Materials Processing

A Unified Approach to Processing of Metals, Ceramics and Polymers

Lorraine F. Francis

• Verlag: Academic Press
• Jahr: 2015
• ISBN:
  9780123851338
• Thema: Technik & Maschinenbau
• Thema: Werkstoffwissenschaft

Materials Processing is the first textbook to bring the fundamental concepts of materials processing together in a unified approach that highlights the overlap in scientific and engineering principles. It teaches students the key principles involved in the processing of engineering materials, specifically metals, ceramics and polymers, from starting or raw materials through to the final functional forms. Its self-contained approach is based on the state of matter most central to the shaping of the material: melt, solid, powder, dispersion and solution, and vapor. With this approach, students learn processing fundamentals and appreciate the similarities and differences between the materials classes.

The book uses a consistent nomenclature that allow for easier comparisons between various materials and processes. Emphasis is on fundamental principles that gives students a strong foundation for understanding processing and manufacturing methods. Development of connections between processing and structure builds on students' existing knowledge of structure-property relationships. Examples of both standard and newer additive manufacturing methods throughout provide students with an overview of the methods that they will likely encounter in their careers.

This book is intended primarily for upper-level undergraduates and beginning graduate students in Materials Science and Engineering who are already schooled in the structure and properties of metals, ceramics and polymers, and are ready to apply their knowledge to materials processing. It will also appeal to students from other engineering disciplines who have completed an introductory materials science and engineering course.

• Coverage of metal, ceramic and polymer processing in a single text provides a self-contained approach and consistent nomenclature that allow for easier comparisons between various materials and processes
• Emphasis on fundamental principles gives students a strong foundation for understanding processing and manufacturing methods
• Development of connections between processing and structure builds on students' existing knowledge of structure - property relationships
• Examples of both standard and newer additive manufacturing methods throughout provide students with an overview of the methods that they will likely encounter in their careers

Chapter 1

Introduction to Materials Processing

Abstract

This chapter defines the field of materials processing and the scope of the text overall. Materials processing is the series of steps that converts a starting material into a useful form with controlled structural features and properties. The importance of materials processing to the discipline of materials science and engineering is described. Three approaches to materials processing are introduced: forming processes (creating shapes using dies, molds and forces), additive processes (creating shapes layer-by-layer using a computer file containing the details of the part shape), and subtractive processes (removing material from a block to leave behind the shape of interest). The chapters and the book focus on forming and additive processes. Examples of these approaches across metals, ceramics, and polymers are given.

Keywords

Materials processing; materials science and engineering; forming processes; additive manufacturing

1.1 Materials Processing: Definition and Scope

Materials processing is used to create all the manmade items that we know from everyday life. Products ranging from simple items, such as plastic wrap and paper clips, to complex multipart designs, such as automotive engines and electronic devices, are made by the same general sequence of events. Ultimately, the materials in these items originate from the earth and its resources. As shown in Figure 1.1, raw materials from the earth are converted, by mechanical, chemical, and thermal processes, to more refined starting materials. These starting materials are then processed into useful products. For example, mineral ores are mined from the earth; metals are then extracted from the ores and processed further to make metal alloys in standard forms, such as slabs, which can be converted into products or components. Likewise, ceramics originate from ores, which are mined and then refined into chemicals and ceramic powders, the starting materials for the creation of ceramic objects. Polymers also follow a similar sequence, often originating from oil. Oil is refined to a monomer (e.g., ethylene), processed into a polymer starting material (e.g., polyethylene pellets), and eventually converted into a polymer part. The initial steps in this complex series of events (i.e., mining and refining of raw materials) are of interest to materials scientists and engineers, but are the primary domain of mining engineers and chemical engineers. Materials engineers are more concerned with the latter steps of synthesizing and formulating the starting materials, especially processing them into useful products. The operations that fit into the box labeled Materials Processing are the focus of this book. That is, the emphasis is on the conversion of starting materials to new forms or shapes that are used in products.

