METHODOLOGY FOR STUDYING THE INFLUENCE OF EXTERNAL FORCES ON ROAD MILLING CUTTERS AND CUTTER WEAR

ABSTRACT

This article has determined that the interaction of the working body of a road milling cutter with asphalt concrete through force depends on the milling depth and speed of movement, and the wear of the cutters depends on the geometric parameters of its installation on the drum and the path traveled. The physical modeling method was used to study the wear of road surface cutters, and as a result, the sample was examined for the presence of defects, and the differences in the geometric dimensions of the base shape were determined. Experimental studies investigated the effect of increasing the cutting depth with increasing speed of the main machine movement on the milling process. It was possible to evaluate different milling modes based on the condition of achieving maximum efficiency of this process. Studies based on physical modeling showed that during the milling process, the highest productivity was achieved when the milling drum speed was up to 10 mm/sec and the rotation frequency was 63 rpm.

АННОТАЦИЯ

В данной статье определено, что взаимодействие рабочего органа дорожной фрезы с асфальтобетоном через силу зависит от глубины фрезерования и скорости движения, а износ резцов — от геометрических параметров его установки на барабане и пройденный путь. Для исследования износа участков дорожного покрытия применялось физическое моделирование, в результате которого образец был обследован на наличие дефектов и выявлены различия в геометрических размерах формы основания. Экспериментальными исследованиями было изучено влияние увеличения глубины резания на процесс фрезерования при увеличении скорости основного движения станка. Это позволило оценить различные режимы измельчения, исходя из условия достижения максимальной эффективности процесса. Исследования, основанные на физическом моделировании, показали, что в процессе фрезерования производительность выше при скорости вращения фрезерного барабана до 10 мм/сек и частоте вращения 63 об/мин.

Keywords: milling depth, feed rate, tool wear, student coefficient, uniaxial compression, wear dynamics.

Ключевые слова: глубина фрезерования, скорость перемещения, износ инструмента, коэффициент Стьюдента, одноосное сжатие, динамика износа.

Introduction

In the world, great importance is attached to the sustainable development of the economy and road networks, the effective use of energy sources in the field of technological machinery, the introduction of resource-saving technologies and their efficiency. Currently, issues aimed at improving the design of the working equipment of road milling machines produced in all developed countries of the world, creating resource-saving materials and increasing their productivity, efficiency and competitiveness occupy a leading position. In this regard, special attention is paid to increasing the service life and efficiency of construction machinery, including by making the surfaces of the working equipment of road milling machines from hard alloys.

Metods

Studies on the external forces acting on the cutters of a road milling machine and the wear of the cutters are found in scientific works using the following methodologies:

The impact of the milling cutters' attachment angles on the drum and their effect on the wear of the milling cutters and the use of coatings to reduce the wear of the working equipment of the milling cutters [1].

In the research, the coefficients of radial, tangential and axial cutting forces were analyzed to determine the wear state of road milling cutters. In this methodology, artificial neural network algorithms were used to assess the development of road milling cutter wear based on the data sequence [2].

Artificial intelligence algorithms are used to control the geometric and performance characteristics of road milling cutters in real time. Offline and online methods are analyzed, and mechanisms are developed that allow optimizing the tool life. This method is used in micro and macro machining, aiming to improve product quality [3].

Results

The study of the interaction of a road milling machine with asphalt concrete through force is carried out in two stages. At the first stage, the influence of the geometric parameters of the working body on the force characteristics of the milling process was studied. This stage should provide the most optimal relationship between the geometric shape of the working body and the depth of work at the lowest values ​​of the average rotational moment. At the second stage of experimental research, the influence of the depth of cut with increasing speed of movement of the main machine on the milling process was studied. At this stage, it is possible to evaluate various milling modes based on the condition of achieving maximum efficiency of the process.

The methodology for conducting experimental research consists of the following main stages:

- selection of research objects;

- preparation of experimental equipment and control and measuring equipment;

- study of the influence of the characteristics of the working environment on the milling process;

- preparation of abrasive material;

- adjustment of the experimental stand and determination of milling parameters;

- cutting material with a milling cutter;

- analysis of the results obtained, conclusions on the stages of research;

The parameters that can be changed during the experiment include:

 -maximum milling depth;

-indicative speed of the moving carriage of the experimental stand.

The controlled parameters of the milling process include the average rotational torque and the longitudinal deformation characteristics of the material (Figure 1).

Figure 1. Typical scheme of road milling machine operation

The average torque was determined by the strain gauge method. A torque meter with an extensometric sensor was used in the work. The strain gauges are placed at an angle of ±45° to the axis of the cylindrical sample (Fig. 2). The deformation properties of the material were studied by the experimental method of quality control.

The use of a full bridge circuit provides good linearity, higher sensitivity to the measured force moment, and compensation for parasitic effects (longitudinal elongation or compression, bending).

When using sliding contacts, the effect of changing their resistance is minimal due to the large resistance of the power supply and the detector from the bridge current.

