Thermal error compensation method for numerical control grinding machine

Abstract

The invention discloses a thermal error compensation method for a numerical control grinding machine. The thermal error compensation method comprises the following steps that S1, the abrasion loss LSM of a grinding wheel is calculated; s2, the thermal deformation LS of the grinding wheel is calculated; s3, calculating the thermal deformation LG of the workpiece; and S4, calculating a thermal error compensation value delta L: delta L = LSM-LS-LG. By compensating the radial thermal expansion of the grinding wheel and the workpiece, over-grinding caused by the radial thermal expansion of the grinding wheel and the workpiece can be reduced, and the machining precision of the numerical control grinding machine is improved; deformation caused by centrifugal force in the running process of the grinding wheel is introduced into compensation of thermal errors, the accuracy of the grinding position of the grinding wheel is improved, and the machining precision of the numerical control grinding machine is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of numerically controlled grinders, and in particular to a thermal error compensation method for numerically controlled grinders. Background Art

[0002] CNC grinding machines are machine tools that use grinding wheels to grind workpiece surfaces through CNC technology. They play an important role in various high-precision manufacturing industries. Grinding, as the final processing of most parts, directly determines the product accuracy and surface quality. In order to improve product quality, the requirements for grinding machine processing accuracy are getting higher and higher.

[0003] The factors that affect the machining accuracy of grinding machines mainly include geometric error and thermal error. The influence of geometric error on machining accuracy can be reduced by means of maintenance and improving manufacturing and assembly accuracy. Thermal error requires a more complex method to suppress. The existing thermal error compensation method mainly compensates for the thermal errors of guide rails and spindles, and lacks research on the thermal error compensation of grinding wheels. The radial thermal error of the grinding wheel has a great influence on the accuracy of the product, especially on the machining accuracy of shaft products or plane products.

[0004] Based on the above technical problems, the present application proposes a thermal error compensation method for a CNC grinder. Summary of the invention

[0005] The purpose of the present invention is to provide a method for compensating thermal errors of a CNC grinding machine to solve the technical problems mentioned in the background technology. The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for compensating thermal errors of a numerically controlled grinding machine comprises the following steps:

[0007] Step S1: align the grinding wheel, obtain the height difference of the grinding wheel before and after wear, and calculate the wear amount L of the grinding wheel. SM ;

[0008] Step S2: Obtain the temperature difference before and after the grinding wheel is working, and calculate the thermal deformation L of the grinding wheel S ;

[0009] Step S3: Obtain the temperature difference before and after the workpiece is processed, and calculate the thermal deformation L of the workpiece G ;

[0010] Step S4, calculating the thermal error compensation value ΔL:

[0011] ΔL=L SM -L S -L G .

[0012] Furthermore, the wear amount L of the grinding wheel SM The calculation steps are:

[0013] Step S11, after the new grinding wheel is assembled, the new grinding wheel is calibrated and the first height H1 is recorded;

[0014] Step S12: Before each grinding process, align the grinding wheel and record the second height H2;

[0015] Step S13: Calculate the wear amount L of the grinding wheel SM ,

[0016] L SM =H1-H2.

[0017] Furthermore, the thermal deformation of the grinding wheel L S The calculation steps are:

[0018] Step S21, obtaining the initial temperature T1 and initial radius R1 of the grinding wheel;

[0019] Step S22, obtaining the working temperature T2 of the grinding wheel;

[0020] Step S23, calculate the thermal deformation L of the grinding wheel S ,

[0021]

[0022] Where α1 is the thermal expansion coefficient of the grinding wheel.

[0023] Furthermore, the calculation steps of the initial radius R1 of the grinding wheel in step S21 are:

[0024] Step S211, obtaining the static radius R0 of the grinding wheel;

[0025] Step S212, obtaining the angular velocity ω of the grinding wheel;

[0026] Step S213, calculating the initial radius R1 of the grinding wheel:

[0027]

[0028] Where E is the elastic modulus of the grinding wheel, v is the Poisson's ratio, ρ is the grinding wheel density, and a and b are constants.

[0029] Furthermore, the static radius R0 of the grinding wheel in step S211 is:

[0030] R0=RL SM

[0031] Where R is the radius of the new grinding wheel.

[0032] Furthermore, the thermal deformation of the workpiece L G The calculation steps are:

[0033] Step S31, obtaining the initial temperature t1 and initial size L of the workpiece;

[0034] Step S32, obtaining the working temperature t2 of the workpiece;

[0035] Step S33: Calculate the thermal deformation L of the workpiece G :

[0036]

[0037] Where α2 is the thermal expansion coefficient of the workpiece.

