EP4003646A1

EP4003646A1 - Abrasive flow machining tool for determining material removal from a workpiece and method for determining the cutting power of a grinding medium

Info

Publication number: EP4003646A1
Application number: EP20750237.8A
Authority: EP
Inventors: Fabio Augusto Wosniak; Patrick Matt
Original assignee: Extrude Hone GmbH
Current assignee: Extrude Hone GmbH
Priority date: 2019-07-31
Filing date: 2020-07-30
Publication date: 2022-06-01
Anticipated expiration: 2040-07-30
Also published as: EP4003646B1; CN114206550A; JP2022543372A; EP4003646C0; DE102019120753A1; DE102019120753B4; WO2021019024A1; US20220258298A1

Abstract

The invention relates to an abrasive flow machining tool (10), comprising a grinding medium driving device (24), which is suitable for moving the grinding medium (14) in a flow direction over a surface of a workpiece (12) and/or through the opening (16) of the workpiece (12), comprising a workpiece holder (18) for holding the workpiece (12) with two parts (20, 22) which are positionable on opposite sides of the workpiece (12), comprising a structure-borne noise sensor (36) for measuring structure-borne noise generated in a workpiece (12) as said workpiece is being machined by a grinding medium (14), and comprising an evaluation unit (38), which is suitable for determining the cutting power of the grinding medium (14) and/or the rate of material removal from the workpiece (12) on the basis of an integral value of the root mean square of the structure-borne noise, measured by the structure-borne noise sensor (36), over time. The invention furthermore relates to a method for determining material removal from a workpiece and to a method for determining the cutting power of a grinding medium.

Description

Flow lapping machine, method for determining a material removal from a workpiece and method for determining the cutting performance of a

Grinding medium

The invention relates to a flow lapping machine, a method for determining a material removal and / or a material removal rate on a workpiece when machining the workpiece in a flow lapping machine and a method for determining the cutting performance of a grinding medium.

Flow lapping machines are used to polish and grind workpieces by passing an abrasive medium under pressure over the workpiece or through an opening extending through the workpiece, the abrasive medium removing material from the workpiece. The grinding medium is usually a viscous medium containing abrasive particles, in particular based on silicone.

The abrasive particles of the abrasive medium wear out when the workpiece is machined, as a result of which the cutting performance of the abrasive medium and a material removal rate decrease. In addition, removed particles remain in the grinding medium. The machining of the workpiece becomes less effective and unpredictable.

If the grinding medium has not yet been used, the cutting performance is usually known. However, it is difficult to determine the cutting performance of an abrasive medium that has been in use for a period of time. To make matters worse, after the abrasive medium has worn out, not the entire amount of the abrasive medium present in the flow lapping machine is replaced, but only a certain proportion of the worn abrasive medium is removed and replaced with unused abrasive medium, so that at no point in time precise information about the cutting performance of the abrasive medium exist. Experienced users can manually feel whether a grinding medium still has sufficient cutting performance or whether it has to be at least partially replaced by unused grinding medium. Such a determination of the cutting line is, however, very imprecise and can hardly be carried out by inexperienced users. It is not possible to determine the grinding medium while the flow lapping machine is in operation.

If the grinding medium is exchanged too early, this results in increased costs, since usable grinding medium is disposed of. If the grinding medium is replaced too late, the material removal rate can decrease to such an extent that workpieces are not sufficiently abraded and parts of poor quality can be fused.

It is therefore an object of the present invention to provide a flow lapping machine which enables workpieces to be machined particularly efficiently. In addition, it is an object of the invention to provide a method for determining a material removal and / or a material removal rate on a workpiece and a method for determining the cutting performance of a grinding medium.

This object is achieved according to the invention by a flow lapping machine for moving grinding media over a surface of a workpiece and / or through the opening of a workpiece, with a media drive device which is suitable for moving the grinding medium over a surface of a workpiece and / or through the opening of the workpiece to move along a flow direction through it, with a workpiece holder for folding the workpiece with two parts that can be positioned on opposite sides of the workpiece, with a structure-borne sound sensor for measuring structure-borne sound that is generated in the workpiece when machining a workpiece with a grinding medium, and with an evaluation unit which is suitable for inferring a cutting performance of the grinding medium and / or a material removal rate on the workpiece based on an integral value of the root mean square of the structure-borne sound measured by the structure-borne sound sensor over time.

Structure-borne noise occurs in the form of acoustic and / or elastic waves in solids when a material undergoes irreversible changes in its internal structure, for example as a result of cracking or plastic Deformation due to aging or temperature gradients, but also due to specific external mechanical forces when processing a solid. Mechanical machining processes can thus be monitored by measuring structure-borne sound signals using a structure-borne sound sensor. The frequency of the structure-borne sound waves is in particular between 50 kFIz and 1 MFIz.

The structure-borne noise signal is stronger the greater the cutting performance or the material removal rate. It can thus be determined on the basis of the structure-borne noise signal whether the machining of a workpiece is effective. There is a high correlation between the root mean square of the structure-borne noise signal and the material removal rate. In particular, the root mean square of the structure-borne noise measured by the structure-borne noise sensor is related to a frictional energy dissipation during machining of the workpiece.

