Search

Revealing the relationship among the machining parameters, surface topography, and functionality-related properties of the machined surface is crucial for obtaining micro-milling surfaces with good functional performance. In the present study, slot micro-milling Ti6Al4V was conducted to investigate the effect of machining parameters on the 3D surface topography, with an emphasis on surface defects, the 3D surface texture parameters, and functionality-related properties of the machined surface. The results show that the 3D surface topography of the machined surface presents obvious anisotropy in slot micro-milling Ti6Al4V. The 2D surface profile shows the non-uniformity along the slot width direction in slot micro-milling Ti6Al4V. The surface defects with different machining parameters are various, such as deep and large feed marks of single cutting, narrow and small feed marks of single cutting, feed marks of multi-cutting, scratch marks, scratch pit, surface tearing, tear pit, back-cutting marks, and metal debris. With the consideration of cutting processing efficiency and surface roughness Sa, it is suggested to adopt the high spindle speed and large depth of cut. At the same time, feed per tooth that is near the minimum cutting thickness is recommended to obtain the minimum surface roughness with the balance of chip thickness accumulation effect and chip removal or surface formation. Moreover, the functionality-related properties of the machined surface, e.g. friction or abrasion contact behaviors, load-bearing capacity, fluid retention properties, fatigue performance, and the machining parameter effect were evaluated with surface texture parameters, such as amplitude parameters, spatial parameters, hybrid parameters, and functional or volume parameters. Our findings are of great significance for shedding light on the relationship between the surface formation mechanism, surface topography, and functionality-related properties of machined surfaces in micro-milling Ti6Al4V. [ABSTRACT FROM AUTHOR]

Surface roughness and residual stress are related to the fatigue life of finished parts. However, experimental investigations lack a deep discussion about the cutting mechanism. Orthogonal cutting simulation for milling or two-dimensional finite element model is the simplification of the actual milling process, which makes it difficult to reflect the milling characteristic in the simulation. In the present study, a three-dimensional coupled thermo-mechanical simulation model was established to analyze the surface roughness and residual stress in milling 5083 aluminum alloy. Explicit dynamic analysis was used as the solution algorithm for the milling process. Implicit analysis was adopted to simulate the process of unloading and cooling. Mesh sensitivity analysis was conducted to identify the mesh size of the workpiece. Node displacement and stress information were output to calculate the surface roughness and residual stress. The effects of cutting parameters on surface roughness and residual stress were discussed by the simulation model. Moreover, milling experiments were conducted to validate the simulation results. It is observed that the surface roughness of the simulation and experiment shows the same trend with the increase of feed per tooth and depth of the cut, which verifies the simulation model. Moreover, the superficial residual stress of the machined surface is the result of the coupled thermo-mechanical with the compressed effect of the tool, the tensile effect of the tool, and thermal load. The superficial residual stress of the machined surface presents compressive stress at a different feed per tooth and spindle speeds. Current findings provide insights for understanding the formation mechanism of the surface topography and residual stress in milling aluminum alloy. [ABSTRACT FROM AUTHOR]

In order to effectively mitigate the oxidation reactions of coal (RC) and gangue (RG) at low temperatures, a comprehensive study was conducted on the mineral composition, structural characteristics, and oxidation behaviors of RC and RG from the same coal seam. Additionally, the thermodynamic attributes of their oxidation processes were evaluated. The results indicate that the mineral composition of RC and RG is similar, primarily comprising kaolinite. However, there are substantial differences in structural characteristics, with RG exhibiting a more stable structure, smaller aromatic layer spacing, and higher degree of graphitization. Additionally, the molecular arrangement is densely packed and orderly, displaying characteristics akin to those of " highly metamorphic coal-like ". RC has a high content of aromatic hydrocarbons and aliphatic hydrocarbons, with long side chains, rendering it more susceptible to oxidation and possessing stronger combustion activity. Upon entry into the oxidation process, RG exhibits a lower initial exothermic temperature due to its strong thermal conductivity and large thermal diffusion coefficient. However, it simultaneously has fewer active functional groups and a higher ash content, limiting its sustained exothermic capacity and prolonging the processes of slow endothermic and rapid exothermic reactions. Conversely, RC, with its high carbon content and abundant active substances, releases heat during oxidation that is 1.7–3.5 times greater than that of RG. Importantly, when RC and RG oxidize together, they exhibit a synergistic effect, promoting the reaction. In the slow endothermic stage, the average activation energy required for CG is 2.64 kJ·mol−1 lower than that for RC. In the rapid exothermic and slow exothermic stages, the actual heat release of CG exceeds the theoretical heat release by 15.95–64.71 J·g−1 and 13.88–56.77 J·g−1, respectively. [ABSTRACT FROM AUTHOR]

Micro-milling force and specific cutting energy play an important role in revealing the micro-milling mechanism. However, it is quite difficult to compare the micro-milling force values from different experiments due to the lack of a representative cutting force parameter to comprehensively evaluate the micro-milling force. Especially, there is no unified formula to accurately calculate the specific cutting energy in micro-milling due to variable chip cross-sectional area and periodically varying micro-milling force. In this work, the micro-milling force was systematically analyzed with fast Fourier transform spectrum analysis, curve shape, and representative parameter evaluation. The quasi-dynamic cutting force, which is represented by the P–V value of cutting force, was adopted to comprehensively evaluate the micro-milling force. The specific cutting energy was calculated with the ratio of quasi-dynamic cutting force and the average undeformed chip thickness. Moreover, the variable regularity of quasi-dynamic cutting force and specific cutting energy on cutting parameters were obtained with the micro-milling experiment. The results show that the quasi-dynamic cutting force first decreases and then increases with the increase of feed per tooth due to the chip accumulation effect. With the increase of spindle speed and depth of cut, the quasi-dynamic cutting force decreases and increases, respectively. The minimum undeformed chip thickness is between 0.3 and 0.5 μm, which is around 0.19 to 0.32 of tool edge radius in micro-milling Ti6Al4V. With the increase of spindle speed and depth of cut, the specific cutting energy shows a decreasing trend and changes a little, respectively. With the decrease of the feed per tooth, the specific cutting force shows a nonlinear increase. Our findings are of great significance for further scientific understanding the micro-milling mechanism from the perspective of cutting force and specific cutting energy. [ABSTRACT FROM AUTHOR]