[0038] The technical solution provided in the embodiments of the present application has at least the following technical effects or advantages:

[0039] 1. By compensating for the radial thermal expansion of the grinding wheel and the workpiece, the over-grinding caused by the radial thermal expansion of the grinding wheel and the workpiece can be reduced, and the machining accuracy of the CNC grinder can be improved;

[0040] 2. The deformation caused by centrifugal force during the operation of the grinding wheel is introduced into the compensation of thermal error, which improves the accuracy of the grinding position of the grinding wheel and further improves the processing accuracy of the CNC grinder. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings in the specification, which constitute a part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0042] Figure 1 This is a flow chart of an embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the drawings and specific implementation methods of the specification. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] like Figure 1 A thermal error compensation method for a CNC grinding machine shown in the figure comprises the following steps:

[0045] Step S1, calculate the wear amount L of the grinding wheel SM ;

[0046] Grinding wheel wear L SM The calculation steps are:

[0047] Step S11, after the new grinding wheel is assembled, the new grinding wheel is aligned and a first height H1 is recorded; the first height H1 is the position information of the Z axis of the CNC grinder when the new grinding wheel is aligned.

[0048] Step S12, before each grinding process, align the grinding wheel and record the second height H2; the second height H1 is the position information of the Z axis of the CNC grinder when the grinding wheel is aligned before each grinding process.

[0049] Step S13: Calculate the wear amount L of the grinding wheel SM ,

[0050] L SM =H1-H2.

[0051] As the grinding wheel wears, the Z-axis position of the CNC machine tool gradually decreases when the grinding wheel is set, and the height difference between the Z-axis position of the CNC machine tool when the new grinding wheel is set gradually increases. The height difference is the wear amount L of the grinding wheel. SM .

[0052] Step S2: Calculate the thermal deformation L of the grinding wheel S ;

[0053] Thermal deformation of grinding wheel L S The calculation steps are:

[0054] Step S21, obtaining the initial temperature T1 and initial radius R1 of the grinding wheel;

[0055] The calculation steps of the initial radius R1 of the grinding wheel are:

[0056] Step S211, obtaining the static radius R0 of the grinding wheel;

[0057] Static radius R0 = RL SM ,

[0058] Where R is the radius of the new grinding wheel, L SM The wear amount of the grinding wheel is the radius R of the new grinding wheel minus the wear amount L of the grinding wheel. SM That is, the radius of the grinding wheel when it is in a static state.

[0059] Step S212, obtaining the angular velocity ω of the grinding wheel; the angular velocity ω of the grinding wheel can be obtained from the spindle speed of the CNC grinding machine.

[0060] Step S213, calculating the initial radius R1 of the grinding wheel:

[0061]

[0062] Where E is the elastic modulus of the grinding wheel, v is the Poisson's ratio, ρ is the grinding wheel density, and a and b are constants.

[0063] In the process of precision CNC grinding, the grinding wheel rotating at high speed will deform under the action of centrifugal force, which will increase the radial size of the grinding wheel and reduce the axial size, thus affecting the grinding accuracy of the grinding wheel. In this embodiment, the radius of the running grinding wheel is used as the initial radius, which can further improve the accuracy of thermal error compensation.

[0064] Step S22, obtaining the working temperature T2 of the grinding wheel; the initial temperature T1 of the grinding wheel and the working temperature T2 of the grinding wheel are both measured in real time by a non-contact temperature sensor such as an infrared thermometer.

[0065] Step S23, calculate the thermal deformation L of the grinding wheel S ,

[0066]

[0067] Where α1 is the thermal expansion coefficient of the grinding wheel.

[0068] Since the radial thermal error of the grinding wheel is compensated in this embodiment, the initial radius R1 of the grinding wheel is taken as the original length. By calculating the temperature change of the grinding wheel and combining the expansion coefficient α1 of the grinding wheel, the radial change of the grinding wheel is calculated, which is the thermal deformation L of the grinding wheel. S .

[0069] The thermal expansion coefficients of commonly used grinding wheels are shown in Table 1:

[0070] Table 1 Thermal expansion coefficient of commonly used grinding wheels

[0071]

[0072] Step S3: Calculate the thermal deformation L of the workpiece G ;

[0073] Thermal deformation of the workpiece L G The calculation steps are:

[0074] Step S31, obtaining the initial temperature t1 and initial size L of the workpiece; the initial size L may be the radius of a shaft product or the thickness of a plane product.

[0075] Step S32, obtaining the working temperature t2 of the workpiece; the initial temperature t1 of the workpiece and the working temperature t2 of the workpiece are both measured in real time by a non-contact temperature sensor such as an infrared thermometer.

