CN110919459B - Method for detecting influence of clamping force on machining deformation of thin-wall part - Google Patents
Method for detecting influence of clamping force on machining deformation of thin-wall part Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
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- B23Q17/002—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring the holding action of work or tool holders
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Abstract
The invention discloses a method for detecting the influence of clamping force on the processing deformation of a thin-wall part, which comprises the following steps: calculating basic conditions to be met by the clamping force; II, secondly: selecting different clamping forces, and clamping under the action of different pressing forces; thirdly, the method comprises the following steps: a clamping mode of surface support and four-point clamping is adopted to carry out milling experiment on the thin plate; fourthly, the method comprises the following steps: measuring the clamping force by using a pressure sensor, and recording the change of the clamping force in the milling process; fifthly: after milling is finished, measuring the flatness of the machined surface by using a three-coordinate measuring machine; sixthly, the method comprises the following steps: through the contrastive analysis of the flatness values under different clamping forces, the influence rule of the clamping force on deformation is obtained, and then the clamping force values under different flatness requirements are obtained. According to the invention, through milling tests under different clamping force conditions, the clamping force at the initial processing time and the change of the clamping force in the processing process are measured, and then the deformation conditions of different thin-wall parts after processing are obtained through the measurement of the surface flatness, so that the influence rule of the clamping force on the flatness is obtained.
Description
Technical Field
The invention belongs to the technical field of machining deformation, and particularly relates to a method for detecting influence of clamping force on machining deformation of a thin-wall part.
Background
In order to meet the structural performance requirements of aircraft structural members, the weight of the aircraft structural members is reduced as much as possible on the premise of meeting the requirements of structural strength and the like, and therefore the aircraft structural members are generally thin-walled structures. With the development of the integration of aviation structural components, the structural components have the characteristics of large size, thin wall and complex structure on the whole. The characteristics of large size and thin wall enable the aviation structural component to be easy to generate processing deformation after processing.
For the installation of a large thin-wall structural member on a fixture, the clamping process mainly depends on a pressure plate. The high-reliability clamping of the structural part can be realized only by a plurality of pressing plates in the clamping process of the structural part. When a pressing plate is used, the pressing force is a key factor in the clamping process.
Thin-walled parts or thin-walled parts are referred to when the thickness of the part or the ratio of the thickness to the overall dimensions is less than 1: 20. The aluminum alloy thin-wall/thin-plate part has the advantages of high specific strength, light relative weight and the like, is widely used in aerospace, but is easy to deform during clamping and processing due to the characteristic of poor rigidity.
The clamp ensures the correct position occupied by the workpiece on the machine tool in the mechanical processing, is an important factor in process planning, and has direct influence on the operation safety and the processing precision of the workpiece. The fixture is used for ensuring the stability of the workpiece in the whole machining process, and machining errors of the workpiece caused by the fixture are important factors which cannot be ignored. The clamping element applies proper clamping force to the workpiece, and when the clamping force is not applied enough, the workpiece generates small displacement or vibration in the machining process and deviates from the original clamping position; when the clamping force is applied excessively, the clamping force can cause the workpiece to generate rebound deformation after being detached from the clamp, and even cause the workpiece to generate deformation in the clamping process.
At present, in order to ensure the stability and reliability of a workpiece in a machining process, a higher pressing force is generally adopted on the premise of not causing deformation of the workpiece. However, the pressing force has a significant influence on the deformation of the workpiece, and an excessive pressing force may cause a more severe deformation phenomenon after the workpiece is machined. Therefore, how to reasonably select the clamping force in the clamping process of the thin-wall part is a precondition for determining the clamping force, and a method for detecting the influence of the clamping force on the machining deformation of the thin-wall part is a key technical problem which needs to be solved urgently.
