Reasonable selection of material for drilling deep-hole drilling inserts
Deep hole drilling with internal chip evacuation is generally divided into single-flute and multi-flute configurations. In China, carbide inserts are widely used for deep-hole drilling tools. There are various types of cemented carbides, including conventional grades such as YG, YT, and YW, as well as advanced options like fine-grained and ultra-fine-grained carbides (e.g., YG6X, YD15), surface-coated carbides (e.g., YB120), and rare-earth-containing alloys (e.g., YW1R). Commonly used insert materials for internal chip removal in deep-hole drilling include YG8, YT15, YT798, and YW1.
Internal chip removal deep-hole drilling is typically performed under closed or semi-closed conditions, leading to poor heat dissipation and difficult chip evacuation. This can cause chip jamming, which may result in drill bit chipping or twisting. Additionally, the cooling fluid may not reach the cutting area effectively, causing excessive tool temperature and accelerated wear. As the depth of the hole increases, the tool overhang also increases, reducing system rigidity. These factors impose special requirements on the selection of insert materials: they must have high strength, hardness, wear resistance, and red hardness. They should maintain their performance at high temperatures and resist abrasive, diffusion, and oxidation wear.
Impact resistance is also crucial because internal chip removal drills are prone to chipping and twisting. The material selection process for these inserts is similar to conventional cutting but varies depending on the workpiece material. For example, when drilling ordinary carbon steel and alloy structural steels, which are relatively easy to cut, the common choices are YT15 for the guide block, and YT789 or YG8 for the outer edge and center teeth.
For high-strength and ultra-high-strength steels, which are more challenging to machine due to chip-breaking difficulties and high cutting forces, YD15 is often selected for its good impact resistance and wear resistance. When machining high-temperature nickel-based alloys, which tend to harden during cutting and generate high temperatures, YD15, YG10H, or 643 are typically used for the outer and inner cutting edges.
Stainless steels, such as 0Cr17Ni4Cu4Nb, 2Cr13, and 1Cr18Ni9Ti, present challenges due to their tendency to work-harden and generate high cutting forces. YG8, YW1, or 813 are commonly used for these materials to ensure sufficient bending strength and wear resistance.
For titanium alloys like TC4, TC6, and TC11, which are known for their high cutting temperatures and tendency to stick to the tool, YG-type carbides are preferred. YG8 or YD15 are suitable for the guide block and cutting edges.
Testing has shown that using appropriate materials and optimizing geometric angles can significantly improve drilling results. For example, in drilling N901 high-temperature nickel-based alloys, YD15, YG10H, or 643 inserts produced stable chips, accurate holes, and good surface finishes. Similarly, drilling 0Cr17Ni4Cu4Nb precipitation stainless steel with YG8, YW1, or 813 inserts yielded excellent results when the cutting parameters were optimized.
In the case of TC4 titanium alloy, using YG8 or YD15 inserts with an optimized geometry led to improved durability, consistent hole sizes, and stable processing quality. The radial force remained stable, and issues like spiral grooves and hole deflection were minimized.
In conclusion, selecting the right insert material for internal chip removal deep-hole drilling is a critical factor in ensuring smooth operation, improving tool life, and achieving high machining accuracy. The choice of material depends on the properties of the workpiece, and for difficult-to-machine materials, carbides like YG8 and YD15 are recommended for their strength, impact resistance, and wear resistance.
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