A calculation model for the depth of laser processing groove of mechanical seal dynamic pressure groove and its construction method

Abstract

The present invention discloses a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove and a construction method thereof, which are used to predict the groove depth under different process parameters. The method comprises the following steps: firstly, the groove depth data under different laser energy densities are obtained through experiments, and a fitting relationship between the groove depth and the laser energy density is obtained; secondly, based on the characteristics of pulsed lasers, the principle of graphic filling and the scanning strategy of a fiber laser engraving machine, a heating time calculation model for laser processing of dynamic pressure grooves is established; finally, a groove depth calculation model for laser processing of dynamic pressure grooves is constructed by combining the fitting relationship and the heating time calculation model. The method can realize the prediction of groove depth under different process parameters, with a small number of experiments, simple operation, high prediction accuracy and wide applicability.

Description

Technical Field

[0001] The invention relates to a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove and a construction method thereof, belonging to the technical field of mechanical seal laser processing. Background Art

[0002] Laser processing has unique advantages in processing various metal and non-metal materials with high hardness, high brittleness and high melting point, and has the characteristics of small heat-affected zone, strong flexibility and high processing efficiency. It has become a mainstream processing method for dynamic pressure groove processing on the seal end face. However, the existing laser processing technology can generally only control the processing accuracy of the dynamic pressure groove depth to the micron level. For dynamic pressure grooves with a depth of several microns (shallow grooves), a slight change in the groove depth will have a significant impact on the sealing performance. Therefore, the processing accuracy of the dynamic pressure groove depth plays an important role in mechanical seals.

[0003] The traditional method of controlling the groove depth of the dynamic pressure groove laser processing often adopts the experimental method, that is, for a certain sealing ring material, a laser engraving machine is used to first process the dynamic pressure groove with a certain set of process parameters, and then the groove depth of the dynamic pressure groove is measured using a surface roughness profile meter. If the actual groove depth deviates greatly from the target groove depth, the process parameters need to be adjusted to repeat the above process, and finally the actual groove depth reaches the target groove depth. The disadvantage of this method is that the groove depth is closely related to the process parameters, material performance parameters, etc., and repeated experiments are required to reach the target groove depth. In addition, when the sealing ring material or the target groove depth changes, repeated experiments are still required, and the experimental cost is high and the processing efficiency is low.

[0004] In recent years, some researchers have conducted research on laser precision machining of dynamic pressure grooves. Mao Wenyuan conducted ACE (Alternating Conditional Expectations) optimization research on laser machining of spiral grooves in dry gas seals and obtained three groups of spiral grooves that meet the requirements of 9.8μm≤h g ≤10.2μm, Ra≤0.8μm design control target process parameters. Wang Yan conducted research on ultrafast laser precision machining of dry gas seals based on ordered modeling design, and achieved precision machining of grooves with a groove depth amplitude fluctuation range of 2μm and a maximum roughness of 0.59μm. However, the above studies have failed to establish a groove depth calculation model under different process parameters. The main reason is that there is a strong nonlinear relationship between the groove depth and the process parameters and material performance parameters. Therefore, there is currently no universal mathematical model for predicting the groove depth. The above research shows that at present, there are few reports on the results of the calculation model of the groove depth of mechanical seal dynamic pressure grooves at home and abroad. Therefore, it is of great significance to carry out research on the calculation model of the groove depth of mechanical seal dynamic pressure grooves by laser processing. Summary of the invention

[0005] In view of this, the present invention aims to provide a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove and a construction method thereof.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] (1) Determine the values ​​of the four process parameters: repetition frequency, scanning speed, filling spacing, and marking times, as well as the range of laser power [P min , P max ];

[0008] (2) The experimental data of groove depth under different laser energy densities were obtained by processing and measuring the dynamic pressure groove, and the fitting relationship between groove depth and laser energy density was obtained by analyzing the experimental data;

[0009] (3) Based on the characteristics of pulsed laser, the principle of pattern filling and the scanning strategy of fiber laser marking machine, a heating time calculation model for dynamic pressure groove laser processing is established;

[0010] (4) Calculating the heating time under a set of fixed process parameters according to the heating time calculation model;

[0011] (5) When the laser energy density is greater than the ablation threshold of the material, the groove depth is proportional to the heating time at the same laser energy density. Combined with steps (2), (3) and (4), a groove depth calculation model for dynamic pressure groove laser processing is established.

