DE102022209160A1 - Method for determining a wear condition of a tool and device therefor - Google Patents

Abstract

The invention relates to a method for determining the state of wear of a tool (2) and/or at least one cutting edge (3), wherein when the tool (2) or the at least one cutting edge (3) is in a new condition, at least one sacrificial workpiece (11, 21) a test measurement is carried out with a test machining, the test machining being monitored by means of at least one measuring device with at least one sensor (12) and measured values of the test measurement being storable in a memory (13), wherein after a defined machining of workpieces (4) by means of the tool (2) or by means of the at least one cutting edge (3) at least one further test measurement with test machining is carried out on the sacrificial workpiece (11, 21), which is monitored by the measuring device with the at least one sensor (12), the measured values being determined a state of wear of the tool (2) and/or the at least one cutting edge (3) is determined, the tool (2) in ei ner predefined feed direction (32) is moved at a predefined feed rate relative to the sacrificial workpiece (11, 21), the sensor (12) absorbing a force exerted by the tool (2) on the sacrificial workpiece (11, 21), the direction the force absorbed is aligned at a predefined angle to the feed direction (32).

Description

technical field

The invention relates to a method for determining the state of wear of a tool, in particular a tool based on hard metal, and a device for this. The tool has a cutting edge whose state of wear is determined using the method. If the tool is a multi-edged tool, the state of wear of at least one cutting edge or multiple cutting edges is determined, which is currently in a ready-to-use setting or position.

State of the art

Milling processes with hard metal-based tools are used, among other things, for machining workpieces. In milling processes in the industrial environment, the workpiece is machined with a defined cutting edge of the tool based on hard metal in a metal-cutting process. A geometrically defined chip is generated when the workpiece is machined.

The tools used and the workpieces to be machined can be made of very different materials.

Accordingly, a pair of materials is created that can vary greatly depending on the material of the tool and the material of the workpiece. This results in various physical variables, such as variables relevant to tool wear, among other things.

The economic and technical service life, also known as the service life, of tools made of a cutting material is determined by the degree of wear of the cutting material.

Therefore, when using a tool, it is fundamentally the goal of the user to utilize the technical service life of the cutting materials of the tool as fully as possible, since the cutting materials used as tools are expensive.

Based on this, there are a whole series of efforts to determine the degree of wear of the tools in order to be able to use the technical service life as much as possible on the one hand, but on the other hand to be able to reliably avoid the risk of tool breakage. If a tool breaks, there is a risk of the workpiece being destroyed in the worst case, which must be prevented in any case.

For example, optical monitoring methods are known in the prior art, in which the cutting edge of the tool is observed by means of a camera. The contour of the cutting edge is compared with specified patterns or dimensions in order to identify a maximum state of wear. If it is detected that the maximum state of wear has been reached, the tool is changed by the output of a corresponding signal or relevant information. If the tool is a multi-edged tool, the cutting edge is changed.

It is also known to measure the temperature at the cutting edge in order to draw conclusions about the degree of wear on the cutting edge. It is also known that force or torque measurements take place.

An analysis of the important failure modes of a cutting edge of a tool shows that the effects of the failure modes on the tool can be very different. The main types of failure are flank wear, crater wear, cutting edge fracture, built-up wear and cracking.

The problem with the known methods for monitoring the state of wear of a cutting edge of a tool is that the effects of all possible pending types of failure are considered in their entirety and no conclusions can be drawn about the individual type of failure from the results of the monitoring.

However, since the effects of imminent wear due to flank wear with an increasing cutting force can essentially be canceled out by the effects of increasing crater wear with a decrease in the cutting force and can also be superimposed by an oscillating force curve due to cracking in the cutting material no reliable, detailed information about an impending failure type can be derived from the known methods.

The methods known in the prior art accordingly have the disadvantage that the course of the wear can only be predicted imprecisely, which means that the tool is typically changed before its maximum state of wear, because there is no risk of a not yet expected Tool breakage still takes place and the usually expensive workpiece is damaged and thus becomes unusable.

This has the consequence that the expensive tools and/or the expensive cutters are replaced earlier than necessary, which unnecessarily increases the overall costs for the machining of a workpiece.

Presentation of the invention, task, solution, advantages

It is the object of the invention to provide a method for determining the state of wear of a tool, in particular a tool based on hard metal, which allows a more detailed consideration of individual types of wear, so that the state of wear of a tool can be better estimated. It is also the object to create a device for improved determination of the state of wear of a tool.

The task of the method is solved with the features of claim 1.

One exemplary embodiment of the invention relates to a method for determining the state of wear of a tool and/or at least one cutting edge, in particular of a tool which is used for machining a workpiece, with the tool or the at least one cutting edge being in a new condition or in a used condition a test measurement with test machining is carried out on at least one sacrificial workpiece, the test machining being monitored by means of at least one measuring device with at least one sensor and measured values of the test measurement being storable in a memory, wherein after a defined machining of workpieces by means of the tool or by means of the at least one Cut at least one further test measurement with test machining on the sacrificial workpiece, which is also monitored by the measuring device with the at least one sensor and measured values of the test measurement can be stored, with the result a state of wear of the tool and/or the at least one cutting edge is determined by means of measured values, the test machining being machining of the sacrificial workpiece, the tool being moved in a predefined feed direction at a predefined feed rate relative to the sacrificial workpiece, the sensor one of the Tool absorbs force exerted on the sacrificial workpiece, the direction of the absorbed force being aligned at a predefined angle to the feed direction. A wear condition of the tool can thus be determined from a comparison of stored measured values from the new condition or from a used condition with measured values from a current condition after workpieces have been machined. The use of a force at the predefined angle, in particular at an angle of 90° to the feed direction, causes the influence of the cutting edge or the tool on the sacrificial workpiece to be sensed, in particular as free as possible from disruptive influences. In principle, any tool can be used as the starting point for determining the state of wear, regardless of whether it is a tool that is new or a tool that is in a used condition and is intended to continue to be used. The angle, in particular 90° to the feed direction, is measured in a plane in which the test machining is carried out, the angle to the feed direction being determined.

