The majority of currently used additive manufacturing (AM) processes are solidification based (SAM). Another class of AM processes consists of those that rely on deformation (DAM) to place material instead of solidification. Although SAM processes are much more widely used, as research and development continues in DAM processes, they are becoming increasingly attractive, especially for the AM of metals. This article discusses some of the more widely used DAM processes, namely ultrasonic additive manufacturing, cold spray process, and friction stir welding, focusing on their applications, advantages, and limitations.

This article focuses on friction stir welding (FSW), where frictional heating and displacement of the plastic material occurs by a rapidly rotating tool traversing the weld joint. Much of the research activity early on pertained to issues related to understanding the process, such as learning about material flow, heat generation, microstructure development, and many other fundamental issues. The article summarizes the results of the research, describing the aspects of how FSW actually accomplishes sound joints in metals without melting them. It discusses the FSW process variations and the practical aspects of heat generation. The article provides information on the effect of welding on material properties and typical alloys in FSW applications. The alloys include 6061 aluminum, 5083 aluminum, 2xxx aluminum, and 7xxx aluminum alloys. The article concludes with a discussion on FSW equipment.

This article discusses the application of friction stir processing (FSP) and friction surfacing for tribological components. It describes the three critical aspects involved in the application of FSP for near-surface material modifications intended for tribological applications. These include tools, processing parameters, and machines. The article also discusses the equipment and processing parameters for friction surfacing. It describes various hybrid stir processing techniques that involve preheating of the workpiece material, especially relatively hard and high-strength ones. The article presents a partial list of surface-modification methods based on FSP. The partial list includes surface hardening, surface composites, and additive coating. The article also provides information on generation of residual stresses in metallic materials and alloys form different variants of FSP.

The friction surfacing process enables deposition of a wide variety of high-specification materials with an ideal metallurgical bond onto a range of metal substrates. This article provides a process description and discusses the equipment used for, and the applications of, friction surfacing.

This article presents an overview of the rules, regulations, and techniques implemented to minimize the safety hazards associated with welding, cutting, and allied processes. Safety management, protection of the work area, process-specific safety considerations, and robotic and electrical safety are discussed. The article explains the use of personal protective equipment and provides information on protection against fumes, gases, and electromagnetic radiation. It concludes with a discussion on safe handling of compressed gases as well as the prevention and protection of fire and explosion.

Friction welding (FRW) is a solid-state welding process in which the heat for welding is produced by the relative motion of the two interfaces being joined. This article provides an outline of the mechanisms of friction heating and discusses the two principal FRW methods: direct-drive welding and inertia-drive welding. It summarizes the similar and dissimilar metals that can be joined by FRW and discusses the metallurgical considerations that govern the properties of the resulting weld.

This article discusses the development of a welding procedure for friction stir welding (FSW), including the process of defining a preliminary procedure, the optimization of parameters, the development of supporting data, and other key features to ensure a successful procedure. The critical features of FSW tool design, initial process parameters, systematic welding trials, and robustness testing are reviewed. The article provides information on the common features of welding procedure qualification. It also includes a table that lists the procedures used in the production of sound friction stir welds in various aluminum alloys.

This article provides information on the practice considerations for the inertia and direct-drive rotary friction welding processes. It presents the tooling and welding parameter designs of these processes. The article discusses the welding of different material family classes to provide a baseline for initial development of a welding parameter set. Common material family classes, including steels, nonferrous metals, and dissimilar metals, are discussed.

This article lists the system parameters of the friction welding process and describes the four categories of monitoring and control of the manufacturing process. It discusses the monitoring methods of a rotary friction welded sample, for determining in-process quality of ferrous alloys, and dissimilar metals using acoustic emission. The article reviews the feasibility of detecting the presence of ferrite during microstructural evolution of friction welding of three austenitic stainless steels: 310, 304, and 255. It also explains the in-process quality control of friction welding.

A key differentiator between friction stir welding (FSW) and other friction welding processes is the presence of a nonconsumable tool in FSW, often referred to as a pin tool to differentiate it from other tooling associated with the process. This article discusses materials for friction stir welding (FSW) pin tools, various tool geometries that have been used, designs for specific applications, predicting and measuring tool performance, and other considerations in FSW pin tool design. The tool materials include tool steels, superalloys, refractory metals, carbides and ceramics, and superabrasives.

