Key Engineering Materials Vols. 656-657

Abstract: Currently, there are several methods for indicating wear of the steel ball and screw shaft components of CNC machining centres. These include wear prediction of the steel ball and screw shaft of the ball screw by using the value of backlash. This value, generally, has to be determined using expensive equipment such as a laser interferometer or a ball bar. In order to reduce the monitoring cost of ball screw wear, especially steel ball wear, a new monitoring technique is introduced. This technique was developed from a correlation between steel ball wear and the surface roughness of the machined surface of a test piece. In this research, the balls were subjected to artificial wear which were achieved by using a barrel tumbling process. Experimental results indicated that ball wear causes increase in surface roughness of a machined test piece. Employing these results, an equation for estimating steel ball wear was developed. Research results also showed that this new technique can reduce monitoring cost significantly compared with the cost of conventional methods.

Abstract: A nanoscale polish process with improved desired characteristics of low roughness and low scratch counts has been developed using a novel polish tape and diamond abrasive on hard glass substrates. For an improved polishing performance with high removal rate properties and preventing scratches, a novel tape was developed having a nanofiber level, densified surface and a flatter surface by slenderizing the fiber and dispersing ultrafine fiber using an innovative technique. Using this novel polishing tape with a fiber size of 200nm, one can produce a 17% lower surface roughness (Ra) (from 1.05A to 0.87A) and a reduced polished surface scratch count of 53 reduced to 18. The novel nanocluster diamond abrasive is synthesized from carbon atoms of explosives created by detonation in a closed chamber under an oxygen leaked atmosphere ambient. Several crystals are bonded together by layers of non-diamond carbon and other elements, forming aggregates with a nanocluster structure. Using this novel nanocluster diamond along with an ultra-fine diamond mixture with a nominal size of 15nm, one is able to produce an improvement of a 48% lower surface roughness Ra (from 0.87A to 0.45A) and a lower polishing surface scratch count reduced from 18 to 7. Overall, these results indicate that a smoother and a reduced scratch polished substrate results in a significant improvement in disk defects and related magnetic performances.

Abstract: The resistance spot weld (RSW) of dissimilar materials betweeen steel and aluminium is generally more complex than that of similar materials due to the extreme differences in the mechanical, physical and chemical properties of the base metals. This study proposed the use of filler material to connect the differences of their properties. Al-Alloy 5083 with thickness of 4 mm and 1.2 mm thick carbon steel SS400 were joined in lap joint types using RSW with the filler materials. The filler materials were a mixture of steel and aluminium in which weight composition variations (Fe:Al) were 90:10; 70:30; 30:70 and 90:10 in percent. The physical properties were examined based on the microstructure using optical microscope while the mechanical properties were measured with respect to the strength and hardness using Universal Testing Machine and Vickers Microhardness respectively. Results showed that weld metals with filler composition of 70:30% had highest shear-strength. The microstructure examinations showed that Microstructure of base metal and HAZ carbon steel was ferrite and perlite while that of weld metal was bainite. There were no significant differences in the microstructures and the hardness of weld metal, HAZ, and the base metal of aluminium alloy-5083 due to nonheat-treatable material.

Abstract: Electric arc furnace dust is a byproduct from steelmaking, contained up to 50%wt of zinc ferrite. It also contains about 10-20%wt of zinc oxide and the other metal oxides. Approximately 100,000 tons of EAF dust are generated per annum within Thailand. All of the dust has been sent to landfill. The objective of this research is to investigate the kinetics mechanism of the decomposition of zinc ferrite in EAF dust to obtain zinc oxide and iron oxide by using iron powder as a reducing agent. The process was carried out by mixing zinc ferrite or EAF dust with iron powder then compressed them in a mold. The samples from compression were treated by pyrometallurgical process. The factors required to be concerned were temperatures, particle sizes of iron powder, and mole ratios of zinc ferrite per iron powder, respectively. The treated samples were analyzed by X-ray diffraction (XRD) in order to characterize zinc ferrite phase transformation. It was found that the quantity of zinc ferrite, both either pure zinc ferrite and zinc ferrite in EAF dust, were decreased after treating by the pyrometallurgical process when increasing treating time from 30 to 180 minutes at 600°C, the particle size of iron powder at 10 micron, and the mole ratio of zinc ferrite per iron powder at 1:3. Moreover about 70%wt of zinc ferrite was decomposed and the products obtained were zinc oxides (ZnO) and iron oxides (Fe₃O₄, FeO, Fe₂O₃). The reduction of zinc ferrite with iron powder was well-defined taking place by diffusion thru product layer control. The activation energy of the reduction process was found to be 47.21±2.83 kJ/mol. Therefore, the decomposition of zinc ferrite by iron powder could be carried out at 1 atm with low pyrometallurgical temperature (600°C) and equipped with hydrometallurgical process to obtain high zinc yield.

