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13ENGINEERING SCIENCES
TOOL FOR RESEARCHING THE DYNAMIC SYSTEM OF METAL-CUTTING MACHINE
1 Walid Ibrahim Alnusirat, assistant professor 2Litvin Oleksandr, assistant professor 3Ibrahim Farhan Alrefo, assistant professor 4Kravez Oleksandr, assistant professor
'Jordan, Salt 19117, Al-Balqa Applied University
2Ukraine, Kyiv, Department of Design of Machine Tools and Machines
National Technical University of Ukraine
«Igor Sikorsky Kyiv Polytechnic Institute»
3Jordan, Salt 19117, Al-Balqa Applied University
4Ukraine, Kyiv, Department of Design of Machine Tools and Machines
National Technical University of
««Igor Sikorsky Kyiv Polytechnic Institute»
DOI: https://doi.org/ 10.31435/rsglobal_ws/30092018/6128
ABSTRACT
Dynamic characteristics of the system flexibility of the machine affect the accuracy of machining, so the study of this problem is very important. Fluctuations of the machine elements significantly affect the error of the shape of the workpiece. The quality of the processing is determined not so much by the static displacements between the tool and the workpiece but the stability of the machine system as a whole. There are many solutions of vibroacoustic diagnostics devices for machines and machine-tools in the related publications. Defects in the spectrum of vibroacustic signals are found in the process of manufacturing and assembling machines in the form of discrete components, parameters of which are used in vibroacoustic diagnostics as informative diagnostic features. Along with that there is, but not so common, another type of dynamic system analysis of the machine, which can be carried out by experimental methods, or, in particular, by simulating the perturbation of a dynamic system by cutting forces of special type. Imitated disturbance is carried out by using a tool of a special form. During the processing cutting edges of the tool create a pseudorandom process with certain statistical characteristics, in particular, the correlation function. The proposed design of the tool makes it possible to perform the research of frequency parameters of the dynamic system of the machine without complex loading devices.
Citation: Walid Ibrahim Alnusirat, Litvin Oleksandr, Ibrahim Farhan Alrefo, Kravez Oleksandr. (2018) Tool for Researching the Dynamic System of Metal-Cutting Machine. World Science. 9(37). doi: 10.31435/rsglobal_ws/30092018/6128
Copyright: © 2018 Walid Ibrahim Alnusirat, Litvin Oleksandr, Ibrahim Farhan Alrefo, Kravez Oleksandr. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
ARTICLE INFO
Received: 24 July 2018 Accepted: 25 September 2018 Published: 30 September 2018
KEYWORDS
machining accuracy, tool,
machine-tool, dynamic system, diagnostics.
Problem statement. In mechanical engineering, the efficiency improvement of machining process can be reached by different ways. Among these the study and proper use of dynamic processes occurring in technological systems is one of the least investigated ways which can open up large production opportunities. It can be primarily applied to the oscillations of technological systems. The development of special measures to reduce the level of oscillations in the technological system is an important task, the solution of which will allow to use more productive modes of cutting while providing the required quality of treated surfaces. To ensure the high technical characteristics of the machine, it is necessary to have quality indicators, such as geometric precision, rigidity, vibration resistance, and others within the specified limits for the whole time of operational activity and provide output of products with the specified accuracy. The solution of this problem is presented in this work.
Analysis of previous researches. Analyses of previous publications related to this problem shows that many different schematic and design solutions of devices and techniques for the study of the dynamic system of metal cutting machine tools are presented in the studies [1-6]. The oscillations of the machine elements significantly affect the error of the workpiece shape. That is, the quality of the processing is determined not so by the static offset between the tool and the work piece, but the stability of the machine system as a whole. Relative oscillations between the workpiece and the instrument occur simultaneously with several frequencies that correspond to different perturbation sources and the system's own oscillation frequencies.
Selection of previously unsettled parts of the general problem. Along with all mentioned above there is another type of analysis of the dynamic system of the machine which is not quite widespread until now. It can be carried out by experimental methods, in particular by simulating the perturbation of the dynamic system by special cutting forces.
