Ottimizzazione statica e dinamica di piastre irrigidite da nervature ottenute mediante punzonatrice

40° Convegno Nazionale AIAS, Palerm

High performance cutting of gamma titanium aluminides: Influence of lubricoolant strategy on tool wear and surface integrity

Heat resistant gammatitaniumaluminidesareintermetallicalloysplannedtobewidelyusedinhigh- performanceaircraftengineswithinthenextfewyears.Thisapplicationfieldisascribedtothe exceptionalmaterialproperties,especiallythelowdensityandauniquestrength-to-weightratiofor titanium-basedalloys,goodoxidationbehaviourandthermalstability,limitedductilityandfracture toughnessbelowbrittle-to-ductiletransition,andgoodcreepresistance. The demandingmachinabilityofgammatitaniumaluminidescanbetracedbacktothesedesirable materialproperties.Consequently,cuttingprocessadaptationisessentialtoobtaincomponents suitabletosatisfystrongregulationsregardingsurfaceintegrity,withoutneglectinganeconomical production.Previousresearchactivitiesconfirmedthatthermalmaterialsofteningduringcuttingdue to thehighspeedmachiningisakeytoreachhighqualitysurfaces,buttoolwearwasidentifiedasthe limitingfactor. The relativelyhighcuttingspeedresultsinhightemperaturesintheshearzoneandthelowthermal conductivityofthe g-TiAl workpiecematerialleadstoanextremethermaltoolload.Furthermore,in combinationwiththeformationofsaw-toothchipsandthediscontinuousflowofthechipalongthe rake face,adhesiveweariscaused. The influenceofconventionalfloodcoolingandhighpressurelubricoolantsupply(wetconditions), cryogeniccoolingwithliquidnitrogen,andminimumquantitylubrication(MQL)wereinvestigatedin longitudinalexternalturningoperations.Toolwear,cuttingforces,chipmorphologyandsurface roughnesswereevaluated.Surfaceintegritywasanalysedintermsofmachinedsurfacedefectsand sub-surfacealterations. The investigationsindicatethatcryogeniccoolingisthemostpromisinglubricationstrategy, meaningthatthethermodynamicalimpactoftheexpandingliquidnitrogenapplieddirectlyclose to thecuttingzonesuccessfullycounteractthehugethermalloadonthetoolcuttingedges,providing potentiallyenormousbenefitsintermsoftoolwearreductionandconsequentsurfacequality improvemen

Effects of cutting angle, edge preparation, and nano-structured coating on milling performance of a gamma titanium aluminide

Gamma titanium aluminides are intermetallic alloys. Recently, they have been evaluated as important contenders for structural applications in the automotive and aerospace sectors. This is due to their excellent high-temperature performances and their significantly lower density compared to Nickel-based superalloys. In this paper, an analysis of machinability of a gamma TiAl obtained via an electron beam melting (EBM) process is presented. The effects of tool geometry modifications, in terms of cutting tool angles and cutting edge preparation, were investigated. The reduction of radial rake angle and the drag finishing process for cutting edge preparation resulted in an increase of the tool life of the carbide end mills. Nanogradient tool coatings were also observed to affect tool wear during milling tests, and the results highlight that AlSiTiN coating performs better compared to CrAlSiN coating. A post-coating polishing treatment was also taken into account, and it allowed a further reduction of tool wear. The overall results indicate that the machinability of this difficult-to-cut material can be significantly improved by an adjustment of the cutting edge geometry, and by using an AlSiTiN coating syste

Experimental and numerical characterization of a mechanical expansion process for thin-walled tubes

Air heat exchangers are made with tubes joined to finned pack. The connection between tubes and fins can be obtained through a mechanical process where an ogive is pushed inside the tube with smaller internal diameter causing its expansion. Residual plastic deformation provides the assembly with the fins. Accurate connection over the whole contact area of the tubes and fins is essential for maximum heat exchange efficiency. The goal of this work is to study and develop a finite element model able to effectively simulate expansion forming, allowing process analysis and, eventually, process optimization. The paper is divided into a first experimental part, where the materials used for the heat exchangers are characterized, and a second numerical part where models have been developed on the basis of the experimental data. The developed models are used to identify the material properties with an inverse method, and then to study the technological process of tube expansion by using a simplified but sufficiently accurate description. The model has proved to be an effective design tool, as it can evaluate the influence of the main parameters on the process and so optimize production according to technological variations

