Precision milling of high volume fraction SiCp/Al composites with monocrystalline diamond end mill

Silicon carbide particle-reinforced aluminum matrix (SiC_p/Al) composites have attracted considerable interest as potential materials due to their excellent engineering properties. Many research works have been done associated with turning SiC_p/Al in the past. However, it still lacks of experience on milling of SiC_p/Al composites. This paper presents an exploratory study on precision milling of SiC_p/Al composites with higher volume fraction (SiC_p, 65 %) and larger particle size. The experiments were conducted on a Kern MMP 2522, high-precision micromilling machine center. A single flute monocrystalline diamond end mill was used to mill straight grooves with cutting parameters in a few micros. The machined surface quality including surface roughness and surface topography were studied. The cutting mechanisms of SiC particle and tool wear characters were also investigated. The results showed that mirror-like surface with surface roughness around 0.1 μm Ra can be achieved by precision milling with small parameters in the range of a few micros. Most of the SiC reinforcements were cut in partial ductile way with microfractures and cracks on the machined surface; tool wear included chipping and cleavage on monocrystalline diamond edge. A large flank wear on tool bottom face was observed and suspected to be caused by coaction of chemical transition and mechanical abrasion.     

Experimental Study on Lubrication Film Thickness Under Different Interface Wettabilities

This paper describes some experimental studies about the effect of interface wettability on hydrodynamic lubrication film thickness by a custom-made slider bearing tester. The lubricated contact pair consists of a fixed-incline slider and a transparent disc, and a thin lubrication film can be generated when the disc rotates. The film thickness was measured by interferometry. The wettability of different slider surfaces was evaluated by the contact angle of the lubricant on them. The relationship of film thickness versus disc speed was measured under different liquid–solid interfaces, and the results showed that slider surfaces with strong wettability to the lubricant could generate higher film thickness. Furthermore, case experiments were carried out to validate the hydrodynamic effect by tailored-slippage. By numerical simulations, the experimental findings were tentatively explained with the phenomenon of wall slippage.     

Wire electrochemical machining using reciprocated traveling wire

Wire electrochemical machining (WECM) is a cutting process in which the workpiece acts as an anode and the wire as a cathode. WECM is typically used to cut plates and exhibits a great advantage over wire electro-discharge machining, namely, the absence of a heat-affected zone around the cutting area. The enhancement of WECM accuracy is a research topic of great interest. In WECM, the homogeneity of the machined slit has a decisive influence on the machining accuracy. This is the first study in which the integration of pulse electrochemical machining (ECM) and a reciprocated traveling wire electrode was used to improve the homogeneity of this slit. The experimental results show that the combination of pulse ECM and a reciprocated traveling wire electrode could enhance the accuracy of WECM and that generally a low applied voltage, pulse duty cycle, and electrolyte concentration; an appropriate traveling wire velocity; and a high pulse frequency and feeding rate enhance the accuracy and stability of WECM. Finally, a microstructure with a slit width of 177 μm, with a standard deviation of 1.5 μm, and with an aspect ratio of 113 was fabricated on a stainless steel substrate measuring 20 mm in thickness.     

Modeling of the static tool influence function of bonnet polishing based on FEA

The purpose of this paper is to investigate the model of the static tool influence function (sTIF) of bonnet polishing (BP). Three kinds of sTIF are mathematically modeled, which are static tool influence function of tilted polishing (sTIF_t), static tool influence function of discrete precession polishing (sTIF_d), and static tool influence function of continuous precession (sTIF_c), respectively. Pressure distribution in the contact area is confirmed based on finite element analysis (FEA) technology. A group of experiments to extract the polishing spots have been conducted to verify the accuracy of the sTIF model. Meanwhile, the difference between sTIF_d and sTIF_c is studied. It turns out that the removal depths of sTIF_d and sTIF_c are almost the same, and the continuous precession polishing can be replaced by discrete precession polishing to ease control in practical polishing process especially for the aspheric surfaces polishing.     

Research on the error analysis and compensation for the precision grinding of large aspheric mirror surface

The purpose of this paper is to propose a compensation grinding method for large aspheric mirror surface. Because the tradition grinding is not suitable for large aspheric mirror surface, in this paper, a grate parallel grinding in 3-axis and an on-machine measurement system are applied. Based on that, it presents the errors that mainly affect the form accuracy and technology of compensation grinding. An experiment of compensation grinding was carried out for large aspheric mirror surface. With the separation of decentering, wheel arc, and residual grinding system error, the PV value further decreased comparing to tradition compensation. These results indicated that this compensation can improve the form accuracy significantly in large aspheric mirror surface grinding.     

