JP2018140466A - Grinding device and grinding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform high precision machining on a workpiece whose stiffness varies while the workpiece rotates once.SOLUTION: The grinding device 100 performs grinding, with a rotary grindstone 9, on the workpiece w fixed to the main spindle 4 toward an oval shape having the straight sections L1, L3 and the curved sections L2, L4 as the final target shape. In a storage unit 15, the target profile as data representing the final target shape of the workpiece w and the correction profile as the outer shape data having the detour portion separated to the outside of the curved section of the final target shape and the straight section of the final target shape are stored. The grinding device 100 initially performs grinding on the workpiece w based on the target profile and then performs grinding based on the correction profile, or performs grinding in reverse order.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a grinding apparatus and a grinding method for grinding a workpiece with a grindstone.

In grinding, grinding is performed by pressing a grindstone while supplying a grinding fluid to the workpiece. Since the workpiece bends due to the pressing force of the grindstone or the dynamic pressure due to the flow rate of the grinding fluid, a technique for grinding in consideration of this bending is known, for example, in Patent Document 1.

In Patent Document 1, the flow rate of the grinding fluid supplied to the grinding point of the workpiece is changed in the rough grinding and finish grinding steps, the pressing force in each state is measured, and the diameter of the measured grinding position is based on the measured grinding position. Machining accuracy is improved by calculating the rigidity of the workpiece and grasping the rigidity.

JP 2014-79848 A

In Patent Document 1, in consideration of dynamic pressure caused by a coolant interposed between a grindstone and a workpiece, the amount of coolant supplied is changed according to the grinding stages of rough grinding and finish grinding. However, it does not take into account the bending of the workpiece due to the change in rigidity that occurs while the workpiece rotates once according to the shape of the workpiece. In the case of a workpiece having a rounded rectangular cross section, the straight portion has a shorter distance in the grinding direction and the rigidity is lower than the curved portion. It was expected that the difference in the partial rigidity of the workpiece during finish grinding would lead to a reduction in machining accuracy. It is predicted that the machining accuracy will be further reduced due to the uncut portion due to the bending of the workpiece. One of the other factors that reduce machining accuracy is a factor due to dynamic pressure generated due to the grinding fluid. In a straight portion with low rigidity, the workpiece is bent due to the dynamic pressure generated due to the grinding fluid, and it is difficult to perform highly accurate machining.

An object of the present invention is to provide a grinding apparatus and a grinding method for performing high-precision processing on a workpiece whose rigidity varies while the workpiece rotates once.

In order to achieve the above object, a grinding apparatus according to the present invention is a grinding apparatus that performs grinding with a rotating grindstone with an oval shape as a final target shape for a workpiece fixed to a spindle.
When a target profile is stored as data representing the final target shape of the workpiece, and a specific part of the final target shape of the workpiece is specified by a start point and an end point, outside the specified range of the final target shape A storage unit that stores a correction profile as external shape data having a detour unit that traces a trajectory that detours outside the final target shape and the specific unit of the final target shape;
A numerical control unit that first performs grinding of the workpiece based on the target profile and then performs grinding based on the correction profile, or performs grinding based on the target profile after grinding based on the correction profile It is characterized by that.

Further, the grinding method according to the present invention is a grinding method for grinding with a rotating grindstone with an oval shape as a final target shape for a workpiece fixed to a spindle.
Storing a target profile as data representing the final target shape of the workpiece;
Further, when a specific part of the final target shape of the workpiece is designated by a start point and an end point, a detour unit that traces a trajectory that detours outside the final target shape outside the designated range of the final target shape; Storing a correction profile as outer shape data having the specific part;
The workpiece is first ground based on the target profile and then ground based on the correction profile, or ground based on the target profile after grinding based on the correction profile.

