CN115828566B - Process design and verification method for consistency of milling surface precision distribution of end mill - Google Patents
Process design and verification method for consistency of milling surface precision distribution of end mill Download PDFInfo
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Abstract
The invention relates to the technical field of milling, in particular to a process design and verification method for consistency of milling surface precision distribution of an end mill, which comprises the following steps of S1, designing a target of consistency of milling side elevation machining errors of the end mill; s2, a design variable identification analysis method for consistency of milling side elevation machining errors of the end mill; s3, milling a design model with consistency of machining errors of the side elevation of the end mill; s4, verifying a design flow of consistency of machining errors of milling side elevation of the end mill. The design target of the consistency of the machining errors of the milling side elevation of the end mill, the design variable of the consistency of the machining errors of the milling side elevation of the end mill, the design model of the consistency of the machining errors of the milling side elevation of the end mill and the verification method of the design flow of the consistency of the machining errors of the milling side elevation of the end mill are provided, the consistency level of the machining precision is improved, and the feasibility and the consistency level of the technical scheme are verified.
Description
The application is a divisional application of application number 202210162380.3, application day 2022, 02 month 22 and the name of the invention of a process design and verification method for milling surface precision distribution consistency.
Technical Field
The invention relates to the technical field of milling, in particular to a process design and verification method for consistency of milling surface precision distribution of an end mill.
Background
How to realize efficient and accurate cutting by milling is an important development direction nowadays, and by virtue of the process characteristics of high efficiency and high accuracy, the milling is an important realization way for high-quality processing of key parts in the high-end manufacturing fields of modern aerospace, medical appliances and the like. During efficient milling, the milling vibration and cutter tooth errors influence the formation process of the processing surface to change continuously, so that the processing surface errors show various change characteristics along the feeding speed direction and the cutting depth direction, and further the processing surface performance is influenced. The measuring method in the prior art judges the whole or partial level of the quality of the processing surface, and researches specific change characteristics of the processing error on the processing surface have ambiguity and uncertainty.
In the existing error measurement method, only the whole or partial level of the processing surface is judged, and the consistency of the processing precision is not deeply researched, so that the control effect of the whole process on the processing surface is affected, and the milling quality of the processing surface is reduced.
Therefore, we propose a process design and verification method for consistency of precision distribution of milling surface.
Disclosure of Invention
The invention aims to provide a process design and verification method for consistency of precision distribution of milling surfaces of an end mill, so as to solve the problems in the prior art.
In order to achieve the above purpose, the present invention provides the following technical solutions: a process design and verification method for milling surface precision distribution consistency specifically comprises the following steps:
s1, designing a target of consistency of machining errors of milling side elevation of an end mill:
providing a design target of consistency of machining errors of milling side elevation of the end mill, and judging consistency of machining surface precision by utilizing the design target, so that consistency of machining surface precision can be improved;
s2, a design variable identification analysis method for consistency of milling side elevation machining errors of an end mill is adopted:
redesign and plan the design variable of the machining surface precision, give out the design variable identification analysis method of the end mill milling side elevation machining error consistency, analyze the influence degree of the influencing factor and its existing interaction, thus control the design variable;
s3, designing a model of consistency of machining errors of milling side elevation of the end mill:
optimizing the existing process design method through design targets and design variables, and providing a new design model for consistency of machining errors of milling side elevation of the end mill;
s4, verifying a design flow of consistency of machining errors of milling side elevation of the end mill, wherein the method comprises the following steps:
and a verification method of the design flow of the consistency of the milling side elevation machining errors of the end mill is provided, so that the machining precision and consistency level of the design model are verified.
In the step S1, when the machined surface is formed, the degree of influence of each factor on the machined surface error is different, the machined surface precision consistency is the variation characteristic of the machined surface precision in the distribution of the feeding speed direction and the cutting depth direction, and in order to evaluate the machined surface precision consistency, a design target of the end mill milling side elevation machining error consistency is provided.
Each influencing factor is obtained from fig. 1, and finally, the variable sets shown in the following formulas are obtained through summarization.
Q＝{n，f z ，a p ，a e ，M，a，d,l,β，θ，Δy} (1)
Wherein n is the rotation speed of the main shaft; f (f) z Feeding amount for each tooth; a, a p Is milling depth; a, a e Milling width; m is milling vibration; a is cutter tooth error distribution; d is the diameter of the milling cutter; l is the length of the blade; beta is the helix angle; θ is the angle error; Δy is the position error.
The design targets are angle errors and position errors and then the machining surface error values are calculated respectively by extracting characteristic points, as shown in fig. 2-5.