The integral value of the root mean square of the structure-borne noise measured by the structure-borne noise sensor over time is specific for a certain material removal. That is, a weight loss of the workpiece can be indirectly determined from the obtained integral value. In this way, an absolute amount of material removed can already be determined while the workpiece is being machined. The integral value is given, for example, in the unit millivolt-seconds [mV.s]. Alternatively, the integral value can also be specified in the unit milliampere seconds [mA.s].

The cutting performance of the grinding medium and / or the material removal rate can in turn be determined on the basis of the weight loss. This enables particularly reliable process monitoring and particularly precise machining of the workpiece. It has been shown that when calculating the material removal by means of the integral value of the quadratic mean, particularly precise values for the material removal rate and for the cutting performance can be determined.

The integral is formed, for example, from a continuous value of the square mean of the structure-borne noise signal.

The material removal rate is calculated in particular by dividing the value of the material removal by the machining time. The cutting performance can be determined by dividing the material removal by the media flow. The media flow corresponds to the amount of fluid moved over the surface of the workpiece or through the opening of the workpiece.

The flow rate depends on the flow cross-section and the flow speed of the grinding medium and can therefore be easily determined. In particular, the evaluation unit can be set up to determine the media flow based on the set process parameters. The flow cross section is known and corresponds, for example, to the cross section of the opening of the machined workpiece.

Suitable software is preferably stored in the evaluation unit for calculating the integral value.

Machining within the meaning of the invention means both targeted machining of a workpiece that is to be manufactured as an end product and machining of a dummy workpiece as an alternative or in addition to the workpiece actually to be manufactured. Reference values, for example, are determined by machining the predetermined dummy workpiece. The processing of the dummy workpiece only serves to measure the structure-borne noise signal. The dummy workpiece can remain mounted in the flow lapping machine for a large number of machining operations.

In order to better evaluate the structure-borne sound signal measured by the structure-borne sound sensor, the signal can be rectified before further evaluation. The rectified signal can then be used to calculate the root mean square.

The workpiece holder preferably has a suitable seal for sealing a main fluid channel in which the grinding medium moves, a section of a surface of the workpiece to be machined and / or the opening of the workpiece being part of the main fluid channel.

The media drive device comprises, for example, at least one positive displacement pump which is suitable for pushing the grinding medium through the main fluid channel. According to one embodiment, a look-up table is stored in the evaluation unit, from which a material removal from the workpiece and / or a cutting performance of the grinding medium can be read off over time using the integral value of the square mean of the measured structure-borne noise signal. The values stored in the look-up table are specific to the material of the workpiece and / or to the grinding medium used. A material removal, in particular a material removal rate and / or a cutting performance, can thus be determined particularly quickly and reliably by means of a look-up table. The values stored in the look-up table were determined, for example, by hardware tests and / or by simulations.

The evaluation unit can have an amplifier for amplifying the signal measured by the structure-borne noise sensor. In this way, a reliable evaluation of the structure-borne sound signals can take place even in the case of weak structure-borne sound signals, for example if only a small amount of material is removed. As a result, a cutting performance of the grinding medium and / or a material removal rate can be determined with particularly high accuracy.

For example, the evaluation unit has at least one filter for filtering out machine frequencies from the signal measured by the structure-borne noise sensor. The filter thus also contributes to the fact that a cutting performance of the grinding medium and / or a material removal rate can be determined with particularly high accuracy.

The filter is preferably an analog filter. In particular, the filter is suitable for filtering out low frequencies in the range of less than 50 kHz and / or high frequencies in the range of more than 1 MHz from the structure-borne sound signal. For this purpose, the filter can be an HP filter or a BP filter.

The filter can also already be integrated in the amplifier, so that the evaluation unit can be particularly compact.

The structure-borne noise sensor can be in direct or indirect contact with the workpiece during operation of the flow lapping machine. Indirect contact can be made, for example, via an additional component that is in direct contact with the workpiece. The additional component should be made of a material that is suitable is to forward the structure-borne noise of the workpiece to the structure-borne noise sensor. For example, a disk or a strip made of aluminum is suitable for this.

Direct contacting has the advantage that the structure-borne sound signal can be transmitted from the workpiece to the structure-borne sound sensor without additional transmission losses. Indirect contact is advantageous if direct contact with the workpiece is difficult due to the size or geometry of the workpiece.

According to one embodiment, the flow lapping machine comprises a bypass channel that runs parallel to a main fluid channel, the workpiece being a dummy workpiece that is arranged in the bypass channel, and the main fluid channel extending over a surface and / or through an opening of an additional workpiece to be machined . Similar to indirect contacting, this embodiment is suitable when relatively small workpieces are processed, in which the structure-borne noise sensor cannot be arranged on the workpiece itself to be processed.

