Multiphysics Modeling of a Metal Foam

In metal foam processing nucleated gas bubbles expand in a heated metal, then the foam cools and solidifies. In this work we use Comsol Multiphysics 4.2 to study heat transfer, growth and movement of hydrogen gas bubbles in liquid aluminium for a metal foam expanding in a 2D mold. In the model, the bubble growth is simulated by using a specific expansion rate, then the movement of hydrogen gas bubbles in liquid aluminium is numerically computed by using the equations of fluid dynamics coupled to the level set method. In spite of the problem complexity and the needed simplifications, the computational model is very well suited to describe satisfactorily heat transfer, bubble expansion, interface movement and fluid flow during the foaming process. Interesting considerations can be drawn regarding the temperature field in the system, the influence of the mold geometry and the resulting expansion of the metal foam

The analysis of tool life and wear mechanisms in spindle speed variation machining

Regenerative chatter vibrations generally limit the achievable material removal rate in machining. The diffusion of spindle speed variation (SSV) as a chatter suppression strategy is mainly restricted to academy and research centers. A lack of knowledge concerning the effects of non-stationary machining is still limiting its use in real shop floors. This research is focused on the effects of spindle speed variation technique on tool duration and on wear mechanisms. No previous researches have been performed on this specific topic. Tool wear tests in turning were carried out following a factorial design: cutting speed and cutting speed modulation were the investigated factors. The carbide life was the observed process response. A statistical approach was used to analyze the effects of the factors on the tool life. Moreover, the analysis was extended to the wear mechanisms involved during both constant speed machining and SSV. The worn-out carbide surfaces were examined under a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Significant differences were appreciated. It was observed that SSV tends to detach the coatings of the inserts, entailing a mechanism that is quite unusual in wet steel turning and thus fostering the wear of the tool. The performed analysis allowed to deduce that the intensified tool wear (in SSV cutting) is mainly due to thermo-mechanical fatigue

Modeling of Transport Phenomena in Metal Foaming

ude gas voids in the material structure with the real possibility to modify ad hoc their physical properties. During the foaming process of a metal, simultaneous mass, momentum and energy transport mechanisms arise. In this work we propose a model considering mass transfer phenomena coupled to the growth and motion of a gas bubble in the liquid metal. The diffusion of the gas in the liquid is studied by applying the Fick's law and convective transport. The equilibrium concentration at the gas-liquid interface is modeled by the Sievert's law with surface tension effects included. The numerical results of the simulation show that the computational model, using the phase field method for capturing the phase interface, can be effective. The computations simulate satisfactorily mass transfer, bubble expansion, interface movement and fluid flow. In this way other physical mechanisms of foaming could be included in a future more comprehensive model

Dynamic Behavior of Hybrid APM (Advanced Pore Morphology Foam) and Aluminum Foam Filled Structures

The aim of this work is to evaluate the effect of different densities of hybrid aluminum polymer foam on the frequency behavior of a foam filled steel structure with different ratios between steel and foam masses. The foam filled structure is composed of three steel tubes with a welded flange at both ends bolted together to form a portal grounded by its free ends. Structure, internal and ground constraints have been designed and manufactured in order to minimize nonlinear effects and to guarantee optimal constraint conditions. Mode shapes and frequencies were verified with finite elements models (FEM) to be in the range of experimental modal analysis, considering the frequency measurement range limits for instrumented hammer and accelerometer. Selected modes have been identified with suitable modal parameters extraction techniques. Each structure has been tested before and after filling, in order to compute the percentage variation of modal parameters. Two different densities of hybrid aluminum polymer foam have been tested and compared with structures filled with aluminum foams produced using the powder compact melting technique. All the foam fillings were able to suppress high frequency membrane modes which results in a reduction of environmental noise and an increase in performance of the components. Low frequency modes show an increase in damping ratio only when small thickness steel frames are filled with either Hybrid APM or Alulight foam

Experimental investigation of energy saving opportunities in tube bending machines

