A method for improving the numerical control machining accuracy of Roots rotor shafts

Abstract

The present invention relates to the technical field of the processing of Roots pump rotor shafts, and provides a method for improving the numerical control machining accuracy of Roots rotor shafts. An initial profile of the rotor shaft profile is generated in CAD, and the tool radius is obtained based on the initial profile; the profile is evenly divided to obtain a number of profile points; a coordinate system is established with the geometric center of the initial profile as the origin, and the coordinates of the profile points are extracted and imported into CAD to generate the profile to be machined; the error between the initial profile and the profile to be machined is judged based on the tool radius to obtain an error result, so as to judge whether the profile to be machined is qualified; if it is qualified, the coordinates of the profile points are copied into the machining program to control the numerical control equipment to machine according to the ratio of 1:1 with the profile to be machined; otherwise, the profile is evenly divided again, and then the above steps are repeated until the profile to be machined is qualified, ensuring the accuracy of the end face profile of the rotor shaft, making the surface texture of its profile more uniform and the profile tolerance of the end face profile meet the preset requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of the processing of Roots pump rotor shafts, and particularly relates to a method for improving the numerical control machining accuracy of Roots rotor shafts. Background Art

[0002] With the rapid development needs of the national industries such as chips, semiconductors, and photovoltaics, the vacuum pump industry that provides production vacuum conditions for them has also developed accordingly. According to the national requirements for environmental protection and energy conservation, the technology of the vacuum pump industry has gradually developed towards the energy-saving and environmentally friendly dry pump technology. As a component of the widely used dry vacuum pump unit, the Roots vacuum pump uses the inlet vacuum suction generated by two completely identical Roots rotors (referred to as rotors) during the conjugate rotation process to transport the gas medium to the outlet. The core technology of this process is the Roots rotor, and the core of the Roots rotor is the profile curve.

[0003] The rotor profile curve affects the overall operating performance of the pump. To machine a Roots rotor with higher precision, a high-precision Roots rotor shaft needs to be machined. However, traditional planers or other numerical control machine tools adopt a machining method of presetting the machining end face profile curve trajectory. When high-precision requirements appear, the precision of the tool path of this method cannot meet the requirements, not only making the surface texture of the profile curve contour of the Roots rotor shaft uneven, but also the profile tolerance not meeting the preset requirements.

[0004] Therefore, a method capable of improving the machining accuracy of the end face profile curve of the Roots pump rotor shaft needs to be proposed. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for improving the numerical control machining accuracy of Roots rotor shafts to solve the problems that when high-precision requirements appear, the precision of the tool path of the existing machining method cannot meet the requirements, the surface texture of the profile curve contour of the Roots rotor shaft is not uniform enough, and the profile tolerance cannot meet the requirements.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for improving the numerical control machining accuracy of Roots rotor shafts, which includes the following steps:

[0008] Step S1, generate the initial contour of the rotor shaft profile curve in CAD, obtain the tool radius of the numerical control equipment based on the initial contour; perform equal division processing on the initial contour to obtain a number of contour points;

[0009] Step S2, establish a coordinate system with the geometric center of the initial contour as the origin, extract the coordinates of the contour points, import them into CAD to generate the contour to be machined; judge the error between the initial contour and the contour to be machined based on the tool radius to obtain an error result, and judge whether the contour to be machined is qualified based on the error result;

[0010] Step S3, if the contour to be machined is qualified, copy the coordinates of the contour points into the machining program of the numerical control equipment, and control the numerical control equipment to perform machining operations in a 1:1 ratio with the contour to be machined to obtain a finished workpiece;

[0011] Step S4, if the contour to be machined is unqualified, perform secondary equal division processing on the initial contour in CAD, and then repeat the above steps until the contour to be machined is qualified.

