KR100563250B1 - Tool Wear Monitoring System with Hybrid Approach to Cutting Force Regulation - Google Patents

Abstract

The present invention relates to a system for effective monitoring of tool wear that causes machining errors and reduced productivity. The object of the present invention is to realize unmanned and automated through tool monitoring in die processing or casting through CNC machining, and ultimately Based on stable processing, high productivity and high efficiency can be achieved.

The present invention applies a hybrid (offline / real-time) scheme for leveling the cutting force. Prediction of cutting force for machining conditions of NC data, optimizing cutting force for machining conditions by optimizing off-line feed rate, and detecting only cutting force change signals due to tool wear by excluding factors caused by cutting conditions from cutting force changes during machining can do. The cutting force increased by tool wear is also leveled by adjusting the feedrate override of the real-time feedrate control module configured with DSP (Digital Signal Processor) to stabilize the process.As a result, the change of the average value of the feedrate override that is reduced Wear can be monitored. Through the present invention, machining unmanned and automated required in CNC machining can be achieved through a tool wear monitoring system for maximizing stability and productivity when machining cutting forces varying from machining conditions and tool wear, respectively, from hybridization leveling. .

Machine Tool, Tool, Tool Wear, NC, Monitoring, Cutting Force, Feed Rate, Override

Description

Tool Wear Monitoring System with Hybrid Approach to Cutting Force Regulation}

The following drawings, which are attached in this specification, illustrate preferred embodiments of the present invention, and together with the detailed description of the present invention, serve to further understand the technical spirit of the present invention. It should not be construed as limited to.

1 is a block diagram of a tool wear monitoring system through a hybrid-type cutting force leveling of the present invention.

2 is a calculation flow chart for leveling cutting forces offline according to the present invention.

3 is a calculation flow chart for leveling cutting forces in real time according to the present invention.

4 is a graph showing the process of real-time cutting force leveling of the present invention.

5 is a graph showing the cutting force leveling according to the hybrid method of the present invention.

Figure 6 is a graph showing the increase in cutting force according to the pure tool wear in the present invention.

Figure 7 is a feedrate override graph for tool wear monitoring in the present invention.

<Explanation of symbols for the main parts of the drawings>

101: CNC machining center 102: offline feedrate optimization module

103: real time feed rate control module 104: machining status monitoring module

201: Initial Condition Input Part 202: Cutting Force Selection

203: Cam data input for cutting force prediction for machining conditions

204: comparison part between cutting reference cutting force and cutting condition cutting force

205: Part of generating optimum feed speed by comparing cutting force

301: spindle drive detection 302: air cut detection

303: Machining standard cutting force selection part through machining recommendation conditions

304: Cutting force signal transmission to real-time feed rate control module

305: change of feedrate override

401: spindle current 402: spindle peak during spindle drive

403: air cut 404: initial contact current of the tool and the workpiece

405: Real time feedrate override diagram.

501: Spindle current diagram before cutting force leveling.

502: Spindle current diagram after leveling cutting force through offline feedrate optimization.

503: Leading spindle current after hybrid cutting force leveling.

601: Leading cutting force increase due to tool wear.

602: cutting force moving average value by tool wear.

603: Linear relationship between tool wear and cutting force.

701: Feedrate override moving average value diagram.

702: Linear relationship diagram between tool wear and feedrate override.

The present invention relates to a system for monitoring tool wear of a machine tool for processing a workpiece, and in particular, to monitor the gradual change of the tool wear as a moving average value of the feedrate override controlled in real time by separating only the cutting force signal due to the tool wear. The present invention relates to a tool wear monitoring system through hybridization of cutting force leveling.

If abrasion occurs during machining, the cutting force increases and the surface quality and machining stability are greatly reduced due to the increase of dynamic instability. The present invention relates to the monitoring of tool wear, which causes the above problems during machining, and is an automated and unmanned process for maximizing the performance of high-efficiency CNC machining (processing stability is required with productivity by maximizing material removal rate per hour). It is a major task for.

Automated and unmanned machining through tool wear monitoring allows the machine to know the machining status without the need for skilled operators, and allows one operator to manage multiple machines and provide productivity and stability even during night unattended machining.

However, the existing tool wear monitoring system uses an expensive sensor or a sensor that is not applicable to gradual tool wear to obtain a wear signal but is applicable to extreme tool breakage. Another problem of the prior art is that it is difficult to effectively separate the signal due to the machining conditions and the tool wear, it is difficult to grasp only the influence of the cutting force by the tool wear. For the separation of the signal, sampling is performed under ideal conditions without tool wear or damage for all sections of the determined path, and the signal is stored in the entire section for the signal exceeding a certain upper limit of the value for each section. Judging by wear or damage to the tool.

However, this technique is quite unproductive because it requires sampling for new machining paths, and in the case of milling where the cutting force is changed irregularly by machining a relatively complex shape compared to turning, it is difficult to set tool wear or breakage thresholds. . Another approach was to measure breakage with a touch sensor, but this was also not possible for real-time measurement during machining and was not suitable for monitoring progressive wear of tools.

