RU2496629C2 - Method of control over multi-blade built-up tool cutting edges state - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: set of invention relates to machining, particularly, to metal cutting tools. After starting the processing, thermal emf is continuously measured for every cutting edge to compare continuously current thermal emf values with preset tolerable thresholds. In case current values equals or exceeds preset threshold, definite relationship is used to define tool wear factor K_t. At 0.1<K_t<0.25 cutting conditions are corrected while at K_t≥0.25 tool is to be replaced.

EFFECT: comprehensive control over conditions of every cutting edge of hard-alloy tool.

8 dwg, 2 tbl

Description

The invention relates to the processing of metals by cutting and is intended to provide a given operating time for automated machine equipment by timely replacement of a tool having chipped cutting edges. The invention can be applied both in commissioning and in automatic modes of operation of automated machines for monitoring the condition of the cutting edges of prefabricated multi-blade tools - milling cutters, countersinks, drilling and boring heads.

Known methods for monitoring and diagnosing the condition of the cutting tool, based on the registration and analysis of the vibroacoustic emission signal (see patent RU No. 2298455 C1, IPC B23B 25/06, B23Q 17/09, publ. 05/10/2007; patent RU No. 2316749 C1, IPC G01N 3/00, publ. 02/10/2008; patent RU No. 2354955 C1, IPC G01N 3/56, G01N 3/58, publ. 05/10/2009). The disadvantage of these methods is that the relationship of the vibro-acoustic signal with tool wear is not always unambiguous, since in addition to the cutting force, the nature of the tool vibrations is influenced by a number of factors that are not directly related to the cutting process, but which reduce the useful value of the useful signal.

A known method of monitoring the condition and position of the cutting edges of single-blade, prefabricated multi-blade and axial tools (see patent RU No. 2320457 C2, IPC B23B 25/06, B23Q 17/09, B23Q 17/22, publ. 03/27/2008), providing in the process processing the workpiece, measuring the electrical voltage using a high-frequency non-contact eddy current sensor and converting the measured signal from each cutting edge to digital, the relative value of which determines the position of the cutting edges of the tool, the amount of wear and beats.

A disadvantage of the known method is that it does not fully take into account the variability of the cutting properties of tool materials within their grades in various batches, which reduces the controllability of tool materials using eddy current sensors and increases the error in controlling wear of tool cutting edges.

The closest method of the same purpose to the claimed one is a method of monitoring the condition of the cutting edges of prefabricated multi-blade tools (see patent RU 2312750 C1, IPC B23Q 17/09, publ. 12/20/2007) made of one material, including a preliminary test passage of the tool on steel a workpiece with conversion of an analog signal of thermoelectromotive force (thermoEMF) of each cutting edge into a digital one using an analog-to-digital converter with a sampling frequency of at least 1 kHz, determination before processing the values thermoEMF of all tool cutting edges and calculation of the arithmetic mean value of thermoEMF, according to which allowable cutting speed is calculated.

The disadvantage of this method is that it allows the calculation and correction of the permissible cutting speed, which provides the specified tool operating time just before the start of processing, but does not allow to identify the chip of the cutting edge of the tool during processing of the workpiece, which leads to premature failures of the cutting tool and reduces reliability his works.

The problem to which the claimed invention is directed, is to provide a given operating time of a multi-blade cutting tool assembly in automatic mode.

The technical result that can be obtained by carrying out the invention is to increase the reliability of the automated machine based on operational monitoring of the state of each cutting edge of a carbide tool.

, где М - количество режущих кромок инструмента со значением термоЭДС меньше предельного значения термоЭДС, N - общее количество режущих кромок инструмента и при 0,1<К_и<0,25 вводят коррекцию режима обработки, а при К_и≥0,25 осуществляют замену инструмента.The specified technical result is achieved by the fact that in the claimed method for determining the wear resistance of a multi-blade tool during processing, the cutting edges of which are made of one material, which includes a preliminary test pass of the tool on the steel billet before processing and converting the analog signal of thermoelectric driving force (thermoEMF) of each cutting edge in digital using an analog-to-digital converter with a sampling frequency of at least 1 kHz and determination before m of processing the thermoEMF values of all tool cutting edges, from the moment the processing starts, the thermoEMF value of each cutting edge is continuously measured and the current values are continuously compared with the set thermoEMF limit value, the cutting thermoEMF value is fixed with a thermoEMF value lower than or equal to the limit value and the tool wear coefficient K is determined _and , depending $${\mathrm{TO}}_{\mathrm{and}}=\frac{M}{N}$$

where M is the number of cutting edges of the tool with a thermopower value less than the limit value of thermopower, N is the total number of cutting edges of the tool and, at 0.1 <K _and <0.25, the correction of the processing mode is introduced, and at K _and ≥0.25, they are replaced tool.

