RU2203778C2 - Method for controlling state of cutting edges of builtup multiblade tools - Google Patents

Abstract

FIELD: metal working with chipping, possibly controlling state of builtup milling cutters, reamers, drilling and boring heads with chipping realized by means of several cutting edges, particularly manual (tuning) operation mode of machine tools, in mode for automatic control of state of cutting edges of builtup multiblade cutting tool for determining admissible cutting rate that provides period of reliable operation and loading degree of cutting edges. SUBSTANCE: method is realized for receiving information relating to state of builtup multiblade hard-alloy tool before using it for working; detecting blade with lowered cutting properties among other blades of tool for determining admissible cutting rate for the whole set of blades and loading degree of separate cutting edges. Method comprises steps of measuring thermo-EMF of each cutting edge; comparing measured values; before starting working during preliminary testing pass of tool on steel blank, converting analog signal of thermo-EMF of each cutting edge to digital signal by means of analog-to-digital converter with discretization frequency no less than 1 kHz; comparing digital values of thermo-EMF for extracting its maximum value in order to set admissible cutting rate; determining loading degree of separate cutting edges of tool according to percentage values of thermo- EMF; according to presence of cutting edges with beating level exceeding admissible one, evaluating state of cutting edges of tool. EFFECT: enhanced reliability and effectiveness of procedures for controlling state of cutting edges. 2 dwg, 1 tbl

Description

 The invention relates to metal processing with chip removal and can be used to monitor the condition of prefabricated milling cutters, countersinks, drilling and boring heads, in which the chip removal process is performed by more than one cutting edge. It can be applied in the manual (tuning) mode of operation of machines and in the mode of automated monitoring of the condition of the cutting edges of a multi-blade assembly tool, based on which the permissible cutting speed is determined, which ensures the period of its reliable operation and the degree of loading of the cutting edges.

 Ensuring the reliability of an automatically performed cutting process on CNC machines, automatic lines using a multi-blade precast carbide tool is directly related to the efficiency and reliability of monitoring its condition, since failures of this type of equipment due to the fault of the tool account for more than 50% of the time of forced outages (see. .K. Starkov, Cutting. Stability and quality management in automated production. M: Engineering, 1989, pp. 113-114).

 Known methods for monitoring the state of a cutting tool in terms of thermopower (see V.K. Starkov, Cutting. Stability and quality control in automated production. M: Engineering, 1989, pp. 119-120), which allow you to control the amount of wear tools during the cutting process with pre-selected cutting conditions.

 The disadvantage of these methods is that they only fix the amount of wear of the cutting edges, but do not provide the ability to control the time of their reliable operation, and also that they cannot be used to monitor the condition of the cutting edges of a multi-blade assembly tool. Operational durability (time of reliable operation) depends on the heterogeneity of quality (cutting properties) of carbide edges assembled in one set of cutters, countersinks, boring or drilling heads (see MM Babich, Carbon heterogeneity and its elimination. Publisher "Naukova Dumka", Kiev, - 1975, p. 5-6) and the level of their runout, which determines the degree of edge loading during the cutting process (see V.K. Starkov, Cutting. Stability and quality management in automated production. M. : Engineering of, 1989, pp. 93-96).

 The closest way to this purpose is to monitor the condition of the cutting edges of the tools (see Yu.A. Leshchenko and S.V. Vasiliev, a.p. 596378, 23 B 25/06, Bulletin 9, 1978), which provides for the process control the use of two cutting edges made of the same material, equalization of the initial values of the thermopower that arises on them, and with the subsequent occurrence of a signal difference during processing, monitoring the state of the cutting edges by the magnitude and sign of the difference in the thermopower data.

 The reasons that impede the achievement of reliability and efficiency of monitoring the condition of the cutting edges of a multi-blade prefabricated tool using the known method include the fact that it has the ability to monitor the condition of only two cutting edges isolated from each other, the thermoEMF of which must simultaneously arrive at a sign-sensitive device. In this way, it is impossible to control the condition of the cutting edges and the degree of their loading (runout) in the kit of a multi-blade tool assembly with more than two edges, for example, multi-tooth end mills with the number of teeth z = 4; 6; 8; 10; 12 etc. This is due to the fact that the cutting process with a multi-blade tool is intermittent and the contact time of one cutting edge (tooth) with metal is measured from one tenth to one hundredth of a second or less. In this case, it is impossible to measure, remember and compare the thermoEMF of each tooth with more than two of them using an analog waveform.

