This article discusses two basic forms of extrusion: cold and hot. It provides information on three types of extrusion processes, namely, direct extrusion, reverse extrusion, and hydrostatic extrusion. The article also discusses the mechanics, analysis, tooling and die design of extrusion as well as thermodynamics. The finite-element method suitable for simulation of metal forming processes is explained. The article examines the extrusion defects that are divided into three different categories including surface, subsurface, and internal type. It includes information on friction and lubrication modeling of extrusion processes. The article also discusses the fundamentals of extrusion technology of titanium alloys and aluminum. It concludes with information on two forms of wear in extrusion, namely, adhesive and abrasive wear.

Machining serves as a more specialized supplement to the forging process, particularly in the formation of cavities and holes. This article provides information on the enclosures, cavities, and holes in hammer and press forgings. It provides a checklist that serves as a guide to the procedure for reviewing the design of cavities and holes to be incorporated in forgings. The article also describes forging designs in which cavities and holes are related to rib and web designs, punchout, piercing, extruding, and combinations of these processes.

This article begins with discussion on forgeability and the factors affecting the forgeability of aluminum and aluminum alloys. It describes the types of forging methods and equipment and reviews critical elements in the overall aluminum forging process: die materials, die design, and die manufacture. The article discusses the critical aspects of various manufacturing elements of aluminum alloy forging, including the preparation of the forging stock, preheating stock, die heating, lubrication, trimming, forming and repair, cleaning, heat treatment, and inspection. It concludes with a discussion on the forging of advanced aluminum materials and aluminum alloy precision forgings.

This article introduces the basic characteristics, processes, and product forms associated with the five major categories of aluminum wrought products, namely, flat-rolled products (sheet, plate, and foil); rod, bar, and wire; tubular products; profiles; and forgings. It summarizes the various product forms in which commonly used wrought aluminum alloys are available. The article also provides design guidelines for aluminum extrusions and discusses various forming methods.

In terms of the design of a forging, flash is an excess or surplus of metal that is trimmed or otherwise removed after forging operations are completed. This article discusses flash components and the functions of flash. It describes a series of conventional and unconventional flash designs and design adjustments, covering several forging processes and configurations. The article concludes with information on the checklists for the convenience of both designers of forgings and designers of forging dies and contiguous flash.

This article summarizes the types of hot working simulation tests such as hot tension, compression, and torsion testing used in the assessment of workability. It illustrates the use of hot torsion testing for the optimization of hot working processes. The article concludes with information on some hot torsion application examples.

Hammers and high-energy-rate forging machines are classified as energy-restricted machines as they deform the workpiece by the kinetic energy of the hammer ram. This article provides information on gravity-drop hammers, power-drop hammers, die forger hammers, counterblow hammers, and computer-controlled hammers. It describes the three basic designs of high-energy-rate forging (HERF) machines: the ram and inner frame, two-ram, and controlled energy flow. The article reviews forging mechanical presses, hydraulic presses, drive presses, screw presses, and multiple-ram presses.

Control of grain flow is one of the major advantages of shaping metal parts by rolling, forging, or extrusion. This article shows the effects of anisotropy on mechanical properties. Cylindrical forgings commonly have a straight parting line located in a diametral plane. The alternate classes of parting lines are called either "straight" or "broken" for brevity. Regardless of whether draft is applied or natural, the forging will have its maximum spread or girth at the parting line. Proper placement of the parting line ensures that the principal grain flow direction within the forging will be parallel to the principal direction of service loading. The article reviews the mutual dependence of parting line and forging process. It provides a checklist for the forging designer that suggests a systematic approach for establishing parting line location. Finally, the article contains examples, with illustrations of parting line locations, accompanied by tables of design parameters.

Retrogression and reaging (RRA) is an established form of postquench aging heat treatment. RRA treatments can be applied to precipitation-hardened aluminum alloys that are used in aerospace applications. This article provides information on the development background of RRA and the steps involved in the RRA treatments. It discusses the process descriptions, applications, microstructural consequences, and limitations of RRA. In addition, the article describes the influence of RRA on mechanical properties.

This article begins with a general review of the effects of changes in stress state on processing of materials. It describes the fundamentals of hydrostatic extrusion and reviews the various issues and benefits associated with hydrostatic extrusion. The article discusses the hydrostatic extrusion of structural alloys, composites, brittle materials, and intermetallics or intermetallic compounds, with examples. It concludes with a discussion on the attempts made to extend the hydrostatic extrusion to higher temperatures.

