Five-axis four-link end milling method for impeller

Abstract

The invention discloses a five-axis four-linkage end milling processing method for an impeller. Two interpolation points are inserted between every two adjacent tool path trajectory points. When moving from a first tool path trajectory point to the first interpolation point, the B-axis rotation angle of the first interpolation point and the B-axis rotation angle of the first tool path trajectory point remain unchanged, and the A-axis needs to be rotated to a position of 1 / 2 of the difference between the rotation angles of the two tool path trajectory points; when moving from the first interpolation point to the second interpolation point, the A-axis rotation angle of the first interpolation point and the second interpolation point remain unchanged, and the B-axis needs to be rotated to the rotation angle value of the second tool path trajectory point; when moving from the second interpolation point to the second tool path trajectory point, the B-axis rotation angle of the second interpolation point and the second tool path trajectory point remain unchanged, and the A-axis needs to be rotated to the rotation angle value of the second tool path trajectory point. During interpolation, one rotation axis remains unchanged and the other rotation axis rotates, thereby completely replacing the five-axis five-linkage end milling processing.

Description

Technical Field

[0001] The invention belongs to the field of multi-axis CNC machine tool cutting and processing, and in particular relates to a method for performing end milling processing on an integral impeller by using a five-axis four-linkage CNC machine tool. Background Art

[0002] Five-axis CNC machine tools are the core equipment in modern advanced manufacturing technology, and they occupy a major position in the field of complex curved surface parts and large precision mold processing. Five-axis CNC milling has good flexibility, high processing efficiency, and good surface quality. The application of CNC programming software such as CATIA, UG, MASTERCAM, CIMATRON, etc. can realize the production and processing of integral impellers, which is also one of the commonly used methods for integral impeller processing. However, five-axis CNC machine tools are expensive and costly due to their complex five-axis continuous motion control system, which limits their popularity.

[0003] According to the different curved shapes of the impeller, the point milling method is usually used when processing on CNC machine tools, but the impeller blades must have good surface quality. Therefore, the rigidity of the machine tool, tool, fixture and the entire impeller must be comprehensively considered, and a reasonable processing technology must be designed to meet the manufacturing requirements of the impeller. Existing commercial CAD / CAM software tools usually only generate five-axis linkage tool paths for traditional five-axis machine tools, which limits the popularity of five-axis five-linkage machine tools.

[0004] In order to improve the impeller machining quality, it is necessary to optimize the tool trajectory of the five-axis CNC machine tool and avoid tool interference and collision. The commonly used optimization methods are: 1. Establish a low-axis system to realize a multi-axis CNC system, and use the additional axis algorithm of the three-axis CNC system, but the implementation process requires the machine tool to be modified. When machining complex surfaces, the tool trajectory planning algorithm is relatively complex and the machining efficiency is low. 2. Adopt a five-axis machining error compensation strategy based on a neural network and consider the error caused by tool wear, but the calculation is too time-consuming. 3. Use an algorithm for rapid detection and correction of collisions between predefined tools and arbitrary workpieces. However, this method cannot generate a continuous tool motion trajectory, resulting in poor surface finish.

[0005] The impeller plunging milling method disclosed in the document with Chinese patent publication number CN104002110 A and titled "A method for plunging an integral impeller based on drilling and milling combination" first uses the bracketing method to evenly divide the rough machining feasible domain of the impeller, construct a conical section family, and then uses the bracketing method to determine the tool center point position and tool axis vector, which is suitable for small diameter tools and five-axis linkage CNC machining centers. Although this machining method uses the bracketing method, it still belongs to the five-axis five-linkage system machining, which requires drilling and milling and plunging to complete. The tool motion trajectory is discontinuous, and the machining is complex and costly. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of complex tool path planning, high cost, poor processing efficiency and processing accuracy in the existing five-axis linkage CNC machine tool processing of integral impellers, and proposes a five-axis four-linkage end milling processing method for impellers, which converts the five-axis five-linkage tool path trajectory into a five-axis four-linkage tool path trajectory to simplify the processing process, reduce processing costs and improve processing accuracy.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A five-axis machine tool including three linear axes X, Y, and Z, a worktable rotation axis A, and a tool swing axis B is used, and the following steps are also included:

[0009] Step 1): Analyze the geometric model of the impeller to be processed and the processing requirements, and generate the tool path trajectory for impeller processing;

[0010] Step 2): kinematic modeling of the five-axis machine tool is performed to obtain tool position data including tool center coordinates and tool axis vectors, and the rotation angles of the A and B axes and the displacements of the three linear axes X, Y, and Z are calculated based on the tool position data;