After a test measurement and after a defined processing of workpieces by means of the tool or by means of the at least one cutting edge, at least one further test measurement with test processing is carried out on the sacrificial workpiece. The tool is used for a defined processing of workpieces, with a defined processing being determined according to a defined tool feed in mm or m during processing or according to a defined removed volume in mm3 or in m3.

In an advantageous exemplary embodiment, it is also expedient if the test machining is a milling machining of a sacrificial workpiece using a tool as a milling tool, in particular with a cutting edge or with a plurality of cutting edges. This allows standardized processing to be carried out, which can be reproduced again and again in the same way in order to be able to determine the influence of wear and the state of wear.

It is also expedient if the tool is moved in a straight line in the predefined feed direction at the predefined feed rate relative to the sacrificial workpiece during the test machining. Because of the rectilinear course, a disruptive influence due to changes in direction is reduced or avoided.

It is also expedient if the angle is aligned in the range from 60° to 120°, in particular approximately 90°, to the feed direction. With such an angle, the disturbing influence of inappropriate influences is reduced, in particular with an angle of 90°.

It is also advantageous if the sensor is a force or pressure sensor which is arranged in such a way that only a force or pressure acts on it which is at an angle in the range from 60° to 120°, in particular about 90°, to the feed dir direction. A force can thus be determined and evaluated in a reproducible direction, which facilitates the reproducibility of the measurement results and their measurement conditions.

The measurement of the force is recorded with high resolution, so that at least one force value or a force curve with several force values can be assigned to each cutting edge of the tool. During one rotation of the tool, for example, at least one force profile, in particular with a maximum, is therefore measured for each cutting edge provided. A maximum force value can then be assigned to the respective cutting edge from the value of the maximum of the force curve. From these force values or from the maximum force values, a mean value can be determined over one or more revolutions of the tool, which can be used to determine the state of wear.

It is particularly advantageous if the state of wear is differentiated according to at least one state of wear of the following types of wear/failure: flank wear, crater wear, built-up edge, crack formation and/or broken edge. Accordingly, the state of wear is specifically assigned to the most probable types of wear/failure, so that the further course of wear can be better estimated as the tool is used further.

It is also advantageous if the state of wear is determined from a respective state of wear consisting of at least flank wear, crater wear, built-up edge, crack formation and/or a broken edge. Correspondingly, an individual state of wear according to the specified types of wear or types of failure is combined in order to determine a general state of wear, which takes into account the considered types of wear/failure as a whole.

It is particularly advantageous if the test measurement is carried out separately with the test machining for each type of wear/failure considered or that a test measurement is carried out with one test machining or several test measurements are carried out with one test machining each and a wear/failure type is determined from this. Accordingly, in an advantageous exemplary embodiment, individual or different test measurements with test processing are carried out on sacrificial materials or on different sacrificial materials with different processing parameters. The processing parameters of the respective test processing are adapted to the type of wear/failure to be detected. In this way, specific consideration can be given to the behavior of the respective type of wear/failure.

Accordingly, the test measurement is carried out with the test processing for one or for several or for each considered type of wear/failure on a sacrificial workpiece provided for this purpose. In this way, specific consideration can be given to the behavior of the respective type of wear/failure.

It is also advantageous if the test measurement is carried out with the test machining for one or for several or for each type of wear/failure under consideration with machining parameters provided for this purpose. In this way, specific consideration can be given to the behavior of the respective type of wear/failure.

It is particularly advantageous if the state of wear is determined by comparing stored measured values and/or stored processed measured values from test measurements on at least one sacrificial workpiece or on a plurality of sacrificial workpieces. This allows the state of wear to be reliably determined.

In this context, it is particularly advantageous if processed measured values have or are first derivatives and/or second derivatives of measured value curves over time. In this way, even small deviations can be better recognized.

It is also advantageous if a recommendation for further use or replacement of the tool and/or the cutting edge and/or cutting edges is made from the determined state of wear or from the determined states of wear. The recommendation can be that the processing is carried out unchanged, that the processing is carried out with different parameters or that the processing is terminated. Machining with modified parameters can be machining with a reduced feed rate, for example.

The object of the device is achieved with the features of claim 14.

An exemplary embodiment of the invention relates to a device for determining the wear status of a tool and/or at least one cutting edge, in particular a tool which is used for machining a workpiece, with a tool having at least one cutting edge for machining a workpiece, with a measuring device at at least one sensor for monitoring a test measurement with test processing and with at least one sacrificial workpiece for carrying out the test measurement with test processing on the sacrificial workpiece, in particular for carrying out a method according to the invention.

In a further exemplary embodiment, it is also expedient if a first receptacle is provided for the sacrificial workpiece and a second receptacle is provided for the sensor, the sacrificial workpiece being coupled to the sensor in such a way that during test processing of the sacrificial workpiece, a force is exerted by the sacrificial workpiece the sensor can be transmitted. This creates a simple arrangement that allows measured values to be recorded in a reproducible manner, so that comparable measured values can be recorded under comparable conditions, so that even only minor signs of wear can be determined.

It is also advantageous if a base body is provided which forms the second receptacle for the sensor, with a carrier being provided which is guided so that it can be displaced in one direction relative to the base body, with the carrier forming the first receptacle and the sensor between the second recording and the carrier is arranged and is subjected to a force. This ensures that the force acts on the sensor in the direction in which the carrier can be displaced relative to the base body, which is also sufficient for the reproducibility of exact conditions.

It is also advantageous if an energy accumulator is provided, which pretensions the carrier towards the sensor. This avoids that undefined states can be avoided and the sensor experiences at least a minimum force due to the preload. It is also advantageous if the preload can be adjusted, in particular by means of an adjusting screw or the like.

It is also advantageous if a transmission element is arranged between the carrier and the sensor, in particular a spherical element as the transmission element. As a result, the force is once again concentrated in one direction on the sensor, so that interference can be largely ruled out.