[0012] Preferably, in the step S1, the process of generating the initial contour of the rotor shaft profile includes:

[0013] Design a Roots rotor shaft profile model in 3D software to obtain the 3D model diagram of the Roots rotor shaft profile. Use the 2D conversion function of the 3D software to convert the 3D model diagram of the Roots rotor shaft profile into a CAD 2D model diagram of the rotor shaft end face profile in a 1:1 ratio, and use the contour of the rotor shaft end face profile in the CAD 2D model diagram as the initial contour.

[0014] Preferably, in the step S1, the steps of obtaining the tool radius include:

[0015] Step S11, starting from the geometric center of the initial contour, extend a number of rays at fixed angular intervals. The rays divide the initial contour into several segments to obtain several equally divided points;

[0016] Step S12, establish a 2D coordinate system with the geometric center of the initial contour as the coordinate origin, and extract the coordinate data of the equally divided points;

[0017] Step S13, import the coordinate data into the machining program, preset a ball cutter radius, start the program for trial operation, and obtain the ball cutter radius value that does not cause undercutting with the new contour formed by the coordinate data, and use this as the tool radius of the numerical control equipment.

[0018] Preferably, in the step S1, the profile equal division processing includes:

[0019] Perform equal arc length equal division processing on the initial contour to obtain a number of segmented points, and use the segmented points as the contour points of the initial contour.

[0020] Preferably, in the step S2, a two-dimensional coordinate system is established with the geometric center of the initial contour as the coordinate origin. The two-dimensional coordinates of the contour points are extracted in the order from the first quadrant to the fourth quadrant, and the extracted two-dimensional coordinates are re-imported into the CAD two-dimensional model drawing to generate a contour to be machined. An error result is obtained through error measurement in the vector direction, and it is judged whether the contour to be machined is qualified based on the error result.

[0021] Preferably, the error measurement in the vector direction includes:

[0022] In the CAD two-dimensional model drawing, using the contour points as the tangent points of the ball cutter of the numerical control device, a number of ball cutter circles are drawn in sequence; then the vector difference between the highest point of the non-machinable blind area between two adjacent ball cutter circles and the initial contour is measured, and the vector difference is used as the error result.

[0023] Preferably, in the step S3, if the error result is within the preset error range, the contour to be machined is qualified; the two-dimensional coordinates of the extracted contour points are copied into the numerical control device processing program, and the processing program adds a Z value to the two-dimensional coordinates. Two different Z values are added to the same two-dimensional coordinate respectively, and the two Z values added between different two-dimensional coordinates are the same. The processing program controls the movement of the numerical control device at the contour points in the order from the first quadrant to the fourth quadrant in the two-dimensional coordinate system, and controls the three-axis numerical control device to make axial movements back and forth between the same two-dimensional coordinates through the Z value, so as to realize contour machining in a ratio of 1:1 with the contour to be machined and obtain a workpiece finished product.

[0024] Preferably, in the step S4, if the error result is not within the preset error range, the contour to be machined is unqualified; the profile line of the initial contour is evenly divided for the second time in CAD to obtain more segmentation points than the previous equal division process. After that, the above steps are repeated until the contour to be machined is qualified.

[0025] Preferably, in step S5, a qualified inspection is performed on the workpiece finished product after machining.

[0026] Preferably, the step S5 includes using a coordinate measuring machine to scan and detect the contour of the workpiece finished product to obtain the profile flatness of the finished surface; if the profile flatness of the finished surface is less than the preset profile flatness, the workpiece finished product is qualified; if the profile flatness of the finished surface is greater than the preset profile flatness, the workpiece finished product is unqualified.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: By continuously performing equal-arc-length equal division processing on the profile of the standard model of the end face of the Roots rotor shaft through CAD drawing software, and judging the error of the to-be-machined profile generated based on the two-dimensional coordinates of each profile point after equal division according to the tool radius of the numerical control equipment. After passing the judgment, the two-dimensional coordinates are imported into the processing program, so that the processing program controls the numerical control equipment to perform sequential processing according to the ratio of 1:1 with the to-be-machined profile, thereby accurately controlling the profile processing operation of the numerical control equipment, ensuring the accuracy of the profile of the end face of the Roots rotor shaft. This not only makes the surface texture of the finished workpiece contour more uniform, but also can effectively reduce the profile error of the end face profile to meet the preset requirements. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a step schematic diagram of the present invention;

[0030] Figure 2 It is a logic flowchart of the present invention. Detailed Embodiments

[0031] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary in nature rather than restrictive.