As shown in fig. 2 to 5, n is taken from the start cutting position to the cutting end position on the actual machining surface and the design reference surface in the feed speed direction and the cutting depth direction at a distance of 0mm, 5mm, 10mm in the feed speed direction and the cutting depth direction of the milling cutter radius of 1/2 of the feed speed direction, respectively xi And n γi Calculating the processing surface error distribution curves of the points corresponding to the feeding speed direction and the cutting depth direction by adopting an error calculation method, dividing the processing surface error into a position error and an angle error, and analyzing the average value of the processing surface characteristic point position errors
. Mean value of position errors of the machining surface feature points +.>
Indicating the average level of the machined surface, the maximum value M of the point position error of the machined surface amax The maximum allowable level of the characteristic point position error is shown to be better as the average value of the characteristic point position error of the machining surface is closer. Minimum value M of processing surface characteristic point position error amin The minimum allowable level of the position error of the feature point is indicated, the closer the minimum allowable level is to the average value of the position error of the feature point of the processing surface, the better the angle error of the feature point is, and the angle error of the feature point is an included angle formed by plane normal vectors of selected feature points of a design reference surface and an actual processing surface, wherein the normal vector of the design reference surface is represented by l, the normal vector of the actual processing surface is represented by Nm, and because the design reference surface has no angle, the angle error is self, and the closer the angle error is to 0, the better the uniformity degree is, and the accuracy uniformity level of the processing surface is analyzed by utilizing an error correlation calculation method. The error calculation formula is shown as follows.
Δy＝y g -y g(0) (2)
In θ 1 For the angle error theta at x g o g y g Projection onto a surface; θ 2 For the angle error theta at y g o g z g Projection onto a surface.
To calculate the error correlation, the feature points of the extracted error distribution curve are respectively used as a reference sequence Y q ap And comparing sequence Y q ap *。
Reference sequence Y for calculating surface errors in feed speed direction using improved gray relative correlation analysis q ap Comparison sequence Y with surface errors in depth of cut q ap * Degree of association between the two. Where q=1 is the machining surface position error sequence and q=2 is the angle error sequence.
γ Ma The closer to 1, the higher the consistency level of the machining precision is, the degree of association is between 0.5 and 0.8 in the past, the patent uses the degree of association of 0.8 as a judging index, characteristic points are extracted from the positions with cutting depths of 0mm, 5mm and 10mm respectively, the characteristic points are analyzed by using spss software, and if the distribution of the characteristic points is normal distribution, the machining quality is good.
In combination with the above method, the evaluation index is given as shown in the following formula.
Wherein M is amax Is the maximum value of the error of the actual machining surface; [ M ] amax ]Is the maximum value of the design reference surface error
The average value of the errors of the actual machining surface is; />
Is the design reference surface error average; m is M amin Is the minimum value of the actual machining surface error; [ M ] amin ]Is the design reference surface error minimum.
Finally, the design target of milling side elevation machining error consistency is obtained, as shown in fig. 6.
The step S2 specifically includes the following steps:
s201, a main design variable identification method:
in the milling process, various design variables influence and even interaction, and the influence of each design variable on the consistency of the machining errors is considered, so that each variable is identified and analyzed.
In the machining process, design variables such as vibration, cutter tooth error and feed quantity of each tooth are directly influenced on a machining surface, the main design variables of the machining surface error are selected from the root distance figure 1 to be the rotating speed of a milling cutter spindle, the feed quantity of each tooth, the cutting depth and the cutting width, the cutter tooth error distribution, milling vibration, the diameter of the milling cutter, the length of a cutting edge and the spiral angle, and the variables are set according to a cutter engineering relation diagram.
Q＝{n，f z ，a p ，a e ，M，a，d,l,β} (7)
In order to identify design variables with direct influence on a processing surface, carrying out single-factor variance analysis on the design variables, and obtaining a ratio of an F value to the mean square of the two design variables in a single-factor variance experiment, wherein Fcrit is a critical value under the corresponding significant level of the F value, and if the F value is larger than Fcrit, the influence is significant; p-value is the confidence probability of the corresponding F value, typically less than 0.05 is a significant effect for both, and less than 0.001 is a highly significant effect. According to variance analysis, the influence degree of the milling vibration, cutter tooth error, feed quantity per tooth, cutting width, cutting depth, milling spindle rotating speed, milling cutter diameter, cutting edge length and spiral angle on all design variables is ranked from large to small, wherein the influence degree of milling cutter diameter, cutting edge length and spiral angle influence factors on consistency of machining surface precision is small, and therefore the design variables are determined to be spindle rotating speed, feed quantity per tooth, milling depth, milling width, milling vibration and cutter tooth error distribution.
S202, identifying the influence degree of the design variable by the method:
the influence degree of each influence factor on the machined surface is different, and in order to improve the consistency of the machined surface precision, the influence degree analysis is performed on each factor, and therefore, a method for analyzing the influence factors of the consistency of the machining errors of the milling side elevation is provided, as shown in fig. 7.
As shown in FIG. 7, first, for the design variables n, f z 、a p 、a e Respectively carrying out surface morphology simulation on the surfaces of the two parts M, a, and then calculating by an error calculation method to obtain an error average value of the position error
The method comprises the steps of carrying out a first treatment on the surface of the Maximum error value M amax The method comprises the steps of carrying out a first treatment on the surface of the Error minimum value M amin The method comprises the steps of carrying out a first treatment on the surface of the And then judging the consistency degree of each design variable by a judging method proposed by the complaint.
