Elliptic flexible hinge machining method

Abstract

The elliptic flexible hinge machining method comprises the steps that cutting force and cutting heat borne by a flexible hinge in the machining process are symmetrically distributed on the left side and the right side through a symmetric cross plunge milling method, and machining parameters and tool parameters of the flexible hinge are obtained; determining the distribution of plunge milling processing position points through cutting contacts on the outline of the elliptic flexible hinge, and solving the plunge milling position; and an initial plunge milling machining code is determined based on the cutter center position and the ellipse parameter until the ellipse parameter # imgabs0 # obtains a complete ellipse arc flexible hinge symmetric cross plunge milling machining program, and the program is imported into a numerical control machine tool to complete finish machining of the flexible hinge. By the adoption of the symmetric cross plunge milling method, cutting force and cutting heat borne by the flexible hinge in the machining process are symmetrically distributed on the left side and the right side, and machining deformation is further reduced.

Description

Technical Field

[0001] The invention relates to the technical field of flexible unit processing, and in particular to a method for processing an elliptical flexible hinge. Background Art

[0002] A flexible hinge is an elastic support with a simple symmetrical structure and a relatively regular shape. It generates a rotational motion around its rotation center under the action of torque. It is widely used in precision flexible mechanisms in the fields of precision measurement and micro-nano positioning. Currently, the commonly used types of flexible hinges include straight beam type, circular arc type and elliptical arc type. In order to obtain high rotation accuracy and greater flexibility, elliptical flexible hinges are increasingly used in the design of precision flexible mechanisms.

[0003] The rigidity of the flexible hinge within its rotation plane is poor. At present, the processing of straight beam and arc-shaped flexible hinges generally adopts wire cutting or CNC boring processing. However, since the wire cutting process releases a lot of heat, there are problems such as thermal deformation when processing flexible hinges with smaller notch thickness, and the efficiency of wire cutting is also low. The CNC boring processing method is only suitable for the precision processing of arc-shaped flexible hinges, and it is difficult to process elliptical flexible hinges using this method. Traditional lateral milling will generate large cutting forces in the radial and tangential directions of the tool. This direction is also the direction where the rigidity of the flexible hinge is weak. During processing, the flexible hinge is very prone to vibration and deformation, which affects the processing contour accuracy of the flexible hinge.

[0004] The current flexible hinge processing method has problems such as low processing accuracy, large processing deformation, unstable processing process, etc. when processing elliptical flexible hinges, making it difficult to achieve precise processing of elliptical flexible hinges. Therefore, a method for processing elliptical flexible hinges is needed. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of the prior art and to propose a method for processing an elliptical flexible hinge.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for processing an elliptical flexible hinge adopts a symmetrical cross-milling method so that the cutting force and cutting heat of the flexible hinge during the processing are symmetrically distributed on the left and right sides, and includes the following steps:

[0008] Obtain the processing parameters of the flexible hinge and the tool parameters, wherein the processing parameters include the spindle speed n s , Plunge cutting feed speed v cut , non-cutting moving speed v move and plunge milling step length Δs;

[0009] The distribution of the plunge milling processing position points is determined by the contact points on the elliptical flexible hinge contour to solve the plunge milling position;

[0010] Based on the tool center position and the ellipse parameters, the initial plunge milling code is determined until the ellipse parameters are The complete symmetrical cross-milling machining path parameters of the elliptical arc flexible hinge are obtained and imported into the CNC machine tool to complete the finishing of the flexible hinge.

[0011] Furthermore, the initial position of the plunge milling is the center of the flexible hinge, and then moves to both ends of the flexible hinge. The processing position of each step is symmetrically cross-processed about the symmetry plane to reduce processing deformation and processing stress.

[0012] Furthermore, when the distribution of the plunge milling processing position points is determined and the plunge milling position is solved, the tool radius r of the boring tool is selected according to the curvature of the ellipse at various locations, and must be smaller than the minimum value of the curvature radius of the ellipse at various locations, that is, smaller than the curvature radius of the ellipse at the end points of the minor axis and the major axis at the same time. The formula is:

[0013]

[0014] r is the tool radius, a and b are the lengths of the semi-minor axis and semi-major axis of the ellipse respectively.

[0015] Furthermore, the distribution of the plunge milling position points is determined by the tangent points on the contour of the elliptical flexible hinge. The coordinates of the tangent points of each step are calculated using a parameterized ellipse expression, and the ellipse parameter increment is solved according to the plunge milling step length. The ellipse parameters of the next step are calculated, and then all the tangent point coordinates are obtained.