[0012] Preferably, the repetition frequency of step (1) is 1 to 100 kHz, the scanning speed is 1 to 10000 mm / s, the filling spacing is 1 to 100 μm, the number of marking times is 1 to 100 times, and the laser power is 1 to 100 W.

[0013] Preferably, the fitting method of the groove depth and the laser energy density is a linear fitting or a nonlinear fitting, and the fitting accuracy of the groove depth and the energy density must be guaranteed. Generally speaking, when the laser energy density is greater than the ablation threshold of the material, there is a linear relationship between the groove depth and the laser energy density, and a linear fitting can be directly used. If there is a nonlinear relationship between the two, a nonlinear fitting is used to finally obtain a fitting relationship between the groove depth and the laser energy density.

[0014] Preferably, the pattern filling method is unidirectional or bidirectional filling, and the filling angle is 0 to 180°.

[0015] Preferably, the dynamic pressure groove has a depth of 1 to 500 μm.

[0016] Preferably, the heating time calculation model for dynamic pressure groove laser processing is:

[0017]

[0018] Where: tht is the heating time; n is the number of markings; τ is the pulse width; f is the repetition frequency; L mark is the marking length; v scan is the scanning speed.

[0019] Preferably, the heating time under a set of fixed process parameters is calculated, and the selected process parameters are the repetition frequency f0, the scanning speed v scan0 , filling spacing S0, marking times n0, and laser power range [P min , P max ], where the selected laser power P min It must be greater than the minimum power required for material gasification.

[0020] Preferably, the end surface shape of the dynamic pressure groove is not limited, including rectangular grooves, triangular grooves, spiral grooves, T-shaped grooves, U-shaped grooves, herringbone grooves, straight grooves, arc grooves and other groove shapes.

[0021] Preferably, the groove depth calculation model of the dynamic pressure groove laser processing is:

[0022]

[0023] Advantages of the present invention: The groove depth calculation model construction method proposed in the present invention has the characteristics of simple process, less number of tests, strong operability, wide application range, etc. The constructed dynamic pressure groove depth calculation model can quickly predict the groove depth values ​​of different process parameters, and has the advantages of high prediction accuracy and fast calculation speed.

[0024] The beneficial effects of the present invention are as follows: the present invention can effectively realize the quantitative control of the groove depth of the dynamic pressure groove. Within the limited process parameter range, any five process parameter values ​​can be given to quickly predict the groove depth value under the process parameters, which can effectively improve the processing efficiency and reduce the processing cost. It can also provide reference and theoretical guidance for the laser processing of various dynamic pressure grooves under different target groove depths. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the present invention;

[0026] Figure 2 The effect of different laser energy density on the depth of the dynamic pressure groove;

[0027] Figure 3 Comparison between the calculated groove depth results and the experimental results. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] Embodiment 1: A mechanical seal dynamic pressure groove laser processing groove depth calculation model and its construction method, comprising the following steps:

[0030] (1) Determine the values ​​of the four process parameters: repetition frequency, scanning speed, filling spacing, and marking times, as well as the range of laser power [P min , P max ];

[0031] (2) The experimental data of groove depth under different laser energy densities were obtained by processing and measuring the dynamic pressure groove, and the fitting relationship between groove depth and laser energy density was obtained by analyzing the experimental data;

[0032] (3) Based on the characteristics of pulsed laser, the principle of pattern filling and the scanning strategy of fiber laser marking machine, a heating time calculation model for dynamic pressure groove laser processing is established;

[0033] (4) Calculating the heating time under a set of fixed process parameters according to the heating time calculation model;

[0034] (5) When the laser energy density is greater than the ablation threshold of the material, the groove depth is proportional to the heating time at the same laser energy density. Combined with steps (2), (3) and (4), a groove depth calculation model for dynamic pressure groove laser processing is established.

[0035] Example 2: Determine process parameters: repetition frequency f0, scanning speed v scan0 , filling spacing S0, marking times n0, laser power range [P min , P max ] Among them, the selected laser power P min It needs to be greater than the minimum power required for material gasification. According to the determined process parameters, the fiber laser marking machine is used to carry out dynamic pressure groove processing under different laser powers, and the groove depth is measured using a surface roughness profile shape measuring machine to obtain the groove depth data under different laser powers.

