How to operate a machine tool

Abstract

In the first step of a method for operating a machine tool using a pump to deliver a cooling lubricant, the tool is inserted into the working spindle of the machine tool. In the second step, a teaching process is performed. The teaching process includes the steps of determining the pump characteristics of the tool, determining the optimal operating point of the pump for the tool, and storing the optimal operating point of the tool in a tool table.

Description

Technical Field

[0001] The present invention relates to an operating method of a machine tool and a machine tool. In particular, the energy consumption of the machine tool should be reduced by determining the optimal operating point of a pump that delivers a coolant lubricant.

[0002] The mixed friction that can occur during machining of a workpiece by a tool in a machine tool is a common problem in such processes. A coolant lubricant (CSS) can reduce friction, thereby reducing tool wear, heating of the workpiece, and the energy required. CSS is used to cool the tool or the workpiece and reduce the friction between the tool and the workpiece. Further, in some machining processes, CSS can also help remove chips from the working environment, improve the dimensional accuracy of the workpiece, and enhance its surface quality. Also, the workpiece can be protected from corrosion. Conventional CSS can also contain additives in addition to water and oil.

[0003] In the prior art, it is common to apply a high predetermined pressure of, for example, 50 to 100 bar to the CSS by a speed control pump, thereby always maintaining a sufficiently high flow rate. However, it has been found that in many cases, a much lower pressure is sufficient to provide effective cooling of the tool. As a result, the energy consumption of the pump can be significantly reduced. Further, it has been found that the surface quality of the workpiece can be improved at a low pressure. Further, the service life of the tool can be increased during operation at a lower pressure.

[0004] The paper "Energyefficient machine tools" by B. Denkena et al., CIRP Annals-Manufacturing Technology 69 (2020) 646-667, provides an overview of techniques for reducing the energy consumption of machine tools. In this paper, process cooling, in particular, is shown to have a significant energy-saving effect. For example, when considering the system characteristics of a machine tool with a speed-controlled high-pressure pump, even a small change in the coolant lubricant throughput can have a significant impact on the output of the electric pump without affecting tool wear, for a particular set of cutting parameters.

[0005] Conventional techniques have shown that significant energy savings can be achieved by modifying the pressure control of the pump that delivers CSS to the volume control system; however, this method has not been used in industry until now. One reason for this is a lack of knowledge about the precise flow rates required for specific tools or machining processes. Another reason may be the absence of suitable flow sensors for measuring CSS flow rates. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Therefore, the present invention is based on the objective of overcoming problems known in the prior art, identifying a method for operating a machine tool that is improved compared to the prior art, and providing an improved machine tool. In particular, the energy consumption of the machine tool is reduced as a result.

[0007] A further objective of the present invention is to improve the surface quality of a workpiece after machining by a machine tool. Furthermore, it is necessary to extend the tool life. [Means for solving the problem]

[0008] This objective is achieved by the method of operating the machine tool described in claim 1, the method of operating the machine tool described in claim 9, and the machine tool described in claim 10. Preferred embodiments of the present invention are defined in the dependent claims, the accompanying drawings, and the following description of exemplary embodiments.

[0009] The method of the present invention can be implemented in virtually any existing numerically controlled machine tool that processes a workpiece using a tool, such as a CNC machine. Such machine tools typically have a tool spindle on which a tool, such as a drill / milling head, is clamped.

[0010] The machine tool also has a pump for supplying a cooling lubricant (CSS) to cool the tool or workpiece. The pump may, in particular, be a speed-controlled high-pressure pump. Furthermore, the machine tool may have a flow sensor for measuring the flow rate of the CSS.

[0011] In the first step of this method, the tool is inserted into the tool spindle of the machine tool. The tool can be removed from, for example, a tool magazine, and this process is preferably performed automatically.

[0012] According to one aspect of the present invention, a teaching process is performed to determine the pump characteristics specific to the tool. The pump characteristics may represent, for example, the dependence between the power consumption and / or speed of the pump and the flow rate of the coolant lubricant through the tool.