[0016] Furthermore, the tool center position of the plunge milling process is solved by the ellipse normal of the current contact point. The tool positions are four points that intersect symmetrically about the flexible hinge, and are used to generate the plunge milling process trajectory. The formula is as follows:

[0017]

[0018] Among them, Q i,j ,j=1,2,3,4 are the tool center positions of the i-th step processing, θ i is the ellipse parameter of the i-th step, o x is the distance from the center of the left and right ellipses to the origin of the coordinate system, λ i is the distance coefficient between the tool center and the cutting contact point in the i-th step, and a and b are the semi-minor axis and semi-major axis lengths of the ellipse, respectively.

[0019] Furthermore, the plunge milling process includes cutting in, cutting out, retracting and lifting the tool, specifically:

[0020] (1) Move the tool horizontally to the center position of the tool to be milled;

[0021] (2) moving downward at the cutting feed rate to remove excess material from the flexible hinge contour;

[0022] (3) After plunge milling, move the tool away from the machined surface and move the center of the ellipse horizontally to avoid damaging the machined surface;

[0023] (4) Move the tool upward to the height of the upper surface to prepare for the next plunge milling;

[0024] Furthermore, the tool advance, tool retract and tool lift are all performed at a non-cutting movement speed.

[0025] Furthermore, the equation of the elliptical arc contour is expressed by a parametric equation, where the center of the ellipse is on the X-axis, and the elliptical arcs on the left and right sides are symmetrical about the Y-axis, as shown in the formula:

[0026]

[0027] Among them, C L (x, y) is the point on the left ellipse arc, C R (x, y) is the point on the right ellipse arc, O L =(-o x ,0) and O R =(o x ,0) are the center points of the left and right ellipses respectively, o x >0, a and b are the lengths of the semi-minor axis and semi-major axis of the ellipse respectively, and θ is the ellipse parameter.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The present invention combines the advantages of boring and plunging. In a single process, the tool is fed along the Z-direction height direction of the flexible hinge, and the main cutting force is also along the tool axis direction. The rigidity of the flexible hinge in this direction is relatively high, and the processing deformation is small and it is not easy to cause processing chatter. At the same time, the symmetrical cross plunging method adopted by the present invention makes the cutting force and cutting heat of the flexible hinge in the processing process symmetrically distributed on the left and right sides, further reducing the processing deformation.

[0030] 2. The processing method proposed in the present invention is not only applicable to elliptical flexible hinges, but also to symmetrical flexible hinges with general curved profiles, providing a CNC processing method for the precision processing of such flexible hinges. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the sequence of the plunging and milling processing trajectory of the flexible hinge of the present invention;

[0032] Figure 2is a relationship diagram of processing parameters of the elliptical flexible hinge of the present invention;

[0033] Figure 3 It is a schematic diagram of the cutting contact point and the plunge milling position of the present invention;

[0034] Figure 4 It is a schematic diagram of the tool advance and retract scheme of the present invention. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] Reference Figure 1-Figure 4 ,A method for machining oval flexible hinge is a machining method based on the combination of boring and plunging milling, including machining parameter selection, cutting contact point solution, plunging milling position solution, tool entry and exit path and end condition.

[0037] Plunging is a milling process that feeds along the spindle direction, and boring is a cutting process that uses a boring tool to expand the hole. The elliptical contour of the elliptical flexible hinge is finely processed by the plunging method. The processing is symmetrical and cross-processed from the center of the flexible hinge to the two ends and about the symmetry plane to reduce processing deformation and processing stress. Figure 1 shown.

[0038] In the attached Figure 2 The equation of the elliptical arc profile is expressed by a parametric equation. An elliptical flexible hinge in the XY plane is used as an example. The center of the ellipse is on the X-axis, and the elliptical arcs on the left and right sides are symmetrical about the Y-axis, as shown in Formula 1:

[0039]

[0040] Among them, C L (x, y) is the point on the left ellipse arc, C R (x, y) is the point on the right ellipse arc, O L =(-o x ,0) and O R =(o x ,0) are the center points of the left and right ellipses respectively, o x >0, a and b are the lengths of the semi-minor axis and semi-major axis of the ellipse respectively, and θ is the parameter of the ellipse.

