Design of elements of specialized technological equipment for finishing processing of parts

This article is devoted to solving the current problem of use of the polyester materials application for the synthesis of specialized technological finishing equipment elements that usually used by enterprises for the repair and maintenance of mining equipment. The article discusses the possibility of the polyester materials application when creating equipment elements. The equipment’s parts are created by using additive technologies, in which the creation of the part occurs by sequential application of material layers. The use of polyester materials makes it possible to reduce labor intensity, increase the economic efficiency of production and ensure compliance with environmental standards both during the production process and during subsequent processing. Based on the modeling results, an analysis of the strength characteristics of the specialized technological equipment reservoirs made of steel 3 (ISO – E 235-C, Fe 360-C) and polyethylene terephthalate (PET plastic) was carried out. The possibility of application of the PET plastic as an analogue material for the reservoir manufacture with the ensuring of the necessary strength characteristics has been established.


Introduction
The characteristics of modern industries reflect a tendency to the reduction of equipment amount with its partial or complete replacement by universal processing centers or specialized technological equipment.The application of universal or specialized equipment allows us to expand the range of processed parts and significantly reduce auxiliary time.The main goal of creating new and modernizing existing production industries is to increase qualitative and quantitative indicators.
Problems that arise during the parts processing are typical both for enterprises producing new products and enterprises for the repair and modernizing existing products.
The current state of the Ukrainian mining industry is characterized by noticeable wear and aging of fixed assets.Currently, a significant part of the equipment has exhausted its planned operational life and needs major repair with simultaneous modernization.This problem requires enterprises to manufacture and replace a huge number of parts and products.During the production process, the problem of cleaning, deburring and rounding of sharp edges arises, which requires the use of finishing and grinding methods.Among the many methods of finishing and cleaning processing, including both classical tumbling and new methods of turbo and water-jet processing, the method of processing parts in free abrasives in vibrating reservoirs stands out.
Vibration finishing processing of parts is a modern finishing method that occupies a special place among the other methods, which include processing with a fixed abrasive tool, processing in rotating drums, shot blasting and water-jet processing.The vibration processing is complex and depends on 2 many factors.The number of factors and the degree of their influence on process performance are the subject of many studies [1 -9].
We also should take into account the high technical requirements for modern vibrating machine tools.They increasingly use complex mechatronic systems that require additional studies [10].
The initial state of the workpiece largely determines the choice of processing modes and methods.Considering the large number of parts subject to vibration processing, as a rule, they are classified according to the type of abrasive processing (cleaning, deburring, grinding, ferrous and non-ferrous metals polishing), material (cast iron, steel, plastics, copper, aluminum and their alloys), weight, dimensions, initial and final state of the surface and structural form [11]. Today, the main feature by which parts are classified is the relationship between part dimensions and the dimensions of tool and reservoir.Based on this condition, parts are divided into 3 main groups: 1. Small parts are parts whose overall dimensions are comparable in size to working medium granules; 2. Medium parts are parts whose overall dimensions exceed the dimensions of the abrasive granule, but in relation to the reservoir their largest linear dimension does not exceed or equal to 1/3 of the reservoir width; 3. Large parts are parts whose overall dimensions exceed 1/3 of the reservoir width.
Processing in free abrasives occurs in the absence of a rigid kinematic connection between the tool and the workpiece.The tools are processing granules that form the working environment.The granules sizes must ensure processing of the entire surface of the part.Studies of abrasive tools are aimed at finding the optimal shape and composition of the abrasive granule [12 -14].Most of the operations for vibration processing are carried out with supply of a liquid solution that forms the required composition used in the reservoir.The action of solutions is enhanced by electrical impulses, creating a joint electrochemical effect.
The main working part of vibration machine tool is the reservoir.The most common reservoir shapes are Ushaped and toroidal.Experimental and theoretical studies of the reservoir are presented by works in which studies are focused on influence of the reservoir shape, its lining, and the location of vibration sources on the process performance [15,16].
Effective vibration processing of parts is possible only in the presence of a stable circulation movement of the entire loadthe processed parts (if they are not fixed), abrasive tools and intensifying solutions.The presence of a circulation flow directly depends on the amplitude and frequency of the pulses generated by the vibration exciter.Modeling of the load mass movement process is not fully studied and requires further research [17].
Finishing processing is applied after mechanical and heat processing.The difficulties that arise at this stage are due, on the one hand, to the wide range of processed parts, and on the other hand, to the choice of processing method.Parts can have different parameters of weight and dimensions, and have a complex shape.Processing methods may impose restrictions on its capabilities, in particular, the overall dimensions of the part may not allow processing on certain machine tools, or the technological capabilities of equipment do not allow achieve the required process performance in terms of quantitative or qualitative indicators.[11,16].
Vibration processing is the method of applying many micro-impacts on the surface that is being treated by the abrasive granules that, in turn, oscillate under the influence of the vibration.The processed parts are loaded into the reservoir of the machine tool, that is then filled with the working medium.Parts can be placed in the reservoir freely or fixed.The vibration processing is dimensionless and does not change the shape and dimensions of the processed parts [12].
The main competitive advantage of this method is the ability to simultaneously process a large number of parts of various shapes and sizes.However, the main factor limiting the application of specialized vibration equipment is the reservoir volume and the characteristics of the material from which it is made.Obviously, the volume of the reservoir depends on its linear dimensions, which in turn determine the overall dimensions of equipment.
The reservoir, as a rule, is the largest element of the structure, therefore, reduction of the reservoir weight has a direct impact on the weight and size characteristics of the equipment.There are several directions to solve this problem, among them are the application of new materials, new design of the reservoir.However, one of the most promising, in the opinion of the authors, is the creation of reservoirs from polyester materials using additive technologies, in which the creation of a part occurs by sequential application of layers of material.The use of additive manufacturing technologies, in contrast to production using classical metalworking equipment, is less labor-intensive and at the same time more profitable from an economic point of view.However, studies on the use of these materials and production methods for creation of finishing equipment elements have not been previously carried out and, accordingly, are of theoretical and practical interest.
The objective of the study is to evaluate the possibility of application of polyester materials for manufacturing the reservoirs of technological equipment.