S203, a design variable coupling effect identification method:
and (3) coupling effect exists in each design variable, performing response surface analysis firstly, performing response surface significance analysis on the response surface model to obtain interaction among influence factors, performing multi-factor variance analysis to obtain coupling effect among the influence factors, providing a central experimental design scheme before performing the response surface analysis, and constructing the response surface model according to the central experimental design scheme and simulation results of the previous design variables, so that a second-order expression is constructed as shown in a formula (8) for analyzing response characteristics of processing surface errors to milling process design variables.
Wherein y is 0 To be initially to a fixed value, p i Is x i Influence coefficient, p ij Is x i And x j Interaction influence coefficient, Q, is the fitting error and noise influence, and is taken as a normal distribution in this model.
And finally, the influence factor coupling action method for obtaining the consistency of the milling side elevation machining errors is shown in fig. 8.
In the step S3, the design model comprehensively utilizes the optimized design and the collaborative design, considers the influence of the machining error and the milling vibration on the machining, improves the machining precision consistency level, takes the machining precision consistency as a constraint condition with the overall machining error level and the consistency of the distribution thereof as a design target, considers the influence degree of each design variable, and establishes a new design model of the machining error consistency of the milling side elevation as shown in fig. 9.
As shown in fig. 9, starting from improving the consistency of machining precision, a design model for milling side elevation machining error consistency starts from researching the characteristic parameters of a milling cutter, the characteristic parameters of the milling cutter are researched through a milling process method and a machine tool to obtain each influence factor, then the surface topography of each influence factor is simulated to obtain machining surface errors and angle errors, machining surface errors are calculated from the feeding speed direction and the cutting depth direction, the machining surface precision integral level and consistency degree of a calculation result are judged through a design target for milling side elevation machining error consistency, if the judgment is not qualified, a new machining precision consistency process scheme is provided for adjusting and planning each design variable through the identification of the machining surface precision integral level influence factor, and the calculation is carried out again. And if the process design scheme is judged to be qualified, carrying out milling experiment verification, if the experiment verifies that the consistency level of the machining precision is improved, indicating the consistency and feasibility of the process design scheme, and if the experiment verification is not passed, redesigning the experiment scheme to carry out judgment.
In step S4, in order to verify the accuracy of the design model of the machining error consistency, a verification method of the design flow of the machining error consistency of the milling side elevation is specifically proposed, as shown in fig. 10.
The verification method is mainly used for verifying the consistency of the machining precision of the design model with the consistency of the machining errors of the milling side elevation by comparing the new process scheme with the old process scheme and the experimental scheme respectively. Firstly, taking n from the actual processing surface and the design reference surface in a new process scheme, an old process scheme and an experimental scheme respectively along the feeding speed direction and the cutting depth direction according to the design target of milling side elevation processing error consistency and the distance of 1/2 milling cutter radius xi And n γi Calculating the feeding speed direction and cutting depth of the points by adopting an error calculation methodThe distribution curve of the machining surface errors in the degree direction is analyzed according to the judgment method to obtain the average value of the position errors and the angle errors of the characteristic points of the machining surface
Maximum value M amax And a minimum value M amin And then carrying out gray correlation analysis calculation on the new process scheme and the old process scheme, judging the consistency of the new process scheme and the old process scheme according to a judging standard, comparing the new process scheme with the old process scheme according to the judging standard, if the correlation of the new process scheme is higher than that of the old process scheme, indicating that the consistency of the new process scheme is high, and comparing the maximum value and the minimum value of errors with the average value of the new process scheme and the experimental scheme, if the new process scheme is closer to the error average value than the maximum value and the minimum value of errors of the experimental scheme, indicating that the accuracy of the new process scheme is high, and the error is small, thereby verifying the consistency of the processing accuracy of the design model.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the design target of the consistency of the machining errors of the milling side elevation of the end mill, the distribution characteristics of the machining surface errors are analyzed, the angle errors and the position errors are obtained by using a characteristic point extraction method, the errors are resolved by using an error resolving method, and finally the consistency of the machining errors is judged by using a relevance analysis method, so that the consistency level of the machining precision is improved;
2. according to the design variables of the consistency of the milling side elevation machining errors of the end mill, the variables are subjected to re-integration planning, related influence factors are separated out, the influence degree of the influence factors is obtained by using a single-factor variance analysis method, and finally the interaction influence degree among the influence factors is obtained by using a multi-factor variance analysis method, so that the influence factors are better controlled, and the consistency of the machining precision is improved;
3. the design model of the machining error consistency of the milling side elevation of the end mill provided by the invention has the advantages that the machining precision consistency level is higher, and the machining precision overall level meets the machining technical requirement, and the precision level and consistency level thereof are obtained;
4. the verification method of the design flow of the consistency of the milling side elevation machining errors of the end mill provided by the invention utilizes a judging method to verify the feasibility and consistency level of a process scheme through experimental comparison.