Figure 1.1 The materials cycle. Materials Processing takes place in the conversion of starting materials to products. Adapted and updated from National Research Council (1974).

Throughout the complex sequence of events shown in Figure 1.1, engineers search for ways to minimize environmental impact, and develop more sustainable practices and process routes. Recycling as products are manufactured and after the end of their useful lives is one effort. Minimizing waste and emissions of pollutants is another important effort. Lastly, engineers seek to develop processes that minimize energy consumption and the emission of greenhouse gases. The move toward sustainability is also leading scientists and engineers to develop new materials that are derived from renewable resources, such as polymers synthesized from biomass feedstocks. One mechanism for tracking progress on these fronts and others is life cycle assessment (LCA). LCA provides a framework for following a product or family of products from “cradle to grave” and determining how to lower environmental impact. See Figure 1.2.

Figure 1.2 Schematic of the typical steps in a life cycle assessment (LCA). LCA is used to track products from production to the end of their useful life. From Cooper and Vigon (2001).

Materials processing is the series of steps that converts a starting material into a useful form with controlled structural features and properties. To successfully complete a materials processing sequence, engineers need to understand a number of fundamental topics, including heat and mass transport, flow, deformation, and phase change. Historically, the study of materials processing has been subdivided according to the type of engineering material. Ceramic processing, metal fabrication and forming, and polymer processing are covered in separate texts. However, common scientific and engineering principles unify the processing of all three classes of engineering materials. These unifying principles are explored throughout this book.

Materials processing is a key element in the field of materials science and engineering (MSE). The foundation of MSE is a set of interrelationships that govern the behavior of all engineering materials, including metals, ceramics, polymers, electronic materials, and composites. See Figure 1.3. One important relationship is between structure and properties. For example, the structure of a metal determines its mechanical strength, and the structure of a semiconductor determines its electrical conductivity. The single term structure covers a broad range of length scales, including atomic structure, interatomic bonding, crystal structure, nanostructure, microstructure, and macrostructure (i.e., size and shape). But how is structure itself determined? There are two important factors. The first is the chemical composition of the material, which controls the atomic structure and the interatomic bonding and affects other levels of structure as well. The second is processing. Materials with the same chemical composition can be processed in different ways to create materials with vastly different microstructures and even crystal structures. Interestingly, there is a connection between a material’s properties, such as melting point or glass transition temperature, and its ability to be processed by different methods. But materials processing is much more than just a scientific pursuit!

Figure 1.3 Interrelationships between processing, structure, and properties of engineering materials.

Materials processing is at the heart of product design. The design of the size, shape, and features of a product hinges on the selection and control of the processing method. Therefore, processing influences the applications that are possible for a given material. Economic factors invade each process step and impact the selection of the processing route. For example, if a company needs to produce 1 million widgets a year, the processing route chosen is different from that chosen for the expectation of 1000 widgets a year and different still from the route selected to make one widget. In addition, the combination of processing method and material is not necessarily the one that results in the best properties, but rather the one that provides acceptable properties and the highest profit. Similarly, the performance of a material, or its ability to retain properties and function over time, can also be affected by the processing route chosen. So, the engineer weighs a myriad of factors in choosing a material and a processing route.

Materials processing should be recognized as one part of the field of manufacturing, commonly defined as the making of goods and articles. In addition to materials processing, manufacturing also includes surface treatment and finishing, the assembly and joining of multiple parts, automation, quality control, and the coordination of multiple steps to create a finished product in an economically viable manner. Manufacturing is a significant segment of the United States and world economies, and a vital component in continuing advances in technology and quality of life that we have come to expect. New developments and improvements in materials processing are essential to the continuing advance of manufacturing and technology.

1.2 Three Approaches to Materials Processing

The goal of materials processing is to convert a shapeless starting material into a useful object with complexity and function. There are three basic approaches to achieving this goal. Examples of these approaches are shown in Figure 1.4.

Figure 1.4 Examples of the three approaches to materials processi...