Claudio Leone

Plasma treatments of polymeric materials and Al alloy for adhesive bonding

Abstract Cold plasma treatments to modify the surface properties of polymeric materials (polyoxyphenylene-polyammide, polycarbonate-ABS) and Al 6061 alloy, have been performed with the aim of increasing the surface adhesion in structural joints. An experimental cold plasma generator working in flow gas (Ar, O 2 , N 2 ) was employed to obtain a localised treatment. Some conventional surface treatments have been employed to compare the results. Joint strength and morphology fracture analysis of the surfaces were done. Results show that cold plasma treatments with oxygen gas lead to higher shear strength and low data dispersion with high quality of the joint. Morphological analysis reveals the different fracture modes to correlate with the surface treatments.

Selective Laser Post-Treatment on Titanium Cold Spray Coatings

The aim of the present work is to investigate the feasibility and effects of a selective postdeposition laser treatment on titanium coatings. Commercially pure titanium grade 2 powders were deposited by means of a cold spray process on aluminum alloy AA2024-T3 sheets. The surface treatment of the coating was realized using a 220 W diode laser. The influence of heat input and dimensional features of coating layer and substrate was assessed by an experimental campaign conducted following a design of experiments approach. Optical and scanning electron microscopy analysis of the microstructure of the deposited and treated material as well as microhardness measurements showed the formation of a compact layer of titanium oxide on the coating surface and the preservation of the temper state of the aluminum substrate.

Ti-6Al-4V Cutting by 100W Fibre Laser in Both CW and Modulated Regime

Titanium and its alloys are nowadays widely used in many sectors: in the medical field (orthopedic and dental ones), in the architectural field, in the chemical plants field and in aeronautic [1]. In this last field it is more and more used both for its contribution to make lightweight and time durable structures and for its compatibility with new materials, first of all Carbon Fiber Reinforced Plastics (CFRP). Cutting of titanium sheets is one of the primary requirements in the fabrication of most of the components. Laser cutting offers several advantages over conventional cutting methods. It includes narrow kerf width (minimum material lost), straight cut edges, low roughness of cut surfaces, minimum metallurgical and surface distortions, easy integration with computer numerically controlled (CNC) machines for cutting complex profiles and importantly non-contact nature of the process (suitable for cutting in hostile environments and in areas with limited access) [2]. However, due to very limited literature available on laser cutting of titanium, it is very difficult to predict the cut surface quality and optimum process parameters for laser cutting, especially when dross-free cuts are required. Laser cutting of titanium and titanium alloys needs to be carried out with an inert gas, this due to the high reactivity of the titanium with the oxygen at high temperatures [3]. However when the available power is limited, as in the present case, the use of a reactive gas (air) can help to achieve cutting speed value reasonable for industrial applications. The aim of this work is to study the cutting of Ti-6Al-4V rolled sheets 1 mm in thickness, by means of a 100 W fibre laser, (SPI-Red Power) working at wavelength  = 1090 nm. The maximum cutting speed were measured in both CW and pulsed regime at different mean power and different duration. Furthermore, the kerf geometry and the heat affected zone (HAZ) were studied decreasing the cutting speed from the maximum to the 80 % of this values. The results obtained showed that both the power and the cutting speed influence the cutting kerf geometry and HAZ. In particular the synergy of power and speed, resulting roughly into the heat input, seems to rule the whole cutting process.