[0041] The present invention adopts a boring and milling cutter for plunge milling to reduce the error caused by the inconsistent radius of the multi-tooth milling cutter. At the same time, the machining radius r of the boring cutter should be smaller than the minimum curvature radius of the elliptical arc to avoid overcutting or undercutting during machining, as shown in Formula 2:

[0042]

[0043] Machining parameters include spindle speed n s , Plunge cutting feed speed v cut , non-cutting moving speed v move and the plunge milling step length Δs, where the plunge milling step length is the distance between the contact points of two adjacent plunge milling contours and the elliptical contour of the flexible hinge.

[0044] After determining the tool parameters and processing parameters, the contact point position of each step of symmetrical cross-milling processing is calculated by the parametric equation of the ellipse, which is respectively determined by the upper and lower points P on the left side of the ellipse and the lower and upper points P on the left side of the ellipse. i,1 ,P i,2 and the upper and lower points P of the right ellipse i,3 ,P i,4 Composition, as shown in formula 3:

[0045]

[0046] Among them, θ i is the parameter of the ellipse in the current step. The ellipse parameters in step 1 are set to 0, and at this time P i,1 and P i,2 Overlap, P i,3 and P i,4 Overlap, ellipse parameter θ during processing i+1 It can be calculated by the plunge milling step length Δs, as shown in Formula 4:

[0047]

[0048] The plunge milling tool is tangent to the elliptical contour, so the tool center position is located on the normal perpendicular line of the ellipse at the tangent contact point. Therefore, the tool center position Q during the current processing can be calculated by formula 5 i,j ,j=1,2,3,4:

[0049]

[0050] Each plunge milling process includes four steps: feed, plunge milling, retract, and lift. Feed moves the tool horizontally to the center position of the tool to be plunged. i,j , height z up ; Plunge milling means cutting feed speed v cut Move downward to height z below , complete the material removal at the current position; retract the tool to move the tool away from the machining surface horizontally to the center of the ellipse O L or R ; Lift the tool from height z below Move up to height z up , to prepare for the next plunge milling; the tool feed, tool retraction and tool lift are all at non-cutting moving speed v movesports.

[0051] In another implementation case, the processing G code program is as follows:

[0052]

[0053] G01 Z=z below F=v cut

[0054] G01 X=-o x (or X=o x )Y=0F=v move

[0055] G01 Z=z up F=v move

[0056] …

[0057] in and Point Q i,j The X and Y coordinates of the

[0058] Each step of processing starts from Q i,j ,j=1,2,3,4 symmetrically and crosswise to reduce the processing deformation caused by uneven force on the flexible hinge. Repeat the steps of formula 4 and 5 until the ellipse parameters are Finish.

[0059] An elliptical flexible hinge is taken as an example to illustrate the implementation of the plunge milling method of the present invention.

[0060] The semi-major axes of the elliptical flexible hinge are a=3 mm and b=5 mm, and the centers of the left and right ellipses are O L =(-3.025,0) and O R =(3.025,0), the Z-axis thickness of the hinge is 3mm, and the minimum notch thickness of the hinge is 0.05mm.

[0061] The radius of the selected plunge milling tool should satisfy both r < 8.333 and r < 1.8. In this case, a boring tool with a diameter of 3 mm can be selected as the machining tool, and the tool radius r = 1.5.

[0062] The selected processing parameters are spindle speed 4000rpm and cutting speed v cut =120mm / min, non-cutting moving speed v mov =1200mm / min, plunge milling step Δs=0.05mm, z up =2mm, z below =-4mm.

[0063] The initial ellipse parameter θ0 = 0, then according to formula 3, the initial contact points are

[0064] According to formula 5, the initial tool center position is

[0065] From formula 4, we can get that the next step ellipse parameter θ1 = 0.01.

[0066] The initial plunge milling G code is G01 X-1.525Y0 Z2 F1200G01 Z-4F120

[0067] G01 X-3.025Y0 F1200G01 Z2 F1200

[0068] G01 X1.525 Y0 Z2 F1200G01 Z-4F120

[0069] G01 X3.025 Y0 F1200G01 Z2 F1200

[0070] From formula 5, the tool center position in step 1 is

[0071] From formula 4, we can get the ellipse parameter of step 2 as θ2 = 0.02. Then the G code of the plunge milling process of step 1 is G01 X-1.5251 Y0.041 Z2 F1200.

[0072] G01 Z-4 F120

[0073] G01 X-3.025Y0 F1200

[0074] G01 Z2 F1200

[0075] …

[0076] G01 X1.5251 Y-0.041Z2 F1200

[0077] G01 Z-4F120

[0078] G01 X3.025 Y0 F1200

[0079] G01 Z2 F1200

[0080] Repeat this process to get the tool position and G code for the plunging process in step 2, step 3, etc.

