Experimental study on milling temperature of the h

2022-08-06
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Experimental study on milling temperature of three-dimensional complex groove milling insert

Abstract: Based on the artificial thermocouple method and the self-designed rotating shaft signal transmitter, a milling temperature test system is established; By means of time conversion, cycle conversion, thermocouple cold end temperature compensation, temperature conversion and curve fitting, the test equations between the temperature at each temperature measurement point of different groove milling insert and the average temperature and time in the tool chip contact area of the rake face are obtained; The application software of experimental data processing is developed. The test results show that the test system has good performance; And the cutting performance of the wave edge milling insert is better than that of the flat rake face milling insert. The research results lay a foundation for the establishment of mathematical model of heating density function and temperature field

1 introduction

bond damage accounts for an important proportion of tool damage. Especially in heavy-duty and intermittent cutting of heat-resistant steel and superalloy, the tool bond damage is more serious. In this paper, 3cr-1mo-1/4v heat-resistant steel is the main research object, which is a newly developed shell material for large chemical vessels. The cutting process of 3cr-1mo-1/4v steel is more difficult than that of stainless steel, and the adhesion between cutter and chip is very serious. The maximum temperature and temperature field in the tool chip contact area of the rake face are the main basis for determining whether the tool bond occurs. The milling temperature plays an important role in studying the bond failure. Therefore, measuring milling temperature, studying temperature field and surface heating density function can provide important data and theoretical basis for studying the bonding failure mechanism of milling insert and groove optimization technology

based on the experiment, this paper studies the instantaneous change law of milling temperature in the process of milling 3cr-1mo-1/4v steel; In addition, the milling temperature of the flat rake face milling insert and the wavy edge milling insert is also studied

2 milling temperature measurement system

in order to study the heating density function and temperature field mathematical model of milling insert with different groove types, the milling temperature of tool chip contact surface is measured by artificial thermocouple method

the basic principle of the artificial thermocouple method is that the hot end of the thermocouple is welded at the position where the blade is scheduled to measure the temperature, and the temperature change on the welding point can be measured through the signal transmission system and the dynamic data acquisition system. The motion of milling machine and milling cutter belongs to the rotating system. The traditional method is to introduce a collector ring into the signal acquisition circuit to realize the information acquisition and transmission of the rotating system. However, there are still some problems to accurately measure the transient temperature value in the cutting area. Because the electric signal of the artificial thermocouple is extremely weak, the error caused by noise may distort the measured value during the signal transmission of the collector ring, and it is not convenient to fix the collector ring. For this reason, the rotating shaft signal transmitter, a signal processing and transmission component of the rotating system, has been designed and developed in this experiment (a utility model patent has been obtained). During cutting, the rotating shaft signal transmitter shall be smooth when applied along with the main shaft 3. To avoid wear and transmission. After the main device is completed, it shall pass through the seat hole of the oil probe on the base, and use a funnel to inject oil into the oil pool. The injected oil depth is 30mm, which can be measured by the oil probe The input end is connected with the two poles of the thermocouple, and the output end is in contact with the brush. The transmitter has the advantages of small volume, easy disassembly and easy operation. It not only has the use performance of the traditional collector ring, but also has strong anti-interference ability. The milling temperature measurement system is shown in Figure 1

Figure 1 Schematic diagram of temperature measurement system

3 software and hardware configuration of milling temperature test system

in order to study the influence of cutting parameters and different blade groove types on the cutting performance of milling insert, two groove type blades are used to cut 3cr-1mo-1/4v steel respectively, and artificial thermocouples are used to collect and process the cutting temperature signals through a/D conversion and dynamic data acquisition and processing system. According to the needs of the test, the preparation of milling insert temperature measuring hole, thermocouple and parameter setting of data acquisition system shall be done well before the test to ensure the smooth progress of the test

1) acquisition of milling insert temperature measuring hole

select the coordinates of measuring points according to the test requirements, as shown in Figure 2. The coordinates of each temperature measuring point are 1 (2, 2), 2 (2, 3.5), 3 (2, 5), 4 (3.5, 2), 5 (3.5, 3.5), 6 (3.5, 5)

Figure 2 distribution of temperature measuring points on the blade

at the bottom of the blade close to the tip, according to the above coordinate points in the direction parallel to the rear surface of the blade, punch a blind hole from the bottom of the blade with an electric spark. The hole diameter is 1 5mm, hole depth is about 4mm. It is required to drill holes for one-time forming, and the maximum hole depth shall be 0.5% less than the blade thickness 5mm。

2) assembly of temperature sensor

the temperature measurement sensor used in this test is a K-type standard thermocouple, its positive pole is nickel chromium alloy wire, and its negative pole is nickel silicon alloy wire. The measuring end of the thermocouple is formed by twisted spot welding. During welding, the power supply voltage is 220V AC. an arc is generated through the graphite electrode to fuse the two poles of the thermocouple. The hot end of the thermocouple is welded to the bottom of the temperature measuring hole of the blade by using the principle of capacitance discharge. After ensuring the insulation between the two poles of the thermocouple and between each pole and the hole wall, fill the fixed temperature measuring hole with epoxy resin. The installation method of thermocouple on the blade is shown in Figure 3

Fig. 3 installation method of thermocouple

3) dynamic data acquisition system and its parameter setting

the fas-4dee-2 dynamic data acquisition and processing system of Beijing Institute of inertial technology is used for the acquisition of test data. The system is the supporting software of the dynamometer. It is based on the windows platform and adopts the standard Windows application interface. Set the system options in advance, set the acquisition mode to "non dynamometer mode", the display mode to "voltage", and the acquisition frequency to 2Hz, that is, collect a point every 0.5s. The lower the acquisition frequency of the system, the less interference the system receives, the more accurate the test data, and the smaller the error