For the first time, it was proposed to continuously measure the thermopower value of each cutting edge of a tool and compare it with the limiting value of thermopower, which makes it possible to determine the tool wear resistance during processing. It was experimentally established that as a limit value of thermopower it is possible to take a value from the range [E] ≤1 mV, which corresponds to the absence of physical contact between the workpiece and the tool. A new parameter has been introduced - the tool wear factor K _and , defined as the ratio of the number of cutting edges with a thermoEMF value less than or equal to the limit to the total number of cutting edges of the tool, which allows for the on-line correction of technological modes to ensure a given tool operating time.

To ensure stable operation of the precast carbide cutting tool (no vibration and preservation of the surface quality of the workpiece), the limit values of the wear coefficient [K _and ] = 0.1 and [K _and ] = 0.25 were experimentally established.

The choice of these values is due to the following reasons.

As the object of research, end mills equipped with eight and ten carbide inserts (cutting edges) were chosen as the most used for roughing and semi-finishing multi-blade machining on automated machines. The lower limit value of the deterioration coefficient [K _and ] = 0.1 corresponds to a cleavage of one cutting edge of a ten-tooth mill, the fact of which does not significantly affect the operational state of the tool. If this value is exceeded, it is necessary to introduce the correction of technological modes to ensure a given tool operating time. The upper limit value of the deterioration coefficient [K _and ] = 0.25 corresponds to the inoperative state of the tool (chipped two cutting edges of an eight-tooth mill) and requires replacement of the cutting tool. Therefore, when the deterioration factor exceeds the upper limit value, tool replacement is also necessary.

It has been established that during multi-blade machining with a tool with a number of cutting edges of less than ten, cleaving even one cutting edge leads to the introduction of correction of technological modes, and for a tool with a number of cutting edges of more than ten, in the case of cleaving only one cutting edge, it is impractical to carry out the correction of modes , since this leads to a decrease in processing productivity, without affecting the state of the tool.

The presence of these distinctive features provides increased reliability of the precast multi-blade cutting tool in automatic mode.

Figure 1 is a diagram illustrating the implementation of a method for monitoring the condition of the cutting edges of a multi-blade tool using the example of processing a steel billet with a face mill with mechanical fastening of replaceable polyhedral carbide inserts; figure 2, figure 3, figure 4 presents a histogram of changes in the values of thermopower of the cutting edges of the eight-tooth face mill at the initial time of processing and at the moments of chipping of the cutting edges; in Fig.5, Fig.6, Fig.7, Fig.8 presents histograms of changes in the values of thermopower of the cutting edges of a ten-pointed face mill at the initial time of processing and at the moments of chipping of the cutting edges.

The method is as follows. In the setup mode of the machine before starting processing the workpiece in the permanent memory of the CNC device record the following information:

1) the number of cutting edges of the tool N;

2) the limit value of thermopower [E], characterizing the breakage (chip, chipping) of the tool cutting edge;

3) the upper and lower limit values of the tool wear coefficient [K _and ].

After the end of the recording procedure, the numerical control device (CNC) 1 (Fig. 1), the machine positions the cutting tool 2 relative to the workpiece 3 and performs a preliminary test pass at fixed processing modes: cutting speed V = 100 m / min, feed S _z = 0 , 1 mm / tooth, cutting depth t = 1 mm. An analog-to-digital converter (ADC) 4 converts the thermoEMF signal E _{i of} each cutting edge 7 of tool 2, which is removed by the current collector 5 and is mounted on the spindle 6 of the machine, into a digital code with a sampling frequency of at least 1 kHz and transfers it to the control memory 1.

Since the start of processing the workpiece 3 in technological modes calculated according to one of the known methods (see patent RU No. 2312750), the current collector 5 continuously measures the value of thermopower E _{i of} each cutting edge 7 of tool 2. The ADC 4 converts the obtained thermopower values into a digital code with a frequency sampling at least 1 kHz and transfers it to the RAM of the CNC 1.

In the process of processing the workpiece, the CNC software 1 continuously compares the current values of thermopower E _i with the limit value of thermopower [E] by checking the conditions

$$E_i\ge \left[E\right]\left(\mathrm{one}\right)$$

If at an arbitrary instant of time, condition (1) is not satisfied, i.e. the thermoEMF of the cutting edge 7 of the tool 2 becomes less than the limit value, then the CNC program 1 calculates the value of the wear coefficient K _and by the formula

, $${\mathrm{TO}}_{\mathrm{and}}=\frac{M}{N}$$

,

where M is the number of cutting edges with a value of thermopower less than the limit value of thermopower;

N is the total number of cutting edges of the tool.

