Method and device for determining clamping quality in a clamping process of cutting tools

Abstract

The present invention relates to a method and a device for determining clamping quality for a tool held in a tool holder, wherein the tool is clamped in the tool holder by a clamping unit and during the clamping process a time curve of at least one system parameter is plotted by a measuring device, from which time curve of the at least one system parameter the clamping quality for a tool held in a tool holder can be determined.

Description

[0001] Method and device for determining the clamping quality during the clamping process of cutting tools

[0002] Technical field of the invention

[0003] The invention relates to a method and a device for determining the clamping quality of a tool held in a tool holder by friction fit.

[0004] State of the art

[0005] In machining, the rotation of a drive spindle must be transferred to a cutting tool. The cutting tool is typically clamped and mechanically connected to the drive spindle using suitable clamping devices or a tool holder. The resulting relative movement between the cutting tool and the workpiece then removes material in the form of a chip. Simultaneously, the cutting tool and the clamping devices are subjected to the forces generated during the machining process. The precision with which the rotational movement of the drive spindle can be transferred to the cutting tool therefore has a decisive influence on the dimensional accuracy of the component being manufactured. One criterion for evaluating how well a cutting tool is clamped in a clamping device during a machining process is the clamping quality of that device.

[0006] The clamping quality of clamping devices can be described by various performance attributes, depending on the application. The term "clamping quality" serves as an evaluation and classification tool to describe and assess the clamping performance of clamping devices in relation to the quality requirements for the clamping device and / or the clamped cutting tool resulting from the machining process. Since the quality requirements for a clamping device resulting from a machining process can vary depending on the manufacturing situation, clamping quality, and therefore clamping grade, cannot be universally defined. Focusing on drilling and milling operations, clamping quality is simplified to the following performance attributes: Minimum runout, maximum transmissible torque, and pull-out force.

[0007] Runout describes the uniformity of a rotating circular profile. Localized or overall deviations from this uniformity are referred to as runout errors and are known to have a (usually negative) impact on the machining process. A runout error occurs when the axis of rotation of the clamped cutting tool, clamping device, or combination thereof does not coincide with that of the drive unit. It must be considered that the reference direction used to assess runout can, in principle, be arbitrarily defined, meaning that a drive unit itself can already exhibit an angular deviation. During the machining process, the cutting tool and clamping devices are subjected to stress and thus loads due to the resulting machining forces.Due to the spindle's rotational movement, the cutting tool is subjected to predominantly transverse forces and torsional stress, depending on the machining strategy. The mechanical coupling between the cutting tool and the clamping device transmits the tool load to adjacent components of the machining chain. If the load becomes so high that the mechanical coupling between the cutting tool and the clamping device is no longer sufficient to hold the former in position, relative movement occurs (usually circumferential sliding), and consequently, tool pullout. The theoretical torque at which the clamped cutting tool or other components of the clamping device first release is referred to as the maximum transmissible torque. Depending on the machining strategy, loads along the axis of rotation (axial) can occur on the tool and, via the mechanical coupling, also on adjacent parts.Excessive axial forces can also lead to tool pull-out. The theoretical axial force at which the clamped cutting tool or other components of the clamping device first release is called the pull-out force. For an ideal clamping system, the lowest possible runout, the highest possible transmissible torque, and the highest possible pull-out force are typically desired.

[0008] For clamping cutting tools, either positive-locking or friction-locking clamping technologies are typically used. In positive-locking systems, the risk of tool pull-out is prevented by the positive locking mechanism, achieved through a defined geometric feature between the cutting tool and the clamping device or between other components of the clamping device. At the same time, the asymmetry resulting from this geometric feature and the achievable manufacturing accuracy of necessary functional surfaces are known to limit the maximum precision attainable with a positive-locking overall system. It is further known that, for this reason, friction-locking clamping systems are generally used for precision work. In friction-locking clamping systems, the mechanical clamping of the cutting tool is defined primarily by the frictional contact between the contacting partners, in addition to the shape of the contacting partners.As a consequence, friction-fit clamping systems are usually very sensitive to changes in the friction conditions between the friction partners, such as damage to the surface structure or contamination of the functional surfaces by friction-altering solids, for example residues from a machining process, and / or liquids, for example a cooling lubricant.