[0036] In order to obtain the relationship between groove depth and laser energy density, the laser power needs to be converted into laser energy density. The expression of laser energy density is:

[0037]

[0038] Where: P is the laser power; r0 is the focus spot radius; f is the repetition frequency;

[0039] The experimental data is processed by linear or nonlinear fitting to obtain the fitting relationship between the groove depth and the laser energy density. For the convenience of description, it is assumed that there is a linear relationship between the groove depth and the laser energy density, and the fitting relationship is:

[0040]

[0041] In the formula: a, b are the intercept and slope of the fitting relationship respectively;

[0042] Assume that the ablation power threshold when the material just vaporizes is P th , and its corresponding ablation energy threshold is F th , then when P≤P th or F≤F th When the groove depth h g = 0 μm. Let h in formula (2) g0 = 0μm, we can get P th 、F th The calculation formula is as follows:

[0043]

[0044]

[0045] The depth of the dynamic pressure groove is related to the energy received by the material surface, that is, it is related to the laser energy density and heating time. The parameters that affect the heating time include repetition frequency, pulse width, scanning speed, and marking length. The calculation expression of the heating time is:

[0046]

[0047] Where: n is the number of markings; τ is the pulse width; f is the repetition frequency; v scan is the scanning speed; L mark Marking length.

[0048] It should be noted that the marking length consists of two parts: the filling line length and the boundary line length. However, during the processing of the dynamic pressure groove, the groove depth is formed by a high-energy density laser beam scanning each filling line in turn. Therefore, when calculating the marking length, the boundary line length can be ignored and only the filling line length can be considered.

[0049] Select repetition frequency f0, scanning speed v scan0 , filling spacing S0, marking times n0, laser power P0 (P min <P0<P max ), the actual groove depth under this set of process parameters is h g0 , the marking length is L mark0 , use formula (5) to calculate the heating time t under this set of process parameters ht0 :

[0050]

[0051] When the laser power is sufficient to cause the material to vaporize, the groove depth is proportional to the absorbed energy. Under the same laser power, the longer the heating time, the greater the groove depth, that is, t ht ∝hg , then:

[0052]

[0053] Combining formulas (2) to (7), the calculation model of the dynamic pressure groove depth can be obtained, and its expression is:

[0054]

[0055] Embodiment 3: The present invention is further described by taking a rectangular dynamic pressure groove as an example.

[0056] The sealing ring material of this embodiment is SiC, the dynamic pressure groove pattern is rectangular, the size is 3×3mm, the pattern filling angle is 90°, and the process parameters are: repetition frequency f0=30kHz, scanning speed v scan0 =432.19 mm·s -1 , filling spacing S0 = 15 μm, marking times n0 = 5 times, laser power range [P min , P max ]=2.8~17.11W.

[0057] According to the determined process parameters, the LM-20 fiber laser engraving machine was used to carry out dynamic pressure groove processing under different laser powers, and the SEF-680 surface roughness profile shape measuring machine was used to measure the groove depth, and the experimental data of groove depth under different laser powers were obtained. At the same time, it can be seen from formula (1) that the laser energy density corresponding to the laser power of 2.8~17.11W is 9.51~58.12J / cm 2 , we can get the influence of different laser energy density on the groove depth, such as Figure 2 As shown in the figure, it can be seen that there is a linear relationship between the groove depth and the energy density. According to formula (2), through linear fitting, we get: intercept a = -7.51257, slope b = 0.879543.

[0058] The ablation power threshold P is calculated by equations (3) and (4): th =2.52W, ablation energy threshold F th =8.56J / cm 2 .

[0059] The filling angle of the rectangular dynamic pressure groove is 90°, that is, the length of each filling line is equal, so the calculation expression of the rectangular dynamic pressure groove heating time is:

[0060]

[0061] Where: L is the length of the dynamic pressure groove; D is the width of the dynamic pressure groove; S is the filling spacing; fix(L / S) represents the rounded value of the L / S calculation result.

