CN106853598A - A kind of cylinder emery wheel curve surface grinding method of virtual ball knife radius - Google Patents

Abstract

The invention discloses a method for grinding a curved surface of a cylindrical grinding wheel with a virtual ball cutter radius, comprising steps: step 1, designing the attitude angle of the cylindrical grinding wheel, and designing the axis of the cylindrical grinding wheel on the normal vector of the tangent point of the curved surface through the virtual ball cutter model The inclination angle; step 2, plan the tool trajectory, determine the tool trajectory according to the surface tangent point normal vector and the virtual ball cutter model, and ensure the inclination angle set in step 1 through a rotation axis of the machine tool. Step 3. Grinding the workpiece according to the tool track by adopting an axial feeding method. The invention can use a cylindrical or quasi-cylindrical grinding wheel for four-axis machining of free-form surfaces, has the characteristics of simple and flexible tool path planning, high machining shape precision and low surface roughness, and is suitable for free-form surfaces of hard and brittle materials such as optical glass processing.

Description

A Surface Grinding Method of Cylindrical Grinding Wheel with Virtual Ball Cutter Radius

technical field

The invention relates to the technical field of precision grinding of free-form surfaces, in particular to a method for grinding a curved surface with a cylindrical grinding wheel with a virtual ball cutter radius, using a cylindrical or quasi-cylindrical diamond cylindrical grinding wheel for a four-axis tool for precision grinding of curved surfaces trajectory method.

Background technique

At present, the grinding of free-form surfaces is mainly processed by single-point diamond or multi-axis grinding wheels. When these two methods are used for grinding, the processing efficiency is low and the tool wears quickly. In addition, the tool trajectory planning method for the related curved surface torus grinding wheel surface grinding has been proposed, but this method is difficult to trim and has low machining accuracy.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for grinding a curved surface of a cylindrical grinding wheel with a virtual ball cutter radius. The invention provides the design of the radius of the virtual ball cutter and the trajectory algorithm model of the diamond cylindrical grinding wheel used in the four-axis machining of the curved surface. The main technical problems to be solved are the design method of the inclination angle of the cylindrical grinding wheel and the planning of the four-axis tool trajectory.

The technical scheme adopted in the present invention is:

A method for grinding a curved surface of a cylindrical grinding wheel with a virtual ball cutter radius, comprising the steps of:

Step 1. Design the attitude angle of the cylindrical grinding wheel, and design the inclination angle of the axis of the cylindrical grinding wheel on the normal vector of the tangent point of the surface through the virtual ball cutter model;

Step 2. Plan the tool trajectory, determine the tool trajectory according to the normal vector of the surface tangent point and the virtual ball cutter model, and ensure the inclination angle set in step 1 through a rotation axis of the machine tool.

Step 3. Grinding the workpiece according to the tool track by adopting an axial feeding method.

Further, the step 1 specifically includes:

Step 11. Design a virtual ball cutter model according to the radius rw of the grinding wheel grinding edge of the cylindrical grinding wheel and the required inclination angle θ of the tool axis vector with respect to the normal vector of the tangent point of the surface. The virtual cutting part of the model circumscribes and surrounds the cylinder The cutting edge of the shaped grinding wheel, the axis direction is consistent with the cylindrical grinding wheel;

Step 12, the radius r of the virtual ball cutter model of the virtual ball cutter model can be expressed as:

Step 13. During processing, use the cylindrical grinding wheel surrounded by the virtual ball cutter model as a ball cutter to set the tool trajectory control point, and rotate around the tool trajectory control point, so that the tool axis vector and the normal vector of the tangent point of the surface maintain an inclined clamp Angle θ, to ensure that the grinding edge can participate in processing.

Further, the step 2 specifically includes:

Step 21. The establishment of the free-form surface model uses the Z-map model to obtain a three-dimensional discrete point cloud. The knife-cut point on any surface is recorded as P ₀ (x ₀ , y ₀ , z ₀ ), and the surface of this point is obtained The normal vector of the upper tangent point is n(x _n , y _n , z _n ), when it is assumed that the virtual ball cutter model surrounding the cylindrical grinding wheel cuts with the tangent point of the processed surface, the control point of the tool trajectory can be obtained as :

