JP7659657B2 - Method and system for processing workpiece - Google Patents

Description

The present invention relates to a method and system for processing a workpiece, and in particular to a system for processing a workpiece by correcting the contour of a tool.

Conventionally, a workpiece machining system (NC machining system) has been known that has a machining machine (NC machine tool) that processes a workpiece by moving a tool relative to the workpiece using an NC program.

In conventional NC machining systems, for example, a tool such as an end mill is rotated while the tool is moved relatively in accordance with specific numbers (numeric values such as decimals) contained in the NC program to machine the workpiece. Here, Patent Document 1 is cited as a document showing the conventional technology.

The applicant has also proposed a technology for correcting the position of a held tool by incorporating an arithmetic formula for calculating the position of the held tool into an NC program (Patent Document 2).

Japanese Unexamined Patent Publication No. 63-233403 Patent No. 6574915

However, tools have contour errors (the difference between the ideal tool contour shape and the actual tool contour shape). In machine tools that perform ultra-precision machining, contour errors of tools such as end mills account for many of the causes of shape errors in workpieces.

According to a technology proposed by the present applicant (Patent Document 2) in which an arithmetic formula for calculating the position of a held tool is incorporated into an NC program to correct the position of the held tool, errors caused by the tool can be completely eliminated.

However, it was not possible to correct machining errors caused by factors other than the tool.

Normally, when correcting machining errors caused by factors other than tools, the only way to make corrections was to measure the machining shape of the machined workpiece on or off the NC machine tool, modify the 3D model in CAD based on the measurement results, and then modify the NC program in CAM based on the modified 3D model.

However, modifying the 3D model required a great deal of work and time.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method and system for machining a workpiece that can correct machining errors without recreating the NC program and machine the workpiece with high precision.

One aspect of the present invention is a method for machining a workpiece executed by a machining system having a workpiece holding means for holding a workpiece, a tool holding means for holding a tool for machining the workpiece held by the workpiece holding means, and a moving means for moving the tool relative to the workpiece in order to machine the workpiece with the tool held by the tool holding means, the method comprising: a first step of determining a first error, which is a contour error of the tool, from the outer shape of the tool measured by a first measuring device; a second step of determining a second error in which a machining error, which is determined from the shape of the machining surface of the workpiece measured by a second measuring device, is converted into a contour error of the tool; and a third step in which the moving means moves the tool relative to the workpiece based on a predetermined NC program, and in the third step, the NC program corrects the position of the tool based on a composite error obtained by adding the second error to the first error.

Another aspect of the present invention is a workpiece processing system for performing the above-mentioned workpiece processing method.

According to the present invention, machining errors can be corrected without recreating the NC program, and the workpiece can be machined with high precision.

1 is a schematic configuration diagram of a processing system that performs a method for processing a workpiece according to an embodiment of the present invention. 1 is a diagram showing a workpiece and a tool in a machine for processing a workpiece according to an embodiment of the present invention; 1 is a diagram for explaining a contour error (first error) of a tool in a machine tool for processing a workpiece according to an embodiment of the present invention. FIG. 1 is a diagram for explaining a contour error (first error) of a tool in a machine tool for processing a workpiece according to an embodiment of the present invention. FIG. 1 is a schematic diagram of a workpiece three-dimensional measuring device configured with a touch sensor mounted on an NC machine tool. 1 is a schematic diagram of a workpiece three-dimensional measuring device that measures the machined shape of a workpiece 5 outside an NC machine tool. 2 is a flowchart showing a processing procedure of a processing machine for a workpiece in the processing system shown in FIG. 1 . FIG. 11 is an explanatory diagram showing a first tool error shape due to a contour error of a tool. 1 is an explanatory diagram showing a machining range of a workpiece that changes depending on the arc radius of a tool and the arc radius of a machined surface of the workpiece; FIG. 6 is a schematic diagram showing how the shape of the machined surface of a workpiece is measured by a workpiece three-dimensional measuring device configured with the touch sensor shown in FIG. 5 . FIG. 11 is an explanatory diagram showing a second tool error shape as a tool contour shape including a compensation value of the tool 3 when there is a 2 μm uncut portion on a 45° surface of the machining surface of the workpiece as an example of the machining error shown in FIG. 10 . FIG. 4 is an explanatory diagram showing a composite tool shape obtained by superimposing a first tool error shape and a second tool error shape together;

We will describe a processing system 1 that performs a processing method for a workpiece according to an embodiment of the present invention.

Figure 1 is a schematic diagram of a processing system 1 that performs a processing method for a workpiece relating to an embodiment of the present invention.

As shown in FIG. 1, the machining system 1 has an NC machine tool 2 such as a machining center as a processing machine, and this NC machine tool 2 uses a tool 3 (machining tool: for example, a ball end mill) to machine a workpiece (workpiece) 5.

This NC machine tool 2 has a workpiece holding unit 7 and a tool holding unit 9, and the tool holding unit 9 is adapted to be moved in a predetermined direction by a moving unit (moving means) 11.

