Mechanical processing of complex profile aluminum products

. The operability of the mechanism or machine design may be impaired due to premature destruction of products of this design. The article considers a method of machining products of a complex profile made of aluminum. The results of theoretical studies and experimental studies are presented. The problems of machining aluminum surfaces were identified. The author has proposed a method of machining aluminum products with a complex profile.


Introduction
The technological requirements imposed on the products manufactured by the industry determine the conduct of research in the field of application of new materials that will be able to fulfill these requirements [1,2]. Thanks to the latest technological advances in the field of engineering, this becomes possible [3].
When operating critical products operating under the influence of gas, hydraulic flows, high temperatures and the destructive environment of aggressive chemical media, their premature destruction occurs [4,5]. As a result of premature destruction of critical products, there is a loss of operability not only of the node in which this product is included, but also of the entire structure/mechanism/machine [6][7].
Products exposed to such harmful effects of an aggressive external environment may have a complex work surface [8]. This surface is in direct contact with an aggressive external environment; therefore, technological quality assurance of complex surfaces is an important task facing researchers and technologists [9,10].

Research object
The operability of products having a complex profile surface, such as turbine blades, oil and gas pipes, rotors, compressors, etc. is ensured at several stages (design, construction, material selection, manufacture) [11]. The strength and reliability of products is determined by their manufacturing technology, which ensures the quality of the part (the amount of surface roughness) [12,13].
The micro-irregularities that occur during the manufacturing and processing of the part are stress concentrators. This explains the significant influence of surface roughness on the resistance to fatigue stresses arising from the operation of the node/mechanism/machine [14]. Cyclic loads entail the occurrence of fatigue cracks in these parts.
An analysis of the design of the parts of the axial compressor, which is used in the oil and gas industry, shows that the requirements for the roughness of the surface of the discs vary in terms of Ra from 1.25 to 2.5 microns, and the blades from 0.32 to 0.63 microns.
The high requirements for the roughness of the working part of the blades and discs of the axial compressor used in the oil and gas industry create the task of technologically ensuring the required surface roughness using a modern finishing operation.

Features of aluminum alloy processing
Aluminum is one of such materials. Aluminum alloys have special properties and are used in various fields of industry. Compared with products made of steel and other ferrous alloys, aluminum alloys have high corrosion resistance, resistance to aggressive environments and chemical effects, low weight. Due to these properties, aluminum products are used in the following industries: chemical, oil and gas, aerospace, automotive, shipbuilding, pharmaceutical, energy, etc. [15][16][17].
On the other hand, aluminum alloys with performance properties that are superior to ferrous metal alloys are difficult to process. Processing of aluminum alloys is a task that currently has no specific solution. It is solved by several methods of surface treatment: a) mechanical processing methods, such as grinding, polishing, etc.; b) chemical processing methods, such as electrochemical treatment, chemical vapor deposition, etc.; c) thermal treatment methods, which may include thermal spraying, physical vapor deposition, etc.
Aluminum and aluminum alloys are among the most commonly used lightweight metal materials because they offer a number of different distinctive mechanical and thermal properties: low specific gravity, high ductility, corrosion resistance, high electrical conductivity. In addition, they are relatively easy to shape, especially with the help of mechanical cutting. In fact, aluminum and its alloys are considered light-workable materials compared to other light materials such as titanium and magnesium alloys.
However, it is known that alloying aluminum with various elements, such as magnesium, manganese, copper, silicon, etc., entails a change in the workability of the alloy [18][19]. This change is described by such negative factors associated with the high viscosity of aluminum alloys as the formation of a build-up on the front surface of the cutting tool, the appearance on the treated surface of a layer with increased microhardness (cleavage), which makes it difficult to achieve a given surface quality, leads to overheating, jamming, breakage of the cutting tool. The size of the build-up and the rivet is affected by the cutting modes, the forces arising during the cutting process, the geometry of the cutting tool, its durability.

