METHOD FOR CORRECTING TOOL PARAMETERS OF A MACHINE TOOL FOR MACHINING OF WORKPIECES

Abstract

A method for correcting tool parameters of a machine tool for machining workpieces includes recording measurement values of measured characteristics as actual values of at least one workpiece machined with the machine tool. The measurement values are compared with the default set values of the workpiece. The measurement values of at least two measured characteristics are recorded from at least two parameters of at least one measured characteristic and/or from at least one measured characteristic and from at least one parameter. An average for a tool correction value is calculated from the measurement values and the corresponding set values, with which a correction of the machine tool is performed.

Claims

1. A method for the correction of tool parameters of a machine tool for machining workpieces, comprising: recording measurement values of measured characteristics as actual values of at least one workpiece machined with the machine tool; comparing the measurement values with default set values of the workpiece, wherein the measurement values that are recorded relate to at least one of: at least two measured characteristics; at least two parameters of at least one measured characteristic; and at least one measured characteristic and of at least one parameter of the same or one of another measured characteristic; calculating an average for a tool correction value from the measurement values and associated set values; and correcting the machine tool using the tool correction value.

2. The method according to claim 1, wherein a weighted average for the tool correction value is calculated from the measurement values.

3. The method according to claim 2, wherein the measured characteristic and/or the parameter with the smallest tolerance is used most strongly in calculating the weighed average.

4. The method according to claim 1, further comprising: performing an assignment of each measured characteristic to at least one machining tool.

5. The method according to claim 1, wherein the tool correction value is calculated continuously from the last n measurements (with n>1).

6. The method according to claim 1, further comprising: visualizing the tool correction value.

7. The method according to claim 6, wherein correcting the machine tool is performed automatically after determining the tool correction value or after confirmation after visualizing the tool correction value.

8. The method according to claim 1, wherein correcting the machine tool is performed after a continuous drift of the measurement values of a measured characteristic and/or a parameter has been detected based on the last n measurements and the measurement values exceed a default threshold value (OG, UG) or a default tolerance value (OT, UT).

9. The method according to claim 8, wherein the threshold value (OG, UG) can be determined.

10. The method according to claim 1, wherein the tool correction value is calculated by considering additional parameters of external factors.

11. The method according to claim 1, further comprising: performing an offset correction when a threshold value (OG, UG) or a tolerance value (OT, UT) of the measurement values of a measured characteristic and/or a parameter is exceeded.

12. The method according to claim 1, further comprising: measuring the workpiece in the machine tool and/or on an external measuring device.

13. The method according to claim 1, further comprising: storing a CAD data record of the workpiece in the tool machine for determining the tool correction value.

14. The method according to claim 1, further comprising: making notification by the machine tool if the measurement values of the measured characteristics and/or parameters are within threshold values (OG, UG) or tolerance values (OT, UT).

15. The method according to claim 1, wherein the tool correction value is calculated considering the measurement values and/or parameters and considering past measurements.

16. The method according to claim 1, further comprising: performing an extrapolation of the tool correction values by taking into account past measurements.

17. The method according to claim 1, further comprising: transferring tool correction values for a first workpiece to other workpieces.

18. The method according to claim 1, wherein the measurement values are recorded from at least one of: the machine tool; an in-line measuring system; and a coordinate measuring device, an articulated arm, a manual measuring device, or another external measuring device.

19. The method according to claim 1, further comprising: performing a visualisation and evaluation of at least one of: individual measured characteristics; parameters; tool correction data; and tool behaviour.

20. The method according to claim 1, further comprising: grouping the measured characteristics according to tool- and/or workpiece-offsets.

21. The method according to claim 1, further comprising: representing the machine tool and other available machine tools in graphics.

22. The method according to claim 1, further comprising: selecting the machine tool when a project is created; displaying all available machine tools; selecting a source for quality data of the workpiece; and reading the quality data in the machine tool.