A control unit 13 (control device) is connected to the NC machine tool 2, and the control unit 13 is equipped with a PC 33a or PC 33 and a CAM 39 which create the NC program used by the control unit 13, and the operation of the NC machine tool 2 is controlled by the control unit 13 based on the NC program created by the PC 33a or PC 33 and CAM 39.

The NC machine tool 2 further includes a tool shape measuring device 31 and a workpiece three-dimensional measuring device 32. The tool shape measuring device 31 and the workpiece three-dimensional measuring device 32 will be described in detail later.

Furthermore, the workpiece 3D measuring device 32 will be described in an embodiment in which measurements are performed on-board the NC machine tool 2, but it may also be capable of performing measurements outside the NC machine tool 2, as described below.

The gist of the present invention is that by incorporating an equation for calculating the position of a tool (held tool) into an NC program and correcting the position of the tool, errors caused by the tool (contour error of the tool itself) and errors caused by factors other than the tool are corrected to machine a workpiece (workpiece).

Here, errors caused by factors other than the tool include errors caused by the shape of the workpiece and errors caused by individual differences in the machining machine.

Errors caused by the shape of the workpiece are errors that occur when cutting resistance changes depending on the shape of the workpiece and the machining allowance of the tool differs. For example, when machining a square-shaped pocket, the cutting resistance is small on straight sections because the tool contacts at one point. On the other hand, the cutting resistance increases on corner sections because the number of contact points of the tool increases. In this case, the cutting resistance changes between straight sections and corner sections, and the amount of tool clearance changes in corner sections, resulting in uncut material.

Errors caused by individual differences in processing machines refer to errors that occur when the tool movement trajectory differs due to the unique characteristics of the processing machine. Differences in the movement of the processing machine appear due to parameters such as the gain of the servo motor. In particular, in processing machines, the tool movement trajectory may be corrected so that the tool moves smoothly, rather than moving precisely along the specified points on the code specified in the NC program. In this case, differences in the movement of the processing machine will cause differences in the tool movement trajectory. In addition, the tool position may be offset from its original position due to mechanical bending caused by the surrounding environment (such as a high-temperature environment) or the influence of the processing machine itself (for example, heat generation). In such cases, differences in the tool movement trajectory will also occur.

Note that errors caused by factors other than tools include errors that occur accidentally, such as due to disturbances, but in this specification we consider reproducible errors, such as machining errors caused by the shape of the workpiece and machining errors caused by individual differences in the processing machine.

That is, in the NC machine tool 2 according to the embodiment, a first tool error shape including errors caused by the tool 3 measured by the tool shape measuring device 31 is obtained, a second tool error shape measured by the workpiece 3D measuring device 32 is obtained so as to cancel out errors caused by elements other than the tool 3, the first tool error shape and the second tool error shape are synthesized, and based on the synthesized tool error shape, the shape of the tool 3 is corrected so as to remove errors caused by the tool 3 and errors caused by elements other than the tool 3, and the workpiece is machined.

The shape correction of tool 3 is performed using a technique in which an arithmetic formula for calculating the position of tool 3 is incorporated into the NC program to correct the position of tool 3.

In Figure 1, the workpiece holding unit 7 is configured to hold a workpiece 5. The tool holding unit 9 is configured to hold a tool 3. The workpiece 5 held by the workpiece holding unit 7 is machined by the tool 3 held by the tool holding unit 9. One example of the machining is cutting.

Figure 2 is a diagram showing a workpiece 5 and a tool 3 in an NC machine tool 2 according to an embodiment of the present invention. In the following description, a ball end mill is used as an example of the tool 3. A cutting edge is provided on the outer periphery of the tool 3.

Here, one specific direction in space is the X direction (X-axis direction; horizontal direction), and another specific direction in space that is perpendicular to the X direction is the Y direction (Y-axis direction; front-to-back direction). The direction perpendicular to the X and Y directions is the Z direction (Z-axis direction; up-down direction). Note that in this definition, the X and Y directions are horizontal directions and the Z direction is the up-down direction, but this is not limited to this. The X or Y direction may be the up-down direction, or the X, Y, and Z directions may be oblique to the horizontal or up-down direction.

To explain further, as shown in Figure 2, the tool 3 is configured with a cylindrical base end 15 and a hemispherical tip end 17. The outer diameter of the base end 15 and the diameter of the tip end 17 are the same, and the tip end 17 is attached to one end of the extension direction of the central axis C1 of the base end 15. The central axis of the tip end 17 and the central axis C1 of the base end 15 are the same.

In this embodiment, a ball end mill is described as tool 3, but this is not limited to this and other tools such as a radius end mill (an end mill with a flat bottom and rounded corners) may also be used.

Here, the center of the circular end face of the tip portion 17 (the end face attached to the circular end face of the base portion 15) is defined as the center C2 of the tip portion 17. This center C2 exists on the central axis C1 of the tool 3.

The cutting edge of the tool 3 is formed on the outer periphery of the tip 17 and on the end of the base 15 (the end on the tip 17 side). The other end of the base 15 of the tool 3 engages with the tool holder 9 and is held by the tool holder.