[0011] Step 3): insert two interpolation points between every two adjacent tool path trajectory points, when moving from the first tool path trajectory point to the first interpolation point, the B-axis rotation angle of the first interpolation point remains unchanged with the B-axis rotation angle of the first tool path trajectory point, and the A axis needs to be rotated to a position of 1 / 2 of the difference between the rotation angles of the two tool path trajectory points;

[0012] When moving from the first interpolation point to the second interpolation point, the A-axis rotation angle between the first interpolation point and the second interpolation point remains unchanged, and the B-axis needs to be rotated to the rotation angle value of the second tool path trajectory point;

[0013] When moving from the second interpolation point to the second tool path trajectory point, the B-axis rotation angle between the second interpolation point and the second tool path trajectory point remains unchanged, and the A-axis needs to be rotated to the rotation angle value of the second tool path trajectory point.

[0014] The advantages of the present invention after adopting the above technical solution are:

[0015] 1. The five-axis four-link end milling process of the present invention can completely replace the five-axis five-link end milling process of the five-axis four-link CNC machine tool, so that the low-cost five-axis four-link CNC machine tool can replace the processing capacity of the expensive five-axis five-link CNC system, and fully tap the potential of the cost-effective five-axis four-link CNC machine tool.

[0016] 2. The present invention realizes tool path trajectory conversion based on the tool path trajectory of five-axis linkage and the relationship between tool position data and the motion axis of the CNC machine tool. In order to ensure the continuity and smoothness of the tool trajectory and to ensure a uniform step length, linear interpolation is performed on the tool center point and the rotating axis is interpolated using a point-by-point comparison method.

[0017] 3. During interpolation, the present invention keeps one rotation axis unchanged and rotates the other rotation axis to 1 / 2 of the original angle difference between adjacent five-axis points, thereby realizing the transformation of five-axis linkage into five-axis four-axis linkage.

[0018] 4. The present invention not only realizes the replacement of five-axis five-linkage complex surface machining with five-axis four-linkage machining, but also greatly improves the nonlinear error generated in the multi-axis machining process, improves the impeller machining quality, provides a new method for machining complex impeller surfaces, and significantly reduces machining costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural diagram of a five-axis CNC machine tool:

[0020] Figure 2 It is a schematic diagram of the machine tool coordinate system;

[0021] Figure 3 This is a schematic diagram of the knife center point interpolation principle;

[0022] Figure 4 It is a schematic diagram of the tool axis vector interpolation principle. DETAILED DESCRIPTION

[0023] See also Figure 1 The impeller five-axis four-linkage end milling processing method of the present invention adopts a widely used five-axis CNC machine tool, which is equipped with a control system and is a swing head and rotary table type five-axis machine tool. It has five motion axes, including three linear axes: X axis, Y axis, and Z axis, and two rotation axes: tool swing axis B and table rotation axis A. It belongs to a swing head and rotary table type five-axis machine tool. This type of machine tool structure is between the double swing head and double rotary table type. The workpiece impeller rotates on the A axis, and the machine tool can process a large range of workpiece sizes.

[0024] The geometric model and processing requirements of the impeller to be processed are analyzed, and the processing process of the impeller is formulated. According to this processing process, CNC programming is performed in the CAM software to generate the five-axis linkage tool path trajectory of the impeller processing, and the machine tool kinematics model is built to obtain the tool position data including the tool center point coordinates (x, y, z) and the tool axis vector (i, j, k), specifically:

[0025] In order to describe the kinematic relationship between tool position data and machine tool axis, a Figure 2 The machine tool coordinate system shown in the figure includes the workpiece coordinate system ( wX w Y w Z w )、Tool coordinate system (O t X t Y t Z t )、B rotary axis coordinate system (O b X b Y b Z b ) and A rotary axis coordinate system (O a X a Y a Z a ). Among them, the tool coordinate system (O t X t Y t Z t )'s coordinate origin O t is the tool center point, B is the rotary axis coordinate system (O b X b Y b Z b )'s coordinate origin O b is the intersection of the tool axis and the B-axis rotary axis. a X a Y a Z a ) Coordinate origin O a Any point on the A-axis rotation axis, the coordinate origin O a You can select any axis on the A axis. b X b Y b Z b )'s coordinate origin O b To the tool center point O t The distance is L.