Disclosure of Invention
Aiming at the current situation that the clamping force range is difficult to determine when the minimum machining deformation is generated in the current thin-wall part clamping process, the invention overcomes the defects of the prior art, and provides a method for detecting the influence of the clamping force on the machining deformation of the thin-wall part. The technical scheme adopted by the invention is as follows:
a method for detecting the influence of clamping force on the processing deformation of a thin-wall part comprises the following steps:
the method comprises the following steps: calculating basic conditions to be met by the clamping force of the thin-wall part;
step two: selecting 3-7 clamping forces, and clamping under the action of different pressing forces;
step three: carrying out milling experiments on the thin-walled workpiece by adopting a clamping mode of surface support and four-point clamping;
step four: measuring the clamping force by using a pressure sensor, and recording the change of the clamping force in the milling process;
step five: after milling is completed, the flatness of the machined surface is measured using a three-coordinate measuring machine. The measuring method is that a probe collects points along a feed path from a position where milling starts, data points are collected on the feed path every time, and the planeness of the processed surface is fitted through a best fit method;
step six: through the contrastive analysis of the flatness values under different clamping forces, the influence rule of the clamping force on deformation is obtained, and then the clamping force values under different flatness requirements are obtained.
The thin-wall part meets the following basic conditions during clamping:
in the milling process, the force balance and the moment balance of the thin-wall part under the action of external force are ensured: e, F is 0, M is 0;
in order to ensure that the thin-wall part is completely fixed, the thin-wall part and the clamping element cannot slide relatively under the action of external force, namely the clamping stability of the thin-wall part. Therefore, at each contact point of the clamping element with the thin-walled part, the normal contact force F of the clamp with the thin-walled partzWith tangential force Fx、FyThe coulomb's law of friction should be satisfied: i Fx|+|Fy|≤μFzWherein mu is the friction coefficient of the clamp and the thin-wall part;
the normal contact force of the clamp and the thin-walled part must be positive, and the normal contact force cannot cause plastic deformation of the thin-walled part: fz≥0，Fz≤syA, wherein syThe compressive yield strength of the material of the thin-walled piece, and A is the contact area of the clamping element and the thin-walled piece.
The invention has the beneficial effects that: the pressing force has important influence on the deformation of the thin-wall part, and the phenomenon of severe deformation of the thin-wall part after processing can be caused by excessive pressing force. Therefore, how to reasonably select the clamping force in the thin-wall part clamping process is a precondition for determining the clamping force, and the method for detecting the influence of the clamping force on the machining deformation of the thin-wall part is a key technical problem which needs to be solved urgently, and the invention has the following advantages: (1) the invention relates to a method for detecting the influence of clamping force on the machining deformation of a thin-wall part, which selects different clamping force on the premise that the clamping force needs to meet basic conditions, carries out milling tests under different clamping force conditions and improves the test reliability. (2) In the milling process of the thin-wall part, the clamping force at the initial processing time and the change of the clamping force in the processing process are measured through the pressure sensor, the deformation conditions of different thin-wall parts after processing are obtained through the measurement of the surface flatness, the influence rule of the clamping force on the flatness is further obtained, an important detection basis is provided for the reasonable selection of the clamping force in the clamping process of the thin-wall part, and therefore the safety and reliability of the aircraft structure in service are guaranteed.
Drawings
FIG. 1 is a schematic view of a process site of the present invention;
FIG. 2 is a schematic view of the feed of the present invention;
FIG. 3 is a graph showing the variation of the clamping force of the platens during the process of the present invention; in the figure: (a) the initial clamping force of the pressure plate is a 300N clamping force variation graph; (b) the initial clamping force of the pressure plate is a 400N clamping force variation graph; (c) the initial clamping force of the pressure plate is a 500N clamping force variation graph; (d) the initial clamping force of the pressure plate is a 600N clamping force variation graph;
FIG. 4 is a schematic view of flatness measurement according to the present invention;
FIG. 5 is a schematic view of the flatness of the machined surface of the present invention;
fig. 6 is a view of the milled back surface at an initial clamping force of 400N in the present invention.
Description of the symbols: 1-a main shaft; 2-a pressure sensor; 3, pressing a first plate; 4, pressing a second plate; 5, pressing a third plate; 6-pressing a fourth plate; 7-a knife handle; 8-cutting tools; 9-a thin-walled part; 10-a workbench.
Detailed Description
In order that the invention may be more clearly understood, the invention is described in further detail with reference to the accompanying drawings.
