CN105739438A - Method for intelligently inhibiting machining vibration - Google Patents

Abstract

The invention discloses a method for intelligently suppressing machining chatter, which is used for suppressing chatter during machining in a machine tool that utilizes tool or workpiece rotation to perform machining, including identifying the chatter at the incubation stage through a machining vibration detection algorithm; If it has not entered the incubating stage, continue processing according to the established cutting parameters; if incubating has started, switch to variable spindle speed control, and use the original spindle speed as a reference to periodically change the set amplitude and frequency. and the depth of cut remain unchanged; when the chatter has entered the breeding stage, the chatter suppression cannot be achieved after the method of variable spindle speed chatter suppression is used, and the machining is stopped. The method of the present invention can identify and control the chatter vibration during the incubation period of the chatter vibration, and does not need to judge whether the machine tool is capable of realizing it before the execution of the control unit. Therefore, chatter-free machining can be realized in the chatter incubation stage, that is, chatter can be detected earlier and chatter can be suppressed earlier.

Description

A Method of Intelligently Suppressing Machining Chatter

technical field

The invention relates to the field of intelligent processing, in particular to a method for intelligently suppressing processing chatter, which is used for suppressing chatter generated during processing in a machine tool that rotates a tool or a workpiece while processing.

Background technique

Machining chatter is an unstable phenomenon that occurs in almost all cutting processes and manifests as severe vibration between the tool and the workpiece. Especially in the cutting of aerospace thin-walled parts, the thinnest part of the workpiece is less than 1 mm, the dynamic performance of the workpiece is very poor, and it is easy to cause chatter. The occurrence of chatter will affect production efficiency and processing quality, and it can also cause excessive noise, tool damage, etc. The harm to product quality, tool and machine tool equipment is beyond doubt.

Research on machining chatter is mainly divided into three aspects. The first aspect is the machining dynamics modeling, by establishing the time-delay differential equation and analyzing its stability lobe diagram to predict chatter. The second type is flutter online detection. Scholars have proposed various flutter features based on different signal processing algorithms, and then compared the flutter features with the set reference value, or used pattern recognition based on the flutter features. Algorithm to realize online detection of flutter. The third aspect is chatter control. Chatter control methods vary widely and can be roughly divided into active control and passive control to achieve chatter-free machining. The purpose of these three aspects of research is the same, that is, to avoid the occurrence of chatter during processing.

The authorized patent with the application number 201010287871.8 discloses an online chatter detection and control device, which includes a chatter detection unit and a chatter control unit, wherein the chatter detection unit is responsible for identifying whether chatter occurs, and the chatter control unit is responsible for detecting After chattering, use variable speed method to suppress chattering. In addition, before the implementation of the chatter control unit, it is necessary to analyze whether the control parameters can be realized by the existing mechanical properties of the machine tool.

However, chatter is a severe vibration. In the technical solution disclosed in the above-mentioned authorized patent, when the chatter has occurred, the surface of the workpiece has been damaged, that is, it has become a substandard product, and the chatter has already caused damage to the tool and machine tool parts. caused damage. In order to maximize the qualified rate and reduce the damage of chatter to cutting tools and machine tool parts, it is necessary to extract and identify chatter during the incubation stage of chatter, and then control it in time. In addition, before the execution of the chatter control unit, it is necessary to judge whether the machine tool can be executed, which further delays the opening time of the chatter control unit, and the damage caused by chatter will increase again.

Therefore, those skilled in the art are devoting efforts to develop a method of intelligently suppressing machining chatter for suppressing chatter generated during machining in a machine tool that performs machining while rotating a tool or a workpiece.

Contents of the invention

In view of the above-mentioned defects in the prior art, the technical problem to be solved by the present invention is to identify and control the chatter vibration during the chatter incubation stage, and it is not necessary to judge whether the machine tool is capable of realizing it before the control unit executes it. Therefore, chatter-free machining can be realized in the chatter incubation stage, that is, chatter can be detected earlier and chatter can be suppressed earlier.

In order to achieve the above object, as shown in Figure 1, the present invention provides a method for intelligently suppressing machining chatter, which is used to suppress chatter generated during machining in a machine tool that utilizes tool or workpiece rotation to perform machining, including the following steps:

Step 1. Through the processing vibration detection algorithm, when the chatter is in the incubation stage, the chatter is identified;

Step 2. If the chatter has not entered the incubating stage, continue processing according to the established cutting parameters; if the chatter has started to incubate, then switch to variable spindle speed control, and use the original spindle speed as a benchmark to perform periodic cutting with the set amplitude and frequency Change permanently, feed rate and depth of cut remain unchanged;

Step 3, when the chatter vibration has entered the breeding stage, the chatter vibration suppression cannot be achieved after using the chatter suppression method of variable spindle speed, then stop the machining.

Further, in step 1, the chatter incubation stage refers to that the characteristic signal of chatter has a large difference in amplitude compared with the host signal.

Further, the detection algorithm amplifies the characteristic signal of the flutter through signal processing.

