Papers by Keyword: Surface Finish

Abstract: This article presents preliminary investigations on the cutting ability of the singer layer metal-bonded cBN grinding wheel manufactured by electroplating method at Vietnamese laboratory. The cutting ability of the grinding wheel is evaluated by two factors: grinding ratio G and surface roughness of workpiece. These results are compared to those of the Japanese grinding wheels. The experimental results showed that the fabricated cBN grinding wheel has good cutting ability with high grinding ratio G. The value of the grinding ratio was 600 to 1800 in the grinding process of SKD11 steel (hardness of 62-63HRC) at the grinding speed V of 12.56m/s, feed rate S of 300mm/min, depth of cut t of 0.01mm. The maximum grinding ratio (1800) is equivalent to the average grinding ratio of the Japanese grinding wheel. The grinding ratio is also maintained up to 26 cutting hours. The good grinding surface was achieved with the average Ra of 2.5μm. In addition, the bonding of cBN abrasive to the wheel body was observed with scanning electron microscope (SEM) of the surface of grinding wheel after the cutting process. The SEM image shown that the cBN abrasive particles were not removed from the wheel surface.

Abstract: Carbon fiber reinforced plastics (CFRP) has been widely used in various aircraft structural components. However, it is difficult for conventional methods such as drilling and helical milling to meet the requirements on high quality and efficient holes creation. Hence a so-called tilt helical milling (THM) method has been proposed. This new method is performed by replacing the revolving motion of the tool in conventional helical milling (CHM) with a conical pendulum motion, in which the tool axis is tilted towards the hole axis at a certain angle. As a step toward the establishment of the new method, in this work, the fundamental drilling characteristics of CFRP by the THM is elucidated by experimentally investigating the effects of tilt angle on thrust force and delamination factor. The obtained experimental results demonstrated that thrust force and delamination factor can be reduced with THM technique. In addition, THM can achieve better hole surface finish than CHM.

Abstract: Electro discharge machining (EDM) as a die sinking process has taken off in 1943. Since then it was known as a non-conventional machining process and its application was limited for processing only electrically conductive materials. Later on, due to the widespread applications, this EDM process is considered conventional as usual. However, in the recent years EDM has gone through considerable changes especially with dielectric fluids, simple to complex geometry, meso to micro sized structures, nanometric surface finish, and so on. In addition, the application of EDM has also been extended for processing electrically semi-conductive and non-conductive materials like ceramics and composites. This paper discussed micro electro discharge machining of non-conductive ceramic materials. It includes detail process development, modelling of material removal rate and surface finish which include the effect of multi spark and random spalling conditions.

Abstract: Surface finish plays a critical role in functional performance of machined components. This study investigates machining finish of Ti-6Al-4V alloy prepared by Additive Manufacturing (AM) with a series of slot-milling experiments. The study compares the machined AMed part with that made of the conventional wrought Ti-6Al-4V. The microstructure of AMed parts is acicular α and Widmanstatten α lath structures compared to lamellar α structure of that in the wrought parts. Due to the unique microstructure from AM process, the AMed parts present higher strength and lower ductility. Therefore, a lower surface roughness is obtained in the milling of AMed parts compared to its counterpart of wrought parts. In addition, the machined surface of AMed parts possesses a topography of discontinued ridges. It is believed that the topography is due to low ductility of AMed part. The results show that the machined AMed part presents better surface finish. The study provides a guidance to optimization of machining parameters for AMed Ti-6Al-4V alloys.

Abstract: Bronze based alloys have come to be used as bearing materials, and require low frictional properties. The present study describes the effects of surface finish machining history on the on tribological properties of sulfide-containing bronze sintered onto a steel disc. The sulfide phase consisted of copper, iron and sulfur, and acted as a solid lubricant. The relative density of the specimen was 90 % and the microstructure showed that the micro-sized sulfide dispersed into the bronze matrix and was accompanied by pores. Various processes, including cutting, burnishing, polishing were, applied to finish the surface. It was found that the area fraction of the sulfide phase depended on the cutting conditions. A further increase in the area fraction was achieved using roller burnishing after the cutting. Tribological properties were evaluated using chromium alloy steel (SUJ2) as the mating surface under dry conditions. The results showed that the friction coefficient depended on the surface finishing process. Therefore, the machining history had an effect on the frictional properties of the sulfide-containing bronze. Optimal cutting conditions for the sulfide containing bronze are also discussed.

