Federica Trovalusci

Nd-YAG Laser Sculpture of WC Punches for Micro-Sheet Forming

A Q-switched Nd-YAG laser was used to sculpt a WC micro-punch in a sintered preform. A cylindrical punch was obtained with a nominal diameter of 400 μm and 80 μm in height. Laser machined surface was characterized both qualitatively and quantitatively by means of scanning surface topography instrument. A 20 μm thick aluminum sheet was micro-punched using a testing machine as a drive and a gasket material for support. The gasket followed the micro-punched disk during all the shearing process, collapsing under the punching load. This simple forming process was defined to reduce the micro-part distortion and to avoid the fabrication of a micro-die. Finally, optical microscopy showed that the punched part had a flat surface in the centre and some anomalies at the edges where the punch melted zones were reproduced.

Direct molding of thermoplastic micro-parts

A new micro-molding machine is described which is used to fabricate micro-parts made of a thermoplastic material. A single pellet is directly molded into a transparent mold by means of a diode laser source. A very low holding pressure is applied and no mold heating system is required; therefore the size of the micro-machine is extremely small as well as the size of the mold. The micro-machine was used to mold three different materials: high-density polyethylene (HDPE), polystyrene (PS) and acrylonitrile–butadiene–styrene (ABS). A process map was initially defined for all the materials by changing the main process variables (i.e. laser power, molding time and focalization condition). In this phase, small disks, 3.5 mm in diameter, were molded and their diameter was measured to evaluate the dimensional accuracy of the process. Subsequently, internal micro-gears in HDPE and PS and a micro-coin in ABS were molded to show the capability of the new process in the replication of the mold cavity.

Filler–matrix interaction in solid-state foaming of composite foams

Solid-state foaming is a relatively new process for producing closed-cell thermoset foams starting from powders. In this study, the possibility of introducing nanoclay into epoxy foams by solid-state foaming was investigated. The nanoclay was found to affect the foaming efficiency and the foam density; even if large nanoclay aggregates are present in the foams, for a small range of filler content (2.5—3 wt%), the mechanical properties are positively influenced, as shown by specific compressive toughness which attains a maximum value. Electron microscope observations provided important information on the dependence of the cell size on the filler percentage, and the presence of a critical size (about 5 μm) of nanoclay aggregates, below which they are coherent with the matrix.

Laser Applications in the Field of Plastics

This chapter highlights the main laser applications in the field of plastic materials. It provides an overview of recent research on this topic; it describes the processes, such as laser cutting and marking, laser welding, laser-assisted micromoulding, laser cure of thermosetting powder for painting, and laser cure of serigraphic ink; and it discusses the results obtained in innovative fields, highlighting advantages and disadvantages in comparison with conventional processes.

Fuzzy model for electrostatic fluidized bed coating

The study concerns the coating process of metal substrates in an electrostatic fluidized bed (EFB).This eco-friendly process is profitably used to coat components of particularly complex shapes. Although this technology is widely spread in several industrial domains, the implementation of appropriate process control procedures is still object of investigation.A model was generated from experimental data with the aim of predicting, for any set of process parameters, the resulting coating thickness of the sample. With a design of experiment (DOE) approach, the experimental investigation, that is the base for the model, quantifies the coating thickness as a function of the main process parameters namely coating time, applied voltage, and gas flow rate fed into the fluidized bed.This study addresses the effect of the inherent uncertainties on the predicted coating thickness caused by the approximation in the model parameters. In particular, a fuzzy-logic based approach is used to describe the model uncertainties and the transformation method is used to propagate their effect on the thickness. The fuzzy results are then compared with the data produced by the experimentation leading to the evaluation of the membership level of the dataset to the uncertain model.Copyright

Diode Laser Cure of Serigraphic Ink

Laser polymerization of serigraphic ink was performed by diode laser (DL). Experimental tests were carried out by depositing a commercial solvent-based ink on a polyvinylchloride (PVC) sheet. Ink cure was obtained using a 940 nm emission wavelength DL with an almost rectangular spot. We considered different values for laser power, scanning rate and focalization distance and several behaviors were observed depending on the laser fluence, from the uncured ink state to substrate warpage and degradation. Both ink thickness measurement and scratch tests were conducted on laser-processed samples. Analysis of experimental results shows that the full cure can occur within an extremely short time and at very low power values.