The technical problem to be achieved in the present invention is as follows.

First, in order to avoid unproductive sampling of all machining paths, the cutting force signals due to tool wear and machining conditions are separated. To this end, the cutting force change for the machining conditions is equalized by optimizing the offline feedrate before machining so that the cutting force does not change during machining.

Second, check the relationship between the physical value of the tool wear and the cutting force due to the tool wear. To do this, compare the measured tool wear signal values with the actual measured physical values of the tool wear and verify the relationship.                         

Third, the cutting force is finally leveled in real time by the tool wear for machining stability and at the same time monitoring the tool wear. To this end, the cutting force due to tool wear during machining is leveled by real-time adaptive control through feedrate override, and tool wear is monitored from the change value of feedrate override.

Specific means of the present invention for achieving the above object,

In the system for monitoring the wear of the tool by leveling the cutting force of the machine tool having a numerical control device,

An offline feedrate optimization module for optimizing the feed rate for the entire processing section so that the cutting force for the machining condition is constant, and transferring the optimized cam data to the numerical control device to induce the feed with the leveled cutting force;

A real time feed speed control module for receiving a cutting signal from the numerical control device and equalizing a change in cutting force by tool wear in real time through a feed rate override command to the numerical control device;

It characterized in that it comprises a machining state monitoring module for monitoring the tool wear from the change value of the feedrate override used in the real-time feedrate control module.

In addition, according to the present invention, the offline feedrate optimization module,

Obtaining a machining reference cutting force from the tool recommendation condition;

Predicting the cutting force through the micro cutting force model by receiving the cam data;

By comparing the predicted cutting force and the cutting reference cutting force, the feed rate is increased when the predicted cutting force is small, and conversely, the feed rate is reduced by optimizing the feed rate when the predicted cutting force is large.

In addition, according to the present invention, the real-time feed rate control module,

Selecting a cutting reference cutting force when the air cut signal is detected after the spindle rotation is detected;

Comparing the machining reference cutting force and the machining measurement cutting force;

When the machining measurement cutting force increases the machining reference cutting force is characterized in that it comprises a step of reducing the feed rate through the feedrate override in real time so that the cutting force can follow the machining reference cutting force.

In addition, according to the present invention, the processing state monitoring module,

By indexing the average moving value of the feedrate override is characterized in that the tool wear and linearly displayed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a tool wear monitoring system through the hybridization of the cutting force leveling.

As shown in FIG. 1, a CNC machining center 101, an offline feedrate optimization module 102, a real-time feedrate control module 103 implemented by a DSP (Digital Signal Processor), and a machining state monitoring module 104 are provided. There are four parts.

The cutting force is predicted from the machining conditions of CAM data through the offline feedrate optimization module, and the feedrate is optimized for every section so that the cutting force for the machining conditions is constant during machining. The optimized cam data is transmitted to the control part of the CNC machining center, where the cutting force is leveled. Changes in cutting forces due to tool wear occurring during machining are leveled by a real-time feed rate control module implemented in the DSP for machining stability.

Here, the feedrate control is performed through the feedrate override, and the change of the feedrate override is monitored in real time through the machining status monitoring module. The relationship between feedrate override and actual tool wear is used to monitor tool wear through feedrate override.

2 is a main operation flow chart of the offline feedrate optimization module. When the tool and the workpiece are selected, the machining reference cutting force 202 is obtained from the machining recommendation condition 201 of the tool. In order to predict the cutting force in the cutting area by the machining condition 203 of the cam data and to level it 204 with the machining reference cutting force, an optimum feed rate 205 is generated in all machining conditions.

3 is a calculation flowchart for leveling a cutting force in real time. Since the cutting force for the processing conditions is leveled as shown in FIG. 2, the change in cutting force due to tool wear during machining is leveled in real time in the same manner as in FIG. 3.

After detecting the peak value of the signal when driving the spindle (301), the air cut is recognized (302), and also the machining reference cutting force is set from the machining recommendation conditions (303). It is transmitted 304 to the feed rate control module. When the wear of the tool occurs during processing, the cutting force is increased, so that the cutting speed during processing is instructed to reduce the feed rate through the feedrate override in real time so as to follow the cutting reference cutting force.

4 shows the change in cutting force in the above described real-time feed rate control module through the spindle current 401 showing a linear relationship with the cutting force. First, when the spindle is driven, a spindle current peak 402 is generated as follows. Then, the air cut is recognized from the spindle current (403), and the actual machining is recognized by the initial contact between the workpiece and the tool (404). In consideration of the selected machining standard, the feedrate override command 405 is provided so that the cutting force and the spindle current in the linear relationship can be leveled so that the cutting force can be followed the machining standard.

Figure 5 shows the results of the cutting force leveling by the machining conditions and the tool wear through a hybrid method.

The first graph 501 shows the result of the machining through the initial CAM data without cutting force leveling. This graph shows the cutting force change due to the machining conditions and the wear of the tool.