In addition, this embodiment offers the additional advantage that the cutting performance of the grinding medium can be determined independently of the material removal rate on the basis of the structure-borne sound signal measured on the dummy workpiece. This is because the material of the dummy workpiece is preferably selected in such a way that no or only very little material is removed from the dummy workpiece. As a result, the dummy workpiece is hardly worn during the operation of the flow lapping machine and can remain installed in the flow lapping machine for the machining of a large number of work pieces to be additionally machined. The structure-borne noise signal measured on the dummy workpiece is therefore almost exclusively caused by the friction of the grinding medium on the dummy workpiece, the greater the friction, the sharper-edged the grinding particles in the grinding medium, i.e. the better the cutting performance of the grinding medium.

Even if no or only very little material is removed from the dummy workpiece, the movement of the grinding medium through the dummy workpiece is understood as machining a workpiece within the meaning of the invention. The flow lapping machine can also comprise two structure-borne sound sensors, with a structure-borne sound sensor being positioned both on the dummy workpiece in the bypass channel and on the additional workpiece to be processed during operation of the flow lapping machine. This enables an even more precise evaluation because, as previously explained, the cutting performance of the grinding medium can be analyzed in the bypass channel in isolation from the material removal, while the structure-borne noise signal measured on the additional workpiece is also influenced by the material removal rate. In particular, in this embodiment two different signals can be measured, a difference between the two signals correlating with a surface improvement. If the machine settings remain the same, both media properties and surface improvements can be monitored.

The flow lapping machine preferably comprises a control unit which is suitable for adapting at least one process parameter based on the cutting performance and / or material removal rate determined by the evaluation unit, in particular during the machining of a workpiece. As a result, a decreasing cutting performance of the grinding medium can be compensated for at least to some extent, so that the grinding medium can be used longer or the workpiece can be machined more effectively.

The process parameters that can be adjusted by the control unit are, for example, a flow rate of the grinding medium through the opening of the workpiece, a fluid pressure of the grinding medium, a counter pressure on the grinding medium and / or a temperature of the grinding medium. By increasing the flow rate, the material removal rate can be increased, especially with the quality of the grinding medium remaining the same. A contact pressure of the grinding medium, in particular the grinding particles, can be adapted to a surface of the workpiece via the fluid pressure of the grinding medium and / or the counter pressure on the grinding medium. The temperature influences the viscosity of the grinding medium, which in turn can affect the flow rate of the grinding medium.

Optionally, the flow lapping machine has a fluid delivery device which is suitable for removing worn grinding medium from the flow lapping machine and supplying unused grinding medium. By such a Fluid delivery device, an automatic exchange of the grinding medium can take place when it is worn.

The object is also achieved according to the invention by a method for determining a material removal and / or a material removal rate on a workpiece when machining the workpiece in a flow lapping machine, with the following steps:

Guiding a grinding medium over a surface and / or through an opening of a workpiece to be processed,

Measuring the structure-borne noise generated in the workpiece during machining,

Formation of a quadratic mean of the measured structure-borne noise signal,

Integrate the root mean square over the processing time, and

Determination of the material removal and / or the material removal rate on the workpiece based on the formed integral. With the method according to the invention, it can already be determined during the machining of the workpiece in the flow lapping machine whether sufficient material has been removed without the workpiece having to be removed from the flow lapping machine. The formation of the integral of the square mean of the structure-borne noise signal has the advantage over the known methods in which only the square mean of the structure-borne noise signal is formed that the absolute material removal that has taken place can be determined at each processing time. Since the amounts of material removed are usually very small and measurement errors occur when the workpiece is weighed, material removal can even be determined more precisely using the method according to the invention than by weighing the workpiece before and after machining.

In particular, the material removal rate is greater immediately after the machining of a workpiece has started than at a later point in time. The lower the surface roughness of the workpiece, the less material is removed. If the material removal rate remains constant, this is an indication that the machining of the workpiece has been completed or that a surface roughness of the workpiece cannot be further improved with the grinding medium used in the flow lapping machine. In addition to the material removal rate, the cutting performance of the grinding medium can also be determined using the integrated square mean of the structure-borne noise signal. This allows conclusions to be drawn about the degree of wear of the grinding medium.

Based on a material removal rate, for example, at least one of the following process parameters is set: a flow rate of the grinding medium, a fluid pressure of the grinding medium, a counter pressure on the grinding medium and / or a temperature of the grinding medium. A suitable setting of the process parameters enables the workpiece to be machined particularly efficiently.

According to one embodiment, at least one process parameter is adapted if the material removal rate measured during machining of the workpiece deviates from a desired material removal rate by more than a defined tolerance value. This enables the workpiece to be machined in a particularly controlled manner. In addition, the processing time for the individual workpieces to be processed can be kept constant by adjusting the process parameters. This means that by adapting the process parameters, it is possible to sufficiently grind the individual workpieces within a defined processing time, even if the cutting performance of the grinding medium decreases.

For example, a reference curve is created that describes a desired course of the material removal rate by storing a course of the material removal rate of a machined workpiece in an evaluation unit, a tolerance range being defined around the reference curve within which the material removal rate should preferably move. The creation of such a reference curve is very easy. With the aid of such a reference curve or with the aid of the tolerance range, it is particularly easy to monitor whether the material removal rate is within a reasonable range or whether the workpiece is being processed effectively.

