Search

The aim of this paper was to investigate the effects of a post-deposition laser treatment on the titanium cold-sprayed coatings. Commercially pure grade 2 titanium powders were deposited onto an aluminum alloys AA2020-T3 substrate, using a commercial cold spray system. Pre-heated helium was employed as powder carrier gas. Coatings were heat treated using a 220 W diode laser, in order to improve the cohesion between titanium particles, reduce the porosity percentage and promote a homogeneous microstructure. Several samples were realized varying the thickness ratio between the two layers and the scan rate of laser source, to reproduce and investigate the effect of different temperature distributions. Geometry features and microstructure of treated zone were assessed by means of conventional optical microscopy and scanning electron microscopy. Microhardness measurements were carried out to evaluate the mechanical properties of the coating layer. A numerical model of the laser treatment was also implemented to discuss the experimental outcomes.

Incremental forming process, in all its variants, results to be ideal when flexibility is required, especially for small-batch and customized production. Two point incremental forming with partial die (TPIF) presents notable advantages compared to single point incremental forming (SPIF) for obtaining components that present both concave and convex zones; on the other hand, these advantages are not so evident in the case of simple geometries. The following study compares the two techniques by geometrical considerations, FEM analyses and experimental evaluations. Cone frusta are obtained starting from aluminum alloy sheets and features like geometric accuracy, forming and setup times, forming forces and deformative states are investigated, in order to highlight differences and similarities between the two techniques. In particular, TPIF allows to obtain geometries very similar to the designed ones, but requires higher setup and forming times.

Cemented carbides present some characteristics that ensure high performances for cutting and wear-resistant tools. The aim of the work is to evaluate the influence of Chromium Carbide and Nickel on the properties (wear and friction) of a cemented carbide constituted by a hard phase of tungsten carbide and a binder phase of cobalt. Different tests were carried out by varying the percentage of Cr3C2 and, for one only case, also Nickel was added. The tests were carried out by a pin-on-disk apparatus and diamond abrasive sheet. The experimental campaign provided tests for different values of load and relative velocity. Friction coefficient was directly evaluated by the apparatus and data on the wear were obtained by measuring the loss of weight of the samples (parallelepipeds with hemispherical head). The tests allowed to determine the percentage of Cr3C2 that ensure an improvement of the aforementioned properties and to highlight the irrelevance of Nickel.

In the manufacturing of metal components both wear and corrosion have to be considered. In particular corrosion is a very important problem in the aeronautic field, were the aluminum alloys are widespread used, but are affected by several corrosion typologies. Furthermore nowadays carbon fiber reinforced plastics (CFRP) are finding an increasing use, but they can induce galvanic corrosion phenomena when coupled with aluminum alloys. To overcome this problem corrosion resistant coating are used on aluminum components. Otherwise titanium alloys have a very high corrosion resistance and furthermore no galvanic corrosion phenomena arise when coupled with CFRP. On these premises the realization of a titanium coating on aluminum components could allow the use of aluminum alloys coupled with CFRP and improve the corrosion resistance of the above mentioned alloys. The aim of this paper is to study a titanium coating builded on an aluminum substrate by means of the cold spray technique. This technique allows to produce near fully dense coatings. Despite the promise this technique has shown, questions remain about the quality of the material deposited in terms of adhesion strength of coating to substrate, and cohesion strength between cold sprayed particles that make up the coating. In this paper titanium coatings on AA 6082 substrate were carried out and tested. In particular pure titanium powder were used to build up the coating. An experimental campaign was carried out including mechanical, microstructural and electrochemical tests. Furthermore sliding tests, by means of a pin-on-disk apparatus, were carried out in order to study the wear properties of the coating. The results obtained showed a quite compact coating with few porosity, moreover the coating showed a good internal cohesion and a good adhesion with the aluminum substrate, also the electrochemical properties were interesting.

