Stano Imbrogno

Finite element modelling of microstructural changes in dry and cryogenic machining AISI 52100 steel

The paper presents the results of investigations of grain size and hardness variation induced by orthogonal machining of hardened AISI 52100 bearing steel in the white layer (WL). The experiments were performed under dry and cryogenic cooling conditions using honed cubic boron nitride tool inserts. The experimental results are compared with a newly developed finite element model to describe microstructural changes and dynamic recrystallisation. Furthermore, the numerical model will be able to suggest if the WL formation is mainly thermally induced through phase transformation or mainly mechanically induced through severe plastic deformation. An iterative procedure was utilised to experimentally calibrate and then validate the proposed model at varying cutting speeds and cutting cooling conditions (dry and cryogenic). This paper is part of a Themed Issue on Recent developments in bearing steels.

Experimental analysis on semi-finishing machining of Ti6Al4V additively manufactured by direct melting laser sintering

The Additive Manufacturing (AM) techniques are particularly appealing especially for titanium aerospace and biomedical components because they permit to achieve a strong reduction of the buy-to-fly ratio. However, finishing machining operations are often necessary to reduce the uneven surface roughness and geometrics because of local missing accuracy. This work shows the influence of the cutting parameters, cutting speed and feed rate, on the cutting forces as well as on the thermal field observed in the cutting zone, during a turning operation carried out on bars made of Ti6Al4V obtained by the AM process called Direct Metal Laser Sintering (DMLS). Moreover, the sub-surface microstructure alterations due to the process are also showed and commented.

Numerical Modelling of Orthogonal Cutting of Electron Beam Melted Ti6Al4V

Finite element analysis of cutting processes of difficult-to-cut alloys is attracting more and more interest among the scientific community thanks to the change of predicting difficult to measure parameters as cutting forces, specific cutting pressures, cutting temperatures and the chip morphology. Aiming at calibrating and validating an FE numerical model, the predicted variables have to be compared with experimental results. Nowadays, Additive Manufactured Titanium alloys are being increasingly employed in the production of surgical implants and aero engine parts, but their peculiar fine acicular microstructure have to be taken into account dealing with their thermo-mechanical behavior as during machining operations. Based on the lack of literature works concerning experimental investigations on the machinability of Additive Manufactured Titanium alloys, this paper is aimed at investigating the cutting forces and temperatures arising during orthogonal cutting of an Electron Beam Melted (EBM) Ti6Al4V alloy.

On the Flow Stress Model Selection for Finite Element Simulations of Machining of Ti6Al4V

Numerical simulation of machining processes represents a promising tool able to reproduce the cutting conditions without the need to perform a large number of experimental tests. In order to obtain reliable results from the finite element method simulation, is then necessary to properly set up the simulation conditions and to implement the most suitable materials behavior according to the real workpiece characteristics. These data are available in commercial softwares libraries but often they have difficulties to properly represent the machined workpiece behavior. Thus, advanced model are implemented in the software to improve the simulations performance and to obtain realistic results. In this work, the more suitable materials flow stress, within those proposed in literature, is sought to simulate the machining process of Ti6Al4V. The results of the simulations have been compared with those obtained experimentally in terms of temperature, chip morphology and cutting force. The results confirm the need to properly select the materials flow stress model according to the physical sample.

High speed machinability of the aerospace alloy AA7075 T6 under different cooling conditions

This paper describes the results of an experimental investigation aimed to st udy the machinability of AA7075 T6 (160 HV) for aerospace industry at high cutting speeds. The paper investigates the effects of different lubri-cooling strategies (cryogenic, M QL and dry) during high speed turning process on cutting forces, tool wear, chip morphology and cutting temperatures. The cutting speeds selected were 1000m/min, 1250m/min and 1500 m/min, while the feed rate values used were 0.1mm/rev and 0.3 mm/rev. The results of cryogenic and M QL application is compared with dry application. It was found that the cryogenic and M QL lubri-cooling techniques could represent a functional alternative to the common dry cutting application in order to implement a more effect ive high speed turning process. Higher cuttingparameters would be able to increase the productivity and reduce the production costs. The effects of the cutting parameters and on the variables object of study were investigated and the role of the differ...

Microstructural and hardness changes in aluminum alloy Al-7075 : Correlating machining and equal channel angular pressing

Recently, the study and understanding of surface integrity of various materials after machining is becoming one of the interpretative keys to quantify a product’s quality and life cycle performance. The possibility to provide fundamental details about the mechanical response and the behavior of the affected material layers caused by thermo-mechanical loads resulting from machining operations can help the designer to produce parts with superior quality. The aim of this work is to study the experimental outcomes obtained from orthogonal cutting tests and a Severe Plastic Deformation (SPD) process known as Equal Channel Angular Pressing (ECAP) in order to find possible links regarding induced microstructural and hardness changes between machined surface layer and SPD-bulk material for Al-7075. This scientific investigation aims to establish the basis for an innovative method to study and quantify metallurgical phenomena that occur beneath the machined surface of bulk material.

2D finite element model and microstructural changes during cutting of Ti6Al4V in dry condition

The main objective of this study is to develop a FE model of the orthogonal cutting process executed on Titanium alloy (Ti6Al4V) under dry condition. In detail, the Abaqus/Explicit 2D formulation has been used to simulate the process and the results provided (temperature and strain rate) where employed to calculate the microstructural and hardness changes on surface and sub-surface. The quantitative analysis in terms of the grain refinement and hardness variation during the cutting process has been provided taking into account the Zener-Hollomon and Hall-Petch equations. The obtained results were compared with the experimental outcomes in order to understand the reliable rate of the model.