In a further exemplary embodiment, it is also expedient if a sacrificial workpiece is provided, which is arranged on the carrier, or if a predefined number of sacrificial workpieces is provided, with the sacrificial workpieces being arranged on the carrier. As a result, the machining of the at least one sacrificial workpiece can be arranged on the carrier, so that the force to be observed can be recorded by the sensor during the machining process of the test machining.

It is also expedient if the at least one sacrificial workpiece is provided and can be processed to determine at least one state of wear or several states of wear or that the individual sacrificial workpieces are each provided and can be processed to determine a state of wear according to a specific type of wear/failure. This enables the tool or the at least one cutting edge to be monitored easily, in particular also with regard to individual states of wear.

It is advantageous if a predefined number of sacrificial workpieces is provided, wherein the individual sacrificial workpieces can each be processed to determine a state of wear according to a specific type of wear/failure.

It is also expedient if several sacrificial workpieces, in particular two or three sacrificial workpieces, made of different sacrificial materials are provided for determining a state of wear according to flank wear, crater wear, built-up edge, crack formation and/or a broken edge. A combined sacrificial workpiece can also be provided, which has several sacrificial materials.

In the method according to the invention, there is also the possibility of supporting a determination of the type of wear/failure by an additional optical check, for example by means of a camera system. For example, it could be that the cutting forces remain constant although a high cutting volume has already been achieved with the tool, from which an increase in the cutting forces would be expected. Therefore, in this operating situation of the tool, it is expected that cratering and flank face wear would occur simultaneously. The cutting forces should increase as a result of the expected flank wear, while the cutting forces should decrease as a result of the expected crater wear, which would lead to an opposite effect with regard to the cutting forces, so that in extreme cases compensating cutting force curves would lead to a constant cutting force, although both the surface wear and crater wear would increase.

In this operating situation, therefore, crater wear can occur in addition to flank wear be present, which reduces the rake angle, which would reduce the cutting forces, thereby significantly increasing the risk of breakage of the tool. An additional process of checking the tool with optical means, for example with a camera, could provide better information about the current operating state or support it in this regard.

Further advantageous configurations are described by the following figure descriptions and by the dependent claims.

character list

• 1 eine schematische Darstellung einer erfindungsgemäßen Vorrichtung zur Durchführung eines erfindungsgemäßen Verfahrens,
• 2 eine schematische Schnittdarstellung eines Ausführungsbeispiels einer erfindungsgemäßen Vorrichtung,
• 3 eine schematische Darstellung zur Erläuterung der Testbearbeitung,
• 4 ein Diagramm zur Erläuterung des erfindungsgemäßen Verfahrens, und
• 5 ein Diagramm zur Erläuterung des erfindungsgemäßen Verfahrens.

The invention is explained in more detail below on the basis of at least one exemplary embodiment with reference to the drawings. It shows:

• 1 a schematic representation of a device according to the invention for carrying out a method according to the invention,
• 2 a schematic sectional view of an embodiment of a device according to the invention,
• 3 a schematic representation to explain the test processing,
• 4 a diagram to explain the method according to the invention, and
• 5 a diagram to explain the method according to the invention.

Preferred embodiment of the invention

The 1 shows a schematic representation of a device 1 with a tool 2 with at least one cutting edge 3, in particular with several cutting edges 3, which is used for machining a workpiece 4, in particular for milling the workpiece 4.

At least one first drive 5 is provided in order to rotate the tool 2 with its at least one cutting edge 3 or with its several cutting edges 3 in order to be able to provide the speed of the tool 2 required for the milling process. The speed of the tool 2 can be controlled by means of the first drive 5, in particular between zero and a maximum speed nMax1.

Furthermore, at least one first actuator 6 is provided in order to be able to displace the tool 2 with its at least one cutting edge 3 or with its multiple cutting edges 3 relative to the workpiece 4 . It makes sense here if the tool 2 can be pivoted and/or moved in particular about at least three axes. The pivoting speed and/or the traversing speed can be controlled by means of the at least one first actuator 6, in particular between zero and a maximum pivoting speed and/or a maximum traversing speed or also called cutting speed or feed rate.

The tool 2 is held interchangeably in a tool holder, which can be driven in rotation and/or pivoted and/or moved by means of the at least one first drive 5 and/or the at least one first actuator 6, so that the tool 2 can be rotated, pivoted and/or moved accordingly. or is movable.

The workpiece 4 is held in a workpiece holder 7 . The workpiece 4 and/or the workpiece holder 7 with the workpiece 4 can optionally be driven in rotation by means of a second drive 8 and/or pivoted and/or moved by means of at least one second actuator 9 . Correspondingly, at least one second drive 8 can optionally be provided in order to be able to set the workpiece 4 in rotation. The speed of the workpiece 4 can be controlled by means of the second drive 8, in particular between zero and a maximum speed nMax2.

Furthermore, at least one second actuator 9 can also optionally be provided in order to be able to displace the workpiece 4 relative to the tool 2 . It makes sense here if the workpiece 4 can be pivoted and/or moved about at least three axes. The swiveling speed and/or the movement speed can be controlled by means of the at least one second actuator 8, in particular between zero and a maximum swiveling speed and/or movement speed.

Furthermore, a holding device 10 is provided, by means of which a sacrificial workpiece 11 can be held. The purpose of the sacrificial workpiece 11 is for the tool 2 to machine the sacrificial workpiece 11 with the at least one cutting edge 3 in order to monitor this test machining using sensors 12 . The data from sensors 12 relating to the test machining is stored, for example, in a memory 13 of a control unit 14 that takes over the control and compared with other test measurements in order to determine a wear condition of the tool 2 and/or the at least one cutting edge 3 or the cutting edges 3.

The state of wear of a tool 2 or a cutting edge 3 or the cutting edges 3 is determined, for example, in direct comparison to the new condition of the tool 2, the cutting edge 3 or the cutting edges 3 . The state of wear can be determined in relation to the specific type of wear/failure.