Drawings
FIG. 1 is a schematic diagram of the influencing factors of the milling process of the present invention;
FIG. 2 is a schematic diagram of a feature point extraction method according to the present invention;
FIG. 3 is a graph showing the error profile of the machined surface in the feed rate direction in accordance with the present invention;
FIG. 4 is a graph showing the error distribution of the machined surface in the depth of cut direction according to the present invention;
FIG. 5 is a schematic view of an angle error model according to the present invention;
FIG. 6 is a flow chart of the design goals of milling side elevation process error consistency of the present invention;
FIG. 7 is a flow chart of a method for analyzing influencing factors of consistency of machining errors of milling side elevation in the present invention;
FIG. 8 is a flow chart of a method for analyzing influence factor coupling effect of consistency of machining errors of milling side elevation in the invention;
FIG. 9 is a flow chart of a design model for milling side elevation process error consistency in accordance with the present invention;
FIG. 10 is a flow chart of a verification method of the design flow of milling side elevation machining error consistency of the present invention;
fig. 11 is a graph showing the distribution trend of the depth of cut z=0 according to the present invention;
fig. 12 is a graph showing the distribution trend of the depth of cut z=5 according to the present invention;
fig. 13 is a graph showing the distribution trend of the depth of cut z=10 according to the present invention;
FIG. 14 is a bar graph of a significant analysis of the process surface position error variation characteristic influencing factors of the present invention;
FIG. 15 is a bar graph showing a significant analysis of the angular error variation characteristic contribution of the tangential plane and xoz plane of the present invention;
FIG. 16 is a bar graph showing a significant analysis of the angular error variation characteristic contribution of the tangential plane and yoz plane of the present invention;
FIG. 17 is a simulation diagram of an experimental machined surface of a new process scheme of the present invention;
FIG. 18 is a line graph of position error reference points for the novel process scheme of the present invention;
FIG. 19 is a plot of angular error between the tangential plane and xoz of the novel process recipe location point;
FIG. 20 is a plot of angular error between the tangential plane and yoz of the position point of the novel process of the present invention;
FIG. 21 is a graph of simulation results of a processing surface of a new process recipe of the present invention;
FIG. 22 is a line graph of simulated position error reference points for the novel process scheme of the present invention;
FIG. 23 is a plot of angular error between the tangential plane of the simulated position point of the novel process scheme of the present invention and xoz;
FIG. 24 is a plot of angular error between the tangential plane of the simulated position point of the novel process scheme of the present invention and yoz;
FIG. 25 is a simulation of the machined surface with only tooth errors in accordance with the present invention;
FIG. 26 is a simulation of a machined surface under the action of milling vibration alone in accordance with the present invention;
FIG. 27 is a graph of a position error curve distribution line under vibration of the present invention;
FIG. 28 is a plot of tangential plane to yoz plane angle error for a point of position under vibratory action of the present invention;
FIG. 29 is a plot of tangential plane to xoz plane angle error for a point of position under vibratory action of the present invention;
FIG. 30 is a histogram of correlation between surface errors in old and new experiments according to the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a technical scheme that: a process design and verification method for milling surface precision distribution consistency specifically comprises the following steps:
s1, designing a target of consistency of machining errors of milling side elevation of an end mill:
and selecting the characteristic points under different cutting depth conditions by a judging method, and analyzing the characteristic points by using statistical analysis software SPSS.
The p-p diagram is taken as a common means for analyzing the variable distribution form, and mainly reflects the trend relation between the accumulated proportion of the selected characteristic point variables and the accumulated proportion of the appointed distribution, so that the distribution situation of the characteristic points can be intuitively reflected. The feature points are selected and tested at three cutting depths of z=0, z=5 and z=10 to see whether normal distribution is obeyed or not. As shown in fig. 11-13:
it can be seen from fig. 11 to 13 that the actual cumulative probability and the expected cumulative probability are approximately in a straight line, so that it can be obtained that the actual machined surface feature points approximately follow normal distribution under different cutting depths.
According to the processing surface error calculating method, the processing surface error is calculated at the position with the cutting depth of z=0 mm, z=5 mm and z=10 mm, an error sequence corresponding to three cutting depth error curves of two types of errors is constructed, the change trend is analyzed by using a gray correlation analysis method, and the consistency analysis result is shown in table 1.
TABLE 1 processing precision consistency analysis
As shown in table 1, the maximum value of the machining surface error is smaller at three different cutting depths, and meets the technical requirement of machining surface precision; and the relevance of the machining errors at a plurality of positions is higher than 0.8, which shows that the precision consistency is better. In order to comprehensively judge the machining surface precision in the cutting depth direction, the average value of the machining error association degree of each cutting depth is adopted as a judging index, and the average value of the error association degree is higher than 0.8, so that the consistency level of the machining precision is good.
S2, a design variable identification analysis method for consistency of milling side elevation machining errors of an end mill is adopted:
in the design variables of the machining surface errors screened by using the design variables of the consistency of the machining errors of the milling side elevation, the rotating speed of the main shaft and the feeding quantity of each tooth can directly influence the vibration and also can influence the vibration period and the cutter tooth errors, so that the rotating speed of the main shaft, the feeding quantity of each tooth, the cutter tooth errors and the milling vibration are used as influencing factors of the machining surface errors, the machining surface errors are analyzed and solved through single factors, and the preliminary design variable variance analysis is carried out on the machining surface errors.