[0032] The terms "including" and "having" and any variations thereof in the present application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products, or devices.

[0033] Referring to "embodiments" in the present application means that the specific features, structures, or characteristics described in combination with the embodiments can be included in at least one embodiment of the present application. The phrase appears at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] Refer to Figures 1 - 2 As shown, an embodiment of the present application provides a method for improving the numerical control machining accuracy of a Roots rotor shaft, which includes the following steps:

[0036] Step S1, generate an initial profile of the rotor shaft profile in CAD, obtain the tool radius of the numerical control equipment based on the initial profile; perform profile equal division processing on the initial profile to obtain a number of profile points.

[0037] Specifically, the process of generating the initial profile of the rotor shaft profile includes:

[0038] Design a Roots rotor shaft profile model in 3D software to obtain a 3D model diagram of the Roots rotor shaft profile. Use the 2D conversion function of the 3D software to convert the 3D model diagram of the Roots rotor shaft profile into a CAD 2D model diagram of the rotor shaft end face profile at a ratio of 1:1, and use the rotor shaft end face profile in the CAD 2D model diagram as the initial profile; convert the 3D model diagram into a CAD 2D model diagram to facilitate subsequent processing of the profile and export of 2D coordinate data.

[0039] To prepare for drawing the ball cutter circle and judging whether the equal division arc length value is qualified later, it is necessary to first obtain the tool radius suitable for machining the profile to be machined. The steps for obtaining the tool radius include:

[0040] Step S11, starting from the geometric center of the initial profile, extend a number of rays at fixed angle intervals. The rays divide the initial profile into several segments to obtain a number of equal division points;

[0041] Step S12, establish a 2D coordinate system with the geometric center of the initial profile as the coordinate origin, and extract the coordinate data of the equal division points;

[0042] Step S13, import the coordinate data into the machining program, preset a ball cutter radius, start the program for trial operation, and obtain the ball cutter radius value that does not cause overcutting with the new profile formed by the coordinate data, and use this as the tool radius of the numerical control equipment.

[0043] In the above technical solution, the fixed angle used for equally dividing the initial profile is 1°, and this method for obtaining the tool radius can simply and quickly find the tool radius suitable for machining the profile to be machined.

[0044] Since the initial profile is a planar closed figure, the coordinates of all points on the initial profile cannot be obtained, so it is impossible to directly control the machining operation of the numerical control equipment through the initial profile. Therefore, in the step S1, the profile equal division processing includes:

[0045] Perform equal arc - length division on the initial contour to obtain a number of segmentation points, and use these segmentation points as the contour points of the initial contour. In this way, each indexing of the tool of the numerical control equipment rotates according to an equal arc length, ensuring that the milling width of the ball - end mill is consistent each time, thereby making the finished contour of the workpiece more uniform and effectively reducing the surface profile error. In this embodiment, the equal arc - length division of the profile line is performed through the fixed - distance equal - division function of CAD to obtain a number of contour points.

[0046] Since the more contour points are obtained, the generated contour to be machined is closer to the initial contour, the machining tool - path trajectory accuracy of the numerical control equipment is higher, and thus the surface texture of the rotor - shaft end - face contour is more uniform and the surface profile error meets the standard. Therefore, the equal - division arc - length value selected during equal - division should not be too large. The appropriate equal - division arc - length value can be selected according to the size of the initial contour. Generally, a data value between 0.5 and 1 can be selected as the first equal - division arc - length value, and usually, obtaining 1000 - 2000 contour points is sufficient.