23. The method according to claim 1, further comprising: displaying on a display or computer associated with the machine tool, at least one of: all available machine tools; a status of each available machine tool; a project running on the machine tool; recent events; and correction values.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Further characteristics and advantages of the invention are shown in the corresponding drawings, in which different characteristics of a manufacturing plant according to the invention are only shown as examples without limiting the invention to these design examples. In the drawings it is presented:

[0071] FIG. 1 a schematic representation of a manufacturing process;

[0072] FIG. 2 an overview of the method according to the invention with a control chart;

[0073] FIG. 3 Measurement values of a trunnion;

[0074] FIG. 4 Measurement values of a slot;

[0075] FIG. 5 a correction of the measurement values averaged from the values in FIG. 3 and FIG. 4;

[0076] FIG. 6 An enlarged display of the correction of FIG. 5;

[0077] FIG. 7 A flow chart for creating a project;

[0078] FIG. 8 A flow chart for the visualisation and calculation of tool correction data;

[0079] FIG. 9 A flow chart for the extrapolation of tool correction values.

DETAILED DESCRIPTION

[0080] FIG. 1 shows a manufacturing plant 1 in which the workpieces 3 are manufactured from the blanks 2, for example by machining with a drill or a milling tool or similar. A measuring device, in this case a coordinate measuring device 4, is used to measure the characteristics of the workpieces 3. These measurement values result in a control chart 5, in which the measurement values are recorded, namely the measurement values 13 and the measurement values 14 of different measured characteristics of the workpiece 3. In the present case, the workpiece 3 has two measured characteristics, namely a bore 6 and a second bore 16. The measurement values of the control chart are transmitted to an analysis unit 7, for example to a computer. The computer analyses the control chart 5. If the values are stable and do not violate a threshold or tolerance value, there is no intervention in the manufacturing process. If the measurement values are not stable, an intervention takes place by further transmitting a correction value, which is determined from the measurement values, to a process control device 8 or directly to the tool machine 9 of the manufacturing plant 1. In the tool machine 9, the tool correction value is used to produce workpieces 3 with a bore 6 or a bore 16, which is within the tolerance range or within default threshold values.

[0081] According to FIG. 2 the measuring machine 9 is shown as well as the coordinate measuring machine 4. The process information 10 is stored in the control chart 5, as already explained. If the control chart is stable, as in the area 5a of the control chart, no action is taken, i.e. process branch 11 continues. If there is a larger deviation of the measurement values from the nominal values, as shown in 5b by the unstable measurement values, the process branch 12, i.e. process intervention is necessary.

[0082] FIG. 3 shows a representation of the measurement values 13 of the outer contour of a trunnion. The diameter is plotted against the time t. The nominal value is 25. If a milling tool used to produce the trunnion wears out over time, a drift occurs, which in the example shown runs against a fixed threshold value of 25.15 (OG) at the time t1. At the time t2 a correction is performed so that the measurement values are back to the nominal value. At the time t3 a further wear of the milling head becomes noticeable and the measurement values show again a drift. At the time t4 there is again a maximum approximation to the threshold value 25.15 (OG), so that at the time t5 a correction follows again.

[0083] As the milling head wears off, the diameter of the milling head becomes smaller so that the diameter of the trunnion becomes larger.

[0084] FIG. 4 shows the measurement values of an inner contour of a slot. The diameter is plotted against the time t. Again, the diameter is plotted against time. When the milling head is worn, the inner contour becomes larger and larger so that the inner contour drifts against a threshold value of 24.8 (UG) at the time t1. A correction is made at the time t2. A further wear of the milling head causes the diameter of the inner bore to decrease again until the time t3, when the measurement value (14) of the diameter of the inner contour exceeds the threshold value 24.85 (UG). At the time t4 a correction is performed.

[0085] In FIG. 5 the diameter is again plotted against time t.

[0086] The measurement values 13 in FIG. 3 are mirrored and dotted at the nominal value 25 (NW). The measurement values 14 of FIG. 4 relating to the slot are shown with a solid line. From these measurement values 13, 14 an average 15 is determined, which is shown as a dotted line in FIG. 5. This average 15 forms the tool correction value.

[0087] As already mentioned, the nominal value NW is entered in FIGS. 3 to 5 at 25. An upper limit OG is 25.15. A lower limit UG is 24.85. The upper tolerance value OT is 25.25 and the lower tolerance value UT is 24.75.

[0088] Instead of the pure averaging as in FIG. 5, a weighting of the characteristics can also be carried out, so that, for example, the tool correction value of the trunnion according to FIG. 3 has a greater weighting than the tool correction value of the slot according to FIG. 4. In this case the average 15 in FIG. 5 is shifted in the direction of the measurement values 13.

