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

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

Procedures for Damping Properties Determination in Metal Foams to Improve FEM Modeling

The aim of this work is to review the available procedures suitable for the determination of damping parameters in literature and standards for porous and dense materials and to evaluate their applicability to metal foams. Preliminary experimental setup and characterization data obtained with the selected procedures are presented and compared with representative FEM models. The experimental dynamic measurement on a test structure is compared with the simulated ones in order to validate the chosen procedure

Experimental comparison between traditional and cryogenic cooling conditions in rough turning of Ti-6Al-4V

Titanium alloys, mainly because of their poor thermal conductivity, need to be cut at relatively low cutting speeds to avoid a severe diffusion wear, with obvious negative consequences on the profitability of machining. An important amount of research activities has been done in order to increase productivity in titanium machining operations and one of the most promising solutions is represented by the use of liquid nitrogen as a coolant during the machining operation. The aim of this paper is to compare traditional and cryogenic turning of Ti6Al4V in a region of cutting parameters particularly relevant to the aerospace industry where no previous data are available. The cutting parameters are those typical of titanium alloys rough machining which is considered, cost-wise, the most important operation because, for aerospace components, the so-called Buy-To-Fly ratio can reach values up to 20:1. The experiments have been performed using a full factorial design in order to statistically evaluate, using ANOVA and regression analyses, the significance of the input factors on the process most interesting outputs. The considered input factors are: type of cooling method, cutting speed and feed rate. The main analysed responses are: tool wear, surface roughness, cutting forces, coefficient of friction and chip morphology. The results show the significance of the cooling method on the tool life and that cryogenic machining is able to increase the tool life with respect to wet cutting. On the other hand, the beneficial effect of the liquid nitrogen cooling is reduced at high cutting speed and feed rate. Besides, the results showed that a small but significant reduction can be achieved for both the repulsion force and the coefficient of friction at the tool-workpiece interface

Abrasive waterjet intensifier model for machine diagnostics

This paper investigates the dynamics of a waterjet plant with multiple phased single-acting plungers. An object oriented dynamic model is proposed and discussed. The simulator may be tuned to generate signals under different health conditions to train multi-fault diagnosis tools. In fact, due to the challenging pressure conditions and the aggressiveness of abrasive materials, the reliability of machine tool components is a major concern. The information throughput provided by the model is validated with respect to real-industrial data, acquired in reference cutting scenarios

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

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

On the mechanics of chip formation in Ti-6Al-4V turning with spindle speed variation

"In order to enhance material removal rate (MRR), a strategy that relies on higher depths of cut could be chosen if vibrational issues due to regenerative chatter did not occur. A lot of research was done to suppress regenerative chatter without detrimental effects on productivity. One of the most interesting chatter suppression methods, mainly due to its flexibility and relative ease of implementation, is spindle speed variation (SSV), which consists in a continuous modulation of the nominal cutting speed. Sinusoidal spindle speed variation (SSSV) is a specific technique that exploits a sinusoidal law to modulate the cutting speed. The vast scientific literature on SSV was mainly focused on cutting process stability issues fully neglecting the study of the mechanics of chip formation in SSV machining. The aim of this work is to fill this gap: thus, finite element method (FEM) models of Ti-6Al-4V turning were setup to simulate both SSSV and constant speed machining (CSM). The models consider both the micro-geometry of the insert and the coating. Numerical results were experimentally validated on dry turning tests of titanium tubes exploiting the experimental assessment of cutting forces, cutting temperatures and chip morphology. Tool-chip contact pressure, tool engagement mechanism and the thermal distribution in the insert are some of the analysed numerical outputs because they cannot be easily assessed by experimental procedures. These quantities were useful to compare thermo-mechanical loads of the insert both in CSM and SSSV machining: it was observed that the loads significantly differ. Compared to CSM, the modulation of the cutting speed involves a higher tool-chip contact pressure peak, a higher maximum temperature and higher temperature gradients that could foster the main tool wear mechanisms. (C) 2013 Elsevier Ltd. All rights reserved.