1,721,038 research outputs found
Experimental approach to UV-laser ablation in drilling of CFRPs
No full textThis paper deals with the application of Nd-YAG laser emitting at 355nm to the drilling
process of Carbon Fiber Reinforced Polyetheretherkethone (PEEK-CF) laminates.
The combination of a modern UV-laser source with a scanning technology enabling
deflection speeds up to 2m/s, suppresses heat affected zones (HAZ) and
consequently detachment of fibers from the polymer matrix. The results show that
minimum HAZ (about 50 μm) is achievable in machining of CFRP composite by using
short pulsed UV laser. The study found that heat is easily accumulated in the material
during laser processing, especially when the carbon fibres are chopped into small
pieces. The paper discusses how to make use of the heat accumulation and how to
avoid its potential damage to the workpiece by modulating the energy density input.
Hatching of superimposed layers of materials is proposed as alternative technique to
trepanning for drilling 1 mm to 5 mm holes on a 2.5 mm thick PEEK-CF laminate
Experimental study on the development of a micro-drilling cycle using ultrashort laser pulses
Full text linkMicroholes for the production of high precision devices were obtained by ultrashort pulsed laser machining of martensitic stainless steels. A micro-drilling cycle based on the sequence of a drilling through phase, an enlargement and finishing phase is proposed in order to solve the trade-off between process time and quality of the ablated surfaces without making use of complex design of experiments. The three phases were studied taking into account the evolution of the microhole shape as a function of the main process parameters (number of passes per phase, incidence angle and radius of the beam trajectory respect to the hole's axis). Experiments testified that the drilling strategy was able to produce cylindrical holes with diameter of 180±2 μm on a 350 μm thick plate in total absence of burrs and debris within a drilling time of 3.75 s. Repeatability tests showed a process capability of nearly 99%. SEM inspection of the inner surface of the microholes showed the presence of elongated and periodic ripples whose size and inclination can be controlled adjusting the incidence angle of the beam over the tapered surface before the ultimate finishing phase
Experimental study on the influence of drill wear in CFRP drilling processes
Full text linkCO2 laser machining represents a flexible technique for the rapid fabrication of miniaturized polymer structures such as polymethylmethacrilate (PMMA) microfluidic devices. A model to estimate the main dimensions (depth and width) of laser machined channels is presented, depending on process parameters (incident power, scanning speed). Blind cavities, to be used as fluid collectors, are machined layer by layer using multiple overlapping sequences of straight grooves with different scanning directions. The proposed technique shows that the removal depth varies proportionally with the number of layers machined, while surface roughness is influenced by the grooves spacing and the orientation of the scanning direction between successive layers. A method for thermally bonding the PMMA sheets, constituting the 3D structure of the chip, is also presented. The combination of high temperatures and a low bonding pressures makes it possible to generate a bulk junction enabling good performances in terms of sealing characteristic
Fatigue analysis of adhesive joints with laser treated substrates
Full text linkAbstractRecent literature works focused on the analysis of laser irradiation on the strength of adhesive joints under quasi-static loading conditions. It has been demonstrated that laser surface preparation allows to remove impurity and weak boundary layers from the mating substrates and, depending on the energy density, it is also able to modify surface morphology promoting mechanical interlocking. In previous works, the authors assessed the effect of Yb-fiber laser ablation over the quasi-static strength and toughness, of aluminum and stainless steel adhesively bonded joints. The experimental results demonstrated the ability of laser irradiation to improve the mechanical properties of the joints. The aim of this work is to extend the scope of previous investigations to fatigue loading. Double Cantilever Beam (DCB) samples with laser treated aluminum substrates have been bonded with a two component epoxy adhesive. For comparison standard degreasing and grit blasting have been also deployed for samples preparation. The results have been compared in terms of cycles to failure and the fracture surfaces have been analyzed by means of Scanning Electron Microscopy (SEM) in order to investigate the mechanism of failure
Experimental approach to the laser machining of PMMA substrates for the fabrication of microfluidic devices