In the scenario of containing the global warming, devising energy savings strategies in industry has become a proper and urgent matter. Since manufacturing is one of the most energy demanding sectors, research and the linked industries started tackling this issue proposing new eco solutions. In this paper, an experimental investigation of the energy saving opportunities in tube bending machines is performed and critically discussed. The analysis is carried out comparing an electrical tube bender and a hydraulic machine of comparable size. The experimental measured are also used to fit energy models that are used to extend the comparison considering different working conditions of the tube- bending machines. The results show that relevant energy savings can be achieved introducing the electrical drives

Model-based broadband estimation of cutting forces and tool vibration in milling through in-process indirect multiple-sensors measurements

In machining processes, cutting forces measurement is essential to allow cutting process and tool conditions monitoring. Moreover, in order to have information about the quality of the milled part, the amplitude of the tool tip vibration would be very useful. Since both the measurements are extremely complicated especially in an industrial scenario, in this study, an in-process model-based estimator of cutting forces and tool tip vibration was designed and properly tested. The developed estimator relies on both a machine dynamic model and on indirect measurements coming from multiple sensors placed in the machine. The machine dynamic model was obtained through an experimental modal analysis session. The estimator was developed according to the Kalman filter approach. The fusion of multiple sensors data allowed the compensation of machine tool dynamics over an extended frequency range. The accuracy of the observer estimations was checked performing two different experimental sessions in which both the force applied to the tool and the tool tip vibration amplitude were measured. In the first session, the tool was excited with different sensorized hammers in order to appreciate the broad bandwidth of the performed estimations. In the second one, real cutting tests (steel milling) were done and the cutting forces were measured through a dynamometer; tool tip vibrations were measured as well. The experimental results showed that the indirect estimation of cutting forces and tool tip vibrations exhibit a good agreement with respect to the corresponding measured quantities in low and high frequency ranges. The contribution of this research is twofold. Firstly, the conceived observer allows estimating the tool tip vibrations that is a useful information strictly connected to the surfaces quality of the processed workpiece. Secondly, thanks to a multi-sensors approach, the frequency bandwidth is extended especially in the low frequency range

Microstructural Study of the Intermetallic Bonding Between Al Foam and Low Carbon Steel

Bonding between a metal foam core and a metallic skin is a pre requisite for the technological application of aluminum foam as filling reinforcement material to improve energy absorption and vibration damping of hollow components. This work is a preliminary study for the microstructural characterization of the interface layer formed between a commercial powder metallurgy (PM) precursor and a steel mould during foaming. The microstructure of the intermetallic layer was characterized by scanning electron microscopy, electron probe microanalysis and nanohardness measurements on the cross section. X-ray diffraction measurements, performed on the foam/substrate surface after stepwise material removal, allow the identification of the intermetallic phases. Two intermetallic layers, identified as Fe2Al5 and FeAl3, characterize the low Si foam/substrate while the AlSi10 foam/substrate interface evidences the presence of three Fe(Si, Al) intermetallic layers with different composition. Two and three different phases of increasing hardness could be distinguished going from the foam to the steel substrate for AlMg1Si0.6 and AlSi10 precursors respectively. The results suggest the importance of elemental diffusion from steel substrate in the molten aluminum matrix (foam). The possibility to control and tailor the microstructural properties of the interface between foam and steel skin is of fundamental importance in the technological process of foam filled structures manufacturing

Diffuse Interface Models for Metal Foams

le interest because of their potential applications in many fields of the industry. To produce a metal foam, a well-established process is starting with a molten metal, then introducing blowing agents to create gas bubbles inside the metal. In this work we use COMSOL Multiphysics® and apply the diffuse interface methods of the phase field technique, in order to model the properties of metal foams and describe the movement of the gas-liquid interfaces. A metal foam represented by a number of bubbles moving in a laminar flow is modeled and simulated. Surface tension effects are considered and repulsive forces between neighboring bubbles are expressed through the disjoining pressure. The numerical results show that diffuse interface methods are effective to model this kind of complex phenomena and that fundamental mechanisms due to surface tension effects an