Papers by Keyword: Grinding

Abstract: The finishing operation (grinding) is a complex task of the field of spiroid worm manufacturing. I am investigating the grinding process of spiroid worm using lathe center displacement on a classical cylindrical grinding machine. The lathe center displacement means the adjustment of the spiroid worm according to the half taper angle to get a horizontal position of the generatix of the taper of the spiroid worm in comparison with the center line of the grinding wheel. In this case the center distance between the spiroid worm and the grinding wheel is permanent during the whole grinding process. This adjustment causes changing angular velocity for the rotation of the spiroid worm that affects to the error of the lead of thread and the error of the position of the pitch circle diameter that can influence the profile accuracy during the whole grinding process.

Abstract: The paper presents the use of integral methods of surface texture evaluation of structural steel samples used in armaments production for the analysis of the functional behaviour of gear surfaces. The aim of the paper is to evaluate the relationship between the quality of the ground surface and the surface after the plasma nitriding process and the functional properties of the surface using unconventional characteristics. These characteristics include Amplitude Distribution and Material Ratio, Autocorrelation Function (ACF), Frequency Spectrum (FS) and Power Spectral Density (PSD). These characteristics can, for example, reveal small changes in surface texture caused by both the cutting tool and surface treatments, such as diffusion nitriding technology, which show only slight changes in standard parameters. Thus, these characteristics can be used as a suitable diagnostic tool for evaluating changes in the functional properties of surfaces. These changes can usually be characterized by wavelength profile inequalities and statistical and spectral properties. In this paper, the surfaces of C45, 15NiCr13, 18CrNiMo7-6 and 16MnCr5 steels after the finishing operation of grinding and further after plasma nitriding are evaluated. Measurement of the standard parameter, i.e. the arithmetic mean height Ra, of ground and nitrided surfaces resulted in the same or slightly higher values after diffusion technology. Using integral characteristics, changes in surface texture were found to be directly related to the functional behaviour of surfaces in interaction and can predict, for example, noise levels, wear and lubrication properties.

Abstract: The grinding technologies are widely used for finishing operations of various types of parts to provide better surface roughness and accuracy for the selected surfaces. Those technologies are expensive and take a lot of time to execute them consequently they are used when it is reasoned. The goal of this research is to compare the manufacturing design processes for horizontal and vertical grinding where the arrangement distinction between them is just the position of the tool axis compared to the machined surface of the workpiece. All of the necessary manufacturing parameters are determined to ease the design process. After the manufacturing design CAM design and CNC program writing are possible if CNC controlled machine is applied. Using of the same manufacturing parameters a comparative manufacturing analysis is done to determine the differences between the two processes.

Abstract: In this work, the influence of different surface roughness and surface treatments on the minimum energy density required to form low-ohmic nickel contacts on n-type 4H-SiC by laser annealing was investigated. The annealing was performed by a frequency-tripled Nd:YVO₄ laser with a pulse duration of 50 ns. To evaluate the effects, the grinded or polished C-side of 4H-SiC wafers with surface roughness between 0.3 and 70 nm was sputter-deposited with nickel and subsequent laser annealed. Sheet resistance measurements showed that the minimum energy density required to achieve a low-resistance contact depends significantly on the surface roughness. The rougher the surface, the lower the minimum energy density to form a low-ohmic contact.

Abstract: A novel approach for processing SiC wafers has been developed to grind then polish 150 and 200mm SiC wafers without lapping. The purpose of this work was to optimize the processing of SiC wafers sliced from boules to finished epi-ready wafers by grinding and chemical-mechanical polishing (CMP). Diamond vitrified wheels were used for coarse and fine grinding to correct the irregular shape of SiC wafers before reducing surface roughness by CMP. 4H-SiC wafers were sliced by diamond embedded/slurry wire saw and laser split techniques. Incoming wafer condition was seen to affect coarse grinding wheel performance depending on incoming surface roughness and shape. Wheel characteristics, including abrasive size, abrasive concentration, and bond structure, were adjusted to improve grinding efficiency based on incoming conditions. Coarse grinding wheels were able to reduce wafer total thickness variation to 3-5um and average surface roughness to 20-30nm (Ra). Fine grinding wheels were optimized to reduce total thickness variation (TTV) below 2um and surface roughness to 1-2nm Ra and peak-to-valley height of 20-30nm (Rt). Coarse and fine wafering time was less than 30 minutes total to remove 50 microns on both Si and C-face per wafer. Surface damage from grinding was removed after one hour of polishing each wafer by CMP, achieving surface roughness of 0.4nm Ra and 5-7nm Rt. The benefit of optimizing coarse and fine grinding of 150 and 200mm SiC wafers is demonstrated by producing flat wafers, which reduced overall processing time to prepare an epi-ready condition by CMP.