The tool 3 held by the tool holding portion 9 rotates (rotates about the central axis C1) to cut the workpiece 5 with its cutting edge.

The moving unit 11 is configured to move the tool 3 relative to the workpiece 5 in order to machine the workpiece 5 with the tool 3. In other words, the moving unit 11 may be configured so that the tool 3 moves relative to the workpiece 5, or the workpiece 5 moves relative to the tool 3.

The control unit 13 is configured to control the moving unit 11 based on the NC program and move the tool 3 relative to the workpiece 5.

To explain further, as shown in Figure 1, the NC machine tool 2 for the workpiece 5 is configured to include a bed 19, a table 21, a column 23, a spindle support 25, a spindle housing 27 and a spindle 29.

The table 21 is supported on the bed 19 via a linear guide bearing (not shown), and is adapted to move (be moved and positioned) relative to the bed 19 in the X direction by an actuator such as a linear motor (not shown).

The column 23 is integrally provided on the bed 19. The spindle support 25 is supported by the column 23 via a linear guide bearing (not shown) and is moved relative to the column 23 in the Y direction by an actuator such as a linear motor (not shown).

The spindle housing 27 is supported on the spindle support 25 via a linear guide bearing (not shown), and is adapted to move relative to the spindle support 25 in the Z direction by an actuator such as a linear motor (not shown).

The spindle 29 is supported on the spindle housing 27 via bearings, and is freely rotatable relative to the spindle housing 27 around the central axis C1 (a central axis shared with the tool 3 extending in the Z direction) by an actuator such as a motor (not shown).

The spindle 29 is provided with a tool holder 9, and the top surface of the table 21 is provided with a workpiece holder 7. This allows the tool 3 to move relative to the workpiece 5 in the X, Y, and Z directions.

Next, we will explain the first tool error shape for removing the contour error (first error) of the tool 3 measured by the tool shape measuring device 31.

In addition, the NC program incorporates an arithmetic formula (for example, a mathematical expression using arithmetic operations, etc.) for calculating the position of the tool 3 (coordinates relative to the workpiece 5), as described below.

In other words, the present invention is configured to synthesize a first tool error shape described below and a second tool error shape described later, and determine the compensation position coordinates when tool 3 moves based on the synthesized tool error shape by solving the above equation.

The position of the tool 3 is corrected using a normal vector V1 to the machining surface at the machining point T1 (details will be described later) of the tool 3 and a contour error with the tool 3. This allows the three-dimensional position of the tool 3 to be corrected in at least one of the X, Y, and Z directions (determined by the shape of the normal vector V1).

To explain further, the contour error of the tool 3 is determined in advance by the tool shape measuring device 31 shown in Figure 1 before the workpiece 5 is actually machined.

The tool shape measuring device 31 is installed at a predetermined position on the NC machine tool 2. Then, the tool 3 is positioned at a position where the shape of the tool 3 can be measured by the tool shape measuring device 31 (laser, camera, etc.) and the tool 3 is rotated (rotates around the central axis C1), so that the outer shape of the tool 3 is measured on the machine (on the NC machine tool 2).

The difference (difference between each part of the tool 3) between the measured outer shape of the tool 3 and the ideal outer shape of the tool 3 (the outer shape of the tool 3 without any shape error) is regarded as the contour error (first error) of the tool 3 itself.

Figure 3 is a diagram illustrating the contour error (first error) of a tool in a workpiece processing machine according to an embodiment of the present invention.

The dashed line in Fig. 3(a) shows the ideal outer shape of the tool 3, and the solid line in Fig. 3(a) shows the actual outer shape of the tool 3 with a shape error. In Fig. 3(a), the tool is not rotating around the central axis C1. Also, the tool 3 shown by the solid line in Fig. 3(a) is positioned slightly off to the right of the central axis C1.

The dotted line in Figure 3(b) shows the outer shape of an ideal tool 3, and the solid line in Figure 3(b) shows the outer shape of an actual tool 3 with a shape error (the tool 3 shown by the solid line in Figure 3(a)) when rotated around the central axis C1.

The outline of the tool 3 shown by the solid line in Figure 3(b) is, naturally, linearly symmetrical with respect to the central axis C1. If the workpiece 5 is machined by the tip 17 of the tool 3, the contour error of the tool 3 can be found in a 1/4 arc of the tip 17 (i.e., a range of 90° angles), as shown in Figure 4.

Figure 4 is a diagram illustrating the contour error (first error) of a tool in a workpiece processing machine according to an embodiment of the present invention.

As an example of a tool shape measuring device 31, one such as that shown in JP 63-233403 A can be used.

In addition, details of the process of removing the contour error of the tool 3 measured by the tool shape measuring device 31 are described in Patent Publication No. 6,574,915 by the present applicant.

Next, in order to remove errors (machining errors) caused by factors other than the tool 3, we will explain the second tool error shape based on machining errors, such as uncut portions of the workpiece 5, measured by the workpiece 3D measuring device 32.

First, we will explain the workpiece 3D measuring device 32 that measures the machined shape of the workpiece 5 on the NC machine tool 2. Figure 5 is a schematic diagram of the workpiece 3D measuring device composed of a touch sensor on the NC machine tool.

