Process and machine tool for machining identical workpieces in series by milling and / or grinding

Abstract

Method for machining identical workpieces (10) in series by milling and / or grinding on a cutting machine tool, for which purpose the workpieces (10) to be machined are clamped in a workpiece holder (40) of the machine tool in chronological sequence and machined by at least one rotationally driven tool (20), characterized in that during a current machining process (n) the process load (R) occurring on the tool (20) and workpiece (10) is determined by detecting the drive power (P) of a tool drive (30) driving the tool (20) and evaluating said power taking into account a correction function (K(V)) for eliminating external interference, wherein the correction function (K(V)) is adapted on the basis of the respectively preceding machining process (n-1) and the beginning of the current machining process (n).

Description

[0001] The invention relates to a method for machining identical workpieces in series by milling and / or grinding, in particular by gear hobbing and / or generating grinding, on a metal-cutting machine tool. The invention further relates to a metal-cutting machine tool, such as, in particular, a gear cutting machine.

[0002] As examples of the state of the art, reference is made to the patent specifications DE 10 2010 023 728 A1, DE 20 2014 104 881 U1, EP 2 732 895 A1 and DE 10 2011 108 972 A1.

[0003] Monitoring and / or control of the machining process can be provided for both milling and grinding. For this purpose, for example, the drive power of the machine tool drive can be recorded. The recorded drive power correlates with the process load, i.e. with the mechanical and thermal loads on the tool and workpiece, and is therefore a measure of the process load. However, the machining process is strongly influenced by external disturbances, such as the coolant supply at the machining point. The recorded drive power must therefore be evaluated in such a way that external disturbances are taken into account and eliminated in order to determine the actual process load. The process load is therefore determined indirectly.

[0004] This can be achieved, for example, through a so-called teach-in process. During teach-in, an idle process is run before each machining process or machining pass. Here, the drive power is recorded and saved as a function of the tool feed path or as a function of the machining time. During the subsequent machining process, the previously recorded idle drive power or its curve serves as a correction value, which is subtracted from the then recorded drive power in order to determine the process load, i.e. the milling or grinding power between the tool and the workpiece. However, this procedure is unsuitable for series production and especially for large-scale production.

[0005] The invention is intended to demonstrate possibilities for optimising the milling or grinding, in particular gear milling or gear grinding, of identical workpieces in series.

[0006] This is achieved with a method according to the invention in accordance with patent claim 1 and with a machine tool in accordance with the independent patent claim. Advantageous developments and refinements of the invention arise analogously for both subject matters of the invention from the dependent patent claims as well as from the following explanations.

[0007] In the method according to the invention for the repeated machining of identical workpieces in series by milling and / or grinding on a machining machine tool, the workpieces to be machined are clamped one after the other, i.e. in chronological sequence, in a workpiece holder of the machine tool and machined by at least one rotationally driven tool (milling or grinding tool), each workpiece being machined in a substantially identical machining process.

[0008] The invention now provides that during a current machining process, the process load occurring on the tool and workpiece is determined by detecting the drive power of a tool drive that rotates the tool and evaluating it taking into account a correction function to eliminate external interference, wherein the correction function is adapted based on the respective preceding machining process and the current machining process that is about to begin, wherein this individual or specific adaptation takes place automatically or automatically for each machining process, ie for each workpiece.

[0009] A machining process is understood to be a complete machining pass during which the clamped workpiece is machined by the tool or by the milling or grinding tool within the intended machining scope.

[0010] The correction function mathematically maps the course of all external disturbances, and in particular the influence of the coolant supply, over the tool feed path or machining time. The correction function can be determined once during an idle process prior to series production. Such an idle process is performed, particularly in the machine tool's setup mode, without a workpiece or without machining intervention.

[0011] The drive power of the tool drive is determined in particular by measuring the mechanical and / or electrical drive power. Measuring the electrical current consumption, the electrical voltage, and / or at least one other measured variable can be considered equivalent, provided that this can be considered in some way a measure of the drive power of the tool drive. The tool drive is typically a tool spindle drive, which is why the drive power can also be referred to as spindle drive power.

[0012] The tool can perform a feed movement relative to the workpiece during the machining process. The correction function for the current machining process is then preferably adjusted by using the recorded drive power of the tool drive in the final feed position during the previous machining process and the drive power of the tool drive in the initial feed position during the current machining process. The correction function for the workpiece currently being machined or for the current machining process can be adjusted, for example, by shifting or offsetting and / or scaling based on these two values.