[0013] The characteristic curve (profile) of a pump can depend on multiple parameters. In particular, the geometric shape of the tool affects the pump characteristics. For example, pre-determining pump characteristics by simulation or numerical calculation is generally very complex. Therefore, it is advantageous to determine pump characteristics empirically through a teaching process.

[0014] The power consumption of a pump, measured in watts, can be determined, for example, by the pump speed and / or pump current. The values ​​of power consumption (watts), / or speed (1 / s), and / or pump current (amperes) can be detected, in particular, by the pump's control device. Power consumption, pump speed, or pump current can be collectively referred to as performance characteristics or parameters.

[0015] Next, the optimal operating point of the pump for the tool can be determined. The operating point is, in particular, a point of pump characteristics. The optimal operating point is characterized in that, in particular, sufficient cooling of the tool is ensured and energy consumption can be minimized.

[0016] According to one preferred embodiment, multiple different optimal operating points can be determined based on different criteria, such as minimum energy consumption, sufficient cooling capacity, maximum tool life, and improved workpiece surface quality. The average of these criteria may be defined as the optimal operating point.

[0017] In a further step of this method, the optimal operating point of the tool is stored in the tool table. When the same tool, or a structurally identical or similar tool, is used to machine the workpiece in subsequent operations, the optimal operating point may be read from the tool table and set. In particular, other machine tools can access the tool table and set the optimal operating point while machining the workpiece.

[0018] For example, a tool table may be provided via a server or cloud to multiple machine tools that may be located in geographically separated locations. For this purpose, the machine tools may be connected to a network via an appropriate interface.

[0019] Therefore, the optimal operating point can be determined for each tool or tool type. Retraining is not required for subsequent machining of the workpiece. The optimal operating point can be obtained and set from the tool table.

[0020] The optimal operating point may be determined by specifying parameters such as pump speed, pump power, or pump current. Even machine tools without flow sensors can be operated at the optimal operating point. A control device, particularly a control device for any suitable machine tool's pump, can be designed to operate at the optimal operating point, for example, through a software update, and as a result, the method according to the present invention can be easily retrofitted to existing machines.

[0021] The teaching process may include detecting performance characteristics of the pump, such as power consumption, pump speed, or pump current. These performance characteristics may be measured or output by, for example, the pump's control device.

[0022] Furthermore, the teaching process may include a step of detecting the flow rate of the cooling lubricant through the tool. For this purpose, the machine tool may have a suitable flow sensor or flow rate sensor.

[0023] In one preferred embodiment, the teaching process may be performed while the machine tool is idling, i.e., without machining the workpiece. In this case, the teaching process is an independent process, but it is performed only once per tool. Furthermore, teaching does not need to be repeated for each machine tool. Therefore, machine tools equipped with flow sensors can be used in particular for this teaching process.

[0024] To record pump characteristics, the pump can be operated with different performance characteristics or pressure settings and / or pump speed and / or power values ​​during the teaching process. The typical pressure of the CSS delivered by the pump may be 40 to 100 bar, preferably 50 to 80 bar.

[0025] According to a further preferred embodiment, the teaching process can be carried out using data detected during the machining of the workpiece or during multiple machining operations. For this purpose, for example, during the machining of one or more workpieces by a machine tool or a plurality of machine tools, it is possible to detect and store the parameters (performance characteristics) of the pump, the CSS flow rate, and the tool used. Then, an evaluation can be performed for each tool or each type of tool, and pump characteristics for each tool or each type of tool may be created.

[0026] The above-described preferred teaching process may be executed, for example, based on the operation data intensively collected and stored for a plurality of machine tools, whereby it becomes possible to create a corresponding tool table in a unified manner. As soon as the optimum operating point of the tool used becomes available, it can be used during subsequent machining. The unifiedly created tool table may be made accessible to all machine tools within the group on the central data storage device, particularly so that the determined optimum operating point can be called. Therefore, each time a tool change is made, the corresponding optimum operating point can be read out and set. For the tools required during the machining of the workpiece, the reading process may be executed in advance. In the case of a machine tool that cannot automatically access the tool table, the optimum operating point for each may be set manually by the user of the machine tool.