[0047] Step S2: Establish a coordinate system with the geometric center of the initial contour as the origin, extract the coordinates of the contour points, and import them into CAD to generate the contour to be machined; judge the error between the initial contour and the contour to be machined based on the tool radius to obtain an error result, and judge whether the contour to be machined is qualified based on the error result.

[0048] Specifically, establish a two - dimensional coordinate system with the geometric center of the initial contour as the coordinate origin, extract the two - dimensional coordinates of the contour points in the order from the first quadrant to the fourth quadrant, and re - import the extracted two - dimensional coordinates into the CAD two - dimensional model diagram to generate the contour to be machined. Obtain the error result through error measurement in the vector direction, and judge whether the contour to be machined is qualified based on the error result.

[0049] Specifically, the error measurement in the vector direction includes:

[0050] In the CAD two - dimensional model diagram, use the contour points as the tangent points of the ball - end mill of the numerical control equipment, and draw a number of ball - end mill circles in sequence; then measure the vector difference between the highest point of the non - milling blind - area region between two adjacent ball - end mill circles and the initial contour, and use the vector difference as the error result.

[0051] In the above technical solution, the two-dimensional coordinates of the contour points can be extracted through Excel, which is convenient for batch processing of data; before re-importing the extracted coordinates into CAD, the coordinate data in Excel can be de-duplicated to prevent data duplication caused by abnormal CAD exports; the movement of the cutting tool of the numerical control equipment on the contour to be machined is simulated by a ball-end mill circle, and each contour point corresponds to a ball-end mill circle tangent to it. The arc length equal division value is judged by the ball-end mill circle to determine whether the contour to be machined is qualified. If the error result is controlled within 1 / 10 of the preset surface contour tolerance, it means that the contour to be machined is qualified; if the error result is not within 1 / 10 of the preset surface contour tolerance, it means that the contour to be machined is unqualified.

[0052] Step S3, if the contour to be machined is qualified, copy the coordinates of the contour points to the numerical control equipment processing program, and control the numerical control equipment to perform processing operations in a 1:1 ratio with the contour to be machined to obtain a finished workpiece.

[0053] Specifically, if the error result is within the preset error range, the contour to be machined is qualified; copy the two-dimensional coordinates of the extracted contour points to the numerical control equipment processing program, and the processing program adds a Z value to the two-dimensional coordinates. Two different Z values are added to the same two-dimensional coordinate, and the two Z values added between different two-dimensional coordinates are the same; the processing program controls the movement of the numerical control equipment at the contour points in the order from the first quadrant to the fourth quadrant in the two-dimensional coordinate system, and controls the three-axis numerical control equipment to move axially back and forth between the same two-dimensional coordinates through the Z value, thereby realizing contour machining in a 1:1 ratio with the contour to be machined to obtain a finished workpiece.

[0054] In the above technical solution, the processing program controls the three-axis numerical control equipment to move axially back and forth between the same two-dimensional coordinates with a gradient of 1 or -1 through the Z value. For example, for the two-dimensional coordinate with contour point coordinates of ( , ), after adding two Z values, it becomes ( , , ), and ( , , ). The processing program controls the cutting tool of the three-axis numerical control equipment to translate from to with a gradient of 1 in the axial direction to complete one axial milling under the two-dimensional coordinate of ( , , ), and then move the cutting tool of the three-axis numerical control equipment to the next contour point in the counterclockwise direction of the point ( , ), which is ( , ), after adding two Z values to it, we get ( , , ), and ( , , ). The machining program controls the tool of the three-axis CNC equipment to translate from to in the axial direction with a gradient of -1, and completes one axial milling in the two-dimensional coordinate of ( , ). By repeating this process, after the tool of the three-axis CNC equipment completes one axial milling at each contour point, the contour machining is completed, and the finished workpiece is obtained. By adding Z values in the machining program, CNC turning centers, vertical machining centers, bedroom machining centers, and data planers with a C-axis (main spindle linkage indexing rotation axis) can achieve contour milling while meeting the requirements of surface contour tolerance.

