Workpiece factors affect toolholder selection
Factors that affect toolholder selection include the machinability of the workpiece material in each job and the configuration of the final part, which determines the size of the shank required to reach a particular profile or feature. The shank should be as simple and easy to use as possible to minimize the possibility of operator error.
The basic components of the machine tool play a key role – fast machine tools with linear guides will take advantage of the shank designed for high-speed applications, while machines with box slots support heavy-duty machining. Multi-tasking machines can perform both turning and milling/drilling operations.
The tool holder can also be selected according to the machining strategy. For example, in order to maximize productivity in high-speed cutting (HSC) processes or in high-performance cutting (HPC) applications, the shop uses different tools, the former involving shallower depth of cut HHS and the latter focusing on adequate power. However, high metal removal rates are produced on machine tools with limited speed.
The low repeatable radial runout helps ensure constant tool engagement, reducing vibration and maximizing tool life. Balance is critical, and high quality shanks should achieve precision balancing at G2, 5-25000 rpm mass (1 g.mm). The shop can determine the tool holder system that can meet its production needs in a cost-effective manner, depending on the actual situation or by consulting the tool supplier.
Each tool holder has its own market segment
Whether simple side-mounted, jacketed, heat-shrinkable, mechanical or hydraulic, the shank should meet specific process requirements.
Collet chucks and interchangeable jackets are the most common round shank technology. The cost-effective ER offers a wide range of sizes and provides sufficient clamping force for reliable light milling and drilling operations. The high-precision ER jacketed shank has low radial runout (< 5μm at the tip) and symmetrical design for high speed operation, while the reinforced version can be used for heavy duty machining. The ER holder facilitates quick changeover and can accommodate a wide range of tool diameters.
The thermal expansion shank provides a strong clamping force with a 3 μm concentricity at 3xD and excellent dynamic balance quality. The compact tool holder design is a good fit for tough part features.
The reinforced shank allows for medium to heavy duty milling, but the clamping force depends on the inner diameter tolerance of the shank and shank. Thermal expansion tools require the purchase of special heating devices, and the heating/cooling process requires more installation time than simply switching the jacket.
Mechanical milling chucks provide high clamping force and high radial rigidity through multiple rows of needle bearings. This design enables heavy-duty milling and quick tool change, but the amount of runout may be greater than the jacket system. Mechanical chucks are typically larger than other toolholder types, which may limit the tool's ability to reach certain part features.
Compared to mechanical chucks, hydraulic chucks that use hydraulic pressure to create a clamping force have fewer internal components and are therefore relatively slimmer in shape. The hydraulic chuck has a low radial runout and is effective for reaming, drilling and light milling at high spindle speeds, but is sensitive to large radial loads.
Spindle or tapered end determines torque transfer capability and tool centering accuracy
Just as important as how the tool holder secures the cutting tool is how to mount the tool holder to the machine tool spindle. Conventional BT, DIN and CAT toolholder tapers are suitable for smaller machine tools, but may be limited in high speed machining. Models that are in double-sided contact with the taper and end faces of the shank provide greater rigidity and precision, especially in the case of large overhangs. Reliable transmission of greater torque requires a larger taper size. For example, the HSK-E32 holder cannot replace the HSK-A125A in heavy-duty machining.
The choice of taper form of the shank usually varies by region. In the mid-1990s, 5-axis machines became more and more popular, and HSK began to emerge in Germany during this period. CAT shanks are primarily used in the United States, while in Asia, BT shanks are very popular and are often tapered/faced double-sided models.
HSK is often used for 5-axis machining. The PSC (Polygon Clamping System: Capto) and KM connections are primarily used in multitasking machines and are based on ISO standards. Both KM and Capto are modular systems that allow the assembly of length-specific tools by combining extension or reduction rods. As multitasking machines become more common, it is becoming increasingly popular to be able to implement machining, milling, drilling and other types of tool holders in a single setup.
The shop must pay attention to the importance of the tool holder in the machining system and understand how to properly match the correct tool holder to specific machine tools, machining strategies and workpieces to increase productivity and reduce costs.
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