MICRO MILLING OF METALLIC MATERIALS - A BRIEF OVERVIEW

Micro milling is an important process of mechanical micromachining, with practical application in aerospace, automotive, mould and die, biomedical, military and microelectronics packaging industries. This article will give a brief overview of the effects and conditions of micro milling with an emphasis on minimum chip thickness, size effect, cutting forces, cutting temperature, tool wear and tool failure, burr formation and surface quality. The case study presented in the present paper refers to the micro milling of an aluminium alloy

Higher education for sustainability: a bibliometric approach—what, where and who is doing research in this subject?

Contextualization: From a very early age, assuming more prominence over the last decades, issues related to sustainability have been taking on a particular interest in the field of research. Although initially the basic concern was at the level of environmental sustainability, the truth is that, progressively, education for sustainability, deeply linked to the science of sustainability, constitutes, together with the latter, the scientific basis for education for the sustainability in higher education, thus emerging a research niche capable of providing greater openness and interaction between higher education institutions and their surroundings. Main aims of the study: Due to the importance that this issue assumes, this article seeks to address the issue of sustainability in higher education, giving particular focus to the analysis at the level of studies that have been developed, which are the main countries and institutions where this has been most researched, as well as which main researchers have been working on this issue. Methodology: For this purpose, and using information taken from the Scopus Database, a bibliometric analysis was carried out, which based on the items “higher education” and “sustainability” allowed to identify a set of 4410 publications. Main results: The results obtained allow to conclude that the number of publications in this area has been observing a significant increase over the last 30 years, with the United States, UK, Spain, Australia and Germany emerging as the countries which publish the most, and within these the Leuphana Universitat Luneburg, RMIT, Hochschule fur Angewandte Wissenschaften Hamburg, Manchester Metropolitan and the Arizona State universities that most publish in this field of research. The five main researchers in the field of higher education for sustainability, were also highlighted. Main contributions: Theoretical and practical contributions were highlighgted, namely, the contribution for government entities and the respective HEIs to reflect on the possible synergies to be developed, as well as to establish strategies and policies promoters of a more efficient and effective investment in research in higher education for sustainabilit

Toolpath and machining parameters optimisation of the cavities of a knee prosthesis tibial insert

The main purpose of this paper is to demonstrate the applicability of conventional cutting tools in the machining of a custom tibial insert of a knee prosthesis. This study also aims to reduce the roughness and minimize the production time. In this work the optimisation of cutting strategies and parameters was achieved through the design and construction of a test-part containing the most important complex surfaces of the femoral cavities, the focus of the study. The milling was carried out in accordance with the Design Of Experiment and the Taguchi method and was performed in two stages to reduce the number of analysed factors. The achieved parameters are applied to the machining of a modelled tibial insert made of UHMWPE, using a NC machine with three axes. The initial parameters studied were the cutting method, axial and radial depth of cut, the direction of the feed and the feed rate. Three strategies were studied: two Blend, resulting in radial and spiral toolpaths, and one Parallel. According to the spiral strategy, an arithmetical mean roughness of R a = 1.1 μm was obtained, representing an improvement of 45% relatively to the initial phase value of 2.0 μm, with the Parallel toolpath. An overall improvement of 34% in time efficiency of the finishing operation was achieved after changing the machine settings. This study supports the conclusion that high-speed milling is an expeditious process to produce customized tibial inserts.publishe

Otimização multiobjectivo usando o método dos elementos finitos na maquinagem sustentável da liga TI6AL4V

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Estudo da maquinabilidade da liga TI-6AL-4V obtida por EBM para aplicação médica

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Multivariate robust modelling and optimization of cutting forces of the helical milling process of the aluminum alloy Al 7075