The method for detecting the influence of the clamping force on the machining deformation of the thin-wall part, which is provided by the embodiment of the invention, is described with reference to fig. 1 to 6. The method comprises the following steps:
the method comprises the following steps: calculating basic conditions to be met by the clamping force of the thin-wall part 9;
step two: selecting 3-7 clamping forces, and clamping under the action of different pressing forces;
step three: carrying out a milling experiment on the thin-wall part 9 by adopting a clamping mode of surface support and four-point clamping;
step four: measuring the clamping force by using a pressure sensor 2, and recording the change of the clamping force in the milling process;
step five: after milling is completed, the flatness of the machined surface is measured using a three-coordinate measuring machine. The measuring method is that a probe collects points along a feed path from a position where milling starts, data points are collected on the feed path every time, and the planeness of the processed surface is fitted through a best fit method;
step six: through the contrastive analysis of the flatness values under different clamping forces, the influence rule of the clamping force on deformation is obtained, and then the clamping force values under different flatness requirements are obtained.
The thin-walled part 9 used in the test was an aluminum alloy 7075-T651 with dimensions 250mm × 120mm × 5 mm. The tool 8 used in the test was a 4-edge carbide end mill, the diameter of the tool 8 being 16mm and the helix angle being 42 °.
And after the clamping force is measured by milling by adopting a pressure sensor, measuring the flatness of the surface of the milled thin-walled part by using a Hakstan three-coordinate measuring machine. Milling parameters are shown in table 1.
TABLE 1 vertical machining center milling parameters
As shown in fig. 1, in the test, the aluminum alloy thin-wall part 9 is milled in a clamping mode by adopting surface support and four-point clamping of the thin-wall part 9; wherein the pressure sensor 2 is located between the pressure plate and the thin-walled part 9 for measuring the clamping force. The force measured is a positive pressure applied by the pressure plate to the thin-walled member 9. The subsequent clamping force is referred to herein as a positive pressure.
The thin-walled part 9 should meet the following conditions when being clamped:
1) during the milling process, the force balance and the moment balance of the thin-wall part 9 under the action of external force should be ensured, as shown in formula (1):
∑F＝0 ∑M＝0 (1)
2) in order to ensure that the thin-walled part 9 is completely fixed, the thin-walled part 9 and the clamping element cannot slide relative to each other under the action of an external force, i.e. the clamping stability of the thin-walled part 9. Therefore, at each contact point of the clamping element with the thin-walled part 9, the normal contact force F of the clamp with the thin-walled part 9zWith tangential force Fx、FyThe coulomb's law of friction should be satisfied:
|Fx|+|Fy|≤μFz(2)
wherein μ is the coefficient of friction of the clamp with the thin-walled member 9.
3) In addition, the normal contact force of the clamp with the thin-walled member 9 must be positive, and the normal contact force cannot plastically deform the thin-walled member 9:
Fz≥0，Fz≤sy·A (3)
wherein s isyThe compressive yield strength of the material of the thin-walled part 9, A being the contact area of the clamping element with the thin-walled part 9
The pressure sensor 2 is made of 45# steel, the thin-wall part 9 is made of 7075 aluminum alloy, and the friction coefficients of the two materials are 0.17. The compressive yield strength of the material of the thin-wall part 9 is 503MPa, and the diameter of the pressure sensor is 25 mm. Therefore, the positive pressure applied by the pressing plate to the thin-wall part 9 is calculated according to the formulas (1), (2) and (3) and meets the condition that F is more than or equal to 140N and less than or equal to 246 KN. On the basis of meeting the conditions, four forces are selected as clamping forces which are respectively 300N, 400N, 500N and 600N. And milling for four times, wherein the same force is applied to the four pressing plates during each milling process. The first applied force was 300N and the second 400N, with a sub-class push. And carrying out three times of feed for each milling process. As shown in fig. 2, where the numbers represent four platen press positions, corresponding to the numbering of the four platens, the arrows represent the feed direction.
The positive pressure of the pressure plate on the thin-wall part 9 is measured by the pressure sensor 2, and the clamping force is displayed and recorded through corresponding data display software. During the milling process of the thin-wall part 9, the clamping force of the four pressing plates on the thin-wall part 9 recorded by the pressure sensor 2 changes, and as shown in fig. 3, the change curve of the clamping force of each pressing plate during the milling process is shown.
