Influence of process parameters on magnetic abrasive machining efficiency

. The development of modern mechanical engineering forces us to constantly improve the technology of processing materials and look for ways not only to improve the quality of products but also to increase the efficiency of the processing process itself. This article discusses an alternative method to finish the product, which can replace the traditional method of grinding, magnetic abrasive treatment. This is a modern solution that allows you to obtain high surface quality of the processed product with minimal defects in their surface layer, and reduce the number of technological operations, which has a beneficial effect on the efficiency of the processing process. The efficiency of the magnetic abrasive machining process, which was determined by the amount of specific removal of the material, is influenced by many parameters, some of which were studied in this article: electromagnetic induction and processing time. The success of the application of magnetic abrasive treatment can also be judged by the topography of the surface of the product made using an electron microscope. The data obtained in the course of the study demonstrated the importance of individual input parameters of the magnetic abrasive treatment process in the formation of the surface layer of the product. According to the results of experimental studies, the dependences of the varied parameters were determined and recommendations were formed to improve the efficiency of the use of the magnetic abrasive process.


Introduction
The development of modern mechanical engineering makes it necessary to constantly improve the technological methods of machining parts to ensure the geometric parameters of the machined product and achieve high surface quality. Traditional methods of finishing products that are currently used are based on the grinding process, which has a negative impact on the surface layer of the workpiece. The presence of high temperatures in the machining area during grinding leads to burn marks and grinding cracks on the surface of the workpiece, which subsequently affects the strength and structural changes. Heating the workpiece during grinding causes thermal deformation, which directly affects its geometrical accuracy, wear resistance and serviceability. Thus, ensuring quality machining of precision products is a complex technological task that requires modern methods of solution.
One possible way to solve the existing problem is to change the product's machining technology and replace the finishing operation with finishing turning using the magnetic abrasive machining (MAM) method [1,2]. This is a state-of-the-art machining approach that allows a high-quality machined product to be produced with minimal surface thermal defects. This method is widely used in the machining of linear and cylindrical parts made of aluminium, brass, steel and other materials [5,7,8].

The study of the MAM process effectiveness
The use of this method is a promising trend in mechanical engineering technology that can not only improve the performance properties and quality characteristics of the product, but can also significantly increase the efficiency of the machining process by reducing process operations. The use of this method is a promising direction in mechanical engineering technology, which can not only increase the operational properties and quality characteristics of the product but also significantly improve the efficiency of machining parts by reducing technological operations.
In this paper, the efficiency of magnetic abrasive machining is investigated using the example of ceramic cutting inserts of the BOK-60. The specific material removal was analysed and the dependence of the process parameters on the MAM on the efficiency of the machining process was revealed.

Research methodology
Magnetic abrasive machining allows dimensionless machining to be realised. The material is removed from the surface of the workpiece by a kind of cutting tool made of magnetic abrasive powder, which is formed by the action of a magnetic field [3]. Magnetic abrasive tool (MAT) is characterised by a high degree of elasticity. The depth of penetration of the grit into the surface of the workpiece is the result of a settled equilibrium between the pressing forces pressing the grit against the workpiece and the resistance forces of the workpiece material against the penetration of the grit.
The performance of magnetic blasting is determined by the mass of material removed, which is calculated by weighing the workpiece before and after blasting. The method of geometrically calculating the volume of workpiece material has a high degree of measurement error due to the small thickness of the removed layer and the temperature deformations of the workpiece.
In order to assess the effectiveness of the process MAM the specific material removal value was applied q, g/cm 2 с area units (1).
= (1) where Q is the mass of the material to be removed, determined by the difference in masses to before and after after MAM; S is the surface area to be treated, cm 2 . Based on a literature review [1,4,6] and the capabilities of a dedicated magnetic blasting facility, two varying parameters were selected that have the greatest influence on the material removal process from the workpiece surface. These parameters include machining time and electromagnetic induction value (Table 1). Other process parameters such as workpiece speed, feed rate, composition MAT, the abrasive powder fraction, the amount of ferro-abrasive mass in the workspace, the clearance between the pole tips remained constant (Table 2). Ceramic plates are clamped in place using a specially designed support fixture BOK-60 and feeding them into the working space. The tool is fed into the magnetic-abrasive powder at a predetermined speed of the machine spindle.
The surface area of the ceramic plate in direct contact with the magnetic-abrasive tool S = 1.7 cm 2 . A diagram of the installation of the unit and the workpiece is shown in figure 1.   Figure 2 (a) shows that the dependence of the specific material removal q on the value of electromagnetic induction B is linear. The amount of material removal increases throughout the range of the varying parameter from 0.35 to 0.95 T. Minimal material removal 0.14 g/cm 2 is observed at an electromagnetic induction value of 0.35 T, and the maximum 0.78 g/cm 2 at 0.95 T. This is because with increasing electromagnetic induction the stiffness increases MAT, The increase in tool hardness also increases the temperature in the cutting zone, which has a negative effect on the quality of the machined surface. An increase in tool hardness also leads to an increase in temperature in the cutting zone, which has a negative effect on the quality of the machined surface. In this study, the range of electromagnetic induction has minimal negative impact on surface quality. Increasing this range can lead to material chipping from the workpiece surface and the emergence of stress concentrators, which have a negative effect on the wear resistance of the product, which requires additional research. Figure 2 (b) shows that the dependence of the specific material removal q on the processing time t is linear, but less steep than the dependence on the electromagnetic induction. In the range from 2 to 12 minutes, the value of specific material removal varies from 0.05 till 0.4 g/cm 2 respectively. This can be explained by the increased number of micro-cutting cycles of each of the grains individually, which are mixed throughout MAM. It can be assumed that over time MAT loses its original cutting capacity and the specific material removal q will then be relatively small or no longer increase at all.

Surface topography
In assessing the effectiveness of the process MAM not only the specific material removal q was investigated, but also the quality of the machined surface of the workpiece. The results were evaluated with a scanning electron microscope MarVision MM320 (Fidure 3). Based on optical inspection, it can be concluded that the process is effective MAM, which can replace the traditional grinding method. The machining process smoothes out the cutting edge of the surface and forms a surface without visible defects: cracks, chips and burrs. However, it is possible to observe residual inheritance which cannot be levelled due to the small thickness of the layer removed from the surface of the workpiece.

Conclusion
Magnetic blasting is an effective surface treatment process which can be used as an alternative to grinding. The following conclusions can be drawn from the analysis and experimental studies: 1. Selected varying parameters MAM (magnitude of electromagnetic induction, machining time) have a significant influence on the efficiency of the machining process; 2. Electromagnetic induction is the most important factor affecting the specific removal of material from the workpiece surface; 3. In the range of electromagnetic induction values from 0.35 to 0.95 T, there is a linear increase in material removal from the product surface; 4. The greatest amount of material removal is observed at an electromagnetic induction of 0.95 T and a treatment time of 12 min; 5. By varying the electromagnetic induction parameters and processing time, it is possible to achieve material removal rates of 0.05 till 0.78 g/cm 2 .