Methods
To conduct studies to assess the possibility of using polyester materials the technological equipment for finishing processing in a free abrasive tool was used.The reservoir internal volume was selected from the condition of the possibility of simultaneous parts processing.
Standard operating modes of the equipment are determined by the specified parameters of the electric motorare 600 and 900 rpm, which are 10 and 15 Hz.The oscillation force under such modes are 2.3 N and 5.3 N, respectively.To conduct studies, in order to ensure a margin of equipment safety and reliability in which new material applicated, an extreme operating mode with an oscillation frequency of 25 Hz and a force of 15 N was chosen.
The initial object of study was a reservoir made of steel 3 (ISO -Е 235-С, Fe 360-C) with an internal volume of 1.3 liters, which was compared with a reservoir made of polyester material with a similar internal volume.The geometric parameters of the internal volume of both reservoirs were the same.

Calculation of the equipment geometric parameters
The calculation of the specialized technological equipment parameters directly depends on the type of part.As is known, the basis for designing of a technological operation is the selection (or design) of equipment and tool.For the design of specialized finishing equipment, there are known studies that present an algorithm for calculating elements, as well as the procedure for designing of Ushaped reservoir for large and long parts.The presented in this work machine tool is designed for small parts finishing processing.Examples of such parts are presented in figures 1, 2.  Processing in free abrasives should ensure processing of the entire surface of part; therefore, for this type of part it is necessary to use an abrasive tool with small geometric parameters.The use of fine abrasive fillers creates difficulties in creating a stable circulation movement of the working medium, which in turn requires careful selection of the frequency and amplitude of vibrations.
Based on the fact, that the parts have small dimensions and for the convenience of processing parameters calculating, the volume of loading mass (worked parts, abrasive tools, chemical solutions) was set is 1 liter.It is known that effective processing in a vibrating reservoir is possible if the load volume is up to 75% of the total reservoir volume.According to the conditions established above, the internal volume of the reservoir was determined to be 1.7 liter.The volume reserve ensures the presence of a zone in which processing is not carried out and does not allow abrasive and chemical solutions to penetrate beyond the reservoir.The shape of the reservoir was adopted as Ushaped, since this shape is widespread and has proven its effectiveness.Let set an equation for calculating the volume of a figure consisting of a parallelepiped and half a cylinder: , where ais length, mm; bis width, mm; his height of the reservoir working volume, mm.Substituting the initial data into the equation, we obtain the required dimensions of the reservoir internal volume, which are presented in figure 3.

