Ultrasonic Welding of Metal Sheets

Susanta Kumar Sahoo, Mantra Prasad Satpathy

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000227291
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Ultrasonic Welding of Metal Sheets covers various aspects of ultrasonic welding (USW) of metal sheets, including the discussion on modeling and numerical simulations of ultrasonic welding to improve this welding process and performance.

This book aims to provide an accessible, comprehensive and up-to-date exposition of the various aspects of joining of dissimilar metal sheets ranging from its fundamentals thorough to metallurgical characteristics covering fundamental concepts, in-detailed explanation about the USW including its implementation, design criteria, work material, welding, thermo-mechanical and research scopes. The book is aimed at researchers, professionals and graduate students in manufacturing, welding, mechanical engineering.

Features

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• The ultrasonic spot welding of various metal sheets is described in simplified expression and concepts are elucidated by relevant illustrations.

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• Discusses modeling and numerical simulations of ultrasonic welding to improve the ultrasonic welding process and performance

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• As opposed to competition in the market, this title provides thorough clarification of ultrasonic spot welding of metal sheets with its applications.

1Introduction

Materials and manufacturing processes have been in use since a long time ago. Over the years, there has been a continuous change in human's need for and choice of materials for various production activities. These activities are sometimes referred to as “ages” when the materials predominantly used had a significant effect on human civilization, such as Stone Age, Copper Age, Iron Age, and (currently) Silicon Age. The contribution of materials in a given society has led to advancement in many sectors, ranging from housing, clothing, transportation, agriculture, medicine, and communication to security and space. The challenges and requirements of the current world are constantly stimulating the invention and advancement of new materials to respond to the complexities of problems. On the one hand, the applications of these new materials let engineers and designers design a myriad of multifaceted structures, but on the other hand, use of these materials also poses a set of unique challenges in terms of integrating a number of components into a single product. These challenges include varying physical, chemical, and mechanical properties, different melting points of materials, and the degree of thinness of sheet materials. For example, mechanical fastening methods, such as self-piercing rivets (SPRs), are usually used to join dissimilar materials in the automotive industry. However, some properties of mechanical fasteners, such as high consumable cost, inconsistent nature, and additional weight, have caused attention to shift toward a robust, fast, and trustworthy welding method. For instance, in the spot welding sector, almost 5,000 weld spots are required to build one car. Numerous welding technologies are present in the current market, but the joining of dissimilar materials is still a challenge.

1.1Fundamentals of Welding

Most manufacturing processes include some series of operations to produce components having different physical, mechanical, chemical, and dimensional properties. Selection of a proper manufacturing process involves factors such as complexity of the product, production rate, and the related economics. Basically, there are four key manufacturing processes (illustrated in Figure 1.1). Joining is one of the ways to assemble components to attain the desired or preferred shape of the end usable product. Welding is the permanent joining process in which metals and nonmetals are joined together, with or without the application of pressure and with or without the addition of filler material [1]. In conventional welding processes, a filler material may be required to assist coalescence. The product created of parts that are joined by welding is called a weldment. Welding is commonly applied to join metal parts, but can also be used to join plastics. In contrast, mechanical joining is a temporary joining process that uses fasteners such as nuts, bolts, screws, rivets, and pins. In both brazing and soldering processes, the materials join with each other while a molten filler metal fills the narrow gap between them through the capillary action effect. If the melting point of the filler metal is above 450°C, the process is known as brazing. However, if the melting point of the filler metal is below 450°C, the process is termed soldering. Likewise, adhesive bonding is a technique of joining two materials using adhesives.

FIGURE 1.1Basic classification of joining techniques among various manufacturing processes.

The various advantages of welding techniques include faster integration time, joints that are stronger than the base metal, economy, the light weight of parts, no restrictions as to the site of manufacture, and high joint efficiency. There is a broad spectrum of welding techniques available in the market. However, the selection of a particular welding process depends on the dimension of the components to be welded, the type of material used, the availability of filler materials, the number of units to be produced, economy, accuracy, and reliability. Over a long period of time, it has been shown that certain specific welding techniques are delivering effective outcomes to various particular sectors: automotive sectors use resistance welding, the shipbuilding and heavy engineering industries utilize submerged arc welding, thermite welding is applied to join railway tracks, and aviation industries and nuclear reactors employ tungsten inert gas welding.

1.2Fusion Welding Techniques and Issues

Fusion welding techniques involve the melting of mating surfaces of the base material as well as the filler materials to form weld beads. Thus, heat is an essential component in this process, and it can be supplied from outside in forms of electric arc, gas, resistance heat, and laser beam [2]. Although there are certain advantages of these processes, some factors really make it a challenging task, especially in the case of joining of dissimilar metals. These issues include the generation of residual stress, distortion, and a heat-affected zone (HAZ). Moreover, the mechanical characteristics of the base metal are also severely affected by this strong heating. During the resistance spot welding (RSW) process, some amount of contact pressure (along with the electric resistance) is required to produce coalescence at the faying surface. RSW is widely used in the automobile, heavy engineering, and electronics sectors due to its fast, automated, and reliable nature. However, this technique encounters many hurdles during the welding of materials of high electrical and thermal conductivities with dissimilar properties [3]. Moreover, the process requires high energy (i.e., 50–100 kilojoules [kJ] per single weld spot) [4]. This process is more prone to form intermetallic compounds during the welding process; create a large HAZ; and suffer distortion, cracks, residual stress, and short electrode life. Figure 1.2 portrays a typical interface failure in RSW.

FIGURE 1.2Interfacial weld defect showing a prominent crack from the RSW process [5].

Laser welding is a type of noncontact technique that joins metal sheets by melting them down in a few seconds. Despite its ability to join multiple layers of sheets by the laser beam, this welding process also has certain drawbacks, such as poor metallurgical affinity, porosity, large intermetallic compound formation, high initial set-up cost, and sensitivity to cracks [6]. The various defects that may be produced during laser welding are depicted in Figure 1.3.

FIGURE 1.3Surface features and defects at cross-sections of weld beads at various laser spot diameters [7].

1.3Solid-State Welding Techniques and Issues

Solid‐state welding is a kind of process in which the faying surfaces of the base material get joined without melting. Pressure must be applied to get a good joint by forming a thick metallic bond between the workpieces. It is worth noting that the temperature involved in all solid-state welding techniques is below the melting point of the base materials. This technique utilizes the combination of heat and pressure for a particular time period to overcome hurdles such as porosity, cracks, and slag inclusions faced by the conventional welding process. Solid-state welding includes the pressure, forge, friction, explosive, diffusion, and ultrasonic welding processes. The basic principle of these processes is the atomic diffusion between the two materials, which will occur when the interatomic distance is below 10 Å. Thus, these types of welding methods require clean and perfectly smooth surf...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Preface
• About the Authors
• Chapter 1 Introduction
• Chapter 2 Fundamentals of Ultrasonic Spot Welding
• Chapter 3 Tool and Fixture Design for Ultrasonic Spot Welding of Dissimilar Metal Sheets
• Chapter 4 Ultrasonic Spot Welding Configuration and Process Parameter Selection
• Chapter 5 Ultrasonic Spot Welding of Dissimilar Metal Sheets
• Chapter 6 Thermo-Mechanical Modeling in Ultrasonic Spot Welding of Dissimilar Metal Sheets
• Chapter 7 Future Research Trends in Ultrasonic Spot Welding of Dissimilar Metal Sheets
• Index