The experimental milling cutter is an integral hard alloy end milling cutter (MC 122-20.0A5B-WJ30 TF) manufactured by Walter company, the tooth pitch of five teeth is equal, the diameter is 20mm, the cutter length is 104mm, and the helix angle is 50 degrees; the machine tool selects a triaxial milling machining center, and the length of a workbench is 1050mm and the width of the workbench is 560mm. The milling mode is direct milling and dry milling, and the milling brand of the titanium alloy is TC4.
The single factor experiment was performed using the basic values of the spindle speed 1144rpm, the feed per tooth of 0.145mm/z, the cutting depth of 0.5mm, and the cutting width of 15mm, and the results of the single factor experimental scheme and the results of measuring vibration acceleration signals are shown in Table 2.
Table 2 single factor experimental protocol variable parameter table
According to the vibration test results of the single factor experimental scheme shown in table 2, the maximum values of the vibration accelerations in three directions are used as vibration characteristics, and variance analysis is adopted to calculate the influence degree of the milling cutter spindle rotating speed, the feeding amount per tooth, the cutting depth and the cutting width on milling vibration.
Combining the actual condition of milling vibration in a milling experiment, and using signal data of maximum values of three-direction vibration acceleration of 5 times of milling experiment, wherein the signal data are a respectively 1 ＝(0.95，2.18，1.77)；a 2 ＝(1.05，5.41，1.24)；a 3 ＝(1.13，2.22，1.84)；a 4 ＝(1.52,5.91，3.21)；a 5 = (1.68,5.75,2.55) (unit: m/s 2 )。
Where n=1718 rpm, f z ＝0.05mm、M 1 (axial error 0.045,0.008,0.016,0.037,0.029; radial error 0.027,0.055,0.017,0.027,0.018) as a basic parameter, and analysis of variance of design variables of the error distribution characteristics of the machined surface was performed, and the analysis results are shown in table 3.
TABLE 3 processing error analysis of variance results
As shown in table 3, the milling spindle rotation speed, the cutter tooth error, the feed per tooth and the F value of milling vibration are greater than Fcrit and the P-value is less than 0.05, which indicates that various influencing factors have a significant influence on the distribution characteristics of the machining error. The analysis of the variance value shows that the influence degree of the influence factor of the processing surface position error: cutter tooth error > per tooth feed > milling vibration = milling cutter spindle rotational speed; degree of influence of factors affecting tangential plane and xoz plane angle error: cutter tooth error > milling cutter spindle rotation speed > milling vibration > per tooth feed; degree of influence of factors affecting tangential plane and yoz plane angle error: milling vibration > per tooth feed amount > cutter tooth error > milling cutter spindle rotation speed.
In order to obtain the influence degree of each influence factor on the machining surface error, the machining error distribution response surface model is subjected to significance analysis, so that the influence significance level of the milling cutter spindle rotating speed, the cutter tooth error, the feeding amount of each tooth and the milling vibration is obtained. If the change in the machining surface error caused by the change itself is larger than the change caused by the random error thereof, the influence factor is considered to have a significant influence on the machining surface error, and the level of the influence significant term (P) of the change in the machining surface position error is shown in fig. 14.
As shown in fig. 14, the significant degree of the influence of the processing surface position error is arranged from large to small as viewed in terms of the P value:
n＞a＞M＞n×a＞f z ×a＞n×f z ＞f z (9)
in the formula, n multiplied by a is the interaction between the rotating speed of the main shaft and milling vibration; f (f) z X a is the interaction of the feed per tooth with milling vibration; n×f z For each tooth feed amount with spindle speed.
In the design variables of the position error change characteristics of the machining surface, the influence probability level of the rotating speed of the milling cutter spindle, the cutter tooth error and the milling vibration is less than 0.01, and the milling vibration is highly influenced; the feed per tooth is relatively weak, but the influence on the position error of the processing surface is still less than 0.05, and the influence is obvious. In the interaction of variables, the interaction effect of the spindle rotating speed and milling vibration is most obvious, the effect of the spindle rotating speed and the feeding amount of each tooth is weaker and still obvious, the probability level of other interaction significant items is more than 0.05, the interaction is weaker or no interaction exists, and the influence on the position error change characteristic of the processing surface is not obvious.
The probability level values of the significant term of the tangential plane and xoz plane angle error variation characteristic influence factor in the machined surface shape error are shown in fig. 15.
As can be seen from fig. 15, the significance of the effect of the tangential plane in the machined surface shape error and the design variable of the xoz plane angle error distribution characteristic is ranked from large to small:
f z ＞f z ×a＞n×a＞n＞M＞M×a＞a＞f z ×M＞n×M (10)
wherein Mxa is the interaction of cutter tooth errors and milling vibration; f (f) z X M is the interaction of the feed per tooth with the cutter tooth error; n×m is the interaction of spindle rotation speed and cutter tooth error.
Among the influencing factors of the tangential plane and xoz plane angle error distribution characteristics, the probability level of the influence significant terms of milling vibration, the feeding amount per tooth, the spindle rotating speed and the interaction with the feeding amount per tooth is smaller than 0.01, and the influence is significant; among other significant factors, the milling cutter tooth error and the spindle rotation speed have higher influence degrees, and the milling vibration has relatively lower influence degrees. In the interaction of each influencing factor, the interaction of the cutter tooth error and other three influencing factors is also more remarkable, which shows that the tangential plane and xoz plane angle error distribution characteristic is mainly influenced by the interaction of milling vibration and cutter tooth error and other variables. The interaction between other influencing factors affects little or no interaction.