Step 22, mobilize a rotating C axis of the machine tool, let the axis of the virtual ball cutter model rotate a certain angle around the control point of the tool trajectory on the workpiece coordinate XOY plane, so that the tool axis vector and the normal vector of the tangent point of the surface maintain an inclined clamp in space Angle θ, to ensure that the grinding edge of the cylindrical grinding wheel surrounded by the virtual ball cutter model participates in the processing. Because the mobilization is to rotate the C axis, the tool axis vector can be expressed as t(x _t ,y _t ,0). According to the above conditions, the tool axis vector and the surface tangent point normal vector satisfy the following equation:

Therefore, if the normal vector of the surface tangent point and the set angle θ are known, the tool axis vector can be obtained;

Step 23. According to the tool trajectory point cloud formed by the obtained tool trajectory control points and the obtained tool axis vector, the four-axis tool trajectory for surface grinding can be planned.

Further, in step 3, the grinding process adopts a four-axis linkage axial numerical control grinding process.

Further, the workpiece to be processed is a hard and brittle material.

Further, the cylindrical grinding wheel is a diamond grinding wheel, the matrix of which is a resin base, the abrasive particle size is 480-4800 mesh, and the concentration is 75-100.

The focus of tool trajectory planning is the establishment of virtual ball cutter model and the determination of tool position and tool space attitude. It is the determination of the tool path control point and the tool axis vector space attitude angle of the virtual ball cutter model of the cylindrical grinding wheel. The control point of the tool path can be determined by the tangent relationship between the virtual ball cutter model and the surface point to be processed, and the tool posture can be determined by the set angle between the tool axis vector and the normal vector of the surface point to be processed and the known Surface tangent point normal vector to determine. And it is realized by one rotational degree of freedom of the machine tool. After confirming the control points of the tool path and the attitude of the tool, the knife-cut point can be found step by step on the free surface to obtain the point of the tool path and adjust the attitude of the tool. A tool planning model for grinding curved surfaces with arbitrary cylindrical grinding wheels is established to realize four-axis grinding of curved surfaces with cylindrical grinding wheels.

Compared with the prior art, the invention has the beneficial effects of not needing complex trimming of the cylindrical grinding wheel, simple interference processing, simple algorithm and wide application range. The machining precision is high, and the surface roughness is small. Experiments have proved that this algorithm can process a mirror effect similar to polishing on the surface of optical glass.

Description of drawings

Figure 1 is a schematic diagram of the virtual ball cutter model.

Figure 2 is a schematic diagram of the four-axis tool trajectory of a cylindrical grinding wheel.

Figure 3 is a schematic diagram of the shape error distribution after finishing.

Figure 4 is a schematic diagram of the shape compensation fitting point cloud.

Fig. 5 is a schematic diagram of the shape compensation fitting path.

Fig. 6 is a schematic diagram of error distribution after compensation processing.

As shown in the figure: 1-cylindrical grinding wheel; 2-radius rw of grinding wheel grinding edge; 3-tool axis vector; 4-surface tangent point normal vector; 5-inclination angle θ; 6-virtual ball cutter model; 7-radius r of the virtual ball cutter model; 8-tool path control point; 9-cutting point; 10-rotation C axis; 11-workpiece coordinate XOY plane.

detailed description

In order to better understand the present invention, the present invention will be further described below in conjunction with the accompanying drawings and examples, but the protection scope of the present invention is not limited to the scope shown in the examples.

As described in Fig. 1 to Fig. 6, a kind of cylindrical emery wheel curved surface grinding method of virtual ball cutter radius, comprises steps:

Step 1, designing the attitude angle of the cylindrical grinding wheel, designing the inclination angle of the axis of the cylindrical grinding wheel on the surface tangent point normal vector 4 through the virtual ball cutter model;

Step 2. Plan the tool trajectory, determine the tool trajectory according to the surface tangent point normal vector 4 and the virtual ball cutter model 6, and ensure the inclination angle set in step 1 through a rotation axis of the machine tool.

Step 3. Grinding the workpiece according to the tool track by adopting an axial feeding method.

Specifically, the step 1 specifically includes:

Step 11. Design the virtual ball cutter model 6 according to the radius rw2 of the grinding wheel grinding edge of the cylindrical grinding wheel 1 and the required tilt angle θ5 of the tool axis vector 3 with respect to the normal vector 4 of the surface tangent point. The virtual cutting part of the model is outside Cut and surround the cutting edge of the cylindrical grinding wheel, the axis direction is consistent with the cylindrical grinding wheel;

Step 12, the radius r7 of the virtual ball cutter model of the virtual ball cutter model can be expressed as:

Step 13, set the cylindrical grinding wheel 1 surrounded by the virtual ball cutter model 6 as a ball cutter during processing Set the tool trajectory control point 8 and rotate around the tool trajectory control point 8, so that the tool axis vector 3 and the surface tangent point normal vector 4 maintain an inclined angle θ5 to ensure that the grinding edge can participate in processing.