As shown generally in Figures 1 and 5, the workpiece 3D measuring device 32 is composed of a touch sensor generally called a touch probe.

This touch sensor 32 is provided separately from the tool 3 on the spindle housing 27 of the spindle support 25 of the NC machine tool 2, and can be replaced with the tool 3. The touch sensor 32 is configured to measure the dimensions of the machined surface of the workpiece 5 machined by the NC machine tool 2.

Then, data on the shape of the machined surface of the workpiece 5 measured by the touch sensor 32 is sent to the PC 33a and stored.

This workpiece 5 is the same (sample) as the workpiece 5 that will be machined in the actual machining process. Therefore, the machined surface of the workpiece 5 will be the same as the machined surface that will be machined in the actual machining process.

As described below, PC 33a uses specified software based on the dimensional data of the measured machined surface of workpiece 5 to obtain measurement points (design values), shape errors, normal vectors of the measurement points, etc. of the measured machined surface of workpiece 5.

In the case of the workpiece 3D measuring device 32 configured with an on-machine touch sensor as shown in Figure 5, the machined surface of the workpiece 5 can be measured without moving the machined workpiece 5 from on the NC machine tool 2.

In this case, however, a mechanism is required that provides a touch sensor 32 in addition to the tool 3 on the spindle housing 27 of the spindle support 25 of the NC machine tool 2.

In the above embodiment, a touch sensor that measures the machined shape of the workpiece 5 on the NC machine tool 2 is used as the workpiece 3D measuring device 32. However, in another embodiment, a workpiece 3D measuring device 51 that measures the machined shape of the workpiece 5 outside the NC machine tool 2 can be used.

Figure 6 is a schematic diagram of a workpiece 3D measuring device 51 that measures the machining shape of a workpiece 5 outside the NC machine tool 2.

As shown in Figure 6, this workpiece 3D measuring device 51 has a table 53 for placing the workpiece 5 machined by the NC machine tool 2 at a predetermined position, and a shape sensor 55 above the workpiece 5 placed on the table 53 for measuring the machined surface of the machined workpiece 5. The shape sensor 55 moves up, down, left and right relative to the fixedly installed workpiece 5 to measure the machined surface of the workpiece 5.

Here, the workpiece 3D measuring device 51 outside the NC machine tool 2 obtains the measurement points (design values), shape errors, normal vectors of the measurement points, etc. based on the data on the dimensions of the machined surface of the measured workpiece 5, and sends them to the PC 33a.

In this embodiment, of course, a work 3D measuring device 51 is required outside the NC machine tool 2 to measure the machining shape of the workpiece 5 and obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc.

Next, referring to Figure 7, the processing procedure for the workpiece (workpiece) by the processing machine according to an embodiment of the present invention will be described.

Figure 7 is a flowchart of the processing procedure for a workpiece by a processing machine according to an embodiment of the present invention.

First, in step S11 of Fig. 7, an NC program for machining the workpiece 5, i.e., the three-dimensional coordinates of the machining path by the tool 3, is generated based on a commercially available CAM. Here, a ball end mill is used as the tool 3.

Next, in step S12, a correction vector (normal vector) is added to the NC program, and in step S13, the NC program is read into the control unit 13 of the NC machine tool 2.

The processing of steps S11 to S13 is performed by PC33a or PC33 and CAM39 which create the NC program.

Here, the position of the tool 3 is corrected using the normal vector to the machining surface at the machining point of the tool 3 and the contour error with the tool 3. This allows the three-dimensional position of the tool 3 to be corrected in at least one of the X, Y, and Z directions (determined by the shape of the normal vector).

Next, in steps S14 to S16 below, we will explain the process of removing errors caused by the tool 3 and errors caused by factors other than the tool.

First, in step S14, the shape of the tool 3 for machining the workpiece 5 is measured by a tool shape measuring device 31 using a laser or the like, a first error, which is a contour error of the tool 3, is obtained from the shape of the tool 3, and a first tool error shape is obtained from the first error (first process). The first tool error shape means the contour shape of the tool 3 including the first error.

That is, as shown in FIG. 1, the tool shape measuring device 31 is installed at a predetermined position on the NC machine tool 2, and the tool 3 is positioned at a position where it can be measured by the tool shape measuring device 31 (laser, camera, etc.), and the tool 3 is rotated (rotated around the central axis C1) to measure the outer shape of the tool 3 on the machine (on the NC machine tool 2).

The difference (difference for each part of the tool 3) between the measured outer shape of the tool 3 and the ideal outer shape of the tool 3 (the outer shape of the tool 3 without any shape error) is calculated and regarded as the contour error (first error) of the tool 3. The outer shape of the ideal tool 3 is stored in the control unit 13 as outer shape data and is defined from the shape and dimensions of the tool 3.

Figure 8 is an explanatory diagram showing the first tool error shape due to the contour error of the tool. As described above, for example, if the contour error of the tool 3 is measured every 0.1°, which is a fine angle, a finely wavy contour error CV1 is obtained as shown by the curve in Figure 8(a).

