] Drill bit wear has an impact on the quality of the holes drilled using them.

[0013] The quality criteria for drilling include, in particular: tolerances on the diameter of the hole; the surface condition of the walls of the hole; the perpendicularity of the axis of the hole with respect to the wall to be drilled; the cylindricity of the hole; the location of the hole; the size of the burr formed on the element to be drilled after drilling; delamination at the exit of a hole made through carbon fiber.

[0014] The wear and tear on the drill bits must also be monitored to avoid: that a worn drill bit is not used to make holes: this leads to the making of holes that do not meet the required quality criteria; that a drill bit not yet worn is replaced prematurely when it could still allow the making of quality holes: this induces excessive consumption of drill bits and significant tooling costs.

[0015] In order to control the wear condition of the drill bits, it is known to equip pneumatic drilling devices with controlled cutting parameters with a cycle counter.

[0016] A cycle counter counts the number of drilling cycles performed with a drilling tool. Each drill bit has a maximum number of drilling cycles, after which it must be replaced. Since the same drill bit can be used for different drilling cycles, particularly in terms of the material(s) drilled, the maximum number of cycles is predetermined experimentally, taking into account the most challenging operating conditions the drill bit will encounter. To achieve this, successive drillings are performed in the laboratory using a drill bit in the most difficult material to drill. After each drilling operation, a check is performed: criteria representative of the quality of the hole (geometric and dimensional tolerances); of the degradation of the sharpness of the cutting edge of the drill bit; of the wear of the clearance faces and the cutting faces of the drill bit; of the chipping of the cutting edge of the drill bit.

[0017] As soon as one of these parameters reflecting drill wear reaches a value from which the drill is considered worn, the number of cycles performed with the drill to reach this wear level is recorded as the limit number of cycles.

[0018] In production, as soon as the number of drilling cycles performed with a drill bit reaches its cycle limit, the drill bit is replaced.

[0019] This type of monitoring is not optimal.

[0020] Indeed, the structures to be drilled during production are complex. These can include, for example, wings or other aircraft structures composed of superimposed layers of different materials. In order to optimize aircraft structures and, in particular, to reduce weight, the materials used and their thicknesses vary from one area to another. This is done to reinforce the structure where the stresses are highest and to avoid oversizing other areas. Consequently, it is not possible to know precisely, for each drilling operation during production, the exact nature of the structure being drilled in terms of materials and layer thicknesses.

[0021] This complexity results in the impossibility of performing drill qualification tests by drilling laboratory samples of structures identical in terms of materials and layer thickness to the structures that will be drilled in production. Instead, drill qualification tests are carried out by drilling using the most unfavorable case as a reference. For this purpose, the holes are drilled through plates of constant thickness with a given material stacking corresponding to the most unfavorable drilling scenario in production.

[0022] This leads to premature replacement of drill bits, as not all drilling is carried out in production in the worst-case scenario.

[0023] This type of monitoring is also not optimal because it does not take into account, in particular: the nature of the material(s) being drilled, and in particular their abrasive effect; the drilling depth; the cutting and feed speeds; whether or not lubrication is used; ...

[0024] However, the wear resistance exerted by each material on the drill bits is different. Indeed, each material exerts different cutting forces (torque along the drill bit's axis of rotation and / or longitudinal thrust along the drill bit's axis of rotation) and / or abrasive effects on the drill bit during drilling.

[0025] Titanium has a chipping effect on the tip and cutting edges of drill bits. Drilling a titanium component can therefore cause the tip of the drill bit used for this purpose to chip. Drilling a hole with a damaged tip results in poor centering of the drill bit and can consequently lead to a poor-quality hole that does not meet the required dimensional and geometric tolerances.

[0026] Carbon fiber is abrasive and tends to dull the cutting edges of drill bits.

[0027] Aluminum alloys can generate a chip that adheres to the drill bit and / or wear down the drill bit coating.

[0028] Therefore, basing drill bit replacement on the number of cycles used and the most demanding operating conditions, without considering the actual wear of the materials drilled during those cycles, does not allow for optimized drill bit replacement management. On the contrary, it leads to replacing drill bits that are not yet worn. Furthermore, drilling cycles may inadvertently start and be stopped before the drill bit even begins to drill. In this case, using a cycle counter results in counting these unintended cycles and thus in premature drill bit replacement.

[0029] The advent of electric drills with controlled cutting parameters has made it possible to control and measure various parameters in real time during drilling, such as: drill rotation speed; drill feed speed; lubrication control, start / stop and flow rate; detection of entry and exit faces of parts to be drilled; detection of material changes; thrust force on the drill; drill drive torque.

[0030] It was therefore considered to evaluate the wear of a drill bit from a measurement of the forces to which it is subjected during its use.

[0031] However, some materials may have different abrasive powers without generating different forces on a drill bit during drilling.

[0032] Taking into account the forces exerted on a drill bit during drilling is therefore not sufficient to correctly assess the stress on drill bits and deduce their level of wear.

[0033] Therefore, there is a need for a technique that optimizes the replacement of drill bits in order to reduce their consumption, i.e., that allows them to be replaced only when necessary. 3. Objectives of the invention

[0034] The invention aims in particular to provide an effective solution to at least some of these different problems.

[0035] In particular, according to at least one embodiment, an objective of the invention is to provide a technique for evaluating drill bit wear that optimizes drill bit use by avoiding: its premature replacement while it is still capable of producing holes that meet the required quality criteria, or its late replacement when its use would lead to the generation of holes that do not meet the required quality criteria.

[0036] Another objective of the invention is to provide, in at least one embodiment, such a technique which makes it possible to optimize the management of a fleet of cutting tools, in particular the renewal of drill bits, by providing for each of these tools a level of wear.

[0037] Another objective of the invention is to provide, in at least one embodiment, such a technique which makes it possible to avoid a degradation in the quality of drilling.

[0038] Another objective of the invention is, according to at least one embodiment, to provide such a technique which is simple and / or reliable and / or efficient. 4. Presentation of the invention

[0039] To this end, the invention proposes a method for evaluating the wear of a drill bit throughout its use for drilling elements to be drilled consisting of at least one layer and at least one material according to claim 1, the wear of said drill bit reflecting its ability to perform a drilling operation meeting at least one drilling quality criterion, said method comprising at least: a step of measuring or detecting at least one parameter having an impact on the wear of said drill bit, said parameter being chosen from the group including: the drilling depth drilled by said drill bit; the entry of said drill bit into an element to be drilled; a step of determining at least one state of use of said drill bit, each state of use being determined according to one of said parameters and being characteristic of one of said drilling quality criteria.

[0040] The invention therefore consists of determining at least one state of use of a drill bit as a function of the drilling depth drilled by it and / or the number of entries into the material of the bit, each state of use being characteristic of a quality criterion of the drilling to be carried out.

[0041] Thus, each drill bit has at least one state of use corresponding to a quality criterion for a drilling operation. It is therefore possible to know at any given time the state of use of a drill bit relative to a drilling quality criterion and thus to determine the drill bit's ability to perform that drilling operation while respecting the quality criterion in question.

[0042] Knowledge of this or these states of use thus makes it possible to optimize the management of the stock of drill bits and to guarantee that quality drilling is carried out.

[0043] The wear condition(s) are determined based on the drilling depth and / or the number of drill bits entered the material. They are therefore more representative of the actual wear level of the drill bit, thus preventing premature replacement.

[0044] According to one possible variant, each state of use is associated with a predetermined maximum threshold, said maximum threshold of each of said states of use being less than or equal to a predetermined maximum state of use beyond which the quality criterion which characterizes said state of use is no longer met.

[0045] The drill bit is no longer usable once the maximum threshold is reached for at least one state of use.

[0046] Thus, according to this aspect, the invention is based on an original approach that consists of determining at least one state of use of a drill bit, characteristic of one of the aforementioned drilling quality criteria, as a function of the drilling depth achieved by the bit or the number of times it enters a workpiece. Furthermore, each state of use is associated with a predetermined maximum threshold, this maximum threshold being less than or equal, for each state of use, to an permissible limit state of use beyond which the quality criterion characteristic of said state of use is no longer met.

[0047] According to prior art techniques, the limit threshold for using a drill bit corresponds to a number of typical drilling cycles, assumed to be representative of the drilling cycles actually carried out, beyond which the quality criteria required for the hole are no longer met.

[0048] According to a different technique, the invention proposes to define the limit threshold of use of a drill bit as a drilling depth or a maximum number of entries in an element to be drilled predetermined during tests and beyond which a quality criterion (tolerances on diameter, surface condition...) of the drilling is no longer met.

[0049] Thus, according to the invention, it is guaranteed that a drill bit will be used as long as it is able to produce a quality drilling.

[0050] The technique according to the invention thus makes it possible to guarantee: the production of quality drill holes; to optimize the consumption of drill bits insofar as they are used as long as they are capable of producing quality drill holes.

[0051] In one possible variant, each state of use is associated with a predetermined maximum threshold, the step of determining at least one state of use of said drill including, during the production of drilling of an element to be drilled using said drill, the qualification of said drill as: "useful forest" as long as the said maximum threshold of at least one state of use of the said forest is not reached; "out-of-service forest" from the moment the maximum threshold of at least one state of use of the said forest is reached.

[0052] Thus, as long as the maximum threshold of at least one state of use is not reached, the drill is considered useful, whereas as soon as the maximum threshold of at least one state of use is reached the drill is considered out of service.

[0053] According to one possible variant, a method according to the invention includes a step of emitting a message, for example visual and / or audible, indicating that the drill is out of service as soon as the qualification "out of service" is assigned to the drill.