 The problem to which the claimed invention is directed, is to increase the reliability and efficiency of monitoring the condition of the cutting edges of multi-blade tools.

 The technical result that can be obtained by carrying out the invention is to obtain information about the condition of a multi-blade carbide tool before starting work, to determine in its set a cutting blade with reduced cutting properties, which sets the permissible cutting speed for the entire set (set) of teeth, and determining the loading of individual cutting edges.

 The specified technical result is achieved by the fact that in the claimed method of monitoring the condition of the cutting edges of prefabricated multi-blade tools made of one material during multi-blade processing, including measuring the thermoelectric power of each cutting edge and comparing them with each other, before processing in the conditions of preliminary test passage of the tool according to steel billet convert the analog thermoEMF signal of each cutting edge into a digital one using an analog-to-digital converter with a sampling frequency at least 1 kHz, compare the values of thermopower in digital form with the allocation of the maximum value of thermopower, which sets the permissible cutting speed, and relative values of thermopower determine the load of individual cutting edges of the tool and the presence of cutting edges with a beating level exceeding the permissible, evaluate the state of the cutting edges of the tool.

 Using the claimed method of analog-to-digital conversion of the thermopower signal of a natural thermocouple with a high sampling frequency (at least 1 kHz) allows you to record the transient process of the occurrence of a thermoelectric signal on the cutting edges of a multi-blade tool in hardware, measure and remember its value, compare the amplitude values and select the maximum value thermoEMF from the entire set of cutting edges and select the allowable cutting speed with orientation to the weakest cutting m properties of the cutting edge of the cutter. In addition, the oscillograms displayed on the block of operational symbolic information (BOSI) of the CNC system allow you to evaluate the level of runout of each cutting edge of the cutter (load) and take the necessary operational measures to eliminate them.

 The use of a high sampling frequency (at least 1 kHz) is due to the fact that for a short contact time of the cutting edge of the cutter with the part (workpiece) of 0.1-0.01 seconds, it is necessary to obtain at least 10 measurements for the reliability of the result, which limits the lower ADC frequency limit at 1000 Hz (1 kHz). The upper limit of the sampling rate can be limited only by the capabilities of the hardware devices of the ADC.

 The analysis of the prior art, including a search by patents and scientific and technical sources of information and identification of sources containing information about analogues of the claimed invention, allowed us to establish that the applicants did not find an analogue characterized by signs of identity to all existing features of the claimed invention, and a definition from the list of identified analogues the prototype as the closest in the totality of the features of the analogue allowed to identify the set of essential in relation to the seen lyami technical result in the distinguishing features of the claimed subject set out in the claims.

 Therefore, the claimed invention meets the requirement of "inventive step" under applicable law.

 In FIG. 1 is a diagram illustrating the implementation of the control method by the example of milling a steel billet with an 8-tooth face mill with cutting edges made of hard alloy. Figure 2 shows the waveform of thermopower of the cutting edges for one revolution of the cutter.

 The method is as follows. Under the control of the CNC computer software complex, the tool 1 is positioned relative to the workpiece 2 in the indicated modes, the cutter is inserted into the part. At the same time, the geometric characteristics of the tool and the part and their relative position should ensure that at any time no more than one cutting edge is in contact with the part. The last condition is necessary to prevent mutual shunting of thermoEMFs of cutting edges connected in parallel to the measuring chain, since their true thermoEMFs are distorted and cannot be the basis for evaluating the properties of these blades. The ADC converts the thermoEMF signal removed by the current collector 3 from the rotary cutter 1 into an 8-bit digital code with a frequency of at least 1 kHz, which is fed into the computer and stored in its RAM. At the same time, the moments of time at which the signal from the sensor 4 of the reverse mark (sealed contact paired with a magnet, an optocoupler, an electrical contact sensor, etc.) are stored in RAM are stored.

 After the set time has passed after the milling cutter has completed one or several revolutions, it is retracted by the command of the CNC computer, the computer proceeds to analyze the received waveforms of the thermoEMF signal of the cutter. Under the control of special computer software algorithms, the data in RAM is reviewed in order to find the most optimal section for further research representing the dynamics of changes in the thermoEMF of individual cutting edges per 1 revolution of the mill, where there is no mutual shunting of the thermoEMF of neighboring cutting edges. An example of such a plot is shown in figure 2.

