CN108776459B - Process method for improving machining precision of five-axis numerical control machine tool - Google Patents

Process method for improving machining precision of five-axis numerical control machine tool Download PDF

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CN108776459B
CN108776459B CN201810771071.XA CN201810771071A CN108776459B CN 108776459 B CN108776459 B CN 108776459B CN 201810771071 A CN201810771071 A CN 201810771071A CN 108776459 B CN108776459 B CN 108776459B
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curved surface
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sampling point
point
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马文魁
吴艳霞
谢秋晨
李宁
武燕
李伟
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Henan Mechanical and Electrical Vocational College
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
    • G05B19/4097—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by using design data to control NC machines, e.g. CAD/CAM
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/35—Nc in input of data, input till input file format
    • G05B2219/35097—Generation of cutter path, offset curve

Abstract

The invention discloses a process method for improving the machining precision of a five-axis numerical control machine tool, which comprises the steps of deviation calculation, point cloud mirror image calculation and theoretical surface adjustment. The invention has the advantages that: the invention provides a process method for improving the machining precision of a complex curved surface five-axis, which considers the influence of various error sources on the machining precision of parts, not only corrects the path of a finish machining tool in time, effectively reduces the rejection rate of the machining of the complex curved surface parts, but also improves the manufacturing machining precision of the five-axis numerical control machine tool.

