Four-axis turning and milling processing method suitable for large-curvature free-form surface processing

Abstract

The application discloses a four-axis turning and milling machining method suitable for machining large-curvature free curved surfaces, and the method comprises the following steps: building a double-rotary-table turning and milling machine tool; analyzing a model file of a workpiece to be machined to obtain a space spiral line, the space spiral line is wound around the surface of a geometric model of the workpiece to be machined, and the space spiral line is a tool contact point path; performing filtering processing on the tool contact point path to remove noise; calculating a tool center path based on the tool contact point path after the filtering processing; calculating the paths of four axes of the machine tool; and inputting the calculated four-axis path data into a machine tool controller for machining. The application can be well suitable for machining curved surface workpieces or free curved surface workpieces, thereby providing necessary supplement for a conventional three-axis turning and milling machining method, and is especially suitable for machining large-curvature free curved surfaces.

Description

Technical Field

[0001] This invention relates to the field of multi-axis CNC machining technology, and in particular to a four-axis milling and turning method suitable for machining free-form surfaces with large curvature. Background Technology

[0002] Currently, three-axis milling and turning solutions are only suitable for machining free-form surfaces with little curvature variation, such as the outer surface of a laptop back cover, where the thickness dimension is much smaller than the dimensions in the other two directions. Figure 1 The turning process of the laptop back cover was demonstrated using a vertical three-axis machine tool. The C-axis made monotonous rotational motion, the X-axis made monotonous linear motion in the horizontal direction, and the Z-axis made reciprocating motion in the vertical direction. Figure 2 The process of turning the side of a cylindrical workpiece with a variable cross-section is shown using a horizontal three-axis machine tool. Figure 3 This is a schematic diagram of a soap-shaped workpiece. The structural feature of its outer surface is the simultaneous presence of the two curved surfaces described earlier, and these two curved surfaces are continuously joined together. If a vertical three-axis machine tool is used to machine this curved surface, some areas will be unmachineable. If a horizontal three-axis machine tool is used, interference will occur when machining reaches the center area of ​​the rotary axis.

[0003] Therefore, there is an urgent need to design a new four-axis milling and turning method to at least partially alleviate or solve the above-mentioned shortcomings of the existing technology. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the above-mentioned defects of existing three-axis machine tools when machining curved or free-form surface workpieces, and to propose a new four-axis turning and milling machining method suitable for machining free-form surfaces with large curvature.

[0005] The present invention solves the above-mentioned technical problems by adopting the following technical solution:

[0006] This invention provides a four-axis milling and turning method suitable for machining free-form surfaces with large curvature. The four-axis milling and turning method includes the following steps:

[0007] Step 1: Set up a dual rotary table milling and turning machine tool, wherein the dual rotary table includes a first rotary axis (B) and a second rotary axis (C);

[0008] Step 2: Parse the model file of the workpiece to be processed to obtain a spatial spiral. This spatial spiral wraps around the surface of the geometric model of the workpiece to be processed. This spatial spiral is the tool contact path.

[0009] Step 3: Filter the tool contact path to remove noise;

[0010] Step 4: Calculate the tool center path based on the filtered tool contact path.

[0011] When using a ball end mill for roughing, the helical path of the cutting tool center is calculated based on the following formula (1):

[0012]

[0013] In the above formula (1), The position vector of the cutting tool center in the workpiece coordinate system. Let be the position vector of the tool contact point in the workpiece coordinate system. Let R be the normal vector at the cutting point, R be the tool radius, and Δδ be the cutting thickness.

[0014] When using a circular lathe tool for finishing, the helical path of the tool center is calculated based on the following formulas (2) and (3):

[0015]

[0016]

[0017] In formulas (2) and (3) above, the plane containing the cutting tool is the plane Σ passing through the Z-axis, and the intersection of plane Σ and the freeform surface to be machined is the space curve Γ. The tangent vector on this space curve Γ at the current cutting point is... The normal plane at the cutting point is Ω, and the vector in the above formula (3) is... It lies within the plane Ω.

[0018] The tool center path calculation methods differ when using a ball end mill for roughing and when using a circular turning tool for finishing. When using a circular turning tool, the tool is considered a circular plane rather than a three-dimensional sphere. This means that the vector formed by the line connecting the tool contact point and the tool center... With normal vector There exists a non-zero included angle θ. It is precisely because of the existence of this non-zero included angle that, as mentioned above, the calculation formula for the tool center path differs between milling cutters and turning tools when calculating the tool center path based on the tool contact point path.

[0019] According to some embodiments of the present invention, the four-axis milling and turning method further includes the following steps:

[0020] Step 5: The paths of the four axes in the computer tool, including two linear axes (X, Z) and two rotary axes (B, C);

[0021] Step 6: Input the four-axis path data calculated in Step 5 into the machine tool controller for processing.