Tool wear monitoring is a fundamental aspect in the evolution of modern machining operations. As the quality of the tool is directly related to the quality of the product, automatic tool wear evaluation is vital to ensure smooth automatic control of machining processes [1]. In this paper, an automatic tool wear detection procedure is presented, where real time collected sequence images of the cutting tool during turning tests are subjected to image processing. The procedure can be divided into four steps: (1) Standardization of tool images; (2) Adjustment of pixel color density to obtain clear edges of the tool wear region; (3) Drawing of the projection line to find out the coordinates of the edge lines; (4) Calculation of tool wear development characteristics. The tool wear characteristics and extension area are evaluated on the basis of the processed edge. One by one, sequence images are processed to automatically provide the growth of tool wear characteristics. In order to verify the procedure accuracy, the tool wear characteristics and extension area are also evaluated manually using a grid number counting technique on paper images. The comparison of the results confirmed that the automatic evaluations achieve a high degree of accuracy. The experimental results indicate that the proposed procedure can be a viable technique to assess the tool wear development characteristics on an on-line basis.

Roll drawing is a technological process that allows to obtain a notable reduction of the drawing force in comparison with the traditional drawing process with converging dies. Consequently, no thermal or chemical treatment of the wire is required and no lubricant is employed, with significant environmental advantages. The drawing force and the geometrical dimensions of the wire are critical parameters for optimal process design. They have been evaluated by analytical models but, owing to the complexity of the process, a three-dimensional FE model has been developed to obtain a more precise method able to control the process.

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.

Backdrawing incremental forming is a multistep sheet metal forming process for manufacturing components with both concave and convex features, without using patterns; this process preserves the characteristic of flexibility typical of incremental forming. The creation of a component with concave-convex shape using this process is described in the present study. In particular, observations on the choice of tools shape and on the influence of the forming steps sequence are highlighted, in order to evaluate the importance of these parameters in terms of certain geometric features, compared with the design specifications. Moreover, the thickness distribution, nowadays used as forming limit parameter, is evaluated.

Incremental forming is a process that can satisfy the most disparate requirements in terms of feasible geometries; in other words it is possible to affirm that it is a very flexible process. Moreover, the high formability of sheets for the process under examination, allows to get considerable drawability levels. The aim of the present paper has been the evaluation of the formability of steel sheets and the achievement of complex geometries by means of incremental forming process. The paper shows how it is possible to use a FE code, previously validated for forming processes, to evaluate the forming limit curves of the steels. The same code has preliminarily been used in order to simulate the formability of a complex geometry component. The experimental phase,consisting in the realization of the component with the complex geometry, has been carried out and it has confirmed the results of the numerical analysis.

The use of laser technology for the welding of automotive drive shafts subject to the action of residual magnetic field

On the numerical modelling of a milling operation: data recovering and interpolation

On the welding of different materials by a diode laser

Hybrid neural network model for the evaluation of the free surface of rolled bar

A correlation between the friction coefficient and the roughness of rolls in a hot flat rolling

Application of Taguchi method to high power diode laser welding of Ti6Al4V

Finite element model for wire filler and autogeneous laser welding heat sources

CLASSIFICATION OF SOUNDNESS OF TITANIUM ALLOYS WELD ON THE BASIS OF FUSED ZONE LEVELS FOR IMPERFECTIONS

EVALUATION OF THE CO2 LASER BEAM WELDING PROCESS EFFICIENCY FOR THE TI6AL4V ALLOY

STUDY OF TITANIUM SHEETS HPDL WELDING PHENOMENON

FUZZY METHODS FOR MECHANICAL PREDICTION OF TI6AL4V CO2 LASER WELDED SHEETS

In this work, a nickel base alloy INCONEL 600 has been welded by means of a 2 kW CO 2 cw laser. In order to evaluate the influence of the basic welding parameters on heat affected zone, weld structure and weld geometry, an accurate analysis has been carried out. The experimental results show a strict correlation between the power beam and the welding speed vs. the weld bead geometry. As the speed increases, so penetration decays. Microhardness tests, micro and macrograph examinations did not reveal, in the range of experimental parameters, any significant alteration in weld bead structure nor the presence of a HAZ. In order to assess process efficiency, the experimental data were processed using the Line Source Model (LSM) which permits to calculate the Melting Ratio (MR) and Energy Transfer Efficiency (ETE).