[0054] This will provide a warning when the drill bit is no longer capable of drilling to the required quality standards. An operator can then easily determine the appropriate time to replace a drill bit, using it while it is still usable and replacing it only when it is no longer functional. The invention thus prevents a degradation in the quality of the drilled holes.

[0055] According to the invention, the determination of at least one state of use of said drill includes a weighting based on the effect of the abrasiveness of the material or materials drilled on the wear of the drill.

[0056] This allows us to take into account the abrasive effect of the materials being drilled on drill bit wear. This consideration further optimizes the assessment of drill bit wear.

[0057] Within the framework of said weighting: Each state of use is considered a deviation from a desired value of the corresponding drilling quality criterion; said deviation varies according to the sum of the corresponding parameter having an impact on the wear of said drill according to a predetermined function.

[0058] In this case, and according to one possible variant, a method according to the invention comprises a preliminary laboratory evaluation step of at least one type of drill bit for at least one material, said evaluation step comprising, for each type of drill bit and for each material: the performance of at least one series of drillings in test specimens made of said material with a new drill bit of the type considered for each of said series; the measurement, after each drilling of said at least one series, of the difference between the value of said or each of said quality criteria and the desired value corresponding to the criterion considered; the recording, for said or each of said quality criteria, of the difference between the value of the quality criterion considered and the desired value as a function of the cumulative parameter affecting the wear of said drill bit corresponding to the quality criterion considered; the continuation of drilling said at least one series until said at least one quality criterion is no longer met;When several series of drillings are carried out, the calculation for said or each of said quality criteria of the average of said deviations as a function of the cumulative parameter having an impact on the wear of said drill corresponding to the quality criterion considered; the calculation for said or each of said quality criteria of a polynomial regression of said deviation or of the average of said deviations as a function of the cumulative parameter having an impact on the wear of said drill corresponding to the quality criterion considered, said polynomial regression constituting said predetermined function used in said weighting.

[0059] This implementation allows for effective weighting based on the abrasiveness of the materials.

[0060] According to one possible variant, a memory is associated with each drill, the evaluation step including a recording step in the memory associated with each drill: of the maximum threshold for at least one state of use specific to a quality criterion and to a parameter having an impact on wear; of at least one polynomial regression: for a given material; for a given quality criterion; for a given parameter having an impact on wear.

[0061] According to one possible variant, a method according to the invention comprises, during the drilling of an element consisting of a stack of layers of different materials, a step of determining at least one state of use of said drill as a function of the drilling depth after drilling each of said layers, the step of determining at least one state of use of said drill, specific to a quality criterion, after drilling a layer comprising for each state of use the following steps: taking into account, at the beginning of the drilling of a given layer, the state of use calculated at the end of the drilling of the previous layer; the polynomial regression corresponding to said drill, to the material of the given layer, and to the quality criterion to which the state of use corresponds as a function of the drilling depth, the inverse function of said polynomial regression, calculation of a first value, result of said inverse function applied to said state of use calculated at the end of the drilling of the previous layer; taking into account the thickness drilled in said given layer, calculation of a second value, sum of the first value and of said thickness drilled in said given layer, calculation of the state of use at the end of drilling of said given layer, resulting from said polynomial regression applied to the second value.

[0062] It is therefore possible to determine usage states closer to reality by taking into account the abrasiveness of the materials drilled within the framework of considering the drilling depth.

[0063] According to one possible embodiment, a method according to the invention comprises successive drilling steps of elements to be drilled comprising at least one layer and at least one material, the material of an element to be drilled with which the drill bit first comes into contact during a drilling step constituting a starting material, said method comprising, during each drilling step of an element to be drilled, a step of determining at least one state of use of said drill bit specific to a quality criterion as a function of the entry of said drill bit into an element to be drilled, the step of determining at least one state of use of said drill bit comprising, for each state of use, the following steps: taking into account, when detecting the entry of said drill into a given element to be drilled, the state of use calculated when detecting the entry of said drill into the element to be drilled in the previous drilling step, the polynomial regression corresponding to said drill, to the attack material of said given element to be drilled, and to the quality criterion to which said state of use corresponds as a function of the detection of the entry of said drill into an element to be drilled, the inverse function of said polynomial regression, calculation of a first value, resulting from said inverse function applied to said state of use calculated in the previous drilling step, calculation of a second value, sum of the first value and the new entry, calculation of the state of use at the end of drilling of said given element to be drilled, resulting from said polynomial regression applied to the second value.

[0064] It is therefore possible to determine usage states closer to reality by taking into account the abrasiveness of the materials drilled in the context of considering the number of entries in the material of a drill bit.

[0065] According to one possible variant, a method according to the invention further includes a step of recording in the memory associated with each drill bit during its use to drill elements to be drilled from at least one state of use.

[0066] According to one possible variant, said at least one quality criterion of a drilling operation belongs to the group comprising: tolerances on the diameter of the hole; the surface condition of the walls of the hole; the perpendicularity of the axis of the hole with respect to the wall to be drilled; the cylindricity of the hole; the location of the hole; the size of the burr formed on the element to be drilled after drilling; delamination at the exit of a hole made through carbon fiber.

[0067] The present invention also relates to a device for evaluating the wear of a drill bit throughout its use for drilling elements to be drilled consisting of at least one layer and at least one material according to claim 11, the wear of said drill bit reflecting its ability to perform a drilling operation meeting at least one drilling quality criterion, said device comprising at least: means for measuring or detecting at least one parameter having an impact on the wear of said drill bit, said parameter being chosen from the group including: the drilling depth drilled by said drill bit; the entry of said drill bit into an element to be drilled; means for determining at least one state of use of said drill bit, each state of use being determined according to one of said parameters and being characteristic of one of said drilling quality criteria.

[0068] According to one possible variant, each state of use is associated with a predetermined maximum threshold, said maximum threshold of each of said states of use being less than or equal to a predetermined maximum state of use beyond which the quality criterion which characterizes said state of use is no longer met.

[0069] According to one possible variant, a device according to the invention comprises means for qualifying said drill bit as: "useful forest" as long as the said maximum threshold of at least one state of use of the said forest is not reached; "out-of-service forest" from the moment the maximum threshold of at least one state of use of the said forest is reached.

[0070] According to one possible variant, a device according to the invention includes means for emitting a message indicating that the drill bit is out of service as soon as the qualification "out of service" is assigned to the drill bit.

[0071] According to one possible variant, each forest is associated with a memory containing: at least one material or at least one group of materials; a maximum threshold for each state of use specific to each material or group of materials, to each parameter affecting wear and to each quality criterion; at least one state of use.

[0072] According to one possible variant, a device according to the invention includes means for recording in the memory associated with said drill, during the production of drilling using said drill of elements to be drilled made of the same given material or the same group of given materials, at least one state of use as being the summation of said corresponding parameter having an impact on the wear of said drill.

[0073] According to the invention, said means of determining at least one state of use of said drill perform a weighting based on the effect of the abrasiveness of the material or materials drilled on the wear of the drill.

[0074] Within the framework of said weighting, of which: Each state of use is considered a deviation from a desired value of the corresponding drilling quality criterion; said deviation varies according to the sum of the corresponding parameter having an impact on the wear of said drill according to a predetermined function.

[0075] According to one possible embodiment, a device according to the invention comprises means for determining at least one state of use of said drill bit as a function of the drilling depth after drilling each of said layers of different materials constituting an element to be drilled, said means for determining at least one state of use of said drill bit after drilling a layer comprising for each state of use: means of taking into account, at the beginning of the drilling of a given layer, the state of use calculated at the end of the drilling of the previous layer; a predetermined polynomial regression of the deviation of said quality criterion to which the state of use corresponds with respect to a desired value as a function of the cumulative drilling depth of said drill, said polynomial regression corresponding to said drill, to the material of the given layer, of the inverse function of said polynomial regression, means of calculating a first value, result of said inverse function applied to said state of use calculated at the end of the drilling of the previous layer;means of taking into account the thickness drilled in said given layer, means of calculating a second value, the sum of the first value and said thickness drilled in said given layer, means of calculating the state of use at the end of drilling of said given layer, resulting from said polynomial regression applied to the second value.

[0076] According to one possible embodiment, a device according to the invention comprises means for determining at least one state of use of said drill bit as a function of the entry of said drill bit into an element to be drilled at each drilling of an element to be drilled comprising at least one layer and at least one material, the material of an element to be drilled with which the drill bit first comes into contact during a drilling step constituting a starting material, said means for determining at least one state of use of said drill bit comprising for each state of use: means of taking into account, when detecting the entry of said drill bit into a given element to be drilled, the state of use calculated when detecting the entry of said drill bit into the element to be drilled in the previous drilling step, a predetermined polynomial regression of the deviation of said quality criterion corresponding to the state of use with respect to a desired value as a function of the cumulative detection of the entry of said drill bit into an element to be drilled corresponding to said drill bit, corresponding to said drill bit, to the attack material of said given element to be drilled, the inverse function of said polynomial regression, means of calculating a first value, resulting from said inverse function applied to said state of use calculated in the previous drilling step, means of calculating a second value, sum of the first value and the new entry, means of calculating the state of use at the end of drilling of said given element to be drilled,resulting from said polynomial regression applied to the second value.

[0077] According to one possible variant, a device according to the invention comprises a memory associated with each drill bit containing: a maximum threshold of at least one state of use; at least one polynomial regression: for a given material; for a given quality criterion; for a given parameter affecting wear; at least one state of use.

