The tremendous popularity of the television show Forged in Fire has introduced a whole new audience to the world of high-performance knives. It has also allowed millions of viewers to better understand the skills involved in hand forging and to appreciate the impressive cutting power and resilience of well-forged blades.
When most people think of forging a blade, they envision the traditional blacksmith model—a lone craftsman laboriously hammering a glowing piece of steel on a classic London anvil. More educated knife enthusiasts might add a trip hammer to that vision, but the basic process remains the same: heat a piece of steel until it is red hot and malleable and use tools, muscle, and lots of skill to pound it into the desired shape. For hand-crafted knives made one at a time, this traditional method works well; however, to adapt the forging process to large-scale production a more efficient and consistent method is required. That method is drop forging.
Drop forging uses a drop hammer—a heavy hammer or series of hammers that are typically raised by hydraulics and allowed to “drop” on the hot steel being forged. Both the hammer and the anvil portions of a drop hammer have specific shapes or are fitted with specially shaped dies that rapidly form the steel to the desired shape as it is forged. In open die drop forging, the dies allow the metal to expand freely to the sides when struck. The steel ingot is processed through a series of successive dies until its final form is achieved. Like hand forging, this method enhances the steel’s mechanical properties, ductility, fatigue resistance, and impact resistance because it refines and directs the grain flow to follow the shape of the piece. The result is a finished part that is stronger and more resilient than one that is cast or machined from solid stock.
The second form of drop forging is closed die or impression forging. This method is similar to the open die process in that it uses dies on both the hammer and anvil; however, these dies are equipped with side enclosures. As the hot steel is struck, the enclosures restrict its expansion and create the part’s finished form more quickly and consistently. The extreme efficiency and part-to-part repeatability of closed die forging makes it the most common method used in large-scale manufacturing.
No matter which forging method is used, the result is generally a near-finished part that still shows some of the “character” of the forging process. The degree to which the part is subsequently ground, sanded, and polished to finish it varies depending upon the nature of the product and the manufacturer’s goals. In many cases, drop forged parts are purposely left slightly rustic to highlight the fact that their “spirit” was indeed bestowed by the forging process.
Drop forging takes the age-old art of hammering hot steel to shape and transforms it into a modern manufacturing process. The resulting parts not only offer performance that transcends ordinary cast or machined pieces, but also reflect the rich history of the blademaker’s art.
Originally appeared in the September 2018 Spyderco byte e-Newsletter.
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