Common cutting tools for CNC machining (II): Tool clamping

The accuracy of the milling cutter can be compared with the accuracy of the measuring tool, so we should pay attention to and understand its correct use, in order to accurately install the milling cutter on the machine for milling. The clamping methods of milling cutter can be roughly divided into the following types: side fixed type, collet type, hydraulic type, tooth fixed type and heat shrinkable type.

Side fixed Weldon

It has extremely high holding force, so it is often used in heavy cutting occasions. It is suitable for heavy cutting of traditional machining methods or traditional machines. However, the disadvantage is that the clamping accuracy is low, and the tool concentricity runout of tolerance after clamping is very high, so it is not suitable for finishing or high-speed milling.

Collet chuck & collet

This is the most commonly used method of gripping milling cutter, because different gripping ranges can be changed only by changing the collet, so it is a good choice for economic consideration. However, because of this design, its holding force is not high and is not suitable for heavy cutting. Moreover, although the tool concentricity run out of tolerance after holding is better than the side fixed type, there is still an error of nearly 0.02mm due to the quality of the collet.

Hydraulic type

This holding method uses the force generated by the pressurized liquid to hold the milling cutter. Because the liquid has the characteristics of flow and can evenly contact with the cutter to produce a close joint, the holding force is high, and the error of the run out of tolerance of the clamped cutter is very small, within 0.01mm. However, due to its complex structure, it is expensive. In addition, its hydraulic system is very fragile, so it needs to be used with extra care to avoid damage.

Fixed screw type

The milling cutter and the handle are combined by locking the teeth. The user only needs to change the type and suitable size of the milling cutter according to the size of the screw teeth. Because the milling cutter is fixed by locking the teeth, the clamping is very stable and is quite suitable for rough machining. In addition, the run out of tolerance error of the cutter is equivalent to that of the collet type, and it is also suitable for finish machining.

Heat shrinking

Based on the principle of thermal expansion and cold contraction, the milling cutter and tool handle are closely combined. When in use, the part of the tool holder holding the milling cutter must be heated to open it, and then put the milling cutter in while opening it. After cooling, it shrinks and fixes the milling cutter. The clamping force generated by this clamping method is very high, which can make the overall rigidity of the tool handle and milling cutter more stable. In addition, the run out of tolerance error of the tool concentricity can reach 0.005mm. Therefore, it is not only suitable for rough machining, but also the best choice for finish machining.

Run out of tolerance:

The life of milling cutter will be deeply affected by different clamping methods. In addition to the clamping rigidity, another is the run out of tolerance. For tungsten carbide milling cutter, every 0.01mm error will cause 10% loss of tool life.

Handle interference:

According to the general machining rule of thumb, when the elongation l of the milling cutter is greater than 5 times of the milling cutter diameter D, that is, l > 5D, the cutting force will affect the cutter and cause the cutter deflection. In the figure on the lower right and left, it can be clearly seen that if the size of the tool holder is much larger than the milling cutter, when machining a deeper area, in order to prevent the tool holder from colliding with the workpiece, the extended length of the milling cutter must be lengthened. At this time, the cutting force F will affect the tool. If a clamping method with less interference can be used at this time, such as heat shrinkable tool holder, there is no need to extend too long milling cutter and considerable rigidity can be maintained.

The above is a summary of the classification, function, advantages and disadvantages of the tool holder. I hope it will be helpful to you.

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