Forging machines use a wide variety of hammers, presses, and dies to produce products with the desired shape, size, and geometry. This article discusses the major types of hammers (gravity-drop, power-drop, high speed, and open-die forging), and presses (mechanical, hydraulic, screw-type, and multiple-ram). It further discusses the technologies used in the design of dies, terminology, and materials selection for dies for the most common hot-forging processes, particularly those using vertical presses, hammers, and horizontal forging machines. A brief section is included on computer-aided design in the forging industry. Additionally, the article reviews specific characteristics, process limitations, advantages, and disadvantages of the most common forging processes, namely hot upset forging, roll forging, radial forging, rotary forging, isothermal and hot-die forging, precision forging, and cold forging.

This article explores the possibilities and limitations imposed by manufacturing processes and materials. Detailed design rules for the processes are presented. The article lists the main features of process groups in a tabular form. The physical characteristics and ratings of relative cost and production factors are also tabulated. The process groups include casting; deformation; powder processing; machining; noncutting; joining; ceramic, glass, and polymer processing; and composites manufacturing.

Cold heading is typically a high-speed process where a blank is progressively moved through a multi-station machine. This article discusses various cold heading process parameters, such as upset length ratio, upset diameter ratio, upset strain, and process sequence design. It describes the various components of a cold-heading machine and the tools used in the cold heading process. These include headers, transfer headers, bolt makers, nut formers, and parts formers. The article explains the operations required for preparing stock for cold heading, including heat treating, drawing to size, machining, descaling, cutting to length, and lubricating. It lists the advantages of the cold heading over machining. Materials selection criteria for dies and punches in cold heading are also described. The article provides examples that demonstrate tolerance capabilities and show dimensional variations obtained in production runs of specific cold-headed products. It concludes with a discussion on the applications of warm heading.

Material extrusion systems are the most common types of additive manufacturing systems, also known as three-dimensional (3D) printers. This article focuses on the general 3D printing processes as can be demonstrated and manipulated in desktop printers. The discussion includes details of the components involved in material extrusion as well as the melt extrusion solidification (during cooling) process, the underlying mechanism of road bonding, and the factors affecting good part quality. The discussion also covers support material, postprocessing, and road-quality considerations and the addition of infill in melt extrusion to the hollow spaces inside an object to give it structural strength. Information is also provided on different materials and associated material properties that affect the rate the printer is able to advance and retract material, thereby affecting the quality and rate at which a part is printed. The final section provides information on the mechanism of viscous extrusion 3D printing.

This article presents an overview of fatigue crack nucleation from the point of view of the material microstructure and its evolution during cycling. It describes the sites of microcrack nucleation at the free surfaces. The article discusses the relation of dislocation structures and surface relief and reviews the mechanisms of crack nucleation. The damage of material due to crack nucleation, the extent (in terms of the number of cycles) of the nucleation stage, and the factors influencing crack nucleation are discussed.

This article focuses on approximate closed-form analytical methods, such as slab and upper bound methods, used for forward and inverse design of metal forming problems. Selected examples of application of these methods to metal forming processes are also discussed.

Aluminum products such as fasteners and automotive components are often produced by cold extrusion because it facilitates high volume production of near-net-shape parts. This article describes the cold extrusion process for aluminum alloys and the associated requirements for tooling, dies, punches, and other equipment. It covers typical tool materials and their working properties, and provides best practices for sizing aluminum slugs and preparing them for use. The article also discusses the wide range of achievable shapes from shallow cup-like extrusions to deep cups and complex parts with longitudinal flutes, stems, and grooves.

Fatigue damage in metals is caused by the simultaneous action of cyclic stress, tensile stress, and plastic strain. This article details the fundamental aspects of the stages of the fatigue failure process. These include cyclic plastic deformation prior to fatigue crack initiation, initiation of one or more microcracks, propagation or coalescence of microcracks to form one or more microcracks, and propagation of one or more macrocracks.

For forming processes, optimization goals range from tuning the process parameters while keeping geometry unchanged to finding optimal geometry for intermediate dies in a multistage forming operation. This article commences with a description on the three salient steps of optimization procedures: defining the objective function, calculating the objective function, and searching an optimum design. It concludes with an example illustrating the optimization of conical-die extrusion.

Ingot casting is the vital conduit between molten metal provided by primary production and recycling, and the manufacture of aluminum and aluminum alloy products. This article discusses various ingot forms, such as remelt ingot, billets, ingots for rolling, fabricating ingot, and particle ingot and powder. It describes the molten metal processing and ingot casting process in terms of open-mold casting and direct chill process. The article examines the continuous processes that provide commercial alternatives to conventional ingot casting. It reviews the postsolidification processes in terms of stress relief, homogenization, and scalping. The article concludes with a discussion on safety limited to ingot casting.