JP3118748B2 - Method and apparatus for controlling feed rate of NC machine tool - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling a feed speed of an NC machine tool.

[0002]

2. Description of the Related Art When a workpiece having a free-form surface such as a die is machined using a tool such as a ball end mill, the machining load may increase. Due to the increase in the processing load, the displacement of the cutting edge of the tool in accordance with the rigidity of the tool system and the rigidity of the spindle system also increases, and as a result, the processing accuracy decreases. In addition, when the feed axis is fed at a constant command feed speed, the processing load fluctuates in a sudden change in the processing shape. If the change in the processing load exceeds an allowable value, tool breakage may occur. Therefore, in order to increase machining accuracy and prevent tool breakage, the command feed speed is normally set to a low value, and there is a tendency to sacrifice overall machining efficiency. One prior art for solving this problem is disclosed in Japanese Patent Application Laid-Open No. 5-200653.
There is a technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-26095. In this method, a rotating milling tool bends due to a load during processing, the amount of the bending is measured by a non-contact displacement meter, and the measurement result is reflected in the in-process processing accuracy control of the workpiece.

[0003]

The problem to be solved by the present invention is disclosed in Japanese Patent Laid-Open No. 5-200.
The technique disclosed in Japanese Patent No. 653 does not measure the amount of deflection of a tool unless machining is actually performed, and is basically feedback control. In the feedback control, the control delay inevitably exists, and if the command feed speed is too fast, the machining load at a certain point increases, the tool bends to a predetermined value or more, and the next instant feedback control has settled to a predetermined deflection. Even so, the processing accuracy at that point in time will be degraded. In addition, a displacement gauge must be installed in the vicinity of the processing area, and depending on the shape of the work, the processing location, etc., a space for installing the displacement gauge cannot be secured, or accurate measurement cannot be performed due to scattering of chips or machining fluid. . The installation of the displacement meter itself unnecessarily complicates the configuration near the processing area. In addition, the processing load may increase rapidly and the tool may be damaged,
There is also a problem that feedback control cannot follow such a sudden load change.

SUMMARY OF THE INVENTION An object of the present invention is to provide a feed rate control method and apparatus for an NC machine tool capable of controlling the feed rate so that the displacement of a cutting edge of a tool has a predetermined value without delay. is there. Another object of the present invention is to automatically determine an optimum feed speed that achieves the target machining accuracy efficiently and without setting a feed speed suitable for each processing portion in advance by an NC processing program or the like. It is. Still another object is to achieve a feed rate control in which tool breakage does not occur due to a sudden load change. Still another object is to avoid using a measuring means such as a displacement gauge and to make the vicinity of a processing area not complicated.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention calculates a load acting on a tool sequentially prior to actual machining, and calculates a predicted displacement of a cutting edge portion of the tool from the calculated load. Determine the amount, compare the predicted displacement amount and the target displacement amount of the cutting edge of the tool corresponding to the target machining accuracy, automatically control the feed rate that affects the displacement of the cutting edge of the tool, The displacement of the cutting edge portion of the tool in actual machining is set so as not to exceed the target displacement. Further, a predicted displacement amount change rate is calculated, a feed speed corresponding to the predicted displacement amount change rate that does not cause tool breakage is obtained, and tool breakage is prevented by machining at this feed speed. The predicted displacement of the cutting edge portion of the tool is determined by considering the rigidity of the entire tool system including the tool and the tool holder, and the rigidity of the entire mechanical system including the main spindle and the spindle head on which the tool is mounted. It is the total displacement at the processing point.

That is, in an NC machine tool for machining a workpiece by giving relative feed by a feed shaft between the workpiece and a tool mounted on a rotary spindle, machining data such as a workpiece shape, a workpiece material, a tool shape, and a tool material. And machining conditions such as spindle rotation speed, feed speed, etc., and a feed shaft position command, sequentially calculate the load acting on the tool prior to actual machining, and calculate the cutting edge of the tool from the calculated load acting on the tool. The predicted displacement amount of the cutting edge portion of the tool is compared with the target displacement amount of the cutting edge portion of the tool corresponding to a preset target machining accuracy. Provided is a feed speed control method for an NC machine tool that controls a feed speed of a relative feed to obtain a desired machining accuracy.