The probability level values for the significant term of tangential plane and yoz plane angle error contributors in machined surface shape errors are shown in fig. 16.
As can be seen from fig. 16, among the factors affecting the tangential plane and yoz plane angle errors in the shape error of the machined surface, the significant degree of influence of the factors is as follows:
M＞f z ＞n×a＞n＞a＞f z ×M (11)
the probability of the influence level of the feed quantity of each tooth and the angle error of the cutter tooth on the bisection plane and the yoz plane is less than 0.01, and the influence degree is obvious; among other significant influencing factors, the interaction influence of the rotating speed of the milling cutter spindle and the cutter tooth error is more significant, and the interaction of the feeding amount per tooth and the cutter tooth error is also more significant. Other influencing factors and the extent of interaction influence are not significant or interaction is absent.
S3, designing a model of consistency of machining errors of milling side elevation of the end mill:
since the new process scheme has obviously improved error distribution characteristics of the processed surface compared with the existing scheme, milling simulation experiments are carried out by using milling parameters in the experimental scheme, and the result of extracting the characteristic points of the processed surface to fit the processed curved surface is shown in fig. 17.
The simulation result is solved through a design target of milling side elevation machining error consistency and a milling machining error position point error solving method, an experimental scheme is divided into 5 cutting periods according to vibration signal characteristics according to the same method, machining surface equations of corresponding surfaces are respectively constructed, after the fitting degree of the machining surface equations is verified to be in accordance with an expected result, finally machining surface error solving is carried out, and an experimental machining surface error distribution curve is shown in fig. 18-20.
As shown in fig. 18-20, the errors of the processing surface of the new process scheme are somewhat similar to the simulation error curves, which initially indicates the accuracy and reliability of the simulation results. There is still a need to verify the error results of the new process scheme in comparison with the old experimental scheme.
The experimental result of the new process scheme and the simulation model are verified to obtain the evaluation index pair of the processing surface errors shown in the table 4, and the relative errors of the evaluation indexes are shown in the table 5.
Table 4 comparison of accuracy evaluation index of solution model
TABLE 5 relative error of accuracy evaluation index of solution model
As shown in tables 4 and 5, in the processed surface error evaluation index data of the experimental scheme, the maximum relative error is 19.85%, the minimum relative error is 1.28%, and the relative error is lower than 20%, which fully indicates that the relative error of the processed surface error average value of the simulation model and the experimental value is smaller, and the simulation error value and the experimental error value are very similar in value, which indicates that the reliability and the accuracy of the simulation method are verified in value.
TABLE 6 correlation between simulation and experimental process errors for the new scheme
The milling processing error characteristic sequence of the experimental scheme is constructed by a processing surface error characteristic point extraction method, and the association degree of the error between the simulation of the new process scheme and the experiment is calculated by a gray association analysis method, wherein the association degree is shown in table 6. The degree of correlation of the machining errors is greater than 0.8, which indicates that the simulated surface of the new process scheme is similar to the error variation of the experimental surface. In combination with the verification of the error values in tables 4 and 5, this demonstrates that the simulation results can accurately characterize the experimental surface.
S4, verifying a design flow of consistency of machining errors of milling side elevation of the end mill, wherein the method comprises the following steps:
in order to verify the processing error distribution condition of the new process scheme, the experimental milling cutter adopts an integral hard alloy end mill (MC 122-20.0A5B-WJ30 TF) manufactured by the Walt company, five teeth with equal tooth pitches, 20mm diameter, 104mm cutter length and 50 DEG helix angle; the machine tool selects a triaxial milling machining center, and the length of a workbench is 1050mm and the width of the workbench is 560mm. The milling mode is direct milling and dry milling, and the milling brand of the titanium alloy is TC4.
In milling, the reasonable selection of cutting parameters can improve the processing efficiency and reduce the production loss, and after milling cutters, processing machine tools and milling workpieces are selected, the cutting parameters are selected within a certain range. The cutting efficiency is an important index for measuring the processing production quality, so that the milling efficiency is ensured to be 300cm 3 /min-380cm 3 On the premise of/min, selecting the rotating speed n of the milling cutter to be 1719r/min and the feeding speed v f 573mm/min depth of cut a p Cutting width a of 10mm e Is 0.5mm.
And constructing a processing error resolving model for the new process scheme, and then calculating the constructed processing surface by using a processing error resolving method, wherein the simulation surface result is shown in fig. 21, and the simulation surface error calculation result is shown in fig. 22-24.
As shown in fig. 22 to 24, among the parameters of the 3-item machined surface errors of the new process recipe, the degree of error variation at each depth is relatively close to that of the old experimental recipe, so that it can be primarily considered that the machined surface uniformity of the new process recipe is improved, but still further verification is required.
In order to obtain the influence degree of milling vibration and cutter tooth error on machining error, simulation and machining error characterization are carried out on only two conditions of vibration action and cutter tooth error action under the milling condition of a new experimental scheme through the above constructed resolving model and machining surface error calculation result, and the results are shown in fig. 25-26.