Specifically, the step 2 specifically includes:

Step 21. The establishment of the free-form surface model adopts the Z-map model to obtain a three-dimensional discrete point cloud. The knife-cut point (9) on any surface is recorded as P ₀ (x ₀ , y ₀ , z ₀ ), and the The surface tangent point normal vector 4 of the point is n(x _n , y _n , z _n ), when it is assumed that the virtual ball cutter model surrounding the cylindrical grinding wheel is cut with the tangent point of the processed surface, this can be obtained Trajectory control point 8 is:

Step 22, mobilize a rotating C-axis 10 of the machine tool, let the axis of the virtual ball cutter model rotate a certain angle around the tool trajectory control point 8 on the workpiece coordinate XOY plane 11, so that the tool axis vector 3 and the surface tangent point normal vector 4 are at In space, the angle of inclination θ5 is maintained to ensure that the grinding edge of the cylindrical grinding wheel 1 surrounded by the virtual ball cutter model 6 participates in processing, because a rotating C-axis 10 is mobilized, so the tool axis vector 3 can be expressed as t (x _t ,y _t ,0), according to the above conditions, the tool axis vector 3 and the surface tangent point normal vector 4 satisfy the following equation:

Therefore, knowing the surface tangent point normal vector 4 and the set inclination angle θ5, the tool axis vector 3 can be obtained;

Step 23, through the tool trajectory point cloud formed by the obtained tool trajectory control point 8 and the obtained tool axis vector 3, the four-axis tool trajectory for surface grinding can be planned.

Specifically, in step 3, the grinding process adopts a four-axis linkage axial numerical control grinding process. In one embodiment, CNC precision five-axis (ULTRASONIC 20 linear) equipment is adopted, and the cylindrical grinding wheel adopts 480# metal bond diamond grinding wheel. The size of the grinding wheel is 24 mm in diameter and 8 mm in thickness, and it is used for axial grinding of free-form surfaces. The workpiece is optical glass of model BAK3, the geometric dimensions are 56mm*14mm*13mm in length*width*height, and a maximum depth of 3.9mm is processed on the surface of 56mm*14mm, the length is 54mm, and the width is 6mm concave free-form surface. The axis of the grinding wheel is parallel to the long side of the workpiece, and it is processed by 4-axis linkage axial grinding. Rough grinding wheel speed 5000 rpm, rough grinding feed rate 800 mm/min, rough grinding depth of cut 50 microns; fine grinding wheel speed 5000 rpm, fine grinding feed rate 800 mm/min, fine grinding depth of cut 20 micron; zero grinding count is 1. The inclination angle θ between the tool axis and the normal line of the processed point is designed to be 30 degrees. The above-mentioned four-axis tool path trajectory planning is used for processing, and the processed surface is tested, and then matched with the theoretical free-form surface. The result is the average shape error of the free-form surface The value is 0.96 microns, and the peak-to-valley PV is 6 microns.

In another embodiment, CNC precision five-axis (ULTRASONIC 20 linear) equipment is adopted, and the cylindrical grinding wheel is a 480# metal bonded diamond grinding wheel. The size of the grinding wheel is 24 mm in diameter and 8 mm in thickness. The same curved surface is processed on the same workpiece under the same processing conditions. The processed curved surface is tested and then matched with the theoretical free-form surface. Data fitting processing is performed on the matching error, and the shape compensation trajectory point cloud and the compensation tool path trajectory are obtained. The inclination angle θ between the cutter axis and the direction of the compensated surface point is designed to be 30 degrees, and the cylindrical grinding wheel adopts 4800# metal bonded diamond grinding wheel. The size of the grinding wheel is 24mm in diameter and 8mm in thickness. The same four-axis tool path trajectory planning is used for surface topography compensation. The speed of grinding wheel is 8000 rpm, the feeding speed of rough grinding is 800 mm/min, and the cutting depth of rough grinding is 1 micron. Zero grinding count is 1. The compensated surface is detected and then matched with the theoretical free surface. The result is that the average value of the shape error of the free-form surface is 0.71 microns, and the peak-to-valley value PV is 4 microns. The resulting roughness was 0.054 microns.