According to the present invention, when the grinding point moves from the curved portion to the less rigid portion, the grindstone and the workpiece are controlled in a non-contact state, and the grindstone once leaves the workpiece during the finish grinding process. As a result, the machining accuracy is improved due to factors such as the bend being reset once. In addition, the generation of dynamic pressure is suppressed by preventing the grinding fluid from accumulating between the rotating grindstone and the workpiece immediately before grinding the linear portion.

1 is a plan view of a grinding device that is a type of machine tool according to Embodiment 1. FIG. 2A is a perspective view, FIG. 2B is a cross-sectional view, and FIG. 2C is a diagram showing another work. FIG. 3A and FIG. 3E show a processing flow, and FIG. 3B, FIG. 3C, FIG. 3D and FIG. 3F show correction profiles in the generation process. FIG. 4 is a diagram illustrating a third embodiment, FIG. 4A illustrates a correction profile, and FIG. 4B illustrates a processing flow.

In general, coolant is supplied to a grinding point during grinding, and at this time, it is known that the workpiece is bent by the dynamic pressure caused by the coolant that has entered between the grindstone and the workpiece and affects the machining accuracy. When the amount of the grinding fluid is large, it bends greatly due to dynamic pressure, and when it is small, it bends small. In rough grinding, the flow rate of the grinding fluid is large, and in finishing grinding, the grinding fluid is small. In the current technology, it has only been studied to reduce the influence of the dynamic pressure change between the grinding stages.

However, the inventors paid attention to the fact that the rigidity of the workpiece changes when the distance in the grinding direction (the radius of the workpiece to the grinding point) changes during one rotation of the workpiece due to the cross-sectional shape of the workpiece. In finish grinding, even if the flow rate of the grinding fluid is the same in one rotation, if the rigidity of the workpiece changes during one rotation, the amount of bending of the workpiece changes in one rotation.

In the case of a workpiece having an oval cross section, for example, in a rounded rectangle (a shape consisting of two parallel lines of equal length and two semicircles), the straight portion is shorter in the grinding direction than the curved portion. Low rigidity. Polygon grinder with such a non-circular cross section (grinding wheel feed (X axis) and spindle rotation (C axis) simultaneous two axis control (CX control)) The object is bent and it is difficult to perform highly accurate processing. Increasing the number of spark-outs and the processing time does not improve the processing accuracy. As a countermeasure, the process was divided into parts using a jig grinder or a surface grinder. As time increased, the phase determination accuracy deteriorated and there was a problem that it was necessary to install a machine tool in addition to the grinding machine.

Therefore, in the present invention, when the grinding point shifts from the curved portion to the portion having low rigidity, the grindstone and the workpiece are controlled in a non-contact state to try to suppress the influence of the difference in partial rigidity.

When machining a workpiece having an oval cross section, the influence of a partial difference in rigidity is suppressed and the machining accuracy is improved. Specifically, it was divided into a plurality of stages of grinding with a target profile according to the target shape and grinding with a correction profile obtained by correcting the target profile. If a part of the final target shape is specified as a specified part at the start and end points for a workpiece that is expected to have a large grinding error, it will be outside the final target shape outside the specified range of the final target shape. A correction profile having a detour portion for tracing a trajectory detouring and a specific portion is created. The correction profile is outer shape data for grinding a workpiece. When the grinding is performed with the correction profile, the workpiece and the grindstone are separated from each other until just before the specific portion is machined, so that the influence of the partial rigidity difference is suppressed.

Below, the grinding apparatus 100 by a present Example is demonstrated. The grinding apparatus 100 includes a work table 2, a Z-axis motor 3, a main shaft 4, a C-axis motor 5, a grindstone base 7, an X-axis motor 8, a rotating grindstone 9 as a processing tool, and a drive for a grindstone. The motor 10 is comprised. In the grinding apparatus 100, the left-right direction is the Z-axis direction, and the front-rear direction is the X-axis direction.