When filtering the curve (contour error CV1) shown in Fig. 8(a) to remove high frequency components, a contour error CV2 with a certain degree of wavyness is obtained as shown by the curve in Fig. 8(b). As described below, correction is performed using the contour shape of tool 3 including the contour error CV2 shown by the curve in Fig. 8(b) as the first tool error shape (hereinafter referred to as the "first tool error shape CV2").

Figure 9 shows the machining range of a workpiece, which changes depending on the radius of the arc of the tool 3 and the radius of the arc of the machined surface of the workpiece. When the difference between the radius of the arc of the tool 3 and the radius of the machined surface of the workpiece 5 is small, the value of the contact length (contact area) CT3 between the workpiece 5 and the tool 3 becomes large.

In this way, even if the shape of the tool 3 used to machine the workpiece 5 is measured by a tool shape measuring device 31 using a laser or the like, a first error is determined from the shape of the tool 3, and a first tool error shape is obtained from this first error, tool correction based on this first tool error shape alone may result in errors (machining errors) caused by factors other than the tool 3.

In order to accommodate such processing errors, the present invention performs the processing from step S15 onwards, as described below.

7, in order to remove machining errors caused by factors other than the tool 3, a second error is obtained by converting the machining error obtained from the shape of the machined surface of the machined workpiece 5 measured by the workpiece three-dimensional measuring device 32 into a contour error of the tool 3, and a second tool error shape is obtained from the second error (second step). The second tool error shape means the contour shape of the tool 3 including the second error.

Below, we will explain in detail how to determine the contour error of the tool 3 from the shape of the machining surface of the workpiece 5 measured by the workpiece 3D measuring device 32, and how to determine the second tool error shape including the second error, which is the contour error of the tool 3.

First, test machining is performed on the test workpiece 5. During the test machining, the movement unit 11 moves the tool 3 relative to the test workpiece 5 based on the NC program. At this time, the NC program corrects the position of the tool 3 based on the correction amount of the NC program as described below. That is, the NC program corrects the position of the tool 3 based on the first tool error shape CV2 including the first error. As a result, the machining error of the workpiece 5 due to the contour error of the tool 3 is corrected, and the tool 3 is operated to machine the test workpiece 5.

As shown in Figure 5, the shape of the machined surface of a machined test workpiece 5 is measured using a workpiece 3D measuring device 32 consisting of a touch sensor mounted on the NC machine tool 2.

That is, before the actual machining, the tip of the touch sensor 32 is brought into contact with the machined surface of the test workpiece 5 machined by the NC machine tool 2 to measure the shape of the machined surface of the test workpiece 5.

Here, this test workpiece 5 is the same as the workpiece 5 for actual machining that will be used in the actual machining (test piece). Therefore, the machined surface of the test workpiece 5 will be the same as the machined surface of the workpiece 5 for actual machining that will be used in the actual machining.

By contacting the tip of the touch sensor 32 with the machined surface of the test workpiece 5, the touch sensor 32 measures the shape of the machined surface of the test workpiece 5. The measurement data is sent to and stored in the PC 33a, which creates the NC program used by the control unit 13.

Based on the measured dimensional data of the machined surface of the test workpiece 5, PC 33a uses specified software to obtain measurement points (design values), shape errors, normal vectors of measurement points, etc.

In other words, PC33a uses measurement software for machine tools developed by, for example, a 3D measuring machine manufacturer, Hexagon, to approach and measure the measurement point from the CAD in the direction of a vector perpendicular to the surface, thereby achieving advanced on-machine measurement and obtaining the measurement point (design value), shape error, normal vector of the measurement point, etc.

Then, the PC 33a compares the measurement points (design values), shape errors, and normal vectors of the measurement points of the test workpiece 5 obtained using the above-mentioned machine tool measurement software with a CAD model that shows the ideal workpiece shape after machining, and calculates and determines the amount of machining error in which part of the machining surface 5a of the test workpiece 5.

Figure 10 is a schematic diagram showing how the shape of the machined surface 5a of the workpiece 5 is measured using a workpiece 3D measuring device 32 consisting of a touch sensor shown in Figure 5.

Figure 10 illustrates an example of a machining error in which there is a 2 μm uncut portion on the 45° surface of the machining surface 5a of the test workpiece 5.

In this embodiment, the machining surface 5a of the test workpiece 5 is measured using a workpiece 3D measuring device 32 consisting of a touch sensor on the NC machine tool 2, and based on the measured dimensional data of the machining surface of the test workpiece 5, the measurement points (design values), shape errors, normal vectors of the measurement points, etc. are obtained on the PC 33a using specified software on the PC 33a.

However, it is also possible to measure the shape of the machined surface of the test workpiece 5 using the aforementioned workpiece 3D measuring device 51 outside the NC machine tool 2, and obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc. from the measurement data.

Next, the PC 33a calculates the amount of machining error in which part of the machining surface 5a of the test workpiece 5. From the calculation data, the PC 33a extracts the tool contour shape including the contour error of the tool 3 obtained to cancel out the machining error of the machining surface 5a of the workpiece 5 as the second tool error shape 3a1.

