Advanced Materials Research Vols. 264-265

Abstract: A theoretical analysis was carried out to investigate the characteristics of plasma arc injected transverse to a transverse-alternating magnetic field. Two mathematical models were developed to describe both the oscillating amplitude of the plasma arc root and the heat flux density distribution of plasma arc on the workpiece surface. The characteristic of plasma arc under the external transverse-alternating magnetic field imposed perpendicular to the plasma current was discussed. The effect of processing parameters, such as working gas flux, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the oscillation and heat flux distribution of plasma arc were also analyzed. The results show that it is feasible to adjust the shape and heat flux density of the plasma arc by the transverse alternating magnetic field, which expands the region of plasma arc thermal treatment and uniforms the heat flux density upon the workpiece. Furthermore, the oscillating amplitude of plasma arc decreases, and the heat flux density gradient upon the workpiece increases with decrease of the magnetic flux density. Under the same magnetic flux density, more gas flux and more arc current cause the oscillating amplitude to decrease. The researches have provided a deeper understanding of adjusting of plasma arc characteristics.

Abstract: Titanium alloys have been widely used in industries, especially aerospace, energy and medical industries, due to their good mechanical and chemical properties. However, titanium alloys are typically difficult-to-cut materials. Milling induced surface integrity, including anisotropic surface roughness, residual stress, surface microstructure alterations and microhardness, has received little attention. This work investigated the effect of machining conditions, especially the federate, on surface integrity of workpiece of Ti-6Al-4V alloy machined using high speed ball end milling process. The experimental tests were performed at various cutting parameters and carried out in dry conditions on a vertical five-axis CNC milling machine, using a coated carbide tool. Surface finish was studied based on 3D topographic maps and microhardness depth profiles beneath the machined surface. Microstructure of the sub-machined surface was observed using an optical microscope in order to investigate the metallurgical deformation. X-ray diffraction analysis is performed to obtain the residual stress distribution beneath the surface.

Abstract: This paper presents an approach to utilize high precision pulsed Nd:YAG laser to fabricate a rough array-pattern on a soda-lime glass plate by a laser-induced backside writing (LIBW) process, and a laser-induced plasma assisted ablation (LIPAA) technique. The current study investigates the effect of process parameters such as single-shot laser exposure time and number of passes on the material removal rate. After depositing 695 nm thick Teflon thin film on the glass plate, the surface of the laser micro-machined template becomes hydrophobic. The surface roughness, annular groove profile and surface micrograph were measured by an atomic force microscope, a profilometer, and a scanning electron microscope, respectively. A uniform liquid droplet by the sessile drop method is generated on the hydrophobic template. Droplet characteristics, such as contacted angle, size, and shape, are measured with a surface tension analyzer and microscope. This work also discusses the relationship between the formed droplets and the process recipe of the micro-machined template. The proposed approach can apply to future for uniform lens array formation.

Abstract: Treatment of alloy steels at cryogenic temperatures increases their wear resistance, which is an important consideration in industrial applications. The treatment of metal samples is performed in a dedicated cryogenic processor, with provisions for precise time/temperature control of the samples on the basis of pre-defined temperature protocols. There is little information on the design and construction of cryogenic processors in the open literature. In this paper, development of a simple and inexpensive programmable processor for treatment of metals at cryogenic temperatures has been presented. Considerations for the selection of suitable cooling method and reduction of liquid nitrogen consumption have been discussed. To demonstrate the usefulness of this processor, a metal sample has been cryotreated. Results of the treatment show a more uniform microstructure and less retained austenite in the treated metal sample, which is due to the transformation of most of austenite into the harder martensite phase. Overall results show that the design methodology presented in this paper can be adopted by other researchers for constructing similar processors for studying the effect of cryogenic temperatures on enhancement of wear resistance and other mechanical properties in metals.

Abstract: A thermal fracture process applied to the brittle materials has become a foremost technology, and applied to cut the LCD glass substrate. One advantage of this process is that the cross-section of cut glass substrate will be smooth with low residual stress after thermal fracture processing. The multi-sphere mirror aims to repeatedly reflect the light energy within upper and lower mirror in order to enhance the laser beam absorption rate of glass under cutting. Moreover, with a proper design of multi-sphere mirror, the energy distribution of applied laser can provide an ideal thermal fracture condition to improve cutting speed of glass substrate. A novel reflective mirror with multi-sphere surface was developed and reported to transform the regular laser energy distribution toward the ideal one. Furthermore, the shape of multi-sphere mirror is optimized by Taguchi method so as to meet the surface requirement that can get the ideal energy distribution. This paper presents a series of simulation results and analysis results of multi-sphere mirror calculated by the TracePro opto-mechanical software.

Abstract: Thermal fracture-cutting technology (TFCT) for brittle materials has become the main technology for LCD glass substrate cutting to meet the low residual thermal stresses requirement. Based on the thermal weight function principle of fracture mechanics, this paper presents thermal weight function distributions for the mode-I and mode-II fracture model, and the fracture phenomenon under a variety of cutting paths, such as tilt crack, split crack, twist crack, and local buckling.

Abstract: The aim of this study is to investigate the effect of scan speed and frequency on surface roughness and engraving depth of AISI H13 hot work tool steel. The experimental studies were conducted by fiber laser marker machine. The relationship between the parameters is showed that the highest surface roughness and depth values were achieved at lowest scan speed (125mm/s). The depth and surface roughness of engraved geometry was decreased at increase in scan speed. It was concluded that, the surface roughness and depth can be controlled by scan speed and frequency.

Abstract: The effects of laser machining process parameters namely, scan speed and frequency on wear performance of AISI H13 hot work tool steel were investigated in this study. The process parameters are combined with wear process factors and the responses of wear tests were evaluated. The results showed that both friction coefficient and wear rate are affected by process parameters. The average friction coefficient and wear rate increased with an increase in frequency at each set of scan speed. Lowest scan speed and highest frequency produced higher surface roughness and rough texture form.

Abstract: CO2 laser - Metal Inert Gas (MIG) hybrid welding process was investigated in the butt welding of Ti-6Al-4V titanium alloy sheets of 3.0mm in thickness. Using a Design of Experiment (DoE) approach, bead on plate tests were planned with the aim to analyze the effect of laser and laser-MIG welding parameters on the bead shape, hardness profiles in the weld cross section and welding efficiency. Butt welds performed in correspondence of the bead on plate working conditions which assure the complete penetration of the samples, the absence of undercuts and the maximum welding efficiency, confirm the results of the bead on plate tests and highlights the gap bridging ability of the hybrid welding process.

Abstract: The high strength to weight ratio and good corrosion resistance of titanium alloys, have led to an increasing use of these materials, particularly in the aerospace industry. The laser cutting technique may be a promising tool in machining titanium alloy parts like those with subsequent welding requirement: in this case, surface quality of the kerf edges is of great importance. The low thermal conductivity and the high chemical activity of titanium alloys lead, in fact, to alterations of the surface properties of the machined zone. This paper presents the results of titanium alloy laser cutting using a 2 kW fiber laser. The cutting process was performed in continuous wave mode and using Argon as shear gas. Laser cuts were realized on titanium alloy Ti6Al4V sheets 1mm thick. Image analysis and microscopy, were carried out to examine the cutting edge quality features including thickness of the recast layer and heat-affected zone.