The purpose of the study is to develop a method of simulated loading of the dynamic system of the metal-cutting machine by cutting forces while processing with a special kind tool.
Verification of vibroacoustic characteristics of the machine is one of the methods for assessing the quality of its manufacturing. Defects in the manufacture and assembly of machine tools are found in the spectrum of vibroacoustic signals in the form of discrete components, parameters of which (amplitude, frequency, phase) are used for vibroacoustic diagnosis as informative diagnostic features [4]. The most complete picture of the technical condition of the machine-tool is provided by its monitoring. Moreover, the following tasks can be solved: continuous monitoring of the vibroacoustic environment to assess operability of the machine; failure diagnostics of separate units and parts; comparison of the oscillation spectra for analysis of trends of the parameters of the machine at work.
The research objective. To achieve this goal, the following tasks need to be solved: to create a special tool in the form of interlocking side mill for stochastic stationary ergodic process of changing the cutting force and to develop a mathematical model for reproduction of the theoretical process. The conditions of the ergodicity of the process impose additional requirements on the probabilistic characteristics of the stationary process.
The first task of this study is the creation of a cutting tool design to study frequency parameters of the dynamic system of the machine without complicated loading devices that generate disturbing loading with different frequencies and disturb the whole range of operating frequencies of the machine during several cycles of processing. The peculiarity of the milling process is its non-stationary nature due to the periodic inputs and outputs of the teeth from contact with the work piece. During the cutting process the load impacts on the spindle. These impacts cause intense torsion oscillations of the drive and the maximum torque, acting on the spindle of the milling machine, can significantly exceed its average value due to pulse loading.
The analysis of the dynamical system of the machine can be carried out by experimental methods, in particular by simulating the perturbation of the dynamic system by the forces of cutting of a special character.
The statement of basic materials. Imitation of disturbance is carried out using a tool of a special form (Fig. 1). Cutting edges of the tool are created by processing a pseudorandom process, which has certain statistical characteristics, in particular correlation function. The proposed design of the tool consists of a mandrel on which a set of six disc cutters is fixed. On each of the cutters, a random profile was created due to the reshaping on the back surface.
The cutting tool of a special form contains a housing 7, which is located in the spindle of the machine, a mandrel 6, on which a set of several, for example, five disk cutters 1, 2, 3, 4, 5 with the same number of cutting edges is installed (Fig. 1, 2). Each milling cutter is a separate functional module, the number of which can be different. On the mandrel 7, a set of milling cutters is fixed with a nut 8. Milling cutters 1-5 are shifted to each other from a triangle and are determined from the
condition of obtaining a random sequence of angles 9I, 92, 93, 94, 95, 96, 97 and 98, the placement of the plates along the cutter periphery (Fig. 3).
The vertices of the teeth of each of the milling cutters are refiled to different heights, which is determined by the radii R1,1; R2.1; R3.1; R4.1; R5,1 within one module (Fig. 3). Due to this form of the tool each of the teeth during processing interacts with the machining surface in unevenly distributed moments of time and removes various allowances. As a result, the dynamic loading of the machine system is formed with a wide spectrum of disturbing frequencies. The location of the cutting edges of the tool is executed in such way that the processing generates a pseudorandom stationary process.
Depending on the technological parameters of the processing (rotation frequency of milling cutters, cutting depth and feed), a pseudo-random process of dynamic loading is formed that interrupts the dynamic system of the machine in the whole range of operating frequencies.
Fig. 1 interlocking side mill for simulated loading of the dynamic system of the machine by cutting
forces
12 3 4 5
Fig. 2 Placement of modules of the interlocking side mill
Fig. 3 Profile of a special milling cutter to form the loading
For each of the milling cutters 1-5, a pseudo-random sequence of values of the depth of re-sharpening is calculated according to Poisson's law of the distribution of a random variable. In addition to the fact that during the processing by a milling cutter a random process of changing the cutting force is modulated in amplitude by changing the depth of cut on each tooth of the milling cutter, the angle at which the next tooth of the milling cutter begins to contact the surface of the same row treated by the previous tooth (Fig. 3) is also randomly being changed, that is, the frequency modulation of the signal occurs.
