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Prediction Of Shear Localization Onset In Machining Of Ti-6al-4v

Diğer Başlık: Ti-6al-4v İşlenmesinde Kesme Lokalizasyonu Başlangıcının Tahmini

Oluşturulma Tarihi: 04-09-2020

Niteleme Bilgileri

Tür: Tez

Alt Tür: Yüksek Lisans Tezi

Yayınlanma Durumu: Yayınlanmamış

Dosya Biçimi: PDF

Dil: İngilizce

Konu(lar): Makina mühendisliği ve makinalar,

Yazar(lar): Yılmaz, Okan Deniz (Yazar),

Emeği Geçen(ler): Oliaei, Samad Nadimi Bavil (Tez Danışmanı), Kılıç, Sadık Engin (Tez Danışmanı),


Yayın Tarihi: 15-01-2020


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Anahtar Kelimeler

Ti-6Al-4V, Machining, Finite Element Method, Shear Localization, Damage.


Özet

Application of lightweight and energy-saving materials plays a significant role in different industries including automotive, aerospace and biomedical, to name a few. One important lightweight material is Ti-6Al-4V titanium alloy known as the working-horse of the titanium industry, because of its excellent chemical and mechanical properties. In spite of its widespread applications, Ti-6Al-4V is known as a difficult-to-cut material because of its low thermal conductivity, its high chemical affinity with most cutting tool materials, low modulus of elasticity and the formation of shear localized (serrated) chips during machining. The latter is of paramount importance, because of the fact that the consequences of the emergence of serrated chip formation in machining are fluctuations in the machining forces, accelerated tool wear, deterioration of the surface quality, reduced accuracy and out-of-tolerance machined components. The prediction of the onset of shear localization is one of the most challenging problems in the field of machining, i.e. determining the conditions in which the chip morphology is changing from continuous to a periodically varying. The issues associated with shear localized chips were the main driving force in the literature for the development of several material models for the simulation of shear iv localization during machining of Ti-6Al-4V titanium alloy. However, the accuracy and capability of the developed models for the prediction of the onset of serrated chip formation during machining Ti-6Al-4V have not been investigated. The aim of this thesis is to evaluate the accuracy of different material models to predict the onset of serrated chip formation during the machining of Ti-6Al-4V. The results of the finite element models are compared with the results of the experiments in terms of machining forces and chip morphology. Ploughing forces are obtained by varying uncut chip thickness at different cutting speeds by using the extrapolation method, and are used to correct cutting and thrust forces. Corrected cutting and thrust forces are used to calculate the Coulomb friction coefficient. Both explicit and implicit finite element codes are used with different material models with/without damage, with/without strain softening. The weakness and strength of each material model have been investigated for the prediction of the critical cutting speed, chip morphology and machining forces. The results of this study revealed that a modified Johnson-Cook material model which includes temperature softening and strain softening in the form of the hyperbolic tangent function is able to give acceptable predictions for the onset of shear-localization during machining of Ti-6Al-4V.



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