[0022] The method described in this disclosure provides a feasible solution beyond traditional three-axis machining methods. It is based on the technical insight that, during the machining of curved surfaces, especially those with large curvature, the workpiece's orientation is continuously changed from a horizontal to a vertical position for machining, thus overcoming the aforementioned shortcomings of existing three-axis machining methods. Furthermore, an additional rotary axis is added to the machining and machining control processes. Of course, in the four-axis milling and turning scheme proposed in this invention, this added rotary axis can be either the B-axis or the A-axis of the machine tool.

[0023] According to some embodiments of the present invention, the first rotating axis (B) in step five is the first drive axis in the machining process, and the path of the first rotating axis (B) is defined as follows:

[0024] The path of the first rotation axis (B) is a linear motion that changes linearly from the starting point to the zero position, and it is defined by the following formula (4).

[0025]

[0026] The starting point is a predetermined angle A, meaning that during the machining process, the B-axis linearly changes from A degrees to 0 degrees. i This represents the path data along the B-axis at the i-th point.

[0027] Furthermore, in step five of the four-axis milling and turning method, based on the angle values ​​of the first rotation axis (B) and the second rotation axis (C) at each point on the NC path, the position vector of the cutting tool center in the workpiece coordinate system is... Rotational transformation into the position vector of the tool center in the machine tool coordinate system Where vector The three components represent the paths of the machine tool's three linear axes (X, Y, Z), i.e., U. x =X,U y =Y,U z =Z.

[0028] According to some embodiments of the present invention, the NC path is path data contained in a numerical control machine tool file (NC file), wherein the NC path includes data for controlling the movement of each axis of the machine tool, and includes path data and speed data of the two linear axes (X, Z) and the two rotary axes (B, C).

[0029] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0030] The positive and progressive effects of this invention are as follows:

[0031] The four-axis milling and turning method of the present invention, applicable to the machining of free-form surfaces with large curvature, is well applicable to the machining of curved or free-form workpieces, thus providing a necessary supplement to conventional three-axis milling and turning methods. Attached Figure Description

[0032] Figure 1 A schematic diagram of the machining process for the back cover of a laptop computer using existing vertical three-axis turning technology.

[0033] Figure 2 A schematic diagram of the machining process for machining a cylindrical side surface using existing horizontal three-axis turning technology.

[0034] Figure 3 This is a schematic diagram of a freeform surface to be machined for an exemplary soap-shaped workpiece.

[0035] Figure 4 This is a schematic diagram showing the positional relationship between the cutting tool and the cutting point in a four-axis milling and turning machining method according to a preferred embodiment of the present invention.

[0036] Figure 5 This is a schematic diagram of the machining process of a four-axis milling and turning method according to a preferred embodiment of the present invention.

[0037] Figure 6 This is a side view of the machining process of a four-axis milling and turning method according to a preferred embodiment of the present invention.

[0038] Figure 7 This is a top view of the machining process of a four-axis milling and turning method according to a preferred embodiment of the present invention. Detailed Implementation

[0039] The preferred embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The following description is exemplary and not intended to limit the present invention. Any other similar situations will also fall within the protection scope of the present invention.

[0040] In the following detailed description, directional terms such as "left," "right," "up," "down," "front," and "back" are used with reference to the directions described in the accompanying drawings. Components in various embodiments of the invention may be positioned in a variety of different orientations; the directional terms are for illustrative purposes and not limiting.

[0041] Among them, reference Figure 4-7 As shown, a four-axis milling and turning method for machining free-form surfaces with large curvature according to a preferred embodiment of the present invention includes the following steps:

[0042] Step 1: Set up a dual rotary table milling and turning machine tool, wherein the dual rotary table includes a first rotary axis (B) and a second rotary axis (C);

[0043] Step 2: Parse the model file of the workpiece to be processed to obtain a spatial spiral. This spatial spiral wraps around the surface of the geometric model of the workpiece to be processed. This spatial spiral is the tool contact path.

[0044] Step 3: Filter the tool contact path to remove noise;

[0045] Step 4: Calculate the tool center path based on the filtered tool contact path.

[0046] When using a ball end mill for roughing, the helical path of the cutting tool center is calculated based on the following formula (1):

[0047]

[0048] In the above formula (1), The position vector of the cutting tool center in the workpiece coordinate system. Let be the position vector of the tool contact point in the workpiece coordinate system. Let R be the normal vector at the cutting point, R be the tool radius, and Δδ be the cutting thickness.

