May 2021 Volume 3

FORGING RESEARCH

kinds of metal materials. These formed and forged products have become an indispensable part of our daily lives. Development in the forming and forging industries accelerated notably over the last 50 years as a result of the invention of computers, CAD, and numerical and analytical techniques. The progression in numerical analysis and modeling has helped engineers to advance their forging and forming processes and equipment designs, which has substantially reduced forging costs and lead time and increased automation and speed to market. 3. Primary Classifications of Metal Forming and Forging 3.1 Bulk forming and incremental forming There are various ways to classifymetal forming processes. Typically, metal forming is divided into two large groups based on the forming processes’ characteristics: bulk forming and incremental forming. The products formed by bulk metal forming, which is also referred to as “conventional forming,” can be further categorized as heavy sections and thin sections according to the products’ attributes. Products with heavy sections are usually processed with forging, rolling, extrusions, and so on. Products with thin sections, such as sheet metal and tubing, are usually processed with stamping, deep drawing, hydroforming and so on. However, some processes (such as extrusions) can be applied to both heavy and thin sections. Incremental forming processes broaden forming capabilities by enabling the production of many products with special features that cannot be easily made (or made at all) with conventional bulk forming processes. The difference between bulk forming and incremental forming is that the latter creates deformation within regions of the workpiece, which experience more than one loading and unloading cycle. Because the tooling only works on a small region, the forming force is much smaller and thus the machine is small and relatively inexpensive. On the other hand, incremental forming processes have limited productivity, but since incremental forming processes are usually versatile, they are very suitable for low- volume production. In general, their forming precision is high so that both near net-shaped and net-shaped parts can be made. Figure 4 lists the common forming process technologies applicable to each category.

(700 BC) Figure 2. Mediaeval smelting furnace with accompanying smithy [2]

Water-powered hammer (1780)

Steam hammer (1860)

Figure 3. Forging machines in the Industrial Age [2] The long evolution of metal forming and forging shows us that in general, modern metal forming theories were built on some simple but important principles that emerged from ancient forming practices. For example, our ancient ancestors knew that heat can soften the metal to make working it easier, repeated forging can refine and densify the metal, and rapid cooling can harden and strengthen the products. These principles have helped frame the two major technical disciplines in metal forming: mechanics and metallurgy [3]. Mechanics, especially plasticity, explain how the tooling interacts with the metal during deformation. Metallurgy studies the interrelationship of the process and the metal being processed. Although there are many technical and economic considerations in selecting a metal forming process, the primary objectives of metal forming as a whole have always been to use plastic deformation to produce a workpiece with the desired shape, strength and durability. During the last 200 years or so, an understanding of the fundamentals of metal forming technologies, materials, and equipment was achieved, which led to rapid expansion and growth of the forming industry. Forgings were no longer limited to simple shapes and rough exteriors. Engineers are now capable of making some tremendously complex shapes with high precision. The products can range from tiny ones weighing just a few grams to gigantic ones weighing thousands of tons, constructed with many

Figure 4. Classifications of metal forming

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FIA MAGAZINE | MAY 2021