Description

Process method for improving machining precision of five-axis numerical control machine tool
Technical Field
The invention relates to the technical field of numerical control machining, in particular to a process method for improving machining precision of a five-axis numerical control machine tool.
Background
In the numerical control machining process of parts, the machining quality of the parts is influenced by a plurality of error sources, such as cutter errors, workpiece positioning errors, machine tool geometric errors and the like. The structure size after the parts are machined cannot be completely consistent with a theoretical model due to the action of multiple error sources, certain geometric dimension errors exist, and particularly for complex curved surface parts with large curvature changes, the dimension errors after the parts are machined can be further increased. The five-axis linkage numerical control machine tool is used as the most common tool for machining the complex curved surface parts, namely, in the five-axis numerical control machining process of the parts, the tool and the parts are ensured to be in the optimal machining state and the occurrence of interference phenomenon is inhibited through continuous adjustment of the position of the tool, so that the improvement of the machining quality of the complex curved surface parts is ensured. In addition, the problems of repeated positioning errors and the like in the part clamping process can be eliminated by the online detection technology, so that the reliability and operability of the part evaluation data are effectively ensured. Therefore, the process method for improving the five-axis machining precision of the complex curved surface is provided on the basis of the online detection data of the five-axis numerical control machine tool of the part, and has important significance for guaranteeing the machining quality of the part.
(1) Cho and Seo et al use an artificial intelligence neural network algorithm to train on-line detection data, thereby achieving improvement of part processing quality. (see Cho M W, Seo T I. mechanical interference compensation using radial basis function network CAD/CAM/CAI integration concept. International Journal of Production Research,2002,40(9): 2159-2174).
(2) Chen and Gao et al analyze the on-line detection data according to the principle of space statistics, decompose the error source in the processing into systematic and random two types, and guide the subsequent part processing based on the systematic and random error sources. (see Chen Y, Gao J, Deng H, et al. spatial statistical analysis and compensation of machining errors for machining surfaces precision Engineering,2013,1(1): 203-212.).
(3) Bi, Huang and the like mainly analyze the influence of machine tool errors on the part machining precision, and an online detection method is used for realizing the identification of the parameters of the established five-axis numerical control machine tool rotating shaft error prediction model, and a specific scheme for reducing the part machining errors by using the model is provided. (see Bi Q, Huang N, Sun C, et al. identification and compatibility of geometrical Errors of Rotary Axes On Five-axis Machine by On-Machine measurement. International Journal of Machine Tools and manufacturing, 2014,89: 182-191).
The machining methods proposed in documents (1) and (2) are mainly still based on three-axis nc machining, and are not applicable to five-axis nc machining.
The mathematical model established in the document (3) only considers geometric errors in the movement process of the machine tool and only has the effect on a single error source, but does not relate to the comprehensive consideration of multiple error sources of the five-axis numerical control machine tool.
Disclosure of Invention
The invention aims to solve the various problems and provides a process method for improving the machining precision of a five-axis numerical control machine tool, which can cope with the influence of various error sources on the machining profile precision.
In order to solve the technical problems, the technical scheme of the invention is as follows: a process method for improving the machining precision of a five-axis numerical control machine tool comprises the following steps:
A. calculating deviation, namely planning sampling points on the curved surface by using theoretical curved surface profile information data, and obtaining coordinates of the sampling points by applying an online detection technology; the sampling point cloud of the actual processing contour is obtained by contacting the surface of the part along the normal direction, and the position deviation of the sampling point to the theoretical curved surface can be expressed as:
Figure GDA0002738866950000021
in the formula (I), the compound is shown in the specification,
Figure GDA0002738866950000022
representing the sampling point QhIs determined by the three-dimensional coordinates of (a),
Figure GDA0002738866950000023
representing the sampling point QhTheoretical point G on theoretical surface contourhThree-dimensional coordinates of (a);
B. point cloud mirror image calculation: taking a sampling point of an actual curved surface profile as basic data, and carrying out reverse offset movement on the sampling point by utilizing a mirror image principle to obtain a mirror image point cloud; let the "mirror image" point be Ui"mirror image" point UiCan be expressed as:
Figure GDA0002738866950000024
in the formula (I), the compound is shown in the specification,
Figure GDA0002738866950000025
and
Figure GDA0002738866950000026
three-dimensional coordinates of a mirror image point and a sampling point respectively; delta EhThe position deviation of the sampling point to the theoretical curved surface is obtained; (n)hx,nhy,nhz) Is a unit normal deviation vector;
C. adjusting a theoretical curved surface: the theoretical surface model adjustment comprises the following specific implementation steps:
1) thickening the theoretical curved surface by DsForming a reference surface set to R and again with DsThe thickness is offset, and a first-stage finish machining curved surface is set to be F, so that the cutting amount in the finish machining stage is kept consistent;
2) carrying out numerical control machining operation on the curved surface F, taking the reference curved surface R as a sampling planning matrix, realizing online detection on the machined curved surface, and storing sampling point cloud data;
3) combining the reference curved surface R, and calculating the position deviation of the sampling point and the point cloud mirror image according to the formulas (1) and (2);
4) calculating the point cloud mirror image to obtain a data point and recording the data point as CjThe theoretical sampling point planned by the reference surface R is denoted as ClThen, the coordinate optimization calculation is carried out on the theoretical sampling point cloud, so that ClTo CjThe maximum distance is minimum, and a corresponding coordinate transformation matrix T is obtained through calculation;
5) adjusting the reference curved surface R according to the coordinate transformation matrix T obtained by calculation, and using D as the adjusted reference curved surface RsReversely biasing to obtain a curved surface S of a second finish machining stage;