[0049] When using a circular lathe tool for finishing, the helical path of the tool center is calculated based on the following formulas (2) and (3):

[0050]

[0051]

[0052] In formulas (2) and (3) above, the plane containing the cutting tool is the plane Σ passing through the Z-axis, and the intersection of plane Σ and the freeform surface to be machined is the space curve Γ. The tangent vector on this space curve Γ at the current cutting point is... The normal plane at the cutting point is Ω, and the vector in the above formula (3) is... Within the plane Ω.

[0053] The tool center path calculation methods differ when using a ball end mill for roughing and when using a circular turning tool for finishing. When using a circular turning tool, the tool is considered a circular plane rather than a three-dimensional sphere. This means that the vector formed by the line connecting the tool contact point and the tool center... With normal vector There exists a non-zero included angle θ. It is precisely because of the existence of this non-zero included angle that, as mentioned above, the calculation formula for the tool center path differs between milling cutters and turning tools when calculating the tool center path based on the tool contact point path.

[0054] The four-axis milling and turning method also includes the following steps:

[0055] Step 5: The paths of the four axes in the computer tool, including two linear axes (X, Z) and two rotary axes (B, C);

[0056] Step 6: Input the four-axis path data calculated in Step 5 into the machine tool controller for processing.

[0057] The method described in this disclosure provides a feasible solution beyond traditional three-axis machining methods. It is based on the technical insight that, during the machining of curved surfaces, especially those with large curvature, the workpiece's orientation is continuously changed from a horizontal to a vertical position for machining, thus overcoming the aforementioned shortcomings of existing three-axis machining methods. Furthermore, an additional rotary axis is added to the machining and machining control processes. Of course, in the four-axis milling and turning scheme proposed in this invention, this added rotary axis can be either the B-axis or the A-axis of the machine tool.

[0058] According to some preferred embodiments of the present invention, the first rotating axis (B) in step five is the first drive axis in the machining process, and the path of the first rotating axis (B) is defined as follows:

[0059] The path of the first rotation axis (B) is a linear motion that changes linearly from the starting point to the zero position, and it is defined by the following formula (4).

[0060]

[0061] The starting point is a predetermined angle A, meaning that during the machining process, the B-axis will linearly change from A degrees to 0 degrees. i This refers to the B-axis path data at the i-th point.

[0062] Furthermore, in step five of the four-axis milling and turning method, the angle values ​​of the first rotation axis (B) and the second rotation axis (C) at each point on the NC path, and the tool center position vector in the workpiece coordinate system... Transformed to the tool center position vector in the machine tool coordinate system Where vector The three components represent the paths of the machine tool's three linear axes (X, Y, Z), i.e., U. x =X,U y =Y,U z =Z, the angle A in the above formula (4) is between 75° and 115°, and preferably 90°.

[0063] According to some embodiments of the present invention, the NC path is path data contained in an NC file for CNC machine tools. The NC path includes data for controlling the movement of each axis of the machine tool, including path data and speed data for the two linear axes (X, Z) and the two rotary axes (B, C). It is understood that NC is a proprietary file format in the field of CNC machining, containing data used to control the movement of each axis of the machine tool.

[0064] The general process is as follows: the engineer inputs the model file to be processed (such as test.stp or test.stl) into CAM software (such as UG), and after the CAM software calculates, it outputs an NC file (such as test.nc). The NC file is then input into the CNC machine tool, and the machine tool controller interprets the NC file and controls the coordinated movement of each axis to achieve machining.

[0065] According to some preferred embodiments of the present invention, the implementation method is roughly as follows.

[0066] First, set up a BC (or AC) dual rotary table machine tool. Second, parse the STL file of the geometry model to be machined to obtain a spatial helix. This spatial helix wraps around the surface of the geometry model, which is the tool contact path, as shown below. Figure 4 As shown.

[0067] Filtering is performed on the tool contact path. In STL files, freeform surfaces are composed of a finite number of triangular patches, meaning the geometric model in the STL file is discrete rather than continuous. This results in noise in the tool contact path data obtained in the previous step, thus requiring filtering.

[0068] Then, calculate the helical path of the tool center. Let the position vector of the cutting point in the workpiece coordinate system be... The normal vector at the cutting point is The tool radius is R, the cutting thickness is Δδ, and the position vector of the tool center in the workpiece coordinate system is... When using a ball end mill for roughing and a round turning tool for finishing, the tool center path is defined as described above and will not be repeated here. The turning tool is equivalent to a circular plane rather than a three-dimensional sphere, meaning that the vector formed by the line connecting the tool contact point and the tool center... With normal vector There exists a non-zero included angle θ, such as Figure 4 As shown.