The workpiece that is used to create the reference curve is preferably measured after machining. If the reference workpiece for good quality is found, the reference curve is saved. If the quality of the workpiece is not in order, the process is repeated with another workpiece.

The reference curve is specific, for example, for machining certain workpieces with a certain grinding medium. For differently shaped workpieces and / or for processing with a different grinding medium, a separate reference curve is preferably created in each case.

If the actual course of the material removal rate is outside the tolerance range, at least one process parameter is preferably adapted when machining the workpiece. In this way, it is possible to react particularly quickly to irregularities in processing.

The storage of the reference curve or the comparison of the material removal rate with the reference curve is preferably carried out by software that can be stored in the control unit or the evaluation unit.

Based on a material removal rate, a request to replace at least part of the grinding medium can be made. A user no longer has to manually check whether the cutting performance of the grinding medium is still sufficient.

The request for replacement occurs in particular when a desired surface quality of the workpiece can no longer be achieved with the abrasive used within an acceptable processing time.

In addition to the aforementioned structure-borne sound signal, a further structure-borne sound signal can be measured on a dummy workpiece and a difference between the two structure-borne sound signals can be formed in order to monitor an improvement in the surface quality of the workpiece. This is possible because a difference between the two signals correlates with a surface improvement. In this way, the surface improvement can be monitored even more precisely.

However, a second structure-borne sound sensor or a dummy workpiece is not absolutely necessary to monitor the surface improvement. Surface enhancement can also be monitored by using the Structure-borne sound signal that occurs at the beginning of a machining process is compared with the structure-borne sound signal that occurs at the end of a machining process, in particular by forming a difference between the two signals.

Furthermore, a structure-borne sound signal that occurs at the beginning of a machining process of a workpiece can be compared with the structure-borne sound signal that is compared at the end of a workpiece that has been manufactured immediately beforehand in order to determine a required surface improvement, in particular based on a difference between the two structure-borne sound signals. Based on the required surface improvement, the evaluation unit can determine an optimal processing time, taking into account the material removal rate, after which a desired surface improvement is achieved. In this way, the machining process can run in a particularly time-optimized manner. This of course only applies if the two workpieces machined one after the other are of the same type.

The exchange of the grinding medium can be done manually or automatically. For example, a user can receive a request to manually replace a predetermined portion of the grinding medium. Alternatively, only an indication can be given that the grinding medium is being exchanged while the automatic exchange is taking place.

The automatic exchange takes place, for example, by means of a fluid delivery device which is suitable for removing worn grinding medium from the flow lapping machine and supplying unused grinding medium.

The object is also achieved according to the invention by a method for determining the cutting performance of a grinding medium, with the following steps:

Directing a grinding medium over a surface and / or through an opening of a reference workpiece,

Formation of a quadratic mean of the measured structure-borne noise signal,

Integrating the root mean square over the processing time, Divide the integral value by the media flow, and

Determining the cutting performance of the grinding medium based on the divided integral value.

Such a method can be used to examine different grinding media for their cutting performance, for example when developing new grinding media.

Further advantages and features of the invention emerge from the following description and from the accompanying drawings, to which reference is made. In the drawings show:

Figures 1 a and 1 b each show a part of a flow lapping machine according to the invention,

Figure 2 shows the course of the quadratic mean of a structure-borne noise signal,

FIG. 3 shows a partial area of a further flow lapping machine according to the invention in the area of a workpiece holder,

FIG. 4 shows a further flow lapping machine according to the invention,

FIG. 5 shows a flowchart for processing a structure-borne sound signal,

FIG. 6 a reference curve which describes a desired course of the material removal rate,

FIG. 7 shows a profile of a material removal rate when machining a workpiece, and FIG

FIGS. 8a and 8b show a profile of a directly measured material removal rate and an indirectly determined material removal rate.

FIGS. 1 a and 1 b each show a flow lapping machine 10 for processing a workpiece 12 with a viscous grinding medium 14 in a sectional view. To process the workpiece 12, the grinding medium 14 can be moved through an opening 16 in the workpiece 12 to be processed. In particular, the grinding medium 14 moves in a main fluid channel 15 which runs through the opening 16 of the workpiece 12.

Alternatively or additionally, the grinding medium 14 can be moved over a surface of the workpiece 12 lying outside the opening 16, the main fluid channel 15 being at least partially delimited by the surface of the workpiece 12.

In FIGS. 1 a and 1 b, the flow lapping machine 10 is shown in different states, in which the grinding medium 14 is moved in opposite directions, as illustrated by arrows, that is to say is pumped back and forth.

To hold the workpiece 12, the flow lapping machine 10 comprises a workpiece holder 18 which has two parts 20, 22 that can be positioned on opposite sides of the workpiece 12. The workpiece 12 is during processing between the two parts 20, 22 of the workpiece holder 18 z. B. axially clamped.

In order to achieve a particularly good seal, seals can be attached to the parts 20, 22 and bear against the workpiece 12 during machining. The seals are preferably metal seals or ceramic seals, namely rubber seals would dampen the structure-borne sound signal.

