Deep hole boring is commonly faced with long tool overhang, weak system rigidity and severe cutting vibration. Excessive vibration will produce chatter marks on the inner hole surface, deteriorate dimensional precision and roundness, accelerate insert wear, and even cause boring bar bending fracture in serious cases. Reasonable selection of boring bar base material and adoption of scientific anti-vibration structure become the core approach to stabilize deep hole machining quality and expand the effective processing depth.

Alloy steel boring bars are the traditional general option. They feature low cost, good toughness and outstanding impact resistance, which are suitable for shallow-to-medium depth rough boring processes. However, the elastic modulus of steel is limited. When the extension length increases, rigidity drops sharply, and vibration becomes prominent, so steel bars are not recommended for high-precision deep hole finishing. Ordinary alloy steel bars are mainly applied in low-demand rough machining scenarios with small batch production and low precision requirements.

Solid cemented carbide boring bars possess much higher elastic modulus than steel bars, bringing obvious promotion of static rigidity under the same specification. Under limited overhang conditions, carbide bars effectively suppress bending vibration and achieve superior finishing stability. Nevertheless, inherent brittleness restricts its application scope. When encountering intermittent cutting or variable impact load, carbide bars are prone to crack or break. Therefore, solid carbide boring bars fit continuous fine boring with moderate overhang, while long-overhang deep hole working conditions still have obvious limitations.

Damped anti-vibration boring bars represent the optimal solution for long-overhang deep hole boring. This type of structure embeds built-in damping assemblies inside the bar body. Vibration energy generated during cutting is consumed via friction, collision or fluid damping inside the structure, which greatly reduces vibration amplitude. Compared with solid carbide bars, vibration-damped bars can obtain stable machining effects under larger overhang ratios. Multiple damping structures are widely adopted, including particle damping, viscous fluid damping and dynamic absorber damping. Users need to select corresponding structural forms according to processing material, cutting speed and overhang length.

Besides material category, external structural design further optimizes anti-vibration performance. Equal-diameter bar bodies are mainstream, while stepped variable-diameter structures can be adopted under specific installation space to improve local rigidity. The transition position between bar body and tool holder should adopt smooth arc transition to avoid stress concentration. The clamping length of the boring bar must be guaranteed; insufficient clamping depth will cause the vibration source to transfer to the connection position and weaken the anti-vibration effect. In addition, internal cooling channel layout cannot be ignored. Unreasonable drilling inside the bar will reduce structural rigidity and induce new vibration points.

Matching principles between material selection and working conditions should be clarified. For rough deep hole boring with short overhang and large impact load, high-toughness alloy steel boring bars can control procurement costs. For continuous fine boring with medium overhang, solid cemented carbide bars balance precision and economy. For precision deep hole machining with large overhang ratio, vibration-damped boring bars must be prioritized to avoid chatter defects. It is inadvisable to blindly pursue high-rigidity materials without combining actual overhang and cutting load, which may lead to unnecessary cost increase without expected machining improvement.