HSK tool shank is a new type of high-speed short taper tool shank developed by the Machine Tool Research Institute of Ahern University of Technology (see Fig. 8-57).
Its structural characteristics are hollow, thin-walled, short taper, and the taper is 1:10;
The end face and cone face are positioned and clamped at the same time, and the positioning of the tool handle in the spindle is over positioning;
Use the external expanding clamping mechanism from the inside out.
Fig. 8-57 HSK Tool System
1. Introduction to HSK Tool System
The most outstanding feature of HSK tool system is the synchronous contact between the end face and the cone face.
During clamping, the conical surface is compressed to produce elastic deformation due to interference at the cone part.
At the same time, the tool handle is axially displaced to the taper hole of the main shaft to eliminate the initial clearance and achieve the fitting between end faces, thus realizing synchronous clamping on both sides (see Fig. 8-58).
That is to say, under the action of enough tension, friction will occur between the taper handle of HSK1:10 hollow tool and the 1:10 taper hole of the main shaft on the entire cone surface and the support plane, providing radial positioning of the closed structure.
As far as its own positioning is concerned, this way of ensuring the simultaneous positioning of cone and end face is essentially over positioning.
However, due to the high mutual position accuracy guaranteed by precision manufacturing, the installation rigidity is enhanced.
The advantages of this positioning are:
(1) It can adapt to high-speed rotation. When rotating at high speed, the cone hole expands due to centrifugal force.
The cone shaft recovers due to elastic deformation, maintains precise contact with the cone hole, and maintains the constraint positioning of the end face and the cone face at the same time.
(2) High repeated positioning accuracy, which can ensure 2 μ m.
(3) Since both axial and radial directions are positioned, the installation is rigid.
(4) It is easy to disassemble, because of the auxiliary separation mechanism, it can also be easily disassembled when the tool is thermal expanded.
(5) The cooling system is complete, and the system has two options: center oil supply and end oil supply.
Fig. 8-58 HSK dual positioning structure
Fig. 8-59 shows the map of HSK tool system.
Fig. 8-59 HSK Tool System Map
According to DIN, HSK toolholders are divided into 6 types.
Fig. 8-60 shows the structure of the six types of tool handles, while Fig. 8-61 shows the sectional view of the six types.
Fig. 8-60 Six Forms of HSK Tool System
Fig. 8-61 Section View of 6 Forms of HSK Tool System
2. Working principle of HSK tool handle
High speed machining tool systems generally adopt double side positioning of cone (radial) and flange end (axial) to realize rigid connection with the spindle.
In order to give full play to the performance of the tool system, an efficient clamping mechanism must be designed to provide sufficient clamping force through this clamping mechanism, so as to ensure the reliable contact between the taper of the tool handle and the taper hole of the spindle, and between the end face of the tool handle and the end face of the spindle.
Therefore, the external expansion clamping mechanism is generally used in the high-speed machining tool system, mainly in three forms (see Fig. 8-62).
Fig. 8-62a shows the short slider wedge clamping mechanism, which is the basic form of the external expansion clamping mechanism;
Fig. 8-62b shows a spherical wedge clamping mechanism, which is used for KM tool shank in the United States;
Fig. 8-62c shows a hanging jaw wedge clamping mechanism, which is used for HSK tool shank.
a) Short slider wedge clamping mechanism
b) Spherical wedge clamping mechanism
c) Suspension claw wedge clamping mechanism
Fig. 8-62 Typical Clamping Form of Tool System
When the HSK tool shank is installed on the machine tool spindle, the hollow short taper shank plays a centering role in the taper hole of the spindle.
When the hollow short taper shank fully contacts the taper hole of the spindle, there is a 0.1mm gap between the end face of the flange plate of the HSK tool shank and the end face of the spindle.
Under the action of the clamping mechanism, the pull rod moves backward (left), the conical surface at the front end of the pull rod expands the clamping jaw radially, the outer conical surface of the clamping jaw then presses against the 30 ° conical surface of the inner hole of the hollow short taper handle, pulls the HSK tool handle to move to the left, and the hollow short taper handle produces elastic deformation, making the end face of the tool handle close to the end face of the main shaft, realizing simultaneous positioning and clamping of the tool handle, the cone face of the main shaft, and the end face of the main shaft.
When loosening the tool handle, the pull rod moves to the right, the elastic collet loosens the inner cone of the tool handle, and the front end of the pull rod pushes the tool handle out to remove the tool handle, as shown in Fig. 8-63.
a) Before clamping b) After clamping
Fig. 8-63 Working principle of HSK tool system
Features of HSK Tool System
The most outstanding feature of HSK tool system is the synchronous contact between the end face and the cone face.
As far as its own positioning is concerned, this way of ensuring the simultaneous positioning of cone and end face is essentially over positioning.
However, due to the high mutual position accuracy guaranteed by precision manufacturing, the installation rigidity is enhanced.
According to DIN, HSK toolholders are divided into 6 types.