Figure 11 is a schematic diagram showing a second tool error shape as a tool contour shape including a compensation value of the tool 3 in the case where there is a 2 μm uncut portion on the surface near 45° of the machining surface 5a of the workpiece 5 as the machining error exemplified in Figure 10. In Figure 11, the solid line shows the tool contour shape, and the dotted line shows the tool contour shape including the compensation value.

As shown by the dotted line in Figure 11, the tool contour shape including the dotted correction value results in a second tool error shape 3a1 that cancels out the 2 μm of unmachined material on the surface near 45° of the machining surface 5a of the test workpiece 5, which is the machining error illustrated in Figure 10.

Here, the second tool error shape 3a1 is a concave shape that cancels out the 2 μm of remaining cutting surface on the surface near 45° of the machining surface 5a of the test workpiece 5.

In other words, if there is a remaining cut on the test workpiece 5, it can be considered the same as if there is a concave in the tool shape. Therefore, by adding a concave to the correction value of the tool shape, the correction works as if there is a concave in the tool, and there is no remaining cut on the workpiece 5.

In addition, if there is over-cutting on the machining surface 5a of the test workpiece 5, the second tool error shape will be a convex shape that cancels out the over-cutting.

Next, in step S16, the control unit 13 combines the first tool error shape CV2 and the second tool error shape 3a1 to create a combined tool error shape (CV2+3a1) (fourth step).

That is, the first tool error shape CV2 including the contour error (first error) of the tool shown in Fig. 8 and the second tool error shape 3a1 including the contour error (second error) of the tool 3 shown in Fig. 11 are superimposed and synthesized to obtain a composite tool error shape (CV2+3a1) as shown in Fig. 12. That is, the composite tool error shape (CV2+3a1) is a tool error shape including a composite error obtained by adding the second error to the first error.

Specifically, the contour of the tool 3 from the first transition point X1 to the second transition point X2 of the second tool error shape 3a1 shown in Figure 11 is replaced with a wavy contour shown by the curve CV2 in Figure 8 (b) to obtain a composite tool error shape (CV2 + 3a1) as shown in Figure 12.

That is, transition points X1 and X2 at which the second tool error shape 3a1 transitions to a concave shape that cancels out the remaining cutting area are determined, and the contour between the transition points X1 and X2 in the first tool error shape CV2 is replaced with the concave shape of the second tool error shape 3a1 to obtain a composite tool shape.

Figure 12 is an explanatory diagram showing a composite tool error shape (CV2 + 3a1) obtained by superimposing and combining the first tool error shape CV2 and the second tool error shape 3a1.

In reality, the shape of tool 3 shown by solid lines in Figure 3 (b) is, of course, linearly symmetrical with respect to the central axis C1.

In other words, since the tip 17 of the tool 3 is linearly symmetrical with respect to the central axis C1, the contour error of the tool 3 is the same on both sides within a 1/4 arc (i.e., an angle range of 90°), as shown in Figure 12.

Therefore, if the workpiece 5 is machined using the tip 17 of the tool 3, the contour error of the tool 3 can be found by determining an arc that is 1/4 of the tip 17 on either side (i.e., an angle range of 90°).

Next, in step S16, a correction amount for the NC program is calculated based on a composite tool shape (CV2+3a1) obtained by superimposing the first tool error shape CV2 and the second tool error shape 3a1 as shown in FIG. 12, and the correction amount is set in the memory of the control unit 13, etc.

Here, the NC program incorporates an arithmetic expression (for example, a mathematical expression using arithmetic operations) for calculating the position of the tool 3 (coordinates relative to the workpiece 5). In other words, the position coordinates when the tool 3 moves are determined by the solution of the arithmetic expression.

In other words, the NC program is configured to correct the position of the tool 3 according to the correction amount using an arithmetic formula in order to eliminate machining errors of the workpiece 5 caused by contour errors of the tool 3, as well as to eliminate machining errors caused by factors other than the tool.

In other words, if specific numbers were used, the NC program would have to be remade each time the machining machine was changed, the tool was replaced, or the tool wore out, but by making it a formula, it is possible to deal with tool contour errors that change from time to time as needed.

In addition, by using an arithmetic formula, the measured tool contour values are stored in variables and calculations (operations) are performed during machining, so once an NC program is created, it can be used continuously. Also, since the calculation of the arithmetic formula of the NC program is performed by the control unit 13, a dedicated device is not required.

The correction of tool position using the above formula is described in detail in Patent No. 6,574,915, a previous application filed by the applicant.

In this embodiment, the process for obtaining the composite tool shape (CV2+3a1) is executed in PC33a. However, the composite process can also be executed in PC33 and CAM39 other than PC33a.

Then, in step S17, the NC machine tool 2 starts the actual machining using the tool 3. The movement unit 11 moves the tool 3 relative to the workpiece 5 for the actual machining based on the NC program (third step).