[0078] According to one possible variant, said at least one quality criterion of a drilling operation belongs to the group comprising: tolerances on the diameter of the hole; the surface condition of the walls of the hole; the perpendicularity of the axis of the hole with respect to the wall to be drilled; the cylindricity of the hole; the location of the hole; the size of the burr formed on the element to be drilled after drilling; delamination at the exit of a hole made through carbon fiber.

[0079] An evaluation device according to the invention can in an alternative be integrated into a drilling device, in particular a drilling device with controlled cutting parameters. 5. List of figures

[0080] Other features and advantages of the invention will become apparent from the following description of particular embodiments, given by way of simple illustration and not limitation, and the accompanying drawings, among which: THE Figures 1a and 1b illustrates diagrams of a drilling device according to the invention, respectively with its removable head attached and detached from the body; the figure 2 illustrates the control scheme of the device Figures 1a and 1b ; there figure 3 illustrates the controller of the device Figures 1a and 1b ; there figure 4a illustrates the end of a drill bit and the figure 4b illustrates a stepped forest; the figure 5illustrates the electrical current consumed by the drive motor rotating a drill bit through layers of aluminum and titanium alloy; the figures 6 , 7 and 8 examples of polynomial regression curves according to the invention; the figure 9 illustrates a curve for determining the state of use of a drill bit using the dynamic method; figures 10a and 10b illustrate flowcharts concerning the qualification of a drill bit according to the simplified method; the Figures 11 And 12 illustrate flowcharts relating to a process according to the simplified method; the figures 13a and 13b illustrate flowcharts concerning the qualification of a drill bit according to the dynamic method; the figures 14, 15 and 16 illustrate flowcharts relating to a process according to the dynamic method of the invention; the figures 17 And 18illustrate examples of data tables collected following laboratory assessments of the evolution of the state of use of a typical forest according to the simplified and dynamic methods. 6. Description of specific embodiments 6.1. Device

[0081] A drilling device or drill for implementing a method according to the invention comprises a drill or a drilling robot with controlled cutting parameters. Such a drilling device is known in itself to a person skilled in the art and is not described in detail here except for the elements more specific to the invention.

[0082] As depicted on the Figures 1a and 1b , such a drilling device 10 includes a housing 11.

[0083] The housing 11 comprises a first portion of the housing 110 and a second portion of the housing 111, which extend substantially perpendicularly to each other. In an alternative, the housing could extend along a single axis and thus not have an essentially T-shaped form.

[0084] The drill includes an output shaft 12 that is movable in rotation and translation about the same axis. This output shaft 12 is connected by means of one or more transmission chains to drive means.

[0085] In this embodiment, the driving means include: an electric drive motor 14 connected to the output shaft 12 by a transmission chain 15 allowing the output shaft 12 to be driven in rotation, and therefore the drill 13 which is attached to it, and an electric feed motor 16, connected to the output shaft 12 by a transmission chain 17 allowing the output shaft 12 to be driven in translation, and therefore the drill which is attached to it.

[0086] Rotational training and rotational training are performed along the same axis. This principle is described in particular in document FR3000693.

[0087] The drilling device includes a removable drill head 301. This corresponds to the second portion of the housing 111 and includes means for securing a drill bit 13 20. Reversible mechanical and electrical linkage means 303 will conventionally be implemented between the removable drill head 301 and the first portion of the housing 110 (i.e. the body of the drill).

[0088] This head includes a memory 135, such as an RFID chip or any other suitable data storage medium. The first portion of the housing 110 will therefore include a reader 25 capable of reading the information contained in the memory associated with the drill head 301.

[0089] The load on the drill bit in the air of a drilling device results essentially from the friction that takes place inside the removable drill head.

[0090] The head includes means 20 for securing a cutting tool 13, for example a drill bit, located at the end of the output shaft 12. These securing means may, for example, include a drill bit clamp. Obviously, these securing means can allow a plurality of different drill bits to be attached to the drill.

[0091] During the life of the drill, information relating to the drill is carried by the memory integrated in the head.

[0092] In one alternative, it could be considered that the memory be integrated directly into the drill.

[0093] In both these variants, we will say that the memory is associated with the drill bit, whether it is integrated into its tool holder or directly into the drill bit.

[0094] An alternative to an RFID tag could be an electronic memory connected to the drill controller via electrical connectors.

[0095] With reference to the figure 4a The point of a drill bit 13 classically comprises a central edge 130 extended laterally by main edges 131 which terminate in cutting edges 132. The cutting edges 132 extend into ribs 133 which spread helically and define the diameter of the drill bit. The surface extending between the central edge 130 and the cutting edges 132, which includes the end point 134 of the drill bit, defines the cone of the drill bit which has a height H. The drill bit can also be a stepped drill bit with different groups of edges (cf. figure 4b ).

[0096] The drill is connected by a cable to a controller 19 which includes control means 18 for the drill. The cable typically includes power supply wires 210 for the motors and communication wires 211. It may also optionally include tubes for fluid(s) such as lubricant.

[0097] As will be explained in more detail later, these control means 18 are specifically configured to control the drill in order to perform drilling operations according to pre-programmed screwdriving strategies and the various stages of a process according to the invention. A drilling strategy conventionally defines the sequence of operations for drilling.

[0098] These control means 18 comprise, in this embodiment, a central unit 181 associated with an execution program stored in a memory 182. The program is coded in such a way as to allow the implementation of the steps of the process according to the invention. This central unit may include a microprocessor.

[0099] This controller 19 includes two power supplies 191, 192 for powering the drill's rotational drive motor 14 and the feed motor 16. These power supplies can, for example, be inverters suitable for powering permanent magnet synchronous motors. These motors are equipped with an angle sensor 141, 161 whose signal, representing the angle of the rotor relative to the stator, is used by the inverters to correctly power the synchronous motors.

[0100] This controller 19 also integrates an interface allowing the programming of drilling strategies. This interface includes an input / output interface 193, a user interface to manage a means of command input 194 (keyboard, touch screen, mouse, ...), and a display means 195 (screen, display, indicator light).

[0101] The drill can itself integrate a human machine interface 24 allowing the start of drilling and the visualization of information relating to the progress of drilling.

[0102] The controller 19 includes a connector 196 for connecting to an electrical power supply. The controller is separate from the drill. In one variant, it could be integrated into the drill, i.e., housed inside the drill's casing.

[0103] The device includes means for measuring at least one piece of information representative of the load on the drill bit during drilling.

[0104] This information includes one or more of the following: torque applied to the drill bit along its axis of rotation; axial thrust force applied to said drill bit; current or electrical power consumed by at least one of the motors of said drilling device, said drilling device comprising a drill bit rotation drive motor and a drill bit translation drive motor.

[0105] The means of measuring at least one representative piece of information about the load on the drill bit during drilling therefore include one or a combination of several of the following means: a torque sensor 22 applied to the drill bit along its axis of rotation; an axial thrust sensor 23 capable of measuring the force applied to the drill bit along its axis of rotation; a current or electrical power sensor 1910 consumed by at least one of the motors.

[0106] These are connected to the control means 18 to process the signals.

[0107] The drilling device includes a device or means for evaluating the wear of a drill bit throughout its use for drilling elements to be drilled consisting of at least one layer and at least one material, the wear of said drill bit reflecting its ability to perform a drilling that meets at least one drilling quality criterion.

[0108] These assessment methods include at least: means for measuring or detecting at least one parameter having an impact on the wear of said drill bit, said parameter being chosen from the group including: the drilling depth drilled by said drill bit; the entry of said drill bit into an element to be drilled; means for determining at least one state of use of said drill bit, each state of use being determined according to one of said parameters and being characteristic of one of said drilling quality criteria.

[0109] Each state of use is associated with a predetermined maximum threshold, said maximum threshold of each of said states of use being less than or equal to a predetermined maximum state of use beyond which the quality criterion which characterizes said state of use is no longer met.

[0110] The device according to the invention includes means for classifying the drill bit as either "out of service" or "usable," which allow: to compare each state of use of a drill with the maximum state of use threshold of each quality criterion recorded in its memory; to qualify the drill as "out of service" as soon as the maximum threshold of a quality criterion is reached, and as a useful drill as long as no maximum threshold is reached.

[0111] The system also includes means of communicating an indication in this regard visually and / or audibly (emission of an alert message, an alarm, etc.).

[0112] As will be described later in relation to the process according to the invention, this is implemented according to a dynamic method which will be described in detail later.

[0113] In the context of implementing a simplified method, which is not part of the invention, the device includes means for determining, during the production of drilling operations using said drill bit in workpieces made of the same material or group of materials, at least one state of wear of the drill bit. These means include means for calculating the cumulative value of the parameter affecting drill bit wear (cumulative depth of drilling or number of drill entries in a workpiece) since the beginning of the drill bit's service life. The device also includes means for recording the state of wear in the drill bit's memory at each drilling operation. These recording means include, in this case, the reader, which also allows writing to the memory associated with the drill bit.

[0114] As part of the implementation of the simplified method, the memory associated with each drill bit may contain the following information: one or more materials and / or groups of materials that can be perforated; a maximum threshold for each state of use specific to each material or group of materials, to each parameter affecting wear and to each quality criterion; at least one state of use.

[0115] In the implementation of the dynamic method, the means of determining at least one state of wear perform a weighting based on the effect of the abrasiveness of the material(s) drilled on drill bit wear. In this case, the determination of the state(s) of wear takes into account the abrasive nature of the drilled material(s), which has an effect on drill bit wear.

[0116] Within the framework of this weighting, and as will become clearer from the forthcoming description of the process: Each state of use is considered a deviation from a desired value of the corresponding drilling quality criterion; said deviation varies according to the sum of the corresponding parameter having an impact on the wear of said drill according to a predetermined function.