6) and planning the machining path of the tool in CAM (computer aid manufacturing) software for the adjusted curved surface model, and generating a finish machining numerical control instruction through post-processing software.
Compared with the prior art, the invention has the advantages that: the invention provides a process method for improving the machining precision of a complex curved surface five-axis, which considers the influence of various error sources on the machining precision of parts, not only corrects the path of a finish machining tool in time, effectively reduces the rejection rate of the machining of the complex curved surface parts, but also improves the manufacturing machining precision of the five-axis numerical control machine tool.
Drawings
Fig. 1 is a schematic diagram of a position deviation of a sampling point of the process method for improving the five-axis machining precision of a complex curved surface relative to a theoretical curved surface.
FIG. 2 is a point cloud mirror image calculation schematic diagram of the process method for improving the five-axis machining precision of the complex curved surface.
FIG. 3 is a schematic diagram of theoretical surface adjustment of the process for improving the five-axis machining precision of a complex surface according to the present invention.
FIG. 4 is a schematic diagram of fine-machining surface adjustment of the process for improving the five-axis machining precision of a complex curved surface according to the present invention.
FIG. 5 is a diagram of a machined part of the process method for improving the five-axis machining precision of a complex curved surface.
FIG. 6 is a comparison diagram of machining quality of the process method for improving the five-axis machining precision of the complex curved surface.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
1. Deviation calculation
The method comprises the steps of planning sampling points of a curved surface by using theoretical curved surface profile information data, realizing online detection of an actually processed curved surface by applying an online detection technology, and recording corresponding sampling point coordinate data information, wherein the coordinate data embody quality information of an actually processed curved surface profile. The sampling point cloud of the actual processing contour is generally obtained by contacting the surface of the part along the normal direction, and as shown in fig. 1, the position deviation of the sampling point to the theoretical curved surface can be expressed as:
Figure GDA0002738866950000031
in the formula (I), the compound is shown in the specification,
Figure GDA0002738866950000032
representing the sampling point QhIs determined by the three-dimensional coordinates of (a),
Figure GDA0002738866950000033
representing the sampling point QhTheoretical point G on theoretical surface contourhThree-dimensional coordinates of (a).
2. Point cloud mirror computation
This methodThe method is characterized in that sampling points of an actual curved surface profile are used as basic data, reverse offset movement is carried out on the sampling points by utilizing a mirror image principle to obtain a mirror image point cloud, and the mirror image point cloud is used as a basis for theoretical curved surface adjustment. As shown in FIG. 2, the "mirror image" point UiCan be expressed as:
Figure GDA0002738866950000034
in the formula (I), the compound is shown in the specification,
Figure GDA0002738866950000035
and
Figure GDA0002738866950000036
three-dimensional coordinates of a mirror image point and a sampling point respectively; delta EhThe position deviation of the sampling point to the theoretical curved surface is obtained; (n)hx,nhy,nhz) Is the unit normal deviation vector.
3. Theoretical curved surface adjusting method
In the process of machining a complex curved surface part by a five-axis numerical control machine tool, due to the influence of various error sources, the problems of 'over-cutting' and 'under-cutting' exist in the machining of the part, the phenomena of 'over-cutting' and 'under-cutting' cannot be avoided by selecting any machining mode, namely, the high-precision machining method can only correct the problems of 'over-cutting' and 'under-cutting' formed by a theoretical cutter path, and the problems of 'over-cutting' and 'under-cutting' cannot be thoroughly solved. Therefore, based on the analysis of the problems, the method aims to redistribute the five-axis machining process of the complex curved surface part, subdivide the process into two-stage finish machining processes, and realize the correction of the final finish machining tool path by utilizing the online detection data and adjusting the theoretical model of the part, thereby effectively reducing the influence of the 'over-cut' and 'under-cut' problems on the machining precision of the part and improving the integral machining quality of the part. The specific implementation steps of the theoretical surface model adjustment are as follows:
the first step is as follows: as shown in figure 3, in order to effectively inhibit the problems of over-cutting and under-cutting, the theoretical curved surface is thickened by DsForming a reference curved surface R and repeating the steps with DsThe thickness is offset to form a first-stage finish machining curved surface F, so that the cutting amount in the finish machining stage is kept consistent;
the second step is that: carrying out numerical control machining operation on the curved surface F, taking the reference curved surface R as a sampling planning matrix, realizing online detection on the machined curved surface, and storing sampling point cloud data;
the third step: combining the reference curved surface R, and calculating the position deviation of the sampling point and the point cloud mirror image according to the formulas (1) and (2);
the fourth step: calculating the point cloud mirror image to obtain a data point and recording the data point as CjThe theoretical sampling point planned by the reference surface R is denoted as ClPerforming coordinate optimization calculation on the theoretical sampling point cloud by utilizing a Sequential Quadratic Programming (SQP) algorithm to enable ClTo CjThe maximum distance is minimum, and a corresponding coordinate transformation matrix T is obtained through calculation;
the fifth step: as shown in fig. 4, the reference curved surface R is adjusted according to the coordinate transformation matrix T obtained by calculation, and the adjusted reference curved surface R' is adjusted by DsReversely biasing to obtain a curved surface S of a second finish machining stage;
and a sixth step: and planning the machining path of the tool in CAM (computer aid manufacturing) software for the adjusted curved surface model, and generating a finish machining numerical control instruction through post-processing software.
4. Experimental verification
In order to verify the feasibility of the scheme, the parts profiles 1 and 2 shown in the attached figure 5 are subjected to numerical control machining by using a traditional method and the method respectively, and the quality of the machined parts is measured. As shown in fig. 6, the overall machining accuracy of the profile 2 is significantly improved relative to the profile 1, thereby verifying the feasibility of the method.