[0009] Mechanical and / or chemical damage and / or contamination of functional surfaces on cutting tools and clamping devices—hereinafter referred to as interfering factors—negatively impact the clamping quality of clamping devices, provided that this results in a negative impact on the friction between the contacting partners. This reduction in clamping quality manifests itself, for example, as an increase in runout, a reduction in the maximum transmissible torque, a reduction in the maximum pull-out force, or any combination thereof. While an increase in runout due to interfering factors can usually be detected before a machining process by measuring the tool outside or inside the machine tool, this is generally not possible for a reduction in the transmissible torque or the reduction in the pull-out force.Determining these values ​​before the machining process is only economically feasible mechanically, through the artificial application of torque and / or axial force. However, since in both cases the clamping connection between the cutting tool and the clamping device, or between individual components of the clamping device, is at least partially loosened, re-clamping is necessary, potentially resulting in a different outcome. Furthermore, this procedure can damage the components involved, as it deliberately induces a partial overload of the clamping system.

[0010] Existing solutions have so far aimed to improve the friction conditions between the relevant friction partners from a technological and manufacturing perspective, for example by changing the surface structure or by consistent cleaning to avoid contamination, or alternatively to switch to a positive-locking clamping system at the expense of the associated disadvantages.

[0011] The present invention is therefore based on the objective of providing a method and a device for determining the clamping quality of a tool held in a tool holder, wherein the presence of disturbances during the clamping process, i.e., during the process in which the cutting tool and the clamping means are transferred from a loose or partially loose state to a combined, clamped state, can be determined. In contrast to existing solutions, the invention described here is distinguished by the fact that the disturbances, or rather the effects of the disturbances, can be determined not during machine operation, i.e., usually while the clamping means is connected to the tool and the drive spindle of the machine tool, but explicitly during the tool preparation (clamping). Summary of the invention

[0012] According to the invention, these objectives are achieved primarily through the subject matter of the independent claims. Further advantageous embodiments are also apparent from the dependent claims and the description.

[0013] In particular, part of these objectives is achieved by a method for determining the clamping quality of a tool held in a tool holder, comprising the provision of the tool holder and the tool, the provision of a clamping unit and the provision of a measuring device which is set up to detect, record and process at least one system parameter of the clamping unit.The method further comprises the following steps: a) preparation of the tool holder by inserting the tool into the tool holder, b) insertion of the prepared tool holder into the clamping unit, c) clamping of the tool in the tool holder by means of the clamping unit, wherein at least one system parameter is recorded by means of the measuring device during the clamping process, and which method is characterized in that during step c) a time course of the at least one system parameter is recorded, from which time course of the at least one system parameter a clamping quality of a tool held in a tool holder can be determined.

[0014] The clamping process in the clamping unit is carried out up to a

[0015] Target span value is executed. Specifically, it depends on the

[0016] Based on tool dimensions, particularly the tool diameter, a target clamping value is defined which is necessary to clamp the tool holder so that the clamping force required for safe operation is present between the tool holder and the tool. This process control preferably takes place automatically, whereby, given comparable input conditions—that is, the state of the clamping unit and the state of other components involved in the clamping process—the same output conditions and the same output result, in particular the clamping quality, can be expected. Conversely, this means that significant changes in the input conditions lead to different output conditions and a different output result, especially a different clamping quality. Insignificant changes in the input conditions, however, do not lead to any change in the output result.With conventional, non-automated clamping systems, the fact that the clamping process is usually carried out manually by a user means that compliance with certain target values ​​(e.g. the target clamping value) is certainly desirable, but by no means guaranteed due to the sole responsibility lying with the user.

[0017] In practice, the existence of disturbances, especially damage to and / or contamination of the tool holder and / or the tool, means a change in the input conditions of the clamping process described above. This type of altered input condition leads to a different output result, as, for example, the maximum transmissible torque is reduced or the runout error is increased—or, in other words, the clamping quality is reduced. The question of when a change in input conditions leads to a different output result depends on various factors and cannot be answered universally. However, it can be stated that for every type of disturbance or combination of different disturbances, a threshold exists, the exceeding of which can be assumed to have a negative impact on the output result.Interferences that reach or exceed this threshold are referred to below as critical or significant interferences. According to the invention, a tool is clamped in a tool holder using the clamping unit during the clamping process. At least one system parameter of the clamping unit can be acquired, recorded, and analyzed as a function of time by the measuring device during this clamping process. There is at least one system parameter, preferably several system parameters, which can not only be measured as simply as possible and with a sufficiently high sampling rate, but whose temporal profile also correlates with the final result.Consequently, the clamping process with a properly cleaned tool holder and tool differs from that with a contaminated tool holder and tool not only in terms of the initial result, particularly the clamping quality, but also in terms of the temporal profile of the aforementioned at least one system parameter, such that the clamping quality can be determined from the temporal profile of this at least one system parameter. Similar conclusions can be drawn for other disturbances. The at least one system parameter can be recorded during the entire clamping process or only during a portion of it; therefore, the temporal profile of this at least one system parameter represents either this system parameter over the entire clamping process or only over a portion of it.