[0117] In this embodiment, the predetermined function is a polynomial regression of the deviation from a desired value of the quality criterion considered as a function of the sum of said corresponding parameter having an impact on the wear of said drill according to a predetermined function.

[0118] In the context of implementing the dynamic method for successively drilling elements made of layers of different materials, and taking into account the drilling depth as a parameter affecting drill bit wear, the device includes means for determining at least one state of use of the drill bit, allowing, for each state of use: to take into account, at the beginning of the drilling of a given layer, the state of use calculated at the end of the drilling of the previous layer; a predetermined polynomial regression of the deviation of said quality criterion to which the state of use corresponds with respect to a desired value as a function of the cumulative drilling depth of said drill, said polynomial regression corresponding to said drill, to the material of the given layer, the inverse function of said polynomial regression, to calculate a first value, result of said inverse function applied to said state of use calculated at the end of the drilling of the previous layer;to take into account the thickness drilled in said given layer, to calculate a second value, the sum of the first value and said thickness drilled in said given layer, to calculate the state of use at the end of drilling of said given layer, resulting from said polynomial regression applied to the second value: this state of use is a deviation from the desired value of the quality criterion considered.

[0119] Within the framework of implementing the dynamic method for successive drilling of elements to be drilled comprising at least one layer and at least one material, the material of an element to be drilled with which the drill bit first comes into contact during a drilling step constitutes a leading material, and taking into account the entry of the drill bit into the element to be drilled as a parameter affecting drill bit wear, the means for determining at least one state of use of the drill bit allow, for each state of use: to take into account, when detecting the entry of said drill bit into a given element to be drilled, the state of use calculated when detecting the entry of said drill bit into the element to be drilled in the previous drilling step, a predetermined polynomial regression of the deviation of said quality criterion corresponding to the state of use from a desired value as a function of the cumulative detection of the entry of said drill bit into an element to be drilled, said polynomial regression corresponding to said drill bit, to the material of the attack of said given element to be drilled, the inverse function of said polynomial regression, to calculate a first value, resulting from said inverse function applied to said state of use calculated in the previous drilling step, to calculate a second value, sum of the first value and the new entry, to calculate the state of use at the end of drilling of said given element to be drilled,resulting from said polynomial regression applied to the second value.

[0120] As part of the implementation of the dynamic method, the memory associated with the drill bit may include, in particular: one or more groups of materials that can be perforated, a maximum threshold for each state of use; at least one polynomial regression: for a given material; for a given quality criterion; for a given parameter affecting wear; at least one state of use.

[0121] The device includes means for determining the drilling depth and / or means for determining the entry of the drill bit into the element to be drilled, this information being necessary for determining the states of use. These means are now described. Real-time detection of the drill bit's passage from air to the element to be drilled or vice versa, or from one material to another

[0122] During drilling, the drill bit travels through the air in an approach phase until it encounters the workpiece. This air is called the approach air. The drill bit then successively encounters the different materials that make up the workpiece until it exits the workpiece. It then travels through the air called the exit air.

[0123] The drilling device includes means enabling the drilling of a workpiece made up of several layers of different materials: to detect in real time a change of material, i.e. passages of the drill bit from the approach air to the element to be drilled or from the element to be drilled to the exit air or from one material to another of the element to be drilled; to identify the material encountered by the drill bit, air being considered as a material.

[0124] These means do not in themselves constitute the object of the present invention. They will be described subsequently and are called means for detecting changes in matter and for determining matter.

[0125] Methods for detecting changes in material encountered by the drill have been described in the past in the context of the development of drills with controlled cutting parameters, for example in patent document EP 0339659.

[0126] The development of such methods became necessary for drilling parts made of several layers of different materials, such as aluminum alloys, titanium, or carbon fiber. These different materials require different cutting parameters; therefore, it was necessary to detect material changes during a single drilling operation to allow the drill's cutting parameters to be adapted to the material encountered. These methods implement real-time measurement, during drilling, of the load values ​​on the drill bit using the previously described methods for measuring at least one representative piece of information on the drill bit load.

[0127] Monitoring the load on the drill bit allows for the detection of sudden increases or decreases in its value, caused by differences in hardness or resilience between the materials drilled. Thus, the figure 5illustrates the electrical current consumed by the drive motor rotating a drill bit through layers of aluminum and titanium alloy.

[0128] These load values ​​depend on the cutting parameters used at the time of measurement, particularly the cutting speed and feed rate. These cutting parameters are those adapted to the material preceding the newly encountered material.

[0129] This means that the magnitude of the load values ​​on the drill bit when it encounters a new material depends on the previous material and does not, in itself, allow for the determination of the type of the new material. Therefore, prior art techniques for detecting material changes require declaring, before drilling, the materials the drill bit will encounter and their layering order.

[0130] The material change detection and material determination methods that can be used within the framework of the present invention do not require specifying either the materials that the drill bit will encounter or their stacking order. This provides greater adaptability of the drilling device to structures to be drilled where the material order and the thickness of the different material layers are not known to the operator beforehand.

[0131] These methods of detecting changes in material and determining material allow: to measure in real time at least one piece of information representative of the load on the drill bit; to detect the increase or decrease in the value of at least one piece of information representative of the load on the drill bit measured and thus deduce the transition of the drill bit from one material to another (transition from the approach air to a material of the element to be drilled or from a material of the element to be drilled to the exit air or from one material to another of the element to be drilled), the detection of an increase or decrease in at least one piece of information representative of the load on the drill bit corresponding to the transition of the drill bit from one material to another; to apply to the drill bit, each time the transition from one material to another is detected, predetermined reference cutting parameters: these reference cutting parameters are the same at each detection of the transition of the drill bit from one material to another,and are maintained for a sufficient duration to allow the drill bits to fully penetrate the new material; to deduce from this at least one representative piece of information about the load on the drill bit measured, while predetermined reference cutting parameters are applied, the material encountered, each material drilled by a given drill bit with given reference parameters generating load values ​​of a given level. For this, the measured value of at least one representative piece of information about the load on the drill bit is compared with a plurality of predetermined representative pieces of information about a reference load, each corresponding to the type of drill bit used and a different material. The material being drilled is then identified as the one whose representative information about the reference load corresponds to the measured value of at least one representative piece of information about the load on the drill bit.or, where applicable, the one whose reference load tolerance interval contains the measured value of at least one representative piece of information regarding the load on the drill bit.

[0132] The values ​​of the reference cutting parameters are chosen based on the predetermined group of materials that the drill bit is likely to drill and also in such a way as not to cause drilling defects or premature wear of the drill bit during the application phase of the reference parameters regardless of the material encountered that is part of the group.

[0133] A type of drill bit is characterized in particular by its shape, material, coating, diameter...

[0134] The memory associated with the drill will contain the data necessary for the implementation of these methods of detecting material changes and determining material composition, among other things: predetermined reference cutting parameters for each material or group of given materials; a range of load values ​​for each material that can contain the load values ​​that drilling the material in question generates on the drill bit when the reference cutting parameters are applied.

[0135] However, these means of detecting material change and material determination may be replaced by any other means enabling recognition of the materials or airs encountered by the drill in drilling action and assuming for example the declaration in the drilling strategy of the materials encountered by the drill during drilling and their stacking order. Measurement of the depths of material drilled by the drill bit

[0136] The drilling device includes means for measuring the drilling depth of the drill bit for each material or group of materials drilled. This measurement is performed between two instants corresponding to the detection of the drill bit's entry into the material or group of materials in question and the drill bit's exit from the material or group of materials in question. These instants will be determined, for example, by the material change detection and material determination means described previously.

[0137] Drilling depth measurement methods could, for example, include an angle sensor for the drill's feed motor. This could be, for instance, a brushless synchronous feed motor. This sensor provides the motor's rotation angle via its signal processing electronics.

[0138] These methods of measuring drilling depth allow: to measure the angle of rotation of the feed motor between two given instants: either between the entry and exit of the drill bit in a given layer of material, possibly part of a group of materials in a workpiece to be drilled. In this case, the device will include means for detecting a change in material, as described previously. Or between the entry and exit of a group of materials in a workpiece to be drilled; to convert the angle of rotation of the motor measured between the two preceding instants into a drilling depth using the transmission ratio of the kinematic chain between the feed motor and the drill bit, which defines the ratio between the number of revolutions of the feed motor and the feed stroke of the drill bit.

[0139] In one variant, the drilling depth measurement means include a speed sensor placed on the drive train between the feed motor and the drill bit. In this case, they allow: to integrate the speed signal provided by the speed sensor as a function of time between two given instants to obtain the rotation angle of the kinematic chain element supporting the sensor: either between the entry and exit of the drill bit in a given layer of material, possibly part of a group of materials in a workpiece to be drilled. In this case, the device will include means for detecting a change in material, as described previously. Or between the entry and exit of a group of materials in a workpiece to be drilled; to deduce from this angle the drill bit displacement using the transmission ratio, which defines the ratio between the number of revolutions of the feed motor and the drill bit feed distance.

[0140] In both the simplified and dynamic methods, the material or group of materials of the element to be drilled can be manually selected using the user interface. 6.2. Process 6.2.1. Simplified Method : without weighting the state of use by the abrasive effect specific to each material.

[0141] The simplified method is applicable for drilling holes in parts made of a single material or made of a stack of layers of different materials having a regular proportion between the thicknesses of these different materials from one hole to the next.

[0142] Respecting this constraint allows the establishment in the laboratory of a maximum threshold of the state of use of the drill in the simplified form of a sum of drilling depth or number of entries of the drill into a part to be drilled.