The flow lapping machine 10 further comprises a media drive device 24 which is suitable for moving the grinding medium 14 over a surface of a workpiece and / or through the opening 16 of the workpiece 12. In the process, material is removed from the workpiece 12, as a result of which the surface of the workpiece 12 is smoothed and polished.

In the exemplary embodiment shown, the media drive device 24 comprises two displacement pumps 26, 28, one of the two displacement pumps 26, 28 pushing the grinding medium 14 through the opening 16, depending on the direction of flow of the grinding medium 14, and the other displacement pump 26, 28 forming a device counteracting the grinding medium 14 that counteracts the flow of the grinding medium 14. A displacement pump 26, 28 each has a piston 30 which is guided in a cylinder 32. The media drive device 24 also comprises a drive element 34 for each displacement pump 26, 28, which is, for example, a hydraulic actuation element or a linear motor actuation element.

When the workpiece 12 is processed with the grinding medium 14, structure-borne sound waves, in particular acoustic and / or elastic waves, arise in it. On the basis of the strength of the structure-borne sound waves, conclusions can be drawn about the effectiveness and the scope of the machining of the workpiece 12. In particular, a strength of the structure-borne sound waves correlates with a material removal rate on the workpiece 12 and / or with a cutting performance of the grinding medium 14.

The cutting performance of the grinding medium 14 is indicated in the unit millivolt seconds per liter [mV.s / l].

The cutting performance indicates how much material is removed per liter of the grinding medium 14 moved over the workpiece 12.

In order to measure the structure-borne sound waves, the flow lapping machine 10 comprises a structure-borne sound sensor 36 which is in contact with the workpiece 12 to be machined.

Furthermore, the flow lapping machine 10 comprises an especially electronic evaluation unit 38. The evaluation unit 38 can receive the structure-borne noise signal measured by the structure-borne noise sensor 36 and in particular form the square mean of the structure-borne noise signal using software and integrate this over time. Alternatively, the evaluation unit 38 can already receive the root mean square of the structure-borne noise signal from an amplifier, for example. The structure-borne sound signal is measured in millivolts or milliamps, for example.

To evaluate the structure-borne noise signal, it is preferably rectified before the square mean is formed.

The course of the quadratic mean of the structure-borne noise signal in millivolts over time in seconds is shown in FIG. 2 as an example for a machining process. In addition, the evaluation unit 38 is suitable for inferring a cutting performance of the grinding medium 14 and / or a material removal rate on the workpiece 12 based on an integral value of the square mean of the structure-borne noise measured by the structure-borne noise sensor 36 over time.

In order to infer the material removal rate or the cutting performance, the evaluation unit 38 in particular first of all determines the material removal based on the integral formed. The integral value is specifically specific for a certain amount of material removed.

In order to determine the material removal rate, the evaluation unit 38 is set up to set the material removal in relation to the processing time.

To determine the cutting performance, the evaluation unit 38 is set up to divide the integral value by the media flow.

To evaluate the structure-borne noise signal, a look-up table 39 can be stored in the evaluation unit 38, from which a material removal on the workpiece 12 and / or a cutting performance of the grinding medium 14 can be read over time based on the integral value of the square mean of the measured structure-borne noise signal. Such a look-up table 39 is illustrated below in FIG.

The flow lapping machine 10 further comprises a control unit 40 which is suitable for adapting at least one process parameter based on the cutting performance and / or material removal rate determined by the evaluation unit 38, in particular during the processing of a workpiece 12. This makes it possible to respond to a changed cutting performance of the Grinding medium 14 and / or to other fluctuations in the machining process, for example to temperature fluctuations.

The process parameters that can be adjusted by the control unit 40 are, for example, a flow rate of the grinding medium 14, a fluid pressure of the grinding medium 14, a counter pressure on the grinding medium 14 and / or a temperature of the grinding medium 14.

With the exception of the temperature of the grinding medium 14, the process parameters mentioned can be set by means of the media drive device 24. For this purpose, a position of the two displacement pumps 26, 28 relative to one another and / or a movement speed of the individual displacement pumps 26, 28 can be adapted.

If, for example, the distance between the displacement pumps 26, 28 or the pistons 30 is reduced, the fluid pressure of the grinding medium 14 is increased. As a result, the grinding particles of the grinding medium 14 are pressed with a higher contact pressure against the surface of the workpiece 12 to be machined and a material removal rate can be increased.

By increasing the flow speed, the material removal rate can also be increased, since more grinding particles are moved over the surface of the workpiece 12 in the same time.

If the pistons 30 of the two displacement pumps 26, 28 are moved at different speeds, in particular if a piston 30 positioned upstream in the flow direction is moved more slowly than a piston 30 positioned downstream, or if its movement is met with a higher resistance, a counter pressure on the grinding medium 14 increase. Whether a piston 30 is mounted upstream or downstream depends in each case on the current direction of flow of the grinding medium 14, which changes after each machining cycle.