[0027] The optimum operating point may be determined based on the type and size of the tool. Correspondingly, the optimum operating point may be stored in the tool table together with the type and size of the tool. Thus, for example, it can be specified that this is the optimum operating point for an M5 drill. Further exemplary types of tools include (turning) chisels, milling tools, planers, rasps, grinding tools, etc., which may exist in multiple sizes and / or geometries. Furthermore, these may be left-handed or right-handed tools.

[0028] Each tool preferably has a unique identifier in a tool storage or tool magazine. Therefore, the optimum operating point can be stored in the tool table together with its identifier. Modern machine tools can usually perform automatic tool changes. During this change, the optimum operating point may be set from the tool table for each case.

[0029] In addition, the optimum operating point may depend on the material of the machined workpiece. Correspondingly, the optimum operating point may be determined according to the material. For example, hard materials require a higher cooling capacity than soft materials and may therefore require a large CSS flow rate. The optimum operating points for different materials can likewise be stored in the tool table. Thus, for a particular tool, there may be multiple optimum operating points for each of the corresponding number of materials.

[0030] Furthermore, the optimum operating point may also depend on the machining process. For example, the desired or required cooling capacity may depend on the speed of the tool spindle. The optimum operating point may preferably be determined and stored for each different machining parameter and / or parameter range. The optimum operating point can be determined using an algorithm. This algorithm can be executed particularly by the control device of the machine tool and / or on a central data processing device such as a server or cloud.

[0031] A preferred method of machining a workpiece using a machine tool having a pump for supplying a cooling lubricant uses a predetermined optimum operating point. This method includes the steps of inserting a tool into the tool spindle of the machine tool, detecting the optimum operating point of the pump according to the inserted tool or according to the inserted tool and the material of the workpiece, and machining the workpiece, and the pump operates at the optimum operating point.

[0032] The step of detecting the optimal operating point of the pump may include, for example, a lookup of the optimal operating point in the tool table. The tool table can be stored locally in the machine tool. Alternatively or additionally, the machine tool may access a centrally stored tool table (e.g., on a server or in the cloud) over a network.

[0033] Such machining methods may be performed on machine tools without flow sensors, because only the predetermined optimal operating point of the pump is read and set for each tool used. Since tools of the same type and size have similar geometric shapes, the predetermined optimal operating point for this tool can be universally applied to any machine tool.

[0034] A preferred machine tool for machining a workpiece comprises a tool spindle for receiving a tool for machining the workpiece, a pump for supplying a cooling lubricant to cool the tool, and a control device for controlling the machine tool. According to the present invention, the control device is configured to perform the method according to the present invention as described above.

[0035] Further advantageous embodiments are shown in the drawings, but will be described in more detail below based on exemplary embodiments in which the invention is not limited. [Brief explanation of the drawing]

[0036] [Figure 1] The pump characteristic curve measured for a milling tool with a diameter of 6 mm (R0.8) is shown. [Figure 2] This figure shows the pump characteristic curve measured for a milling tool with a diameter of 3 mm (F0.2). [Figure 3] This figure shows the pump characteristic curve measured for a 2.5 mm diameter drill. [Figure 4] This figure shows the pump characteristic curve measured for an 8.9 mm diameter drill. [Figure 5]The pump characteristic curve measured for a 14mm diameter drill is shown. [Figure 6] This figure shows a comparison of pump characteristic curves measured for different tools. This figure is based on the paper B. Denkena et al. “Energy efficient machine tools”, CIRP Annals-Manufacturing Technology 69(2020) 646-667. [Figure 7] This demonstrates the teaching process for different tools. [Figure 8] This demonstrates the teaching process for different tools. [Figure 9] This document presents an algorithm for determining the optimal operating point of a tool. [Modes for carrying out the invention]

[0037] In the preferred embodiments of the present invention described below, the same reference numerals indicate the same or equivalent components.

