Hard turning is a machining process that involves single-point cutting of workpieces with hardness exceeding HRC 45. It has become a key area in tool development, especially as new high-hardness and complex materials have emerged. Initially focused on hardened steels like gear steel, bearing steel, and die steel after heat treatment, hard turning now extends to materials such as thermal spray coatings, chrome-nickel alloys, heat-resistant nickel base alloys, and stellite cobalt alloys.
Currently, PCBN (Polycrystalline Cubic Boron Nitride) tools are the leading choice for ferrous metal machining due to their exceptional wear resistance. Their lifespan is typically several times longer than that of cemented carbide or ceramic tools. PCBN tools have also played a significant role in localization efforts, with innovations like Valin’s BN-K10 grade PCBN tool capable of machining tungsten carbide with hardness above HRC 70—marking a first in China. This tool is widely used in mining machinery, wear-resistant castings, rolling mills, and high-hardness pump components like high-chromium alloy cast iron impellers.
Compared to grinding, hard turning reduces capital investment in machine tools and allows for more flexible production. It also improves equipment utilization. In terms of quality, about 80% of the heat generated during hard turning is carried away by chips, significantly reducing the risk of grinding burns. Additionally, hard turning can be 4–6 times faster than grinding, and the resulting chips are easier to recycle.
Hard turning is often used as the final machining step to eliminate the need for grinding, which carries its own risks. The performance of the machine tool, including clearance, rigidity, accuracy, geometric precision, and electronic control functions, directly affects the success of the hard turning process. While it can replace grinding for many applications, some ultra-precise or special parts still require traditional grinding, especially when machine tool limitations exist.
Although hard turning isn't a complete replacement for ultra-precision grinding, it has replaced a significant portion of grinding processes, lowering overall manufacturing costs. A notable example is the use of Valin’s BN-H20 tool in hard turning hardened steel gears, achieving surface roughness of Ra 0.4 (equivalent to Rz 3.2), fully meeting gear grinding requirements.
BN-H20 and BN-H10 are typical PCBN grades used for finishing hardened parts. They come in standard CNC inserts, as well as custom boring tools, grooving cutters, and other forming tools. For high-hardness materials with large machining allowances, the BN-S20 grade PCBN tool offers excellent performance, capable of handling up to 10mm of material removal. This tool uses ceramic bonding agents instead of metal, providing better impact resistance and high-temperature wear resistance.
At the 2007 launch of BN-S20, it broke previous limitations in hard turning, proving effective even for heavy intermittent roughing. This breakthrough had a major impact on the tool industry. Today, with advancements in ceramic-bonded CBN tools, the balance between wear resistance and impact toughness has improved, making it possible to avoid time-consuming annealing and secondary quenching steps. The BN-S20 grade is also effective for austenitic stainless steel, high-temperature alloys, and other difficult-to-machine materials.
With continuous improvements in tool materials, design, and manufacturing techniques, Chinese-made tools have reached a high level of quality. PCBN tools have led the way in localization, offering cost-effective and efficient alternatives to imported options. As the demand for efficiency and cost reduction grows, the variety and quantity of locally produced tools will continue to expand, further strengthening China's position in the global tool market.
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Dongguan Jiufukai Hardware Products Co., Ltd , https://www.jfkspring.com