Precision machine tools paired with advanced cutting tools provide outstanding metal cutting productivity. The tool holder, as the critical interface between the cutting tool and the machine tool spindle, is critical to achieving high productivity. Tool manufacturers offer a variety of toolholder types, each designed to perform optimally in specific machining applications. Therefore, a shop should choose a tool holder based on its specific process and the parts it produces. However, while shops want to use the most advanced machine tool technology and cutting tool materials, they often don’t pay much attention to the selection, application and maintenance of the holder that best suits their specific production needs.
All Hilts Are Not The Same
No one handle system is perfect. Toolholders built for high-speed finishing operations often lack the rigidity and strength required for efficient machining, such as roughing rough castings. Conversely, toolholders for roughing often lack the dynamic balance that allows them to run smoothly at high speeds during finishing operations. Additionally, the thick design and bulk of the roughing toolholder may limit its reach to finer or deeper part features. Difficult-to-machine materials require toolholders with increased strength and rigidity. In addition, the vibration damping ability of the tool holder and the ability to deliver coolant are also important selection criteria.
Using an inappropriate tool holder can lead to dimensional errors and scrapped parts, as well as excessive wear on the machine tool spindle, reduced tool life and increased risk of tool breakage. In non-critical jobs, a good, inexpensive tool holder may yield satisfactory results. However, in operations where repeatable accuracy must be achieved, especially where the scrapping of expensive workpieces reduces the profitability of the part, investing in high-quality, application-focused toolholders can protect against such unplanned losses at a lower cost.
Some shop managers may find it cost effective to use long toolholders in a variety of applications. However, using the shortest tool holder possible will maximize rigidity, reduce vibrations that degrade surface quality, and preserve tool life.
The tool holder accounts for less than 2% of the total production cost. Even halving the cost of the tool holder is a negligible saving on the total production cost, while scrapped workpieces or tool breakage have a significant impact on costs. High-quality tools and holders increase metal cutting productivity for an immediate return on tool investment. Especially in industries such as aerospace component manufacturing where process stability is critical, many manufacturers focus on purchasing quality tools to avoid producing defective parts or wasting time on troubleshooting and Production is interrupted. Aerospace manufacturers often take a longer time to validate new toolholder concepts before proceeding to production certification.
Workpiece Factors Affect Tool Holder Selection
Factors that influence toolholder selection include the machinability of the workpiece material in each job and the configuration of the final part, which determine the size of the toolholder needed to reach a particular profile or feature. Tool holders should be as simple and easy to use as possible to minimize the possibility of operator error.
Regardless of the tool holder technology used, the rigidity of the machine tool, spindle power and ability to produce tight tolerances will determine what operations are possible. For example, trying to produce micron tolerances on worn machine tools is impractical.
The basic building blocks of the machine play a key role—fast machines with linear guides will take advantage of tool holders designed for high-speed applications, while machines with box grooves support heavy-duty machining. Multitasking machines can perform turning and milling/drilling operations simultaneously.
The tool holder can also be selected according to the machining strategy. For example, to maximize productivity in high-speed cutting (HSC) operations or in high-performance cutting (HPC) applications, shops use different tools, the former involving shallower Produces higher metal removal rates on machines with limited speeds.
Low repeatable radial runout helps ensure constant tool engagement, reducing vibration and maximizing tool life. Balance is critical, high quality toolholders should be precisely balanced at G2,5-25000 rpm mass (1 g.mm). Shops can, on a case-by-case basis, or consult with tool suppliers, determine a toolholder system that can cost-effectively meet their production needs.
Each Handle Has Its Own Market Segment
Whether simple side-set, jacketed, heat-shrinkable, mechanical or hydraulic, tool holders should meet specific process requirements. For example, simple end mill holders for side shank tools are strong, easy to use, transmit high torque, and provide a secure and robust clamping with strong pull-out resistance. These holders are great for heavy-duty roughing, but lack precise concentricity. Often, they are inherently unbalanced and cannot be used effectively in applications that use high RPMs.
