Compensation method for spindle radial runout based on the law of thermal error and machining time

Abstract

The present invention discloses a spindle radial runout compensation method based on the law of thermal error and processing time. The present invention establishes a calculation formula for the spindle radial runout under load, so that the lathe control system calculates and predicts the spindle radial runout according to the calculation formula for the spindle radial runout under load when the workpiece is being fine-machined, and changes the cutting depth of the tool according to the predicted spindle radial runout to compensate for the spindle radial runout, so that the movement path of the tool is consistent with the change law of the spindle radial runout, so that the radius of the workpiece after cutting is equal to the preset radius of the workpiece after fine-machined. The present invention can achieve radial runout compensation for the workpiece during fine-machined processing, so that the influence of the spindle radial runout caused by the temperature difference between the front and rear ends of the spindle on the processing accuracy is quickly and efficiently improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of radial runout compensation, and in particular relates to a spindle radial runout compensation method based on the law of thermal error and machining time. Background Art

[0002] Turning is a commonly used machining method. During turning, due to the temperature difference between the front and rear ends of the spindle during operation, the spindle's radial runout occurs, which in turn causes radial runout of the workpiece. This radial runout of the workpiece can seriously affect the machining accuracy of the workpiece, especially during the finishing process. The spindle's radial runout is a function of the machining time and the load on the spindle's front end. In particular, the load on the spindle's front end varies with cutting depth, feed rate, and workpiece mass. The impact on machining accuracy is difficult to control during actual machining. Therefore, how to quickly and effectively compensate for the spindle's radial runout error has become an important issue that needs to be addressed. Therefore, it is necessary to design a machining path compensation method for the spindle's radial runout error during turning. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a spindle radial runout compensation method based on the law of thermal error and processing time.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention provides a spindle radial runout compensation method based on the law of thermal error and processing time, specifically as follows:

[0006] Step 1: Establish the temperature difference T between the front and rear ends of the spindle under no-load conditions 无 and the spindle rotation time t 轴 Functional relationship of spindle radial runout A 无 and the spindle rotation time t 轴 The functional relationship between the spindle radial runout A and the external load N generated by the workpiece on the lathe spindle under load, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t 轴 The functional relationship of .

[0007] Step 2: The temperature difference T between the front and rear ends of the spindle under load is the temperature difference T between the front and rear ends of the spindle under no load at the preset compensation time E. 无 Temperature change T caused by friction at the front end of the spindle under load 有 The difference in the accumulated value from the start of finishing to the preset compensation time E, that is, t 工 The finishing time of the workpiece currently completed;

[0008] Temperature change T caused by friction between the workpiece and the lathe spindle's external load at the front end of the spindle 有 for

[0009]

[0010] Where Q is the heat generated by the friction between the workpiece and the external load on the spindle at the front end of the spindle, m 轴 is the mass of the spindle, c is the specific heat capacity of the spindle material;

[0011] The heat Q generated by the friction caused by the workpiece on the lathe spindle external load at the front end of the spindle is

[0012] Q=F×Δx

[0013] Where F is the friction force generated by the workpiece on the lathe spindle under external load, and F = μ × F c , μ is the friction coefficient of the bearing supporting the main shaft, F c is the centrifugal force generated by the workpiece under the influence of the spindle radial runout, Δx is the rotational displacement of the spindle relative to the tool;

[0014] The centrifugal force F generated by the workpiece under the influence of the spindle radial runout c for

[0015]

[0016] Where m is the real-time mass of the workpiece during machining, V is the linear velocity of the cylindrical surface of the workpiece, and V = 2πrn / 60, n is the spindle speed, r is the rotation radius of the workpiece, and r = r 工 +A,r 工 is the radius of the workpiece before finishing. When calculating r here, A is substituted with the spindle radial runout compensated by the previous preset compensation moment E. When calculating the spindle radial runout compensated by the first preset compensation moment E, r is calculated by substituting A with the spindle radial runout A under no-load conditions. 无 Substitution.