Therefore, to determine the new condition of the tool 2 and/or the cutting edge 3 and/or the cutting edges 3 as a starting point for the later determination of the state of wear, test machining steps are carried out as test millings on the sacrificial workpiece 11 . The measured values of physical variables of this new condition determined by means of the sensor(s) 12 are stored as a reference pattern for the new condition.

A test measurement or test measurements, which is or will be carried out on the sacrificial workpiece 11, is or will be carried out again at a later point in time after the machining of workpieces. During these renewed test measurements, measured values are again recorded by the sensor 12 or the sensors 12 in order to compare them with the measured values of the new condition. In the case of the measured values, not only the absolute values of the measured values are explicitly taken into account during the evaluation, but the course of the measured values over time can also be taken into account. In this case, both the absolute value of measured values and/or the chronological progression of measured values can be used for the evaluation. For example, a development and/or an imminent probability of failure can be determined or inferred therefrom.

In the case of repeated test measurements on the sacrificial workpiece 11, correspondingly repeated measured values are taken, which are assigned to the respective test measurement. Such test measurements can be taken at regular and/or irregular intervals and/or event-dependent in order to determine the respective state of wear of the tool 2 and/or the cutting edge 3 and/or the cutting edges 3 at the time of the test measurement.

As explained above, a comparison is made between the measured values of the corresponding test measurement and the measured values of the test measurement in new condition. In this way, a state of wear can be determined. A chronological development of wear states can also be determined if data from different test measurements are evaluated. Advantageously, a comparison between different test measurements can optionally also be carried out in order to identify a development of wear states.

Correspondingly, a test measurement can be carried out in the new state with test measurements for a current state of wear, these test measurements being carried out accordingly with a tool which is currently being used when machining workpieces 4 . In addition to the actual value of the state of wear, the course of the values as a function of the period of use of the tool is also advantageous in order to be able to derive a qualified statement about the state of wear of the tool 2, the cutting edge 3 and/or the cutting edges 3. Specific materials and/or specific process parameters and/or specific milling methods are used to determine the state of wear with regard to the individual types of wear/failure considered, in which the measured values are recorded on the sacrificial workpiece 11 .

The specific milling processes can be used at a defined cutting speed, rotational speed, feed rate, with up/down milling and/or up/down milling in order to determine the respective specific state of wear.

It has been shown that the materials used as the sacrificial workpiece 11 and the process parameters and/or milling methods used in the test measurements for the optimal determination of the respective state of wear with regard to the type of wear/failure under consideration can be different, so that it is advantageous if depending on the type of wear under consideration Type of wear/failure a different or adapted sacrificial workpiece 11 is used and different or adapted process parameters and/or milling methods are used.

It is therefore advantageous if a method for determining a state of wear is optionally defined for the method according to the invention, in which a corresponding measurement is carried out as a reference cut when using a new tool 2 as a cutting tool for each type of wear/failure considered. If, for example, three types of wear/failure are considered, then three test measurements are carried out in new condition as reference cuts, one reference cut each for each possible type of failure considered, each with specific parameters and/or specific milling methods on a specific sacrificial workpiece 11 in each case.

In each case, measured values are recorded by means of at least one sensor 12, with a time profile of the measured value being recorded during the test measurement, and the absolute values of the measured values thus being determined. Additionally or alternatively, the change in the course of the measured value over time, the first derivation as a function of time and/or the second derivation can also be determined tion of the measured value can be determined as a function of time.

At predefined intervals, such as at predefined time intervals and/or depending on the event, test measurements can be taken during processing, such as milling, on the individual available sacrificial materials with the framework conditions specified in each case, such as with the first test measurement in new condition, compared and the course or the courses of the measured values are determined or updated in the sense of a history.

The test measurements, also referred to as reference cuts, are carried out on specific sacrificial materials depending on the types of wear/failure considered.

The sacrificial materials used can be arranged on the same measuring device with the sensors 12 provided, provided that comparable signals/physical quantities are used to determine the specific state of wear. If several different signals/physical quantities are required, several measuring devices with corresponding sensors 12 can also be used.

A multifunctional measuring device with different sensors 12 for determining different signals/physical variables, which are used to determine the state of wear, would also be advantageous.

Using an evaluation unit 15 provided, which can be embodied, for example, as the control unit 14 or which can also be provided as a separate evaluation unit 15, it is possible, on the basis of the measured values determined and their time profiles, to calculate first derivatives and/or second derivatives as values and/or or their time courses to recognize the respective tool condition or wear condition depending on the specific type of wear/failure and/or the specific probability of failure.

The overall condition of the tool and the probability of failure can also be recognized by defined algorithms. For this purpose, the different measured values and/or wear states for each type of wear/failure are processed together and, depending on the overall result of this processing, a recommendation for the remaining use and/or further use of the tool, the cutting edge 3 and /or the cutting edges 3 are issued.

For example, a recommendation can be given according to which the cutting speed should be reduced, the feed increased or an immediate tool change or cutting edge change should be carried out.

In an exemplary embodiment according to the invention, it is advantageous, for example, if the measuring device provided with the at least one sensor 12 with the clamped sacrificial materials is designed individually for each type of wear/failure. The measuring devices can also form a technical unit.

Alternatively, the measuring device with the arranged or clamped sacrificial materials can also be designed as a multifunctional element and form a technical unit.

In an advantageous embodiment of the invention, it is optionally also advantageous if the measuring device with the arranged or clamped sacrificial material or with the arranged or clamped sacrificial materials as an independent, in particular preassemblable, unit in a processing space of a device for processing workpieces, such as a machine tool , can be arranged.

For example, the measuring device can be arranged on a machine table of the device for machining workpieces or can be integrated into the machine table.