The common structural features of the six types of HSK tool holders are:
(1) The most prominent feature of HSK tool system is that the end face and cone face contact at the same time.
When clamping, because the taper surface of the spindle hole and the taper surface of the tool handle have an interference, the taper surface of the tool handle is compressed to produce elastic deformation.
At the same time, the tool handle is axially displaced to the taper hole of the spindle to eliminate the initial end clearance, so as to achieve the fitting between the end faces.
In this way, the double-sided synchronous clamping is realized.
As far as its positioning is concerned, this way of ensuring the simultaneous positioning of cone and end face is essentially over positioning.
The positioning accuracy of HSK tool handle includes radial positioning accuracy and axial positioning accuracy.
In terms of radial positioning accuracy, the radial accuracy of the HSK interface is determined by the cone contact characteristics, that is, the matching condition between the big end of the HSK tool handle cone and the big end of the spindle taper hole, which is consistent with the 7:24 taper tool handle (both of them have radial accuracy of 0.2 μ m ）.
The axial accuracy of the HSK interface is located by the contact end face, which can reach 0.2μm, while the 7:24 taper tool shank is located only by the taper shank, and the axial positioning error is 15μm.
The axial accuracy of HSK interface is not affected by the clamping force, but only determined by the structure.
Because the end face of the tool shank plays a supporting role after the end face is fitted, the axial string of the tool shank caused by the expansion difference between the spindle hole and the tool shank during high-speed machining can be prevented, and the axial accuracy is improved.
(2) Hollow thin wall structure.
The hollow thin wall structure is an important feature of HSK tool holder, and it is a necessary structure to ensure the work of HSK tool system.
To achieve the “simultaneous contact between the end face and the cone face” mentioned in the previous article, the cone face must produce elastic deformation.
Compared with solid tool shank, hollow thin-walled shank is much easier to produce elastic deformation and requires much less clamping force;
At the same time, when the spindle rotates at a high speed, the radial expansion of the hollow thin wall has little difference with the taper hole in the spindle, which is conducive to maintaining the reliable contact of the taper in a large speed range.
The hollow shank of HSK tool handle also provides the installation space for the clamping mechanism to achieve clamping from inside to outside.
The advantage of this clamping method is that the centrifugal force is converted into the clamping force, which makes the tool holder more reliable when working at high speed.
In addition, the hollow shank of HSK tool handle is also convenient for the supply of internal cutting fluid.
(3) 1:10 short cone.
7: 24 The reason why the taper tool handle adopts a large taper long structure is that there is a gap between the tool handle and the end face of the spindle, and the long taper surface is used to support the tool system of the tool handle.
However, HSK tool handle adopts simultaneous contact and positioning of the end face and cone face.
After the end face is fitted, the end face of the tool handle has played a role in supporting the tool handle.
In this way, the contact length between the spindle and the cone has little impact on the rigidity of the tool system.
In order to overcome the impact of processing errors on the double-sided over positioning structure, the contact length of the cone face can only be shortened as far as possible.
Similarly, the influence of over positioning on manufacturing accuracy when using end face positioning was not considered in the design of 7:24 taper tool holder.
Due to the large cone angle, when the diameter direction of the cone produces an error of 1μm, the allowable axial end face position error is only about 3μm (while the allowable axial end face position error can be about 10μm when using a 1:10 taper tool handle), which requires very high manufacturing accuracy of the system.
In addition, since the friction coefficient of steel is about 0.1, in order to ensure the self-locking of the tool handle after clamping, the taper of the tool handle cannot be greater than 0.1 in principle, but too small a taper will increase the friction of the taper of the tool handle.
Therefore, HSK tool handle finally adopts a 1:10 short cone.
(4) The strict interference amount of the cone surface ensures that the connection stiffness is affected by the HSK tool shank cone size and the fitting condition of the tool shank cone and the spindle cone hole.
On the one hand, in order to maintain high rigidity of HSK tool shank in a large working load range, it is necessary to ensure that there is enough clamping force transmitted to the end of the tool shank to make it closely fit with the end face of the spindle, which requires that the interference between the taper of the tool shank and the taper hole of the spindle should not be too large;
On the other hand, in order to ensure that the connection stiffness of the tool handle will not drop sharply during heavy load, it is necessary to ensure that the interference fit between the taper of the tool handle and the taper hole of the spindle is large enough.
Therefore, the machining accuracy of the taper part of the tool shank and the taper hole of the spindle is highly required.
In fact, the formulation of HSK handle 1:10 is only an approximation. ISO12164 clearly stipulates that the taper of HSK tool shank is 1:9.98, while the taper of spindle is 1:10.
Such provisions ensure that the big end of the cone first contacts during the tightening connection between the taper of the tool handle and the taper hole of the spindle.
With the occurrence of elastic deformation, the tool handle and the end face of the spindle are in full contact through positioning, which is conducive to ensuring the strict interference of the cone surface, reducing the clamping force consumed by the cone surface, so that most of the clamping force can be effectively transmitted to the contact end face, thus ensuring the bearing capacity of the HSK interface.