[0017] Rotational displacement of the spindle relative to the tool:

[0018] Δx=2πr 轴 n×t 工 / 60

[0019] Where r 轴 The radius of the main axis, t 工 The finishing time of the workpiece currently completed;

[0020] Where m = m 总 -m 切 , m 总 is the total mass of the workpiece before finishing, m切 is the mass of the removed part during workpiece finishing, m 切 =H×S×q, H is the height of the cylinder, and H=nf×t 工 , f is the feed rate of the tool, S is the bottom area of ​​the cylinder, and S=π[(r 完 +a p ) 2 -r 完 2 ], r is the preset radius of the workpiece after finishing, ap is the preset cutting depth of the tool, and q is the density of the workpiece material;

[0021] but

[0022] m=m 总 -nft 工 ×π[(r 完 +a p ) 2 -r 完 2 ]×q

[0023]

[0024] The temperature difference T between the front and rear ends of the spindle under no-load condition is obtained by the above equation and fitting. 无 and the spindle rotation time t 轴 Substitute the functional relationship of into the calculation formula of the temperature difference T between the front and rear ends of the spindle under load, and the calculation formula of the temperature difference T between the front and rear ends of the spindle under load is obtained as follows:

[0025]

[0026] Step 3: During the workpiece machining process, when the workpiece is being fine-machined, the lathe control system substitutes the calculated external load N generated by the workpiece on the lathe spindle and the temperature difference T between the front and rear ends of the spindle under load into the spindle radial circular runout A under load and the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t. 轴 The function relationship is used to predict the spindle radial circular runout in real time, and the preset tool cutting depth is changed according to the predicted spindle radial circular runout, so that the radius of the workpiece after cutting is equal to the preset radius of the workpiece after finishing, thereby realizing the spindle radial circular runout compensation during the finishing of the workpiece.

[0027] Preferably, the process of step 1 is as follows: the lathe spindle is idling at a preset speed n, and the temperature difference between the front and rear ends of the spindle and the radial runout of the spindle are detected and recorded multiple times within a preset time period t0 during the spindle idling process; the temperature difference data between the front and rear ends of each spindle and the corresponding spindle rotation time t are compared. 轴 Fitting is performed to obtain the temperature difference T between the front and rear ends of the spindle under no-load conditions.无 and the spindle rotation time t 轴 The functional relationship between the radial runout data of each spindle and the corresponding spindle rotation time t 轴 Perform fitting to obtain the spindle radial runout A under no-load conditions. 无 and the spindle rotation time t 轴 Then, different values ​​are uniformly selected within the preset range of the external load generated by the workpiece on the lathe spindle. For the external load value generated by each selected workpiece on the lathe spindle, the temperature difference between the front and rear ends of the spindle and the radial circular runout of the spindle are detected and recorded multiple times within a preset time period t0 during the spindle rotation at a preset speed n. The external load data generated by each workpiece on the lathe spindle are compared with the corresponding temperature difference data between the front and rear ends of the spindle and the spindle rotation time t. 轴 The spindle radial runout data is fitted to obtain the spindle radial runout A under load, the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t. 轴 The functional relationship of .

[0028] More preferably, the temperatures at the front end and rear end of the spindle are measured respectively by two temperature sensors, and the radial runout of the spindle is measured by a dial indicator.

[0029] Preferably, the external load N generated by the workpiece on the lathe spindle when the tool processes the workpiece and the centrifugal force F generated by the workpiece under the influence of the spindle radial circular runout are c Equal; in the process of calculating the external load N in step 1, the value A is directly substituted with the spindle radial runout value detected. In step 3, when calculating the external load N, the value A is directly substituted with the value F c The process is exactly the same.

[0030] Preferably, the temperature difference between the front and rear ends of the spindle is T 无 and the spindle rotation time t 轴 The functional relationship is

[0031]

[0032] Where θ1 is the coefficient of change of temperature difference and time unit, and θ1 = 1°C / s.