где Т - заданная стойкость инструмента, мин;
S - подача, мм/об;
t - глубина резания, мм;
Е - термоэлектродвижущая сила естественной термопары инструмент - стальная заготовка, мВ;
A, k, z - постоянные, определенные из условия предварительной обработки (А=625; k=24,7; z=0,24).The reverse mark signal (black bar in the center) is used to identify individual cutting edges numbered from 1 'to 8' on the thermoEMF waveform (Fig. 1). The computer programmatically recognizes that there are no signals on the waveform of thermoEMF of cutting edges located at positions 5 'and 8' of the cutter, unstable thermoEMF at the cutting edge of pos. 3 ', on the basis of which the operator or programmatically using special algorithms concludes that these cutting edges are not loaded, do not participate in cutting, which is a consequence of their beating in excess of the permissible values. The average amplitudes of thermoEMF have cutting edges pos. 1 ', 2', 4 ', 6'. Using the algorithm for finding the maximum number in a given set, the computer determines the cutting edge with the highest thermoEMF in the set - pos. 7'-10.43 mV. Based on this, it is concluded that the cutting edge in this position will be subject to the most intense wear, and to ensure the specified resistance of the entire cutter, it is necessary to orient it according to the resistance of this cutting edge. In this case, the allowable cutting speed for the cutter is calculated by a known method (patent 2063307, Russia, C1, B 23 B 25/06. Bulletin 19 of 07/10/96) using the formula (1):

where T is the specified tool life, min;
S - feed, mm / rev;
t is the cutting depth, mm;
E - thermoelectromotive force of a natural thermocouple tool - steel billet, mV;
A, k, z are constants determined from the pre-treatment condition (A = 625; k = 24.7; z = 0.24).

 Then, or on the basis of a program analysis of the beat level (number of cutting edges), the computer or operator concludes that it is advisable to replace the cutter with another (in this case, the thermopower measurement cycle is repeated for the new cutter), and the recommended value of the permissible cutting speed is provided in the CNC system, which ensures the specified the resistance period of the cutter as a whole. It is allowed the computer to work in dialogue with the operator with the output of the necessary oscillograms (status maps of the instrument) to the display.

 Using the proposed method for controlling the cutting edges of prefabricated multi-blade tools, it is possible to calculate (manually or automatically) the allowable cutting speed taking into account the cutting properties (thermoEMF) of their edges at the initial stage of the processing process, as well as adjust the cutting speed during processing taking into account their wear.

 The proposed method takes into account the specific feature of the work of the cutting edges of a prefabricated multi-blade carbide tool that its total durability (time of reliable operation) is determined not by the average cutting ability of the entire set of inserts (edges), but by a cutting edge or a group of edges with reduced cutting properties.

 This method does not regulate the nomenclature of the grades of carbide cutting edges used and at the same time allows predicting the load and wear rate of individual edges, taking into account the inevitable factor of their runout.

 The results of the comparative experimental verification of the proposed method are shown in the table. Six sets of eight-tooth face mills with a diameter of 125 mm, equipped with T15K6 and T5K10 five-sided carbide inserts during 40K steel processing, were subjected to resistance tests. In all cases, the cutter resistance was set to 120 minutes. The cutting conditions and test results are shown in the table.

 At mill 1, the thermopower waveform of which is shown in FIG. 2, after the completion of the first series of tests, cutting edges were replaced by turning the same inserts in the holder (mills 2 and 3). Mills 4 and 5 were similarly equipped with T5K10 plates. The range of variation of the thermoelectric properties of the cutting edges in the cutter set corresponded to the range of their dispersion in the delivery lot and was evaluated under the conditions of the trial cutter passage through the steel billet. The maximum value of thermopower from a set of cutting edges was distinguished by analog-to-digital conversion and was used in the calculation formula (2) to determine the allowable cutting speed, which takes into account the cutting properties and machinability of steel billets by the value of thermopower (patent 2063307, Russia, C1, V 23 B 25 / 06. Bull. 19 of 07/10/96).