[0076] Step S33: Calculate the thermal deformation L of the workpiece G ,

[0077]

[0078] Where α2 is the thermal expansion coefficient of the workpiece.

[0079] Since this embodiment compensates for the radial thermal error of the grinding wheel, the initial size L of the workpiece is taken as the original length. By calculating the temperature change of the workpiece and combining the expansion coefficient α2 of the workpiece, the change of the workpiece in the radial direction of the grinding wheel is calculated, which is the thermal deformation L of the workpiece. S .

[0080] The thermal expansion coefficients of commonly used workpiece materials are shown in Table 2:

[0081] Table 2 Thermal expansion coefficients of common workpiece materials

[0082]

[0083] Step S4, calculating the thermal error compensation value ΔL:

[0084] ΔL=L SM -L S -L G .

[0085] Based on the position of the grinding wheel of the CNC grinder, the wear amount L of the grinding wheel is compensated SM , minus the thermal deformation L of the grinding wheel S And the thermal deformation of the workpiece L G , the actual required position of the grinding wheel can be obtained, avoiding over-grinding due to heat generation during the grinding process and improving the processing accuracy of the product.

[0086] As the grinding wheel grinds along the surface of the workpiece, the heat accumulated in the grinding wheel and the workpiece will gradually rise. By measuring the temperature of the grinding wheel and the workpiece in real time with an infrared thermometer, the thermal error compensation value can be adjusted in real time, thereby avoiding deviations in the initial and final dimensions of the workpiece and improving processing accuracy.

[0087] The technical solution provided in the embodiments of the present application has at least the following technical effects or advantages:

[0088] 1. By compensating for the radial thermal expansion of the grinding wheel and the workpiece, the over-grinding caused by the radial thermal expansion of the grinding wheel and the workpiece can be reduced, and the machining accuracy of the CNC grinder can be improved;

[0089] 2. The deformation caused by centrifugal force during the operation of the grinding wheel is introduced into the compensation of thermal error, which improves the accuracy of the grinding position of the grinding wheel and further improves the processing accuracy of the CNC grinder.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, 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 compensating thermal errors of a CNC grinding machine, characterized in that: The following steps are involved: Step S1: align the grinding wheel, obtain the height difference of the grinding wheel before and after wear, and calculate the wear amount L of the grinding wheel. SM ; Step S2: Obtain the temperature difference before and after the grinding wheel is working, and calculate the thermal deformation L of the grinding wheel S ; Step S3: Obtain the temperature difference before and after the workpiece is processed, and calculate the thermal deformation L of the workpiece G ; Step S4, calculating the thermal error compensation value ΔL: ΔL=L SM -L S -L G 。 2. A method for compensating thermal errors of a CNC grinding machine according to claim 1, characterized in that: Grinding wheel wear L SM The calculation steps are: Step S11, after the new grinding wheel is assembled, the new grinding wheel is calibrated and the first height H1 is recorded; Step S12: Before each grinding process, align the grinding wheel and record the second height H2; Step S13: Calculate the wear amount L of the grinding wheel SM , L SM =H1-H2.

3. A method for compensating thermal errors of a CNC grinding machine according to claim 2, characterized in that: Thermal deformation of grinding wheel L S The calculation steps are: Step S21, obtaining the initial temperature T1 and initial radius R1 of the grinding wheel; Step S22, obtaining the working temperature T2 of the grinding wheel; Step S23, calculate the thermal deformation L of the grinding wheel S , Where α1 is the thermal expansion coefficient of the grinding wheel.

4. A method for compensating thermal errors of a CNC grinding machine according to claim 3, characterized in that: The calculation steps of the initial radius R1 of the grinding wheel in step S21 are: Step S211, obtaining the static radius R0 of the grinding wheel; Step S212, obtaining the angular velocity ω of the grinding wheel; Step S213, calculating the initial radius R1 of the grinding wheel: Where E is the elastic modulus of the grinding wheel, v is the Poisson's ratio, ρ is the grinding wheel density, and a and b are constants.

5. The method for compensating thermal error of a CNC grinding machine according to claim 3, characterized in that: The static radius R0 of the grinding wheel in step S211 is: R0=R-L SM Where R is the radius of the new grinding wheel.

6. The method for compensating thermal error of a CNC grinding machine according to claim 1, characterized in that: Thermal deformation of the workpiece L G The calculation steps are: Step S31, obtaining the initial temperature t1 and initial size L of the workpiece; Step S32, obtaining the working temperature t2 of the workpiece; Step S33: Calculate the thermal deformation L of the workpiece G : Where α2 is the thermal expansion coefficient of the workpiece.

Images