[0081] At this point, the G code program for the symmetrical cross-milling of the complete elliptical arc flexible hinge is obtained, which can be imported into the CNC machine tool to complete the fine processing of the flexible hinge.

[0082] In a single machining, since the tool is fed in the Z-direction height direction of the flexible hinge, the main cutting force is along the tool axis direction, and the rigidity of the flexible hinge in this direction is relatively high, the machining deformation is small, and machining chatter is not easy to occur.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, and they should be covered by the protection scope of the present invention.

Claims

1. A method for processing an elliptical flexible hinge, characterized in that: The symmetrical cross-milling method is used to make the cutting force and cutting heat of the flexible hinge symmetrically distributed on the left and right sides during the processing, including the following steps: Obtain the processing parameters of the flexible hinge and the tool parameters, wherein the processing parameters include the spindle speed n s , Plunge cutting feed speed v cut , non-cutting moving speed v move and plunge milling step length Δs; The distribution of the plunge milling processing position points is determined by the contact points on the elliptical flexible hinge contour to solve the plunge milling position; Based on the tool center position and the ellipse parameters, the initial plunge milling code is determined until the ellipse parameters are The complete symmetrical cross-milling machining path parameters of the elliptical arc flexible hinge are obtained and imported into the CNC machine tool to complete the finishing of the flexible hinge.

2. The method for processing an elliptical flexible hinge according to claim 1, characterized in that: The initial position of plunge milling is the center of the flexible hinge, and then moves to the two ends of the flexible hinge. The processing position of each step is symmetrically cross-processed about the symmetry plane to reduce processing deformation and processing stress.

3. The method for processing an elliptical flexible hinge according to claim 1, characterized in that: Determine the distribution of the plunge milling processing position points. When solving the plunge milling position, the tool radius r of the boring tool is selected according to the curvature of the ellipse at various locations. It must be smaller than the minimum value of the curvature radius of the ellipse at various locations, that is, smaller than the curvature radius of the ellipse at the end points of the minor axis and the major axis at the same time. The formula is: r is the tool radius, a and b are the lengths of the semi-minor axis and semi-major axis of the ellipse, respectively.

4. The method for processing an elliptical flexible hinge according to claim 1, characterized in that: The distribution of the plunge milling position points is determined by the tangent points on the contour of the elliptical flexible hinge. The coordinates of the tangent points in each step are calculated using a parameterized ellipse expression. The ellipse parameter increment is solved according to the plunge milling step length, and the ellipse parameters of the next step are calculated to obtain the coordinates of all the tangent points.

5. The method for processing an elliptical flexible hinge according to claim 1, characterized in that: The tool center position of the plunge milling process is solved by the ellipse normal of the current contact point. The tool positions are four points that intersect symmetrically about the flexible hinge, and are used to generate the plunge milling trajectory. The formula is as follows: Among them, Q i,j ,j=1,2,3,4 are the tool center positions of the i-th step processing, θ i is the ellipse parameter of the i-th step, o x is the distance from the center of the left and right ellipses to the origin of the coordinate system, λ i is the distance coefficient between the tool center and the cutting contact point in the i-th step, and a and b are the semi-minor axis and semi-major axis lengths of the ellipse, respectively.

6. The method for processing an elliptical flexible hinge according to claim 1, characterized in that: The plunge milling process includes cutting in, cutting out, retracting and lifting the tool, specifically: (1) Move the tool horizontally to the center position of the tool to be milled; (2) moving downward at the cutting feed rate to remove excess material from the flexible hinge contour; (3) After plunge milling, move the tool away from the machined surface and move the center of the ellipse horizontally to avoid damaging the machined surface; (4) Move the tool upward to the height of the upper surface to prepare for the next plunge milling.

7. The method for processing an elliptical flexible hinge according to claim 6, characterized in that: The tool advance, tool retract and tool lift are all performed at non-cutting movement speed.

8. The method for processing an elliptical flexible hinge according to claim 1, characterized in that: The equation of the elliptical arc contour is expressed by a parametric equation, where the center of the ellipse is on the X-axis, and the elliptical arcs on the left and right sides are symmetrical about the Y-axis, as shown in the formula: Among them, C L (x, y) is the point on the left ellipse arc, C R (x, y) is the point on the right ellipse arc, O L =(-o x ,0) and O R =(o x ,0) are the center points of the left and right ellipses respectively, o x >0, a and b are the lengths of the semi-minor axis and semi-major axis of the ellipse respectively, and θ is the ellipse parameter.

Images