Abstract: Belonging to the class of chromium tool steels, AISI H11 possesses very good toughness and hardness, and is therefore suitable for hot metalforming jobs performed at very high loads. Mostly used in fabrication of helicopter rotor blades, H11 also has great potential as a die steel in hot-work forging and extrusion. This alloy steel can be heat treated to increase the service life and dimensional accuracy of the die and tooling. Main aim of the current investigation was to formulate an optimum heat treatment strategy for H11 steel, especially for hot work applications. High-speed milling and electric discharge machining were used to fabricate samples for tensile and impact testing. After various types of heat treatment (annealing, austenitizing, air cooling or oil quenching, single and double tempering), these samples were tested for hardness, toughness (impact), yield strength, tensile strength, and ductility. Microstructural analysis was also performed to analyze the effect of heat treatment on mechanical properties. As tempering temperature increases, hardness initially increases and then starts to gradually decrease; impact strength first decreases and then increases; and yield strength exhibits a fluctuating pattern of initial decline followed by an increase and another decrease. Even though H11 steel is highly suitable for both hot and cold-work, it is surprisingly not a common choice for metalworking dies and tools. Results presented here can encourage die designers and hot-work practitioners to explore the versatility of this tool steel, and to adopt appropriate heat treatment strategies for different applications.

Abstract: Direct metal lamination using arc discharge was applied to the repair of metal components such as metallic parts, dies and molds by adding equivalent metal to them. In this method, a heat-affected zone which has different mechanical properties from the base metal is formed near the laminated metal. This is because the rapid temperature change by welding heat input can cause phase transformation or metallic structure change. Therefore, the mechanical properties of the laminated metal, heat-affected zone and base metal after repair by direct metal lamination need to be explored. In addition, the region which needs to be repaired must be removed in advance because worn and defective parts aren’t adequate as the base for lamination of further layers. Thus, the most suitable removal shape for repair by direct metal lamination was investigated. Finally, the hardness distribution and toughness of the metal components after repair was explored. It was found that the hardness distribution of metal components after repair was uneven. However, the toughness of the heat-affected zone was found to be comparable to those of the laminated metal and the base metal.

Abstract: In this study, we investigated the possibility of smoothing a GaN substrate utilizing ultraviolet (UV) assisted polishing method in potassium hydroxide (KOH) solution. In this polishing method, GaN substrate was excited by an UV radiation, and then an oxide layer on the GaN substrate was formed by photochemical reaction. Simultaneously, generated oxide layer was removed by synthetic quartz tool and chemically etched by KOH solution. Finally, smoothed GaN surface could be realized. The surface quality and removal depth were measured and evaluated using a scanning white light interferometer and Normalski type differential interference microscopy. Obtained results show that the surface morphology and the removal rate are strongly dependent on the existence of the UV irradiation. Moreover, the processed surface has revealed that many scratches on the preprocessed GaN surface could be completely removed. The microroughness of the processed GaN surface profile was improved to be 0.18 nm (Rms), 1.06 nm (Rz).

Abstract: A production-scale multiwire saw machine and 4 inch sapphire ingots were used in this study. The diamond wire used in the study had a core diameter of 0.1mm with an attached diamond particle size of 8–12μm. This study uses the Taguchi method and Grey relational analysis on the key diamond wire parameters which are electroplated nickel layer thickness, diamond wire tension, diamond wire speed and sapphire ingot feed rate, in order to simultaneously optimize the cutting performance in the diamond wire sawing of sapphire ingots. Based on the analysis, the nickel layer thickness and wire speed are the first and second most significant factors with 31.7 and 29.9% effects on cutting performances. The optimal control factors were then simultaneously evaluated for Ra, material removal rate, diamond wire wear rate and TTV and were found at optimization to be 14 μm nickel layer thickness, 15NT wire tension, 800m/min wire speed and 0.2mm/min feed rate, respectively. Compared with current standard condition, this improved process obtained from the optimization of diamond wire electroplated nickel layer thickness and saw machine parameters in the diamond wire sawing of sapphire ingots can achieve a 33% lower Ra, a 20% lower diamond wear rate, a 13% lower TTV and a 20% higher material removal rate, simultaneously.

Abstract: The sulfur granulation roller (rotoformer) mechanism and cooling steel conveyor is important clusters in sulfur granulation system. This paper presents method to design rotoformer, apply goal: create a continuous pressure for a regular granulation on steel conveyor. There are also mechanism that granulates and maintains temperature so that sulfur is not stuck and not solidify in the supplying pipes. Moreover, this paper shows the solution to cool the steel conveyor, filter system has temperature sensors which ensure the decreasing of temperature over the length of steel conveyor. This will help the granulation of sulfur, formed sulfur will has right size and shape.

Abstract: Glass materials are widely used in products such as optical components and semiconductor devices. In these products, precision welding techniques of glass are required to manufacture small and complicated shape. The laser welding method can perform the joining without an intermediate layer and an adhesive agent. In addition, an ultra-short pulse laser can reduce the heat affected zone with the high space accuracy. However, heating and cooling cycles are repeated even in the case of ultra-short pulsed laser. The temperature distribution and change of molten area are influenced not only by laser energy condition but also focusing condition. Therefore in this study, effects of focusing condition of laser beam on micro-welding characteristics of glass were experimentally investigated by using a picosecond pulsed laser. A usage of object lens with the spherical aberration correction led to a large molten area even at the same pulse energy, which related to the efficient welding of glass materials. An optical system with the spherical aberration correction led to stabilizing the shape of molten area, which resulted in the reliable weld joint.