A machine tool precision and stiffness retention quick test method and device

Abstract

The application discloses a kind of machine tool precision and rigidity retention quick test method and device, it is related to numerical control machine tool performance test technical field, test method steps are: static and dynamic force loading test is carried out to the machine tool to be measured;The degradation data of each precision and rigidity of machine tool is measured;Accelerated degradation data is converted to conventional working condition;The precision and rigidity retention of each machine tool is calculated.Testing device includes lower platform, electric cylinder, electric cylinder fixed tooling, hooke hinge, upper platform, tool holder clamp, simulation tool holder, for realizing the synchronous loading of static and dynamic force of three directions X, Y, Z of the machine tool to be measured.This method and device are based on simulation and acceleration of actual service condition of vertical machining center, can realize the precision and rigidity retention of vertical machining center in machine, synchronous, quick test, provide test technical support for the improvement of performance retention capability of domestic machine tool.

Description

Technical Field

[0001] The present invention relates to the technical field of CNC machine tool performance testing, in particular to a method and device for quickly testing the accuracy and rigidity retention of a machine tool. Background Art

[0002] Precision and rigidity are two key performance characteristics of machine tools. Precision determines the level of machining accuracy of machine tools, while rigidity determines the strength of machine tool machining capabilities. At present, preliminary explorations have been carried out at home and abroad on the test methods for the precision retention of machine tool functional components, but few people have mentioned the test of machine tool rigidity retention. Patent CN104020716A discloses a detection device for the precision retention of CNC turntables, which realizes the detection of the precision retention of CNC turntables by simulating the actual cutting load on the test bench. Patent CN108972149A discloses a CNC tool holder machining accuracy and rotation accuracy retention test device and detection method, which are used to accurately simulate the cutting force actually applied to the CNC tool holder to test the machining accuracy and rotation accuracy retention. Patent CN109406143A discloses a ball screw pair precision retention test device and method based on real working conditions, which are used to test the degradation of the precision of the ball screw pair of machine tools under real load conditions. Patent CN116804591A discloses a test bench for the accuracy retention of multiple parallel linear guide rails under variable loads, which is used to simultaneously accelerate the accuracy degradation process of multiple linear guide rails.

[0003] After years of development, the initial manufacturing accuracy and rigidity of domestically produced high-end machine tools have gradually approached the levels of advanced foreign products. However, compared with foreign high-end products, the ability of domestically produced machine tools to maintain their initial manufacturing accuracy and rigidity during service (i.e., their precision and rigidity retention) remains relatively weak. During service, the decline in accuracy and rigidity exhibits long, slow, and nonlinear characteristics. Traditional on-site tracking testing methods are inefficient, requiring testing times of months to years.

[0004] Through the analysis of existing research on machine tool precision and stiffness retention testing, it was found that: (1) the current application of relevant testing technologies is limited to functional components such as CNC turntables, CNC tool holders, ball screws and rolling guides, and there is a lack of relevant testing technology research at the machine tool level; (2) the existing testing methods are all carried out on the test bench, and there is a lack of loading devices that can simulate cutting loads on the machine; (3) there is still a lack of research on machine tool stiffness retention testing methods, and no one has mentioned the simultaneous testing method of precision and stiffness retention. At present, there is still a lack of rapid testing methods and devices for the precision and stiffness retention of machine tools in China. Therefore, it is urgent to invent a rapid testing method and device for machine tool precision and stiffness retention to achieve rapid acquisition of the precision and stiffness retention level of the machine tool in a short period of time. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for quickly testing the accuracy and rigidity retention of a machine tool, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for quickly testing the accuracy and stiffness retention of a machine tool, which realizes the synchronous and rapid testing of the accuracy and stiffness retention of the entire machine tool, comprising the following steps:

[0007] Step 1: Perform static and dynamic force loading tests on the machine tool under test;

[0008] Step 2: Measure the degradation data of various precision and stiffness of the machine tool;

[0009] Step 3: Convert the accelerated degradation data to normal working conditions;

[0010] Step 4: Calculate the accuracy and rigidity retention of the tool.

[0011] The present invention further illustrates that, according to the maximum feed speed v of each axis of the machine tool max , Maximum feed resistance F max and the maximum spindle speed V max , set 3 loading load levels, load the machine tool in sequence according to the 3 loading load levels, and set the loading time of each load level to H;

[0012] Among them, the three loading load levels are S1, S2, and S3, and H is 40h.

[0013] The present invention further illustrates that measurements are performed at equal time intervals, the measurement interval is set to T, loading is stopped every time T time has passed, and instruments are used to measure and record the various accuracies and stiffnesses of the machine tool, including the positioning accuracy of each of the X, Y, and Z axes, the straightness in the X-axis Y direction, the straightness in the X-axis Z direction, the straightness in the Y-axis X direction, the straightness in the Y-axis Z direction, the straightness in the Z-axis X direction, the straightness in the Z-axis Y direction, and the degradation data of the static stiffness of each of the X, Y, and Z axes;

[0014] T is set to 8h, and measurements are taken 5 times under each load level. After the data measurement is completed, loading is continued, and loading and measurement are repeated until the total loading time reaches the set 120h, and the test is terminated.