[0026] In the initial state of the machine tool, the tool axis is parallel to the Z axis and the tool coordinate system origin O t With workpiece coordinate system O w The origin coincides. Through the tool coordinate system (O t X t Y t Z t ) relative to the B rotary axis coordinate system (O b X b Y b Z b ) rotation, B rotary axis coordinate system (O b X b Y b Z b ) relative to the A rotary axis coordinate system (O a Xa Y a Z a ) and the A rotary axis coordinate system (O a X a Y a Z a ) relative to the workpiece coordinate system (O w X w Y w Z w ) The coordinate transformation of the rotation can obtain the kinematic model of the machine tool, and obtain the coordinates of the tool center point (x, y, z) and the tool axis vector (i, j, k): x, y, z are the tool center point relative to the workpiece coordinate system (O w X w Y w Z w ), i, j, k are the coordinates of the tool axis relative to the workpiece coordinate system (O w X w Y w Z w ) direction.

[0027]

[0028]

[0029] In the formula, (m x ,m y ,m z ) are the origin of the A rotary axis coordinate system O a In the workpiece coordinate system (O w X w Y w Z w ) in the position; θ A is the angle of rotation of the turntable A axis, θ B is the rotation angle of the swing head B axis; s x 、s y 、s z They are the displacements of the three linear axes of the machine tool, X, Y and Z.

[0030] According to the machine tool kinematic model of equations (1) and (2), the tool position data is used to solve the motion components of each axis of the machine tool, that is, the angle θ of the A axis rotation A 、B axis rotation angle θ B Specifically:

[0031] Since the rotation angle range of the B axis in the five-axis CNC machine tool is -90°~90°, it can be obtained from formula (1):

[0032] j 2 +k 2 =cos(θ B )2 (3)

[0033] According to equations (1) and (3), the angle of rotation of the B axis can be obtained as:

[0034]

[0035] There are several cases for solving the A-axis angle:

[0036] ①When k>0 and j>0, according to the formula Calculate the angle θ of the A-axis rotation A .

[0037] ②When k<0 and j>0, according to the formula Calculate the angle θ of the A-axis rotation A .

[0038] ③When k<0 and j<0, according to the formula Calculate the angle θ of the A-axis rotation A .

[0039] ④When k>0 and j<0, according to the formula Calculate the angle θ of the A-axis rotation A .

[0040] ⑤When k=0 and j>0, according to the formula Calculate the angle θ of the A-axis rotation A .

[0041] ⑥When k=0 and j<0, according to the formula Calculate the angle θ of the A-axis rotation A .

[0042] ⑦When k>0 and j=0, according to the formula θ A =0 to find the angle θ of A axis rotation A .

[0043] ⑧When k<0 and j=0, according to the formula θ A =π to find the angle θ of A axis rotation A .

[0044] Calculate the angle θ of the A-axis rotation A The angle of rotation of the B axis is θ B Then, the displacements of the three linear axes, X-axis, Y-axis and Z-axis, are further calculated according to formula (2):

[0045] X=x+sin(θ B )×L (5)

[0046] Y=m y +cos(θ A )×(ymy )-sin(θ A )×(zm z ) (6)

[0047] Z=m z -L×(1-(cos(θ B )))+sin(θ A )×(ym y )+cos(θ A )×(zm z ) (7)

[0048] According to the tool center point coordinates (x, y, z) and the tool axis vector (i, j, k), a five-axis five-link tool path trajectory is obtained, and a tool path trajectory interpolation algorithm is used between two adjacent five-axis five-link tool path trajectory points to convert the five-axis five-link into a five-axis four-link. The tool path trajectory interpolation algorithm is to find one or more interpolation points between two adjacent five-axis five-link tool path trajectory points, so that the machine tool motion between the first trajectory point to the interpolation point, the interpolation point to the adjacent interpolation point, and the interpolation point to the second trajectory point is converted from five-axis five-link to five-axis four-link. Therefore, at the interpolation point, the motion of a certain motion axis must be limited.

[0049] It can be seen from formula (2) that the size of the tool center point coordinate (x, y, z) value is affected by the movement of the X, Y, Z linear axes and the A, B axis rotation axes, while the size of the tool axis vector (i, j, k) is only affected by the movement of the A, B rotation axes. When machining the impeller, the tool center point coordinate (x, y, z) in the tool position data determines the tool position, and the tool axis vector (i, j, k) determines the tool posture. If the movement of a certain linear axis is to be restricted, the influence of the rotation axis on the position coordinate cannot be controlled, which will have a great impact on the tool path trajectory. If the movement of one of the rotation axes is restricted, the change in the tool center point position caused by the rotation axis can be compensated by other linear axes. The change in position caused by the rotation axis when the rotation axis is restricted. Therefore, the tool path trajectory interpolation algorithm used in the present invention interpolates between two five-axis five-linkage tool path trajectory points by limiting one of the A-axis rotation axis and the B-axis rotation axis, thereby converting the five-axis linkage machining into five-axis four-linkage machining.

