Advanced Materials Research Vol. 445

Abstract: This paper describes the development of a computer model used to analyze the heat flow during pulsed Nd:YAG laser spot welding of dissimilar metals; stainless steel AISI 302 to low carbon steel AISI 1008. The model is built using ANSYS FLUENT 6.3 software where almost all the environments simulated to be similar to the experimental environments. A simulation analysis was implemented, based on conduction heat transfer, out of the key hole where no melting occurs. The effect of laser power and pulse duration was studied. Four peak powers 5, 5.5, 6.5 and 7 kW were varied during pulsed laser spot welding (keeping the energy constant), also the effect of four pulse durations 5, 6, 6.5 and 7 ms (with constant peak power), on the transient temperature distribution and weld pool dimensions was predicted ,using the present simulation. It was found that the present simulation model can give an indication for choosing the suitable laser parameters (i.e. pulse duration, peak power) during pulsed laser spot welding of dissimilar metals.

Abstract: The paper presents pulsed Nd:YAG laser welding of the 304 stainless steels. The welding tests were carried out with various operational parameters. The effects of laser welding variables on the geometry, microstructure and solidification of the weld are considered. The austenitic or ferritic solidification is produced in the 304 austenitic stainless steel depended upon the cooling rate and its chemical compositions. The possiblity of austenitic solidification compared with the ferritic solidification decreases with the chromium to nickel equivalent ratio and that increases with cooling rates. Moreover, more δ ferrite is obtained if the cooling rate is increased or the higher power laser is used. The surface of fracture samples was considered and the reason for failure was investigated. The study shows that the fracture is in ductile type.

Abstract: The study was conducted to investigate the effects of laser beam position on the weld microstructure of AISI 630 and AISI 321 stainless steels. The optical and scanning electron microscopy and x-ray diffraction of the weld microstructures were carried out. The results showed that if the laser beam was focused at the interface, austenite, marensite and ferrite microstructures were formed at the weld region. If the laser beam was focused toward the AISI 630 stainless steel denoted as sample P in the manuscript, the martensitic-ferritic microstructures were produced in the weld cross section. If the laser beam was focused toward the AISI 321 stainless steel designated as sample A in the text, the austenitic microstructure was produced in the weld bead. The maximum hardness in all samples was occurred at the AISI 630 interface.

Abstract: This research aims to establish the influence of different factors on the dimensions accuracy in laser cutting. Samples with different thickness were made of DC01 EN 10130 steel. On each sample 32 round or square holes were cut in 4 rows by different laser beam movement schemes linear, zig-zag and random. The tests were made by pulse CO₂ laser with regimes, recommended for each sheet thickness, by the machine operating manual. The diameters of the round holes and the dimensions of the square holes along the laser head and the table axes were measured by a projector. The varying intervals of the dimensions and the shape deviations were calculated. It was established that three groups of factors influence on the dimensions accuracy in laser cutting: factors, related to the machine, laser parameters power, laser cutting speed and focus distance, determining the technological process parameters, and the material characteristics thermal physical properties and sample sizes. Factors, related to the machine, exert effect mainly on the intervals of dimensions varying, while the laser parameters and the material properties influence on the dimensions value independently of the cutting scheme. In the all laser cutting schemes the increasing of the sample thickness leads to the larger interval of the dimensions varying and increasing of the shape deviation. Nomenclature

Abstract: This paper presents a fast fabrication process of microfluidic channels with quartz substrates. Microchannels were ablated on the surface of quartz samples with a CO₂ laser. Double sided Pressure Sensitive Adhesive (PSA) was applied to bond the samples with scribed microchannels to flat glass sheets. Dimensions of the fabricated channels were characterised with optical microscopy and laser profilometry. The recorded data was modelled with a BoxBehnken experiment design using Response Surface Methodology. Characterisation included also the measurement of optical transmission through the processed glass and measurement of flow rate through the fabricated channels. With an average width of 165 µm and depth of 280µm, fabricated channels had appropriate dimensions for a range of microfluidic applications. A significant width of the laser processed channels provided 100% transmission for a wide range of the optical spectrum. These fabricated channels were also shown to not significantly retard the fluid flow rate thus making these channels applicable for integration into numerous detection systems for chemical separation applications.