Abstract: The work addresses the issues of increasing processing accuracy and productivity by controlling technological connections that act during the formation of shaped surfaces by grinding and plastic deformation, presents the main indicators of the quality of teeth on the working surface, provided by the developed technology, with a decrease in the maximum value of the actual cutting depth by more than 1.5 times when grinding toothed surfaces by copying, determined influence of the position of the workpiece on the accuracy of the pitch and half-angles of the profile for rolling threads of high precision by radial feed, the purpose of which is movement and measurement, design features determined of rollers for thread rolling on workpieces with low rigidity with tangential feed, the parameters of their threads, including the functional and structural relationship of the helix angles with the dimensions of the rolled thread.

Abstract: Cement production is currently very energy-intensive, with the grinding process consuming the majority of the total energy in cement production. Therefore, there is a constant search for ways to reduce this amount of energy while maintaining the same grinding efficiency. The main goal of the article is to investigate the effect of grinding intensifiers, which should reduce the energy needed to grind raw materials. Potentially usable technologies in the field of mechanochemical activation are investigated, i.e., high-speed grinding through grinding in a laboratory planetary mill and disintegrator. High-speed disintegrator grinding technology is much more efficient than planetary grinding technology. Already during the first passage through the disintegrator, an increase in the specific surface area from 200 m²/kg to 280 m²/kg was recorded, with an estimated stay of the particle in the grinding space for 3-5 seconds. Using a planetary mill, the particles would have to remain in the grinding chamber for approximately 2 minutes to achieve such an increase in specific surface area. However, with further drops, the efficiency decreases, which is due to the high tendency to aggregation and agglomeration in this milling technology.

Abstract: The methods of influence on the material using different energy sources are considered. The role of friction in several technological processes is emphasized. The technological process of heat treatment is proposed, which allowed to restore the properties of rolled rolls that were lost due to incorrect grinding conditions. Application of the proposed technological process has shown that: 40X steel can be hardened to martensite in oil, water, and in a 10 % aqueous solution of NaCI salt, but with different results (i); the most effective hardening mode for 40X steel rolls is quenching with cooling in a 10 % aqueous solution of NaCI salt and subsequent high-temperature tempering, which is necessary to remove dangerous residual stresses (ii); the structure of the surface working layer of 40X steel rolls, after the selected optimal heat treatment regime, consists of fine-needle martensite and a small amount of Cr carbides (iii); closer to the core of the rolls, in addition to martensite, there are areas of troostite-bainite structure (iv); the resulting structure of the rolled rolls is capable of ensuring their efficient and long-term operation, but under optimal conditions, when the rolls' heating temperatures do not exceed 200 °C, and the proposed temperature conditions are recommended for both operation and routine maintenance associated with periodic restorative grinding of the working surfaces of the rolled rolls (v).

Abstract: The grinding processes of shaping materials are one of the oldest known. However, the first grinding machine tool did not appear until the beginning of the 19^th century. Industries as important as the automobile would not have been possible without its invention. One of the machine tools that made this development possible was the universal grinding machine patented by Joseph R. Brown in 1877. Unfortunately, none of these early machine tools have been preserved and only the patent remains. Therefore, in this work, a virtual model of this first universal grinding machine has been developed by applying reverse engineering techniques. For this purpose, the existing data in the patent and in some machine treatises of that time have been used. Based on this information, the functionality of each of its components have been interpreted and analyzed. Starting from a set of hypotheses, a scaled and parameterized functional 3D model has been developed. Additionally, a kinematic study of the grinding wheel drive system has been carried out. Hence, this digital model ensures the durability of an important piece of the universal industrial heritage. Furthermore, it can be used as a teaching tool for engineering students, showing the operation of a machine tool belonging to a historical context different from the current one, which does not differ substantially in its architecture of modern universal grinding machines.

Abstract: Fixed platforms employed in oil & gas shallow waters industry are subjected to dynamic loads created by winds, waves and currents. However, such loads can produce fatigue damage, like localized cracking in the weld toes of T-welded connections of the submerged structures of fixed platforms. Therefore, to repair localized cracking, a technique that combines grinding and wet welding can be applied at the weld toes of submerged structural connections. Accordingly, in the present work it is presented a methodology to restore the fatigue life of T-welded connections fabricated with A36 plate steel. Consequently, T-welded connections samples were prepared and tested under intact, grinding and grinding-wet-welding repair conditions. For the repair conditions, the weld toes were grinded 6 mm and 10 mm, and wet welding was deposited to fill the grinded material in a hyperbaric chamber, which simulated 50 m, 70 m and 100 m water depths. Afterwards, the repaired connections were subjected to fatigue loads, and the S-N curves were measured for intact and repair conditions. Fatigue results showed that the combined repair technique was able to restore the fatigue life of T-welded connections for a maximum water depth of 50 m. Nonetheless, for water depths of 70 m and 100 m the fatigue life was smaller than for 50 m, but higher compared to the only grinding repair condition.