L. A. C. De Filippis

An investigation of rapid prototyping of sand casting molds by selective laser sintering

Among the layer fabrication techniques, selective laser sintering (SLS), is widely used for manufacturing various products made of different materials (i.e., polycarbonates, nylons, polyamides, sand casting, metal powders, and others). The SLS of precoated foundry sands allows the aggregation of adjacent particles, which are then cemented by furnace heat treatment. Moreover, geometrically complex molds and cores not obtainable with conventional methods can be realized by this method. In this article, the optimization of laser parameters is reported for fabricating transitory molds for foundry applications. Lasercron sand, a quartz sand with a thin phenolic resin coating often used for SLS applications, was tested. The CO2 and diode lasers were used for this study. After some preliminary tests, experimental design techniques were applied to investigate the influence of some processing parameters, i.e., laser power, scan speed, and scan spacing (hatch). Their interactions were evaluated using response surfa...

MULTI-OBJECTIVE OPTIMIZATION OF ALUMINIUM FOAM MANUFACTURING PARAMETERS

Aluminium foams are a new class of materials with low densities, la rge specific surface and novel physical and mechanical properties. Their applications are extremely varied: for light weight structural components, for filters and electrodes and for shock or sound absorbing products. Recently, interesting foaming technology developments have proposed metallic foams as a valid commercial chance; foam manufacturing techniques include solid, liquid or vapour state methods. The foams presented in this study are produced by Melt Gas Injection (MGI) process starting from melt aluminium. The objective of this paper is to develop a method for the analysis of the effects of process parameters on the quality of foam parts and to determine their optimal combination. The effects of the foaming parameters are studied by the Taguchi method, applied to design an orthogonal experimental array. A multi-objective optimization approach is then proposed by simultaneously minimizing the relative density and maximizing the absorbed energy efficiency. (Received in July 2008, accepted in December 2008. This paper was with the authors 2 months for 1 revision.)

Morphological Investigation of Foamed Aluminum Parts Produced by Melt Gas Injection

Porous metal materials are a new class of materials with low densities, large specific surface, and novel physical and mechanical properties. Their applications are extremely varied: for light weight structural components, for filters and electrodes, and for shock or sound absorbing products. Recently, interesting foaming technology developments have proposed metallic foams as a valid commercial chance; foam manufacturing techniques include solid, liquid, or vapor state methods. The foams presented in this study are produced by Melt Gas Injection (MGI) process starting from melt aluminum. The aim of this investigation is to obtain complex foamed aluminum parts in order to make the MGI more flexible. This new method, called MGI-mould process, makes possible to produce 3D-shaped parts with complicated shape or configuration using some moulds obtained by traditional investment casting process.

Laser welding of the AA 2024-T3 aluminum alloy by using two different laser sources (Nd:YAG or CO2)

In this experimental work the weldability of an Al alloy AA 2024-T3 by using two different laser sources, (CO2 and Nd:YAG), has been tested for experiments. A ROFIN SINAR, 1500 W continuous wave (c.w.) max power level, emitting at 10.6 μm, and a HAAS TRUMPH source, 3000 W max power level, pulsed beam, that produces na 1.06 μm wavelength have been used. The thicknesses employed are 0.8-1.6 and 2.0 mm for the Nd:YAG, 1 and 1.6 mm for the CO2. In order to define a possible laser welding process optimisation versus the best quality and relative mechanical properties of the butt joints, different laser working parameters have been studied and experimented. Moreover two diverse welding techniques, that is by using a filler wire or without one have been applied and the relative results have been compared. The best selected butt joints have been cahracterized by some visual examinations, micro and macrographs of transverse sections, micro-hardness data and plots as well as some tensile tests. Finally, according to the results as above, physical-technological evaluations and comparisons have been reported.

A Preliminary Study on Adhesion on Steel Cylinder Filled with Aluminum Foam

In the last decades, metallic foams found commercial and industrial interests, thanks to their physical properties combined with good mechanical characteristics. Metal foam structures are very light and they can be used to reduce the weight of machinery without compromising the mechanical behavior. In this work, a study of the direct junction of metal foam with metal massive components was carried out. Aluminium foams were manufactured starting from commercial foamable precursors. First of all, attention was paid to the repeatability of foaming process. Then, a direct connection between the foamed samples and the steel shell elements was pursued. The materials that seemed to facilitate the formation of an intermetallic layer were studied and the geometry of the steel mould and the most useful way to place the precursor in the steel mould and then in the furnace were considered. To evaluate the produced aluminum foam, morphological and mechanical characterizations were done. Results showed that, keeping constant the contour conditions, it was possible to control the process and a first result, in terms of interaction between foam and mould, was obtained using an X210Cr12 steel as mould material. The SEM observation revealed the presence of an intermetallic phase.

A quantitative evaluation of the L.B.W. efficiency on AISI 304 bead on plates welded under different focusing and tilted laser beam conditions

The aim of this search is to evaluate the WE (Welding Efficiency) of each beads versus the different positions of the laser beam optical focus (positive or negative or zero values) respect to the work-piece surface and also versus different laser beam incidence angles (80° and 70°) by using two laser power levels (2 and 2.5 KW) and two welding speeds (3 and 6 m/min). The WE values have been reported on two DA.LU. method plots and the relate evaluations regarding the same ones as well as the recorded best parameters have been evidenced.

CO2 laser welding of aluminium shipbuilding industry alloys: AA 5083, AA 5383, AA 5059, and AA 6082

Aluminum alloys are interesting in many and many industrial applications, from the classical aircraft industry to rail and road vehicles manufacturing (High Speed Train, Car Structure and Body). Recently much more attention for Aluminum Alloys, 5000 and 6000 Series, has been carried out by Shipbuilding Industry, especially for using in the H.S.L.C. (High Speed Light Craft). Therefore the aim of this experimental work has been to study, develop and test a reproducible CO2 laser welding procedure and technique of four specific alloys, that is AA 5083, AA 5383, AA 5059 (Al-Mg Alloys), and AA 6082 (Al-Mg-Si Alloy). Different techniques, methodologies, covering gases, nozzles, focusing lenses and mirrors, welding speed range, laser power range (1000 and 2500 W) have been carefully experimented. The melted zones properties have been evaluated by cross sections, and some visual inspections by a NIKON LUCIA Imaging System correlating each experimental test, results and evaluations to the adopted process parameters and to the thermo-physical properties of the tested alloys.

AISI 304 laser prototyping by different techniques

The laser forming process of metal sheet has been investigated and has proved to be adequate to rapid prototyping. In order to successfully apply this technique, a deep understanding of laser-material interaction is required. Since the AISI 304 stainless steel is widely used for deformation processes, the authors decided to investigate its laser forming behavior. The forming effect has been evaluated in terms of the bending of sheet-shaped specimens. The influence of the main technological and geometrical parameters of the process were investigated by a factorial design, i.e. ANOVA and Surface Response. The experimental results were used to built a neural network that is able to predict some process parameters once the designer has fixed the initial and final geometry of the specimen. The obtained results show that the laser bending of AISI 304 can be a valid alternative to conventional forming and prototyping techniques.