In order to adapt the temperature of the grinding medium 14, a heating and / or a cooling sleeve or the like can additionally be provided. The heating or cooling sleeve is arranged around the cylinder 32, for example.

In the exemplary embodiment illustrated in FIGS. 1 a and 1 b, the structure-borne noise sensor 36 is in direct contact with the workpiece 12.

However, it is also conceivable that the structure-borne noise sensor 36 is in indirect contact with the workpiece 12, in particular via an additional component 42 such as an aluminum disc. This is illustrated schematically in FIG. 3, only the area around the workpiece 12 being shown for the sake of simplicity. The additional component 42 can be part of the workpiece holder 18. FIG. 4 shows a further flow lapping machine 10 according to the invention. For the same structures with the same functions that are known from the above embodiment, the same reference symbols are used below and reference is made to the preceding explanations, the differences between the respective embodiments being discussed below to avoid repetition.

In the embodiment shown in FIG. 4, the flow lapping machine 10 comprises a bypass channel 46 which runs parallel to the main fluid channel 15, which is not visible in FIG.

In this case, the workpiece 12 is a dummy workpiece 12 a which is arranged in the bypass channel 46.

The main fluid channel 15 extends in the illustrated embodiment through the opening 16 of an additional workpiece 12b to be machined.

Alternatively, as already mentioned above, the main fluid channel 15 can extend over a surface of the workpiece 12b to be machined.

In this case, the flow lapping machine 10 can comprise two structure-borne sound sensors 36, with a structure-borne sound sensor 36 being positioned both on the dummy workpiece 12a in the bypass channel 46 and on the additional workpiece 12b to be processed when the flow lapping machine 10 is in operation. This allows the machining process to be monitored even more precisely.

Such a construction of the flow lapping machine is particularly advantageous if the workpiece 12b to be machined is shaped such that the structure-borne noise sensor 36 cannot be properly mounted on the workpiece 12b, in particular if the workpiece 12b is relatively small.

Another advantage of such a construction of the flow lapping machine is that the cutting performance of the grinding medium 14 can be determined independently of the material removal rate on the basis of the structure-borne noise signal measured on the dummy workpiece 12a. In addition, with the aid of a structure of this type, the surface improvement can be monitored particularly precisely by determining a difference between the workpiece 12a and the workpiece to be machined 12b measured structure-borne sound signal is formed. This difference correlates with the surface improvement.

The dummy workpiece 12a is preferably made of a harder material than the workpiece 12b. As a result, little or no material is removed from the dummy workpiece 12a and it can remain in the flow lapping machine 10 for a large number of machining operations.

To hold the dummy workpiece 12a, a workpiece holder, not shown for the sake of simplicity, is preferably provided, which is designed like the workpiece holder 18.

In a further embodiment, not shown, a structure-borne sound sensor 36 can only be arranged on the dummy workpiece 12a. This is the case in particular if the workpiece 12b to be additionally processed is either too small or is shaped in such a way that the structure-borne noise sensor 36 cannot be properly positioned on the workpiece 12b.

FIG. 5 illustrates the processing of a structure-borne sound signal that was measured by the structure-borne sound sensor 36.

The structure-borne sound signal is first output as a raw signal 37 by the structure-borne sound sensor 36.

The raw signal 37 is then rectified in a rectifier 41, which can be part of the evaluation unit 38.

FIG. 5 also shows that the evaluation unit 38 can have an amplifier 48 for amplifying the structure-borne sound signal measured by the structure-borne sound sensor 36.

Furthermore, the evaluation unit 38 optionally has a filter, in particular an HP filter 50 and / or a bandwidth filter 52 for filtering out machine frequencies from the signal measured by the structure-borne noise sensor 36.

The rectifier 41, the HP filter 50, the amplifier 48 and the bandwidth filter 52 are contained, for example, in what is known as an acoustic emission coupler, which is available under the trade name Piezotron® coupler, for example to be expelled. Such acoustic emission couplers already have an integrated RMS converter for evaluating the structure-borne noise signal. That is to say, such a sound emission coupler can already determine the root mean square of the structure-borne sound signal and make it available in the evaluation unit 38 for further evaluation. In addition, the raw signal of the structure-borne noise signal can be provided.

A method according to the invention for determining a material removal and / or a material removal rate on a workpiece 12, 12a, 12b when machining the workpiece 12, 12a, 12b in a flow lapping machine 10 and / or for determining a cutting performance of the grinding medium 14 is explained, in particular in the Machining of the workpiece 12, 12a, 12b in a flow lapping machine 10 as described in connection with FIGS. 1 to 4.

When machining a workpiece 12, a grinding medium 14 is passed over a surface and / or through an opening 16 of the workpiece 12, 12a, 12b to be machined. This takes place in particular by means of the media drive device 24 described above.

The structure-borne noise generated in the workpiece 12, 12a, 12b during machining is measured, in particular with the structure-borne noise sensor 36.

The quadratic mean of the measured structure-borne noise signal T _R S is then determined in the evaluation unit 38, in particular in a sound emission coupler.

In the following, the quadratic mean is integrated over the processing time.