[0038] Figures 1 to 5 show exemplary pump characteristic curves for five different tools. After inserting each tool shown, the pump for delivering the coolant lubricant CSS is operated under multiple performance characteristics, and the flow rate Q of CSS through the tool is measured.

[0039] In Figures 1 to 5, the pump's power consumption P, in units of watts, is plotted against the flow rate Q, in units of liters / minute, in all cases. Each pump characteristic curve shows three exemplary operating points indicated by large points. The top point corresponds to pump pressure control at 80 bar. The middle point corresponds to pump pressure control at 40 bar. The bottom point indicates the optimal operating point for volume control in each case.

[0040] Figure 1 shows, as an example, the pump characteristic curve measured for a milling tool with a diameter of 6 mm (R0.8). Figure 2 shows, as an example, the pump characteristic curve measured for a milling tool with a diameter of 3 mm (F0.2). Figure 3 shows, as an example, the pump characteristic curve measured for a drill with a diameter of 2.5 mm. Figure 4 shows, as an example, the pump characteristic curve measured for a drill with a diameter of 8.9 mm. Figure 5 shows, as an example, the pump characteristic curve measured for a drill with a diameter of 14 mm.

[0041] Table 1 below summarizes the parameters determined at the optimal operating point of a volume-controlled pump compared to conventional control at 40 bar or 80 bar pressure for the exemplary tools shown in Figures 1 to 5. These values ​​correspond to three points in Figures 1 to 5, where the upper point corresponds to 80 bar pressure, the middle point to 40 bar pressure, and the lower point to volume control (see also labels in Figure 1).

[0042] [Table 1]

[0043] As can be seen from the values ​​in Table 1, the pump output P required in the case of volume control is significantly reduced compared to the case of pressure control, while still achieving a large flow rate sufficient to cool each tool. Therefore, energy consumption can be significantly reduced. The lower CSS pressure results in better surface quality of the machined workpiece and can increase the service life of the tools. Furthermore, test results have shown that the service life of tools with volume control can be increased by up to 26%.

[0044] Surprisingly, it was confirmed that the surface quality of machined workpieces can also be significantly improved during tool cooling and lubrication with flow control. In summary, Table 2 below compares the surface quality of workpieces machined with a 10 mm diameter drill at different pump power settings, as an example. Here, for each different power setting of the pump, multiple holes, e.g., six holes, were drilled adjacent to each other in the workpiece. The surfaces of the holes and the workpiece were then measured.

[0045] The measured variables or pump parameters are listed in the first column of Table 2. Measurements were performed at four different power settings of the pump. The results are shown in columns 2 through 5 of the table. The table entries indicate, for each case, the number of holes out of six that exceeded the tolerance value specified below each.

[0046] The fourth row of Table 2 shows the number of times, in each case, the measured holes as a whole were outside the acceptable limit of 10 μm. Note that a single hole may fall outside multiple acceptable limits simultaneously.

[0047] These results indicate that flow control yields optimal results at a flow rate of 6 l / min. In this case, the six holes were outside the acceptable range only twice. In contrast, with conventional 80 bar pump control using prior art, the six perforated holes were outside the acceptable range 16 times.

[0048] [Table 2]

[0049] Figure 6 is from the English paper translated by B. Dekenaetal, “Energyefficient machine tools”, CIRP Annals-Manufacturing Technology 69 (2020) 646-667. The paper “EnergyEfficientMachining with OptimizedCoolantLubricationFlowRates”, by B. Dekenaetal, Procedia CIRP 24:25-31, is cited here as the source of the figures. Figure 6 shows a comparison of pump characteristic curves for different tools.

[0050] In Figure 6, the pump pressure p is plotted against the flow rate Q. The pump output corresponding to the pressure p is shown by the color of the curve. For a 12 mm diameter end mill, as an example, a decrease in output from a conventional pump pressure of 80 bar (point A) to 40 bar (point B) is shown, which is 77%. The optimal operating point may exist at an even lower pump pressure of approximately 20 bar.