Figure 2. Connection using a bridge of strain gauges and sliding contacts in the cylindrical intermediate element of the momentometer:

a - schematic diagram; b - real configuration with strain gauges oriented in the opposite direction

The initial operating parameters for road milling cutters subjected to rapid wear under the influence of a fixed abrasive with local impact loading are as follows [4,5]:

- cutter geometry (length L, body diameter D, cutter tip height H); - asphalt concrete milling modes (depth of the milling drum into the asphalt concrete R, cutter rotation speed V); - physical and mechanical properties of asphalt concrete (Student strength limit in uniaxial compression σ_sj, tensile strength limit σ_b).

Discussion

When studying the wear of road milling cutters, the sample was initially examined for defects, and differences in  the geometric dimensions of the base shape were identified (Figure 2):

ΔD=D_Bbaz –D_Vsinov , ΔL= L_Bbaz –L_Vsinov, Δα= α_Bbaz –α_Vsinov,                    (1)

where D_v is the diameter of the cutter body around the cutter tip; L is the length of the cutter tip; α is the angle between the side surface and the horizontal of the cutter.

The geometric characteristics of the tested cutter were measured using a template and a micrometer, including the cutter height (H, mm), cutter tip height (N_H, mm), and cutter cross-sections (D_H, D_I -D_V mm) with an accuracy of ±0.01 mm. The weight of the samples (m₁) was measured on an analytical balance with an accuracy of 1*10^-4 g.

To determine the wear intensity of the test cutter, its volume was measured using the “copying” method. To obtain copies of the geometric shape of the hard alloy cutter tip before and after the test, the shape was recorded using a plastic mass, after which the copy was filled with a dyed alcohol solution of constant density. The volume of the copy was determined using a graduated cylinder, and then the mass of the cutter tip was calculated (m_H=ρ_HV_j). The mass of the body was determined by the difference between the mass of the entire cutter (m₁) and the mass of the cutter tip (m_H) m_k=m₁-m_H.

Based on this, the number of parallel determinations of the sample size n is found, according to which the confidence interval of the determined parameters is equal to Ẋ=10% [6,7]. This value is necessary to obtain, with a certain level of confidence, the average value of Ẋ, which differs from the average value of the total sums by less than ε ± 10% on the basis of partial sums.

Figure 3. Scheme of incisor wear measurement locations in studies conducted according to [8]

                               (2)

Thus, it can be argued that in order to adequately determine the dynamics of erosion, it is necessary to determine the erosion of more than 4 cuts for given conditions.

Taking into account the number of determinations n according to GOST R 50779.21-2004 [8,9], we determine the largest permissible unavoidable estimate S₁ for the mean square deviation δ:

S₁=M_k*S                                                        (3)

where Mk=1.085: the coefficient value when n=4.

The value of S is found by the following formula:

.                                     (4)

It is known from the determination of confidence limits for the mean value (arithmetic mean of the square of the deviations of the variance of the variance of the variance) that the variance of the variance is unknown [10].

                                                    (5)

The Student coefficient t_γ is equal to 1.638 for γ₁= γ₂=09 and n=4. Therefore, the maximum allowable value of S₁ according to formula (3) is equal to:

                             (6)

In general, the research on the eating of midges consisted of several stages..

Initial inspection and determination of the initial parameters of the cutter: height (N, mm), cutting edge height (N_n, mm), section diameter (D_H, D_I-D_V, mm), cutter mass (m1), cutting edge mass (m_n1).

Selection of the basic shape.

Determination of the installation location of the cutting tool under test on the milling drum.

ambient temperature T, S (measured using a Metiascope);

-asphalt concrete strength in uniaxial compression σ_sj, measured in MPa, kgf/cm².

Installing the cutter on the milling drum.

Selecting test parameters:

selection of the angle of attack (measured using a caliper and micrometer);

-milling depth, mm;

-feed rate, m/s;

-processing time, sec, h;

-description of the material being processed.

Conducting an experiment.

Removing the cutter from the drum.

Cleaning the test cutter from abrasive particles, mud, and soil. Processing in an alcohol solution.

Determination of the cutting parameters after testing: height (N, mm), cutting tip height (N_n, mm), cross-sectional diameter (D_N, D_I-D_V, mm), sample mass (m₂), cutting tip mass (m_n2).

Determining the wear of the cutting edge after machining, taking into account the correction coefficients of the abrasive material:

Δm=(m₂-m₁)*K (7)

ΔL=(L₂-L₁)*K (8)

Conclusion

The interaction of the working body of the road milling cutter with asphalt concrete through force was determined primarily by the milling depth and speed of movement, and the wear of the cutters was determined based on the geometric parameters of its installation on the drum and the path traveled. In addition, the rotational speed of the drum in both cases is of great importance. Experimental studies were conducted on the basis of physical modeling. In order to conduct a full-fledged experimental study of the milling process, it was possible to study its force characteristics and wear of the cutters, and at the end of the work to compare the results with the calculated values. The index “H” refers to the original parameters, the index “M” refers to the model parameters. The range of changing the milling depth is from 10 mm to 50 mm, taking into account the scale factor k₁=10. For the experiment, the kinematic parameters of a typical Planer SF 1500 milling cutter with a speed of movement of up to 10 mm/s and a rotation frequency of 63 rpm were used.

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