The work table 2 is moved by driving the Z-axis motor 3. A Z-axis encoder 3 a is attached to the Z-axis motor 3. The main spindle 4 on the left side in FIG. 1 on the work table 2 rotates the workpiece w around the C axis cx as the center of rotation. The main shaft 4 is rotated by driving a C-axis motor 5.

The grinding wheel base 7 is supported so as to be movable in the X-axis direction. The movement of the grinding wheel base 7 is performed by driving the X-axis motor 8. An X-axis encoder 8 a is attached to the X-axis motor 8. A rotating grindstone 9 is supported on the left side of the grindstone base 7 so as to be rotatable around the grindstone shaft 11. The rotating grindstone 9 has a disk shape. The rotating grindstone 9 is rotated by a drive motor 10 for the rotating grindstone 9.

The grinding device 100 is a computer numerical control device (CNC), and includes a storage unit 15 and a CPU 16 as a numerical control unit 200. The storage unit 15 stores a target profile, a correction profile, and a control program 15a executed by the CPU 16. The target profile is target shape data of the workpiece w. The correction profile is data created based on the target profile. The correction profile includes the straight line immediately before the straight line portion in the target shape, and traces a trajectory that bypasses the outside of the curved portion instead of the curved portion. This is corrected shape data in which a detour part is newly added. The numerical control unit 200 includes an input unit 12 that receives data input by an operator and a monitor 13 that displays data for the operator.

By executing the control program 15a by the CPU 16, the numerical control unit 200 creates machining data based on the target profile, and controls the motor driving unit 17 based on the machining data. At this time, in the first grinding process, the motor driving unit 17 is controlled by the processing data based on the target profile and the correction profile.

The motor drive unit 17 is connected to the X-axis motor 8 and the X-axis encoder 8a, the Z-axis motor 3 and the Z-axis encoder 3a, and the C-axis motor 5 and the C-axis encoder 5a. The motor drive unit 17 drives the Z-axis motor 3, the C-axis motor 5, and the X-axis motor 8. When position control based on machining data is executed in the control program 15a to grind the workpiece w, the motor drive unit 17 moves the Z-axis direction position of the work table 2, the rotation angle of the spindle 4, and the spindle 4 The relative position with respect to the grinding wheel base 7 is controlled.

The position detector 18 receives the rotation angle of the Z-axis motor 3 and detects the position of the work table 2 in the Z-axis direction, and receives the rotation angle of the X-axis motor 8 and detects the position of the grinding wheel base 7 in the X-axis direction. To do. Further, the position detection unit 18 receives the rotation angle of the C-axis motor 5 and detects the rotation angle of the main shaft 4. When the workpiece w is ground by the machining data, the position detection unit 18 detects the position of each operating unit as position data based on the input position information, and the position data is stored in the control program 15a. Provide feedback.

FIG. 2 shows a work w. The workpiece w is ground from a round bar, and the center of the round bar coincides with the rotation center (C axis cx) of the main shaft 4. The cross-sectional shape that is the final shape of the workpiece w has an outer periphery around the rotation center (C-axis cx) of the main shaft 4, and the outer periphery is composed of at least one straight line and a curve. In this example, the workpiece w is a rounded rectangle composed of two equal-length parallel lines and two semicircles, which is a kind of oval shape, and shows a symmetrical shape. The numerical controller 200 stores a target profile that represents the shape of the outer periphery of the final workpiece w. The target profile has straight portions L1 and L3 and curved portions L2 and L4, and the straight portions L1 and L3 are parallel to each other. As the workpiece w having such a shape, for example, a fine punch mold is known. The rounded rectangular workpiece w is set in advance in the grinding apparatus 100 as a template so that the operator can select one of the oval shapes having an outer periphery composed of a straight portion and a curved portion.