[0051] Figure 7 illustrates the teaching process. In Figure 7, a tool magazine containing several different tools is shown on the left. For each tool in the tool magazine, a teaching process can be performed to determine the optimal operating point of the pump, which is then written to the tool table. In the illustrated example, the optimal operating point may be written to the tool table as a correction parameter K to a conventional operating point, for example, 80 bar. This correction parameter K is preferably a dimensionless number less than 1 (for example, the quotient of 80 bar to the pressure at the optimal operating point).

[0052] Figure 8 shows the configuration for performing the teaching process and determining the pump characteristics. The tool is clamped within the tool spindle. A speed-controlled pump supplies CSS to cool the tool. A flow sensor measuring the flow rate Q is placed in the CSS flow path. The pump controller sequentially sets several different pump parameters (or performance characteristics). The determined values ​​can then be plotted as pump characteristics and evaluated to determine the optimal operating point, which is then written to the tool table.

[0053] Figure 9 shows an exemplary method for determining the optimal operating point. In the left-hand diagram of Figure 9, an exemplary pump characteristic curve is plotted, where the pump pressure p is plotted against the pump flow rate Q. The slope of this line can be understood as the overall relationship between the tool pressure p and the flow rate Q, and is therefore a tool-specific parameter.

[0054] In the next step (the diagram on the right in Figure 9), the straight line moves parallel to the pump characteristic curve until it contacts it tangentially at a certain point. This point of contact is defined as the optimal operating point of the tool and can be stored in the tool table as appropriate.

[0055] An exemplary method for determining the optimal operating point from the pump characteristic curve, as described with reference to Figure 9, may be stored and executed as an algorithm in the control device of the machine tool, or it may be executed by a server or cloud computing device.

[0056] The features, claims, and drawings described above may be important individually or in combination for implementing the present invention in its various forms.

Claims

1. A method of operating a machine tool equipped with a pump for supplying a cooling lubricant, The steps include inserting a tool into the tool spindle of the machine tool, A step in the teaching process, A step of determining the pump characteristics of the tool, A step of determining the optimal operating point of the pump for the aforementioned tool, Steps include storing the optimal operating point of the tool in the tool table. A step of performing a teaching process that includes, A method of operating a machine tool, comprising the following features.

2. The aforementioned teaching process is The steps include detecting the performance characteristics of the pump, A step of detecting the flow rate of the cooling lubricant passing through the tool. Equipped with, The pump characteristics represent the dependence between the performance characteristics of the pump and the flow rate of the cooling lubricant through the tool. The method according to claim 1.

3. The teaching process is performed while the machine tool is idling without machining the workpiece, and the pump is operated at multiple pressure settings. The method according to claim 2.

4. The aforementioned teaching process is performed using data detected during the machining of the workpiece. The method according to claim 2.

5. The aforementioned teaching process is carried out using data from multiple machine tools. The method according to claim 4.

6. The optimal operating point is determined according to the type of tool. The method according to any one of claims 1 to 5.

7. The optimal operating point is determined according to the type of tool and / or the material of the workpiece being processed. The method according to claim 4 or 5.

8. The aforementioned optimal operating point is determined by executing the algorithm. The method according to any one of claims 1 to 7.

9. A method of machining a workpiece using a machine tool that has a pump for supplying a cooling lubricant, The steps include inserting a tool into the tool spindle of a machine tool, A step of detecting the optimal operating point of the pump according to the inserted tool, or A step of detecting the optimal operating point of the pump according to the inserted tool and the material of the workpiece, The steps include: machining the workpiece while the pump operates at the optimal operating point; A method for machining a workpiece, comprising the following features.

10. A machine tool for processing a workpiece, A tool spindle for receiving the tool used to machine the workpiece, A pump for supplying a cooling lubricant to cool the aforementioned tool, A control device for numerically controlling the aforementioned machine tool, Equipped with, The control device is configured to perform the method described in any one of claims 1 to 9. Machine tools.

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