Computational analysis of micromachining Ti6Al4V titanium alloy

Tamara Novakov, Purdue University

Abstract

Micromachining has been a developing field for decades which has mostly been focused on the semiconductor industry. Today, processes such as mechanical micro milling are pursued due to the increased need for mechanical features on the micro scale. Mechanical micromachining work presented in this research contributes to the field by exploring the problems in micro machining with a focus on titanium alloys, a topic both challenging and rewarding thanks to its rising importance for the development of medical devices and biotechnology, electronics, optics, aerospace, environmental sciences, communications, automotive, as well as die and mold design. Many approaches have been taken to understand the behavior on such a small scale including experimental work, finite element analysis (FEA), molecular dynamics (MD) as well as analytical approaches. The purpose of the presented study was to investigate micromachining of Ti6Al4V using Finite Element Analysis utilizing a custom material model incorporating strain hardening, strain rate sensitivity, thermal softening and a damage model in order to account for all the phenomena occurring in the material during a cut on a micro scale. Computational simulations have been conducted using the Third Wave AdvantEdge™ software which is a Lagrangian finite element analysis package focused on the machining industry. The aim of the study was to determine the influence of the machining parameters on the minimum uncut chip thickness, the influence of the tool nose radius on the minimum uncut chip thickness as well as cutting and thrust forces, and determining the mechanism of chip formation on the micro scale. Considering the fact that the minimum amount of removed material dictates the precision and delicacy of the micromachining process, the focus of this study was to determine where the stable machining with true chip formation seizes and unstable machining characterized with burr formation begins with the aim of developing machining parameter recommendations for tool/work material pairs. Micromachining parameters for Ti6Al4V/carbide and Ti6Al4V/diamond pairs has been developed and presented together with the analysis of the chip formation mechanism as well as cutting and thrust force analysis. Contribution to the field can be summarized as: determination of the constitutive material model to be used in the finite element analysis incorporating strain hardening, thermal softening, strain rate sensitivity and a damage model; contributions to the field of computational analysis through the development of a number of finite element simulations by varying parameters such as rotational speed, feed/tooth, tool material and tool nose radius; computational verification of experimental and computational work done by other authors; observations regarding the differences between macro and micro machining including chip formation mechanisms and minimum uncut chip thickness; observations regarding the health concerns in workers in the micro manufacturing industry exposed to particles of size less than 10ìm as well as a new classification of process stability resulting in stability chart development which would enable easy determination of micro machining parameters yielding stable machining processes.

Degree

Ph.D.

Advisors

Jackson, Purdue University.

Subject Area

Biomedical engineering|Mechanical engineering

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