Polishing Characteristics of Cemented Carbide Using Cubic Boron Nitride Magnetic Abrasive Powders.

This paper describes the application of bonded magnetic abrasive powders (MAPs) in the magnetic abrasive finishing (MAF) process. In order to improve the poor finishing performance and short service life of MAPs in polishing super-hard materials, a double-stage atomization technique was used to successfully manufacture MAPs with a CBN as an abrasive phase. The prepared results show that CBN abrasives with their original structure were deeply and densely embedded on the surface of spherical MAPs. Based on the MAF process, a five-level and four-factor central composite design experiment was carried out to verify the developed MAPs polishing performance on the finishing of cemented carbide parts (864 Hv). Working gap, rotational speed, feed rate of a workpiece, and mesh number of MAP were considered as influence factors. The analysis data was used to understand different interactions of significant parameters. A regression model for predicting the change of surface roughness was obtained, and the optimal parameter combination was figured out through a solution of a quadratic equation in Design-Expert software. According to MAF results, the strong cutting ability of atomized CBN MAPs improved the surface roughness of cemented carbide by over 80% at the optimum parameters. The strong cutting ability of atomized CBN MAPs can produce good surface quality on the hard materials. The findings of this research can promote a large-scale application of MAF technology in the surface polishing of hard materials.

Experimental Research and Optimization of Ti-6Al-4V Alloy Microgroove Machining Based on Waterjet-Guided High-Power Laser.

In order to improve the tribological properties of Ti-6Al-4V alloy and further broaden the application scope of titanium alloy materials in the industrial field, a preparation method of a waterjet-guided high-power laser processing surface microgroove was studied. In this paper, a multifocus coupling lens was innovatively designed to replace the spherical lens in the traditional waterjet-guided laser coupling device, which avoids the gas explosion phenomenon in the coupling of the high-power laser and waterjet, and realizes the high-quality coupling of the high-power laser and water beam fiber. Then, with the microgroove morphology as the response target, the single-factor test and response surface test of the water-guided laser processing microgroove were carried out. Based on the experimental results, an approximate mathematical model of the response surface between the process parameters and the microgroove topography target was constructed, and the quantitative relationship between the waterjet-guided laser processing parameters and the target response was studied. At the same time, the optimal combination of process parameters was obtained by multiobjective optimization, so as to effectively improve the microgroove morphology. This technology provides method guidance and a decision-making reference for subsequent waterjet-guided laser processing of titanium alloy surface functional microstructures.

Effect of static alignment deviation on coupling efficiency and beam quality of water beam fiber.

In this paper, the problems of decreasing coupling efficiency and energy distribution divergence of water beam fiber caused by static alignment deviation are studied. Based on the basic conditions of coupling between laser and water beam fiber, the mathematical model of coupling efficiency of water beam fiber is established, and the calculation equation of coupling efficiency is modified. The variation of coupling efficiency and energy distribution of water beam fiber under the influence of static alignment deviation is analyzed by numerical simulation, and the correctness of theoretical derivation and simulation model is verified by experiments. The results show that the lateral deviation changes the transmission path of laser in the water beam fiber to a large extent, and its influence on the energy distribution in the water beam fiber is greater than that of longitudinal deviation and angular deviation.

Pollution characteristics, spatial distribution, and source identification of heavy metals in road dust in a central eastern city in China: a comprehensive survey.

Road dust enriched with heavy metals (HMs) is detrimental to ecosystems and human health in urban environments. In this study, it is to explore the concentrations, spatial distribution, contaminated levels, and source identification of six HMs (lead (Pb), zinc (Zn), copper (Cu), cobalt (Co), chromium (Cr), and nickel (Ni)) based on 130 road dusts in Xinyang urban area. The results indicated that the contents of Pb, Zn, Cu, and Co were higher than the background values in more than 99% of the samples, and their average concentrations were 15.2, 9.2, 8.6, and 6.3 times the background value, respectively. The spatial distribution of high-value areas for Pb, Zn, Cu, Cr, and Ni was more similar, which was associated with traffic density near major roads and population and settlement patterns. Co was relatively different from the five elements, which was distributed in the areas of residence, commerce, and industry. Furthermore, the investigated HMs were clearly polluted, with Pb, Zn, Cu, and Co indicating high levels of contamination, while Cr and Ni were moderately polluted. The comprehensive pollution of the six HMs was mostly moderate to heavy in this study. Moreover, three sources of HMs designated by correlation analysis (CA) and principal component analysis (PCA) were mixed traffic emissions and industrial waste for Cu and Cr; automotive emissions for Pb, Ni, and Zn; and mixed domestic waste and industrial activities for Co, with contributions of 42.3%, 46.4%, and 11.3% via the principal component analysis-multiple linear regression (PCA-MLR) model. The multi-factor index for pollution assessment combined with source identification is extremely effective and practical for providing reliable data support and a theoretical reference for pollution monitoring and governance.