[0050] The tool path interpolation is linear interpolation, which is used to interpolate the tool center coordinates (x, y, z) data. During interpolation, one rotation axis remains unchanged, and the other rotation axis is rotated to 1 / 2 of the original angle difference of the adjacent five-axis points. The number of interpolation points is selected as 2.

[0051] like Figure 3 As shown, two adjacent five-axis five-link tool path trajectory points are M and N, and two adjacent tool path trajectory points are between M and N. Two points C are inserted between M and N.11 , C 21 In order to ensure uniform step size, the interpolation point C 11 , C 21 Evenly distributed on the linear tool path between MN. Interpolation point C 11 , C 21 The coordinates of the tool center point are (x C1 ,y C1 , z C1 )、(x C2 ,y C2 , z C2 ), the tool axis vectors of interpolation points M and N are (i0, j0, k0) and (i1, j1, k1) respectively, and the interpolation point C 11 , C 21 The angle of the rotation axis is (B c1 , A c1 )、(B c2 , A c2 ), the corresponding tool axis vector is (i c1 , j c1 , k c1 )、(i c2 , j c2 , k c2 ).in,

[0052]

[0053] like Figure 4 As shown, according to formulas (3)-(7), the displacement of the X, Y, and Z linear axes and the rotation angles of the A and B rotation axes of the first tool path trajectory point M can be calculated as (X0, Y0, Z0, B0, A0), and the displacement of the X, Y, and Z linear axes and the rotation angles of the A and B rotation axes of the second tool path trajectory point N can be calculated as (X1, Y1, Z1, B1, A1). At this time, points M and C 11 , C 21 The angle values ​​of the B and A axis rotation axes of N are (B0, A0) respectively. (B1, A1), then the tool path points M, C 11 , C 21 , N is the five-axis four-linkage trajectory point. Its corresponding machine tool coordinates are as follows:

[0054] M(X0,Y0,Z0,B0,A0),

[0055]

[0056]

[0057] N(X1,Y1,Z1,B1,A1).

[0058] The first interpolation point C 11 Keep the B axis unchanged and transform the A axis or keep the A axis unchanged and transform the B axis. Take the first interpolation point C between the tool position points of the five-axis linkage 11 Keeping the B axis unchanged, take the A axis transformation as an example to solve the tool axis vector of the interpolation point. When moving from the first tool path point M to C 11 When the C 11 The B-axis angle between point A and point B remains unchanged, that is, c1 = B0, the A-axis angle rotates to 1 / 2 of the angle interpolation from point M to the second tool path point N, that is, Then, when from C 11 Move the point to the first interpolation point C 21 When the C 11 Dot and C 21 The A-axis angle of the point remains unchanged, that is, The B axis angle rotates to the angle value of point N, that is, B c2 =B1. Finally, when 21 When point moves to point N, make C 21 The B-axis angle between point and point N remains unchanged, that is, B1, and the A-axis angle rotates to the angle value of point N, that is, A1.

[0059] Then the interpolation point C 11 , C 21 The corresponding rotation axes are:

[0060]

[0061]

[0062] Find the interpolation point C 11 , C 21 The angle of the rotation axis (B c1 , A c1 )、(B c2 , A c2 ) and then substitute into formula (1): The calculation principle can be used to obtain the interpolation point C 11 , C 21 The corresponding tool axis vector (i c1 , j c1 , k c1 )、(i c2 , j c2 , k c2 ),Right now:

[0063]

[0064] When moving from point M to point C 11 When the C 11 The B-axis angle between point A and point B remains unchanged, that is,c1 = B0, the A-axis angle rotates to 1 / 2 of the interpolation angle from point M to point N, that is, Then, when from C 11 Move point to C 21 When the C 11 Dot and C 21 The A-axis angle of the point remains unchanged, that is, The B axis angle rotates to the angle value of point N, that is, B c2 =B1. Finally, when 21 When point moves to point N, make C 21 The B-axis angle between point and point N remains unchanged, that is, B1, and the A-axis angle rotates to the angle value of point N, that is, A1.

[0065] An embodiment of the present invention is provided below:

[0066] The material of the impeller to be processed is forged aluminum, which is processed by CNC turning to form the basic shape of a rotating body, and the meridian accuracy is required to be guaranteed. Generally, the rough machining to fine machining tools are determined according to the distance between the impeller blades and the chamfer requirements. Ball-end cutters or taper ball-end cutters of different specifications can be used. The impeller to be processed in the present invention uses a two-edge ball-end cutter of R2 and R1.5.