At this time, the NC program corrects the position of the tool 3 based on the correction amount of the NC program. That is, the NC program corrects the position of the tool 3 based on the tool error shape including a composite error obtained by adding the second error to the first error. In this way, the machining error of the workpiece 5 caused by the contour error of the tool 3 and the machining error of the workpiece 5 caused by elements other than the tool 3 can be corrected, and the tool 3 can be operated to machine the workpiece 5.

In this embodiment, the NC machine tool 2 eliminates contour errors of the tool 3 and also eliminates machining errors caused by factors other than the tool 3, thereby achieving very accurate machining.

In addition, according to the NC machine tool 2 in this embodiment, an arithmetic formula for calculating the position (coordinate value) of the tool 3 is incorporated into the NC program, eliminating the need to recreate the NC program each time a tool is replaced or worn out.

The present invention is not limited to the above-described embodiments of the invention, but can be embodied in other forms by making appropriate modifications.

For example, in addition to correcting the errors caused by the tool 3 and the errors caused by factors other than the tool 3 described above, the amount of wear on the tool 3 from the start to the end of machining of the workpiece 5 with the tool 3 can be measured, and the NC program can be corrected taking into account the machining errors caused by factors other than the tool 3 described above, as well as the shape of the tool 3 that changes due to this amount of wear, thereby machining the workpiece 5 with higher precision.

The correction of the NC program taking into account the shape of the tool 3 that changes due to the amount of wear is described in detail in Patent No. 6,574,915, a previous application filed by the applicant.

In addition, in the above-described embodiment, when the first tool error shape CV2 including the contour error of the tool shown in Figure 8 and the second tool error shape 3a1 including the contour error of the tool 3 shown in Figure 11 are superimposed and synthesized to obtain a synthesized tool error shape (CV2 + 3a1) as shown in Figure 12, the contour of the tool 3 from the first transition point X1 to the second transition point X2 of the second tool error shape 3a1 shown in Figure 11 is replaced with the wavy contour error CV2 shown by a curve in Figure 8 (b) to obtain a synthesized tool error shape (CV2 + 3a1) as shown in Figure 12, but this is not limited to this and the synthesis may also be performed as follows.

That is, a second tool error shape 3a1 including the contour error of the tool 3 shown in Figure 11 can be added to the portion of the wavy contour error CV2 shown by a curve in Figure 8 (b) that corresponds to the surface near 45° of the machining surface 5a of the workpiece 5 to obtain a composite tool error shape (CV2 + 3a1).

In addition, as a means for measuring the shape of the machined surface of the workpiece 5 and obtaining the measurement points (design values), shape errors, normal vectors of the measurement points, etc. from the measurement data, a workpiece 3D measuring device 32 consisting of a touch sensor is used on the NC machine tool 2, and in the PC 33a, the measurement points (design values), shape errors, normal vectors of the measurement points, etc. are obtained using a specified software on the PC 33a based on the measured dimensional data of the machined surface of the machined workpiece 5, and outside the NC machine tool 2, a workpiece 3D measuring device 51 is used to obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc., but this is not limited to this and any form is acceptable as long as the shape of the machined surface of the workpiece 5 can be measured and the measurement points (design values), shape errors, normal vectors of the measurement points, etc. can be obtained from the measurement data.

In the above-described embodiment, prior to the actual machining, a test workpiece 5 is machined to correct machining errors of the workpiece 5 due to contour errors of the tool 3 and machining errors of the workpiece 5 due to factors other than the tool 3. That is, the outline of the machining method according to this embodiment is as follows.

(1) Before the test machining, the shape of the tool 3 is measured to obtain a first tool error shape (step S14 in FIG. 7).
(2) Test processing is performed on a test workpiece 5.
(3) The machined surface of the test workpiece 5 is measured to obtain a second tool error shape (step S15 in FIG. 7).
(4) The first tool error shape and the second tool error shape are synthesized to obtain a synthetic tool error shape, and a compensation amount is calculated from this synthetic tool error shape and set in the control unit 13 (step S16 in FIG. 7).
(5) Using the calculated correction amount, machining is performed on the workpiece 5 for main machining (step S17 in FIG. 7).

However, the machining method according to this embodiment may be carried out during the actual machining without performing test machining. For example, the machining method according to this embodiment is carried out during the initial machining of the workpiece 5 for the actual machining. The outline of the machining method in this case is as follows.

(1) Before the actual machining, the shape of the tool 3 is measured to obtain a first tool error shape (corresponding to step S14 in FIG. 7).
(2) Processing is performed on the workpiece 5 for main processing.
(3) The machined surface of the workpiece 5 for main machining is measured to obtain a second tool error shape (corresponding to step S15 in FIG. 7).
(4) The first tool error shape and the second tool error shape are synthesized to obtain a synthetic tool error shape, and a compensation amount is calculated from this synthetic tool error shape and set in the control unit 13 (corresponding to step S16 in FIG. 7).
(5) In the second and subsequent machining operations, the calculated correction amount is used to perform the main machining on the workpiece 5 for main machining (corresponding to step S17 in FIG. 7).

