JPH0857748A - Numerical control system - Google Patents

Abstract

PURPOSE: To make the cutting speed constant regardless of the cutting point of a ball end mill and enable feed synchronous with the rotating speed change of a spindle tool in a numerical control system for a machining center using the ball end mill as the spindle tool and having X-axis, Y-axis and Z-axis feed shafts performing die-machining according to a machining program. CONSTITUTION: A tool radius ratio computing part 11 obtains a tool radius ratio RR, a ratio between the radius of a ball end mill at a cutting point and a tool diameter, from the moving quantity of each feed shaft outputted from a shaft distributor 4. A rotating speed computing part 12 obtains a spindle tool rotating speed command S' from the tool radius ratio RR and the command spindle tool rotating speed S read by an interpreting part 2. A feed speed computing part 10 obtains the command feed speed Ft per minute from the spindle tool rotating speed command S' and the command feed speed Fs per every rotation read by the interpreting part 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a numerical control device of a machining center for machining a die or the like by using a ball end mill as a spindle tool, and particularly, the number of revolutions of the spindle tool is changed according to the change of the machining shape. The present invention relates to a numerical control device that makes a cutting speed of a tool constant by making it possible, and further enables a feed synchronized with the rotation speed of a spindle tool.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an example of a conventional numerical control device for a machining center. The conventional technique will be described with reference to FIG. First, the interpretation unit 2 reads the machining program 1 created in advance by the operator block by block,
From the block BL, the command feed speed Ft and the command position G,
The command spindle tool rotation speed S and the like are read. The feed unit amount determination unit 7 calculates the feed unit amount ΔFt per function generation period from the command feed speed Ft. The function generator 3 interpolates the path to the command position G for each function generation cycle according to the feed unit amount ΔFt to obtain the movement amount ΔP. The axis distributor 4 has a movement amount Δ
P is distributed to the movement amounts Δx, Δy, and Δz of the respective feed axes. The servos 5x, 5y, 5z of each feed axis are Δ
According to x, Δy, Δz, the motors 6x, 6y,
Drive 6z. On the other hand, the spindle servo 8 rotates the spindle motor 9 according to the spindle tool rotation speed S (hereinafter, referred to as a command spindle rotation speed) instructed by the machining program 1.

As described above, the conventional numerical control device controls the movement of the tool along the instruction path of the machining program while rotating the spindle tool in accordance with the instructed spindle tool rotation speed to machine the workpiece. Has become.

[0004]

Generally, a ball end mill is used as a tool in the machining of a mold having many curved surfaces, but the tip of the ball end mill has a hemispherical shape so that any part can be cut. This is because. As shown in the cross-sectional view of the ball end mill in FIG. 3, for example, on a processing surface having an inclination A, a point a is in contact with the processing surface, so that cutting is performed at the point a. Actually, the ball end mill rotates and cuts, but such a point is referred to as a "cutting point" for convenience.
Similarly, cutting is performed at the cutting point b on the processing surface having the slope B.
However, in the conventional numerical control device described above, since the spindle tool rotates according to the spindle tool rotation speed commanded by the machining program, if the commanded spindle tool rotation speed is constant,
The cutting speed is slower at the cutting point b having a shorter distance Rb to the rotation axis than at the cutting point a having a long distance Ra to the rotation axis. Therefore, when die machining with a large number of curved surfaces is performed by a cutting method with a constant number of revolutions, the cutting speed becomes uneven due to the position of the cutting point, that is, the inclination of the machined surface. Since this is reflected on the processed surface, the finish becomes uneven, and there is a problem that the quality of the processed die cannot be improved by the above cutting method. Further, there is a problem in that the tool itself also becomes uneven in wear, the overall tool life is not extended, and the cost is high. Especially near the tip of a tool with an extremely slow cutting speed, a large load is applied, so it is easy to chip,
This leads to a further reduction in tool life. As a countermeasure, there is a method to describe the command rotation speed of the spindle tool according to the change of the command path when creating the machining program, but when this method is applied, the machining program for die machining is generally long, There was a problem that it took a lot of time and effort to create a machining program.