Magnetic monitoring of topsoil and street dust in Xinyang (China) and their environmental implications.

The magnetic measurement is an effective tool to identify the source of pollutants and diagnose the urban pollution. In this study, 132 group samples (that topsoil and street dust were sampled at the same location is regarded as a group) were collected from Xinyang, central eastern China. In addition, the background samples (19 topsoils under woodland around the outskirts) were also sampled. Herein, the aim was to investigate and compare the magnetic characteristics of both topsoil and street dust, and further to discuss the source and environmental implications using magnetic and diffuse reflection spectrum methods. The following points are highlighted: (1) the primary magnetic carrier of both materials was magnetite and that of the background sample were magnetite and maghemite. Furthermore, the ferrimagnetic mineral concentration and magnetic domain follow the order: street dust > topsoil > background sample. (2) The source of both materials was mainly from anthropogenic activities (e.g. industrial and traffic vehicles). The difference between them was the contribution related to natural sources (e.g. parent materials), which was negligible in street dust, and played a secondary role in topsoil. (3) Both materials showed that areas with a higher intensity of anthropogenic activities had higher pollution level, whereas areas with a lower anthropogenic intensity had lower pollution level.

Process Parameters Optimization Using Taguchi-Based Grey Relational Analysis in Laser-Assisted Machining of Si3N4.

Despite extensive research over the past three decades proving that laser-assisted machining (LAM) is effective for machining ceramic materials, which are affected by many machining parameters, there has been no systematic study of the effects of process parameters on surface quality in LAM ceramic materials. In this paper, the effects and optimization of laser power, spindle speed, feed rate, and cutting depth on surface roughness and work hardening of LAM Si3N4 were systematically studied, using grey relational analysis coupled with the Taguchi method. The results show that the combination of machining parameters determines the material removal mode at the material removal location, and then affects the surface quality. In ductile material removal mode, both the value of surface roughness and work hardening degree are smaller. Decreased surface roughness and work hardening degree can be obtained with smaller cutting depth and higher laser power.

Identifying environmental pollution recorded in street dust using the magnetic method: a case study from central eastern China.

Urban street dust constitutes important intermediate products for the transmission of solid organic and inorganic pollutants in the urban environment. In this study, 133 street dust samples were collected from Xinyang to explore their magnetic characteristics, spatial distribution, and environmental implications using magnetic measurements. The results are as follows. (1) There were ferrimagnetic, antiferrimagnetic, and paramagnetic (e.g., lepidocrocite) minerals in the dust. Among these, the dominant magnetic carriers were ferrimagnetic minerals. Furthermore, magnetite was a first-order ferrimagnetic carrier. (2) The magnetic domains of the dust were pseudo single-domain to multi-domain. (3) The magnetic concentration (χ and SIRM) of dust were 2.6 and 4.1 times higher than those of background samples that were not polluted by urban and anthropogenic activities, respectively. Therefore, we conclude that the dust consisted of high concentration of ferrimagnetic minerals and coarse magnetic particles. (4) The magnetic distribution was spatially different. The industrial area, which was the most polluted sampling area, had the highest magnetic concentration and the coarsest magnetic particles. This was attributable to industrial emissions, fossil fuel combustion, and exhaust emissions from heavy-laden trucks. Residential and commercial areas, which were the second most polluted areas, had higher concentration and coarser particles. This was primarily due to the high population density and traffic activities of mini-cars (i.e., high flux and exhaust emissions). Hence, the conclusion is that the magnetic characteristics, spatial distribution, and the sources of dust are dictated by anthropogenic activities. Our results indicate that the magnetic method is a highly effective tool to monitor urban environmental pollution.

Fractal Characteristics of Chip Morphology and Tool Wear in High-Speed Turning of Iron-Based Super Alloy.

Considering that iron-based super alloy is a kind of difficult-to-cut material, it is easy to produce work hardening and serious tool wear during machining. Therefore, this work aims to explore the chip change characteristics and tool wear mechanism during the processing of iron-based super alloy, calculate the fractal dimensions of chip morphology and tool wear morphology, and use fractals to analyze their change trend. Meanwhile, a new cutting tool with a super ZX coating is used for a high-speed dry turning experiment. The results indicate that the morphology of the chip is saw-tooth, and its color changes gradually, due to the oxidation reaction. The main wear mechanisms of the tool involve abrasive wear, adhesive wear, oxidation wear, coating spalling, microcracking and chipping. The fractal dimension of the tool wear surface and chip is increased with the improvement of cutting speed. This work investigates the fractal characteristics of chip morphology and tool wear morphology. The fractal dimension changes regularly with the change of tool wear, which plays an important role in predicting this tool wear. It is also provides some guidance for the efficient processing of an iron-based super alloy.