In addition, in the second and subsequent machining operations, the above steps (2) to (5) may be performed for each machining operation, or the above steps (2) to (5) may be performed periodically when a certain number of machining operations have been performed. In addition, when the main machining includes multiple steps such as rough machining, medium machining, and finishing machining, it is preferable to measure the machined surface of the workpiece 5 for main machining after the final finishing step. In addition, when the machined surface of the workpiece 5 for main machining is measured, if there is no machining error or the machining error is smaller than the reference value for judging whether the machining is good or bad, steps (4) to (5) may be skipped.

In the case of the method of performing correction using test machining shown in the former, the correction of machining errors is reflected when performing actual machining. The actual machining in (5) in the former method is performed on a workpiece 5 for actual machining that is different from the test workpiece 5 for which the machining surface was measured in (3) to obtain the second tool error shape. On the other hand, in the case of the method of performing correction during actual machining shown in the latter, the correction of machining errors may be reflected during actual machining of the next workpiece 5 for actual machining, or may be reflected during correction machining of the same workpiece 5 for actual machining. In other words, the actual machining in (5) in the latter method may be performed on a new workpiece 5 for actual machining that is different from the workpiece 5 for actual machining for which the machining surface was measured in (3) to obtain the second tool error shape, or may be performed on the workpiece 5 for actual machining for which the machining surface was measured in (3) to obtain the second tool error shape.

1. Machining system 2. NC machine tool 3. Tool (ball end mill)
3a1 Second tool error shape 5 Workpiece (work)
5a Machining surface 7 Workpiece holding section 9 Tool holding section 11 Moving section 13 Control section 31 Tool shape measuring device 32, 51 Work three-dimensional measuring device 33 PC
39 C.A.M.
41, 43 Machining path C1 Center axis C2 Center CV1, CV2 Contour error CV2 First tool error shape 3a1 Second tool error shape T1 Machining point X1 First transition point X2 Second transition point

Claims (5)

A workpiece holding means for holding a workpiece;
a tool holding means for holding a tool for processing the workpiece held by the workpiece holding means;
a moving means for moving the tool held by the tool holding means relative to the workpiece in order to process the workpiece with the tool,
a first step of determining a first error, which is a contour error of the tool determined from an outer shape of the tool measured by a first measuring device;
a second step of calculating a second error by converting a machining error calculated from a shape of a machined surface of the workpiece measured by a second measuring device into a contour error of a tool;
and a third step of the moving means moving the tool relative to the workpiece based on a predetermined NC program,
In the third step, the NC program corrects the position of the tool based on a combined error obtained by adding the second error to the first error,
the first step includes a process of measuring a shape of the tool by the first measuring device and determining a contour error between the measured outer shape of the tool and an ideal outer shape of the tool as the first error;
the second step includes a process of measuring a shape of the machined surface of the workpiece by the second measuring device, and determining, as the second error, a contour error of a tool that cancels out a machining error that is a difference between the measured shape of the machined surface of the workpiece and an ideal shape of the machined surface of the workpiece;
a measurement point, a shape error, and a normal vector of the measurement point of the measured machining surface of the workpiece are obtained from the shape of the machining surface of the workpiece measured by the second measuring device, and the second error is calculated from the measurement point, the shape error, and the normal vector of the measurement point of the machining surface of the workpiece. A workpiece holding means for holding a workpiece;
a tool holding means for holding a tool for processing the workpiece held by the workpiece holding means;
a moving means for moving the tool held by the tool holding means relative to the workpiece in order to process the workpiece with the tool,
a first step of determining a first error, which is a contour error of the tool determined from an outer shape of the tool measured by a first measuring device;
a second step of calculating a second error by converting a machining error calculated from a shape of a machined surface of the workpiece measured by a second measuring device into a contour error of a tool;
and a third step of the moving means moving the tool relative to the workpiece based on a predetermined NC program,
In the third step, the NC program corrects the position of the tool based on a combined error obtained by adding the second error to the first error,
the first step includes a process of measuring a shape of the tool by the first measuring device and determining a contour error between the measured outer shape of the tool and an ideal outer shape of the tool as the first error;
the second step includes a process of measuring a shape of the machined surface of the workpiece by the second measuring device, and determining, as the second error, a contour error of a tool that cancels out a machining error that is a difference between the measured shape of the machined surface of the workpiece and an ideal shape of the machined surface of the workpiece;
The first step further includes a process of extracting a contour shape of a tool including the first error as a first tool error shape,
The second step further includes a process of extracting a contour shape of a tool including the second error as a second tool error shape,
The method for processing the workpiece comprises the steps of:
a fourth step of calculating a correction amount of the NC program based on a composite tool error shape obtained by combining the first tool error shape and the second tool error shape,
A method for machining a workpiece, characterized in that in the third step, the NC program corrects the position of the tool based on the correction amount. The method for processing a workpiece according to claim 1 or 2,
A method for machining a workpiece, characterized in that the NC program incorporates an arithmetic formula for calculating the position of the tool, and the NC program corrects the position of the tool using the arithmetic formula. The method for processing a workpiece according to claim 1 or 2,
2. A method for machining a workpiece, wherein the tool is a ball end mill or a radius end mill for machining the workpiece. A workpiece processing system for carrying out the workpiece processing method according to claim 1 or 2.

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