[0033] Preferably, the spindle radial runout A under no-load conditions 无 and the spindle rotation time t 轴 The functional relationship is

[0034]

[0035] Where θ2 is the coefficient of variation of the spindle radial runout with time unit, and θ2 = 1 μm / min.

[0036] Preferably, the spindle radial runout A and the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t 轴 The functional relationship is

[0037] A=0.1052N×θ3+0.1896t 轴 ×θ2+0.05263T×τ

[0038] Where τ is the unit variation coefficient of the spindle radial runout and temperature difference, and τ = 1 μm / °C; θ3 is the unit variation coefficient of the spindle radial runout and load, and θ3 = 1 μm / N.

[0039] The present invention has the following beneficial effects:

[0040] The present invention can compensate for the radial runout of the spindle during the fine machining of the workpiece, so that the influence of the radial runout of the spindle caused by the temperature difference between the front and rear ends of the spindle can be quickly and efficiently improved; specifically, the present invention calculates and predicts the radial runout of the spindle when the workpiece is fine-machined by establishing a calculation formula for the radial runout of the spindle under load conditions (when the lathe processes the workpiece), and changes the cutting depth of the tool according to the predicted radial runout of the spindle to compensate for the radial runout of the spindle, so that the movement path of the tool is consistent with the change law of the radial runout of the spindle, and thus the radius of the workpiece after cutting is equal to the preset radius of the workpiece after fine machining, thereby improving the machining accuracy of the workpiece. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the embodiments.

[0042] The present invention provides a spindle radial runout compensation method based on the law of thermal error and processing time, specifically as follows:

[0043] Step 1: The lathe spindle is idling at a preset speed n, and the temperature difference between the front and rear ends of the spindle and the spindle radial runout are detected and recorded multiple times within a preset time period t0 during the spindle idling process (the total time of the workpiece finishing can be taken, wherein the time from the spindle starting to stable rotation is short and can be ignored). In this embodiment, t0 = 30s; the temperature difference data between the front and rear ends of each spindle and the corresponding spindle rotation time t 轴 Fitting is performed to obtain the temperature difference T between the front and rear ends of the spindle under no-load conditions. 无 and the spindle rotation time t 轴 The functional relationship between the radial runout data of each spindle and the corresponding spindle rotation time t 轴 Perform fitting to obtain the spindle radial runout A under no-load conditions. 无 and the spindle rotation time t 轴Then, different values ​​are uniformly selected within the preset range of the external load generated by the workpiece on the lathe spindle. For the external load value generated by each selected workpiece on the lathe spindle, the temperature difference between the front and rear ends of the spindle and the radial circular runout of the spindle are detected and recorded multiple times within a preset time period t0 during the spindle rotation at a preset speed n. The external load data generated by each workpiece on the lathe spindle are compared with the corresponding temperature difference data between the front and rear ends of the spindle and the spindle rotation time t. 轴 The spindle radial runout data is fitted to obtain the spindle radial runout A under load, the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t. 轴 The functional relationship of .

[0044] The temperatures at the front and rear ends of the spindle are measured by two temperature sensors, and the radial runout of the spindle is measured by a dial indicator.

[0045] The external load N generated by the workpiece on the lathe spindle when the tool processes the workpiece and the centrifugal force F generated by the workpiece under the influence of the spindle radial circular runout c Equal; the centrifugal force F generated by the workpiece under the influence of the spindle radial circular runout c for

[0046]

[0047] Where m is the real-time mass of the workpiece during machining, V is the linear velocity of the cylindrical surface of the workpiece, and V = 2πrn / 60, r is the rotation radius of the workpiece, and the rotation radius r of the workpiece is the radius r before the workpiece is finished. 工 The sum of the radial runout of the spindle, that is, r = r 工 +A, where A is calculated by directly substituting the detected spindle radial runout value into it, and n is the spindle speed.

