Microfabrication and Precision Engineering

Research and Development

J. Paulo Davim, J Paulo Davim

• Publisher: Woodhead Publishing
• Year: 2016
• Print ISBN: 9780857094858
• eBook ISBN: 9780857094865
• Topic: Technik & Maschinenbau
• Subtopic: Maschinen- und Anlagebau

Microfabrication and precision engineering is an increasingly important area relating to metallic, polymers, ceramics, composites, biomaterials and complex materials. Micro-electro-mechanical-systems (MEMS) emphasize miniaturization in both electronic and mechanical components. Microsystem products may be classified by application, and have been applied to a variety of fields, including medical, automotive, aerospace and alternative energy. Microsystems technology refers to the products as well as the fabrication technologies used in production.With detailed information on modelling of micro and nano-scale cutting, as well as innovative machining strategies involved in microelectrochemical applications, microchannel fabrication, as well as underwater pulsed Laser beam cutting, among other techniques, Microfabrication and Precision Engineering is a valuable reference for students, researchers and professionals in the microfabrication and precision engineering fields.- Contains contributions by top industry experts- Includes the latest techniques and strategies- Special emphasis given to state-of-the art research and development in microfabrication and precision engineering

1

Modeling of micro- and nano-scale cutting

R. Rentsch¹, A.P. Markopoulos² and N.E. Karkalos², ¹Bremen University, Bremen, Germany, ²National Technical University of Athens, Athens, Greece

Abstract

This chapter highlights the modeling techniques used for the simulation of micro- and nano-scale cutting. Specifically, the text thoroughly describes modeling with the Finite Elements method for the preparation of microscale cutting models. Important parameters, including tool and workpiece geometry, meshing, and formulation are discussed. Additionally, separate sections of the chapter cover friction and material modeling for microcutting with Finite Elements. For nanoscale cutting, modeling with the Molecular Dynamics method is described. This section presents the representation of workpiece microstructure, potential functions, boundary conditions, and numerical integration at the atomic level. Furthermore, a bibliographic review for all the above parameters, for both modeling techniques, is included.

Keywords

Microcutting; nanoscale cutting; finite elements; molecular dynamics; modeling; simulation; materials modeling; microstructure; potential function

1.1 Introduction

Technologies for processing various materials and manufacturing components that possess features from a few nm to a few hundreds of μm are in use in contemporary industry. These micro- and nano-machining processes shape parts by removing unwanted material, carried away from the workpiece, usually in the form of chips. Evaporation or ablation may take place in some machining operations. The specific term cutting describes chip formation by the interaction of a wedge-shaped tool with the workpiece surface; the chip forms as a result of their relative movement. These machining operations include processes such as turning, milling, and drilling, usually described by the accompanying prefix micro- or nano-, depending on the scale of reference. In contemporary industry, abrasive processes, such as grinding, have great importance in cutting. Micro- and nano-cutting are more advantageous than other processes, since it is possible to machine a variety of materials in complex shapes with excellent surface finish and tight tolerances.

Until 2016, cutting and grinding at micro- and nano-scale have been studied theoretically and experimentally (Alting, Kimura, Hansen, & Bissacco, 2003; Brinksmeier et al., 2006; Byrne, Dornfeld, & Denkena, 2002; Corbett, McKeown, Peggs, & Whatmore, 2000; Dornfeld, Min, & Takeuchi, 2006; Madou, 2002; Mamalis, Markopoulos, & Manolakos, 2005; Masuzawa, 2000; Rentsch, 2009). The small dimensions of workpieces, cutting tools, and cut depths bring up a number of issues that may play no significant role in traditional machining but are of significance in micro- and nano-cutting. For example, in microcutting, features known as minimum chip thickness and size effect influence the underlying mechanisms of chip formation. It is not always feasible to carry out experimental work in order to overcome micro- and nano-scale manufacturing component problems. Moreover, increased demand, innovation, reliability, and cost reduction requirements need to be satisfied. Modeling and simulation techniques exist to aid engineers and scientists who use them in a variety of ways. These include: reducing experimental time and testing, giving insight into complex phenomena, exploring possibilities, reducing complexity and learning cycles of a process, increasing accuracy, and optimizing processes and products. However, in the related processes, the actual material removal can be limited to the surface of the workpiece (i.e., only a few atoms or layers of atoms). Inherent measurement problems and the lack of more detailed experimental data limit the possibility to develop analytical and empirical models as more assumptions need to be made. Therefore, modeling and simulation with advanced and specialized methods are employed. The following paragraphs focus on modeling with the finite elements method (FEM) for microscale cutting and molecular dynamics (MD) for nanoscale cutting. The main principles of the aforementioned techniques, the fields of application, limitations, considerations, and an up-to-date bibliography are provided within this chapter.

1.2 Modeling of microscale cutting

1.2.1 Minimum chip thickness and size effect

The set-up used in the modeling of microscale cutting is similar to the one used in the macroscale traditional cutting processes (i.e., a wedge-like tool is removing material from a surface). All the geometrical features and kinematic characteristics of the tool and workpiece are identifiable. However, downscaling all phenomena in order to apply the same theories in both the micro and macro regime proves to be inadequate. There are features of machining and phenomena that are considerably different in micromachining and do not allow for such a simplification. These differences arise when considering the chip formation process, the resulting cutting forces, the surface integrity, and tool life.

In Fig. 1.1, the orthogonal cutting model corresponding to microscale cutting may be observed. At this level, the depth of cut may be well below 10 μm with an anticipated surface roughness of only a few nm. The cutting edge, no longer be considered sharp, has a cutting edge radius comparable in size to the uncut chip thickness. Although the rake angle of the tool indicated in Fig. 1.1 is positive, the actual the effective rake angle participating in the processes is negative. In this case, the elastic-plastic deformation of the workpiece material and ploughing need to be taken into account, as well as the elastic recovery at the clearance face.

Figure 1.1 Orthogonal microcutting.

As explained above, one may deduct the existence of a removable minimum chip thickness from the workpiece surface in a mechanical micromachining operation. A stagnation point above which a chip is formed and below only elastic-plastic deformation takes place is assumed. The stagnation point is connected to a stagnant angle θ_m, which with the tool edge radius determines the value of the minimum uncut chip thickness, h_m (Malekian, Mostofa, Park, & Jun, 2012):

$h_{\mathrm{m}}=r_{\mathrm{e}}(1-\mathrm{cos...}$

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• About the editor
• Preface
• 1. Modeling of micro- and nano-scale cutting
• 2. Machining scale: Workpiece grain size and surface integrity in micro end milling
• 3. Micromachining technique based on the orbital motion of the diamond tip
• 4. Microelectrical discharge machining of Ti-6Al-4V: Implementation of innovative machining strategies
• 5. Microelectrochemical machining: Principle and capabilities
• 6. Microchannel fabrication via direct laser writing
• 7. Underwater pulsed laser beam cutting with a case study
• 8. Glass molding process for microstructures
• Index