[0069] Let Σ be the plane containing the cutting tool insert, and let Γ be the intersection of plane Σ and the freeform surface to be machined. Let Γ be the tangent vector at the cutting point on curve Γ. The normal plane at the cutting point is Ω. Based on relevant theories of differential geometry, it is known that vectors... With normal vector All lie within the plane Ω, and the normal vector Circumferential vector Rotating by a certain angle can be related to vectors Coincidence can also be considered as the normal vector The vector can be obtained by projecting it onto the plane Σ. like Figure 5 As shown. As mentioned earlier, the helical path of the cutting center can be calculated based on the following formula:

[0070]

[0071]

[0072] Then, the paths of each axis of the computer tool can be calculated. During the machining process, the B-axis, as the first driving axis, requires path planning. The simplest path is linear motion, that is, the B-axis path data changes linearly from the starting position to the zero position. Assuming the starting position of the B-axis is 90 degrees, and there are n points on the NC path, then it can be defined as follows:

[0073]

[0074] In the above formula, i∈[1,2,…,n]. The path of the C-axis at each point on the NC path is the angle between the plane Σ and the XOZ plane in the workpiece coordinate system (i.e., the plane defined by the X and Z axes). Having the B and C angles, we can then determine the position vector in the workpiece coordinate system. Perform a rotational transformation to obtain its position vector in the machine tool coordinate system. vector The three components are the paths of the three linear axes of the machine tool, namely: U x =X,U y =Y,U z =Z. Since the plane Σ passes through the Z-axis, theoretically U y The constant value means that there are only four axes of actual motion: the X-axis, Z-axis, B-axis, and C-axis.

[0075] Finally, the calculated four-axis path data is input into the machine tool controller for processing.

[0076] The four-axis milling and turning method according to the above-described preferred embodiments of the present invention is well applicable to machining curved or free-form workpieces, thereby providing a necessary supplement to conventional three-axis milling and turning methods, and is particularly suitable for machining free-form surfaces with large curvature.

[0077] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A four-axis milling and turning method suitable for machining free-form surfaces with large curvature, characterized in that, The four-axis milling and turning machining method includes the following steps: Step 1: Set up a dual rotary table milling and turning machine tool, wherein the dual rotary table includes a first rotary axis (B) and a second rotary axis (C); Step 2: Parse the model file of the workpiece to be processed to obtain a spatial spiral. This spatial spiral wraps around the surface of the geometric model of the workpiece to be processed. This spatial spiral is the tool contact path. Step 3: Filter the tool contact path to remove noise; Step 4: Calculate the tool center path based on the filtered tool contact path. When using a ball end mill for roughing, the helical path of the cutting tool center is calculated based on the following formula (1): （1） In the above formula (1), The position vector of the cutting tool center in the workpiece coordinate system. Let be the position vector of the tool contact point in the workpiece coordinate system. Let R be the normal vector at the cutting point, and R be the tool radius. For cutting thickness; When using a circular lathe tool for finishing, the helical path of the tool center is calculated based on the following formulas (2) and (3): （2） （3） In formulas (2) and (3) above, the plane containing the cutting tool is the plane passing through the Z-axis. ,flat The intersection with the freeform surface to be processed is a space curve. The space curve The tangent vector at the current cutting point is The normal plane at the cutting point is In the above formula (3), the vector formed by the line connecting the tool contact point and the cutting tool center is... Located in the plane Inside; Step 5: The paths of the four axes in the computer tool, including two linear axes (X, Z) and two rotary axes (B, C); Step 6: Input the four-axis path data calculated in Step 5 into the machine tool controller for processing.

2. The four-axis milling and turning machining method as described in claim 1, characterized in that, The first rotary axis (B) in step five is the first drive axis in the machining process, and the path of the first rotary axis (B) is defined as follows: The path of the first rotation axis (B) is a linear motion that changes linearly from the starting point to the zero position, and it is defined by the following formula (4). （4） The starting point is a predetermined angle A, which means that during the machining process, the B-axis changes linearly from A degrees to 0 degrees. This refers to the B-axis path data at the i-th point. Furthermore, in step five of the four-axis milling and turning method, based on the angle values ​​of the first rotation axis (B) and the second rotation axis (C) at each point on the NC path, the position vector of the cutting tool center in the workpiece coordinate system is... Rotational transformation into the tool center position vector in the machine tool coordinate system , where vector The three components represent the paths of the machine tool's three linear axes (X, Y, Z), i.e. .

3. The four-axis milling and turning machining method as described in claim 2, characterized in that, The NC path is the path data contained in the NC file used by CNC machine tools. The NC path includes data for controlling the movement of each axis of the machine tool, including path data and speed data for the two linear axes (X, Z) and the two rotary axes (B, C).

4. The four-axis milling and turning machining method as described in claim 2, characterized in that, The angle A in the above formula (4) is between 75° and 115°.

5. The four-axis milling and turning machining method as described in claim 4, characterized in that, In the above formula (4), angle A is 90°.

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