[0055] Step S4, if the to-be-machined contour is unqualified, perform quadratic curve equal division processing on the initial contour in CAD, and then repeat the above steps until the to-be-machined contour is qualified.

[0056] Specifically, if the error result is not within the preset error range, the to-be-machined contour is unqualified; perform quadratic curve equal division processing on the curve of the initial contour in CAD to obtain more segmentation points compared with the previous equal division processing, and then repeat the above steps until the to-be-machined contour is qualified.

[0057] In the above technical solution, by continuously refining and equally dividing the initial contour curve, the purpose of reducing the surface contour tolerance of the end face curve of the Roots rotor shaft is achieved; it should be noted that the first equal division processing operation needs to be cancelled before performing the quadratic curve equal division processing, and in order to ensure that the quadratic curve equal division processing is an effective operation, the equal division arc length value selected for the second time cannot be greater than that of the first time.

[0058] In one embodiment, it further includes step S5, performing a qualification inspection on the finished workpiece after machining.

[0059] Specifically, step S5 includes using a coordinate measuring machine to scan and detect the contour of the finished workpiece to obtain the surface contour tolerance of the finished product; if the surface contour tolerance of the finished product is less than the preset surface contour tolerance, the finished workpiece is qualified; if the surface contour tolerance of the finished product is greater than the preset surface contour tolerance, the finished workpiece is unqualified.

[0060] In the above technical solution, by using a coordinate measuring machine to scan and detect the contour of the finished workpiece, it further ensures that the surface contour tolerance of the obtained finished workpiece meets the machining requirements.

[0061] The method for improving the numerical control machining accuracy of the Roots rotor shaft continuously performs equal-arc-length equal division processing on the profile curve of the standard model of the Roots rotor shaft end face through CAD drawing software, judges the error of the machined profile generated based on the two-dimensional coordinates of each contour point after equal division according to the tool radius of the numerical control equipment. After passing the judgment, the two-dimensional coordinates are imported into the machining program, so that the machining program controls the numerical control equipment to perform sequential machining according to the ratio of 1:1 with the machined profile based on the coordinates of the contour points, thereby accurately controlling the contour machining operation of the numerical control equipment, ensuring the accuracy of the profile curve of the Roots rotor shaft end face. It not only makes the surface texture of the finished workpiece contour more uniform, but also can effectively reduce the profile error of the end face profile curve to meet the preset requirements.

[0062] The specific embodiments described above further elaborate on the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for improving the numerical control machining accuracy of a Roots rotor shaft, characterized in that It includes the following steps: Step S1, generate the initial profile of the rotor shaft profile in CAD, obtain the tool radius of the numerical control equipment based on the initial profile; perform profile equal division processing on the initial profile to obtain several profile points; Step S2, establish a coordinate system with the geometric center of the initial profile as the origin, extract the coordinates of the profile points, and import them into CAD to generate the profile to be machined; judge the error between the initial profile and the profile to be machined based on the tool radius to obtain an error result, and judge whether the profile to be machined is qualified based on the error result, including establishing a two-dimensional coordinate system with the geometric center of the initial profile as the coordinate origin, extracting the two-dimensional coordinates of the profile points in the order from the first quadrant to the fourth quadrant, and re-importing the extracted two-dimensional coordinates into the CAD two-dimensional model diagram to generate the profile to be machined, obtaining the error result through error measurement in the vector direction, and judging whether the profile to be machined is qualified based on the error result; Step S3, if the profile to be machined is qualified, copy the coordinates of the profile points to the numerical control equipment machining program, and control the numerical control equipment to perform machining operations in a 1:1 ratio with the profile to be machined to obtain a workpiece finished product, including if the error result is within the preset error range, the profile to be machined is qualified; copy the extracted two-dimensional coordinates of the profile points to the numerical control equipment machining program, and the machining program adds a Z value in the two-dimensional coordinates, where two different Z values are added to the same two-dimensional coordinate respectively, and the two Z values added between different two-dimensional coordinates are the same, and the machining program controls the movement of the numerical control equipment at the profile points in the order from the first quadrant to the fourth quadrant in the two-dimensional coordinate system, and controls the three-axis numerical control equipment to make axial movements back and forth between the same two-dimensional coordinates through the Z value, so as to realize profile machining in a 1:1 ratio with the profile to be machined and obtain a workpiece finished product; Step S4, if the profile to be machined is unqualified, perform secondary profile equal division processing on the initial profile in CAD, and then repeat the above steps until the profile to be machined is qualified.