Abstract: Micro milling is discussed to fabricate micro-scale structures on titanium alloy thin wires. A machine tool was developed to conduct the milling operations with improving the clamping stiffness. A 0.3 mm diameter wire inserted into polyurethane tubes was clamped on an R-shaped groove on the machine table. The cutting tests were conducted with or without the polyurethane tube support. The machining shapes, the surface finishes and the cutting forces were measured to verify the effect of the polyurethane tube and machine table clamping system on stability in the cutting process. The groove direction is out of the feed direction of the end mill without the polyurethane tube support. The micro grooves are machined properly with a fine surface in the feed direction with the support. The cutting forces change periodically with the cutting thickness and the rotation of the cutter in milling. Non-symmetric grooves are also machined with the developed clamping system.

Abstract: A great deal of effort and research has been dedicated to recycled aluminum alloys, mainly to recycling processes and to the mechanical properties of recomposed parts; however, very limited work has been oriented towards the machinability of recycled aluminum materials. Recycled and recomposed aluminum parts sometimes need machining to obtain the final usable part shape and for assembly purposes. The acceptability of using recycled materials in design and engineering applications depends not only on their mechanical properties, but also on their machinability. This paper investigates the machinability of recycled aluminum alloys based on surface finish, cutting forces and chip formation. Two recycled foundry aluminum alloys were used: one from aluminum can covers and another from aluminum chips produced during machining. The machining operations investigated included turning and drilling under dry and wet conditions. The two tested recycled aluminum alloys showed different machinability behaviors and different part quality characteristics, suggesting that it would be desirable to consider separating aluminum wastes and chips considered for recycling by origin or type prior to melting and recasting.

Abstract: Machining of titanium alloys generates enormous amount of heat at the chip-tool interface leading to poor machinability. Use of coolants in the form of gas based lubricants is another approach for controlling the temperature at the cutting zone. The current research investigates the effect of gaseous cooling using CO₂ and cryogenic cooling using LN₂ at the tool rake face during machining of Ti6Al4V. The effect of both the cutting environments was analyzed at low and high level of cutting conditions through FE Model highlighting on thermal softening and through the experimental output responses emphasizing on cutting forces, surface finish and chip microstructure, etc.

Abstract: The formation and growth of the intermetallic were frequently discussed since lead free solder took place replacing the lead solder. However, the effect of multiple reflow process on the intermetallic morphology that was subjected to aging still needs further investigation. Thus, this study aimed to investigate the effect of second reflow towards the intermetallic compound formation and growth. Two types of surface finishes were used such as Immersion Tin (ImSn) and Electroless Nickel Immersion Gold (ENIG). Both test boards were reflowed once with Sn-3Ag-0.5Cu at the temperature of 225 °C and soaking for 8 seconds. Then, they were reflowed again at the same temperature for 25 minutes prior to an isothermal aging process for 250, 500, 1000 and 2000 hours at the temperature of 150 °C. The ProgRes C3 IM7200 Optical Microscope and ImageJ were used for the microstructural study, which includes morphology and thickness. Results indicated that IMC thickness formed between solder and ImSn surface finish increased significantly with 1.28 µm incremental when exposed to the second reflow. Whereas the IMC thickness of ENIG surface finish was increased for up to 0.15 µm. In addition, ENIG showed higher activation energy as compared to ImSn.

Abstract: Surface finishes on copper pads have been known to be one of influential factor in the solder joint quality. This due to the difference in interfacial reaction and intermetallic compound formation on solder pad was strongly influence by the type of surface finishes. Deposition times during immersion plating process on copper pads are important as the thickness of coating will decide several properties of surface finish, such as wettability during soldering process. Thus, this study aims to investigate the effect of deposition time of immersion gold coating on wettability of the surface finish and how it affect the formation of intermetallic compounds on solder joint. In this works, deposition time of copper pads in immersion gold solution were varied from 3 minutes up to 15 minutes. The thickness of immersion gold layer that form on Cu pads were then measured using Scanning Electron Microscopy (SEM). As the main objective of this study is to study the effect of deposition time during immersion plating process towards solder joint, the pads were reflowed along with Sn-3.0Ag-0.5Cu solder in furnace under temperature 250 °C for 25 minutes. Then, the cross sections of the solder joints were examined using optical microscope in order to measure the wetting angle and thickness of intermetallic compound formed; which acceptable value in industrial area, should be below 40 ̊ and below 4μm as reflow respectively.