By calculating by using a milling error forming process calculating method, only the cutting depth errors of all the positions under the action of cutter tooth errors are the same, wherein the position error of a processing surface is 0.010, and the two angle errors are 0, namely theta 1 、θ 2 0, Δy is 0.008. Since milling vibration has a certain influence on the tool contact relationship and the influence on machining errors can be revealed by error resolution, only the machining surface error point resolution under the vibration action is shown in fig. 27-29.
As shown in fig. 27-29, the machining surface error under the combined action is obviously different from the machining surface error under the vibration action, which means that the cutter tooth error, the feeding amount of each tooth and other factors have a certain influence on milling vibration, and compared with the error under the combined action, the variation degree of the error distribution curve of the cutting depth at three places is more consistent.
In order to reveal the influence degree characteristics of cutter tooth errors and milling vibration on the forming process of the machining surface under the new technological scheme, the association degree of error distribution and simulated machining surface error distribution under the action of the two single factors is calculated by using a gray association analysis method, and the analysis results are shown in table 7.
TABLE 7 correlation of processed surface errors
As shown in table 7, only the correlation degree between the machining error and the experimental error under the action of the cutter tooth error is about 0.6, and the correlation degree of the milling vibration is about 0.75-0.81, which indicates that the milling vibration plays a major role in the formation process of the milling machining error.
And according to the calculation result of the processing error forming process, comparing the overall level of the processing surface errors of the depths of 3 places, and calculating the difference between the simulation results of the new process scheme and the old process scheme, as shown in table 8.
TABLE 8 integral level differences of process surface errors for New and old Process schemes
As shown in table 8, the difference between the overall error levels of the new and old schemes is small, and the overall variation level of each error is calculated as follows: the position error of the new process scheme is reduced by 0.13% compared with the old process scheme, the included angle error between the tangential plane and the xoz surface is increased by 0.09%, and the included angle error between the tangential plane and the yoz surface is increased by 0.05%, which indicates that the overall horizontal change of the errors of the two process schemes is smaller.
The machining precision consistency of the simulated machining surface is analyzed by milling the design target of the machining error consistency of the side elevation and combining the single factor influence analysis of the constructed machining error, and the analysis result is shown in table 9.
Table 9 milling accuracy consistency analysis
The results of the simulation surface accuracy consistency analysis of the original and new solutions are compared, and the average value of the correlation degree of each machining error is used as the comprehensive judgment result of the machining accuracy consistency, as shown in fig. 30.
As shown in fig. 30, the surface consistency results for the new protocol were significantly improved over the old protocol. Since the degree of association is less than 0.5 as uncorrelated, the uncorrelated case is not taken into consideration when the degree of association is calculated to be increased. Through calculation, the consistency of the position error distribution of the processing surface is improved by 11.96%, the consistency of the error distribution of the included angle between the tangential plane and the xoz surface is improved by 11.5%, and the consistency of the error distribution of the included angle between the tangential plane and the yoz surface is improved by 17.48%.
Compared with the original process scheme, the novel process scheme has the advantages that the integral condition of the machining surface errors is kept at the original level, the consistency level of the machining surface precision is effectively improved, and in conclusion, the novel design model for the consistency of the machining errors of the milling side elevation can enable the machining surface precision to be kept at the original level at the integral degree, and meanwhile, the consistency and reliability of the machining surface precision can be improved.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (1)
1. The process design and verification method for the consistency of the milling surface precision distribution of the end mill is characterized by comprising the following steps: the method specifically comprises the following steps:
s1, designing a target of consistency of machining errors of milling side elevation of an end mill:
providing a design target of consistency of machining errors of milling side elevation of the end mill, and judging consistency of machining surface precision by utilizing the design target;
when the machining surface is formed, the degree of influence of each factor on the machining surface error is different, the machining surface precision consistency is the change characteristic of the distribution of the machining surface precision along the feeding speed direction and the cutting depth direction, in order to judge the machining surface precision consistency, a design target of the machining error consistency of the milling side elevation of the end mill is provided, and a variable set is Q= { n, f is obtained according to the summary of a plurality of influence factors z ，a p ，a e M, a, d, l, beta, theta, deltay }, wherein n is the rotation speed of the main shaft; f (f) z Feeding amount for each tooth; a, a p Is milling depth; a, a e Milling width; m is milling vibration; a is cutter tooth error distribution; d is the diameter of the milling cutter; l is the length of the blade; beta is the helix angle; θ is the angle error; Δy is the position error;
the position error calculation formula is as follows: Δy=y g -y g(0) ；
S2, a design variable identification analysis method for consistency of milling side elevation machining errors of an end mill is adopted:
redesign and plan the design variable of the machining surface precision, give out the design variable identification analysis method of the end mill milling side elevation machining error consistency, analyze the influence degree of the influence factors and the interaction existing in the influence degree, so as to control the design variable;
the method specifically comprises the following steps of:
s201, a main design variable identification method;