The present invention has been made in view of the above problems, and an object of the present invention is to make the cutting speed constant irrespective of the cutting point of the ball end mill, and further to perform the feed synchronized with the rotational speed of the spindle tool. It is to provide a numerical control device that enables the numerical control.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a numerical control device for a machining center having a ball end mill as a main spindle tool and having respective feed axes of X-axis, Y-axis and Z-axis for performing die machining according to a machining program. The above-mentioned object of the present invention is from the movement amount of each feed shaft of the X-axis, Y-axis and Z-axis output from the shaft distributor, from the cutting point of the ball end mill to the rotation axis of the ball end mill. A tool radius ratio calculation unit for obtaining a tool radius ratio which is a ratio of a distance and a tool diameter of the ball end mill, and a spindle tool rotation speed command is obtained from the tool radius ratio and a spindle tool rotation speed commanded by the machining program. From the rotation speed calculation unit that outputs to the spindle servo system, the spindle tool rotation speed command, and the command feed speed per revolution commanded by the machining program It is achieved by providing a feeding speed calculating unit for obtaining a feedrate per minute.

[0007]

According to the numerical controller of the present invention, the distance from the cutting point of the ball end mill to the rotation axis of the ball end mill (hereinafter referred to as the radius at the cutting point, based on the movement amount of each feed shaft output from the shaft distributor). (Named) and the tool radius, which is the ratio between the tool radius and the tool radius, and the cutting speed can be kept constant by changing the spindle tool rotation speed according to the tool radius ratio. And the feed rate can be changed in synchronization with the rotation speed of the spindle tool.

[0008]

EXAMPLE The cutting speed is determined by the radius and the number of revolutions of the spindle tool. When the radius is the tool diameter R of the ball end mill and the rotation speed is the command spindle tool rotation speed S, the cutting speed V is expressed by Equation 1.

## EQU1 ## V = 2.pi.R.times.S Further, when the radius at the cutting point at which the actual cutting is performed is R'and the spindle tool rotation speed is S ', the cutting speed V'is expressed by the same equation 2 as the equation 2.

## EQU2 ## V '= 2.pi.R'.times.S' In order to keep the cutting speed constant at V of the formula 1, V '= V is set, and the formula 3 is obtained from the formulas 1 and 2.

[0009]

## EQU00003 ## 2.pi.R'.times.S '= 2.pi.R.times.S When the formula 3 is transformed to derive the spindle tool rotation speed S', the formula 4 is obtained.

## EQU00004 ## S '= (2.pi.R.times.S) /2.pi.R' = (R / R '). Times.S, that is, R / R', which is the ratio of the tool radii, is used as the coefficient of the command spindle tool rotation speed S to obtain S '. Is decided. Below, R /
R'is referred to as "tool radius ratio RR".

Here, in FIG. 4, the spindle rotation axis of the tool is Z
Axis, cutting point is W, the center of the hemisphere at the tip of the ball end mill is O, the foot of the perpendicular line drawn from the cutting point to the tool rotation axis is H, the end point of the feed axis movement amount ΔP is E, and the cutting point is point E When the foot of the perpendicular line drawn on the XY plane including is V, the two right triangles ΔWOH and ΔWEV have a similar relationship, and the tool radius ratio RR WO / WH is equal to WE / WV.
Since WE is equal to the feed axis movement amount ΔP and WV is equal to the Z axis movement amount Δz, the tool radius ratio RR can be obtained by Equation 5.

RR = R / R '= WO / WH = WE / WV = | ΔP | / | Δz | = √ (Δx ² + Δy ² + Δz ² ) / | Δz | In this way, the tool radius ratio RR is commanded By setting the coefficient of the tool rotation speed S, the spindle tool rotation speed S ′ for keeping the cutting speed constant is determined.

FIG. 1 is a block diagram showing an example of the configuration of a numerical controller according to the present invention based on the above-mentioned idea. The machining program 1, the interpreter 2, the function generator 3, the axis distributor 4, the feed axis servos 5x, 5y, 5z, the feed axis motors 6x, 6y, 6z, the feed unit amount determiner 7, and the spindle servo 8 are provided.
Since the spindle motor 9 is the same as the one in the prior art which has already been described, the description thereof will be omitted. The tool radius ratio calculation unit 11 uses the movement amounts Δx, Δy, and Δz of the respective feed shafts input from the shaft distributor 4, as described above.
Ask for. The rotation speed calculation unit 12 multiplies the tool radius ratio RR obtained by the tool radius ratio calculation unit 11 and the spindle tool rotation speed S instructed by the machining program 1 to obtain a spindle tool rotation speed command S ′, and the spindle servo 8 Is output to the feed rate calculation unit 10. However, when the obtained S'exceeds the maximum spindle tool rotation speed of the machine, the maximum spindle tool rotation speed of the machine is changed to S '.
And The spindle servo 8 rotates the spindle tool according to the given spindle tool rotation speed command S '. In addition, the feed rate calculation unit 1
In the case of 0, the spindle tool rotation speed command S'is multiplied by the command feed speed Fs per revolution to obtain the command feed speed Ft per minute. Then, a function is generated with the obtained Ft as the command feed speed. By doing so, the feed rate is synchronized with the rotational speed of the spindle tool, and the cutting amount per blade of the ball end mill becomes constant.