[0018] In a first embodiment, step c) of the inventive method involves recording the time course of a plurality of system parameters and / or a combination of at least two system parameters. From this time course of the plurality of system parameters and / or the combination of at least two system parameters, the clamping quality of a tool held in a tool holder can be determined. Determining the clamping quality of a tool held in a tool holder based on a plurality of system parameters and / or a combination of at least two system parameters increases the accuracy and robustness of the determination.

[0019] Advantageously, the acquired system parameter(s) can be subjected to signal processing, which in particular includes the application of filtering, transformation, normalization, standardization, and resampling operations. However, other known signal processing methods are also conceivable.

[0020] Filter operations, for example, use high-pass and low-pass filters to remove or minimize measurement noise (smoothing effect). Transformation operations adjust the measurement data by applying a predefined calculation rule to the entire dataset, thereby implementing a predictable change. Normalization and standardization operations achieve advantageous harmonization of the measurement data for subsequent processing. Resampling operations generate measurement signals with the same clock speed and duration for further processing.

[0021] The assessment of the clamping performance is also advantageously divided into at least two levels of detail. In the first level, the clamping performance determined based on the temporal profile of at least one system parameter is simplified and divided into two classes, for example, "good" and "poor," regardless of the type of disturbance responsible for a poor result. In the second level, the clamping performance determined based on the temporal profile of the at least one system parameter is divided into a finite list of previously defined classes. This division means that not only the result (good / poor) but also potentially the cause of this result can be derived from the knowledge of the class assignment.An explanatory list of possible second-level detail classes includes, for example, the classes "tension OK", "contaminated by liquid", "contaminated by particles", "contaminated by liquids and particles", "mechanical damage to tool holder", "chemical damage to tool holder" and "mechanical and chemical damage to tool holder".

[0022] According to another embodiment, the clamping quality is determined using an algorithm, in particular a machine learning algorithm. Since, on the one hand, the differences between the temporal profile of at least one system parameter with and without significant disturbances are marginal, and on the other hand, the system parameters are subject to variation due to manufacturing and application factors, classification by visual observation of the temporal profile of the at least one system parameter or by comparing individual descriptive parameters of this profile (e.g., slope, curvature, maximum value) is not effective.

[0023] For this purpose, an algorithm, in particular a machine learning algorithm, can be applied, which is provided with the time course of at least one system parameter and a related, otherwise determined clamping quality, for example by measuring the runout error, the maximum transmissible torque and / or the pull-out force, as data, and which describes a function or a relationship or a dependency of the data on the basis of known target values ​​(labels) and data points (features).

[0024] The algorithm is trained using a finite training set with known labels (labeled data), which is known as supervised learning. Specifically, this means that in a first step, labels and their underlying parameters are defined, and then controlled test data is collected based on this. For example, a finite set of test measurements is performed with a correctly cleaned tool holder and tool, taking into account manufacturing variations (production tolerances) and coupling dependencies, i.e., dependencies in the coupling between the tool holder and a spindle.

[0025] In a further step, a finite number of test measurements of the voltage quality are performed, incorporating various disturbances. This generates a large dataset that can be used to train the model. Because the class assignment is known for each individual measurement, the data is labeled. During the algorithm's learning process, patterns are recognized in the data, allowing for subsequent assignment to the known classes.

[0026] A further advantage is that a predicted clamping quality can be determined based on the recorded time course of the system parameter(s). Knowing the time course of at least one system parameter allows for a prediction of the expected clamping quality value. This can also include, in particular, a prediction of the maximum transmissible torque, the minimum runout error, and / or the pull-out force.