[0048] Temperature difference T between the front and rear ends of the spindle under no load 无 and the spindle rotation time t 轴 The functional relationship is

[0049]

[0050] Where θ1 is the coefficient of variation of temperature difference and time unit, and θ1 = 1°C / s;

[0051] Spindle radial runout A under no-load condition 无 and the spindle rotation time t 轴 The functional relationship is

[0052]

[0053] Where θ2 is the coefficient of variation of the spindle radial runout with time unit, and θ2 = 1 μm / min;

[0054] The spindle radial runout A, the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t 轴 The functional relationship is

[0055] A=0.1052N×θ3+0.1896t 轴 ×θ2+0.05263T×τ (2)

[0056] Where τ is the unit variation coefficient of the spindle radial runout and temperature difference, and τ = 1 μm / °C; θ3 is the unit variation coefficient of the spindle radial runout and load, and θ3 = 1 μm / N.

[0057] Step 2: The temperature difference T between the front and rear ends of the spindle under load is mainly affected by the spindle's no-load friction and the external load friction generated by the workpiece. It is the temperature difference T between the front and rear ends of the spindle under no-load at the preset compensation time E. 无 The temperature change T caused by the friction of the external load at the front end of the spindle under load 有 The difference in the accumulated value from the start of finishing to the preset compensation time E, that is, t 工 The finishing time of the workpiece currently completed;

[0058] Temperature change T caused by friction between the workpiece and the lathe spindle's external load at the front end of the spindle 有 for

[0059]

[0060] Where Q is the heat generated by the friction between the workpiece and the external load on the spindle at the front end of the spindle, m 轴 The mass of the spindle can be found in the relevant information of the lathe, and c is the specific heat capacity of the spindle material, which can be obtained by consulting the information;

[0061] The heat Q generated by the friction caused by the workpiece on the lathe spindle external load at the front end of the spindle is

[0062] Q=F×Δx

[0063] Where F is the friction force generated by the workpiece on the lathe spindle under external load, and F = μ × F c , μ is the friction coefficient of the bearing supporting the main shaft, and by consulting the data, we can get that F c F is the centrifugal force generated by the workpiece under the influence of the spindle radial runout. c When calculating the rotation radius r of the workpiece, the spindle radial runout compensated by the previous preset compensation moment E is substituted into A. When calculating the spindle radial runout compensated by the first preset compensation moment E, Fc In the calculation formula, the rotation radius r of the workpiece is calculated by using the spindle radial runout A under no-load conditions. 无 Substitute, Δx is the rotational displacement of the spindle relative to the tool;

[0064] The rotation displacement Δx of the spindle relative to the tool is

[0065] Δx=2πr 轴 n×t 工 / 60

[0066] Where r 轴 is the spindle radius, t 工 The finishing time of the workpiece currently completed;

[0067] but

[0068]

[0069] Among them, the workpiece quality changes with the processing time during the processing, and m=m 总 -m 切 , m 总 is the total mass of the workpiece before finishing, m 切 is the mass of the removed portion during workpiece finishing. The removed portion of the workpiece can be approximately regarded as a cylinder, so m 切 =H×S×q, H is the height of the cylinder, and H=nf×t 工 , f is the feed rate of the tool, S is the bottom area of ​​the cylinder, and S=π[(r 完 +a p ) 2 -r 完 2 ], r is the radius of the workpiece after finishing, a p is the cutting depth of the tool, q is the density of the workpiece material;

[0070] but

[0071] m=m 总 -nft 工 ×π[(r 完 +a p ) 2 -r 完 2 ]×q

[0072]

[0073] The temperature difference T between the front and rear ends of the spindle under no-load condition is obtained by the above equation and fitting. 无 and the spindle rotation time t 轴Substitute the functional relationship of into the calculation formula of the temperature difference T between the front and rear ends of the spindle under load, and the calculation formula of the temperature difference T between the front and rear ends of the spindle under load is obtained as follows:

[0074]

[0075] Where E is the preset compensation moment. For example, a finishing process can compensate for the large spindle radial runout at several moments during finishing. It should be noted that during cutting, the mass of the workpiece is constantly changing, and the centrifugal force generated by the workpiece is constantly changing. In addition, the finishing time is short, and heat can be considered to be accumulating on the spindle. Therefore, the temperature change expression caused by the friction caused by the workpiece on the external load of the lathe spindle at the front end of the spindle from the start of finishing to each preset compensation moment E is integrated, and the cumulative value is calculated, so that the real-time and accurate error compensation amount can be calculated later to ensure the accuracy of the compensation.

