PET polymer ablation using excimer laser for nozzle plate application

Abstract

Polyethylene terephthalate (PET) film drilling using a 248 nm excimer laser through photomask projection is presented. The parameter effects of laser fluence, shot number and repetition rate on the processing results are examined. A high quality microhole array with 50 μm thick PET film is fabricated. When the projection process is carried out, the diameter differences in the microhole in the front and back side of PET are observed. This causes a conical shape in the kerf. The formation of this conical shape in terms of the laser process parameters is discussed. The process parameter effects are investigated and characterised to improve the PET microhole laser machining quality.     

Interfacial reaction mode and its influence on tensile strength in laser joining Al alloy to Ti alloy

Abstract

In order to obtain a robust dissimilar joint of Al/Ti alloys, a filler wire of Al–12 wt-%Si and 45° V shape groove on the base metal were used during CO₂ laser welding. Heat input had evident influence on the interfacial reaction mode. It was found that a dissolution mode for low heat input and a melting mode for high heat input exist at the joint interface, which was analysed from thermodynamic point of view. Tensile strength of the joints in the dissolution mode reached as high as 296 MPa, which was significantly higher than that in the melting mode.     

Effect of laser fluence on surface microstructure of alumina ceramic

Abstract

The present study discusses the microstructure development during surface modifications of alumina ceramic using high power continuous wave Nd:YAG laser. Laser fluence influenced the microstructure in terms of changes in morphology and (1 1 0) crystallographic texture of the surface grains. The microstructural observations can be used to establish the guidelines for optimising the laser fluence to achieve the desired morphology of the surface grains and extent of texture in the surface modified alumina ceramic.     

Hydrodynamical phenomena in the process of laser welding and cutting

Abstract

The main objective of the paper is to outline the 'bridges' existing between the outcomes of fundamental researches and the results of investigations in the field of industrial laser materials processing (LMP). An analysis is presented on the models based on non-stationary hydrodynamic phenomena caused by deeply penetrating high power CW laser beam into materials. This is typical of laser welding (LW) and laser cutting (LC). A physical analysis pertaining to melt removal and melt layer instability mechanisms of gas jet assisted CW–CO₂ laser fusion cutting is presented. The models deliberated here are melt squeezing out by gas pressure gradient, melt dragging by the friction force between melt surface and gas flow, formation of moving shelves at the cutting front. In case of high laser intensity, radiative flux interacts with material causing dynamical thermal transport onto the surface and phase transition at solid–liquid–gas interfaces. The solution is based on the non-stationary variables. Under these conditions the Mach number varies significantly due to laser intensity associated with laser flux energy instabilities. The connection among material surface temperature, laser intensity, laser flux and pressure in the plasma cloud is brought out. In addition, novel mechanisms based on hydrodynamics are proposed.     

Laser welding of copper–nickel alloys: a numerical and experimental analysis

Abstract

Melt run trials were carried out on Cu–Ni bars using a CO₂ laser source in order to analyse the effects of welding parameters (i.e. laser power, welding speed) on geometrical characteristics and on the microstructure of the bead. Experimental results were then used to determine the source parameters to be employed in a finite element model (FEM) of the welding process, with particular attention paid to the thermal field induced by the laser beam. A specific procedure, named 'automatic remeshing technique', was used in order to minimise the computation time. The aim was to create a reliable numerical model, suitable for the optimisation, in practical cases, of welding processes of these kinds of materials. A good correlation, in terms of predicted cooling rates, with the values calculated from SDAS measurements, was observed.     

Method for welding highly crack susceptible magnesium alloy ZK60

Abstract

The highly crack susceptible magnesium alloy ZK60 plates of 2 mm thickness were successfully welded by laser beam welding (LBW) with filler strip, which has the advantages of low heat input and capability of adjusting the compositions of weld metal to a less susceptible level. The effects of the compositions of filler strips on the microstructures and mechanical properties of the joints were investigated. Compared with autogenous LBW, LBW with filler strip can produce a narrower joint and avoid the cracks and pits, which severely worsen mechanical properties of the joints. When the filler strip of ZK40 alloy is employed, the grains in fusion zone can be refined, and a high quality joint, with the ultimate tensile strength of 322 MPa up to 90·7% of the base metal, is obtained.     

Welded seam 3D calculation and seam location for welding robot system

Abstract

Using laser scanning techniques, scanning lens rotating around a laser diode and a circular laser trajectory was projected onto the surface of a weldment to detect it. Furthermore, one novel vision sensor based on the circular laser is developed. The three-dimensional (3D), circular laser based seam location sensor is investigated. On the basis of the light path system, 3D calculation algorithm is brought forward and used to locate the welded joint. After image denoise, filter, segmentation and thinning, characteristic points of the welded joint could be detected real time using a proposed vision sensor and confirmed by real experiments of butt welded joints with I groove and V groove, and lap, and fillet and ramp welded joints. The results show that circular laser based vision sensor can be used in seam locating and its calculation precision meets the requirement of seam tracking.     

Effects of Laser Irradiation on Surface Properties of Poly(ethylene terephthalate)

The influence of the ArF laser irradiation on the surface energy of poly(ethylene terephthalate) was investigated. An effort was also made to elucidate the physical and chemical phenomena affecting surface energy (SE). The surface chemical changes, occurring upon the irradiation, were monitored by X-ray photoelectron spectroscopy (XPS) and the changes in the surface geometrical structure were investigated by atomic force microscopy (AFM). The contact angle values obtained with test liquids of different polarity (water and diiodomethane) were measured while the surface energy was calculated by the Owens–Wendt method. The nature of the physico-chemical changes occurring in the poly(ethylene terephthalate) surface layer upon ArF laser irradiation depended mostly on the energy per unit area of the laser pulse and the number of the laser pulses. The polar and dispersive components of the surface energy increased as a result of increasing the number of the laser pulses of energy which were below that of the PET ablation threshold.