Next, check the calculated value of the deterioration coefficient with lower K _and = 0.1 and upper K _and = 0.25 limit values.

If K _and ≤0.1 then the processing of the workpiece continues at predetermined process conditions.

In the event that 0.1 <K _and <0.25, a correction of the technological processing modes is introduced and transmitted using the CNC unit 1 to the drive of the main movement 8 of the machine.

If K _and ≥0.25, the CNC Unit 1 generates a technological team to replace the cutting tool 2 and transmits the corresponding signal to the control system of the tool magazine 9 of the machine.

The proposed method is most effective for roughing and semi-finishing of structural carbon and alloy steels with a multi-blade tool equipped with carbide inserts of the corresponding grades (for example, TT7K12, T5K10, T5K12, T14K8, VK6, VK8, VK10), which is associated with significant loads on the tool cutting edges at large volumes of cut material with the specified types of cutting.

An experimental verification of the proposed method was carried out when machining structural carbon steel 45 with a face mill with a diameter of D _f1 = 100 mm, equipped with eight five-sided carbide inserts of the T5K10 grade and a face mill with a diameter of D _f2 = 120 mm equipped with ten five-sided carbide plates of the grade T7K12. In the study, the following parameters of the cutting process were set: feed per tooth S _z = 0.2 mm / tooth and milling width B = 100 mm for both sets of inserts; milling depth t ₁ = 1 mm, and t ₂ = 3.5 mm, the limiting value of thermopower [E] = 0.5 mV. The specified tool operating time for the first set was T ₁ = 120 min and T ₂ = 150 min for the second set. The permissible cutting speed V _d was calculated according to the prototype (see patent RU No. 2312750): V _{d (1)} = 152 m / min for the first set of inserts, V _{d (2)} = 114 m / min for the second set of inserts.

In table 1 and figure 2, figure 3, figure 4 provides information about the initial state (figure 2) and the moments of chips (figure 3, figure 4) of the cutting edges of the eight-tooth face mill. In table 2 and in FIG. 5, FIG. 6, FIG. 7, and FIG. 8, information is given on the initial state (FIG. 5) and chipping moments (FIG. 6, FIG. 7, FIG. 8) of the cutting edges of a ten-tooth face cutters.

Из результатов, приведенных в таблицах 1 и 2 и на фиг.3, фиг.4, фиг.6, фиг.7, фиг.8 видно, что предлагаемый способ позволяет зафиксировать скол любой режущей кромки многолезвийного твердосплавного инструмента за счет непрерывного контроля значений термоЭДС каждой режущей кромки и по величине расчетного коэффициента К_и оперативно вводить коррекцию технологических режимов для поддержания заданного времени работы инструмента, что обеспечивает повышение надежности работы автоматизированного станка.

From the results shown in tables 1 and 2 and in FIG. 3, FIG. 4, FIG. 6, FIG. 7, and FIG. 8, it can be seen that the proposed method allows to fix the chip of any cutting edge of a multi-blade carbide tool due to the continuous monitoring of thermopower values each cutting edge and according to the value of the calculated coefficient K _and promptly introduce the correction of technological modes to maintain a given tool operating time, which improves the reliability of the automated machine.

Claims (1)

The method for determining the wear resistance of a multi-blade tool, the cutting edges of which are made of one material, during the processing, including pre-processing a test pass of the tool along the steel billet with conversion of the analog signal of the thermoelectric driving force (thermoEMF) of each cutting edge to digital using an analog-to-digital converter with sampling frequency of at least 1 kHz and determination before processing thermopower values of all tool cutting edges, characterized in that from the moment the processing starts, the thermopower of each cutting edge is continuously measured and the current thermopower of each cutting edge is continuously compared with the set limit value of the thermopower, the value of the thermopower of the cutting edge is fixed with a thermopower value below or equal to the limit value and the tool wear coefficient K _and according to $${\mathrm{TO}}_{\mathrm{and}}=\frac{M}{N}$$

,
where M is the number of cutting edges of the tool with a value of thermopower less than the limit value of thermopower,
N is the total number of cutting edges of the tool
and at 0.1 <K _and <0.25, the correction of the processing mode is introduced, and at K _and ≥0.25, the tool is replaced.

Images