Further, in an NC machine tool for machining a workpiece by giving a relative feed by a feed shaft between the workpiece and a tool mounted on a rotary spindle, machining data such as workpiece shape, workpiece material, tool shape, tool material, etc. And spindle speed,
Machining conditions such as feed speed and a feed shaft position command are used to sequentially calculate the load acting on the tool prior to actual machining, and the predicted displacement of the cutting edge portion of the tool is calculated from the calculated load acting on the tool. The calculated predicted displacement amount change rate is calculated from the calculated predicted displacement amount, and the calculated predicted displacement amount change is calculated from a previously stored relationship between the displacement amount change rate of the cutting edge portion of the tool and the feed speed at which tool breakage does not occur. NC that determines a feed rate corresponding to the feed rate and sets the determined feed rate as an actual machining feed rate.
A method for controlling a feed rate of a machine tool is provided.

In an NC machine tool for machining a workpiece by giving a relative feed by a feed shaft between the workpiece and a tool mounted on a rotary spindle, machining data such as a workpiece shape, a workpiece material, a tool shape, and a tool material are provided. And spindle speed,
A predicted load acting on the tool is sequentially calculated prior to actual machining from machining conditions such as a feed speed and a feed shaft position command, and a predicted displacement amount of a cutting edge portion of the tool is calculated from the calculated load acting on the tool. Is calculated from the obtained predicted displacement amount to calculate the predicted displacement amount change rate, and the calculated predicted displacement amount of the cutting edge portion of the tool and the target displacement of the cutting edge portion of the tool corresponding to a preset target machining accuracy. Amount and compare the amount to the first
Determine the feed speed of, the second feed speed corresponding to the calculated predicted change amount change rate from the previously stored relationship between the change amount change rate of the cutting edge portion of the tool and the feed speed at which tool breakage does not occur, A feed speed control method for an NC machine tool is provided in which the first feed speed is compared with the second feed speed, and the smaller feed speed is used as the actual machining feed speed.

In an NC machine tool for machining a workpiece by giving a relative feed by a feed shaft between the workpiece and a tool mounted on a rotary spindle, machining data such as a workpiece shape, a workpiece material, a tool shape, and a tool material are provided. From the machining data stored in the storage means, machining conditions such as the spindle rotation speed and feed speed commanded by the NC machining program, and the feed shaft position command. Load calculation means for calculating the load acting on the tool, displacement amount calculation means for calculating the predicted displacement amount and the predicted displacement amount change rate of the cutting edge portion of the tool from the load acting on the tool calculated by the load calculation means; Comparing the calculated predicted displacement of the cutting edge portion of the tool with the target displacement amount of the cutting edge portion of the tool corresponding to a preset target machining accuracy, and according to the comparison result, The feed rate is determined, and a second feed rate corresponding to the calculated predicted displacement rate is calculated from a relationship stored in advance between the rate of change of the cutting edge portion of the tool and the feed rate at which tool breakage does not occur. Feed speed control means for comparing the first feed speed and the second feed speed, and controlling the feed speed so that the smaller feed speed becomes the actual machining feed speed. A control device is provided.

[0010]

The load acting on the tool is calculated by the load calculating means from the processing data, the processing conditions and the position command, prior to the actual processing. Then, the displacement calculating means obtains a predicted displacement of the cutting edge of the tool corresponding to the calculated load from the relationship between the displacement of the tool cutting edge stored in advance and the load acting on the tool. By comparing the predicted displacement amount with a preset target displacement amount, if the predicted displacement amount is equal to or less than the target displacement amount, the machining proceeds at the commanded feed speed,
When the predicted displacement amount is larger than the target displacement amount, the feed speed is reduced, and the feed speed is controlled so that the actual displacement amount becomes substantially equal to the target displacement amount, and the machining is advanced. By sequentially performing such control of the feed speed, it is possible to perform the processing while maintaining the target processing accuracy even in the processing in which the processing load varies. The feed speed at the time of actual machining in this case is defined as a first feed speed.

The relationship between the rate of change of the amount of displacement of the cutting edge of the tool and the feed rate at which tool breakage does not occur is stored in the storage means in advance. With reference to this relationship, a feed rate corresponding to the predicted displacement rate change rate calculated by the displacement quantity calculation means is obtained, and this feed rate is sent to the feed rate control means as a second feed rate. Then, the feed speed at the time of actual machining becomes the second feed speed, and tool breakage does not occur. Further, the first feed speed and the second feed speed are obtained, and the smaller one of the first feed speed and the second feed speed is set as the feed speed at the time of actual processing, whereby the processing accuracy falls below the target accuracy.
In addition, machining that does not cause tool breakage can be performed.