In one exemplary embodiment, it is advantageous if the sensors for the function of measuring the signals and/or physical quantities during the test processing of the sacrificial workpiece 11 made of the sacrificial material, i.e. the measuring device, and the clamping of the sacrificial workpiece 11 or the sacrificial workpieces 11 made of the sacrificial material or are housed from the sacrificial materials in one array or in two separate arrays or units. The measuring device can be arranged, for example, between the tool and a drive unit, such as a drive spindle.

In a further exemplary embodiment, a tool 2 with at least one cutting edge 3 can be identified by using at least one sensor 12 and the state of wear or states of wear can be stored individually for each type of wear, which is particularly advantageous for tools 2 that are only used temporarily.

Alternatively or additionally, the sensor 12 could also be arranged in the drive train, esp especially between the drive 5 and the actuator 6.

The tool 2 according to the invention is in particular a multi-edged milling tool, the cutting edges 3 being based on a hard metal.

Advantageously, the tool and/or the cutting edges are exchangeable.

It is also advantageous if the tools are highly positive tools. The use of highly positive tools means the use of tools with a decreasing rake angle or with a reduced rake angle compared to conventional tools with the usual rake angles. The development of highly positive tools, i.e. with a decreasing rake angle, means that different advantages can be exploited when machining using highly positive tools. These advantages are primarily significantly reduced cutting forces. Due to the lower cutting resistance as a result of the reduced angle, a lower energy conversion is also generated during cutting, which results in significantly reduced heat absorption on the workpiece to be machined and also on the tool. As a result, the thermal expansion is lower and the accuracy of the method increases. In roughing processes, a significantly higher machining volume per unit of time can therefore be expected with comparable heat absorption on the workpiece. Likewise, less drive energy is required in an advantageous manner.

However, the described advantages of highly positive tools come at the price of a greater tendency for highly positive tools to break. Due to the reduced rake angle, the probability of failure increases sharply, especially in the case of impact loads, especially at the end of the service life.

The method according to the invention for determining the state of wear of a tool therefore offers the possibility of better monitoring the use, in particular also of highly positive tools, and of predicting or estimating their wear or failure before damage occurs to the workpiece. This has the advantage that the market penetration of highly positive tools can be accelerated with the advantages mentioned.

The possible types of failure or wear considered are, for example, cutting edge fracture, flank wear, crater wear, built-up edge formation and/or crack formation. These types of wear and failure are considered in more detail below.

Cutting edge breakage:

A cutting edge fracture occurs when the tool is subjected to excessive mechanical stress. This type of wear can also occur as a result of other types of wear. Crater wear, built-up edges, high flank wear and/or other process-influencing elements, such as vibrations or incorrectly selected cutting parameters, can lead to a broken edge. In addition, an inhomogeneity of the hard metal can lead to local spalling. For example, in the case of abrasive materials, if the Co content in the hard metal is too low, breakouts can occur on the cutting edge of the cutting edge.

In order to avoid edge breakage, an appropriate countermeasure should be taken. A tool, such as an indexable insert, with a defined cutting geometry cannot be used equally well for all materials. The cutting edge fracture is the result of a cutting edge that is subjected to too much stress and can be seen as the final instance in all of the following types of wear. Cutting edge breakage is to be avoided in all machining operations. The cutting parameters are decisive for this. These should be adjusted in good time when wear begins.

A brittle material with good transmission of structure-borne noise is suitable for carrying out the test measurement on a sacrificial material as a sacrificial workpiece. Climb milling can be carried out, for example, which generates a pronounced signal peak when the cutter blade enters the workpiece. Normal feed rates and cutting speeds specific to the sacrificial material can be used. A structure-borne noise measurement, ie a vibration measurement and/or a structure-borne noise measurement in combination with a force measurement and/or also in combination with optical monitoring, for example by means of a camera system, can be carried out for sensing.

This can be checked, for example, on a sacrificial workpiece made from a sacrificial material with AlSi2.

• Der Freiflächenverschleiß ist eine der häufigsten Verschleißarten in der Zerspanung. Diese Verschleißart tritt meist bei zu geringem tatsächlichem Freiwinkel, bei abrasiven Werkstoffen oder bei zu hoch gewählter Schnittgeschwindigkeit auf. Freiflächenverschleiß kommt sehr häufig beim Schlichten vor, da beim Schlichten die Schnittgeschwindigkeit hoch und der Vorschub gering ist. Durch die hohe Schnittgeschwindigkeit erhöht sich die Temperatur und dadurch lösen sich Mikropartikel des Hartmetalls im Schneidstoff. Zudem erhöht sich die Reibung zwischen Schneide und Werkstoff, da sich das Werkzeug durch die niedrige Vorschubgeschwindigkeit eine längere Zeit im Eingriff befindet.

flank wear:

• Flank wear is one of the most common types of wear in machining. This type of wear usually occurs when the actual clearance angle is too small, with abrasive materials or when the selected cutting speed is too high. Flank wear is very common fig in finishing because the cutting speed is high and the feed rate is low in finishing. Due to the high cutting speed, the temperature increases and as a result, microparticles of the hard metal are dissolved in the cutting material. In addition, the friction between the cutting edge and the material increases because the tool is engaged for a longer time due to the low feed rate.

The solution and example is to reduce the cutting speed. When machining the material GGG60 or GGG70, premature flank wear can be seen. To counteract this flank wear, the cutting speed is reduced, for example. For example, the cutting speed can be reduced from 240 m/min to 210 m/min. This optimization can increase the service life by 25%.

A ductile/soft material can be considered as the sacrificial material, possibly also a plastic composite material. A counter-rotation method can be used, for example with a gentle entry with an increase in the chip thickness and the cutting forces. With increasing flank wear, the material tends to “smear away”.

The limit can be detected much better with soft material. Very low feed rates can be used here. A low cutting speed and possibly also running through a speed scale can be used. A force measurement can be carried out.

This can be checked, for example, on a sacrificial workpiece made from a sacrificial material with GGG60 or GGG70.

crater wear:

Crater wear is thermal diffusion that occurs on the rake face due to mechanical abrasion between the workpiece and the tool. This type of wear is an indication that the cutting speed selected is too high for an unfavorable cutting material and/or insufficient cooling and lubrication during the machining process.

