Abstract: Machining represents a thermo-mechanical reaction based on factors such as plasticity, wear and friction. The experimental design consists of conducting a series of turning trials on a titanium alloy Ti6Al4V using combinations of cutting parameters namely spindle speed (n) of 770 rpm; feed rate (f) of 0.2 and 0.4 mm/rev; and depth of cut (d) of 1 and 2 mm. The length of cut (L) of 10 mm remains constant for all trials. All trails are done under dry conditions. In this paper, a detailed investigation has been carried out to study the temperature at shear zone and the effect of cutting variables on temperature has been evaluated. The temperature in shear zone for each trial was measured using an infrared thermal camera.
Abstract: The Teflon coating on the hardened aluminum surface is the process of creating a film on the smooth surface which requires three layers of coating and each layer must be cured at a certain temperature. Due to a complexity of the process, peel off defect is one of the intimidate defects in the coating process. The objective of this research is, therefore to determine optimal coating parameters in order to reduce the peel off. A robot attached with a spray gun at the end effector is used to spray Teflon onto the hardened aluminum work-piece. Typically, there are three steps coating process i.e. primer, middle, and top. In this research, only the prime coating layer is studied due to the fact that the peel off defect normally occurs from this layer. A curing temperature immediately after coating is one of the root causes besides air pressure, an angle of the spray gun and fan pattern. Therefore, the experimental design technique is used to determine the relationship among these mentioned variables and identify the optimal condition. The 2k factorial is used in the experimental design and analysis of variance is used to analyze the result. It is found that the optimal condition of curing temperature at 95 degree Celsius, air pressure at 2.5 bars, a gun angle at 60 degrees, and the fan size at 5 Volt setting at the robot controller provides a better result. The peel off defect is reduced from 2.88 to 1.60 percent.
Abstract: Nickel based alloys have found their wide range of applications in the automotive, oil and gas, and aerospace industries due to their excellent mechanical and thermal properties. However, these alloys impose greater challenges to conventional machining techniques due to their extreme hardness. Therefore, non-traditional machining process like micro-electro discharge machining, which is a non–contact machining process, comes into consideration. In this study, the machinability of Ni based X-alloy was investigated using micro-EDM process with the aid of coated and uncoated tools. From the experimental results, it was evident that the machining time was reduced with the increase of discharge energy for both the coated and uncoated tools. Increase in discharge energy also resulted in enlargement of entrance diameter and overcut. However, the non-conductive nature of coating caused in the reduction of overcut for machining using coated tools. The tool wear was found to reduce with the increase of discharge energy due to shorter machining time at higher discharge energy. Finally, crater size also increased with the increased discharge energy. The coated tools resulted in bigger crater sizes than uncoated tools at 1000 rpm, however, for higher tool rotation the difference was not significant.
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: Laser bonding welding test of the lap joint between steel and Al was conducted. The microstructure analysis is carried out by means of metallographic microscope, which provides an important theoretical and experimental basis for the popularization and application of laser welding of steel / aluminum dissimilar metal structures. The results showed that under the conditions of 1650W laser power, 35m/s welding speed, +3mm defocus amount and 25L/min flow rate of Ar as the protective gas, there are no cracks, pores and inclusions in the weld zone. The fusion line is smooth and smooth. Under the conditions of 1650W laser power, 38m/s welding speed, +3mm defocus amount and 25L/min flow rate of Ar as the protective gas, the overall appearance of the weld zone of the laser welding joint, there are serious cracks, pores and other defects in the weld area. In the P=1680W, V=35mm/s, f=+1mm, q=20L/min, the crystal structure appeared, in the process of cooling, the crack expands and forms a radial shape under the action of internal stress.
Abstract: The paper studies the technology of producing composite materials and coatings by means of high-velocity oxygen-fuel spraying (HVOF) in a protective atmosphere. We have developed technologies for the formation of nanostructured surface layers made of multicomponent materials in the conditions of high-velocity oxygen-fuel spraying in order to improve operational properties and expand functional capabilities of engineering products. We optimized technological parameters and constructed nomograph of the process. We described a modernized GLC-720 unit which implements the resource-saving technology for the formation of nanostructured surface layers on cylindrical details, and makes it possible to produce HVOF in a protective atmosphere and thermomechanical processing in a single technological cycle.
Abstract: In the paper we studied surface layered compositions "steel-TiNiCo-B4C-Co" with the use of materials with shape memory effect for rotor-screw propellers operating in Arctic conditions. We carried out the analysis of technological modes of surface modification, studied structural parameters of TiNiCo-B4C-Co composition. We demonstrated the functional-mechanical properties of the "steel-TiNiCo-B4C-Co" composition with preliminary thermomechanical treatment, which showed an increase in the durability of rotor-screw propellers with TiNiCo-B4C-Co surface composite layers.
Abstract: Unlike the conventional heat treatments, laser hardening process can selectively and locally harden the workpiece surface with minimum part distortion, thus making the process suitable for small or thin workpieces. To elucidate a better understanding of process performance, this paper presents an investigation of laser hardening process for AISI 420 martensitic stainless steel. A nanosecond pulse laser was used as a heat source to harden the metal surface. The effects of laser power scan overlap and scan speed on micro-hardness and case depth were experimentally examined. The results revealed that the micro-hardness of stainless steel surface increased from 242 HV to 1700 HV without any sign of surface melting. The depth of hardened layer was found to be 60-80 µm depending on laser power, scan speed and scan overlap applied. In addition, the scan overlap of 50% was recommended to lessen the deviation of micro-hardness across the laser-scanned area.
Abstract: Large temperature gradient was introduced to improve the removal rate of metal impurity in silicon ingot during direction solidification. The concentration of metal impurities in the silicon ingot with a large temperature gradient is 0.96 ppmw. The solidification time is reduced by 20% due to the fast speed of crystal growth improved; meanwhile the purity is increased by 64%.