Laser Cutting of Aluminium Sheets with a Superficial Cold Spray Titanium Coating

In the manufacturing of metal components both wear and corrosion have to be considered. In particular, corrosion is a primary problem in the aeronautic field, where the aluminium alloys are affected by several corrosion typologies. Furthermore, nowadays carbon fibre reinforced plastics (CFRP) are finding an increasing use, but they can induce galvanic corrosion phenomena when coupled with aluminium alloys. To overcome this problem, corrosion resistant coatings are used on aluminium components. On these premises, the realization of a titanium coating on aluminium components could allow the coupling of CFRP and aluminium alloys, improving the corrosion resistance. Cold Spray Deposition is a recent technology to realize these coatings. This technology allows the production of near fully dense coatings on metallic surfaces. In many applications the coated aluminium sheets have to be machined (cut or drilled). Machining with conventional cutting methods leads to both tool wear and damages in the coating. Laser cutting represents a promising alternative: it does not involve any mechanical cutting force or tool wear and, thanks to the small laser beam spot, it allows to realize complex shapes. In this paper, laser cutting of an Al alloy sheet (0.6 mm thick) coated with Ti Alloy, was studied. The adopted laser source was a 150 W, lamp pumped Nd:YAG, specifically developed for micro-machining operations on metals. During the tests, the process parameters (cutting speed, pulse duration and entrance side) were changed and the kerf geometry was analysed as a function of the process parameters.

Cutting of thin metal sheets using Nd:YAG lasers with different pulse duration

An experimental investigation on the laser cutting of thin metal sheets using a Q-switched diode pumped Nd:YAG laser and a conventional lamp pumped Nd:YAG laser with pulse duration of 150 ns and 0.3 ms respectively is described in this paper. Using the laser with short pulses the lower single pulse energy was not sufficient to remove the material along the entire thickness of the sheet in a single laser scan and multi-passes were required. However, short pulses with higher peak power densities allowed to produce precise cuts with a smaller width than long pulses. These two cutting processes by a multi-passes laser scan (using short pulses of 150 ns) and by a single laser scan (using long pulses of 0.3 ms) were compared in terms of laser energy, machining time and process performance. It was also observed that, when using short pulses, the groove geometry was different depending on the number of passes and the material removal rate due to the laser scan significantly decreases when the groove depth increases.

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.

Study and integration of microtechnologies for smart assembly of hybrid micro-products

Hybrid micro-products permit innovative applications in many fields from industry to health. To reduce their cost and increase their diffusion into market, efficient and smart automatic assembly systems must be developed. This paper presents the results of a project carried out jointly by five university laboratories for assessing and developing suitable technologies that have been integrated into an automatic assembly micro-factory.

Experimental investigation on CFRP milling by low power Q-switched Yb:YAG laser source

In the present study, laser milling of CFRP plate by means of a 30W Q-Switched Yb:YAG fiber laser is investigated through statistical analysis. Milling tests were performed at the nominal power changing the pulse power; the scanning speed, the hatch distance and the released energy. Design of Experiments (DoE) and ANalysis Of VAriance (ANOVA) were applied with the aim to improve the process performances in term of material removal rate and heat affected zone extension. The results show that, the adopted laser is an effective solution for the CFRP milling. Moreover, adopting an accurate approach to the problem, process variability and material damages can be easily reduced.

Laser ablation of maskant used in chemical milling process for aerospace applications

Chemical etching is a non-traditional machining process where a chemical solution is used to remove unwanted material by dissolution. To shape the etched area, before the process, a chemical inert paint (maskant) is applied on the surface. Then the maskant is trimmed away and the uncovered area is subject to the etching. The maskant cut could be obtained mechanically or by laser ablation. In this work, the effect of process parameters, cutting speed and beam power, on interaction phenomena and defect formation in laser cutting of polymeric maskant is studied, using a 30W CO2 laser source.

On the influence of different superficial laser texturing on the deposition of powders through cold spray process

ABSTRACT Cold spray is a technique allowing the deposition of metallic powders on several different substrates. The deposition process is ruled by different factors, among these, of particular interest are the superficial roughness and texturing of the substrate. The aim of this research was to study the influence of different superficial texturing on the deposition process of aluminium powders on an AA 2024 T3 plate. Samples with different superficial texturing were produced by laser engraving through a Yb:YAG fibre laser, varying the laser treatment parameters. Aiming to highlight the influence of the laser treatment, the deposition process was carried out on all the samples under the same spraying condition. The cross-section of the interface between the substrate and the coating and the microstructure of the coating itself were observed to study the influence of the superficial texturing on the coating formation. It was found that the superficial texturing influences both the adhesion mechanism and the microstructure of the coating.