Crater wear can usually be reduced or avoided by optimizing the tool cooling and reducing the cutting speed. Machining a flange made of steel 1.4301 at a selected cutting speed of 180 m/min causes premature crater wear. The addition of coolant and reducing the cutting speed to 120 m/min eliminated crater wear and increased tool life by 30%.

A tough material can be used as the sacrificial material. A reverse flow method can be used, for example with a gentle entry with increasing chip thickness and cutting forces. Normal feed values can be used here. Specific cutting speeds can be used depending on the sacrificial material. A force measurement or optionally a force measurement in combination with optical monitoring can be used.

This can be checked, for example, on a sacrificial workpiece made from a sacrificial material with steel 1.4301 or 1.2738.

• Eine zu geringe Schnittgeschwindigkeit oder ein zu geringer Zahnvorschub kann zu einer Aufbauschneide führen. Hierbei kommt es zu Materialaufklebungen auf der Spanfläche des Werkzeugs. Vor allem bei zähen Materialien, wie bei rostfreien Stählen, Aluminium und Stähle mit niedrigem Kohlenstoffgehalt, kann es zu der Aufbauschneidenbildung kommen.

Built-up edge formation:

• A cutting speed that is too low or a tooth feed that is too low can lead to a built-up edge. This results in material sticking to the cutting face of the tool. Edge build-up can occur, especially with tough materials such as stainless steel, aluminum and steel with a low carbon content.

The built-up edge can be counteracted by increasing the cutting speed and more precise coolant supply. Roughing a forging die made of steel 1.2738 revealed the following problem. At a cutting speed of 180 m/min, after a short period of use, there was a significant amount of material sticking to the cutting surface of the tool, i.e. an indexable insert. This led to an unpredictable breaking of the cutting edge after a service life of approx. 66 m per cutting edge. Increasing the cutting speed to 210 m/min resulted in a 15% longer tool life. This can be checked, for example, on a sacrificial workpiece made from a sacrificial material with steel 1.4301 or 1.2738.

A tough material can be used as a sacrificial material in the opposite direction or in the synchronous direction. Normal feed rates may be used, such as normal cutting speeds specific to the sacrificial material. A force measurement or optionally a force measurement in combination with optical monitoring can be used.

• Dabei wird die Rissbildung des Werkzeugs während der Zerspanung betrachtet.

cracking:

• The formation of cracks in the tool during machining is observed.

The harder the carbide of the tool, the lower the toughness of the tool material. Crack formation is very common due to the high dynamic and thermal loads on the carbide cutting edge. The behavior of a crack formation in the hard metal is difficult to predict. Crack propagation can very quickly cause the tool, for example an indexable insert, to fail so that the tool can no longer be used.

A crack in a tool tends to propagate on the flank face. After the crack has grown, neither the cutting edge nor the contact surface is functional. Built-up edge is one of the most common causes of cracking during the machining process. The chips stuck to the cutting edge absorb the cutting forces and at the same time store the high heat. Accordingly, they cause the spalling on the cutting edge. The chips penetrate into the crack gaps and generate indefinite stresses, which further influence the course of the crack formation. Severe temperature changes and the constant cutting in and out during milling result in so-called comb crack formation on the cutting edge.

The following measures can be taken to counteract the formation of cracks and comb cracks: If cracks form due to high mechanical loads, the tooth feed should be reduced so that the fatigue strength of the cutting material is maintained. If cracks form due to built-up edges, the countermeasures for avoiding built-up edges must be applied, see above under the topic of built-up edges. Measures can be taken against temperature fluctuations if comb cracks form. Dry machining or sufficient cooling lubricant supply as well as reducing the cutting speed can help.

During the face milling of a forging die made of the material 1.2738, at a cutting speed of 180 m/min, clear built-up edges formed. This resulted in the end of the tool life due to a broken cutting edge at 66 m/cutter. To avoid breaking the cutting edge, the cutting speed has been increased to 240 m/min. This measure extended the tool life to 74 m/cutter. The resulting increase in temperature during the milling process defined the new end of service life due to crater wear.

Ultimately, an average cutting speed of 200 m/min was the goal. The new end of tool life could be increased to 81 m/cutter thanks to process-reliable flank wear.

A brittle material with good transmission of structure-borne noise can be used as the sacrificial material. Up-cut milling can be used. In particular, low feed rates specific to the sacrificial material chosen can be employed. A structure-borne sound measurement, such as a vibration measurement, can be carried out.

This can be checked, for example, on a sacrificial workpiece made from a sacrificial material with steel 1.4301 or 1.2738.

To carry out the method for analyzing different types of failure or wear of the tool, it has therefore proven to be advantageous if materials with steel 1.4301 or steel 1.2738, GGG60 or GGG70 and AlSi2 or similar materials are used as sacrificial materials.

Correspondingly, to analyze the corresponding wear or failure mode, test machining can be carried out on the corresponding sacrificial materials under the specified process conditions.

In a preferred exemplary embodiment, the method according to the invention provides in particular that the test machining is machining of the sacrificial workpiece, the tool being moved in a predefined feed direction at a predefined feed rate relative to the sacrificial workpiece, the sensor exerting a force exerted by the tool on the sacrificial workpiece Absorbs force, the direction of the absorbed force being aligned at a predefined angle to the feed direction.

The 2 shows a schematic sectional view of an embodiment of a device according to the invention for carrying out a test processing and a test measurement.

Milling of a sacrificial workpiece can be performed as a test machining using a tool as a milling tool, in particular with one cutting edge or with a plurality of cutting edges.

The 2 shows a device 1 for determining a state of wear of a tool 2 and/or at least one cutting edge 3, in particular of a tool 2 according to FIG 1 , wherein a holding device 10 is provided with a first receptacle 20 for at least one sacrificial workpiece 21. In 2 various sacrificial workpieces 21 are indicated schematically, which are arranged in a stepped manner on top of one another. Also can one another arrangement can be provided, for example only one sacrificial workpiece 21.