[0143] It includes, in particular, with reference to the figure 10a , a step 90 laboratory evaluation including a step 91 determination of maximum usage state thresholds, and a step 92 recording in the memory associated with each drill of the regulation parameters specific to it. i. Determination of the maximum usage state threshold in the laboratory

[0144] The purpose of step 91 of determination is to determine a maximum threshold of state of use beyond which a drill of a given type drilling a given material or group of materials no longer makes it possible to create holes that meet at least one quality criterion.

[0145] To determine this maximum threshold, a laboratory test is implemented. Such a test comprises a series of steps that differ depending on whether the criterion taken into consideration is the drilling depth achieved by the drill bit or the number of drill bit entries into an element to be drilled. i.1 Drilling depth

[0146] Step 91, determining a maximum wear threshold for each type of drill bit for each quality criterion, where the drilling depth is considered a parameter affecting drill bit wear, will now be described with reference to the figure 10b .

[0147] This involves, for each type of drill bit, and for each material and group of materials, performing at least one series of drillings in test specimens made of said material or group of materials with a new drill bit of the type considered in each of said series (step 931). These drillings are performed with cutting parameters adapted to the material or group of materials. They include one or a combination of several of the following parameters: cutting speed; feed rate; rotational frequency; type and level of lubrication; chip extraction; amplitude and frequency of the vibratory drilling component.

[0148] Compliance with at least one quality criterion will be verified during each of these drilling operations.

[0149] Said at least one quality criterion for a drilling operation belongs to the group comprising: tolerances on the diameter of the hole; the surface condition of the walls of the hole; the perpendicularity of the axis of the hole with respect to the wall to be drilled; the cylindricity of the hole; the location of the hole; the size of the burr formed on the element to be drilled after drilling; delamination at the exit of a hole made through carbon fiber.

[0150] Each of the quality criteria has, for a given drilling, a nominal value and a predetermined tolerance range depending on the quality that the drilled hole must exhibit.

[0151] The verification of compliance with each of the quality criteria therefore corresponds to checking whether the observed value of the criterion during each series of drilling is within the corresponding tolerance range or not (step 932).

[0152] During each drilling series, a usage status is calculated for the said quality criterion or each of said criteria (step 933). In this embodiment, it corresponds to the calculation of the cumulative drilling depth since the beginning of the series.

[0153] The drilling of said at least one series is continued until said at least one quality criterion is no longer met, i.e. until its nominal value is no longer within the corresponding tolerance range (step 934).

[0154] For each series, a state of use is recorded for said or each of said quality criteria as the limit of the state of use which is permissible when the corresponding quality criterion is no longer met (step 935): thus, for each series of drilling, we obtain a limit of drilling depth which is permissible for each quality criterion beyond which this quality criterion is no longer met.

[0155] When several series of drillings are carried out, the average of the permissible usage state limits recorded during the series corresponding to the usage state considered is calculated for said or each of said states of use (step 936).

[0156] A maximum threshold for a state of use is then determined for said or each of said quality criteria, said maximum threshold being equal to or less than said limit or average of limits of permissible state of use corresponding to the quality criterion considered (step 937).

[0157] At the end of this evaluation, a maximum threshold of state of use is obtained for each type of drill bit, in this case a maximum drilling depth, for each material and / or group of materials and for each quality criterion.

[0158] Thus, for a drill bit of a given type, we will obtain for each quality criterion a maximum drilling depth as the maximum threshold of state of use for such and such material and / or for such and such group of materials.

[0159] For example: For drilling titanium elements with a given drill type, the maximum permissible drilling depth beyond which the drilling diameter is no longer suitable will be W meters; for drilling elements comprising successive layers of titanium, aluminum and carbon fiber with a given drill type, the maximum permissible drilling depth beyond which the drilling taper is no longer suitable will be X meters. i.2 Drill bit entry into an element to be drilled

[0160] The evaluation of drill types, where the drill entry into a drilling element is considered a parameter affecting drill wear, will now be described with reference to the figure 10b.

[0161] This is identical to the one just described when the parameter taken into consideration is the drilling depth, except that rather than measuring the cumulative drilling depth during each series until each of the quality criteria is no longer met, here we measure the cumulative number of drill entries into a test specimen (step 933'), that is to say the total number of drill entries into an element to be drilled since the beginning of the series.

[0162] At the end of this evaluation, we obtain for each type of drill bit a maximum threshold of state of use, in this case a maximum number of entries of the drill bit into an element to be drilled, for each material and / or group of materials and for each quality criterion.

[0163] Each material group includes a lead material, that is, the material that is drilled first. Thus, in the case of material groups, the maximum number of material entries for a given group will be linked to its lead material.

[0164] Thus, for a drill bit of a given type, we will obtain for each quality criterion a maximum number of entries into an element to be drilled as the maximum threshold of state of use for such and such material and / or for such and such group of materials.

[0165] For example: For drilling titanium parts or parts whose first layer is titanium with a given type of drill bit, the maximum permissible number of drill bit entries in a part to be drilled beyond which the diameter of the hole is no longer suitable will be Y entries; for drilling aluminium parts or parts whose first layer is aluminium with a given type of drill bit, the maximum permissible number of drill bit entries in a part to be drilled beyond which the taper of the hole is no longer suitable will be Z entries. i.3 Recording

[0166] The evaluation also includes a recording step 92 in the memory 135 associated with each of the 13 drills: of one or more materials and / or groups of materials; of a maximum threshold of state of use (maximum drilling depth or maximum number of entries in an element to be drilled) for each quality criterion and for each material and / or group of materials and for the parameter(s) having an impact on the wear of the drill bit taken into consideration.

[0167] The recording of this information in the memory associated with the drill will be carried out by the department in charge of the tools and may be prepared in anticipation of future applications.

[0168] Following preliminary laboratory evaluation of different drill types, a database of drill types is created, each associated with specific drilling parameters for each material or group of materials that can be drilled. Depending on the nature of the drilling (for example, its diameter, the materials to be drilled, etc.), a drill type suited to that drilling will be selected, with the corresponding drilling parameters retrieved from the drill's associated memory. i.4 Data from the evaluation

[0169] Following laboratory evaluation, for example, a table such as the one shown can be obtained for each type of tool (drill bit). figure 17 mentioning a maximum threshold of state of use for each quality criterion, each parameter taken into consideration (drilling depth or number of entries in the element to be drilled, and each material or group of materials. ii. Application of the process in production ii.1 Taking into account the drilling depth

[0170] With reference to the figure 11 , in order to carry out successive drilling operations of elements to be drilled made of the same given material or of the same given group of materials, the appropriate drill bit is chosen from the bank of available drill bits and secured to the end of the output shaft of the drilling device (step 110).

[0171] Each drilling operation is then carried out according to the pre-programmed strategy in the selected controller 19 (step 112), with the material or material group of the elements to be drilled being selected (step 113).

[0172] The controller 19 reads, by means of the RFID tag reader 25, the contents of the memory 135 associated with the drill bit 13 in order to collect the data relating to the material or group of materials to be drilled (step 114). The drill bit is then rotated and translated towards the element to be drilled, and the drilling operation continues by drilling the element (step 116) until the drill bit exits the element to be drilled (step 117). Determining the depth drilled by the drill bit

[0173] During each drilling operation, the depth of penetration achieved by the drill bit is measured using drilling depth measuring devices. The procedure includes: a step 115 of detecting the entry of the drill into the element to be drilled, that is to say a step of detecting the passage of the drill from the approach air to the element to be drilled; a step 117 of detecting the exit of the drill from the element to be drilled, that is to say a step of detecting the passage of the drill from the element to be drilled to the exit air; a step 118 of measuring the distance of displacement of the cutting tips of the drill between the entry of the drill into the element to be drilled and the exit of the drill from the element to be drilled.

[0174] Determining the drilling depth during a drilling operation can be achieved in various ways using angle or speed sensors placed on the kinematic chain between the feed motor and the drill bit. Total depth drilled by the drill bit

[0175] With each new drilling operation, the depth drilled by the drill bit is added to any depth already recorded in its memory from previous drilling operations (step 119). The drill bit's memory thus contains the total drilling depth since the beginning of its use. Determination of state of use

[0176] The total depth drilled by the drill bit constitutes a state of use of the drill bit. This is compared with the maximum permissible depth thresholds of each quality criterion recorded in the drill bit for the material or group of materials from which the successively drilled elements are made (step 120).

[0177] As soon as the maximum threshold of a quality criterion is reached, the drill is classified as "out of service drill" and an indication (visual, audible or other) to that effect is notified so that the drill can be replaced and quality holes can be drilled (step 121).

[0178] Otherwise, the drill bit is classified as a "serviceable drill bit" (step 122). Further drilling cycles can then be performed with this drill bit until it is classified as a "disposable drill bit". ii.2. Taking into account the entry of the drill bit into an element to be drilled

[0179] When the parameter taken into account to determine the state of use of the drill bit is no longer the drilling depth but the entry of the drill bit into the element to be drilled, the procedure is identical to that which has just been described in relation to this latter parameter, except with regard to the following elements (with reference to the figure 12 ).

[0180] As in the previous variant, the material to be drilled is selected at the beginning of each drilling operation for elements made of a single material. In the case of elements made of a given stack of materials, the material of the first layer, called the attack material, is also selected at the beginning of each drilling operation (step 113'). Determining entry into an element to be drilled

[0181] In this case, rather than including a step to measure the drilling depth for each drilling operation, the process includes, for each drilling operation, a step 115 to detect the entry of the drill bit into the element to be drilled. This step is identical to that implemented in the previous variant when determining the drilling depth. Total number of drill bits entered into a drilling element

[0182] With each new drilling operation, the drill bit's entry into a workpiece is added to any entries already recorded in its memory from previous drilling operations (step '119'). The drill bit's memory thus contains the total number of entries into a workpiece since it began use. Determination of state of use

[0183] The total number of drill entries into a drilled element constitutes a drill usage state. This is compared with the maximum entry thresholds for each quality criterion recorded in the drill for the material of which the drilled elements are made or the first layer of the group of materials of which the drilled elements are made successively drilled (step 120').