Friction stir welding (FSW) involves plastic deformation at high strain rates and elevated temperatures with resultant microstructural changes leading to joining. This article provides a link between deformation and FSW process parameters and summarizes the results of experimental temperature measurements during FSW of various metals. It considers the physical explanation of the heat input during FSW and the possible methods of their estimation. The article presents the experimental results of two analytical models, supplemented by experimental/numerical flow models on material flow during FSW. The types of defects, processing parameters affecting the generation of these defects, and results of theoretical models and simulations to understand the formation and control of defects during FSW are discussed. The article concludes with information on the microstructure and its distribution produced during FSW.

This article is a compilation of definitions for terms related to welding fundamentals and all welding processes. The processes include arc and resistance welding, friction stir welding, laser beam welding, explosive welding, and ultrasonic welding.

This article discusses the fundamentals of friction stir welding (FSW) and presents governing equations and an analytical solution for heat transfer. It provides the solutions for structural distortion in FSW. The article describes various techniques that have been adopted to solve the equations and simulate the FSW process. The techniques include modeling without convective heat transfer and modeling with convective heat transfer in a workpiece. The article concludes with information on active research topics in the simulation of FSW.

Friction welding is based on the rapid introduction of heat, causing the temperature at the interface to rise sharply and leading to local softening. This article illustrates the basic principles of direct-drive rotational friction welding and inertia friction welding. Modeling the effective friction response of the materials is central to simulating the welding process. The article discusses a series of distinct frictional stages during continuous drive friction welding. Modeling of the evolution of the thermal field has been an important objective since the early days of rotational friction welding. The article describes analytical thermal models and numerical thermal models for rotational friction welding. It concludes with information on the modeling of residual stresses.

This article briefly reviews the general causes of weldment failures, which may arise from rejection after inspection or failure to pass mechanical testing as well as loss of function in service. It focuses on the general discontinuities observed in welds, and shows how some imperfections may be tolerable and how the other may be root-cause defects in service failures. The article explains the effects of joint design on weldment integrity. It outlines the origins of failure associated with the inherent discontinuity of welds and the imperfections that might be introduced from arc welding processes. The article also describes failure origins in other welding processes, such as electroslag welds, electrogas welds, flash welds, upset butt welds, flash welds, electron and laser beam weld, and high-frequency induction welds.

This article describes the mechanism, advantages and disadvantages, fundamentals, capabilities, variations, equipment used, and weldability of metals in solid-state welding processes, including diffusion bonding, explosion welding, friction welding, ultrasonic welding, upset welding, and deformation welding.

This article discusses the classification of the attachment and joining methods in plastics, including mechanical fastening, adhesive bonding, solvent bonding, and welding. It describes the mechanical fastening techniques used to join both similar and dissimilar materials with machine screws or bolts, nuts and washers, molded-in threads, self-threading screws, rivets, spring-steel fasteners, press fits, and snap fits. The article explains solvent bonding used for thermoplastic parts, and tabulates the solvent types used with various plastics. It also describes the surface preparation of plastics, chemical treatment for adhesion, and tabulates the adhesive types for bonding plastics to plastics and plastics to nonplastics. The article briefly describes the welding processes of thermoplastics, including fusion welding (hot-tool, hot gas, extrusion, and focused infrared), friction welding (vibration, spin, and ultrasonic), and electromagnetic welding (resistance, induction, dielectric, and microwave). It concludes with the evaluation of welds using destructive and nondestructive testing.

The effective integration of aluminum metal-matrix composites (Al-MMCs) into useful structures and devices often requires an understanding of the weldability of Al-MMCs that includes a thorough knowledge on the effects of various interactions between matrix and reinforcement. This article provides a detailed discussion on weldability and the effect of viscosity, chemical reactions, and solidification on weldability. It discusses different welding processes, namely, gas-tungsten arc welding, gas-metal arc welding, laser-beam welding, electron-beam welding, resistance welding, friction welding, transient liquid phase bonding, and capacitor discharge welding.

This article describes general welding characteristics such as weld microstructure and weldability. The correlations of preheating and postweld heat treatment practices with carbon contents and welding characteristics of martensitic stainless steels are reviewed. The article contains a table that lists the electrodes and welding rods suitable for use as filler metals in the welding of martensitic stainless steels. It provides specific arc welding procedural recommendations for the commonly welded martensitic stainless steels. Martensitic stainless steel joining methods such as laser-and electron-beam welding, resistance welding, flash welding, and friction welding, are discussed.