[0012]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of a feed rate control device for an NC machine tool according to the present invention.
FIG. 3 is a flowchart illustrating an example of a feed speed control method for an NC machine tool according to the present invention. FIG. 3 is a graph illustrating an example of a relationship between a displacement amount of a cutting edge portion of a tool and a load acting on the tool. 5 is a graph showing an example of a relationship between a displacement rate of a cutting edge portion of a tool and a feed speed at which tool breakage does not occur.

As shown in FIG. 1, the NC machine tool according to the present invention has a basic configuration in which an NC machining program 1 is inputted to an NC device 3 and a machine tool 5 is controlled. On the other hand, data necessary for the feed speed control is stored in the storage means 9 from the input means 7 in advance. The data to be stored include tool number, tool holder type, tool type (square end mill, ball end mill, etc.), tool dimensions (length, diameter, tip sphere radius, number of teeth, etc.), tool material, work number, Processing data such as work shape and work material. The relationship between the displacement of the cutting edge of the tool and the load acting on the tool, and the relationship between the rate of change of the displacement of the cutting edge of the tool and the feed rate at which tool breakage does not occur, are described below. It is stored corresponding to the type of the holder, the type of the tool, and the like. The load calculating means 11 receives a work number, a tool number, machining conditions such as a spindle rotation speed and a feed speed, and a position command of each feed axis from the NC machining program read and interpreted by the NC device 3, and receives a work number, Machining data corresponding to the tool number is received from the storage means 9, and a load acting on the tool is sequentially calculated prior to actual machining.

The displacement calculating means 13 includes a load calculating means 11
And the relationship between the load and the displacement of the cutting edge of the tool stored in advance in the storage means 9 (in a table, in a mathematical expression, in a relation curve, etc.). Then, the predicted displacement amount is calculated.
When the calculation result is sent to the feed speed control means 15, the feed speed control means 15 first compares the calculated result with the target displacement of the cutting edge of the tool corresponding to the target machining accuracy stored in advance. Then, a command for controlling the feed speed during the actual machining is issued to the NC device 3 in accordance with the comparison result, so that the displacement of the cutting edge portion of the tool during the actual machining is substantially equal to the target displacement. Examples of the command for controlling the speed include a method of instructing the servo control unit of the NC, a method of automatically dividing and changing blocks of the NC machining program to control the speed command, and the like. The predicted displacement of the cutting edge portion of the tool obtained by the displacement calculating means 13 is determined by the rigidity of the entire tool system including the tool and the tool holder, and the rigidity of the entire mechanical system including the spindle and the spindle head on which the tool is mounted. And the total displacement at the machining point of the tool taking into account

Further, the displacement calculating means 13 differentiates the calculated predicted displacement with respect to time to calculate a predicted displacement change rate. A feed rate corresponding to the predicted change rate of change is determined by using a relationship between the change rate of the displacement of the cutting edge portion of the tool and the feed rate at which no tool breakage is stored in advance in the storage means 9. 15 By using the feed speed as the feed speed at the time of actual machining, the feed speed control means can process the workpiece at a feed speed at which tool breakage does not occur.

Next, the operation of the present invention will be described with reference to the flowchart of FIG. First, the load calculating means 11 processes machining data such as a work shape, a work material, a tool shape, and a tool material;
Processing conditions such as the spindle rotation speed and the feed speed, and the position command of the feed shaft are read (step S1), and the load acting on the tool is calculated by a predetermined logic (step S2). Next, the displacement calculating means 13 calculates a predicted displacement and a predicted displacement change rate of the cutting edge portion of the tool corresponding to the load (step S3). The calculated predicted displacement is compared with the target displacement of the cutting edge of the tool corresponding to the target machining accuracy given in advance (step S4). If the predicted displacement is equal to or less than the target displacement, the command feed speed is maintained. The processing may be advanced by using the first feed speed Fa (step S5). That is, the load acting on the tool is not large enough to reduce the machining accuracy to a target value or more.