The material removal and / or the material removal rate on the workpiece 12, 12a, 12b can then be determined on the basis of the integral formed.

As an alternative or in addition to the material removal and / or the material removal rate, a cutting performance of the grinding medium 14 can be determined on the basis of the integral formed.

In addition to the integral value, the raw signal 37 of the structure-borne noise signal can also be output. If the material removal rate measured during the machining of the workpiece 12, 12a, 12b deviates from a desired material removal rate by more than a defined tolerance value, at least one process parameter is preferably adapted.

In particular, based on a material removal rate, at least one of the following process parameters is set: a flow rate of the grinding medium 14, a fluid pressure of the grinding medium 14, a counter pressure on the grinding medium 14 and / or a temperature of the grinding medium 14.

In order to be able to determine in a particularly simple manner whether the material removal rate runs in a desired range, a reference curve is preferably created which describes a desired course of the material removal rate.

The reference curve is created, for example, by recording a course of the material removal rate of a machined workpiece 12, 12a, 12b during machining. The machined workpiece 12, 12a, 12b is then subjected to a quality check and a measurement of the removal. If the workpiece 12, 12a, 12b has been found to be in order, the recorded material removal rate is stored as a reference curve in the evaluation unit 38.

Such a reference curve is illustrated in FIG. The course of the material removal rate is plotted over time.

In addition, a tolerance range is defined around the reference curve within which the material removal rate should move. The tolerance range is illustrated in FIG. 6 by dashed lines around the reference curve.

If, when machining a workpiece 12, 12a, 12b, it is established that the actual progression of the material removal rate is outside the tolerance range, at least one process parameter is adapted, for example, when machining the workpiece 12, 12a, 12b. This is intended to ensure that the material removal rate follows the course of the reference curve again. More precisely, the aim is to ensure that the machined workpiece 12, 12a, 12b is qualitatively in order after machining has been completed. However, if the grinding medium 14 is worn to a certain extent, that is, if a cutting performance of the grinding medium 14 has significantly decreased, the course of the material removal rate can only be influenced slightly by the variation of process parameters. Effective machining of a workpiece 12, 12a, 12b, which leads to a qualitatively acceptable result, is then no longer possible.

Therefore, based on a material removal rate, a request is made to replace at least part of the grinding medium 14, in particular if the actual material removal rate is below the tolerance range, as shown in FIG. 7, for example.

It can also be seen from FIGS. 6 and 7 that the material removal rate approaches a constant value towards the end of the machining time. The difference between a maximum value that occurs at the beginning of the machining time and the end value at the end of the machining time describes the surface improvement achieved.

In order to determine an optimal machining time for a workpiece 12, 12b, at the beginning of a machining process the end values of the material removal rate of an already machined workpiece 12, 12b can be compared with the maximum value of a subsequently manufactured workpiece, in particular the difference can be calculated. In this case, the difference correlates with the desired surface improvement.

According to a further inventive method, a cutting performance of a grinding medium 14 can be determined in that grinding medium 14 is passed over a surface and / or through an opening of a reference workpiece 12, the structure-borne sound generated in the reference workpiece 12 is measured and the root mean square of the measured structure-borne sound signal is measured. The integral is then formed over the root mean square and the integral value is divided by the medium flow rate of the cutting medium 14. The cutting performance of the grinding medium 14 can be determined on the basis of the divided integral value. As a result, the method according to the invention is suitable for investigating or developing new grinding media. If only the cutting performance of a grinding medium 14 is to be examined without a workpiece being produced in the process, only a dummy workpiece 12a or a reference workpiece is usually arranged in the flow lapping machine 10. FIGS. 8a and 8b graphically illustrate a profile of a directly measured material removal rate over a number of machining cycles (FIG. 8a) and a profile of an indirectly determined material removal rate, i.e. a profile of the integral value of the root mean square of the structure-borne noise signal over the number of machining cycles (FIG. 8b). The material removal rate measured directly is given in mg / L. The material removal rate measured indirectly is given in mV.s / L.

The material removal rate or the integral value is determined individually for each processing cycle. A processing cycle corresponds in particular to a cycle in which the grinding medium 14 is moved by the media drive device 24 in a flow direction.

It can be seen from FIGS. 8a and 8b that the course of the directly measured material removal rate correlates strongly with the course of the integral value over the machining cycles. It is thus clear that a cutting performance of the grinding medium 14 and / or a material removal rate on the workpiece 12 can be deduced from the integral value of the root mean square of the structure-borne noise measured by the structure-borne noise sensor 36 over time.

Claims

1 . Flow lapping machine (10) for moving abrasive media (14) over a surface of a workpiece (12) and / or through the opening (16) of a workpiece (12), with a media drive device (24) which is suitable for carrying the abrasive medium (14 ) to move over a surface of a workpiece (12) and / or through the opening (16) of the workpiece (12) in a flow direction, with a workpiece holder (18) for holding the workpiece (12), with two on opposite sides of the Workpiece (12) positionable parts (20, 22), with a structure-borne noise sensor (36) for measuring structure-borne noise, which is generated in the machining of a workpiece (12) with a grinding medium (14), and with an evaluation unit (38) which is suitable to use an integral value of the root mean square of the structure-borne sound measured by the structure-borne sound sensor (36) over time to a cutting performance of the grinding medium (14) and / or a material removal rate on the workpiece (12) conclude.