[0089] As shown in FIG. 6, averaging has an influence on the correction. FIG. 6 shows how the measurement values 13 of FIG. 3 run against the upper limit value OG=25.15, i.e. there is a continuous drift. The correction does not take place up to the nominal value NW=25 as in FIG. 3 but based on the averaging to a nominal value greater than 25, for example 25.05.

[0090] Similarly, the measurement values 14 of the slot are corrected based on the averaging in such a way that they are slightly overcorrected, i.e. not to the nominal value NW=25, but to a value below 25, i.e. 24.95 for example.

[0091] FIGS. 3 and 4 show the measurement values of various workpieces measured over time t. This means that not a single measurement data record of a characteristic is recorded, but rather the drift is recorded over a certain period of time and/or over a certain number of workpieces or characteristics, for example five or ten characteristics, and then a correction is performed.

[0092] FIGS. 3, 4 and 5 define upper tolerance values OT, lower tolerance values UT, upper threshold values OG and lower threshold values UG. The tolerance values OT and UT are specified by the manufacturing specification. The threshold values OG and UG can be defined.

[0093] FIG. 7 shows a flow chart for the creation of a project. In a first step 17, the corresponding tool corrections are defined for the various tools of a machine tool 9 (not shown in FIG. 7). Furthermore, 3 measured characteristics are defined for the various workpieces. These values of the tools, the tool corrections and the measured characteristics are assigned one to another in step 18. The assignment can be done automatically or manually. In processing stage 19, a link is made between the tools and the measured characteristics and between the tool corrections and the measured characteristics.

[0094] According to this method, each measured characteristic 6, 16 is assigned to at least one machining operation. Furthermore, the measured characteristics are grouped according to tools and/or work offsets.

[0095] When creating a project, a machine tool is selected and all available tools of the machine tool are displayed. Furthermore, a source for the quality data of the workpiece is selected and the quality data are read into the machine tool.

[0096] FIG. 8 shows a flow chart for the calculation and visualisation of tool correction data. According to FIG. 8, parameters such as process parameters or process data of the external factors are also considered in step 18 when calculating the tool correction value.

[0097] If a threshold value (OG, UG) or a tolerance value (OT, UT) of the measurement values of a measured characteristic and/or a parameter is exceeded, an offset correction or a tool correction is carried out.

[0098] Measurement values are archived from past measurements. These are stored and saved as historical measurement values. A tool correction value can be calculated considering the measurement values and/or parameters and considering the past measurements (historical measurement values).

[0099] Furthermore, a visualisation and evaluation of individual measured characteristics and/or parameters and/or tool correction data and/or tool behaviour is carried out. The tools can be represented in graphics upon visualisation.

[0100] When creating a project, a machine tool is selected and all available tools of the machine tool are displayed. In addition, a source for the quality data of the workpiece is selected and the quality data is read into the machine tool.

[0101] FIG. 9 shows a flow chart for the extrapolation of the tool correction values. According to this design example, an extrapolation of the tool correction values is carried out, considering the past measurements. Based on the past measurements, for example, a point can be made as to when a tool is subject to such great wear that it must be replaced. Based on the past measurements, it can be determined, for example, that the tool must be replaced after machining 5,000 workpieces at a time. This value is included in the calculation and an analysis unit decides whether a tool- or work-offset correction is to be carried out.

[0102] It is also possible to transfer tool correction values for a first workpiece to other workpieces.

REFERENCE FIGURES

[0103] 1 Manufacturing plant [0104] 2 Blanks [0105] 3 Workpiece [0106] 4 Coordinate measuring device [0107] 5 Control chart [0108] 5a Stable measurement values [0109] 5b Unstable measurement values [0110] 6 Measured characteristic [0111] 7 Analysis unit [0112] 8 Process control device [0113] 9 Machine tool [0114] 10 Process information [0115] 11 Process branch [0116] 12 Process branch [0117] 13 Measurement value trunnion [0118] 14 Measurement value inside slot [0119] 15 Average [0120] 16 Bore [0121] 17 Process step [0122] 18 Process step [0123] 19 Processing stage [0124] OT Upper tolerance value [0125] UT Lower tolerance value [0126] OG Upper threshold value [0127] UG Lower threshold value [0128] NW Nominal value