Aesthetic Diode Laser Welding of Stainless Steel

In the present study the use of diode laser for stainless steel aesthetic welding is considered. In fact the surface smoothness of the weld bead, attributed to the mode stability of the laser system, suggests its application for aesthetic weld joint. The aims of this work were to: define a process map, based on an aesthetic criterion; mechanically characterize the weld joints (by Vickers micro-hardness and tensile test); analyse the surface of the specimens in terms of roughness. Moreover, gas tungsten-arc (TIG) weld joints were carried out and analogously tested to make a comparison with the diode laser results. Good aesthetic butt joints were obtained with diode laser welding. The same results were found working with constant power speed ratio (i.e. constant fluence). Comparison between TIG and Laser Beam Welding (LBW), showed no significant difference in roughness, while ultimate tensile load was higher for TIG welding. The differences in joint strength depend on the different cross-sectional area and on the extension and microstructure of the base metal, heat-affected zone and melted zone. However, diode laser technology allows to obtain smaller bead size.

The mechanisms of material removal in the fluidized bed machining of polyvinyl chloride substrates

In this paper, the mechanisms of material removal during the fluidized bed machining (FBM) of polymeric substrates are analyzed. Cylindrical components composed of polyvinyl chloride (PVC) were exposed to the impact of abrasives while rotating at high speed within a fluidization column. The interaction between the Al2O3 abrasive media and the PVC surfaces was studied to identify the effect of the main process parameters, such as the machining time, the abrasive mesh size, and the rotational speed. The change in the surface morphology as a function of the process parameters was evaluated using field emission gun—scanning electron microscopy (FEG-SEM) and contact gauge profilometry. An improvement in the finishing of the processed surfaces was achieved, and the related mechanisms were identified. The roles of the impact speed and the contact conditions between the abrading particles and the substrate were also investigated.

Custom Painting by Means of Powder Coating and Localized Heating

A custom painting process was defined for the customization of coated or uncoated sheet metals. A diode laser was used to polymerize the deposited scripts. In the case of scripts with a high line thickness, an IR lamp was preferred to the laser source to improve the coating aesthetics. In order to show the process feasibility, an L-shaped script was considered and several process parameters were changed. Painting tests were carried out on sheet metals subjected to cataphoresis treatment and on coated sheet metals, visual inspection and scratch tests were also performed to characterize the processed specimens.

Double Indentation of Laser Welded Butt Joints of Stainless Steel Sheets

In this study, an easy and innovative technique for laser welded butt joint characterization is proposed. AISI 304 sheets, 1.25 mm in thickness, were welded in the butt configuration by means of a high power diode laser (HPDL). Different combinations of the process parameters were considered. For each combination, during the process different thermal cycles were induced in the material generating heat affected zones, which were subsequently tested by the double indentation test method. This test was performed on the sheets by means of two co-axial flat indenters, 1 mm in diameter, made of tungsten carbide (WC); the upper indenter penetrates at a constant rate (0.1 mm/min) into the material, whereas the lower indenter acts as a support. On each side of the seam, 10 indentations were performed at fixed positions with different distance from the centre of the seam, to obtain a load map correlated to the mechanical properties. By comparing the maps of the different laser welded joints, a clear effect of the laser scan speed and the power was found. Furthermore, a wake field effect is recognizable, in fact the loads are symmetric as regards the seam, and there is a clear trend in the direction of the laser path. These results confirm the effectiveness of this method, which is also suitable for on-line application because a very small indentation is left on the sheet.