The creation of a correction profile by the control program 15a will be described with reference to FIG.
When grinding of the rounded rectangular workpiece w is selected, in FIG. 3A, the numerical control unit 200 displays the target profile on the monitor 13 so as to set the start point and end point of the straight line for the operator. (Steps s1, s2, FIG. 3B). Since the workpiece w has two straight portions L1 and L3, the operator inputs the start point (c1, c2) and the end point (t1, t2) of each straight portion L1, L3 using the input unit 12. To do. The numerical control unit 200 grasps the lengths and inclinations of the straight line portions L1 and L3 from the start point (c1, c2) and the end point (t1, t2).

The numerical controller 200 extends the straight portions L1, L3 from the starting points c1, c2 of the straight portions L1, L3 in the opposite direction to the grinding direction a, and sets the new starting points as correction starting points (a1, a2) ( Step s3, FIG. 3C). Extension parts (e1, e2) are added to the straight lines L1, L3 on the straight lines. Then, an interpolation unit (p1, p2) that continues from the correction start point (a1, a2) to the end point (t1, t2) is obtained (step s4, FIG. 3D). The interpolation units (p1, p2) may not be smoothly continuous as long as they do not overlap the target profile. When the process is completed for all the start points (c1, c2) and end points (t1, t2) (step S5), the process ends. The interpolating part p1 and the extending part e1 constitute a detour part u1 that is separated outside the curved part L4, and the interpolating part p2 and the extending part e2 constitute a detouring part u2 that is separated outside the curved part L2. The reason why the extension portions (e1, e2) are added to the straight lines L1, L3 is that the possibility of crossing the target profile with respect to the oval workpiece w is eliminated. As long as the extended portions (e1, e2) are lines continuously connected to the straight portions L1, L3, they may not necessarily be straight lines, but may be curved lines.

The trajectory newly created by the above processing (straight line portion L1, straight line portion L3, detour portion u1, detour portion u2) is stored in the storage unit 15 as a correction profile. The detour part u1 and the detour part u2 are for causing the rotating grindstone 9 to trace a trajectory that detours outside the curved portions L2 and L4 of the target profile. The detour part u1 and the detour part u2 are also shape data for specifying a shape that does not intersect with the curved line parts L2 and L4 but is separated from the outside. The bypass portion u1 and the bypass portion u2 are used for finish grinding as if they were target shape data.

Since the target profile is generally not set as a mathematical expression representing a straight line portion or a curved portion with respect to the numerical control unit 200, it is generally set as a collection of points representing a contour. As in 3A, the operator uses the input unit 12 to specify the straight line part. On the other hand, a target profile is set as a mathematical expression representing a straight line portion or a curved portion with respect to the numerical control unit 200, or the numerical control unit 200 calculates an inclination from a collection of points representing an outline, If it is possible to automatically grasp a continuous portion as a straight line portion, the numerical control unit 200 automatically determines the start point (c1, c2) and the end point (t1, t2) from the target profile instead of steps s1 and s2. Extraction is sufficient.

FIG. 3E shows a control program 15a for simply creating a correction profile when the straight portions L1 and L3 are parallel. This process is a process of multiplying the correction profile by 1 in the horizontal direction and N times (greater than 1) vertically in the vertical direction around the C axis cx (step s6). The straight line portions L1 and L3 are assumed to be parallel to the vertical direction. If it is a specific use, a correction profile (FIG. 3F) can be created for many workpieces w by the process of step s6. The straight portions L1 and L3 are extended in the vertical direction with the C axis cx as a center, whereby an extension portion e1 and an extension portion e2 are obtained. Although the curved portions L2 and L4 are deformed, the interpolating portions p1 and p2 are continuously connected to the linear portions L1 and L3 extending vertically without interfering with the curved portions L2 and L4. As a result, the detour portions u1 and u2 can be easily generated without specifying the start and end points of the straight line portions L1 and L3.

Further, when the position of the workpiece w is deviated from the C-axis cx as shown in FIG. 2C, it is multiplied by N up and down around an appropriate position at the center of the parallel straight portions L1 and L3, and the C-axis cx A correction profile can be created by converting to a coordinate system centered on.