After milling is completed, the flatness of the machined surface is measured using a three-coordinate measuring machine. The measuring method is that the probe collects points along the feed path from the position where milling starts, the measuring schematic diagram is shown in fig. 4, 20 points are collected on each feed path, 60 points are collected in total, and the planeness of the processed surface is fitted through a best fit method.
As shown in fig. 5, the flatness measurement results of this test are shown. With the increase of the initial clamping force, the flatness of the milled surface has a trend of increasing, then decreasing and then increasing, and the minimum value of the flatness is positioned at the initial clamping force of 500N.
As shown in fig. 6, the acquired 60 points were fitted with Matlab R2014a to obtain a planar profile. When the initial clamping force is 400N, the contour diagram of the milled surface is obtained, the milled plane of the thin-wall part 9 is in a convex shape, the color distribution is gradually changed, the color near the middle is lighter, and the color distribution is darker when the color tends to reach the two ends. The clamping force applied to the two ends of the thin-wall part 9 fluctuates up and down in the machining process, so that the clamping force is firstly reduced and then increased from the beginning to the end of milling when the thin-wall part 9 is fed every time, namely the clamping force at the two ends of the thin-wall part 9 is large, and the clamping force near the middle of the thin-wall part 9 is reduced, so that the two ends of the thin-wall part 9 generate an over-cutting phenomenon in the cutting process, large deformation is generated, and the machining precision is influenced.
Claims (2)
1. A method for detecting the influence of clamping force on the machining deformation of a thin-wall part is characterized by comprising the following steps:
1.1: calculating basic conditions to be met by the clamping force of the thin-wall part (9);
1.2: selecting different clamping forces, and clamping under the action of different pressing forces;
1.3: carrying out milling experiments on the thin-wall part (9) by adopting a clamping mode of surface support and four-point clamping;
1.4: measuring the clamping force by using a pressure sensor (2), and recording the change of the clamping force in the milling process;
1.5: after milling is finished, measuring the planeness of the processed surface by using a three-coordinate measuring machine, wherein the measuring method comprises the steps of collecting points by a probe along a feed path from a position where milling is started, collecting data points on the feed path every time, and fitting the planeness of the processed surface by using a best fit flat method;
1.6: through the contrastive analysis of the flatness values under different clamping forces, the influence rule of the clamping force on deformation is obtained, and then the clamping force values under different flatness requirements are obtained.
2. The method for detecting the influence of the clamping force on the machining deformation of the thin-walled part according to claim 1, wherein the thin-walled part (9) meets the following basic conditions during clamping:
2.1. during the milling process, the force balance and the moment balance of the thin-wall part (9) under the action of external force are ensured: e, F is 0, M is 0;
2.2. in order to ensure that the thin-walled part (9) is completely fixed, the thin-walled part (9) and the clamping element cannot slide relatively under the action of external force, namely the clamping stability of the thin-walled part (9), at each contact point of the clamping element and the thin-walled part (9), the normal contact force F of the clamp and the thin-walled part (9)zWith tangential force Fx、FyThe coulomb's law of friction should be satisfied: i Fx|+|Fy|≤μFzMu is the friction coefficient of the clamp and the thin-wall part (9);
2.3. the normal contact force of the clamp with the thin-walled part (9) must be positive, and the normal contact force cannot cause plastic deformation of the thin-walled part (9): fz≥0，Fz≤syA, wherein syIs the compressive yield strength of the material of the thin-wall part (9), A is a clamping elementThe contact area of the piece and the thin-wall piece (9).
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| CN112296755A (en) * | 2020-11-05 | 2021-02-02 | 上海智能制造功能平台有限公司 | Method and device for separating clamping force deformation and cutting force deformation errors of workpiece |
| CN114273936A (en) * | 2021-11-22 | 2022-04-05 | 北京航空航天大学 | Clamp with clamping force measuring function and using method thereof |
| CN114986255B (en) * | 2022-07-18 | 2022-11-04 | 西安智衍数字科技有限公司 | Clamping force judgment method and system |
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