Experimental evaluation of polycrystalline diamond tool geometries while drilling carbon fiber-reinforced plastics

Polycrystalline diamond (PCD) drills are commonly employed in carbon fiber-reinforced plastic (CFRP) drilling to satisfy hole quality conditions with an acceptable tool life and productivity. Despite their common use in industry, only a small number of studies have been reported on drilling CFRPs with PCD drills. In this study, drilling performances of three different PCD drill designs are investigated experimentally using thrust force, torque, and hole exit quality measurements. Results show that work material properties, drilling conditions, and drill design should all be considered together during the selection of process parameters, and the relationships among these factors are quite complex.     

Feasibility study on optimized process conditions in warm tube hydroforming

Feasibility study has been performed to estimate the optimized process conditions in warm tube hydroforming based on the simulated annealing optimization method. Precise prediction and control of process parameters play an important role in forming at warm conditions. Optimal pressure and feed loading paths are obtained for aluminium AA6061 tubes through the simulated annealing algorithm in conjunction with finite element simulations. Numerous axisymmetric geometries are investigated and the effects of expansion ratio, corner fillet to thickness ratio, and initial diameter to thickness ratio are studied. For the feasibility estimation, warm hydroforming experiments have been conducted on aluminum AA6061 under optimal designed conditions. The results show that the optimization procedure used in this research is a reliable and feasible tool in determination of optimal process conditions for the sound warm hydroforming process.     

Effective predictions of ultimate tensile strength,peak temperature and grain size of friction stir welded AA2024 alloy joints

A series of welds were made by friction stir welding (FSW) under different welding and rotation speeds. A 2D ultimate tensile strength (UTS) map was developed based on various experimental data to predict the UTS of friction stir welded AA2024 alloy joints. The accuracy of the UTS map was evaluated by comparing the estimated UTS with the corresponding experimental results from the FSW of the same material available in the open literature. Analytical models were developed to estimate the peak temperature and grain size in the nugget zone. The predicted optimal peak temperature and welding and rotation speeds for AA2024 were within the windows of 400–465 °C, 175–350 mm/min and 800–1,200 rpm, respectively, under which the joint tensile strength could be higher than 458 MPa (about 94.6 % of the base metal) and the estimated average grain sizes in the nugget zone were about 2–3.9 μm.     

Effect of Storage Conditions and Antioxidants on the Oxidative Stability of Sunflower–Chia Oil Blends

The mixture of different proportions of sunflower with chia oil provides a simple method to prepare edible oils with a wide range of desired fatty acid compositions. Sunflower–chia (90:10 and 80:20 wt/wt) oil blends with the addition of rosemary (ROS), ascorbyl palmitate (AP) and their blends (AP:ROS) were formulated to evaluate the oxidative stability during storage at two temperature levels normally used, cool (4 ± 1 °C) and room temperature (20 ± 2 °C) for a period of 360 days. Peroxide values (PV) of the oil blends with antioxidants stored at 4 ± 1 °C showed levels ≤10.0 mequiv O₂/kg oil; the lowest levels of PV were found for blends with AP:ROS. Values higher than 10.0 mequiv O₂/kg were observed between 120–240 days for oil blends stored at 20 ± 2 °C. Similar trends were observed with p-anisidine and Totox values. The oxidative stability determined by the Rancimat method and differential scanning calorimetry showed a greater susceptibility of the oils to oxidative deterioration with increasing unsaturated fatty acids content. The addition of antioxidants increased the induction time and decreased the Arrhenius rate constant, indicating an improvement in the oxidative stability for all the oil blends. Temperature had a strong influence on the stability of these blends during storage.     

Synthesis and caracterization of macromonomers of poly (2-methyl-2-oxazoline)-allyl by an acid exchanged clay as eco-catalyst

The different polymer networks were constructed by two kinds of associations, one is host-guest inclusion between P(AM/A-β-CD/NaA) and P(AM/BHAM/NaA), and the other is hydrophobic association of P(AM/BHAM/NaA). Under the high-speed shearing, the viscosity survival and recovery rate of different systems were investigated. The results show the inclusion complex (CD:BHAM = 2:1) has excellent shearing resistance performance, and it was also verified by dynamic light scattering (DLS). This is mainly because the strength of inclusive association is stronger than that of hydrophobic one. The conclusion was proved by time-temperature superposition as well. It shows that the activation energy E _a of the inclusion complex (CD:BHAM = 2:1), which represents the strength of association, has a maximum value, while the activation energy E _b of P(AM/BHAM/NaA) has also a maximum one because of the multiple associative sites of hydrophobic associations. The activation energy values of the inclusion complex (CD:BHAM = 1:1) are intermediate since there are two kinds of associations in this solution. This is exactly the reason that the complex (CD:BHAM = 1:1) has the best emulsifying property. Moreover, the conclusions related to emulsifying property have been verified by using a laser particle size analyzer and Turbiscan lab stability.