[0062] Select process parameters: repetition frequency f0 = 30kHz, scanning speed v scan0 =432.19 mm·s -1 , filling spacing S0 = 15μm, marking times n0 = 5 times, laser power P0 = 7.28W, the groove depth h under this set of process parameters g0 =14.43 μm. The heating time t under this set of process parameters is calculated using formula (6): ht0 =4.558412×10 -3 s.

[0063] The calculation model of the dynamic pressure groove depth can be expressed as:

[0064]

[0065] Figure 3 The figure shows the comparison between the calculated and experimental results of the groove depth under different filling spacings. Process parameters: laser power 13.88W, repetition frequency 30kHz, scanning speed 361.52mm / s, marking times 4 times, and filling spacing 6-21μm. It can be seen from the figure that with the increase of the filling spacing, the calculated groove depth and the experimental groove depth gradually decrease, and the two groove depths have the same change trend with the filling spacing. In addition, it can be seen from the figure that under the same filling spacing, the difference between the calculated groove depth and the experimental groove depth is small. Among them, the calculated groove depth results under the filling spacing of 6-21μm are 80.34-23.16μm, and the experimental groove depth results are 87.15-25.09μm. The maximum error (absolute value) is 10.57%, and the minimum error (absolute value) is only 5.67%. It shows that the dynamic pressure groove depth calculation model proposed in the present invention has a high calculation accuracy.

[0066] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and invention of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove, characterized in that: The method steps are as follows: (1) Determine the values ​​of the four process parameters: repetition frequency, scanning speed, filling spacing, and marking times, as well as the range of laser power. P min , P max ]; (2) The experimental data of groove depth under different laser energy densities were obtained by processing and measuring the dynamic pressure groove, and the fitting relationship between groove depth and laser energy density was obtained by analyzing the experimental data; (3) Based on the characteristics of pulsed laser, the principle of pattern filling and the scanning strategy of the fiber laser marking machine, a heating time calculation model for dynamic pressure groove laser processing is established; The heating time calculation model for the dynamic pressure groove laser processing is: ； Where: t ht is the heating time; n is the number of markings; τ is the pulse width; f is the repetition frequency; L mark is the marking length; v scan is the scanning speed; (4) Calculate the heating time under a set of fixed process parameters according to the heating time calculation model; (5) When the laser energy density is greater than the ablation threshold of the material, the groove depth is proportional to the heating time at the same laser energy density. Combined with steps (2), (3) and (4), a groove depth calculation model for dynamic pressure groove laser processing is established; The calculation model of the groove depth of the dynamic pressure groove laser processing is: ； Where: h g To calculate the groove depth; f is the repetition frequency; P is the laser power; n is the number of markings; v scan is the scanning speed; L mark is the marking length; r 0 is the focus spot radius; τ is the pulse width; t ht0 For a set of known process parameters (repetition frequency f 0. Scanning speed v scan0 , fill spacing S 0. Marking times n 0) The action time required to process a certain size of dynamic pressure groove, P th is the ablation power threshold.

2. The method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove according to claim 1, characterized in that: The repetition frequency is 1-100kHz, the scanning speed is 1-10000mm / s, the filling spacing is 1-100μm, the number of marking times is 1-100 times, and the laser power is 1-100W.

3. The method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove according to claim 1, characterized in that: The fitting method of the groove depth and the laser energy density is linear fitting or nonlinear fitting.

4. The method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove according to claim 1, characterized in that: The graphic filling is unidirectional or bidirectional filling, and the filling angle is 0~180°.

5. The method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove according to claim 1, characterized in that: The dynamic pressure groove has a depth of 1 to 500 μm.

6. The method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove according to claim 1, characterized in that: The heating time under a certain set of fixed process parameters is calculated, and the selected process parameter is the repetition frequency f 0. Scanning speed v scan0 , fill spacing S 0. Number of markings n 0, and the laser power range [ P min , P max ], where the selected laser power P min It must be greater than the minimum power required for material gasification.

7. The method for constructing a groove depth calculation model for laser processing of a mechanical seal dynamic pressure groove according to claim 1, characterized in that: The end surface shape of the dynamic pressure groove is not limited, and can be any one of a rectangular groove, a triangular groove, a spiral groove, a T-shaped groove, a U-shaped groove, a herringbone groove, a straight groove, and an arc groove.

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