[0015] The present invention further illustrates that the specific method of step three is:

[0016] Power law function Fit the degradation trajectories of various precision and stiffness to obtain the degradation functions of various precision and stiffness over time under various accelerated stress levels;

[0017] Based on the three-stress acceleration model, the relationship between the degradation trajectory parameters a, b and the stress level is obtained, and the values ​​of the parameters a and b of the degradation trajectory equations of various precision and stiffness of the machine tool under conventional working conditions are solved, realizing the conversion of accelerated degradation data to conventional degradation data.

[0018] The present invention further illustrates that the three-stress acceleration model is:

[0019] lnη(α0,α1,α2,α3,α4,α5)=lnα0-α1ζ1-α2ζ2-α3ζ3-α4ζ1ζ2-α5ζ1ζ3

[0020] Among them, η is the degradation trajectory parameter, ζ1, ζ2, and ζ3 represent the stress levels of feed rate, static force, and dynamic force, respectively. α0, α1, α2, α3, α4, and α5 are unknown parameters, which are solved based on the degradation data at each stress level.

[0021] The present invention further illustrates that the step 4 uses the following formula to calculate the various precisions and rigidity retention of the tool machine:

[0022]

[0023] Where, is the degree-keeping function; is the degradation function under normal working conditions; is the failure threshold of each accuracy and stiffness.

[0024] A rapid testing device for machine tool accuracy and rigidity retention comprises a lower platform, an electric cylinder, an electric cylinder fixing fixture, a Hooke's hinge, an upper platform, a tool holder fixture, and a simulated tool holder, and is used to achieve synchronous loading of static and dynamic forces in the X, Y, and Z directions of the machine tool under test.

[0025] The present invention further illustrates that the tool holder fixture includes a three-dimensional force sensor, a locking nut, a bearing seat, a tool holder sleeve, a tool holder end cover, and a bearing;

[0026] Among them, the three-dimensional force sensor is fixed to the upper platform by bolts, the bearing seat is connected to the three-dimensional force sensor by bolts, the tool holder sleeve and the bearing seat are connected by bearings, and the bearings are fixed by the locking nut, the tool holder sleeve is connected to the simulated tool holder by threads, and the simulated tool holder is further fixed by the tool holder end cover.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) This invention proposes a full-process method for rapid testing of various precision and stiffness retention of machine tools based on static and dynamic load loading. It covers the test method, data processing method, and evaluation method. It can realize the synchronous and rapid testing of the precision and stiffness retention of the entire machine tool, significantly reducing time cost and material consumption.

[0029] 2) Based on the above test method, the present invention designs a rapid test device for the accuracy and stiffness retention of a vertical machining center from the perspective of simulating actual cutting loads, which can realize on-machine synchronous loading of the static and dynamic forces in the three directions of X, Y, and Z of the machine tool being tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 This is a flow chart of the rapid testing method for machine tool accuracy and rigidity retention;

[0032] Figure 2 This is a schematic diagram of the overall structure of a rapid testing device for machine tool accuracy and rigidity retention;

[0033] Figure 3 This is a schematic diagram of the tool holder fixture structure of a rapid testing device for machine tool accuracy and rigidity retention;

[0034] In the figure: 1. Lower platform; 2. Electric cylinder; 3. Electric cylinder fixing fixture; 4. Hooke's hinge; 5. Upper platform; 6. Tool holder fixture; 7. Simulated tool holder; 8. Three-dimensional force sensor; 9. Locking nut; 10. Bearing seat; 11. Tool holder sleeve; 12. Tool holder end cover; 13. Bearing. DETAILED DESCRIPTION

[0035] The following is a non-limiting detailed description of the technical solutions of the present invention in conjunction with preferred embodiments and the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0036] Taking the rapid test of various precision and rigidity retention of a three-axis vertical machining center as an example, the implementation mode of the present invention is described in detail.

[0037] See also Figure 1 The present invention provides a technical solution: a method for quickly testing the accuracy and rigidity retention of a machine tool, comprising the following steps:

[0038] Step 1: Perform static and dynamic force loading tests on the machine tool under test at multiple loading levels according to the maximum operating parameters of the machine tool;

[0039] Step 2: measuring the degradation data of various precision and rigidity of the machine tool at a set time;

[0040] Step 3: Use function fitting to calculate the degradation trajectory and convert the accelerated degradation data to normal working conditions;

[0041] Step 4: Calculate the accuracy and stiffness retention of the tool according to the degradation data.