[0184] As soon as the maximum threshold of a quality criterion is reached, the drill is classified as "out of service drill" and an indication to that effect is notified so that the drill can be replaced and quality holes can be drilled (step 121).

[0185] Otherwise, the drill bit is classified as a "serviceable drill bit" (step 122). Further drilling cycles can then be performed with this drill bit until it is classified as a "disposable drill bit".

[0186] The usage status is updated by the controller after each drilling operation in a table of the type shown. fig.17 . 6.2.2. Dynamic Method : with weighting based on the materials pierced

[0187] Unlike the simplified method, the dynamic method allows the determination of the wear state of a drill bit to be weighted according to the abrasiveness of the materials drilled by it; it therefore allows for a series of drillings where the proportion between the thicknesses of the layers of the different materials has a large variability from one drilling to the next. i. Preliminary evaluation of the abrasive effects specific to each material in the laboratory

[0188] A method according to the invention includes a preliminary evaluation step aimed at assessing the abrasive effect of different materials on a drill bit and consequently on its ability to create holes meeting various quality criteria. This step is carried out under laboratory conditions, i.e., outside of production. It is essentially a pre-configuration step prior to use.

[0189] The preliminary laboratory evaluation focuses on the combination of a drill bit and a removable head. Removable heads can be of different types.

[0190] A type of drill bit is characterized in particular by its shape, material, coating, diameter...

[0191] A type of drill is characterized in particular by its transmission, its motor, its dimensions...

[0192] With reference to the figure 13a This preliminary laboratory evaluation step 1300 includes, in particular: a step 131 of determining regression curves and maximum thresholds of usage states, and a step 132 of recording in the memory associated with each forest the regulation parameters specific to it. i.1. Regression curve and maximum usage state threshold

[0193] The objective of this evaluation is to establish, for a given material and a given drill bit used with appropriate cutting parameters, a relationship between the cumulative drilling depth or the number of entries and the deviation from a given quality criterion. This relationship will take the form of a mathematical function.

[0194] The quality criteria for drilling that can be taken into consideration belong to the group including: tolerances on the diameter of the hole; the surface condition of the walls of the hole; the perpendicularity of the axis of the hole with respect to the wall to be drilled; the cylindricity of the hole; the location of the hole; the size of the burr formed on the element to be drilled after drilling; delamination at the exit of a hole made through carbon fiber.

[0195] Each quality criterion has, for a given hole, a nominal value and a predetermined tolerance range based on the required quality of the drilled hole. Each quality criterion also has a predetermined desired value based on the required quality of the drilled hole. This value is preferably located within this tolerance range.

[0196] Step 131, determining regression curves and maximum usage state thresholds, includes, with reference to the figure 13b, for each type of drill bit, and for each material, the performance of at least one series of drillings in test pieces made of said material with a new drill bit of the type considered in each of said series (step 1331).

[0197] After each drilling of said at least one series, the difference between the value of said or each of said quality criteria selected in relation to said desired value corresponding to the criterion considered is measured (step 1332).

[0198] For example, when respecting a diameter tolerance, the deviation can be the difference between the actual diameter and the midpoint of the tolerance. Ideally, this deviation should be zero when the drill bit is new, and it can increase as the drill bit wears until it reaches a value beyond which the drill bit is no longer within the required tolerance.

[0199] The difference between the value of the quality criterion considered in relation to the desired value based on the cumulative effect of the parameter affecting the wear of the drill bit is recorded for the said or each of the said quality criteria (step 1333).

[0200] The drilling of said at least one series is continued until said at least one quality criterion is no longer met (step 1334), that is, until its value is no longer within the corresponding tolerance range.

[0201] When several series of drillings are carried out, a calculation is carried out for said or each of said quality criteria of the average of said deviations as a function of the sum of the parameter having an impact on the wear of said drill (step 1335).

[0202] A calculation is performed for said or each of said quality criteria of a polynomial regression of said deviation or of the average of said deviations as a function of the sum of the parameter having an impact on the wear of said drill (step 1336).

[0203] For each drill bit type, each material, and each quality criterion, a polynomial regression curve is obtained showing the difference or the average difference between the value of the quality criterion in question and the corresponding desired value, based on the cumulative effect of the parameter influencing drill bit wear, i.e., the drilling depth or the number of times the drill bit enters a material being drilled. It is by taking these regressions into account that the wear level of a drill bit can be weighted according to the abrasiveness of the materials being drilled.

[0204] Such a curve is visible at the figure 6This figure illustrates, for each drill bit (five in the example shown) of the same type used in a series of drilling operations, the regression curve representing the variation in the deviation from the drilling quality criterion considered in the test (deviation from the desired diameter, from the desired taper, etc.) as a function of the parameter affecting drill bit wear considered in the test (drilling depth or number of entries in a drilled element). The average regression curve obtained from all the curves is also shown on the graph. figure 6 .

[0205] A maximum threshold (maximum permissible deviation) is set for the difference between the observed value of each quality criterion during drilling and the corresponding desired value (maximum permissible deviation). This threshold is chosen such that beyond it, the quality criterion is no longer met.

[0206] Thus, for each type of drill, we obtain a regression curve illustrating the variation of a parameter affecting drill wear as a function of a deviation from the desired value of a quality criterion, and this for each material and for each parameter affecting drill wear taken into consideration and for each quality criterion taken into consideration. There figure 7 This illustrates, for example, the variation in the deviation from the desired diameter as a function of the drilling depth of a given material 1 using a drill bit of a given type. figure 8illustrates for example the variation of the deviation from the desired diameter as a function of the drilling depth of a given material 2 using a drill of a given type. i.2. Registration

[0207] Evaluation 1300 also includes a recording step 132 in the memory 135 associated with each of the drills 13: of one or more groups of materials; of a polynomial regression function of the deviation or the mean of the deviations between the value of the quality criterion considered and said desired value for each material, for the parameter(s) having an impact on wear taken into consideration, and for each quality criterion; of the inverse function of each polynomial regression function; of a maximum permissible threshold for each quality criterion, for each group of materials and for the parameter(s) having an impact on wear taken into consideration.

[0208] The recording of this information in the memory associated with the drill will be carried out by the department in charge of the tools and may be prepared in anticipation of future applications.

[0209] Following the preliminary laboratory evaluation of different types of forests, a database is thus obtained that can be used to assess the state of use of each type of forest in a production situation. i.3. Data from the preliminary assessment

[0210] Following the preliminary evaluation, one can, for example, obtain for a given tool type (drill), a table such as that of the figure 18 mentioning for each quality criterion, for each parameter taken into consideration (drilling depth or number of entries in the element to be drilled), and for each material a polynomial regression function and its inverse function, as well as a maximum threshold. ii. Application of the process in production ii.1. Taking into account the drilling depth

[0211] With reference to the figure 14 To perform a drilling operation on an element comprising a stack of successive layers of different materials forming a material group, the appropriate drill bit, equipped with its removable head, will be selected from the available drill bit bank and attached to the drilling device (step 140: Drill Bit Selection). The appropriate drilling strategy is also selected (step 141: Drilling Strategy Selection). When several material groups are stored in the drill bit's memory, the selected drilling strategy may trigger the selection of the corresponding group.

[0212] The controller 19 then reads, using the RFID tag reader 25, the contents of the memory 135 associated with the drill 13 (step 143 of reading the memory associated with the drill).

[0213] The drilling operation is then started (step 144) according to the strategy pre-programmed in controller 19, which includes the approach of the drill bit to the workpiece, drilling, the removal of the drill bit from the workpiece, and the retraction of the drill bit. A drilling strategy is defined for each type of hole drilled with a given drill bit in a part made up of several layers of material. It defines the cutting parameters for each phase of the drilling: approach of the drill bit to the workpiece, drilling of each layer of material, removal, and retraction of the drill bit.

[0214] Material change detection and material determination methods are implemented from the beginning of the drilling operation.

[0215] During the progression of the drill bit towards the part to be drilled and then through the part to be drilled, the means of detecting material change and material determination implement a step of detecting the entry of the drill bit into the part to be drilled or of detecting the passage of the drill bit from one layer of material to the next (step 145).

[0216] An entry into the part to be drilled is differentiated from a change of material by the fact that it consists of the passage of approach air into a solid material and a change of material by the passage of one solid material into another.

[0217] Each step 145 of detecting an entry into the workpiece or a change in material (passage of the drill bit from one material to another) is followed by a step 146 of determining the material encountered. Identifying the exit air as the material encountered constitutes a step in detecting the drill bit's exit from the workpiece.

[0218] Each time a new material is identified (step 146), the drilling device controller applies the cutting parameters adapted to that material to the drill bit to proceed with drilling it (step 147).

[0219] After the drill bit has passed through the part to be drilled, which results in the detection of the exit air as material encountered by the drill bit (step 148), the controller causes the retraction of the drill bit (retraction step 149).

[0220] Once the drill bit has fully retracted, the motors are stopped and a drilling report is recorded by the controller and possibly exported to a computer network to ensure production traceability (step 150).