[0013] The method according to the invention does not require the above-described teaching process, so that the workpieces can be clamped and machined directly one after the other. Non-productive times are thus avoided, which is advantageous for the output. Furthermore, all changes in external disruptive influences in the series production process are continuously recorded and taken into account when determining or determining the process load. This applies in particular to the cooling lubricant supply at the machining point, which has a significant and usually variable influence on the required drive power and must therefore be taken into account when determining the actual process load. This is achieved according to the invention by adapting the correction function to the individual process. The invention particularly improves the methods for gear hobbing or gear grinding known from the prior art.The invention is ideally suited for series and especially large-scale production of identical gears.

[0014] The process load determined using the method according to the invention can subsequently be used for monitoring, in particular automated monitoring, of the (cutting) machining process. Monitoring is essentially carried out in real time. The process load influences the component quality (including dimensional accuracy) of the component to be manufactured (preferably a gear). If, for example, the determined process load lies within a defined range, it can be assumed that the currently manufactured component has a specified component quality. Determining the process load can thus be used for ongoing quality monitoring and component-specific quality documentation. Monitoring the machining process also allows conclusions to be drawn about the condition (wear level) of the tool.

[0015] The process load determined according to the method according to the invention can subsequently also be used to control the current machining process or the current workpiece machining. If the process load, which is determined essentially in real time, deviates from a target value or lies outside a defined range, corrective intervention in the current machining process can be made by changing at least one manipulated variable, for example by changing the feed rate of the tool, the speed or rotational speed of the tool and / or possibly also the speed or speed of the workpiece and / or, especially in the case of gear milling or gear grinding, the shift position of the tool (by so-called shifting, i.e. tangential displacement relative to the workpiece) in a control loop.

[0016] The process load determined according to the method according to the invention can also be used to influence the subsequent machining process, for example by changing the shift position of the tool, which is carried out in particular in an automated manner, or by replacing the tool, which can also be carried out in an automated manner.

[0017] The machine tool according to the invention for machining workpieces by milling and / or grinding, in particular by gear milling and / or gear grinding, comprises: - at least one workpiece holder for holding the workpieces to be machined; - at least one tool holder or tool spindle for receiving at least one milling or grinding tool, in particular a gear milling or gear grinding tool; - at least one tool drive (tool rotary drive) or tool spindle drive for the rotary drive of the tool holder or tool spindle and the milling or grinding tool accommodated therein; - at least one measuring device, such as a measuring sensor, for directly or indirectly measuring the drive power of the tool drive or tool spindle drive; and - an evaluation device which is designed to determine the process load occurring on the tool and workpiece automatically during a current machining process by evaluating the recorded drive power or spindle drive power, i.e. measured with the measuring device, taking into account a correction function for eliminating external interference, the correction function being adapted on the basis of the respective preceding machining process and the current machining process which is about to begin.

[0018] Due to its features, the machine tool according to the invention is suitable for carrying out the method according to the invention or for a use corresponding to the method.

[0019] It is preferably provided that the evaluation device is further designed to control the current machining process, as explained above, and for this purpose is also connected to the control device of the machine tool in order to be able to effect a corresponding control of the machine tool.

[0020] The evaluation device is preferably a computer or similar device, which can be equipped with appropriate software programs. The computer can be located internally or externally to the machine tool. This can also be a subsequently installed computer, for example, retrofitted to an existing machine tool. The invention is therefore suitable for both new machines and existing or used machines.

[0021] The method according to the invention is, in particular, a method for machining identical workpieces in series by gear hobbing and / or generating grinding on a machine tool, in particular a gear hobbing or generating grinding machine. The method according to the invention is used, in particular, for the machining and / or machining of gear teeth in the series production of gears (gear manufacturing). Gear hobbing or generating grinding is preferably carried out using a helical gear cutter or grinder. The machine tool according to the invention is preferably a gear hobbing or generating grinding machine and, in particular, a (machining) gear cutting machine. The preceding explanations apply analogously.

[0022] The invention is explained in more detail below using the example of generating grinding of gears with reference to the figures in the drawing. The features shown in the figures and / or explained below can further develop the invention, even independently of specific combinations of features. Fig. 1 illustrates in a perspective view a generating grinding process for the production of a gear. Fig. 2 shows the generating grinding process from Fig. 1 in a different representation, where the coolant supply at the machining point is also shown. Fig. 3 illustrates in a diagram the determination of the process load for the Fig. 1 and Fig. 2 shown generating grinding process. Fig. 4 shows a diagram illustrating the adjustment of the correction function to determine the process load.