FIG. 2 is a flow chart showing an example of the operation in one function generation cycle of the numerical controller according to the present invention. The feed speed calculation unit 10 multiplies the command feed speed Fs per revolution and the spindle tool rotation speed command S ′ to obtain the command feed speed Ft per minute (step S1). The feed unit amount determination unit 7 obtains the feed unit amount ΔFt per function generation cycle from the command feed speed Ft per minute (step S2). The function generator 3 obtains the feed axis movement amount ΔP along the command path from the command position G and the feed unit amount ΔFt (step S3). The shaft distributor 4 calculates the moving amount ΔP of the feed axis by the moving amount Δ of each feed axis.
It is distributed to x, Δy, and Δz and is output to the servo of each feed axis (step S4). Movement amount of each feed axis Δx, Δy, Δz
Is also output to the tool radius ratio calculation unit 11, and the tool radius ratio RR is calculated based on these values (step S5). In the rotation speed calculation unit 12, a tool radius ratio RR and a command spindle tool rotation speed S are multiplied to obtain a spindle tool rotation speed command S ', which is output to the spindle servo 8 and a command per minute in the next function generation cycle. It is also sent to the feed speed calculation unit 10 to obtain the feed speed Ft (step S6). In addition, the movement amounts Δx, Δy of the respective feed axes received by the tool radius ratio calculation unit 11,
The Δz and the spindle tool rotation speed command S ′ received by the feed speed calculation unit 10 can be obtained from the outputs of the servos of the feed axes and the spindle servo, respectively.

[0013]

As described above, according to the numerical control device of the present invention, the cutting speed can be made constant by determining the rotational speed of the spindle tool according to the cutting point of the tool. A good machined surface can be obtained without any modification and by the same machining operation as the conventional one. Furthermore, the wear of the tool itself is reduced and the tool life is extended. Moreover, the feed rate is changed in synchronization with the changing number of revolutions of the spindle tool, so the amount of cutting per blade is constant,
It is possible to obtain a better machined surface with uniform rakes.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a numerical controller according to the present invention.

FIG. 2 is a flowchart showing an operation example in one function generation cycle of the numerical control device of the present invention.

FIG. 3 is a diagram showing that the cutting speed differs depending on the cutting point.

FIG. 4 is a diagram showing a relationship between a tool radius ratio and a feed shaft movement amount.

FIG. 5 is a block diagram showing a configuration example of a conventional numerical control device.

[Explanation of symbols]

 10 Feed rate calculation unit 11 Tool radius ratio calculation unit 12 Rotation speed calculation unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G05B 19/416

Claims (2)

[Claims] 1. A numerical control device for a machining center having a ball end mill as a main spindle tool and having X-axis, Y-axis and Z-axis feed axes for performing die machining according to a machining program, which is output from an axis distributor. X axis,
A tool radius ratio for obtaining a tool radius ratio, which is a ratio of a distance from a cutting point of the ball end mill to a rotation axis of the ball end mill and a tool diameter of the ball end mill, based on a movement amount of each of the Y-axis and Z-axis feed axes. The rotation speed of the ball end mill is calculated by a calculation unit and a rotation speed calculation unit that outputs a spindle tool rotation speed command from a spindle radius rotation speed commanded by the machining program and the machining program to a spindle servo system. A numerical controller characterized in that a cutting speed is made constant by changing the distance according to a change in the distance. 2. A feed rate calculation unit for obtaining a command feed rate per minute from the spindle tool rotational speed instruction and a command feed rate per revolution commanded by the machining program, and the per minute instruction The numerical controller according to claim 1, wherein the rotation speed of the ball end mill and the feed speed are synchronized by generating a function of the movement amount of the ball end mill according to the feed speed.