Collets and interchangeable collets are the most commonly used round shank 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. The high-precision ER collet holder features low radial runout (< 5µm at the nose) and a symmetrical design that balances high-speed operations, while the reinforced version can be used for heavy-duty machining. ER holders allow for quick changeovers and can accommodate a wide range of tool diameters.
Shrinkfit holders provide strong clamping force, 3 μm concentricity at 3xD, and excellent balance quality. The compact shank design provides excellent access to tricky part features.
Reinforced holders allow for moderate to heavy duty milling, but clamping force depends on the shank and holder ID tolerances. Shrinkable tools require the purchase of a special heating device, and the heating/cooling process requires more setup time than simply switching jackets.
Mechanical milling chucks provide strong clamping force and high radial rigidity through multi-row needle bearings. The design allows for heavy-duty milling and quick tool changes, but the runout may be greater than with collet systems. Mechanical chucks are often larger in size than other toolholder types, which may limit the tool’s reach to certain part features.
Compared to mechanical collets, hydraulic collets, which use oil pressure to generate the clamping force, have fewer internal components and are therefore relatively slimmer in 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.
Just as important as how the tool holder holds the cutting tool is how the tool holder is mounted on the machine tool spindle. The spindle or tapered end of the tool holder determines the torque transfer capability and the accuracy of tool alignment. Traditional BT, DIN and CAT shank tapers are suitable for smaller machines but may be limited in high speed machining. Models with double-sided contact with the shank taper and end face provide increased rigidity and precision, especially at large overhangs. Reliable transmission of higher torques requires larger taper sizes. For example, the HSK-E32 holder cannot replace the HSK-A125A in heavy duty machining.
The choice of shank taper form generally varies by region. The mid-1990s saw the rise of 5-axis machines, and it was during this period that HSK began to emerge in Germany. CAT holders are mainly used in the US, while in Asia, BT holders are very popular and are often taper/face contact models.
HSK is often used for 5-axis machining. PSC (Polygon Clamping System: Capto) and KM connections are mainly used on multi-task machines and are ISO-standard. Both KM and Capto are modular systems that allow tools of specific lengths to be assembled by combining extensions or reducers. As multi-tasking machines become more common, toolholders capable of turning, milling, drilling and other types of machining in a single setup are becoming more and more popular.
Despite the performance of a dedicated toolholder system, the shop must calculate profitability. Dedicated systems from a single supplier tend to be more expensive and have limited tooling options.
Cost And Other Considerations
While the base cost of hydraulic or mechanical toolholders is higher than that of jacketed or shrink-fit toolholders, there are other factors involved in the latter, such as the cost of the shrink-fit heating system, and the cost of changing the tool. time. In addition, each tool diameter also needs to have a corresponding shrinkable tool holder. Relatively speaking, in the collet chuck system, only need to switch the collet to adapt to different diameters.
Machine operators and tool maintenance personnel are absolutely required to use tool holders correctly. Like machine tools and other manufacturing equipment, toolholders require proper use and maintenance to maximize their benefits and potential. For example, the operator must fully insert the shank into the shank, and improper insertion can cause the tool to vibrate or even eject with loss of accuracy. Following tool assembly specifications is critical. When tightening the collet, the operator must not use the extended handle to apply excessive torque, which can twist the collet and cause misalignment of the tool.
Tool maintenance is also important, but often overlooked. Operators should always clean tool holders before use and should also check machine tool spindles. The handle should be stored in a clean and dry place with a cover to protect the cutter cone. Hydraulic chuck oil pressure should be checked regularly.
Summarize
Cnc Machining Shops must appreciate the importance of toolholders in their machining systems and understand how to properly match the right toolholder to a specific machine tool, machining strategy and workpiece can increase productivity and reduce costs. At the same time, toolholder manufacturers offer a comprehensive selection of toolholders (see note) designed to meet individual process requirements.
Future technological improvements will no longer be limited to the tool holder itself. Tool management using software and RFID tags is an element of data-based manufacturing and is becoming more common. Advances in toolholder technology include sensor-equipped toolholders that monitor forces on the toolholder in real time. The data collected allows operators to make adjustments to machining parameters during the machining process, even automatically via artificial intelligence (AI) linked to the machine control unit. These and other new technologies will further increase the production contribution of tool holders in machining operations.