[0023] Hobbing and generating grinding are common manufacturing processes in the production of gears. Hobbing or generating grinding takes place on a metal-cutting machine tool (hobbing and / or generating grinding machine) which has at least one workpiece holder for holding the workpieces to be machined and at least one tool holder or tool spindle for holding a worm-shaped hobbing or generating grinding tool. For hobbing or generating grinding, a workpiece to be machined is clamped in the workpiece holder and machined with the milling or grinding tool. The workpiece and the hobbing or grinding tool are rotated, resulting in a worm gear-like machining engagement between the workpiece and the tool. In addition to its rotation, the milling or grinding tool can be moved in an axial direction relative to the workpiece (so-called feed) in order to create or maintain the tooth gaps on the workpiece.to edit.

[0024] Fig. Figure 1 shows such a generating grinding process (continuous generating grinding), in which the workpiece 10, which is a gear to be manufactured with a toothing 11 to be produced, is machined by a grinding tool designed as a grinding worm 20. Both the workpiece 10 and the grinding worm 20 perform different but coordinated rotary movements U1 and U2. The grinding worm 20 is accommodated in a tool spindle (not shown). The tool spindle, together with the grinding worm 20 accommodated therein, is rotationally driven by a tool spindle drive 30 with the spindle drive power P. In addition to its rotation U2, the grinding worm 20 performs a feed movement V relative to the workpiece 10 (a kinematic reversal of the feed V is also possible).A complete feed movement from an (upper) initial feed position to a (lower) final feed position is referred to as a machining cut. A machining process or machining pass comprises at least one machining cut. The arrow S illustrates a possible shift movement of the grinding worm 20.

[0025] Fig. Figure 2 shows the same generating grinding process in an axial plan view of the grinding worm 20. Also shown are the workpiece holder or workpiece table 40 and the cooling lubricant supply F at the machining point by means of at least one nozzle 50.

[0026] The Fig. 1 and Fig. The components shown in Figure 2, with the exception of the workpiece 10, are part of a gear cutting machine. This gear cutting machine may also include the tool spindle (not shown), a control device for controlling the gear cutting machine, at least one measuring device for measuring the spindle drive power P, and an evaluation device for determining the process load, as explained below.

[0027] The invention provides that during a current machining process, the process load or grinding load occurring on the grinding worm 20 and on the workpiece 10 is determined by detecting the spindle drive power P of the tool spindle drive 30 and evaluating it taking into account a correction function to eliminate external interference, such as the cooling lubricant supply F. The correction function is adapted for the current machining process based on the previously completed machining process and the current machining process that is about to begin. This is explained below with reference to Fig. 3 and Fig. 4 is explained as an example for a single-cut machining process, whereby the explanations apply analogously to a multi-cut machining process.

[0028] Fig. Figure 3 schematically illustrates the curve P(V) of the measured spindle drive power P [in kilowatts] as a function of the feed path or feed position V [in millimeters] during a machining process. The values ​​given are only examples. Instead of the spindle drive power P, for example, the electrical current consumption of the tool spindle drive 30 can also be measured. The spindle drive power P or the electrical current consumption can also be recorded or measured as a function of the machining time.

[0029] In order to determine the process or grinding load between tool 20 and workpiece 10 from the measured spindle drive power P or its curve P(V), external interference must be taken into account and eliminated. This is done using a previously determined correction function K(V), which maps the curve of all external interference over the feed path V of the grinding worm 20 or, alternatively, the machining time. By subtracting the correction function K(V) from the recorded power curve P(V) of the tool spindle drive 30, the function or curve R(V) of the process or grinding load R can be determined or calculated. The same applies analogously to individual values.

[0030] The invention now provides that the correction function K(V), determined once before the start of series production or series production in idle mode, is first described mathematically (e.g., by a polynomial function, logarithmic function, or exponential function) and then adjusted for each machining process or machining pass. For the adjustment, the spindle drive power PE,n-1 measured and stored in the final feed position of the previous machining process n-1 and the spindle drive power PA,n measured and stored in the initial feed position of the current machining process n are used, whereby the correction function K(V) is shifted and / or scaled until it finally lies between the two values ​​PA,n and PE,n-1. This is Fig.4. The adjustment or adaptation can be carried out, for example, using a ray theorem calculation, whereby the mathematical description of the correction function K(V) as such remains unchanged.