[0076] In this embodiment,

[0077]

[0078] Step 3: During the workpiece machining process, when the workpiece is being fine-machined, the lathe control system substitutes the external load N generated by the workpiece on the lathe spindle calculated by formula (1) and the temperature difference T between the front and rear ends of the spindle under load calculated by formula (3) into the spindle radial runout calculation formula of formula (2) to predict the spindle radial runout in real time, and changes the preset tool cutting depth according to the predicted spindle radial runout so that the radius of the workpiece after cutting is equal to the preset radius of the workpiece after finishing, thereby achieving compensation for the spindle radial runout during the finishing of the workpiece, so that the influence of the spindle radial runout caused by the temperature difference between the front and rear ends of the spindle is quickly and efficiently improved. Among them, the actual radius of the workpiece after cutting is equal to the radius of the workpiece before finishing minus the value of the real-time tool cutting depth. The predicted spindle radial runout value is superimposed on the preset tool cutting depth in real time, thereby fine-tuning the real-time tool cutting depth, so that the actual radius of each position of the workpiece after cutting is closer to the preset radius of the workpiece after finishing.

Claims

1. A spindle radial runout compensation method based on the law of thermal error and machining time is characterized by: The details are as follows: Step 1: Establish the temperature difference T between the front and rear ends of the spindle under no-load conditions 无 and the spindle rotation time t 轴 Functional relationship of spindle radial runout A 无 and the spindle rotation time t 轴 The functional relationship between the spindle radial runout A under load and the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t 轴 Functional relationship of Step 2: The temperature difference T between the front and rear ends of the spindle under load is the temperature difference T between the front and rear ends of the spindle under no load at the preset compensation time E. 无 Temperature change T caused by friction at the front end of the spindle under load 有 The difference in the accumulated value from the start of finishing to the preset compensation time E, that is, t 工 The finishing time of the workpiece currently completed; Where m 轴 is the mass of the spindle, c is the specific heat capacity of the spindle material; the heat generated by the friction caused by the workpiece on the external load of the lathe spindle at the front end of the spindle is: Q=F×Δx Where F is the friction force generated by the workpiece on the lathe spindle under external load, and F = μ × F c , μ is the friction coefficient of the bearing supporting the spindle; the centrifugal force generated by the workpiece under the influence of the spindle radial circular runout is: Where m is the real-time mass of the workpiece during machining, V is the linear velocity of the cylindrical surface of the workpiece, and V = 2πrn / 60, n is the spindle speed, r is the rotation radius of the workpiece, and r = r 工 +A,r 工 is the radius of the workpiece before finishing. When calculating r here, A is substituted with the spindle radial runout compensated by the previous preset compensation moment E. When calculating the spindle radial runout compensated by the first preset compensation moment E, r is calculated by substituting A with the spindle radial runout A under no-load conditions. 无 Substitution; The rotation displacement Δx of the spindle relative to the tool is Δx=2πr 轴 n×t 工 / 60 Where r 轴 is the radius of the principal axis; Where m = m 总 -m 切 , m 总 is the total mass of the workpiece before finishing, m 切 is the mass of the removed part during workpiece finishing, m 切 =H×S×q, H is the height of the cylinder, and H=nf×t 工 , f is the feed rate of the tool, S is the bottom area of ​​the cylinder, and S=π[(r 完 +a p ) 2 -r 完 2 ],r 完 is the radius of the preset workpiece after finishing, a p is the preset cutting depth of the tool, q is the density of the workpiece material; but m=m 总 -nft 工 ×π[(r 完 +a p ) 2 -r 完 2 ]×q The calculation formula for the temperature difference T between the front and rear ends of the spindle under load is: Step 3: During the workpiece machining process, when the workpiece is being fine-machined, the lathe control system substitutes the calculated external load N generated by the workpiece on the lathe spindle and the temperature difference T between the front and rear ends of the spindle under load into the spindle radial circular runout A under load and the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t. 轴 The function relationship is used to predict the spindle radial circular runout in real time, and the preset tool cutting depth is changed according to the predicted spindle radial circular runout, so that the radius of the workpiece after cutting is equal to the preset radius of the workpiece after finishing, thereby realizing the spindle radial circular runout compensation during the finishing of the workpiece.