[0042] See also Figure 2 The test device used to implement the above test method includes a lower platform 1, an electric cylinder 2, an electric cylinder fixing fixture 3, a Hooker hinge 4, an upper platform 5, a tool holder fixture 6, and a simulated tool holder 7. It can realize the synchronous loading of static and dynamic forces in the three axes of X, Y, and Z of the machine tool under test, meeting the requirements for rapid testing of the accuracy and rigidity retention of the above machine tools.

[0043] See also Figure 3 The tool holder fixture 6 includes a three-dimensional force sensor 8, a locking nut 9, a bearing seat 10, a tool holder sleeve 11, a tool holder end cover 12, and a bearing 13;

[0044] The three-dimensional force sensor 8 is fixed to the upper platform 5 by bolts, and the bearing seat 10 is connected to the three-dimensional force sensor 8 by bolts. The tool holder sleeve 11 and the bearing seat 10 are connected by a bearing 13, and the bearing 13 is fixed by a locking nut 9. The tool holder sleeve 11 is connected to the simulated tool holder 7 by a threaded connection, and the simulated tool holder 7 is further fixed by the tool holder end cover 12.

[0045] Furthermore, when the test device is in use, the lower platform 1 is fixed on the machine tool workbench, the simulated tool holder 7 is connected to the machine tool spindle, and the Hook hinge 4 is driven by three electric cylinders 2 to drive the upper platform 5 and the simulated tool holder 7 to synchronously apply static and dynamic loads in the X, Y, and Z directions to the machine tool, thereby completing the installation of the test device.

[0046] Specifically, the specific method for performing static and dynamic force loading tests on the machine tool under test in step 1 is:

[0047] Install the test device in this solution on a three-axis vertical machining center. For details, refer to the above test device installation content.

[0048] According to the operating parameters of the maximum feed speed, maximum feed resistance and maximum spindle speed of the machine tool X, Y and Z axes, three loading load levels are set, namely S1, S2 and S3. Table 1 shows the method for selecting the loading load level values.

[0049] Table 1 Method for selecting the numerical value of loading level

[0050]

[0051] Preferably, v max Set the maximum feed speed of each axis of X, Y, and Z to 36m / min, F max Set the maximum feed resistance of X, Y, and Z axes to 3000N, 3000N, and 2000N respectively. max Set the maximum spindle speed to 6000 rpm;

[0052] Specifically, in S1, the feed speeds of the X, Y, and Z axes were set to 9, 9, and 9 m / min, respectively; the static forces of the X, Y, and Z axes were set to 750, 750, and 500 N, respectively; the amplitudes of the dynamic forces of the X, Y, and Z axes were set to 150, 150, and 100 N, respectively; and the frequencies of the dynamic forces of the X, Y, and Z axes were set to 10, 10, and 10 Hz, respectively;

[0053] In S2, the X, Y, and Z axis feed speeds were set to 18, 18, and 18 m / min, respectively; the X, Y, and Z axis static forces were set to 1500, 1500, and 1000 N, respectively; the X, Y, and Z axis dynamic force amplitudes were set to 300, 300, and 200 N, respectively; and the X, Y, and Z axis dynamic force frequencies were set to 20, 20, and 20 Hz, respectively;

[0054] In S3, the X, Y, and Z axis feed speeds were set to 27, 27, and 27 m / min, respectively; the X, Y, and Z axis static forces were set to 2250, 2250, and 1500 N, respectively; the X, Y, and Z axis dynamic force amplitudes were set to 450, 450, and 300 N, respectively; and the X, Y, and Z axis dynamic force frequencies were set to 30, 30, and 30 Hz, respectively;

[0055] The machine tool is loaded in sequence according to three loading levels, and the loading time of each load level is set to H, preferably H is 40h.

[0056] The specific method for measuring the degradation data of various precision and stiffness of the machine tool in step 2 is as follows:

[0057] Perform measurements at equal time intervals, set the measurement interval to T, stop loading after each loading time T, and use instruments such as laser interferometers and static stiffness testers to measure and record the degradation data of various precision and stiffness of the machine tool, including the positioning accuracy of each axis of X, Y, and Z, the straightness of the X-axis in the Y direction, the straightness of the X-axis in the Z direction, the straightness of the Y-axis in the X direction, the straightness of the Y-axis in the Z direction, the straightness of the Z-axis in the X direction, the straightness of the Z-axis in the Y direction, and the degradation data of the static stiffness of each axis of X, Y, and Z;

[0058] For example, if T is set to 8h, and each load level is loaded for 40h, measurements are taken 5 times under each load level. After the data measurement is completed, loading is continued, and loading and measurement are repeated until the total loading time reaches the set 120h, and the test is terminated.