Helical milling is an advanced hole-making process and different approaches considering controllable variables have been presented addressing modelling and optimization of machining forces in helical milling. None of them considers the importance of the noise variables and the fact that machining forces components are usually correlated. Exploring this issue, this paper presents a multivariate robust modelling and optimization of cutting forces of the helical milling of the aluminum alloy Al 7075. For the study, the tool overhang length was defined as noise variable since in cavities machining there are specific workpiece geometries that constrain this variable; the controllable variables were axial feed per tooth, tangential feed per tooth and cutting speed. The cutting forces in the workpiece coordinate system were measured and the components in the tool coordinate system, i.e., the axial and radial forces, were evaluated. Since these two outcomes are correlated, the weighted principal component analysis was performed together with the robust parameter design to allow the multivariate robust modelling of the mean and variance equations. The normal boundary intersection method was used to obtain a set of Pareto robust optimal solutions related to the mean and variance equations of the weighted principal component. The optimization of the weighted principal component through the normal boundary intersection method was performed and the results evaluated in the axial and radial cutting forces components. Confirmation runs were carried out and it was possible to conclude that the models presented good fit with experimental data and that the Pareto optimal point chosen for performing the confirmation runs is robust to the tool overhang length variation. Finally, the cutting force models were also presented for mean and variance in the workpiece coordinate system in the time domain, presenting low error regarding the experimental test, endorsing the results.publishe

Multi-objective robust design of helical milling hole quality on AISI H13 hardened steel by normalized normal constraint coupled with robust parameter design

Helical milling is a hole-making process which has been applied in hardened materials. Due to the difficulties on achieving high-quality boreholes in these materials, the influence of noise factors, and multi-quality performance outcomes, this work aims the multi-objective robust design of hole quality on AISI H13 hardened steel. Experiments were carried out through a central composite design considering process and noise factors. The process factors were the axial and tangential feed per tooth of the helix, and the cutting velocity. The noise factors considered were the tool overhang length, the material hardness and the borehole height of measurement. Response models were obtained through response surface methodology for roughness and roundness outcomes. The models presented good explanation of data variability and good prediction capability. Mean and variance models were derived through robust parameter design for all responses. Similarity analysis through cluster analysis was realised, and average surface roughness and total roundness were selected to multi-objective optimisation. Mean square error optimisation was performed to achieve bias and variance minimization. Multi-objective optimisation through normalized normal constraint was performed to achieve a robust Pareto set for the hole quality outcomes. The normalized normal constraint optimisation results outperformed the results of other methods in terms of evenness of the Pareto solutions and number of Pareto optimal solutions. The most compromise solution was selected considering the lowest Euclidian distance to the utopia point in the normalized space. Individual and moving range control charts were used to confirm the robustness achievement with regard to noise factors in the most compromise Pareto optimal solution. The methodology applied for robust modelling and optimisation of helical milling of AISI H13 hardened steel was confirmed and may be applied to other manufacturing processes.publishe

Multivariate GR&R through factor analysis

Several measurement tasks present multivariate nature. In the cases with quality characteristics highly correlated within groups, but with a relatively small correlation between groups, the available multivariate GR&R methods are not suitable to provide a correct interpretation of the results. The present work presents a new multivariate GR&R approach through factor analysis. Factor analysis is a multivariate statistical method which focuses on the explanation of the covariance structure of the data. Through orthogonal rotation of the factors a suitable structure can be achieved with loadings easy to relate the variables to the factors. The proposed multivariate GR&R method through factor analysis is described and applied in the quality evaluation of holes obtained through helical milling process of AISI H13 hardened steel. The method succeeded in achieving a simple structure, with one factor related to the roughness outcomes and other related to the roundness ones, simplifying the gage capability evaluation.publishe

Tool wear in dry helical milling for hole-making in AISI H13 hardened steel

Helical milling is a hole-making process which can be applied to achieve high-quality finished boreholes in hardened steels. Due to the drilling process limitations, which are intensified when applied in hardened steels, the helical milling process can be applied on hole-making tasks in moulds and dies industry, since milling have been widely applied in moulds and dies machining to replace high-cost operations like grinding and electrical discharge machining. However, to succeed in achieving high-quality boreholes in hardened parts, which presents high added value due to previous operations, tool wear in the helical milling of hardened steels should be more investigated. In the present study, dry helical milling tool life tests were conducted in AISI H13 hardened steel parts, varying the cutting velocity. The flank wear on frontal cutting edges was progressively measured through optical microscopy, and SEM/EDS was performed in frontal and peripheral worn cutting edges. The wear occurred progressively in the flank of the frontal cutting edges with adhesion and oxidation as main wear mechanisms. In the peripheral edges, coating loss, and adhesion of workpiece material in the tool clearance surface were observed, besides fracture in the tool nose flank with the highest cutting velocity. A nested ANOVA was performed to evaluate the burr height in the borehole exit. The tool life stage was statistically significant in the burr height.publishe