Ti–6Al–4V is an alloy increasingly used in aeronautics due to its high mechanical properties coupled with lightness. An effective technology used to manufacture titanium components with a reduced buy-to-fly ratio is laser beam welding. Previous studies showed that the key factor that rules the mechanical properties and the fatigue life of the joint is its morphology. The aims of this paper were to investigate the influence of the geometrical features of the joints (height of the top and root reinforcement, depth and radius of the underfill, and the valley–valley underfill distance) on their mechanical properties and also to conduct a finite element (FE) analysis on the real geometry of the welded joints. Ti–6Al–4V rolled sheets 3.2 mm thick were welded in butt joint configuration using a laser source and their performance was studied in terms of weld morphology, microstructure, Vickers microhardness and fatigue life. A full factorial plan, designed varying the welding speed and laser power, was carried out. The real geometry and then the joint morphology were studied through an innovative approach: for each specimen, both the total weld face and the total root surface were acquired using a confocal microscope. Finally, through these acquisitions, the clouds of points of the scanned surfaces were used in order to carry out a FE analysis capable of providing a stress concentration factor, K t , value for each detected joint. The main results are the realization of a reliable FE model by an experimental agreement and the relationship found amongst the fatigue performances and some noticeable metallurgical and geometrical features, such as the underfill depth and the aspect ratio defined as the ratio between the maximum height of the joint and the valley–valley underfill distance.

The aim of the present work is to investigate the feasibility and effects of a selective post-deposition 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 micro hardness 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.

Incremental sheet forming is a relatively new technology with a deformation strategy that resembles the layered manufacturing principle of rapid prototyping; thanks to this, it can represent a viable way to form metal and polymer sheets, guaranteeing high customization and cost-effectiveness. On the other hand, and particularly when considering thermoplastic sheets, the components obtained by this process suffer from peculiar defects like, for example, twisting and wrinkling. A way of reducing the risk of such defects is to optimize the toolpath strategy to lower in-plane forming forces. To pursue this aim, the present work follows a numerical approach; a commercial FE code was used to simulate the incremental forming of polycarbonate sheets by varying the toolpath strategy. The investigation of some features like the forming forces and the deformation states was carried out, with the goal of determining an optimized toolpath strategy for the reduction of the incremental forming forces and the consequent expectation of reduced risk of failures and defects for incremental formed polymer sheets.

Considering that nowadays the interest in the use of bio-composite materials is increasing more and more, this work is focused on the manufacturing of lightweight components based on hemp fibres for future applications, for example as a core for sandwich structures. Three different no-complex processes were used: a conventional hand lay-up, an unconventional infusion process and a hand lay-up process followed by injection moulding. They were used to produce bio-composite structures using an epoxy resin and/or a polyurethane foam as matrix. Depending on the process used for the manufacturing, laminates with different values of density were obtained. A detailed study in terms of both static and dynamic properties was carried out and the different mechanical behaviour for each sample typology was highlighted. The results showed that the process in which both the epoxy resin and the polyurethane foam were used as matrix allowed to obtain laminates with lower density and higher specific mechanical properties.

The use of hybrid structures made of CFRP and titanium alloys is growing more and more in the last years in the aerospace industry due to the high strength to weight ratio. Because of their very different characteristics, the mechanical fastening represent the most effective joining technique for these materials. As a consequence, drilling process plays a key role in the assembly. The one shot drilling, i.e. the contemporary drilling of the stack of the two materials, seems to be the best option both in terms of time saving and assembly accuracy. Nevertheless, due to the considerable different machinability of fiber reinforced plastics and metallic materials, the one shot drilling is a critical process both for the holes quality and for the tools wear. This research was carried out to study the effectiveness of new generation tools in the drilling of CFRP/Titanium stacks. The tools are made of sintered grains of tungsten carbide (WC) in a binder of cobalt and coated with Diamond like carbon (DLC), and are characterized by a patented geometry; they mainly differ in parent WC grain size and binder percentage. Both the cutting forces and the wear phenomena were accurately investigated and the results were analyzed as a function of number of holes and their quality. The results show a clear increase of the cutting forces with the number of holes for all the used drilling tools. Moreover, abrasive wear phenomena that affect initially the tools coating layer were observed. © 2016 Author(s).