2. Flow lapping machine (10) according to claim 1, characterized in that a look-up table (39) is stored in the evaluation unit (38) from which a material removal on the workpiece based on the integral value of the square mean of the measured structure-borne noise signal over time (12) and / or a cutting performance of the grinding medium (14) can be read.

3. Flow lapping machine (10) according to one of the preceding claims, characterized in that the evaluation unit (38) has an amplifier (48) for amplifying the signal measured by the structure-borne noise sensor (36).

4. Flow lapping machine (10) according to one of the preceding claims, characterized in that the evaluation unit (38) has at least one filter (52) for filtering out machine frequencies from the signal measured by the structure-borne noise sensor (36).

5. Flow lapping machine (10) according to one of the preceding claims, characterized in that the structure-borne sound sensor (36) is in direct or indirect contact with the workpiece (12) during operation of the flow lapping machine (10).

6. Flow lapping machine (10) according to one of the preceding claims, characterized in that the flow lapping machine (10) comprises a bypass channel (46) which runs parallel to a main fluid channel (15), and that the workpiece (12) is a dummy workpiece (12a) which is arranged in the bypass channel (46), the main fluid channel (15) extending over a surface and / or through an opening (16) of an additional workpiece (12b) to be machined.

7. flow lapping machine (10) according to claim 6, characterized in that the flow lapping machine (10) comprises two structure-borne sound sensors (36), wherein during operation of the flow lapping machine (10) both on the dummy workpiece (12a) in the bypass channel (46) and on the In addition to the workpiece (12b) to be machined, a structure-borne sound sensor (36) is positioned.

8. flow lapping machine (10) according to any one of the preceding claims, characterized in that the flow lapping machine (10) comprises a control unit (40) which is suitable for determining at least one process parameter based on the cutting performance and / or material removal rate determined by the evaluation unit (3) adapt, in particular while machining a workpiece (12).

9. Flow lapping machine (10) according to claim 8, characterized in that the process parameters that can be adjusted by the control unit (40) include a flow rate of the grinding medium (14), a fluid pressure of the grinding medium (14), a counter pressure on the grinding medium (14) and / or are a temperature of the grinding medium (14).

10. flow lapping machine (10) according to one of the preceding claims, characterized in that the flow lapping machine (10) has a fluid conveying device which is suitable for removing worn grinding medium from the flow lapping machine (10) and supplying unused grinding medium.

1 1. Method for determining a material removal and / or a material removal rate on a workpiece (12) when machining the workpiece (12) in a flow lapping machine (10), with the following steps:

Guiding a grinding medium (14) over a surface and / or through an opening (16) of a workpiece (12) to be machined,

Measuring the structure-borne noise generated in the workpiece (12) during machining,

Formation of a quadratic mean of the measured structure-borne noise signal,

Integrate the root mean square over the processing time, and

Determination of the material removal and / or the material removal rate on the workpiece (12) based on the formed integral.

12. The method according to claim 1 1, characterized in that a cutting performance of the grinding medium (14) is determined on the basis of the integrated square mean of the structure-borne sound signal divided by a flow rate of the grinding medium.

13. The method according to claim 1 1 or 12, characterized in that based on a material removal rate at least one of the following process parameters is set: a flow rate of the grinding medium (14), a fluid pressure of the grinding medium (14), a counter pressure on the grinding medium (14) and / or a temperature of the grinding medium (14).

14. The method according to any one of claims 1 1 to 13, characterized in that at least one process parameter is adjusted if the material removal rate measured during the machining of the workpiece (12) deviates from a desired material removal rate by more than a defined tolerance value.

15. The method according to any one of claims 1 1 to 14, characterized in that a reference curve which describes a desired course of the material removal rate is created by storing a course of the material removal rate of a machined workpiece (12) in an evaluation unit (38), and a tolerance range is defined around the reference curve within which the material removal rate should move.

16. The method according to claim 15, characterized in that at least one process parameter is adapted when machining the workpiece (12) if the actual course of the material removal rate is outside the tolerance range.

17. The method according to any one of claims 1 1 to 16, characterized in that, based on a material removal rate, a request to replace at least part of the grinding medium (14) takes place.

18. The method according to any one of claims 1 1 to 17, characterized in that a further structure-borne sound signal is measured on a dummy workpiece (12a) and a difference between the two structure-borne sound signals is formed in order to monitor an improvement in the surface quality of the workpiece (12).

19. A method for determining the cutting performance of a grinding medium (14) with the following steps:

Guiding a grinding medium (14) over a surface and / or through an opening of a reference workpiece (12),

Measuring the structure-borne noise generated in the reference workpiece (12), - Forming a quadratic mean of the measured structure-borne noise signal

Integrating the root mean square over the processing time,

Divide the integral value by the media flow, and

Determining the cutting performance of the grinding medium (14) based on the divided integral value.