[0027] Advantageously, the tool is a shank cutting tool with at least a partially rotationally symmetrical shank. A wide variety of cutting tools, especially shank cutting tools, are used for different machining situations, differing, among other things, in their shank diameter. This has led to a gradation of toolholders depending on the size of the cutting tools to be used. Each size is only compatible with a limited range of shank diameters. Crucially, for the method of determining the clamping quality of a tool held in a toolholder, these toolholders differ in size, especially in diameter, and require different target clamping values ​​and clamping forces when using the clamping unit.

[0028] Preferably, the tool holder is a force-fit clamping system, preferably a friction-fit clamping system, further preferably a friction-fit clamping system comprising a collet with an external cone and a central recess for receiving a tool and a collet holder with a receiving cone for clamping and fixing a tool in the collet, wherein the external cone of the collet and the receiving cone of the collet holder are complementary.

[0029] When using a force-fit clamping system, the cylindrical surface of the tool held in the tool holder and at least the contact surfaces of the tool holder that are in contact with this cylindrical surface can be considered functional surfaces. Furthermore, auxiliary components can be included, which are defined as components positioned between the tool and the tool holder. These include, for example, collets and reducing sleeves. The contact surfaces between the tool and the auxiliary components, as well as any contact surfaces between several auxiliary components, are also considered functional surfaces. Contamination and / or damage to one or more functional surfaces can reduce the clamping quality.

[0030] According to a further embodiment of the invention, the system parameter is a hydraulic pressure, an electric current, an electric voltage, or an acoustic signal. This is based on the understanding that the time course of a hydraulic pressure, the time course of an electric current, in particular the motor current drawn by an electric motor to operate a hydraulic pump, an electrical voltage, in particular the motor voltage drawn by an electric motor to operate a hydraulic pump, or the time course of an acoustic signal recorded by a microphone fulfills the conditions described above for an ideal state variable. Specifically, this means that sufficiently large deviations in the time course of these state variables result in a change in the output, i.e., a change in the voltage quality.The reason for this is that these state variables, or rather the cause of their altered course, react similarly sensitively to disturbances as voltage quality does.

[0031] A second part of the invention is achieved by a device for determining the clamping quality of a tool held in a tool holder according to the inventive method. This device comprises a measuring device configured to detect, record, and process at least one system parameter of a clamping unit. It is conceivable that a clamping unit or a tool holder itself includes such a device for determining clamping quality, and in particular a measuring device. Alternatively, the device for determining clamping quality can be designed as a separate device from the clamping unit and / or the tool holder and connected to the clamping unit and / or the tool holder.

[0032] Another aspect of the present invention relates to a device for clamping a tool in a tool holder, comprising a clamping unit, wherein the tool can be inserted into the tool holder and clamped therein by means of the clamping unit, and which device is characterized in that it further comprises a device for determining the clamping quality of the tool held in the tool holder. The device for clamping a tool can further comprise a regulated or unregulated control for controlling the clamping process, or the clamping process can be carried out manually.

[0033] For clarity, the clamping process has so far been simplified and described as the process of clamping a tool in a tool holder, but this should not be considered limited to that. The inventive method and device are equally suitable for determining the clamping quality of a tool already held in a tool holder during the process of releasing the tool from the tool holder.

[0034] Brief description of the drawings

[0035] It shows

[0036] Figure 1 shows a schematic representation of an embodiment of the method for determining the clamping quality of a tool held in a tool holder, and

[0037] Figure 2 shows a schematic representation of an embodiment of a device for clamping a tool in a tool holder comprising a device for determining the clamping quality of the tool held in the tool holder.

[0038] Preferred embodiments of the invention Figure 1 schematically shows the process of method 100 according to one embodiment of the invention.

[0039] Method 100 comprises steps 101 to 108. The preparatory steps 101 to 103 comprise step 101, wherein the tool holder 10 and the tool 20 are provided; step 102, wherein the clamping unit 30 is provided; and step 103, wherein a measuring device 40 is provided, which measuring device 40 is configured to detect, record, and process at least one system parameter of the clamping unit 30.

[0040] Method 100 further comprises step 104, wherein the tool holder 10 is prepared by inserting the tool 20 into the tool holder 10, and step 105, wherein the prepared tool holder 10 is inserted into the clamping unit 30.