This solution develops this field of technology in comparison with the prior art constructions.
The scheme of the formation of a random process during processing is shown in Figure 4.
Fig. 4. The scheme of the formation of a random loading in the successive processing by teeth of
milling cutters
To determine the characteristics of the random process of the imitating loading, we consider the scheme of the layer formation that is cut away by each tooth of milling cutter (Figure 5)
Fig.5. Elements of cutting mode and cutting layer geometry for machining with cylindrical milling
cutter
As it is shown in the scheme the angle of contact (the central angle corresponding to the arc of the contact of the milling cutter with the work piece) is possible to determine. It can be found in A OTE
cos8 = —7- = 1--; Si = arccos (1 — —)
1 A/ d ^ di'
/2 1
The thickness of the cut away layer ai is the variable distance between two consecutive positions of the cutting surface (formed by the cutting edges of two adjacent teeth) measured in the radial direction. For a straight-flute milling cutter, the value of ai is constant over the entire length of the tooth and can be determined using A MKH:
a. =S siny.,
1 z T v
Where yy is the instantaneous contact angle corresponds to the given position of the milling cutter tooth. When the tooth enters the work piece, the thickness of the cut layer is zero. When the tooth drops out of the contact with the work piece, the thickness of the cutting away layer corresponds to the angle of full contact and has the maximum value of amax:
am =S sin5 = 2S yit/D; sin8 = V 1-cos2 8 =2f^n z z \ / D .
The area of the cut away layer of a tooth of the milling cutter
f. = ab. = B ■ S sin y;
On the basis of the given dependences, it is possible to calculate the characteristics of a random process of imitation loading, namely the level and nature of vibrations that are generalized indicators of the dynamic quality of the machine, and sometimes - the uniform criteria for its normal functioning. The sequence of pulses of each cutter generates a pseudo-random process in the sum The empirical formula for determining the strength Pz, which generates random vibration.
CptXpz^-a^)Ypz Bqpzz
p (a ) = —_siy_k
z ' s ' T^UP wP p .
D Pzn Pz
Conclusions. The suggested design of the tool allows to perform the research of the frequency parameters of the dynamic system of the machine without complex loading devices generating disturbing loading of various frequencies and performing perturbations in the entire frequency range of the machine for several processing cycles.
REFERENCES
1. Patent of Russian Federation of the USSR MKI B23C5/04 (2007.01). Interlocking side mill / Artamonov E.V., Vasylkovych V.A., Chuikov R.S.; Patentee: State Educational Institution "Tiumen State Oil and Gas University". Applied for 05.04.2006; published 10.12.2007.
2. Patent of Russian Federation MKI B23C5/04_(2011.01). Cylindrical milling cutter / Aidel Yu., Zudau P., Merz Yu, Kipping Matthias (DE); Patentee: SMS Siemag Aktiengesellschaft (DE). Applied 11.02.2008, published 20.11.2011.
3. Patent of Russian Federation of the USSR 2348492 MKI B23C5/10 (2006.01) B23C5/20. Rotary cutting tool with insert cutters of non-regular orientation /Long T. G. II (US), Craig K.A. (US), Dudzinsky Ronald L. (US), Frota de Sousa R.F., Gaintane H.M. (US), published 10.03.2009.
4. Arshanskyi M. M., Shcherbakov V. P. Vibration diagnostics and precise control of machining on metal cutting machines - Moscow: Mechanical Engineering, 1988 - 136 p.
5. Altintas Y., Engin S., Budak E. Analytical Stability Prediction and Design of Variable Pitch Cutters // ASME J. Eng. Indus., 1999. v.l21.-pp.l73-178.
6. Sastry Sridhar, Kapoor Shiv G., DeVor Richard E. Floquet theory based approach for stability analysis of the variable speed face-milling process // ASME J. Eng. Indus. 2002. - vol. 124. - pp. 10-17.