FIG. 4 shows a third embodiment. In this embodiment, a correction profile for an arbitrary oval shape VL (FIG. 4A) is created. The oval shape VL has one round formed by a continuous convex curve. As a preparation stage, finish grinding is performed on the workpiece w having such an oval shape VL based on the target profile on a trial basis. An error from the target profile is verified for the workpiece w after grinding. A region with a large error is identified (identifying portions L5 and L6). When a region with a large error continues continuously, it is determined that the workpiece rigidity is low, and start points c1 and c2 and end points t2 and t2 (assumed to be ground clockwise in FIG. 4A) of the large region.

In FIG. 4B, the numerical control unit 200 displays the target profile on the monitor 13 and urges the operator to set the start points and end points of the specifying units L5 and L6 (steps s11 and s12). The operator uses the input unit 12 to input the start point (c1, c2) and the end point (t1, t2) obtained in the preparation stage.

The control program 15a obtains the slope at each of the start point (c1, c2) and the end point (t1, t2). This can be calculated from the relationship between adjacent points at the start point (c1, c2) and the end point (t1, t2). Lines representing inclinations calculated at the start point (c1, c2) and the end point (t1, t2) are shown as straight lines sb1 to sb4 in FIG. 4A.

The numerical controller 200 extends the straight lines sb4 and sb2 from the starting points c1 and c2 in the opposite direction to the grinding direction a, and sets the new starting points as corrected starting points (a1 and a2) (step s13). Extension parts (e1, e2) are added to the specific parts L5, L6. Then, the interpolation unit (p1, p2) that continues from the end point (t1, t2) to the correction start point (a1, a2) is obtained (step s14, FIG. 4B). The interpolation units (p1, p2) may not be smoothly continuous as long as they do not overlap with the target profile, but in this embodiment, the interpolation units (p1, p2) A circular arc cr1 inscribed in the straight lines sb1 and sb2 and a circular arc cr2 inscribed in the straight lines sb4 and sb3 were used.

For the curved line portion L4 and the curved line portion L2 that are outside the range specified by the start point (c1, c2) and the end point (t1, t2), detour portions u1, u2 are formed on the outside thereof. That is, the interpolation unit p1 and the extension unit e1 constitute a detour unit u1 that is separated to the outside of the curved portion L4 (between the start point (c1) and the end point (t2)). Further, a detour part u2 that is outside the curved part L2 (between the start point (c2) and the end point (t1)) is configured by the interpolation part p2 and the extension part e2. When the process is completed for all the start points (c1, c2) and end points (t1, t2) (step S15), the process ends.

(Grinding procedure using target profile and correction profile)
Next, a grinding procedure using the target profile and the correction profile will be described. The grinding procedure is common in Examples 1 to 3.

First, rough grinding of the workpiece w having an oval cross section is performed. In this method, rough grinding is performed in a state in which a finishing allowance is left with respect to the target profile by a method similar to the conventional method. Next, finish grinding is performed. The finish grinding is performed using the target profile to finish the straight portions L1 and L3 (or specific portions L5 and L6) and the curved portions L2 and L4. Next, grinding with a correction profile is performed. During the grinding with the correction profile, the curved portions L2 and L4 are not ground. Alternatively, grinding using a correction profile may be performed next to rough grinding, and then grinding using a target profile may be performed.
In rough grinding, grinding using a target profile may be performed, and then grinding using a correction profile may be performed, or grinding using a correction profile may be performed followed by grinding using a target profile.