[0221] Each time a change in material is detected (step 145), which corresponds to the end of drilling the layer of material that has just been drilled, a step of determining at least one state of use of said drill as a function of the drilling depth is implemented (step 160).

[0222] For this reason, with reference to the figure 15 The drilling depth through the newly drilled layer of material is determined (step 161'). This calculation is performed as described above in relation to the simplified method, taking into account not the entry time of the drill bit into the element to be drilled and the exit time of the drill bit into the air, but the entry time of the drill bit into the layer in question and the exit time of the drill bit from that layer.

[0223] The step of determining at least one state of use of said drill bit after drilling a layer includes the following steps for each state of use: taking into account, at the beginning of the drilling of the layer of material which has just been drilled (step 162), the state of use calculated at the end of the drilling of the previous layer (if the layer which has just been drilled is the first, this state of use is zero) (step 1621); of the polynomial regression corresponding to said drill, to the material of the layer which has just been drilled, and to the quality criterion to which the state of use corresponds as a function of the depth drilled (step 1622), of the inverse function of said polynomial regression (step 1623), calculation of a first value, result of said inverse function applied to said state of use calculated at the end of the drilling of the previous layer (step 163);taking into account the thickness drilled in said layer which has just been drilled (step 164), calculation of a second value, sum of the first value and of said thickness drilled in said layer which has just been drilled (step 165), calculation of the state of use at the end of drilling of said given layer, resulting from said polynomial regression applied to the second value (step 166): this state of use is a deviation from the desired value of the quality criterion considered. ;

[0224] This principle is represented by the curve illustrated in the figure 9 for an example in which elements to be drilled are successively drilled, comprising the stacking of two different materials called material 1 and material 2, taking into consideration the depth drilled as a parameter having an impact on the drilling depth and the desired diameter as a criterion of drilling quality.

[0225] The first material to be drilled is material 1. After drilling through this layer of material 1, the drilled depth is determined. From this drilled depth and the curve of the figure 7 The corresponding usage state E1 is determined, that is, the deviation from the target diameter, and this is recorded in the drill's memory. This gives us the first portion P1 of the curve of the figure 9 We then begin drilling the next layer of material 2. Once this is complete, we determine the drilling depth. Then, using the usage state value E1 previously calculated after drilling the previous layer of material 1, we apply the inverse function of the curve shown to the figure 8to determine the corresponding drilling depth. The value of the drilling depth achieved through layer 2 is added to this value. Then, from the sum of these depths, the value is determined from the curve of the figure 8 The corresponding usage state E2 is recorded in the drill's memory. This gives us the second portion P2 of the curve of the figure 9 Next, drilling begins on a new layer of material 1. Once this is complete, the drilling depth is determined. Then, using the value of the usage state E2 previously calculated after drilling the previous layer of material 2, the inverse function of the curve illustrated is applied to the figure 7to determine the corresponding drilling depth. The value of the drilling depth achieved through layer 1 is added to this value. Then, from the sum of these depths, the value is determined from the curve of the figure 7 The corresponding usage state E3 is recorded in the drill's memory. Drilling continues until the maximum usage state threshold, in other words the maximum deviation tolerated from the quality criterion under consideration, is reached.

[0226] Each time a new layer of material is pierced, a state of use is thus determined for each quality criterion.

[0227] When the parameter affecting drill wear is drilling depth, then the state of use for each criterion will be a deviation from the desired value of that criterion determined by taking into consideration the polynomial curves of the drilled materials expressing the variation of such a deviation as a function of drilling depth.

[0228] Each state of use is compared to the corresponding maximum permissible threshold (step 170).

[0229] As soon as a state of use reaches its maximum permissible threshold, then the drill is classified as "out of service drill" and this information is notified (step 171).

[0230] As long as no state of use reaches its maximum permissible threshold, the forest is classified as a "useful forest" and this information is notified (step 173). ii.2. Taking into account the number of drill entries in an element to be drilled

[0231] When the parameter affecting drill wear taken into account is no longer the drilling depth but the number of drill entries into an element to be drilled, the operation of the process is identical except for the following, except that the calculation of the state of use is only carried out once per drilling of an element to be drilled, this after the identification in step 145 of the entry into the part to be drilled.

[0232] The polynomial curves considered are those expressing the variation of the deviations of the quality criteria from the desired values ​​as a function of the number of entries of the drill bit in an element to be drilled, as well as the corresponding maximum thresholds.

[0233] The process includes successive drilling steps of elements to be drilled comprising at least one layer and at least one material, the material of an element to be drilled with which the drill bit first comes into contact during a drilling step constituting an attack material.

[0234] With reference to the figure 16 The process includes, at each drilling operation, a step (180) for determining the material to be drilled into the element being drilled. This step operates according to the same principle as the material determination step described in the previous variant.

[0235] The process includes, during each drilling step of an element to be drilled, a step 160' of determining at least one state of use of said drill bit as a function of the entry of said drill bit into an element to be drilled, the step of determining at least one state of use of said drill bit comprising, for each state of use, the following steps: Taking into account, upon detection of the entry of said drill bit into a given element to be drilled (step 1600), the state of wear calculated upon detection of the entry of said drill bit into the element to be drilled in the previous drilling step (if the drilled element is the first one that the drill bit drills, the state of wear is zero) (step 16001), the polynomial regression corresponding to said drill bit, to the material of the cutting edge of said given element to be drilled, and to the quality criterion to which said state of wear corresponds as a function of the detection of the entry of said drill bit into an element to be drilled (step 16002), the inverse function of said polynomial regression (step 16003), calculation of a first value, resulting from said inverse function applied to said state of wear calculated in the previous drilling step (step 1601), calculation of a second value, sum of the first value and the new entry (step 1602), calculation of the state of use at the end of drilling of said given element to be drilled,resulting from said polynomial regression applied to the second value (step 1603).

[0236] Each time a new layer of material is pierced, a state of use is thus determined for each quality criterion.

[0237] The usage status is updated by the controller after each drilling operation in a table of the type shown. figure 18 . 6.3. Variants

[0238] In variations of the simplified and dynamic methods: only one quality criterion or a plurality of quality criteria may be taken into consideration for the qualification of a drill bit; only one parameter having an impact on the wear of the drill bit or both may be taken into consideration for the determination of states of use.

[0239] Within the dynamic method, the material or group of materials of the successively drilled elements can be specified in the drilling strategy rather than automatically detected. In the case of a group of materials, the stacking order of the layers will also be specified. When considering the number of entry points in a drilled element, the starting material of the group of materials comprising the successively drilled elements can also be manually selected rather than automatically detected.

[0240] In another variant, material change detection will use the time derivative of the value of at least one piece of information representing the load on the drill bit. In this case, the method will include a step of calculating the time derivative of the measured value of the load on the drill bit, which will be compared with a predetermined threshold. Reaching this threshold will correspond to a material change. This threshold will be predetermined experimentally for each material and for each drill bit type by drilling it with a drill bit and determining an average time derivative value of at least one piece of information representing the load on the drill bit, which will be recorded as the threshold.

[0241] For certain quality criteria, the difference between the value of the quality criterion and its desired value, based on the cumulative drilling depth or the cumulative number of material entry points, can change abruptly after a certain drilling depth or number of entry points. For other quality criteria, this difference can, on the contrary, change gradually. In the first case, the simplified method, not covered by the present invention, will preferably be implemented, while in the second case, the dynamic method according to the principle of the invention will preferably be implemented. A hybrid method, not covered by the present invention, combining the simplified and dynamic methods is also conceivable. It could consist of calculating in real time a usage state as the cumulative drilling depth of a material during the drilling of a part made of several different materials.

[0242] Thus, in variations, certain criteria can be determined, during the implementation of the same process, using the dynamic method and others using the simplified method. An example of a technical solution was described above for determining the moment the drill bit enters the element to be drilled, the moment it exits, as well as for detecting the drill bit's passage from one layer to another of a material and for identifying that material. These techniques are described for illustrative purposes and could be replaced by different solutions known to those skilled in the art. Such techniques can be based on measuring changes in the load on the drill bit, which allows for the detection of material changes.

Claims

1. A method for assessing the wear of a drill bit (13) throughout its use for drilling elements to be drilled comprising at least one layer and of at least one material, the wear of said drill bit (13) reflecting its ability to perform a drilling which meets at least one quality criterion of a drilling, said method comprising at least: - a step (115) of measuring or detecting at least one parameter having an impact on the wear of said drill bit (13), said parameter being - the drilling depth drilled by said drill bit (13); or - the entry of said drill bit (13) into an element to be drilled; - a step of determining (160) at least one state of wear of said drill bit (13), each state of wear being determined according to one of said parameters and being characteristic of one of said quality criteria for a drilling; characterised by determining (160) at least one state of wear of said drill bit (13) comprising a weighting based on the effect of the abrasiveness of the drilled material(s) on the wear of the drill bit (13), as part of this weighting: - each state of wear being assimilated to a deviation from a desired value of said quality criterion of the corresponding drilling; - said deviation varying according to the sum of said corresponding parameter having an impact on the wear of said drill bit (13) according to a predetermined function.

2. A method according to claim 1, wherein each state of wear is associated with a predetermined maximum threshold, said maximum threshold for each of the said states of wear being less than or equal to a predetermined maximum state of wear beyond which the quality criterion characteristic of said state of wear is no longer met.

3. Method according to claim 2, wherein each state of wear is associated with a predetermined maximum threshold, said step of determining (160) at least one state of wear of said drill bit (13) comprising, during the making in production of drillings of an element to be drilled using said drill bit (13), the qualification of said drill bit (13) as: - "serviceable drill bit" as long as said maximum threshold of said at least one state of wear of said drill bit has not been reached; - "drill bit out of service" from the moment the maximum threshold of at least the state of wear of said drill bit (13) has been reached.

