Analysis of Nanoscratch Mechanism of C-Plane Sapphire with the Aid of Molecular Dynamics Simulation of Hcp Crystal

In this study, single groove nanoscratch experiments using a friction force microscope (FFM) with a monocrystalline diamond tip were conducted on a c-plane sapphire wafer to analyze the ductile-regime removal and deformation mechanism including the anisotropy. Various characteristics, such as scratch force, depth, and specific energy for each representative scratch direction on the c-plane of sapphire, were manifested by the FFM, and the results of the specific scratch energy showed a trend of six-fold symmetry on taking lower values than those of the other scratch directions when the scratch directions correspond to the basal slip directions as . Since this can be due to the effect of most probably basal slip or less probably basal twinning on the c-plane, a molecular dynamics (MD) simulation of zinc, which is one of the hexagonal close-packed (hcp) crystals with similar slip/twining systems, was attempted to clarify the phenomena. The comparison results between the nanoscratch experiment and the MD simulation revealed that both the specific scratch energy and the burr height were minimized when scratched in the direction of the basal slip. Therefore, it was found that both the machining efficiency and the accuracy could be improved by scratching in the direction of the basal slip in the single groove nanoscratch of c-plane sapphire.

MODELING AND OPTIMIZATION OF HOLE ACCURACY AND DRILLING TIME IN MAGNESIUM AZ31 PLATE

Owing to the advancement in the field of materials, different range of grades have been developed. The machinability examination of these newer grades must be carried out for future applications. One such newer grade of magnesium with AZ31 is deemed for study during the drilling process. The independent parameters considered are spindle speed (SS), feed rate (FR) and drill bit diameter (DBD). The dependent parameters considered are burr height (BH), burr thickness (BT), drilling time (DT) and surface roughness (SR). Improving hole accuracy is essential for manufacturing superior products, which is discussed in this work. At the same time, the machining time has also to be minimized to increase the production rate. With these objectives, the experimental investigation is made. Further, an analytical model for predicting the responses is developed; later, optimization is carried out to obtain the desired responses through the desirability function approach. The multi-objective optimization suggests the SS of 1100[Formula: see text]rpm, the FR of 0.198[Formula: see text]mm/rev., and the DBD of 6[Formula: see text]mm for reducing the entire dependent is reckoned.

Characteristics and mechanism of top burr formation in micro-milling LF21

During micro-milling aluminum alloy LF21 process, it tends to produce large top burr usually detected at the top of slot walls. Therefore, the machining accuracy and quality of the micro-parts are difficult to satisfy. To suppress burr and achieve the higher machining quality of machined LF21 micro-parts, this paper using the Johnson Cook constitutive model establishes a two-dimensional finite element simulation model to obtain a better recognition of burr formation mechanismis and a three-dimensional finite element simulation model to better simulate burr formation process and measure burr height. Furthermore, effective validation experiments for the proposed models are conducted, good agreements are achieved in the cutting force and top burr height between the experiments and simulations. Last, this study explores the formation mechanism of top burr in micro-milling LF21 and reveal the law of the influence of cutting parameters on top burr height based on the simulation and experimental results. The research guides the selection of cutting parameters in micro-milling LF21 process.

An investigation on formation of burrs during milling of aluminium alloy under wet condition

Undesirable burrs are created out of a machining process. The objective of the present work is to explore the suitable condition to obtain no burr, or negligible burr, around the edge of a machined product at wet condition. Face milling experiments have been carried out on blocks made of aluminum alloy (Alloy-4600M) with a single, coated-carbide inserted cutter for observing the nature of burr formation. Depth of cut has been maintained constant at 3 mm for all sets of experiments. In each experiment set, three cutting velocities (170 m/min, 237 m/min and 339 m/min) and three in-plane exit angles of 30°, 60° and 90° are provided at three different feeds of 0.08 mm/tooth, 0.1 mm/tooth and 0.12 mm/tooth. First set of experiments are done without any exit edge bevel. Similar sets of experiments are carried out with 15° and 30° exit edge bevel angles to find out the condition for minimum burr. The bevel is made of a height of 3 mm. In the present experimental investigation, a minimum burr height of as low as 3 micron is obtained at an in-plane exit angle of 30° and exit edge bevel angle of 15° under the machining condition of 339 m/min cutting velocity and 0.1 mm/tooth feed.

Surface Textured Drill Tools—An Effective Approach for Minimizing Chip Evacuation Force and Burr Formation During High Aspect Ratio Machining of Titanium Alloy

The real challenge pertaining to high aspect ratio drilling is the rapid increase in chip evacuation force due to the chip clogging phenomenon occurring at higher drilling depths. The clogged chips will further impede the reachability of cutting fluid at the machining zone leading to the tool temperature buildup. This will eventually result in the catastrophic failure of the tool. Hence, in the present work, an attempt has been made to minimize the chip evacuation force by functionalizing the drill tool surfaces based on the laser microtexturing principle. Microscale textures in the form of circular dimples were created on the flute and margin side of the drill tool with an objective to control the sliding friction, thereby minimizing the chip clogging effect. The effectiveness of the functionalized drill tools were assessed mainly based on the variation in thrust force and torque. Drilling experiments showed a net reduction of 17.18% in thrust force and 26.98% in torque while machining Ti–6Al–4V using the flute and margin textured tool, which justified the effectiveness of micro scale textures in minimizing the chip evacuation forces. The experimental analysis was further extended in terms of burr height evaluation, where FMT tools were found to be highly effective in burr height reduction (1.29 mm), showing a net reduction of 54.26% when compared with the non-textured tool. The outcomes from this research work will be highly beneficial for the manufacturing industries including aerospace, automobile, and spacecraft as high aspect ratio drilling of titanium alloys are still categorized to be the most challenging machining process owing to its lower thermal conductive property.