[0031] This preferred option for curve fitting for the correction function K(V) is based on the finding that no material is removed in the starting position or initial feed position and in the end position or final feed position of the feed movement V, and thus the spindle drive powers PA and PE measured in these feed positions are comparable to those during idle operation. Therefore, no separate idle operation needs to be performed before a machining process or machining pass n in order to determine a correction function K(V),n for this machining process n. The described adjustment of the correction function K(V), which was determined, saved, and mathematically described once before the start of series production during idle operation, is sufficient.In an advantageous manner, the current situation of the cooling lubricant supply F at the machining point is inevitably taken into account, which, due to braking and hydromechanical conveying effects, has a considerable influence on the spindle drive power P to be used or its curve P(V), whereby the cooling lubricant supply F can change during series production due to process factors.

[0032] With the described adaptation of the correction function K(V), the correction function K(V),n relevant for this machining process n is already determined at the beginning of the current machining process or machining pass, so that the instantaneous process load or grinding load R between grinding worm 20 and workpiece 10 can be determined or calculated, as explained above, in real time at any time during the ongoing machining process n from the measured spindle drive power P. The determined actual process load R or its curve R(V) can then be used for monitoring and, in particular, for real-time monitoring and / or for controlling the current machining process n, as explained above.The determination and adaptation of the correction function K(V), as well as the monitoring and / or control of an ongoing machining process n, is carried out using an evaluation device, which is preferably connected to the control device of the gear cutting machine.

[0033] The preceding explanations apply analogously to gear hobbing for the production of gears. However, the invention is also suitable for other workpiece types and / or for other milling or grinding processes, such as external cylindrical grinding. Reference symbol 10 Workpiece 11 Gearing 20 tools 30 Tool drive 40 Workpiece holder 50 nozzle F Coolant supply K(V) correction function P Drive power (tool drive) PA drive power (initial position) PE drive power (end position) P(V) power curve R Process load R(V) process load curve S Shift0 U1 Rotary movement (workpiece) U2 Rotary movement (tool) V feed n current processing process n-1 preceding processing process n+1 subsequent processing process

Claims

[1] Method for machining identical workpieces (10) in series by milling and / or grinding on a cutting machine tool, for which purpose the workpieces (10) to be machined are clamped in a workpiece holder (40) of the machine tool in chronological sequence and machined by at least one rotationally driven tool (20), characterized by that during a current machining process (n) the process load (R) occurring on the tool (20) and workpiece (10) is determined by recording the drive power (P) of a tool drive (30) driving the tool (20) and evaluating it taking into account a correction function (K(V)) for eliminating external interference, wherein the correction function (K(V)) is adapted on the basis of the respectively preceding machining process (n-1) and the beginning of the current machining process (n). [2] Method according to claim 1, characterized bythat the correction function (K(V)) was determined once in a previous idle operation of the machine tool. [3] Method according to claim 1 or 2, characterized by that the tool (20) executes a feed movement (V) during the machining process, wherein the drive power (PE,n-1) of the tool drive (30) in the final feed position of the preceding machining process (n-1) and the drive power (PA,n) of the tool drive (30) in the initial feed position of the current machining process (n) are used to adapt the correction function (K(V)). [4] Method according to one of the preceding claims, characterized by that the determined process load (R) is subsequently used to monitor the current machining process (n). [5] Method according to one of the preceding claims, characterized bythat the determined process load (R) is subsequently used to control the current machining process (n). [6] Method according to claim 5, characterized by that the control is carried out by changing the feed rate and / or the speed of the tool (20). [7] Method according to one of the preceding claims, characterized by that the determined process load (R) is subsequently used to influence a subsequent machining process (n+1). [8] Machine tool for machining workpieces (10) by milling and / or grinding, comprising a workpiece holder (40) for holding the workpieces (10) to be machined, a tool holder for holding a milling or grinding tool (20) and a tool drive (30), characterized bya measuring device for measuring the drive power (P) of the tool drive (30) and by an evaluation device which is designed to automatically determine the process load (R) occurring on the tool (20) and workpiece (10) during a current machining process (n) by evaluating the measured drive power (P) taking into account a correction function (K(V)) for eliminating external interference, wherein the correction function (K(V)) is adapted on the basis of the respectively preceding machining process (n-1) and the beginning of the current machining process (n). [9] Machine tool according to claim 8, characterized by that the evaluation device is further designed to control the current machining process(es) and is also connected to a control device of the machine tool for this purpose. [10] Machine tool according to claim 8 or 9, characterized bythat the evaluation device is a subsequently installed computer.

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