Full text linkThis paper deals with CO 2 laser machining of a suitable amorphous polymer (PMMA) as a flexible technique for the rapid fabrication of miniaturized structures such as microfluidic devices. A model to estimate the main dimensions (depth and width) of the grooves produced by the laser on PMMA is presented, taking into account the influence of the main process parameters (incident power, scanning speed and spot diameter). This theoretical model allows to control the engraving process showing that laser could represent a valid alternative for the production of microchannels. PMMA single-use devices are found to be easier to manufacture with respect to the conventional glass or silicon products. In a second step, IR laser vaporization is adopted for the removal of a single layer of PMMA. This is achieved using multiple overlapping sequences of straight grooves with different scanning directions. The proposed technique showed that the removal depth varied proportionally with the number of layers machined, while surface roughness is influenced by the grooves spacing and the orientation of the scanning direction between successive layers. A method for thermally bonding the PMMA sheets, constituting the 3D structure of the chip, is also presented. The combination of high temperatures and low bonding pressures makes it possible to generate a bulk junction enabling good performances in terms of sealing characteristics
Layered Laser Vaporization of PMMA Manufacturing 3D Mould Cavities
No full textThis paper deals with an innovative technique concerning CO2 laser machining in order to create 3D cavities to be used as moulds for the casting of polymer resins, vaporizing PMMA layer by layer. The removal of a single layer is achieved using multiple overlapping straight grooves. The groove profile (depth and width) has been predicted by theoretical models which investigate the influence of cutting sequence, number of passes, laser beam scanning speed and radiant flux. The removal depth varies proportionally with the number of layers, while the surface roughness, influenced by the grooves spacing and the orientation of the scanning direction between successive layers, cannot be decreased under a minimum value
Analysis of the material removal mechanism in the sawing of marble
No full textThe present research aims at consolidating the theoretical aspects related to the use
of chain-saw machines in the quarrying of marble. Cutting conditions conventionally
adopted during quarrying operations have been reproduced in an experimental set-up
and forces exerted during the material removal have been monitored by means of a
piezoelectric dynamometer.
The complex action of the chain into the stone has been decomposed into simpler
conditions by analyzing each tool singularly. Once established the effect of every
single tool, three main tools with different geometries have been tested varying the
rake angle γ. Data relative to the monitored forces revealed that better proficiencies, in
terms of feed force reduction, can be obtained with negative values of the rake angle
while the effects on the cutting force can be retained negligible. A wide overview on
the experimental tests was also given to asses the repeatability of the obtained
results
The influence of laser welding configuration on the properties of dissimilar stainless steel welds
Full text linkLaser beam welding of dissimilar ferritic/martensitic stainless steels was performed in constrained butt joint configuration with the objective of identifying the influence of the melting ratio between the two base metals on the ultimate shear strength of the welds. Based on a full factorial design, experiments demonstrated that varying the incidence angle up to 45° and offsetting the focal position with respect to the materials’ interface within the limits imposed by the laser spot diameter are a reliable method to control the melting ratio and maintaining the expected resistance length at the material interface. The weld configuration parameters were correlated by means of the analysis of variance (ANOVA) method with shear resistance length and the melting ratio: the incidence of surface cracks can be significantly reduced increasing the ferritic steel area, involved in the formation of seam, over 60 % of the whole melt zone. Push-out tests performed on the specimens revealed that such a configuration has beneficial aspects on the ultimate shear strength of the seam meaning that the prevailing effect is the decreased brittleness of the weld by decreasing its carbon content under 0.5 % in weight
PROPAGAZIONE DI DIFETTI A FATICA IN GIUNTI INCOLLATI CON ADERENDI SOTTOPOSTI AD UN TRATTAMENTO DI ABLAZIONE LASER
No full textLayered laser vaporization of PMMA manufacturing 3D mould cavities
Full text linkThis paper deals with an innovative technique concerning CO2 laser machining in order to create 3D cavities to be used as moulds for the casting of polymer resins, vaporizing PMMA layer by layer. The removal of a single layer is achieved using multiple overlapping straight grooves. The groove profile (depth and width) has been predicted by theoretical models which investigate the influence of cutting sequence, number of passes, laser beam scanning speed and radiant flux. The removal depth varies proportionally with the number of layers, while the surface roughness, influenced by the grooves spacing and the orientation of the scanning direction between successive layers, cannot be decreased under a minimum value
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