Furthermore, a second receptacle 22 is provided for the sensor 12, on which the sensor 12 is arranged. The at least one sacrificial workpiece 21 is coupled to the sensor 12 in such a way that a force can be transmitted from the sacrificial workpiece 21 to the sensor 12 during test processing of the sacrificial workpiece 21 .

For this purpose, the holding device 10 has a base body 23 which is arranged, for example, on a machine table 24 of the processing machine, such as the milling machine.

The base body 23 forms the second receptacle 22 for the sensor 12 .

Furthermore, a carrier 25 is provided, which is guided to be displaceable in one direction relative to the base body 23 . The carrier 25 forms the first receptacle 20 for the sacrificial workpiece 21 .

The sensor 12 is arranged between the second receptacle 22 and the carrier 25 and is subjected to a force by the carrier 25 .

An energy accumulator 26, such as a spring element, is optionally provided, which is supported on the base body 23 on the one hand and on the carrier 25 on the other hand. As a result, a force is applied to the carrier 25 against the sensor 12 . In this way, the sensor 12 is preloaded and placed in a defined state. In this case, the force accumulator 26 is advantageously supported on the base body 23 on a contact surface of an adjusting screw 27, so that the prestressing of the force accumulator 26 can be adjusted.

It is also provided in an advantageous exemplary embodiment that a transmission element 28 is arranged between the carrier 25 and the sensor 12 in order to be able to align and/or define the direction in which the force is introduced onto the sensor. The advantage here is that it can be achieved that with a point contact, for example, due to the spherical transmission element 28, only compressive forces can be transmitted in the normal direction, so that interference can be reduced.

The carrier 25 is guided in the base body 23 by means of a guide 29 in such a way that the carrier 25 is mounted so that it can be displaced relative to the base body 23 in a defined direction. For this purpose, the base body 23 has at least one guide column 30 which is guided through a guide bushing 31 so that the carrier 25 can only be displaced in the longitudinal direction of the guide column 30 .

At least one sacrificial workpiece 21 is provided on the carrier 25 and is arranged fastened on the carrier 25 . Alternatively, a predefined number of sacrificial workpieces 21 is provided. For example, a sacrificial workpiece 21 is provided or two or three sacrificial workpieces 21 made of different sacrificial materials are provided for determining a state of wear according to flank wear, crater wear, built-up edge, crack formation and/or a broken edge.

For the method, the tool 2 is moved in a straight line in the predefined feed direction 33 at the predefined feed rate relative to the sacrificial workpiece 21 during the test machining. The force is measured in a force direction 34, which the sensor 12 detects, at a defined angle α to the feed direction 32. It is advantageous here if the angle α is aligned in the range from 60° to 120°, in particular approximately 90°, such as 90°, to the feed direction 32, see FIG 2 .

The sensor 12 is a force or pressure sensor, which is arranged in such a way that only one force acts on it, the force direction 34 of which is aligned at an angle α in the range of 60° to 120°, in particular approximately 90°, to the feed direction 32.

During a test machining, the sacrificial workpiece 21 is milled along the feed direction 32 of the tool 2 at the feed rate of the tool 2 by means of the tool 2, in particular in a rectilinear direction. The force direction 34 of the detected force is essentially perpendicular to the feed direction 32 . This can reduce interference.

Using the device 1 according to the invention, a specific “tool/sacrificial material reference curve” can be generated for the different tools 2, such as different milling cutter types, see FIG 4 . According to this reference curve 4 can be generated by measuring the forces Fy on the defined sacrificial workpiece 21 with a new tool 2 . Both the course of the force as a function of time and the peak values of the forces that occur per cutting edge 3 are determined, see FIG 5 . In 5 shows an example of the force Fy as a function of time during a test machining.

After the test measurement with this new tool 2 on a sacrificial workpiece 21, in the further course of use of the tool 2 usual workpieces used the tool 2 on a workpiece to be machined and thus worn.

In a repetitive process, such as an iterative process, further reference points of the reference curve of the 4 generated in which chips are removed at intervals to be defined on the sacrificial workpiece 21 under optionally the same process conditions and the resulting forces/force curves Fy are measured.

By lining up the force values of the individual measurements, the reference curve of the 4 determine depending on the degree of wear of the cutting edges 3 or the tool 2.

The degree of wear and the permissible limits of wear of the tool or the cutting edges 3 are defined visually. The force value that is present at the just permissible wear is stored as a limit value and can later be stored as a "switch-off warning point".

For test machining, in addition to recording the force Fy that occurs with defined cutting parameters, the course of the cutting force can also be recorded according to 5 be identified and recorded. This progression corresponds to a “genetic” fingerprint, so to speak, of the tool 2 used, such as a milling tool, and of each individual cutting edge 3. With every iterative process in which the current state of wear is recorded and compared via the applied force Fy in comparison to the stored reference curve, the force curve of each tool 2 or each individual cutting edge 3 over time is also compared with the original force curve of the new tool or the new milling cutter. This comparison shows whether, in addition to the "normal" wear, there is a special event such as a broken edge or crater wear.

The advantage here is that to assess the current wear situation of the tool 2 or the cutting edges 3, only the force profile of one revolution of the milling cutter is required. It can thus be assumed that the sacrificial material is used to a minimum.