2. The method for improving the numerical control machining accuracy of a Roots rotor shaft according to claim 1, characterized in that In the step S1, the process of generating the initial profile of the rotor shaft profile includes: Design the Roots rotor shaft profile model in 3D software to obtain the 3D model diagram of the Roots rotor shaft profile, use the 2D conversion function of the 3D software to convert the 3D model diagram of the Roots rotor shaft profile into a CAD 2D model diagram of the rotor shaft end face profile in a 1:1 ratio, and use the rotor shaft end face profile in the CAD 2D model diagram as the initial profile.

3. The method for improving the numerical control machining accuracy of the Roots rotor shaft according to claim 2, characterized in that In the step S1, the steps of obtaining the tool radius include: Step S11, starting from the geometric center of the initial profile, extend several rays at fixed angle intervals, and the rays divide the initial profile into several segments to obtain several equal division points; Step S12, establish a two-dimensional coordinate system with the geometric center of the initial profile as the coordinate origin, and extract the coordinate data of the equal division points; Step S13: Import the coordinate data into the machining program, preset a ball cutter radius, start the program for trial run, and obtain the ball cutter radius value that does not cause overcutting with the new contour formed by the coordinate data, and use this as the tool radius of the numerical control equipment.

4. The method for improving the numerical control machining accuracy of the Roots rotor shaft according to claim 3, characterized in that In the step S1, the profile line equal division processing includes: Perform equal arc length equal division processing on the initial contour to obtain a number of segmentation points, and use the segmentation points as the contour points of the initial contour.

5. The method for improving the numerical control machining accuracy of a Roots rotor shaft according to claim 1, characterized in that The error measurement of the vector direction includes: In the CAD two-dimensional model drawing, use the contour points as the tangent points of the ball cutter of the numerical control equipment, and draw a number of ball cutter circles in sequence; then measure the vector difference between the highest point of the non-machinable blind area between two adjacent ball cutter circles and the initial contour, and use the vector difference as the error result.

6. The method for improving the numerical control machining accuracy of a Roots rotor shaft according to claim 1, characterized in that: In the step S4, if the error result is not within the preset error range, the contour to be machined is unqualified; perform secondary profile line equal division processing on the profile line of the initial contour in CAD to obtain more segmentation points than the previous equal division processing, and then repeat the above steps until the contour to be machined is qualified.

7. The method for improving the numerical control machining accuracy of the Roots rotor shaft according to claim 1, characterized in that, It further includes the following steps: Step S5: Perform a qualified inspection on the finished workpiece after machining.

8. The method for improving the numerical control machining accuracy of a Roots rotor shaft according to claim 7, characterized in that: The step S5 includes using a coordinate measuring machine to scan and detect the contour of the finished workpiece to obtain the profile accuracy of the finished surface; if the profile accuracy of the finished surface is less than the preset profile accuracy, the finished workpiece is qualified; if the profile accuracy of the finished surface is greater than the preset profile accuracy, the finished workpiece is unqualified.

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