Abstract: Laser cutting of aluminum-silicon sheet is carried out. The influence of laser output power on the kerf width is examined in details. The lump parameter analysis is introduced to predict the kerf width size. The percentage of kerf width size variation due to different laser output power levels is formulated. It is found that the kerf width size predicted agrees well with the experimental data. The influence of laser output power on the kerf width size is more pronounced for power levels 350 W. Keywords: laser cutting, aluminum-silicon, kerf width

Abstract: Parameters on a CO₂ laser machine effects the variations on hole diameters. In this study, a CO₂ laser machine is used for drilling processes. Processing parameters are selected between 1.2-4 mm workpiece thickness, 2500-4000 W laser output power, -4 to 2 laser focus setting, 8-14 bar assisted gas pressure and 500-1200 Hz laser frequency. After the drilling process, with the diameter measurements, pictures were taken with an optic microscope then the effect of the processing parameters on hole diameter variations were investigated.

Abstract: Laser welding of plastic materials has a wide range of applications in the packaging, medical, electronics and automobile industries provided it can predict high quality welds compared with other joining methods. Laser welding process parameters can affect the quality of welds. In this paper, Artificial Neural Network (ANN) is used to model the effects of laser power, welding speed, clamp pressure and stand-off distance on weld lap-shear strength in laser transmission welding (LTW) of acrylic (polymathy methacrylate). A set of experimental data on diode laser weld lap-shear strengths was used to train and test the ANN from which the neurons relations were gradually extracted to develop a model. The developed ANN model can be used for the analysis and prediction of the complex relationships between the above mentioned process parameters and weld lap-shear strength. The results indicated that increase in laser power and clamp pressure increases the weld lap-shear strength whereas welding speed and stand off distance had a decreasing affect on shear strength at high value.

Abstract: In the present study, hydroxyapatite was synthesized from local gypsum by microwave-hydrothermal method. Different percentage amounts of zirconia (0, 20, 30 and 40 wt.%) and poly-methyl methacrylate (40, 50 and 60 wt.%) mixed with hydroxyapatite (HA) for six hours. These powder mixture were deposited using deposition machine to produce specimens. These specimens were sintered at a temperature of 140°C with holding time for 1 hour into the green parts. These green parts were sintered at temperature of 1450°C with holding time for 2 hours. This process produces porous hydroxyapatite-zirconia composites with porosity between 62.76-73.92 percent. These composites were examined by XRD, XRF, SEM-EDX, BET analysis and compressive strength testing. Compressive strength of porous hidroxyapatite-zirconia composite decreased from 3.706 to 0.039 MPa when percentage amounts of zirconia increased up to 40 wt.%. This caused by several factors i.e. increased porosity, grain zirconia cracked, zirconia reacted with HA to produce CaZrO₃, β-TCP and α-TCP, HA matrix cracks because of the phase change of tetragonal-zirconia into monoclinic-zirconia.

Abstract: In this work, biodegradable polymer was prepared from thermoplastic sago starch (TPSS) plasticized with glycerol. In order to improve the properties of the TPSS, Montmorillonite (MMT), a kind of reinforced additive was used in the preparation of montmorillonite-reinforced thermoplastic sago starch (MTRSS) composites via hot pressing method. The fabricated samples were investigated through X-ray diffractometry, Fourier transform infrared (FT-IR) as well as thermal and morphological properties. FT-IR patterns show that in the MTRSS composites, the C-O groups of sago starch molecules shifted to higher wave number, while the reactive hydroxyl groups of MMT shifted to the lower wavenumber. On the other hand, X-ray diffraction revealed that MMT restrained the crystallization of MTRSS and intercalated in TPSS. Thermogravimetric analysis (TGA) revealed that the thermal stability of MTRSS was better than those of TPSS. In addition, the scanning electron micrograph results show that MMT were uniformly dispersed in the TPSS.