где Т - заданная стойкость инструмента, мин;
S - подача, мм/зуб;
t - глубина резания, мм;
Е - максимальная термоэлектродвижущая сила режущей кромки в паре со стальной заготовкой, определенная с помощью АЦП, мВ;
D - диаметр фрезы, мм;
В - ширина фрезерования, мм;
m, x, y, u, p - показатели степени при стойкости Т, глубине фрезерования t, подаче на зуб S_z, ширине фрезерования В и диаметре фрезы D соответственно;
A, k, z - постоянные, определенные из условия предварительной обработки (А=625; k=24,7; z=0,24).

where T is the specified tool life, min;
S - feed, mm / tooth;
t is the cutting depth, mm;
E is the maximum thermoelectromotive force of the cutting edge paired with a steel billet, determined using the ADC, mV;
D is the diameter of the cutter, mm;
In - the width of the milling, mm;
m, x, y, u, p - degree indicators with resistance T, milling depth t, feed per tooth S _z , milling width B and mill diameter D, respectively;
A, k, z are constants determined from the pre-treatment condition (A = 625; k = 24.7; z = 0.24).

 Permissible cutting speeds for mills 7 and 8 were determined without monitoring the condition of the cutting edges according to the standard method (see the Handbook of a machine-building engineer in 2 volumes / Borisov VB, Borisov EI Vasiliev V.N. and others. under the editorship of A.G. Kosilova and R.K. Meshcheryakov, 4th ed. revised and added - M .: Mashinostroenie, 1985, v. 2, p. 282). The condition for reliable operation of the cutter was the absence of vibrations exceeding the permissible level, and preservation of the specified resistance for 120 minutes. Additionally, the value of the coefficient of uneven wear of the cutting edges in each set was evaluated as the ratio of the maximum value of the chamfer of wear along the rear face to the minimum.

 Mills 1 ... 6, the cutting speed for which was determined by the formula (2), taking into account the maximum value of the thermoEMF of the cutting edges in the set, remained operational for 120 minutes, that is, before the forced change of the tool. They had an uneven wear coefficient in the range 1.2 ... 1.59. This value can be accepted as satisfactory, since the recorded unevenness of wear did not cause a deviation in the normal course of the milling process.

 Mills 7 and 8 did not provide operability up to a predetermined time of 120 minutes and had a coefficient of uneven wear of the cutting edges of 2.92 and 2.4, respectively. The reason for the premature wear and failure of these cutters is the high cutting speeds obtained by calculation according to the standard method, and the inability of carbide inserts with different cutting properties of the edges in one set to work for a specified time at the calculated speeds. This applies primarily to carbide inserts with an increased value of thermopower (10.7 mV for T15K6 and 12.6 mV for T5K10), which are the weakest links in a set of multi-blade tools. The higher wear rate of these edges compared to other inserts predetermined the failure of the cutters in operation. The lack of reliable and effective monitoring of the condition of the cutting edges in this case adversely affects the performance of the cutters in a given period of resistance.

 The results of comparative endurance tests confirmed the previously noted feature of existing standard methods for choosing the permissible cutting speed: they are oriented to high and identical cutting properties of carbide insert edges in batches and do not take into account the heterogeneity of cutting edges in a set of multi-blade tools.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed invention:
- the tool that performs the claimed invention, when it is implemented, is intended for use in metalworking for automatic or manual monitoring of the condition of the cutting edges of prefabricated multi-blade tools, based on which the permissible cutting speed is determined, which ensures the period of its reliable operation and the degree of loading of the cutting edges when working on milling CNC machines, OTs (interactive mode of preparation of control programs);
- for the claimed invention in the form described in the independent clause of the claims below, the possibility of its implementation using the means and methods described above in the application is confirmed;
- a tool embodying the claimed invention, when implemented, is able to ensure the achievement of the technical result perceived by the applicants.

 Therefore, the claimed invention meets the requirement of "industrial applicability" under applicable law.

Claims (1)

 A method for monitoring the condition of the cutting edges of prefabricated multi-blade tools made of the same material during multi-blade processing, including measuring the thermoEMF of each cutting edge and comparing them with each other, characterized in that before the start of processing in conditions of preliminary test passage of the tool on a steel billet, an analog signal is converted thermoEMF of each cutting edge in digital using an analog-to-digital converter with a sampling frequency of at least 1 kHz, the thermoelectric power is compared DS in digital form with the allocation of the maximum value of thermoEMF, which sets the permissible cutting speed, and the relative values of thermoEMF determine the load of individual cutting edges of the tool and the presence of cutting edges with a beat level exceeding the permissible value, assess the condition of the cutting edges of the tool.

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