(Experimental result)
From a round bar having a diameter of 4 mm, grinding was performed using a rounded rectangular shape of 3 × 1 mm in length and width as a target profile. After rough grinding, first, finish grinding was performed based on the target profile. The error in the straight portions L1 and L3 at the end of finish grinding by the target profile was 17.3 μm. If grinding is further advanced, a target profile in which the target shape is slightly reduced must be newly created. In the experiment, CX control was performed so that the grinding part of the rotating grindstone 9 traces the correction profile in which the straight line part is set longer than the finished shape by the target profile. As a result, while the rotating grindstone 9 is moving along the curved portions L2 and L4, the rotating grindstone 9 and the workpiece w are not in contact with each other, and are brought into contact (cut) when moving to the straight portions L1 and L3.
As a result, the shape error was 6.7 μm, and the processing accuracy was improved.

When grinding a workpiece with an oval cross section by CX control, the grinding wheel and workpiece are controlled in a non-contact state when the grinding point moves from a curved portion to a straight portion with low rigidity. It is considered that the machining accuracy was improved because the state where the grindstone once separated from the workpiece once occurred during the process, and the bending was once reset. In addition, it is considered that the fact that the grinding fluid does not accumulate between the rotating grindstone 9 and the workpiece w immediately before the grinding of the straight portion suppresses the generation of dynamic pressure and contributes to the improvement of machining accuracy.

In the above embodiment, it may be determined in advance whether or not to create a correction profile and perform grinding by this. In this case, if the ratio or difference between the maximum diameter portion r1 and the minimum diameter portion r2 (FIG. 2A) of the workpiece w is smaller than a predetermined value, grinding for creating a correction profile is not performed. If it does, the numerical control part 200 may judge. In this case, the operator is not prompted to input using the monitor 13 (steps s1 and s2) in FIG. 3A.

2 Work table 3 Z-axis motor 4 Spindle 5 C-axis motor 7 Grinding wheel base 8 X-axis motor 9 Rotary grindstone 10 Drive motor 11 Grinding wheel shaft 12 Input unit 13 Monitor 15 Storage unit 15a Control program 16 CPU
100 Grinding machine 200 Numerical control unit w Workpiece

Claims (5)

In a grinding machine that performs grinding with a rotating grindstone with the oval shape as the final target shape for the workpiece fixed to the spindle,
When a target profile is stored as data representing the final target shape of the workpiece, and a specific part of the final target shape of the workpiece is specified by a start point and an end point, outside the specified range of the final target shape A storage unit that stores a correction profile as external shape data having a detour unit that traces a trajectory that detours outside the final target shape and the specific unit of the final target shape;
A numerical control unit that first performs grinding of the workpiece based on the target profile and then performs grinding based on the correction profile, or performs grinding based on the target profile after grinding based on the correction profile A grinding apparatus characterized by that.
2. The grinding apparatus according to claim 1, wherein when the final target shape of the workpiece is selected to be an oval shape having an outer periphery composed of a linear portion and a curved portion, the numerical control unit sets a start point and an end point of the linear portion. Grinding apparatus characterized by having the operator prompt to specify.
2. The grinding apparatus according to claim 1, wherein the numerical control unit determines whether or not to perform grinding for creating a correction profile from a ratio or difference between the maximum diameter and the minimum diameter of the workpiece.
In the grinding method of grinding with a rotating grindstone with the oval shape as the final target shape for the workpiece fixed to the spindle,
Storing a target profile as data representing the final target shape of the workpiece;
Further, when a specific part of the final target shape of the workpiece is designated by a start point and an end point, a detour unit that traces a trajectory that detours outside the final target shape outside the designated range of the final target shape; Storing a correction profile as outer shape data having the specific part;
A grinding method comprising first grinding the workpiece based on the target profile and then grinding based on the correction profile, or grinding based on the target profile after grinding based on the correction profile.
In a grinding method for grinding with a rotating grindstone with a rounded rectangular shape having a straight part parallel to the vertical direction as the final target shape for the workpiece fixed to the spindle,
Storing a target profile as data representing the final target shape of the workpiece;
Further, the correction profile in which the final target shape is 1 time in the horizontal direction and N times in the vertical direction (greater than 1) is stored.
A grinding method characterized in that the workpiece is first ground based on the target profile and then ground based on the correction profile.