If the predicted displacement exceeds the target displacement in step S4, a first feed speed Fa obtained by performing a deceleration control by applying an override calculated as follows to the commanded feed speed is obtained in step S6. An embodiment of the deceleration control in step S6 will be described with reference to FIG. The graph of FIG. 3 is an example showing the relationship between the displacement amount of the cutting edge portion of the tool and the machining load acting on the tool. The deceleration rate of the above-mentioned deceleration control, that is, the override, is the value of the machining load at the target displacement amount. Is divided by the machining load value at the predicted displacement amount. Therefore, during actual machining, the command feed speed is decelerated by applying this override, and as a result, the displacement of the cutting edge of the tool is substantially equal to the target displacement, and the machining accuracy is maintained at the target machining accuracy.

Next, a second feed speed Fb corresponding to the predicted change rate of the displacement is obtained from the relationship between the change rate of the displacement of the cutting edge of the tool illustrated in FIG. 4 and the feed rate at which the tool is not damaged (FIG. 4). Step S7). In step S8, step S5
Or, the first feed speed Fa obtained in S6 and the step S7
Is compared with the second feed speed Fb obtained in the above, and when Fa is equal to or less than Fb, the feed speed F at the time of actual machining is set
a (step S9), and when Fa is larger than Fb, the feed speed F during actual machining is set to the second feed speed Fb (step S10). Then, the actual machining of the portion where the load is calculated in step S2 is performed at the feed speed F (step S1).
1) The processing from step S1 is repeated until all machining is completed (step S12), and feed speed control is performed so that machining always proceeds at the optimum feed speed.

The first aspect of the present invention relates to processing at the feed rate Fa determined in step S5 or S6, and relates to feed rate control for ensuring that the processing accuracy does not exceed the target processing accuracy. is there. The second aspect of the present invention relates to machining at the feed rate Fb obtained in step S7, and relates to feed rate control for preventing tool breakage. The invention according to claims 3 and 4 is an invention comprising a series of steps described in the present embodiment, and relates to a feed speed control for securing machining accuracy and preventing tool breakage.

In this embodiment, in order to obtain the feed rate F, the predicted displacement amount and the predicted displacement rate change rate of the cutting edge of the tool are once determined from the load acting on the tool, and then the feed rate F is determined. Although the case of performing various processing of was described,
There is also a method of obtaining from the load acting on the tool. That is,
The load calculated by the load calculating means 11 is used as the predicted load, and the predicted load change rate is calculated from the time differential value. Then, the first feed speed is determined by comparing the predicted load with the target load acting on the tool corresponding to the preset target machining accuracy. Further, the relationship between the load acting on the tool and the feed speed at which no tool breakage occurs is stored in the storage means 9 in advance, and a feed speed corresponding to the predicted load change rate is obtained, and this is set as a second feed speed Fb. It is. When both the processing accuracy and the prevention of tool breakage are targeted, the process of setting the smaller one of Fa and Fb as the feed speed F in actual machining is the same as that of the present embodiment.

[0021]

As described above, according to the present invention, the predicted displacement amount of the cutting edge portion of the tool is sequentially obtained prior to the actual machining, and is compared with the target displacement amount.
The first feed speed at which the actual displacement of the cutting edge of the tool does not exceed the target displacement is automatically determined, and the feed speed can be controlled. Therefore, high-precision machining without control delay is realized. Further, when the NC machining program is created, the trouble of setting the feed speed in accordance with the machining location is eliminated. On the other hand, a second feed speed at which tool breakage does not occur is determined from the predicted displacement amount change rate, and tool breakage can be prevented by performing actual machining at this feed speed. And the first
By comparing actual feed speed with the second feed speed and performing actual machining at the smaller feed speed, feed speed control satisfying machining accuracy and prevention of tool breakage can be performed. Further, since there is no need to use a displacement meter that directly measures the amount of displacement of the tool, the vicinity of the processing area does not have a complicated configuration.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram illustrating an example of a feed speed control device for an NC machine tool according to the present invention.

FIG. 2 is a flowchart illustrating an example of a feed speed control method for an NC machine tool according to the present invention.

FIG. 3 is a graph showing an example of a relationship between a displacement amount of a cutting edge portion of a tool and a load acting on the tool.

FIG. 4 is a graph illustrating an example of a relationship between a displacement rate of a cutting edge portion of a tool and a feed speed at which tool breakage does not occur.

