Multifractal analysis of ultrasonically machined surfaces of cylindrical quartz crystals: the effect of the abrasive grits

Since synthetic quartz is essential to produce 3-D resonators for numerous applications in precision electronics, in this work the surface topography of cylindrical quartz bars is investigated using the multifractal technique. The cylindrical bars were manufactured with ultrasonic machining using with five SiC grits ranging from 6 to 50 µm. The machined surfaces were initially characterized by contact profilometry and scanning electron microscopy (SEM). The multifractality of the machined surfaces was scrutinized using a box-counting method applied to the images obtained with 500X magnification. The multifractal spectrum indicated that the fractal dimension f(α) and the width of the fractal spectrum Δα are dependent on the grit size, but this dependence is not monotonic. The lowest (negative) value for Δf(α) was found for 25 µm grits indicating that for these grits the lower frequency events (grooves with tens µm width occurring along the USM direction) controls the surface topography much more than high frequency events related to brittle microcracking. The abrasive wear due to the continuous slurry recycling in lateral tool-workpiece interfaces contributed to smooth the groove texture as well as the sharpness of microscopic indentations, which remained observed on the surfaces machined with 50 µm grits. The opposite paths observed for the arithmetical mean deviation of the measured profile (Ra) and Δf(α) parameters with the cutting rate measured for each grit size were valuable to differentiate flat-rough and unlevelled-rough topographies in quartz bars.

EXPERIMENTAL MILLING STUDIES ON HARDENED STEELS - A REVIEW

Hardened steels have numerous applications in the construction of molds and dies due, in particular, to their outstanding thermo-mechanical characteristics, such as wear resistance and high stiffness, but especially dimensional stability at high temperatures. Machined surfaces are conditioned to have important tribological characteristics. Thus, a high quality of machined surfaces is achieved by milling processes with high cutting speeds. These types of processes even manage to replace grinding or electro-erosion machining processes with a solid electrode. The paper presents a review of experimental studies in recent years from industry and scientific research. Issues are outlined which justify the utility of machining hard metals by machining processes, with a focus on machining by milling processes. Starting from input parameters, such as technological parameters, blank material, cutting tool material and machining environment, their influence is analysed on output parameters, such as chip morphology, cutting tool wear and surface integrity.

A Critical Study on Computation of Cutting Forces in Metal Cutting

Tool behavior in metal cutting is inevitable since they are typically required to produce components with high precision. This would have a profound impact on efficiency and costs of machining. The cutting forces involved at chip tool interface and the surface finish of the machined surfaces are the two major facets to gauge the performance of tool. The prediction by a statistical model, and the experimental values recorded using various sensors especially dynamometers are different approaches to critically analyze the cutting forces. Many researchers use to extensively practice these methodologies for their research activity. The aim of current research is to critically analyze & summarize approaches i.e., experimental/predictive available for gauging the cutting forces with user suggestion.

Effect of indirect cryogenic cooling on the machining accuracy and tool vibration in the turning of polysulfone

Cutting deformation and cracks are common problems during the machining of precise polymer parts. This paper aims to explore the effect of different conditions on the contour profile of machined surfaces and tool vibration. Turning experiments of polysulfone (PSU) were performed under three conditions: dry, conventional flood cooling, and indirect cryogenic cooling. Then the formation mechanism of machined surfaces contour profile under different cutting conditions was clarified by the Eyring equation from the perspective of molecular chains relaxation time. Furthermore, extension models of crazing and cracks were proposed through the microscopic morphology of machined surfaces and the discriminant formula of crazing generation to explain the differences in tool vibration. The results indicated that the indirect cryogenic cooling condition with the internally cooled cutting tool could significantly improve the machinability of polysulfone, and have an excellent performance on the contour profile of machined surfaces with and the inhibition of crazing. Compared with dry and conventional flood cooling, indirect cryogenic cooling could reduce the mean of the Contour profile (Ra) by 40.3% and 30.1% and the machining accuracy error by 41% and 83%. The indirect cryogenic cooling method proposed in this work provides a reference for the cryogenic machining for polymers.

Study On Cutting Force and Tool Vibration For Optimization of Depth of Cut in Ultra-Precision Planing Process of the Master Mold For Retro-Reflection Film

The micro-triangular pyramid patterns are widely used in advanced optical components with retro-reflection characteristic. The performance of the retro-reflection is affected by an effective area, and it can be maximized by machined surface without defects such as edge blunt, burr, surface roughen. The ultra-precision planing process is well-known that can fabricate superior surface when the depth of cut (DOC) is applied to minimum depth above the critical value to prevent the size effect. However, it was very difficult to determine a DOC without comparing of quality of machined surfaces through the ultra-high magnification measuring instrument such as SEM. In this study, the critical DOC which is key parameter was analyzed using cutting force and tool vibration signals. These signals were converted to specific cutting resistance and frequency spectrum, respectively. As a result, spectrum frequency signal was more effective and accurate than specific cutting energy, and critical DOC was determined to 1µm. This proposed process was validated by comparing the quality variation of the machined surfaces with analysis result based on cutting signals. Finally, a master mold with area of 250mm2 for fabrication of the retro-reflection film was manufactured by applying optimized DOC, and the retro-reflection film was fabricated by press molding process. This retro-reflection film was clearly recognized at a distance of 100m from light source with low power.