Choosing the right tool holder is the key to controlling costs

In the cutting process, the tool holder is the key interface between the tool and the machine tool. In all machining occasions, whether or not the correct shank is selected will affect many factors such as: dimensional accuracy, surface quality, replacement time, and tool wear, which ultimately affect the quality and cost of the processed workpiece.

Figure 1 As a critical interface between the tool and the machine tool, the tool holder affects the quality of the machined workpiece

Just as there are different processing applications, there is no single tool holder available on the market for all machining needs. Therefore, with the development of processing technology, SCHUNK has developed five different high-precision tool holder systems for more than 30 years. With these sets of tool holders, the user can meet the needs of a variety of cutting tasks. Its applicable industries range from micro-machining in the electronics and watch industries to the high speed machining of metal cutting (HPC/HSC); it has both high-value and high-precision tool holders, as well as inexpensive and high-quality tool holders suitable for large-cut machining.

Clamping accuracy determines the dimensional accuracy of the workpiece being machined

High-precision tool holders, such as the TENDO hydrostatic expansion shank and the TRIBOS stress-locking shank, have been calibrated with a series of dynamic balances in addition to the high structural dimensions ensured in the manufacture, in order to achieve a very high clamping rotation accuracy. With this feature not only can improve the quality of the workpiece, but also greatly reduce the processing costs. The processing costs thus consumed are significantly lower than the traditional processing costs, because the use of high-precision tool holders extends the service life of the tool. The TENDO hydrostatic expansion clamping technology (figure 2) and TRIBOS stress-locking clamping technology (figure 3) save cost by up to 27% compared to traditional spring-loaded toolholders due to reduced tool wear. .

Figure 2 Tendo hydrostatic expansion tool chuck shows excellent gripping accuracy and high repeatability and excellent vibration damping

Fig. 3 When Tribos stress-locking clamping technology is used, the tool holder clamps the tool by the elastic deformation of the clamping hole. Because of its different structural features, the tool can be clamped from 0.3 to 32 mm.

SCHUNK's high-precision tool holder system has extremely high clamping rotation accuracy, allowing the user to precisely machine the workpiece and achieve extremely high dimensional accuracy. Although the heat-shrink shank and the high-precision spring shank can be delivered with high clamping rotation accuracy, there are still differences due to different clamping techniques. Experiments show that the thermal shrinkage tool holder gradually loses the clamping accuracy due to its thermal expansion; however, the TENDO or the TRIBOS tool holder clamped at room temperature due to the deformation of the static pressure oil chamber deforms the tool several times after it is replaced. The radial jerk can still be maintained within 0.003mm.

In terms of vibration damping, the SCHUNK shank system values reflect a very wide range of adaptability. Among them, the TENDO hydrostatic expansion shank and the TRIBOS-R stress-locking shank perform particularly well. The TENDO hydrostatic expansion shank grips the tool through the symmetric internal wall of the oil chamber. By using a hex wrench to tighten the compression bolt, the pressure is evenly transmitted to each part of the oil chamber. The inner wall of the oil chamber is pressed evenly and symmetrically to expand in the direction of the axis, thereby clamping the tool. With each clamping and loosening, the pressurizing bolts are fixed to the same position, which ensures the repetitive clamping accuracy. Since the vibration damping of oil is greater than that of steel, the TENDO holder also has extremely high damping properties. Similarly, the TRIBOS-R type stress-locking shank adopts a cavity structure filled with plastic damping material, and also has similar damping characteristics, so as to achieve a very quiet processing effect. The SINO general purpose shank is equipped with plastic material lining and therefore has similar advantages.

Experiments have proved that if the user chooses a clamping technology with vibration damping, the investment is worthwhile. Due to the effect of damping, the cutting state of the tool is improved, the tool is well protected and its service life is extended. As the experimental results show, the tool life can be extended by up to 47% due to the improved vibration characteristics (Figure 4). At the same time, the user can also obtain better workpiece surface quality.

The vibration damping characteristics of the shank of Figure 4 have a decisive influence on the service life of the tool. Tests show that the tool life can be extended by up to 47% when using the Tendo hydrostatic expansion toolholder

Another benefit of the shank with vibration damping is its effect on the spindle of the device. If the damping is weak, the vibration will be directly transmitted to the spindle; and the shank with the vibration damping characteristics will play a buffer role. This will protect the spindle and the more expensive parts of the equipment while extending the life of the spindle.

When a larger cutting task is completed, a higher radial force acts on the shank. If you want to achieve a large amount of cutting in a short period of time, it is recommended to use a system that can withstand this radial force. SINO-R powerful shank, TRIBOS-R shank and CELCIO heat shrink technology shank are all good choices. Each of these toolholder systems has a high radial stiffness and can be processed smoothly with large cutting volumes. The first two systems also have excellent vibration damping characteristics.

Faster tool change and shorter replacement time

For customers who often need to change the tool, the changeover time also has an important effect when choosing the right toolholder. The TENDO hydraulic tool holder and the SINO universal tool holder can be replaced within 30 seconds by using a simple hex wrench or crescent wrench. It does not require the use of peripherals, and not only has a short change time, but also no additional cost. Heat-shrinkable toolholders require special heat-shrinking equipment. The purchase price is around 10,000 euros. Compared with other toolholder clamping technologies, the heat-shrinking tool holder takes the longest time, and the replacement time, including the cooling of the heated tool holder, requires 10 minutes. In many facelifts, this is very unfavorable.

The smaller the workpiece or the larger the angle of rotation, the more important the overall dimensions of the shank. Especially in cutting operations in narrow spaces, the sleeker TRIBOS-S or the extra-long TENDO-LSS holders are ideal. At the same time, these two devices are also suitable for high speed machining. Among them, the TRIBOS-SVL tool holder extension lever (Fig. 5) can also be combined with different tool holders to complete the machining of the difficult-to-machine parts. Since the extension rod's clamping accuracy is within 0.003mm, the use of such extension rods in many applications can eliminate the need for expensive special tools.

Figure 5 TRIBOS-SVL tool holder extensions can be combined with different tool holders for precise machining of difficult-to-machine parts

In order to carry out micro-cutting operations for tools with a diameter of 0.3 to 3 mm, SCHUNK can supply TRIBOS-Mini units. This device is very popular in medicine, molds, electronic appliances and watches.

SCHUNK has performed hardness tests on tool holders and also provided specimens for various clamping systems. As a result, holders have a major influence on the service life of the tool and the load on the spindle of the machine. A tool holder system with tool protection can be a factor that restricts cost increases and shows great potential for cost savings.

The price of the shank of Fig. 6 only accounts for a very small part of the overall cutting cost, but in the long run, cheaper tool holders can also result in extremely high costs.

In the initial investment, the acquisition cost of the tool holder became a major consideration, but the cost savings associated with the processing time soon attracted attention. Surprisingly, the acquisition cost of the tool holder has little effect on the overall cutting cost, as the comparison between the static pressure expansion tool holder and the heat shrinkable tool holder shows that although the cost of the heat shrinkable tool holder is low, it is With the use of the TENDO hydraulic tool holder 19h, the cost of machining with the TENDO hydraulic tool holder has become significantly lower. After 100 hours of effective use between the lowest and most expensive systems, the difference in processing costs between the two reached 771 euros.