[Explanation of symbols]

 Reference Signs List 3 NC device 5 Machine tool 9 Storage means 11 Load calculation means 13 Displacement calculation means 15 Feed speed control means

Continuation of front page (56) References JP-A-7-51996 (JP, A) JP-A-3-161240 (JP, A) JP-A-9-38843 (JP, A) JP-A-2-108105 (JP) , A) JP-A-9-16265 (JP, A) JP-A-8-152908 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23Q 15/00-15/28 G05B 19/18-19/46 B23Q 5/00-5/58 B23Q 17/00-23/00

Claims (4)

(57) [Claims] 1. A method of machining a work by giving a relative feed by a feed shaft between the work and a tool mounted on a rotary spindle.
In the C machine tool, machining data such as work shape, work material, tool shape, tool material, and machining conditions such as spindle rotation speed and feed speed;
The load acting on the tool is sequentially calculated prior to actual machining from the feed shaft position command, and the predicted displacement of the cutting edge portion of the tool is calculated from the calculated load acting on the tool. The predicted displacement amount of the blade portion is compared with a target displacement amount of the cutting edge portion of the tool corresponding to a preset target machining accuracy, and a feed speed of the relative feed is controlled according to the comparison result to obtain a desired machining accuracy. And a feed speed control method for an NC machine tool. 2. A method of machining a workpiece by giving a relative feed by a feed axis between the workpiece and a tool mounted on a rotating spindle.
In the C machine tool, machining data such as work shape, work material, tool shape, tool material, and machining conditions such as spindle rotation speed and feed speed;
The load acting on the tool is sequentially calculated from the feed shaft position command prior to actual machining, and the predicted displacement of the cutting edge portion of the tool is calculated from the calculated load acting on the tool. From the relationship between the change rate of the displacement of the cutting edge portion of the tool and the feed rate at which tool breakage does not occur, a feed rate corresponding to the calculated change rate of the calculated displacement is calculated from A feed rate control method for an NC machine tool, wherein the determined feed rate is used as an actual machining feed rate. 3. A method of machining a workpiece by giving a relative feed by a feed axis between the workpiece and a tool mounted on a rotating spindle.
In the C machine tool, machining data such as work shape, work material, tool shape, tool material, and machining conditions such as spindle rotation speed and feed speed;
A predicted load acting on the tool is sequentially calculated from the feed shaft position command prior to actual machining, and a predicted displacement amount of the cutting edge portion of the tool is calculated from the calculated load acting on the tool. The predicted displacement amount change rate is calculated from the amount, and the calculated predicted displacement amount of the cutting edge portion of the tool is compared with the target displacement amount of the cutting edge portion of the tool corresponding to a preset target machining accuracy, and the comparison result is obtained. A first feed speed is obtained in accordance with the following formula, and a second feed rate corresponding to the calculated predicted change rate change rate is calculated from a previously stored relationship between the change rate of the displacement of the cutting edge portion of the tool and the feed rate at which tool breakage does not occur. A feed speed control method for an NC machine tool, wherein a feed speed is obtained, the first feed speed is compared with a second feed speed, and a smaller feed speed is set as an actual machining feed speed. . 4. A method of machining a workpiece by giving a relative feed by a feed axis between the workpiece and a tool mounted on a rotating spindle.
In a C machine tool, storage means for storing processing data such as a work shape, a work material, a tool shape, and a tool material in advance; processing data stored in the storage means; a spindle rotation speed and a feed commanded by an NC processing program; Load calculating means for sequentially calculating a load acting on the tool prior to actual machining from processing conditions such as speed and a feed shaft position command; and cutting of the tool from the load acting on the tool calculated by the load calculating means. A displacement amount calculating means for calculating a predicted displacement amount and a predicted displacement amount change rate of the blade portion; and the calculated predicted displacement amount of the cutting edge portion of the tool, and a cutting edge portion of the tool corresponding to a preset target machining accuracy. The first feed speed is determined based on the comparison result with the target displacement amount, and the first feed speed is determined from the previously stored relationship between the displacement change rate of the cutting edge portion of the tool and the feed speed at which tool breakage does not occur. A second feed speed corresponding to the calculated predicted displacement amount change rate is obtained, the first feed speed and the second feed speed are compared, and feed is performed so that the smaller feed speed becomes the actual machining feed speed. A feed speed control device for an NC machine tool, comprising: feed speed control means for performing speed control.