Further, the detection algorithm is implemented based on signals during processing.

Further, the signal is one of sound signal, acceleration signal, force signal, spindle motor current and feed shaft motor current.

Further, the detection algorithm extracts the characteristic index of the signal, and compares it with a predetermined threshold to determine whether the chatter has entered the incubation stage.

Further, the detection algorithm extracts the features of the signal, and judges whether the flutter has entered the breeding stage through a classification method.

Further, in step 2, the amplitude and frequency of the variable spindle speed control are determined in advance before machining.

The method of the present invention can identify and control the chatter vibration in the incubation stage of the chatter vibration, and does not need to judge whether the machine tool is capable of realizing it before the execution of the control unit. Therefore, chatter-free machining can be realized in the chatter incubation stage, that is, chatter can be detected earlier and chatter can be suppressed earlier.

The idea, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings, so as to fully understand the purpose, features and effects of the present invention.

Description of drawings

Fig. 1 is a principle flow chart of the present invention;

Fig. 2 is a flowchart of the steps of a preferred embodiment of the present invention.

detailed description

As shown in Figure 2, a preferred embodiment of the intelligent method for suppressing machining chatter of the present invention comprises the following steps:

(1) Before processing, use the synchronous action in the advanced programming in the CNC system to write the CNC program for changing the spindle speed. The way of changing the spindle speed is to take the spindle speed of the main program as the benchmark (such as 300 revolutions) in the form of sine Periodic changes, the initial phase is arbitrary, the frequency is 3Hz, and the amplitude is 50 revolutions.

(2) The variable spindle speed program is embedded in the entire machining NC program as a synchronous action waiting for activation.

(3) Acquire the sound signal in processing, set the sampling frequency to 100kHz, and input the signal into the acquisition device.

(4) Realize the extraction of flutter feature index in the computer. Here, the weighted wavelet packet entropy is taken as an example. The sliding window is 1000 points without overlap, that is, the weighted wavelet packet entropy is calculated every 10ms and the preset flutter has been calculated. Threshold comparison for entering the breeding stage, if the weighted wavelet entropy is less than the threshold, the chatter has entered the breeding stage, otherwise, the chatter has not entered the breeding stage. In the machining process, there are material inhomogeneity, cutting force fluctuation, chip interference, and time-varying machining dynamics, all of which will affect the chatter feature index, making it fluctuate. Therefore, in order to reduce the false alarm rate, a three-point moving average method is used, and the moment when the threshold is crossed for the first time is recorded as the moment when the flutter enters the gestation stage.

(5) When the flutter has entered the breeding stage, send instructions to the PLC through the computer to realize the required 24V switching voltage. Use the PLC to start the synchronous action, so that the spindle speed changes periodically according to the frequency and amplitude preset in step (1) to suppress chatter. At the same time, the feed rate and depth of cut remained constant.

(6) When the chatter vibration has entered the breeding stage, the chatter vibration suppression cannot be achieved after using the chatter suppression method of variable spindle speed, and the machining is stopped.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (8)

1. A method for intelligently suppressing machining chatter, used to suppress chatter generated in machining in a machine tool that utilizes tool or workpiece rotation to process, is characterized in that, comprising the following steps: Step 1. Through the processing vibration detection algorithm, when the chatter is in the incubation stage, the chatter is identified; Step 2. If the chatter has not entered the incubating stage, continue processing according to the established cutting parameters; if the chatter has started to incubate, then switch to variable spindle speed control, and use the original spindle speed as a benchmark to perform periodic cutting with the set amplitude and frequency Change permanently, feed rate and depth of cut remain unchanged; Step 3, when the chatter vibration has entered the breeding stage, the chatter vibration suppression cannot be achieved after using the chatter suppression method of variable spindle speed, then stop the machining. 2 . The method for intelligently suppressing processing chatter according to claim 1 , wherein in step 1, the chatter incubation stage means that the characteristic signal of chatter has a large amplitude difference compared with the host signal. 3 . 3. The method for intelligently suppressing machining chatter as claimed in claim 1, wherein in step 1, the detection algorithm amplifies the characteristic signal of the chatter through signal processing. 4. The method for intelligently suppressing machining chatter as claimed in claim 1, characterized in that, in step 1, the detection algorithm is implemented based on signals in the machining process. 5. The method for intelligently suppressing machining chatter as claimed in claim 4, wherein the signal is one of a sound signal, an acceleration signal, a force signal, a spindle motor current and a feed axis motor current. 6. The method for intelligently suppressing processing chatter as claimed in claim 4, wherein in step 1, the detection algorithm extracts the characteristic index of the signal and compares it with a predetermined threshold to determine whether the chatter has entered gestation stage. 7. The method for intelligently suppressing machining chatter as claimed in claim 4, wherein in step 1, the detection algorithm extracts the characteristics of the signal, and judges whether the chatter has entered the incubation stage by a classification method. 8. The method for intelligently suppressing machining chatter according to claim 1, characterized in that in step 2, the amplitude and frequency of the variable spindle speed control are determined in advance before machining.