The interest for natural fibers as reinforcement in composites is growing for a large number of products also for aeronautic applications, where the flame retardant requirement is fundamental. In this research, ammonium polyphosphate was incorporated as flame retardant into hemp/epoxy biocomposites produced by infusion technology. Cone calorimeter, vertical burning, dynamic mechanical analysis and bending tests were performed in order to study fire and mechanical behavior of the produced biocomposites with different percentage of ammonium polyphosphate. The results showed a decisive improvement of the flame properties; no-effect on their mechanical properties and on the technological feasibility of the process were observed. Therefore, the addition of ammonium polyphosphate enhanced flame retardancy of hemp/epoxy-resin biocomposites without sacrificing their mechanical properties.

This paper investigates the mechanical properties in term of compression, tensile, flexural and shear strength of a new hemp core based on woven fabric. The hemp core is manufactured by means an innovative vacuum infusion process in which the input both of epoxy resin and of air was allowed. In addition, a comparison among this and others more known materials used as core in sandwich structures was carried out. The results showed that the core under investigation has higher mechanical properties, without shear and indentation failure during the tests on the respective sandwich structures.

Cold Gas Dynamic Spray is an emerging coating technology based on the use of a supersonic gas jet to accelerate (up to 1000 m/s) and to impact a powder, with size ranging from 1 to 50 μm in diameter, on a substrate. Due to the high speed, during the impact, the powder undergoes a severe plastic deformation such that it adheres on the substrate. Thanks to this method, it is possible to produce up to fully dense metallic coatings on substrates of different materials. With this technology, different kinds of powder (metals, polymers, ceramics, composite materials and nanocrystalline powders) or their mixing can be deposited. Among the various possible powders that can be deposited by cold spray, titanium is one of the most attractive materials thanks to its potential applications. A titanium layer produced onto a softer materials (i.e. aluminium alloys) could improve both the corrosion resistance and the wear properties of the components. However, the coating made with this technique could be affected by several problems, such as porosity, high roughness and low mechanical properties. A possible solution for this issues is the use of laser remelting post-deposition treatment. The present investigation deals with the application of a continuous wave diode laser in order to change the coating properties and metallographic structure. With this aim, laser remelting of a titanium cold sprayed layer were carried out on samples of grade 2 titanium alloy, 5 mm thick, obtained by cold spray technique, by using a 220 W diode laser at different scan speed. In order to avoid the influence of the particular substrate, the laser remelting process was carried after the detachment of the coating from the substrate. After laser treatments, light and SEM microscopy were carried out to analyze the geometry of remelted zone and the evolution of its microstructure morphology. Moreover, micro-hardness measurements were made to evaluate the mechanical properties. Three different metallurgical structures corresponding to the remelted zone, the heat affected zone and base material were observed. The remelted zone showed an elliptical shape, with a depth up to 0.7 mm and a martensitic microstructure. Furthermore, in this zone, hardness higher than the base material (more than threefold) was found. In conclusion, it is possible to affirm that the laser remelting is a promising technique to improve the superficial properties of titanium cold sprayed layers.

Cold roll forming is a process for plastic deformation, which allows realizing profiles, with a defined section and established length, from the plastic deformation of a metal sheet. The sheet is induced to cross several stands of rolls, arranged along the same axis of advancing. The rolls induce plastic deformation in the sheet and then lead it to the desired geometric configuration. In order to control the geometric parameters of the plate during the profiling, it was created a FEM model to simulate the final stage of the technological process, developed by an industrial production line of a company located in Naples (Italy), that sells tubes with several cross sections. In this phase, the semi-finished product, having a circular cross section, is forced to cross through four stands of rolls. In this way, it changes the geometric condition of the cross section from circular to square. The model was carried out using a non-linear calculation code, which allows analyzing the parameters of interest in the different process steps. The results, obtained numerically, were compared with the experimental ones through the measurement of five specimens, obtained directly from technological process. The values of percentage deviation, regarding the external dimension and the thickness, for each step of advancement, do not exceed the 3% of error. Then, the analysis results denote the capability to simulate the cold roll forming process using finite element method.