[0041] In step 106, the tool 20 is clamped in the tool holder 10 using the clamping unit 30, whereby at least one system parameter is recorded during the clamping process by means of the measuring device 40. During the clamping process, step 107 is also performed, in which a time course of the at least one system parameter is recorded, from which the clamping quality of the tool 20 held in the tool holder 10 can be determined. The method 100 also includes step 108, in which the clamping quality of the tool 20 held in the tool holder 10 is determined from the time course of the at least one system parameter. Step 108 can be performed essentially simultaneously with or after a time delay from step 107.The determination of the clamping quality during step 108 can be followed by further steps (not shown), which may be carried out simultaneously or at different times, and in these further steps, for example, an assessment of the determined clamping quality takes place.

[0042] Figure 2 schematically shows the device 2 for clamping the tool 20 in the tool holder 10 comprising the clamping unit 30, which clamping unit 30 includes the chuck adapter 32, the sleeve holder 33 and the clamping device 34.

[0043] The exemplary tool holder 10 is a friction-fit clamping system and comprises the collet 12 and the collet holder 11. To clamp the tool 20 in the tool holder 10, the tool 20 is inserted into the collet 12 and the collet 12 is pressed into the collet holder 11. For this purpose, the sleeve holder 33 is connected to the collet 12 and the chuck adapter 32 to the collet holder 11, and the clamping device 34 is configured to manipulate the chuck adapter 32 and the sleeve holder 33 such that the collet 12 is pressed into the collet holder 11. This process is to be understood as the clamping process.

[0044] The device 2 further comprises a device for determining a clamping quality 1 of the tool 20 held in the tool holder 10. The device for determining a clamping quality 1 comprises the measuring device 40, which measuring device 40 is set up and connected to the clamping device 34 in such a way as to detect, record and process at least one system parameter of the clamping unit 30.

Claims

Patent claims 1. Method (100) for determining the clamping quality of a tool (20) held in a tool holder (10), comprising - Provision of the tool holder (10) and the tool (20), - Provision of a clamping unit (30), - Provision of a measuring device (40) which measuring device (40) is configured to detect, record and process at least one system parameter (31) of the clamping unit (30), wherein the method (100) further comprises the following steps: a. Preparation of the tool holder (10) by inserting the tool (20) into the tool holder (10), b. Insertion of the prepared tool holder (10) into the clamping unit (30), c. Clamping of the tool (20) in the tool holder (10) by means of the clamping unit (30), wherein at least one system parameter (31) is detected by means of the measuring device (40) during the clamping process, and which method (100) is characterized in that during step c) a time course of the at least one system parameter (31) is recorded, from which time course of the at least one system parameter (31) the clamping quality of a tool (20) held in a tool holder (10) can be determined.

2. Method (100) according to claim 1 or 2, characterized in that in step c) the temporal course of a plurality of plant parameters (31 ) and / or a combination of at least two plant parameters (31 ) is recorded, from which temporal course of the plurality of plant parameters (31 ) and / or the combination of at least two plant parameters (31 ) the clamping quality of a tool (20) held in a tool holder (10) can be determined.

3. Method (100) according to one of the preceding claims, characterized in that the recorded plant parameter (31 ) or the recorded plant parameters (31 ) are subjected to signal processing.

4. Method (100) according to one of the preceding claims, characterized in that the clamping quality is subdivided into at least two levels of detail.

5. Method (100) according to one of the preceding claims, characterized in that the determination of the clamping quality is carried out by means of an algorithm, in particular an algorithm for machine learning.

6. Method (100) according to one of the preceding claims, characterized in that a predicted voltage quality can be determined on the basis of the recorded temporal progression of the system parameter(s) (31).

7. Method (100) according to one of the preceding claims, characterized in that the tool (20) is a shank cutting tool with a shank that is at least partially rotationally symmetrical.

8. Method (100) according to one of the preceding claims, characterized in that the tool holder (10) is a force-fit clamping system. 17 9. Method (100) according to claim 1 , characterized in that the system parameter (31) is a hydraulic pressure, an electric current, an electric voltage or an acoustic signal.

10. Device (1) for determining the clamping quality of a tool (20) held in a tool holder (10) according to a A method according to one or more of claims 1 to 9, comprising a measuring device (40) which measuring device (40) is configured to detect, record, and process at least one system parameter (31) of a clamping unit (30).

11. A device (2) for clamping a tool (20) in a tool holder (10) comprising a clamping unit (30), wherein the tool (20) can be inserted into the tool holder (10) and clamped therein by means of the clamping unit (30), and which device (2) is characterized in that it further comprises a device (1) for determining a clamping quality of the tool (20) received in the tool holder (10) according to claim 10.

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