2. The spindle radial runout compensation method based on the thermal error and processing time law according to claim 1 is characterized in that: The process of step 1 is as follows: the lathe spindle is idling at a preset speed n, and the temperature difference between the front and rear ends of the spindle and the radial runout of the spindle are detected and recorded multiple times within a preset time period t0 during the spindle idling process; the temperature difference data of the front and rear ends of each spindle and the corresponding spindle rotation time t are compared. 轴 Fitting is performed to obtain the temperature difference T between the front and rear ends of the spindle under no load conditions. 无 and the spindle rotation time t 轴 The functional relationship between the radial runout data of each spindle and the corresponding spindle rotation time t 轴 Perform fitting to obtain the spindle radial runout A under no-load conditions. 无 and the spindle rotation time t 轴 Then, different values ​​are uniformly selected within the preset range of the external load generated by the workpiece on the lathe spindle. For the external load value generated by each selected workpiece on the lathe spindle, the temperature difference between the front and rear ends of the spindle and the radial circular runout of the spindle are detected and recorded multiple times within a preset time period t0 during the spindle rotation at a preset speed n. The external load data generated by each workpiece on the lathe spindle are compared with the corresponding temperature difference data between the front and rear ends of the spindle and the spindle rotation time t. 轴 The spindle radial runout data is fitted to obtain the spindle radial runout A under load, the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t. 轴 The functional relationship of .

3. The spindle radial runout compensation method based on the thermal error and processing time law according to claim 2, characterized in that: The temperatures at the front end and rear end of the spindle are measured respectively by two temperature sensors, and the radial runout of the spindle is measured by a dial indicator.

4. The spindle radial runout compensation method based on the law of thermal error and machining time according to claim 1, characterized in that: The external load N generated by the workpiece on the lathe spindle when the tool processes the workpiece and the centrifugal force F generated by the workpiece under the influence of the spindle radial circular runout c Equal; in the process of calculating the external load N in step 1, the value A is directly substituted with the spindle radial runout value detected. In step 3, when calculating the external load N, the value A is directly substituted with the value F c The process is exactly the same.

5. The spindle radial runout compensation method based on the law of thermal error and machining time according to claim 2, characterized in that: Temperature difference T between the front and rear ends of the spindle under no load 无 and the spindle rotation time t 轴 The functional relationship is Where θ1 is the coefficient of change of temperature difference and time unit, and θ1 = 1°C / s.

6. The spindle radial runout compensation method based on the law of thermal error and machining time according to claim 2, characterized in that: Spindle radial runout A under no-load condition 无 and the spindle rotation time t 轴 The functional relationship is Where θ2 is the coefficient of variation of the spindle radial runout with time unit, and θ2 = 1 μm / min.

7. The spindle radial runout compensation method based on the law of thermal error and machining time according to claim 1, characterized in that: The spindle radial runout A, the external load N generated by the workpiece on the lathe spindle, the temperature difference T between the front and rear ends of the spindle under load, and the spindle rotation time t 轴 The functional relationship is A=0.1052N×θ3+0.1896t 轴 ×θ2+0.05263T×τ Where τ is the unit variation coefficient of the spindle radial runout and temperature difference, and τ = 1 μm / °C; θ3 is the unit variation coefficient of the spindle radial runout and load, and θ3 = 1 μm / N.

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