[0059] The specific method for converting accelerated degradation data to normal operating conditions in step 3 is:

[0060] According to the degradation data measured in step 2, the power law function is used to fit the degradation trajectory of each accuracy and stiffness to obtain the degradation function of each accuracy and stiffness over time under each accelerated stress level. Where a and b are unknown parameters, which are solved based on the degradation data;

[0061] Using the three-stress acceleration model:

[0062] lnη(α0,α1,α2,α3,α4,α5)=lnα0-α1ζ1-α2ζ2-α3ζ3-α4ζ1ζ2-α5ζ1ζ3

[0063] The relationship between the degradation trajectory parameters a, b and the stress level is obtained, and the values ​​of the parameters a and b of the degradation trajectory equations of the machine tool's various precision and stiffness under normal working conditions are solved to realize the conversion of accelerated degradation data to normal working condition degradation data; where η is the degradation trajectory parameter; ζ1, ζ2, and ζ3 represent the stress levels of feed speed, static force, and dynamic force, respectively; α0, α1, α2, α3, α4, and α5 are unknown parameters, which are solved based on the degradation data under various stress levels.

[0064] The specific method for calculating the accuracy and rigidity retention of the tool in step 4 is as follows:

[0065] According to the degradation trajectory equations of various machine tool precision and stiffness under normal working conditions obtained in step 3, the following formula is used to calculate the various machine tool precision and stiffness retention:

[0066]

[0067] Where, is the degree-keeping function; is the degradation function under normal working conditions; is the failure threshold of each accuracy and stiffness.

[0068] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will appreciate that modifications may be made to the technical solutions described in the aforementioned embodiments, or that some of the technical features may be replaced with equivalents. Such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for quickly testing the accuracy and rigidity retention of machine tools, characterized by: The following steps are involved: Step 1: Perform static and dynamic force loading tests on the machine tool under test; set three loading load levels based on the operating parameters of the maximum feed speed, maximum feed resistance, and maximum spindle speed of each axis of the machine tool, and load the machine tool in sequence according to the three loading load levels. The loading time for each load level is set to H; Step 2: Measure the degradation data of various precision and stiffness of the machine tool; perform equal time interval measurement, set the measurement interval time to T, stop loading every T time, use instruments to measure and record the degradation data of various precision and stiffness of the machine tool; continue loading after the data measurement is completed, and repeat the loading and measurement until the total loading time reaches the set value of 3H, and then end the test; Step 3: Convert the accelerated degradation data to normal working conditions; use the power law function Fit the various precision and stiffness degradation trajectories to obtain the degradation functions of various precision and stiffness over time under various accelerated stress levels; based on the three-stress acceleration model, obtain the relationship between the degradation trajectory parameters a, b and the stress level, solve the values ​​of the parameters a, b of the machine tool's precision and stiffness degradation trajectory equations under normal working conditions, and realize the conversion of accelerated degradation data to normal working condition degradation data; the three-stress acceleration model is: ； in, η is the degradation trajectory parameter, ζ 1. ζ 2. ζ 3 represent the stress levels of feed rate, static force and dynamic force respectively, α 0, α 1, α 2, α 3. α 4. α 5 is an unknown parameter, which is solved based on the degradation data at each stress level; Step 4: Calculate the various precisions and rigidity retention of the tool machine. Use the following formula to calculate the various precisions and rigidity retention of the tool machine: ； Where, is the degree-keeping function; is the degradation function under normal working conditions; is the failure threshold of each accuracy and stiffness.

2. A method for rapidly testing the accuracy and rigidity retention of a machine tool according to claim 1, characterized in that: The degradation data includes the positioning accuracy of each axis, the straightness of each axis in the other two directions, and the static stiffness of each axis.

3. A rapid testing device for machine tool accuracy and rigidity retention, suitable for the testing method according to any one of claims 1-2, characterized in that: The device comprises a lower platform (1), an electric cylinder (2), an electric cylinder fixing fixture (3), a Hooke's hinge (4), an upper platform (5), a tool holder fixture (6), and a simulated tool holder (7), and is used to realize synchronous loading of static and dynamic forces in three directions (X, Y, and Z) of a machine tool under test.

4. A rapid testing device for machine tool accuracy and rigidity retention according to claim 3, characterized in that: The tool handle fixture (6) includes a three-dimensional force sensor (8), a locking nut (9), a bearing seat (10), a tool handle sleeve (11), a tool handle end cover (12), and a bearing (13); The three-dimensional force sensor (8) is fixed to the upper platform (5) by bolts, the bearing seat (10) is connected to the three-dimensional force sensor (8) by bolts, the tool holder sleeve (11) and the bearing seat (10) are connected by a bearing (13), and the bearing (13) is fixed by the locking nut (9), the tool holder sleeve (11) is connected to the simulated tool holder (7) by a threaded connection, and the simulated tool holder (7) is further fixed by the tool holder end cover (12).

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