Tool holders serve as a crucial link between the machine spindle and the cutting tool.Although the cost of tool holders may seem insignificant compared to the overall cost of a machining center, they play a crucial role in connecting the machine spindle and the cutting tool. Therefore, selecting the most appropriate tool holder is essential, as its quality can significantly influence the overall machining performance. With the increasing application of modern large-scale high-speed machining equipment in production, selecting the appropriate tool holder to match rising spindle speeds and ensure high-precision mold surface machining has become particularly important.

Types and Features of Tool Holders

1.Hydraulic Tool Holders

Hydraulic tool holders clamp the tool using a combination of a screw, piston, and sleeve. The clamping force is generated hydraulically by turning the screw.These tool holders offer extremely high radial runout accuracy (≤3μm) and repeatable clamping precision (≤3μm). Since the tool is clamped within a hydraulic chamber, hydraulic tool holders also provide excellent vibration damping, preventing material damage caused by tool vibration, thereby improving both the surface quality of the workpiece and the tool life. Hydraulic tool holders are maintenance-free, dust-proof, easy to use, and provide secure clamping.

2.Stress-locking Tool Holders 

Stress-lockingt tool holders clamp the tool through the elastic deformation of a polygonal bore. Ingeniously designed, these holders are especially suitable for high-speed machining.Their main advantage lies in the slim design, which increases the tool’s machining range and even allows for clamping of shorter cutting tools, thus reducing user costs. There are mainly two types on the market: slender holders, ideal for flexible handling of complex tasks; and rigid holders, which are thicker and harder, offering better machining quality. These holders do not require external clamping devices, and tool changes take just a few seconds, making them highly suitable for applications requiring frequent tool changes.

3. Universal Tool Holders

Universal tool holders suit light, medium, and heavy-duty machining, employing mechanical expansion technology similar in principle to hydraulic holders but operated mechanically. They provide effective vibration damping, extending tool life and enhancing workpiece surface finish. With radial runout accuracy up to 0.005 mm and a relatively low cost, they offer excellent value. Flexible clamping is possible via standard intermediate sleeves, with precise axial length adjustment using internal set screws.

4. Shrink Fit Tool Holders

Shrink fit tool holders use the principle of thermal expansion and contraction to clamp tools. Induction heating expands the clamping bore, allowing tool insertion; upon cooling, the holder contracts to grip the tool securely. They deliver very high clamping force, withstand high torque, and achieve radial runout accuracy of ≤3 μm. Compact in design, they offer relatively weaker vibration damping performance.

Key Considerations for Selecting a Tool Holder

①Machining Requirements: Select the tool holder size based on the machinability of the workpiece material and the part geometry, ensuring access to specific contours or features.

②Machine Characteristics: Select tool holders optimized for high-speed applications on fast machines, and high-rigidity tool holders for heavy-duty machining.

③Machining Strategy: For High-Speed Cutting (HSC) or High-Performance Cutting (HPC), use tool holders with low radial runout and excellent dynamic balance.

④Tool holder material: Typically alloy steel or carbon steel, offering high strength and toughness.

⑤Cooling Method: Select internal or external cooling based on the workpiece material and tool characteristics.

Conclusion

There is no one-size-fits-all solution for selecting the right tool holder system—it depends on the specific application. Understanding a tool holder’s static and dynamic characteristics is essential. Different tool holder systems vary in clamping principle, design, and application, each with distinct advantages. A highly rigid tool holder may not suit all machining tasks, and a tool holder ideal for high-speed machining might not meet heavy-duty requirements. Therefore, engineers must comprehensively consider multiple factors—especially clamping force, radial run-out accuracy, and dynamic balance quality at high speeds—to minimize vibration and ensure machining quality and efficiency.