On high-speed turning of a third-generation gamma titanium aluminide

Gamma titanium aluminides are heat-resistant intermetallic alloys predestined to be employed in components suffering from high mechanical stresses and thermal loads. These materials are regarded as difficult to cut, so this makes process adaptation essential in order to obtain high-quality and defect-free surfaces suitable for aerospace and automotive parts. In this paper, an innovative approach for longitudinal external high-speed turning of a third-generation Ti-45Al-8Nb- 0.2C-0.2B gamma titanium aluminide is presented. The experimental campaign has been executed with different process parameters, tool geometries and lubrication conditions. The results are discussed in terms of surface roughness/integrity, chip morphology, cutting forces and tool wear. Experimental evidence showed that, due to the high cutting speed, the high temperatures reached in the shear zone improve chip formation, so a crack-free surface can be obtained. Furthermore, the use of a cryogenic lubrication system has been identified in order to reduce the huge tool wear, which represents the main drawback when machining gamma titanium aluminides under the chosen process condition

Sheet metal plate design: a structured approach to product optimization in the presence of technological constraints

Geometrical optimization of structural components is a topic of high interest for engineers involved with design activities mainly related to mass reduction. The study described in these pages focuses on the optimization of plates subjected to bending for which stiffness is obtained by a pattern of ribs. Although stiffening by means of ribs is a well-known and old technique, the design of ribs for maximum stiffness is often based on practice and experience. Classical optimization methods such as topological, topographical and parametric optimization fail to give an efficient design with a reasonable programming effort, especially when dealing with many and complex constraints. These constraints are both technical and technological. A most promising technique to obtain optimal rib patterns was to define a set of feasible rib trajectories and then to select the subset with the most efficient combinations. The result is not unique and a method to select the optimal patterns is required. In fact, the stiffening effect increases with increasing rib length, but at a greater cost. A trade-off must be found between structural performance and cost: The tools to guide this selection process is the main objective of the paper, with particular attention in evaluating the stiffening due to the presence of beads on the plate with a close link with the production system and possible technological constraints which can occur during manufacturing processes, such as minimum rib distance or the presence of discontinuities or the presence of holes or other elements on the plate. A special tool with enforced rib cross section is considered, and optimal rib deployment has to be found. Numerical examples attached show the methodology and obtainable results. \ua9 2011 Springer-Verlag London Limited

Hourly simulations of an hospital building for assessing the thermal demand and the best retrofit strategies for consumption reduction

In the framework of energy saving and environmental protection, the role of the energy consumption in buildings is crucial. For existing buildings and especially for public ones, it is mandatory to correctly select and realize suitable retrofitting interventions to reduce costs and increase the efficiency. In fact, innovative solutions for both the envelope and the plants renovation are often very expensive and the correct choice becomes critical for the sustainability from the economic point of view. The aim of the present paper is to propose a methodology to optimize the process of selection for the retrofit interventions, here applied to a case study of the Monoblocco Pavilion at the San Martino Hospital in Genova, Italy. The building thermal behaviour is dynamically simulated by means of an Energy Plus model in order to evaluate the energy needs for both heating and cooling purposes. The base case scenario is evaluated in terms of key performance indicators (KPIs) and compared with benchmark values in order to select the more suitable intervention actions. For the analysed case study, the innovative retrofit solutions are fa\ue7ade void insulated panels, smart rotating windows with different emissivity glass and sunlight carrying optical-fibres coupled with dimmed LED lighting system. The technologies are combined in different intervention packages that are then compared in term of energy saving and economic sustainability by means of the estimation of hourly values of energy consumption and the assessment of the Simply Pay Back Period (SPB) of the investment