[0067] The five-axis CNC machine tool equipped with Sinumerik 828D control system is a swing head and rotary table type five-axis machine tool, which can realize any four-axis linkage at the same time. The machine tool has a total of five motion axes, including three linear axes (X / Y / Z) and two rotation axes (tool swing axis B and table rotation axis A), and belongs to the swing head and rotary table type five-axis machine tool. The structure of this type of machine tool is between the double swing head and double rotary table type. Since the impeller rotates on the A axis, the machine tool can process a relatively large range of impeller sizes. The machine tool parameters are shown in Table 1.

[0068] Table 1 Main parameters of machine tools

[0069]

[0070]

[0071] Import the impeller model into UG10.0, select the impeller processing module, and set the geometry, tool and other processing information in turn. Formulate the impeller processing procedures, select reasonable parameters, and generate the five-axis five-link tool path trajectory. According to the interpolation algorithm, the tool position data of each trajectory exported is interpolated in MATLAB, the tool center point coordinates and tool axis vector of the interpolation point are calculated, and a new five-axis four-link tool position file is generated and imported into UG10.0.

[0072] Through the UG10.0 software machine tool processing simulation module, the interpolation data is integrated, the tool path generated by the interpolated tool position data is simulated, and the five-axis four-link machining trajectory of the impeller is simulated to check whether there is a tool interference problem. After simulation, the five-axis four-link machining trajectory does not have problems such as tool interference and collision, and actual processing tests can be carried out.

[0073] Produce the post-processing program for this five-axis vertical CNC machining center, and generate the CNC machining program that can be run on the machine tool by post-processing the tool location file.

Claims

1. A five-axis four-linkage end milling method for an impeller, using a five-axis machine tool including three linear axes X, Y, and Z, a worktable rotation axis A, and a tool swing axis B, characterized in that The following steps are also included: Step 1): Analyze the geometric model of the impeller to be processed and the processing requirements, and generate the tool path trajectory for impeller processing; Step 2): kinematic modeling of the five-axis machine tool is performed to obtain tool position data including tool center coordinates and tool axis vectors, and the rotation angles of the A and B axes and the displacements of the three linear axes X, Y, and Z are calculated based on the tool position data; x, y, z are the tool center point relative to the workpiece coordinate system (O w X w Y w Z w ), i, j, k are the coordinates of the tool axis relative to the workpiece coordinate system (O w X w Y w Z w ), the tool center coordinates (x, y, z) and the tool axis vector (i, j, k) are: (m x ,m y ,m z ) are the positions of the origin of the A-axis coordinate system in the workpiece coordinate system, θ A is the A-axis rotation angle, θ B is the B-axis rotation angle, L is the distance from the tool center to the B-axis rotation center, s x 、s y 、s z They are the displacements of the three linear axes X, Y and Z of the machine tool; B axis rotation angle When k>0 and j>0, the A-axis rotation angle When k<0 and j>0, When k<0 and j<0, When k>0 and j<0, When k=0 and j>0, When k=0 and j<0, When k>0 and j=0, θ A =0; when k<0 and j=0, θ A =π; The displacements of the three linear axes X, Y, and Z are: X = x + sin (θ B )×L,Y=m y +cos(θ A )×(ym y )-sin(θ A )×(zm z ), Z = m z -L×(1-(cos(θ B )))+sin(θ A )×(ym y )+cos(θ A )×(zm z ); Step 3): insert two interpolation points between every two adjacent tool path trajectory points, when moving from the first tool path trajectory point to the first interpolation point, the B-axis rotation angle of the first interpolation point and the B-axis rotation angle of the first tool path trajectory point remain unchanged, and the A axis needs to be rotated to a position of 1 / 2 of the difference in the rotation angles of the two tool path trajectory points; When moving from the first interpolation point to the second interpolation point, the A-axis rotation angle between the first interpolation point and the second interpolation point remains unchanged, and the B-axis needs to be rotated to the rotation angle value of the second tool path trajectory point; When moving from the second interpolation point to the second tool path trajectory point, the B-axis rotation angle between the second interpolation point and the second tool path trajectory point remains unchanged, and the A-axis needs to be rotated to the rotation angle value of the second tool path trajectory point.

2. The impeller five-axis four-linkage end milling method according to claim 1 is characterized by: The two interpolation points C 11 , C 21 The knife axis vector (i c1 , j c1 , k c1 )、(i c2 , j c2 , k c2 ) are: A0 and B0 are the A and B axis rotation angles of the first tool path trajectory point, and A1 and B1 are the A and B axis rotation angles of the second tool path trajectory point.

3. The impeller five-axis four-linkage end milling method according to claim 1 is characterized by: In step 3), the two interpolation points are evenly distributed on the path between the two tool path trajectory points.

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