1. Workpiece factors affect toolholder selection
Factors that influence toolholder selection include the machinability of the workpiece material in each job and the configuration of the final part, which can determine the toolholder size needed to achieve a specific profile or feature. The tool handle should be as simple and easy to use as possible to minimize the possibility of operator error.
The basic building blocks of the machine tool play a key role - a fast machine with linear guides will take advantage of a toolholder designed for high-speed applications, while a machine with a box groove supports heavy-duty machining. Multi-tasking machines can perform turning and milling/drilling operations simultaneously.
The tool holder can also be selected according to the machining strategy. For example, shops use different tools to maximize productivity in high-speed cutting (HSC) operations, which involve shallow depths of cut (HHS), or in high-performance cutting (HPC) applications, which focus on high-power cutting. However, machine tools with limited speed produce high metal removal rates.
Low repeatable runout helps ensure a constant amount of tool engagement, reducing vibration and maximizing tool life. Balance is crucial and high quality toolholders should be precision dynamically balanced at G2,5-25000 rpm mass (1 g.mm). Job shops can determine the toolholder system that can cost-effectively meet their production needs based on actual conditions or by consulting with tool suppliers.
2. Each tool holder should meet specific process requirements.
Whether simple side-fastened, jacketed, heat shrinkable, mechanical or hydraulic, toolholders should meet specific process requirements.
Spring collets and interchangeable collets are the most commonly used round toolholder technologies. The cost-effective ER style is available in a variety of sizes and provides sufficient clamping force for reliable light milling and drilling operations. High-precision ER colleted toolholders feature low runout (< 5µm at the tool tip) and a symmetrical design balanced for high-speed operations, while reinforced versions are available for heavy-duty machining. ER toolholders allow for quick changeovers to accommodate a variety of tool diameters.
The shrinkfit holders provide strong clamping force, have 3 μm concentricity at 3xD and have excellent balancing qualities. The compact handle design provides excellent access to tricky part features.
Reinforced toolholders allow for medium to heavy-duty milling, but clamping force depends on the inner diameter tolerance of the toolholder and toolholder. Shrink-fit tools require the purchase of a special heating device, and the heating/cooling process requires more setup time than simply switching the collet. The mechanical milling chuck provides strong clamping force and high radial rigidity through multiple rows of needle bearings. This design enables heavy-duty milling and quick tool changes, but runout may be greater than with a collet system. Mechanical chucks are often larger in size than other toolholder types, which can limit the tool's reach to certain part features.
Compared to mechanical chucks, hydraulic chucks, which use oil pressure to generate clamping force, have fewer internal components and therefore have a relatively slimmer profile. Hydraulic chucks have low radial runout and are effective for reaming, drilling and light milling at high spindle speeds, but are sensitive to large radial loads.
3. The spindle or tapered end determines the torque transmission capability and tool alignment accuracy
Just as important as how the tool holder holds the cutting tool is how the tool holder is mounted to the machine tool spindle. Traditional BT, DIN and CAT toolholder tapers are suitable for smaller machine tools but may be limited in high-speed machining. Versions with double-sided contact on the taper and end face of the tool holder provide greater rigidity and accuracy, especially with large overhangs. Reliably transmitting more torque requires larger taper sizes.
The choice of toolholder taper pattern often varies by region. HSK began to emerge in Germany in the mid-1990s, when 5-axis machine tools were becoming more and more popular. CAT toolholders are primarily used in the United States, while in Asia BT toolholders are very popular and are often available in double-contact/contact versions.
HSK is commonly used for 5-axis machining. PSC (Polygonal Clamping System: Capto) and KM connections are mainly used on multi-task machine tools and are based on ISO standards. Both KM and Capto are modular systems that allow the assembly of tools of specific lengths by combining extension or reduction rods. As multi-tasking machine tools become more common, toolholders that can perform turning, milling, drilling and other processing types in one setup are becoming more and more popular.
4. Summary
Job shops must appreciate the importance of toolholders in their machining systems and understand how to properly match the right toolholder with a specific machine tool, machining strategy and workpiece to increase productivity and reduce costs.
Future technological improvements will no longer be limited to the tool handle itself. Tool management using software and RFID tags is an element of data-based manufacturing and is becoming increasingly common. Advances in toolholder technology include toolholders equipped with sensors that monitor forces on the toolholder in real time. The data collected allows operators to make adjustments to machining parameters during machining, even automatically through artificial intelligence (AI) connected to the machine control unit. These and other new technologies will further increase the production contribution of toolholders in the machining process.