Selection of frequency, amplitude and force created by the vibration exciter
In the applicated equipment, an electric motor is used as a drive, which, through an elastic coupling, transmits a rotating force to the shaft on which an eccentric (unbalance) that creates vibrations is attached.Processing in such equipment is carried out at a reservoir oscillation frequency of 10 and 15 Hz, and an oscillation amplitude of 2.5 and 3 mm, respectively.The vibration force created by the vibration exciter is 2.3 and 5.3 N, respectively.
The maximum operating frequency for the presented machine tool is 15 Hz, however, for modeling, a frequency of 25 Hz was chosen, at which the vibration force was 15 N.The selection of such parameters was carried out in order to ensure reliability and safe operation of the equipment.
The final parameters of the amplitude and frequency characteristics (AFC) of the equipment are summarized in table 1.

Study of influence of the reservoir material on its strength characteristics
The reservoir of specialized vibration equipment is the main working body on which the productivity of the process depends.The study by reservoir improvement is aimed at both intensifying the processing and reducing the metal consumption of equipment.Most reservoirs are made of metal.Manufacturing of metal reservoirs is complex and expensive.The use of new materials for the manufacture of reservoirs is a relevant topic for research.The search of material is similar to metal in terms of strength characteristics is an actual topic for research.In particular, for long parts processing in vibration reservoir, experimental studies on the creation of a reservoir from composite materials were presented [18], which confirmed the effectiveness of the composite materials application for the production of the reservoir.Application of such material allowed to reduce the reservoir weight by 70% while maintaining strength characteristics.
The main criterion for the effectiveness of using a new material is the preservation of strength characteristics of reservoir.Polyethylene terephthalate (PET plastic) was chosen as an analog material for steel 3 (ISO -Е 235-С, Fe 360-C).3D models of reservoirs made of corresponding materials are presented in figures 4 and 5.The geometric dimensions of the reservoirs internal volumes were the same for both models.The technological capabilities of the equipment made it possible to produce a reservoir from PET plastic with a minimum wall thickness of 10 mm.This value was taken as the minimum thickness of the reservoir wall made of PET plastic for further modeling, the thickness of the reservoir walls made of steel 3 (ISO -Е 235-С, Fe 360-C) was 3 mm.
The next stage was modeling, which compared the characteristics of a metal reservoir and a PET plastic reservoir in order to select satisfactory strength indicators, as well as determine the required wall thickness of a PET plastic reservoir.The analysis of stresses, displacements and deformations of the reservoirs is presented in figures 6 -8, the minimum and maximum values of stresses, displacements and deformations are presented in table 2.
As a result of the modeling, it was found that the strength characteristics of a reservoir made of PET plastic with a wall thickness of 10 mm are lower than those of a reservoir made of steel 3 (ISO -Е 235-С, Fe 360-C) with a wall thickness of 3 mm.Such results are quite predictable.The reservoir is subjected to constant alternating loads, therefore the safety factor of the endurance limit is critical for it.For steel 3 (ISO -Е 235-С, Fe 360-C), the endurance limit value is 0.5 of the tensile strength value, for various plastics its value lies in the range of 0.2...0.8 [19].Finite element calculations showed that the stresses arising during operation of both metal and plastic reservoirs are 2 orders less than the tensile strength of the material, which ensures operation for a long time.A significant safety margin and the capabilities of modern 3D printers make it possible to produce hollow reservoir, reducing its weight and manufacturing cost.
Thus, the strength characteristics of reservoir made of PET plastic with a wall thickness of 10 mm are sufficient and provide a safety margin under the specified operating modes.In this case the manufacturing a reservoir from PET plastic can significantly reduce the labor intensity and cost of reservoir, with maintaining the required safety margin.

Figure 3 .
Figure 3. Internal dimensions of the reservoir working volume.

Figure 4 .
Figure 4. Model of the reservoir from steel 3, wall thickness -3 mm.

Figure 5 .
Figure 5. Model of the reservoir from PET plastic, wall thickness -10 mm.

Table 1 .
Operating modes of the equipment.

Table 2 .
Indicators of stresses, displacements and deformations of steel 3 and PET plastic reservoirs.