Claims (1)

1. A process method for improving the machining precision of a five-axis numerical control machine tool is characterized by comprising the following steps: the method comprises the following steps:
A. calculating deviation, namely planning sampling points on the curved surface by using theoretical curved surface profile information data, and obtaining coordinates of the sampling points by applying an online detection technology; the sampling point cloud of the actual processing contour is obtained by contacting the surface of the part along the normal direction, and the position deviation of the sampling point to the theoretical curved surface can be expressed as:
Figure FDA0002738866940000011
in the formula (I), the compound is shown in the specification,
Figure FDA0002738866940000012
representing the sampling point QhIs determined by the three-dimensional coordinates of (a),
Figure FDA0002738866940000013
representing the sampling point QhTheoretical point G on theoretical surface contourhThree-dimensional coordinates of (a);
B. point cloud mirror image calculation: taking a sampling point of an actual curved surface profile as basic data, and carrying out reverse offset movement on the sampling point by utilizing a mirror image principle to obtain a mirror image point cloud; let the "mirror image" point be Ui"mirror image" point UiCan be expressed as:
Figure FDA0002738866940000014
in the formula (I), the compound is shown in the specification,
Figure FDA0002738866940000015
and
Figure FDA0002738866940000016
three-dimensional coordinates of a mirror image point and a sampling point respectively; delta EhThe position deviation of the sampling point to the theoretical curved surface is obtained; (n)hx,nhy,nhz) Is a unit normal deviation vector;
C. adjusting a theoretical curved surface: the theoretical surface model adjustment comprises the following specific implementation steps:
1)thickening the theoretical curved surface by DsForming a reference curved surface R and repeating the steps with DsThe thickness is offset to form a first-stage finish machining curved surface F, so that the cutting amount in the finish machining stage is kept consistent;
2) carrying out numerical control machining operation on the curved surface F, taking the reference curved surface R as a sampling planning matrix, realizing online detection on the machined curved surface, and storing sampling point cloud data;
3) combining the reference curved surface R, and calculating the position deviation of the sampling point and the point cloud mirror image according to the formulas (1) and (2);
4) calculating the point cloud mirror image to obtain a data point and recording the data point as CjThe theoretical sampling point planned by the reference surface R is denoted as ClThen, the coordinate optimization calculation is carried out on the theoretical sampling point cloud, so that ClTo CjThe maximum distance is minimum, and a corresponding coordinate transformation matrix T is obtained through calculation;
5) adjusting the reference curved surface R according to the coordinate transformation matrix T obtained by calculation, and using D as the adjusted reference curved surface RsReversely biasing to obtain a curved surface S of a second finish machining stage;
6) and planning the machining path of the tool in CAM (computer aid manufacturing) software for the adjusted curved surface model, and generating a finish machining numerical control instruction through post-processing software.
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CN103218475A (en) * 2013-03-14 2013-07-24 天津大学 In-process evaluation based complex spatial surface error feedback compensating method
CN104057363A (en) * 2014-06-10 2014-09-24 浙江大学 Three-axis numerical control machine tool geometrical error compensation method based on workpiece model rebuilding
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