4 milling temperature test

1) test conditions and methods

test conditions workpiece size: 220mm × 190mm × 120mm; Material: 3cr-1mo-1/4v steel; Service specification: 16mm × The 16mm square indexable milling insert is the traditional flat rake face milling insert and the wave edge milling insert developed by Harbin University of technology. See Table 1 for its geometric parameters and materials

this test is carried out on x5030a vertical lifting table milling machine, and the diameter of the face milling cutter is 160mm. Table 1 blade geometric parameters and material

blade type front angle rear angle edge inclination grade waveform edge milling insert 8 ° 7 ° +15 ° ~ -15 ° yt535 flat front face milling insert 0 ° 7 ° 0 ° yt540

Table 2 test cutting parameters

cutting speed (m/min) feed rate (mm/min) back feed rate (mm) 27.646, 40.212, 55.29219, 36681, 1.5, 2.5, 3

test methods the cutting parameters for the test are shown in Table 2 b

in order to obtain enough data points and minimize the number of tests, the single factor method was used to select the combination of test parameters in the test. Three groups of tests were carried out: the first group took the cutting speed vc=55.292m/min as the constant value, and changed the feed rate, back feed rate and blade groove shape respectively; The second group takes the feed rate vf=36mm/min as the fixed value, and changes the cutting speed, back feed and blade groove shape respectively; In the third group, the back feed ap=2mm was taken as the constant value, and the milling temperature test was carried out by changing the cutting speed, feed rate and blade groove shape respectively

2) test results

during milling, due to the alternating change of cutting and air cooling, the temperature on the tool surface changes periodically. When the tool cuts into the workpiece, high temperature is generated on the tool chip contact surface and transmitted to the tool body, resulting in a large temperature gradient; When the tool is cooled when cutting out the workpiece, the tool chip contact area suddenly cools down, and the temperature in the tool body redistributes. When cutting in again, the temperature rises sharply. This is also confirmed by the milling temperature value collected by the computer. A set of data with test parameters vc=55.292m/min, ap=2mm, vf=36mm/min is selected as an example. The temperature curve collected by the dynamic data acquisition and processing system is shown in Figure 4, in which the abscissa is the cutting time and the ordinate is the temperature difference electromotive force after amplification

Fig. 4 diagram of transient temperature change in the cutting area

5 test data processing and analysis

the data collected by the dynamic data acquisition system is the temperature difference electromotive force at each instant of the temperature measurement point in the milling process. Its size is greatly affected by the temperature measurement system itself and the external environment, and the temperature difference electromotive force change curve displayed by the acquisition system is not a continuous curve in a cutting cycle; In addition, the temperature at the temperature measuring point obtained by the artificial thermocouple method is not the temperature on the rake face, and the cold end temperature of the thermocouple is not 0 ℃. In order to obtain the real temperature on the tool chip contact area of the rake face, explore the internal relationship between the temperature and the corresponding cutting time, and establish the experimental equation, it is necessary to process the original test data according to the mathematical means, and extract the required data from the numerous data for my use. Here, a group of data with cutting test parameters vc=55.292m/min, vf=36mm/min and ap=2mm are taken as examples to illustrate the processing methods and steps

1) calculation of cutting cycle

if the cutter head diameter d0, workpiece width AE and spindle speed n (RPM) are known, the cut in time ti is

ti=arcsin (AE) 1d03n (1)

the rotation cycle of the cutter head is t=60/n, then the cut-out time to is

to=1 (180 ° -arcsinae) 3nd0 (2)

the cut in and cut-out time under different cutting conditions can be obtained by substituting n, AE and d0 into the above formula.B. For standard cutting conditions: vc=55.292m/min, ae=120mm, d0=160mm, the corresponding cut in and cut out time is ti=0.1472s, to=0.3983s, and the rotation cycle of the cutter head is t=0.5455s

2) time conversion

since the points collected by the dynamic data acquisition and processing system are not within a cutting cycle, it is necessary to convert these points into a cycle. When the cutting reaches the steady state, its value changes periodically, so as long as the temperature time curve in one cycle is simulated, it can represent the temperature change in the whole cutting process

select the first temperature measuring point on the wave edge milling insert to explain the conversion process: take a certain cutting time after the cutting reaches the steady state as the time conversion reference point, and take 23S here, then the cutting time is 23S ti=22.8528s; If 22.8528s is taken as time 0 of the user-defined time, the time period for the tool to cut on the workpiece is: 22.8528s+nt ~ 23s+nt (n is a non negative integer); However, since the signal acquisition cycle is 0.5s and the acquisition time is 0s, 0.5s and 1s, it is meaningful only when the acquisition time happens to be within the cutting time period. Therefore, it is necessary to calculate the time corresponding to the acquisition point in the cutting time period. C ++ builder program is compiled to perform this operation (the original program is omitted due to space limitation). The output results S1 ~ S2 of the visual control listbox1 are the points within the cutting time period. Judge whether the collected points are within the cutting time period according to the output results. For example, within 49.5000 ~ 49.6472s, one point has been collected (49.5s); However, during the period of 50.0455 ~ 50.1927s, no acquisition was conducted

3) cycle conversion

after extracting the appropriate time from the acquisition curve through time conversion, it is necessary to convert it into a time within a cycle to facilitate calculation. After the cutting reaches the steady state, the change of cutting temperature can be regarded as a periodic function, and its period is the rotation period of the tool. Therefore, all points can be converted to one cycle (due to space constraints, the c++ builder program for calculating cycle conversion is omitted). The value corresponding to the string S1 in the program is the time of the acquisition point,

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