Magnetic-abrasive finishing
One of these methods is the process of magnetic abrasive finishing (MAF). MAF is a method of surface treatment and improvement of its quality, which is beginning to find wide application in modern metalworking enterprises [20].
The figure shows a diagram of the magnetic abrasive processing process, where the workpiece is located between two poles of different polarity. The power supply is connected to copper coils that generate a magnetic field when current is applied to them [21][22][23]. As a cutting tool, a mixture of magnetic and abrasive particles is used, which is called a magnetic abrasive powder. When the magnetic abrasive powder is placed between the poles with the power on, that is, in the formed magnetic field, it will be held at the poles, forming a cutting tool -a ferromagnetic brush.
The ferromagnetic brush can have different stiffness. This is regulated by changing the voltage applied to the magnetic coils [24]. Fig. 1. The effect of abrasive grains on the surface of the workpiece during magnetic abrasive treatment [18] Magnetic abrasive powder consists of magnetic and abrasive particles. Abrasive particles are necessary for removing the material, that is, surface treatment. Magnetic particles act as "holders" for abrasive particles [25]. They form groups of four magnetic particles and hold abrasive particles together [26].
As a result of the influence of a magnetic field on an abrasive particle, two forces act on it -the normal Fn and the tangential Ft. The normal force is directed perpendicular to the surface of the workpiece and pushes the abrasive particle into this surface. The tangential force is directed parallel to the treated surface and drags the abrasive particle along the treated surface, removing the material layer. The normal Fn and tangential Ft forces form the resulting force F [27].
To improve the quality of processing and increase its productivity, various types of movements can be brought to the poles and the workpiece -rotational, translational rectilinear, curvilinear and a combination of movements.

Experimental research
Experimental studies were carried out on an installation for magnetic abrasive processing based on a CNC milling machine, the design of which is shown in fig. 2. The CNC magnetic abrasive machining device includes a base with retaining elements, racks, core housings, cores, pole tips, adjusting screws and electromagnetic coils.
Racks are installed on the base, on which the core housings are attached. The core housings serve, on the one hand, to provide directivity during the reciprocating movement of the cores, which is carried out by means of adjusting screws; on the other hand, to fix electromagnetic coils on them, and in order to reduce the load on the core housings, electromagnetic coils are mounted on retaining elements.

Fig. 2. Model of the installation for magnetic abrasive treatment [5]
The validation of the magnetic abrasive unit was previously carried out using a model. The measurement of the magnetic induction in the working gap using a hall sensor coincided with the simulated magnetic field in the ANSYS Maxwell program. The validation of the existing installation for magnetic abrasive treatment using computer and mathematical modeling tools in the ANSYS Maxwell software environment made it possible to determine the optimal voltage and current modes supplied to the inductors.
The workpiece was processed under the following operating parameters (table 1). Mass of magnetic abrasive powder q 160 g 6 Working gap δ 3 mm Magnetic abrasive powder FeTiC, based on titanium carbide (about 55%), was used as a cutting tool. The dispersion of the powder was about 180-200 microns.

Results
As a result of magnetic-abrasive processing of a billet made of aluminum alloy AMc, which is a shaft with a spherical body at the end, it turned out to improve the surface roughness.
With the help of an electron microscope, photographs of the surface of the workpiece were obtained before (Fig. 3, a) and after (Fig. 3, b) magnetic abrasive exposure.
With the help of a profilometer, measurement protocols were obtained containing a profile of surface micro-roughness before (Fig. 4, a) and after processing (Fig. 4, b), as well as surface roughness values according to the parameters Ra and Rz. The surface roughness of the workpiece made of aluminum alloy AMc as a result of magnetic abrasive treatment has changed from 1.322 microns to 0.785 microns according to the parameter Ra. According to the obtained photos of the surface of the workpiece, there is a qualitative improvement in the condition of the surface: there are no furrows obtained by the cutter during turning, the number of scratches decreases, the surface acquires a matte, uniform color.

1.
Based on the results of theoretical and experimental studies of the possibility of magnetic abrasive treatment of composite surfaces made of aluminum alloy, the following conclusions can be drawn: 2. Products operating under the influence of aggressive media and subjected to fatigue loads need modern processing technology, which will ensure the requirements for qualitative indicators of surface condition (roughness); 3. Aluminum alloys are difficult-to-process materials, since in the process of their processing there are processes of caricature and build-up. The use of such a modern technology of final processing as magnetic abrasive treatment will avoid the occurrence of the above processes; 4. Validation of the existing installation for magnetic abrasive treatment using mathematical and computer modeling tools in the ANSYS Maxwell software environment allows you to assign the operating parameters of magnetic abrasive treatment in advance. The use of computer modeling tools will make it possible to determine the movements of the magnetic abrasive powder in the working gap under the influence of the emerging magnetic field; 5. The final processing of the composite surface of the billet made of aluminum alloy of the AMc, which is a shaft with a spherical body at one end, showed the prospects of using the method of magnetic abrasive treatment for the purpose of technological provision of surface roughness. The data obtained as a result of the experiment indicate a qualitative improvement in the state of surface roughness.