The second graph 502 shows the leveling of the cutting force by the processing conditions through the offline feedrate optimization module. The third graph 503 shows the leveling of the cutting force due to tool wear occurring during machining through the real-time feed rate control module after leveling the cutting force by the processing conditions through the above module.

The relationship between tool wear and cutting force during such machining is shown in the graph of increase 601 of cutting force due to pure tool wear of FIG. 6. Due to the offline feedrate optimization, the change in cutting force during machining in the graph is mainly due to tool wear and the inhomogeneity of the workpiece. Among them, the cutting force due to tool wear gradually increases, and the cutting force due to the inhomogeneity of the workpiece changes irregularly like noise. Among them, the moving average value 602 of the cutting force is shown on the graph in order to make the relationship between the cutting force change only by the tool wear only sensitive. The relationship between the actual measured tool wear for moving average values of increased cutting force is shown. A linear relationship 603 between tool wear and cutting force is shown.

However, since the change in cutting force due to the tool wear is leveled through the feedrate override of the real-time feed rate control module for stabilization of the process, the tool wear is monitored through the feedrate override graph for the tool wear monitoring of FIG. 7.

As described above, the average moving value 701 of the feedrate override is shown in the graph to find the feedrate override for leveling the cutting force increased by the tool wear. The relationship between the actual measured tool wear and the average travel values of the reduced feedrate override for the equalization of the increased cutting forces is shown. A linear relationship 702 can be seen between the average value of tool wear and feedrate override.

Here, the feedrate override is expressed as a moving average so that only insensitive and progressively changing tool wear can be monitored for factors such as inhomogeneity of the workpiece during processing.

In this way, the average value is obtained by sampling a certain amount of the cutting signal and the feedrate override commanded in real time, and the initial sample value is obtained after a predetermined time to reduce the influence of noise factors irrelevant to tool wear.

For example, if you average 1000 data, the sample frequency is 100Hz, and you receive 1000 data for the first 10 seconds, average it, and after 1 second you receive 100 new data collected for 1 second. Discard 100 data and get a new moving average.

The tool wear monitoring system through the hybridization of cutting force leveling described above separates the cutting force change due to the machining condition from the cutting force change due to the tool wear and changes in real time to stabilize the cutting force change due to the tool wear during machining. Tool wear can be monitored by monitoring the feedrate override.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto, and the technical idea of the present invention and the following by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

According to the tool wear monitoring system through the cutting force leveling of the hybrid method of the present invention as described above, it is possible to monitor the tool wear that occurs gradually during machining. This is the basis for automation and unmanned CNC machining.

In addition, the tool wear monitoring system through the hybridization of the cutting force leveling method of the present invention optimizes the feed rate for the machining conditions offline in the process of distinguishing the cutting force changes due to the machining conditions and the tool wear and feeds the cutting force that changes during machining in real time. Stabilization through control and monitoring of tool wear improves productivity and stability.

This is a tool wear monitoring system that satisfies the requirements of high efficiency machining in the mold sector, which is recently attracting attention. to be.

As a result, successful night automation and unmanned machining in CNC machining also enable efficient night machining, and can produce productive and objectively stable machining even in workshops that lack skilled personnel.

Claims (4)

In the system for monitoring the wear of the tool by leveling the cutting force of the machine tool having a numerical control device (CNC), The offline feedrate optimization module 102 optimizes the feedrate for the entire cutting section so that the cutting force for the machining conditions is constant, and transmits the optimized CAM data to the numerical control device to induce the feed with the leveled cutting force. )and; A real time feed rate control module 103 for receiving a cutting signal from the numerical control device and equalizing the change in cutting force by tool wear in real time through a feed rate override to the numerical control device; Tool wear monitoring system through the hybridization of the cutting force leveling, characterized in that it comprises a machining state monitoring module 104 for monitoring the tool wear from the change value of the feedrate override used in the real-time feed rate control module (103). The method of claim 1, The offline feedrate optimization module 102, Obtaining a machining reference cutting force from the tool recommendation condition; Predicting the cutting force through the micro cutting force model by receiving the cam data; Comparing the predicted cutting force and the cutting reference cutting force increases the feed rate when the predicted cutting force is small, and vice versa by reducing the feed rate when the predicted cutting force is large. Tool wear monitoring system through leveling of cutting force. The method of claim 1, The real time feed rate control module 103, Selecting a cutting reference cutting force when the air cut signal is detected after the spindle rotation is detected; Comparing the machining reference cutting force and the machining measurement cutting force; When the machining measurement cutting force increases the machining reference cutting force, the cutting speed leveling method of the hybrid method includes a command to reduce the feed rate through the feedrate override in real time so that the cutting force can follow the machining reference cutting force. Wear monitoring system. The method of claim 1, The processing state monitoring module 104, Tool wear monitoring system through the hybridization of the cutting force leveling, characterized in that the index of the average moving value of the feedrate override is displayed linearly with the amount of tool wear.

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