The above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, on the basis of the above description, other changes or changes in different forms can also be made. It is not necessary and impossible to exhaustively list all the implementation manners here. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (6)

1. a cylindrical emery wheel curved surface grinding method of virtual ball cutter radius, is characterized in that, comprises steps: Step 1, cylindrical grinding wheel attitude angle design, design the inclination angle of the cylindrical grinding wheel axis on the surface tangent point normal vector (4) through the virtual ball cutter model; Step 2, plan the tool trajectory, determine the tool trajectory according to the surface tangent point normal vector (4) and the virtual ball cutter model (6), and ensure the inclination angle set in step 1 through a rotation axis of the machine tool. Step 3. Grinding the workpiece according to the tool track by adopting an axial feeding method. 2. the method for curved surface precision grinding of arbitrary grinding wheel curved surface profile according to claim 1, is characterized in that, described step 1 specifically comprises: Step 11. Design a virtual sphere according to the grinding wheel grinding edge radius rw (2) of the cylindrical grinding wheel (1) and the inclination angle θ (5) of the required tool axis vector (3) with respect to the surface tangent point normal vector (4) The knife model (6), the virtual cutting part of the model circumscribes and surrounds the cutting edge of the cylindrical grinding wheel, and the axis direction is consistent with the cylindrical grinding wheel (1); Step 12, the virtual ball cutter model radius r (7) of the virtual ball cutter model (6) is expressed as: $\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; ;</span>$ Step 13. During processing, use the cylindrical grinding wheel (1) surrounded by the virtual ball cutter model (6) as a ball cutter to set the tool path control point (8), and the tool path control point (8) rotates to make the tool axis vector (3) Keep the angle of inclination θ(5) with the normal vector of the tangent point of the surface (4), so as to ensure that the grinding edge can participate in the processing. 3. the method for curved surface precision grinding of arbitrary grinding wheel curved surface profile according to claim 1, is characterized in that, described step 2 specifically comprises: Step 21. The establishment of the free-form surface model adopts the Z-map model to obtain a three-dimensional discrete point cloud. The knife-cut point (9) on any surface is recorded as P ₀ (x ₀ , y ₀ , z ₀ ), and the The normal vector (4) of the tangent point on the surface of the point is n(x _n , y _n , z _n ), when it is assumed that the virtual ball cutter model surrounding the cylindrical grinding wheel cuts with the tangent point of the processed surface, this can be obtained The tool path control point (8) is obtained as: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; ry</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\\ {\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; rz</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\end{array}\right.<span\; class="notranslate">\; ;</span>$ Step 22, mobilize a rotating C axis (10) of the machine tool, let the axis of the virtual ball cutter model rotate a certain angle around the tool trajectory control point (8) on the workpiece coordinate XOY plane (11), so that the tool axis vector (3) and The inclination angle θ (5) of the surface tangent normal vector (4) in space is to ensure that the grinding edge of the cylindrical grinding wheel (1) surrounded by the virtual ball cutter model (6) participates in processing. Because the mobilization is the rotating C axis (10), the tool axis vector (3) can be expressed as t(x _t ,y _t ,0). According to the above conditions, the tool axis vector (3) and the surface tangent point normal vector (4) satisfy the following equation: $\left\{\begin{array}{c}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\end{array}\right.$ Therefore, the surface tangent point normal vector (4) and the set inclination angle θ (5) are known, and the tool axis vector (3) can be obtained; Step 23, through the tool trajectory point cloud formed by the obtained tool trajectory control points (8) and the obtained tool axis vector (3), the four-axis tool trajectory for surface grinding can be planned. 4. The method of using any grinding wheel curved surface profile for curved surface precision grinding according to claim 1, characterized in that: the workpiece to be processed is a hard and brittle material. 5. the cylindrical emery wheel curved surface grinding method of a kind of virtual ball cutter radius according to claim 1, is characterized in that: described cylindrical emery wheel (1) is a diamond cylindrical emery wheel, and its substrate is a metal base, and abrasive grain size The mesh is 480-4800, and the concentration is 75-100. 6 . The method for grinding a curved surface of a cylindrical grinding wheel with a virtual ball cutter radius according to claim 1 , wherein in step 3, the grinding process adopts a four-axis linkage axial numerical control grinding process. 7 .