Reference List

1

contraption

2

Tool

3

cutting edge

4

workpiece

5

first drive

6

first actuator

7

workpiece holder

8th

second drive

9

second actuator

10

holding device

11

sacrificial workpiece

12

sensor

13

Storage

14

control unit

15

evaluation unit

20

first shot

21

sacrificial workpiece

22

second shot

23

body

24

machine table

25

carrier

26

energy accumulator

27

adjustment screw

28

transmission element

29

guide

30

guide column

31

guide bush

32

feed direction

34

direction of force

Claims (21)

Method for determining the state of wear of a tool (2) and/or at least one cutting edge (3), in particular a tool (2), which is used for machining a workpiece (4), with the Tool (2) or the at least one cutting edge (3) on at least one sacrificial workpiece (11, 21), a test measurement with test machining is carried out, the test machining being monitored by means of at least one measuring device with at least one sensor (12) and measured values of the test measurement in can be stored in a memory (13), wherein after a defined machining of workpieces (4) by means of the tool (2) or by means of the at least one cutting edge (3), at least one further test measurement with test machining is carried out on the sacrificial workpiece (11, 21). , which is also monitored by the measuring device with the at least one sensor (12) and Measured values of the test measurement can be stored, a state of wear of the tool (2) and/or the at least one cutting edge (3) being determined on the basis of the measured values determined, the test machining being machining of the sacrificial workpiece (11, 21), the tool ( 2) it is moved in a predefined feed direction (32) at a predefined feed rate relative to the sacrificial workpiece (11, 21), the sensor (12) recording a force exerted by the tool (2) on the sacrificial workpiece (11, 21), wherein the direction of the received force is oriented at a predefined angle to the feed direction (32). procedure after claim 1 , characterized in that the test machining is a milling of a sacrificial workpiece (11, 21) using a tool (2) as a milling tool, in particular with a cutting edge (3) or with a plurality of cutting edges (3). procedure after claim 1 or 2 , characterized in that the tool (2) is moved during the test machining in a straight line in the predefined feed direction (32) at the predefined feed rate relative to the sacrificial workpiece (11, 21). procedure after claim 1 , 2 or 3 , characterized in that the angle is aligned in the range of 60° to 120°, in particular approximately 90°, to the feed direction (32), in particular the angle is not equal to a zero angle. procedure after claim 1 , 2 , 3 or 4 , characterized in that the sensor (12) is a force or pressure sensor which is arranged in such a way that only a force acts on it which is at an angle in the range from 60° to 120°, in particular approximately 90°, to the feed direction (32) is aligned. procedure after claim 1 , 2 , 3 , 4 or 5 , characterized in that the state of wear is distinguished according to in particular at least one state of wear of the following types of wear/failure: flank wear, crater wear, built-up edge, crack formation and/or broken edge. procedure after claim 1 , 2 , 3 , 4 , 5 or 6 , characterized in that the state of wear is determined from in particular at least one respective state of wear from flank wear, crater wear, built-up edge, crack formation and/or a broken edge. Method according to one of the preceding claims, characterized in that the test measurement is carried out separately with the test machining for at least one or for each type of wear/failure under consideration, or that a test measurement is carried out with a test machining or several test measurements are carried out with one test machining each and a wear is derived from this -/failure type is determined. Method according to one of the preceding claims, characterized in that the test measurement is carried out with the test machining for one or for several or for each type of wear/failure under consideration on a sacrificial workpiece (11, 21) provided for this purpose. Method according to one of the preceding claims, characterized in that the test measurement is carried out with the test machining for one or for several or for each type of wear/failure considered with machining parameters provided for this purpose. Method according to one of the preceding claims, characterized in that the state of wear is determined by comparing stored measured values and/or stored processed measured values from test measurements on at least one sacrificial workpiece (11, 21) or on a plurality of sacrificial workpieces (11, 21). procedure after claim 11 , characterized in that processed measured values have or are time first derivatives and/or second derivatives of measured value profiles. Method according to one of the preceding claims, characterized in that a recommendation for further use or replacement of the tool (2) and/or the cutting edge (3) and/or the cutting edges (3) is derived from the determined state of wear or from the determined states of wear. he follows. Device (1) for determining the state of wear of a tool (2) and/or at least one cutting edge (3), in particular a tool (2) which is used for machining a workpiece (4), with a tool (2). at least one cutting edge (3) for machining a workpiece (4), with a measuring device with at least one sensor (12) for monitoring a test measurement with test machining and with at least one sacrificial workpiece (11, 21) for carrying out the test measurement with test machining on the sacrificial workpiece ( 11, 21), in particular for carrying out a method according to one of the preceding claims. Device (1) after Claim 14 , characterized in that a first receptacle (20) is provided for the sacrificial workpiece (11, 21) and a second receptacle (22) is provided for the sensor (12), the sacrificial workpiece (11, 21) being connected to the sensor ( 12) is coupled that during test machining of the sacrificial workpiece (11, 21), a force can be transmitted from the sacrificial workpiece (11, 21) to the sensor (12). Device (1) after claim 15 , characterized in that a base body (23) is provided, which forms the second receptacle (22) for the sensor (12), a carrier (25) being provided, which is guided displaceably in one direction relative to the base body (23). is, wherein the carrier (25) forms the first receptacle (20) and the sensor (12) is arranged between the second receptacle (22) and the carrier (25) and is subjected to a force. Device (1) after Claim 16 , characterized in that an energy accumulator (26) is provided, which biases the carrier (25) towards the sensor (12). Device (1) after Claim 16 or 17 , characterized in that between the carrier (25) and the sensor (12) a transmission element (28) is arranged, in particular a spherical element as a transmission element (28). Device (1) according to one of the preceding Claims 14 until 18 , characterized in that a sacrificial workpiece (11, 21) is provided, which is arranged on the carrier (25) or that a predefined number of sacrificial workpieces (11, 21) is provided, the sacrificial workpieces (11, 21) on the carrier (25) are arranged. Device (1) according to one of the preceding claims, characterized in that the at least one sacrificial workpiece (11, 21) is provided and can be processed to determine at least one state of wear or several states of wear or that the individual sacrificial workpieces (11, 21) each to determine a state of wear are designed and machinable according to a specific wear/failure mode. Device (1) after claim 20 , characterized in that in particular two or three sacrificial workpieces (11, 21) made of different sacrificial materials are provided for determining a state of wear according to flank wear, crater wear, built-up edge, crack formation and/or a broken edge.

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