The journey of cutting tool materials has been nothing short of transformative, progressing from high carbon steel to advanced composites like cemented carbide and beyond. Back in the 1800s, high carbon steel and alloy carbon steel were considered state-of-the-art for machining applications. Then came the accidental discovery of Mushet Steel, followed by the introduction of high-speed steel (HSS) in the early 1900s, which marked a major leap forward in tool durability and performance. Around this time, cast alloy cutting tools emerged, offering significant improvements in machining efficiency compared to their HSS counterparts.
A monumental shift occurred in the 1930s with the adoption of cemented carbide, also referred to as sintered carbide or tungsten carbide. This material consists of hard carbide grains bonded together with a metallic binder. Early versions of cemented carbide tools were brazed onto tool bodies, but the industry soon shifted its attention to indexable inserts. These inserts are manufactured by compacting a slurry of cemented carbide into molds, though the initial compacts are soft and porous. To achieve the desired hardness and strength, these inserts undergo a high-temperature sintering process. Some inserts are additionally ground for precise dimensions and thicknesses, and some are coated with thin layers to boost performance.
Compared to HSS tools, cemented carbide tools exhibit superior wear and heat resistance, enabling higher cutting speeds and feeds. This results in faster machining cycles and reduced costs. However, they are more prone to brittleness, necessitating robust spindles and fixtures. As such, cemented carbide tools are predominantly used in CNC machinery, whereas HSS tools remain common in manual setups. Cermet, a blend of cemented carbide with added titanium carbide particles, boasts exceptional wear resistance and delivers excellent surface finishes. Yet, it lacks the ability to handle high compressive stresses and is best suited for shallow cuts and lower feeds.
Ceramic tools excel in machining scenarios where materials like hardened steel, cast iron, or heat-resistant superalloys generate excessive wear or heat. Polycrystalline cubic boron nitride (CBN), an extremely costly material, is ideal for cutting hardened steel or gray cast iron, often integrated into tooling through welding onto a cemented carbide base. On the other hand, polycrystalline diamond (PCD) shines in machining non-ferrous materials such as aluminum, though it's unsuitable for steel or cast iron due to thermal degradation.
In the past, tools had to be resharpened or reformed once worn. With the advent of indexable inserts, this process has become obsolete thanks to their precise fit and easy replacement. This innovation has made indexable inserts the cornerstone of modern CNC machining. Their widespread use has not only enhanced machining precision but also contributed to greater operational efficiency.
To sum up, the evolution of cutting tool materials has profoundly influenced the machining industry, fostering more efficient and accurate operations. Starting with high carbon steel and alloy carbon steel, we've seen revolutionary advancements through HSS, cast alloy tools, and cemented carbide. Today, indexable inserts made from cemented carbide, cermet, ceramic, CBN, and PCD dominate the field, delivering unmatched wear resistance, heat tolerance, and machining speeds. Their tight tolerances make them a go-to solution for CNC applications, ensuring both precision and productivity in modern manufacturing.
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