in the milling process, under the condition that a plurality of design variables influence or even interact, the influence of each design variable on the consistency of the machining error is considered, each variable is identified and analyzed, the main design variables of the machining surface error are selected to be milling cutter spindle rotating speed, feeding quantity of each tooth, cutting depth, cutting width, cutter tooth error distribution, milling vibration, milling cutter diameter, cutting edge length and helix angle, in order to identify the design variables which directly influence the machining surface, single-factor variance analysis is carried out on the design variables, F value is obtained in a single-factor variance experiment and is the ratio of mean square of the two design variables, fcrit is a critical value under the corresponding significant level of the F value, and F value is larger than Fcrit, so that the influence is significant; p-value is the confidence probability of the corresponding F value, typically less than 0.05 is that there is a significant effect on both, less than 0.001 is a highly significant effect; according to variance value analysis, the influence degree of milling vibration, cutter tooth error, feed quantity per tooth, cutting width, cutting depth, milling main shaft rotating speed, milling cutter diameter, cutting edge length and spiral angle on all design variables is ranked from large to small, wherein the influence degree of milling cutter diameter, cutting edge length and spiral angle influence factors on consistency of machining surface precision is small, and therefore the design variables are determined to be main shaft rotating speed, feed quantity per tooth, milling depth, milling width, milling vibration and cutter tooth error distribution;
s202, a method for identifying the influence degree of design variables;
first toDesign variables n, f z 、a p 、a e Respectively carrying out surface morphology simulation on the surfaces of the two parts M, a, and then calculating by an error calculation method to obtain an error average value of the position error
Maximum error value M amax The method comprises the steps of carrying out a first treatment on the surface of the Error minimum value M amin The method comprises the steps of carrying out a first treatment on the surface of the Then judging the consistency degree of each design variable by the proposed judging method;
s203, designing an identification method of variable coupling effect;
each design variable has coupling effect, response surface analysis is firstly carried out, response surface significance analysis is carried out on the response surface model to obtain interaction between influence factors, multi-factor variance analysis is finally carried out to obtain coupling effect between the influence factors, a central test design scheme is put forward before the response surface analysis is carried out, and then the response surface model is constructed according to the central test design scheme and simulation results of the previous design variables, so that a second-order expression is constructed for analyzing response characteristics of processing surface errors to milling process design variables
Wherein y is 0 To be initially to a fixed value, p i Is x i Influence coefficient, p ij Is x i And x j Interaction influence coefficient, Q is fitting error and noise influence, and normal distribution is taken in the model;
s3, designing a model of consistency of machining errors of milling side elevation of the end mill:
optimizing the existing process design method through design targets and design variables, and providing a new design model for consistency of machining errors of milling side elevation of the end mill;
starting from the improvement of the consistency of machining precision, the design model for the consistency of the machining errors of the milling side elevation of the end mill researches the characteristic parameters of the end mill through a milling process method and a machine tool to obtain all influence factors, then carries out surface appearance simulation on all the influence factors to obtain machining surface errors and angle errors, carries out machining surface error calculation on all the influence factors from the feeding speed direction and the cutting depth direction, judges the overall level of the machining surface precision and the consistency degree of the calculated result through the design target of the consistency of the machining errors of the milling side elevation, and if the judgment is not qualified, carries out adjustment planning on all the design variables through the identification of the overall level influence factors of the machining surface precision, and proposes a new machining precision consistency process scheme for solving the machining surface errors again; if the process design scheme is judged to be qualified, milling experiment verification is carried out, if the experiment verifies that the consistency level of the machining precision is improved, the consistency and the feasibility of the process design scheme are indicated, and if the experiment verification is not passed, the experiment scheme is redesigned to be judged;
s4, verifying a design flow of consistency of machining errors of milling side elevation of the end mill, wherein the method comprises the following steps:
the method mainly comprises the steps of comparing a new process scheme with an old process scheme and an experimental scheme to verify the consistency of the machining precision of a design model with the consistency of the machining errors of the milling side elevation; firstly, respectively taking n from actual processing surfaces and design reference surfaces in a new process scheme, an old process scheme and an experimental scheme according to the design targets of consistency of milling side elevation processing errors along the feeding speed direction and the cutting depth direction according to the distances of 0mm, 5mm and 10mm in the 1/2 milling cutter radius pitch and the cutting depth direction xi And n γi Calculating the processing surface error distribution curves of the points corresponding to the feeding speed direction and the cutting depth direction respectively by adopting an error calculation method, and analyzing the average value M of the position error and the angle error of the processing surface characteristic points according to a judging method a Maximum value M amax And a minimum value M amin Then, the new process scheme and the old process scheme are subjected to gray correlation analysis and calculation, the consistency of the new process scheme and the old process scheme is judged according to a judgment standard, the new process scheme and the old process scheme are compared according to the judgment standard, and if the correlation of the new process scheme is higher than that of the old process scheme,the new process scheme is high in consistency degree, the new process scheme and the experimental scheme are compared with each other by comparing the error maximum value and the error minimum value to the average value, and if the new process scheme is closer to the error average value than the experimental scheme error maximum value and the experimental scheme error minimum value, the new process scheme is high in precision and small in error, so that the processing precision and consistency level of the design model are verified.
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