Tool Encyclopedia

1. Hollow-taper-shank Tooling: HSK

HSK turning tool holder

What is HSK ?

The abbreviation HSK stands for "Hohl Schaft Kegel," which, literally translated into English, means "hollow-shank taper." Among U.S. end users it is more commonly referred to as "hollow-taper-shank tooling."

Fig.1. HSK turning tool holder.

HSK tooling encompasses a range of tapered toolholder shanks and mating machine-spindle receivers. Compared with traditional steep-taper shanks, HSK shanks are shorter and are hollow, and they clamp from the inside. They incorporate drive keys that engage milled key-slots in machine spindles, and their hollow walls deflect slightly when inserted into spindle receivers.

Why HSK tooling system?

HSK is a taper standard designed for High Speed machining that provides high rigidity and high stability while high speed machining.

The HSK tooling systems offer advantages in terms of accuracy, repeatability, weight and fast tool changing cycles. The HSK family of tools and toolholders originated in Germany in the late 1980s to meet the needs of machining with higher spindle speeds. HSK tooling technology is being widely used in the automotive and aerospace industries.

The use of HSK assemblies has been growing significantly since 1993, when DIN (the German standardization organization) issued the HSK shank standard. Currently there are more then 50,000 spindles, equipped with the HSK interface, operating worldwide and the number grows exponentially. HSK technology in metal cutting industry is equivalent to the appearance of the microchip in electronics. It stimulates progressive evaluation of the conservative cutting tool industry. It forces everyone to revise production environment, and re-consider manufacturing methods. A majority of producers of vertical and horizontal machining centres utilize HSK toolholders.

Here is given as an example a short list of the most widely used machine models:

Haas : VF-1, VF-2, ES-5T,HS-4
Okuma : MB-46, MB-56, MA-400, MA-500
Mori Seiki : NV-400, NV-5000, NH-4000, NH-5000
Doosan : VM-series, HC-series
Mazak : e-410, e-500, e-650, e-800, e-1060, e-1550, e-1850

HSK types

HSK tooling includes six types (forms) of toolholder shanks: A, B, C, D, E and F and various machine-spindle receivers are available to each. The choice of form depends on application requirements such as torque and spindle speed.

HSK A is typically deployed on applications between 12 and 25,000 rpm, while HSK E is advisable for higher speeds. In fact, the full range comprises six types, A to F. Types E and F are designed for low torque and very high spindle speeds on auto toolchange machines. Types A and C serve applications requiring moderate torque and moderate-to-high spindle speeds, having a drive slot on the end of the taper. (A is for automatic tool changing, and C is for manual changing.) Types B and D are designed for high torque applications with moderate-tohigh spindle speeds, having a drive slot on the flange. (B is for automatic changing and D is for manual changing.)

HSK advantages

HSK boring bar holder

Fig.2. HSK boring bar holder.

It's not hard to understand why HSK is becoming popular in machine shops seeking to reduce cycle times. Current standard-taper toolholder styles such as CAT V-flange, BT, and NMTB have severe limitations in high-speed machining applications. In comparison, HSK toolholders provide superior rigidity and repeatability at aggressive cutting parameters. HSK's shorter, more gradual taper helps prevent the holder from pulling out of the spindle at high speeds. And since the toolchanger arm doesn't have to pull the HSK shank out as far as it would a standard-taper shank to clear the spindle, HSK holders can reduce the time for changing tools by 75%. This exerts a lot of force on the HSK flange, which provides high radial and axial rigidity.

Properly specified and applied, HSK tooling can optimize time in the cut for all machine tools, while it ensures consistent radial and axial accuracy. It is lighter, shorter, stiffer, and more precise than any competitive quick-change tooling technology, and it is the only technology currently available that is designed to perform at tomorrow's spindle speeds. With these advantages going for it, the HSK revolution is ready to begin.

Briefly speaking, HSK is a toolholding system that is a rigid, lightweight, and capable of high radial and axial accuracy. In addition, the system is suitable for very-high-speed rotary applications.

Hollow-taper-shank Tooling: HSK disadvantages. Comparison with CAT/DIN/BT

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