4. A method according to claim 3, comprising a step (121) of transmitting a message indicating that the drill bit (13) is out of service as soon as the qualification "out of service" is attributed to the drill bit.

5. A method according to any one of claims 1 to 4, comprising a preliminary laboratory evaluation step (1300) of at least one type of drill bit (13) for at least one material, said evaluation step (1300) comprising for each type of drill bit (13) and for each material: - making (1331) at least one series of drillings in test pieces made of said material with a new drill bit of the type considered in each of said series; - measuring (1332), after each of the drillings of said at least one series, the deviation between the value of said quality criterion or each of said quality criteria with respect to said desired value corresponding to the criterion considered; - recording (1333), for said or each of said quality criteria, the deviation between the value of the quality criterion considered with respect to said desired value according to the accumulation of the parameter having an impact on the wear of said drill bit (13) corresponding to the quality criterion considered; - continuing (1334) drillings of said at least one series until said at least one quality criterion is no longer met; - when several series of drillings are made, calculating (1335) for said or each of said quality criteria the average of said deviations according to the sum of the parameter having an impact on the wear of said drill bit (13) corresponding to the quality criterion considered; - calculating (1336) for said or each of said quality criteria a polynomial regression of said deviation or the average of said deviations according to the accumulation of the parameter having an impact on the wear of said drill bit (13) corresponding to the quality criterion considered, said polynomial regression constituting said predetermined function used in said weighting.

6. A method according to claim 5, a memory being associated with each drill bit (13), said evaluation step (1300) comprising a recording step (135) in the memory associated with each drill bit of: - the maximum threshold for at least one state of wear specific to a quality criterion and to a parameter having an impact on the wear; - at least one polynomial regression: - for a given material; - for a given quality criterion; - for a parameter having an impact on the given wear.

7. A method according to claim 5 or 6 comprising, during the drilling of an element made of a stack of layers of different materials, a step (160) of determining at least one state of wear of said drill bit (13) based on the drilling depth at the end of the drilling of each of said layers, the step (160) of determining at least one state of wear of said drill bit (13) at the end of the drilling of a layer comprising for each state of wear the following steps: - taking account, at the beginning of drilling (162) of a given layer, of - the state of wear calculated after drilling the previous layer (1621); - the polynomial regression corresponding to said drill bit (13), to the material of the given layer, and to the quality criterion to which the state of wear corresponds according to the drilled depth (1622), - the inverse function of said polynomial regression (1623), - calculating (163) a first value, being the result of said inverse function applied to said state of wear calculated at the end of the drilling of the previous layer; - taking into account (164) the thickness drilled in said given layer, - calculating (165) a second value, being the sum of the first value and of said thickness drilled in said given layer, - calculating (166) the state of wear at the end of the drilling of said given layer, resulting from said polynomial regression applied to the second value.

8. A method according to claim 5 or 6 comprising successive steps of drilling elements to be drilled comprising at least one layer and of at least one material, the material of an element to be drilled with which the drill bit (13) first comes into contact during a drilling step constituting a striking material, said method comprising during each drilling step of an element to be drilled a step (160') of determining at least one state of wear of said drill bit (13) depending on the entry of the said drill bit (13) into an element to be drilled, the step (160') of determining of at least one state of wear of the drill bit (13) comprising for each state of wear the following steps: - taking into account, when detecting (1600) the entry of said drill bit (13) into a given element to be drilled, - the state of wear calculated when detecting the entry of said drill bit (13) into the element to be drilled of the previous drilling step (16001), - the polynomial regression corresponding to said drill bit (13), to the striking material of said given element to be drilled, and to the quality criterion to which said state of wear corresponds according to the detection of the entry of said drill bit (13) into an element to be drilled (16002), - the inverse function of said polynomial regression (16003), - calculating a first value, resulting from said inverse function applied to said state of wear calculated in the previous drilling step (1601), - calculating (1602) a second value, being the sum of the first value and the new entry, - calculating (166) the state of wear at the end of the drilling of said element to be drilled, resulting from said polynomial regression applied to the second value.

9. A method according to claim 7 or 8, further comprising a step of recording in the memory associated with each drill (13) during its use for drilling elements to be drilled of at least one state of wear.

10. A method according to any one of claims 1 to 9, wherein said at least one quality criterion of a drilling belongs to the group comprising: - the tolerances on the diameter of the drilling; - the surface condition of the walls of the drilling; - the perpendicularity of the drilling axis with respect to the wall to be drilled; - the cylindricity of the drilling; - the location of the drilling; - the size of the burr formed on the element to be drilled after drilling; - the delamination at the exit of a hole made through the carbon fibre.

11. Device for assessing the wear of a drill bit (13) throughout its use for drilling elements to be drilled comprising at least one layer and of at least one material, the wear of said drill bit (13) reflecting its ability to perform a drilling which meets at least one quality criterion of a drilling, said method comprising at least: - means for measuring or detecting at least one parameter having an impact on the wear of said drill bit, said parameter being - the drilling depth drilled by said drill bit (13); or - the entry of said drill bit (13) into an element to be drilled; - means for determining at least one state of wear of said drill bit, each state of wear being determined according to one of said parameters and being characteristic of one of said quality criteria of a drilling. characterised by said means for determining at least one state of wear of said drill bit, performing a weighting based on the effect of the abrasiveness of the drilled material(s) on the wear of the drill, as part of this weighting: - each state of wear being assimilated to a deviation from a desired value of said quality criterion of the corresponding drilling; - said deviation varying according to the accumulation of said corresponding parameter having an impact on the wear of said drill according to a predetermined function.

12. Device according to claim 11, wherein each state of wear is associated with a predetermined maximum threshold, said maximum threshold of each of the said modes of wear being less than or equal to a predetermined maximum state of wear beyond which the quality criterion characteristic of said state of wear is no longer met.

13. Device according to claim 12, comprising means for qualifying said drill bit as: - "serviceable drill bit" as long as said maximum threshold of said at least one state of wear of said drill bit has not been reached; - "drill bit out of service" from the moment the maximum threshold of at least one state of wear of said drill bit has been reached.

14. Device according to claim 13, comprising means for transmitting a message indicating that the drill bit is out of service as soon as the qualification "out of service" is attributed to the drill bit.

15. Device according to any one of claims 11 to 14, wherein each drill bit is associated with a memory containing: - at least one material or at least one group of materials; - a maximum threshold for each state of wear specific to each material or group of materials, to each parameter having an impact on the wear and to each quality criterion; - at least one state of wear.

16. Device according to claim 15, comprising means for recording in the memory associated with said drill bit, during making in production, using said drill bit, drillings of elements to be drilled made from a same given material or a same given group of materials, at least one state of wear as being the accumulation of said corresponding parameter affecting the wear of said drill bit.

17. Device according to any one of claims 11 to 16 comprising means for determining at least one state of wear of said drill bit based on the drilling depth at the end of the drilling of each of said different material layers from which an element to be drilled is composed, said means for determining at least one state of wear of said drill bit at the end of the drilling of a layer comprising for each state of wear: - means of taking account, at the start of drilling a given layer, of - the state of wear calculated at the end of drilling the previous layer; - a predetermined polynomial regression of the deviation of said quality criterion to which the state of wear corresponds with respect to a desired value according to the accumulation of the drilling depth of said drill bit, said polynomial regression corresponding to said drill bit, to the material of the given layer, - the inverse function of said polynomial regression, - means for calculating a first value, resulting from said inverse function applied to said state of wear calculated at the end of the drilling of the previous layer; - means of taking into account the thickness pierced in the said given layer, - means for calculating a second value, the sum of the first value and said thickness drilled in said given layer, - means for calculating the state of wear of said given layer at the end of the drilling, resulting from said polynomial regression applied to the second value.

18. Device according to claim 17 comprising means for determining at least one state of wear of said drill bit based on the entry of said drill bit into an element to be drilled for each drilling of an element to be drilled comprising at least one layer and of at least one material, the material of an element to be drilled with which the drill bit first comes into contact during a drilling step constituting a striking material, the said means of determining at least one state of wear of said drill bit comprising for each state of wear: - means for taking account, when detecting the entry of said drill bit into a given element to be drilled, of - the state of wear calculated when the entry of said drill bit into the element to be drilled of the previous drilling step is detected, - a predetermined polynomial regression of the deviation of said quality criterion to which the state of wear corresponds with respect to a desired value according to the cumulative detection of the entry of said drill bit into a drill bit element said polynomial regression corresponding to said drill bit, to the striking material of said given element to be drilled, - the inverse function of said polynomial regression, - means of calculating a first value, resulting from the said inverse function applied to the calculated state of wear at the previous drilling step, - means of calculating a second value, being the sum of the first value and the new entry, - means for calculating state of wear at the end of the drilling of said given element to be drilled, resulting from said polynomial regression applied to the second value.

19. Device according to claims 11 to 18, comprising a memory associated with each drill bit containing: - a maximum threshold of at least one state of wear; - at least one polynomial regression: - for a given material; - for a given quality criterion; - for a parameter having an impact on the given wear; - at least one state of wear.

20. Device according to any one of claims 11 to 19, wherein said at least one quality criterion of a drilling belongs to the group comprising: - the tolerances on the diameter of the drilling; - the surface condition of the walls of the drilling; - the perpendicularity of the drilling axis with respect to the wall to be drilled; - the cylindricity of the drilling; - the location of the drilling; - the size of the burr formed on the element to be drilled following a drilling; - the delamination at the exit of a hole made through the carbon fibre.