ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2026 14 Metal additive manufacturing (AM) is widely considered a modern technology, attracting hundreds of millions of dollars in research, development, and deployment activity over the past two decades. This investment boom was enabled by the parallel maturation and democratiza- tion of motion control systems, robotics, and software in the 21st century. However, AM has deep roots in the history of welding and arguably has existed under different names since antiquity, embodying the need to increase manufacturing productivity and unlock new capabilities. EARLY BEGINNINGS While certainly not the first, a famous example of ancient AM is the Iron Pillar of Delhi (Fig. 1)[1]. Produced circa 400 AD, the pillar was forged by hammering small batches of iron produced by the bloomery process into a larger body of wrought iron. Manually working the wrought iron at an elevated temperature takes advantage of solid-state forge welding to combine separate chunks of material. Working a hot, yet still solid, material was accessible to ancient man, who was unable to produce and control the elevated temperatures necessary to melt iron and steel. With a few exceptions, most metal AM processes use welding methods to melt or otherwise bond material; the two most common mechanisms are solid-state and fusion welding. The 1600-year-old Iron Pillar of Delhi was produced via forge welding of 20-30 kgs of wrought iron lumps. Forge welding is a solid-state process wherein atomic bonds are created by intimate contact between adjacent materials in the absence of phase change when exposed to high temperatures, pressures, or mechanical energy. Solid-state welding currently finds AM applications in the sintering of green bodies produced via binder jet AM and additive friction stir deposition. Whereas solid-state processes were available to ancient man by elevating iron to a red heat in a furnace,[2] fusion welding—which, when applied to AM, is classified per ISO/ASTM 5900 as directed energy deposition (DED)— utilizes focused energy sources such as an electric arc, laser, or electron beam to fuse and join material with filler metal or autogenously in the absence of filler. This requires technology that can heat material fast enough to melt it before the heat escapes to adjacent material and the surroundings. For example, an elementary thermodynamic calculation shows that heating from room temperature and fusing one gram of iron in one second requires approximately 900 W, assuming perfect insulation (a highly optimistic estimate). The focused and powerful energy sources necessary for fusion welding were enabled by the development of oxygen-fuel and electrical power equipment in the 18th, 19th, and early 20th centuries. The English scientist Edmund Davy discovered acetylene in 1836. But it was not until the late 19th century that oxy-acetylene welding became practical due to both the development of low-cost acetylene production and safe methods for storing pressurized acetylene. Between 1903-1906, French engineers Edmond Fouché and Charles Picard patented blowpipes designed to reduce the risk of flashback, making the oxy-acetylene welding process safer and more accessible[3,4]. Oxy-acetylene welding provided a portable, intense energy source suitable for manual welding on an industrial scale with the products of combustion serving as a shielding gas for the liquid weld pool. However, the process soon yielded to electric welding due to the ubiquity and controllability of electrical power. The establishment of the electric welding industry was predicated on the invention of the voltaic pile by Alessandro Volta of Italy in 1799, which enabled the study of continuous bursts of current[5]. Discovery of the continuous electric arc is variably attributed to Vasilii Petrov of Russia in 1802 or Sir Humphry Davy of Britain prior to his public demonstrations in 1808. Both scientists utilized carbon electrodes and the recently invented voltaic pile to supply the current[6]. The first documented joining of materials using a continuous arc discharge was by French electrical engineer Auguste de Mèritens, who patented carbon arc welding in 1881 utilizing a single carbon electrode in a handheld holder for the joining of lead plates[7]. The introduction of filler metal into the electric arc was patented by the American Charles Lewis Coffin in 1889. He describes two methods wherein an arc is either struck between two electrodes or between an electrode and the work. In either case, one electrode is composed of filler metal that fuses and falls onto the weld joint (Fig. 2)[8]. THE RISE OF AUTOMATION The desire for improved welding Fig. 1 — The Iron Pillar of Delhi is an early example of additive manufacturing, produced by forge welding together small batches of bloomery iron[1]. Fig. 2 — An illustration from C.L. Coffin’s 1889 patent showing two different electrical methods for introducing filler metal into a welded joint. The dark electrode labeled “C” is in both cases composed of filler metal[8].
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