Axial cutting force also
influences the CAT connections axial repeatability, reducing the attainable level of
machining accuracy. On the other hand, the HSK interface has flange-to-flange contact
between shank and spindle, which eliminates the affect of the axial force on finished part
collisions, repair ability, and spindles are all influenced by HSK and steep-taper
connections. A CAT shank will wear the front of a spindle and cause it to
bell mouth. When
machining at spindle speeds above 8000 rpm, spindle walls expand faster than the CAT
shank, which is fairly rigid. As a result, the draw bar force pulls the shank axially into
the spindle. This movement changes the Z-position of the tip and locks the toolholder
inside the receiver when the spindle halts for a tool change.
problems dont occur with the HSK interface. Dual contact on taper and flange defines
the constant position of the tool tip independent of rotation speed. Also, the HSK taper
expands radially at a higher rate than the spindle receiver. This design feature ensures
permanent contact between the spindle walls and the tool holder during low and high-speed
machining. On the other hand, we don't yet have enough data to generalize about the wear
rate of HSK spindles.
not difficult to find a company that can regrind a CAT spindle and socket for reuse. But
special material deposit (coating) techniques and grinding should be used to compensate
for wear or damage on an HSK spindle. These techniques maintain the integrity between the
socket and face. Not very many organizations provide this service, and regrinding an HSK
spindle is a finicky, expensive operation requiring a skilled operator, a very precise
machine, and an excellent gagging system.
other hand, during collisions a CAT spindle will be more severely damaged than an HSK
spindle. During a collision the CAT shank, which is very strong, transfers high forces
through the interface to the spindle. Because the HSK shank is hollow, thin, and
lightweight, it acts as a fuse during a collision, breaks, and protects the more expensive
spindle from severe damage.
change stroke and time correlate. The low weight and moment of inertia of the HSK shank
and the tapers short length contribute to fast tool change times. Its
difficult to achieve comparable performance with a steep-taper or straight-shank
interface. For comparable steep-taper and HSK shanks, the HSK gage line diameter is about
half that of the steep taper. Also, the HSK interface does not require a retention knob
for clamping, which further reduces tool change stroke.
for varying cutting conditions was a requirement faced by the HSK working group. As
mentioned above, the CAT interface has serious problems at high rpm.
tooling and clamping system avoids these problems by preloading in the shank-receiver area
and establishing a solid face-to-face contact between mating components. For low-speed,
high-torque work, drive keys were optimized using FEA. A controlled amount of face draw
helps generate friction between the HSK shank and spindle receiver, which increases torque
different types of HSK shanks and spindle receivers can handle a broad range of
manufacturing needs. Types A and C are used for general machining (A for automatic tool
change, C for manual tool change). The B and D units are intended for high torque
transmission and for stationary (turning) applications. Type B is meant for automatic tool
change, D for manual change. Finally, the E and F types are recommended for low-torque,
super-high rotational speeds with automatic tool change. Completely symmetric,
theyre designed as balanced tools.
connections can be used for both milling and turning work, which helps to reduce the
shop-floor tooling inventory.
weight or mass of HSK tools is usually less than that of comparable steep-taper tools
because of the HSK shanks hollow design and shorter taper length. In cases where the
front part of the component becomes heavier than the shank, however, the center mass is
displaced toward the front of the tool. This displacement can create a toppling moment
when the tool is automatically changed. In addition, because the HSK shank is hollow, it
doesnt allow use of the shank to locate its cutting-tool-holding features. So, in
some instances, HSK end mill and collet chuck adapters can be longer than steep-taper
and manual tool changes are allowed for by the design of the HSK interface. Referring to
Figure 3, shanks A, B, E, and F are recommended for automatic tool change. They include
precision-ground V-grooves and auto operator location slots. Shanks A and B also have a
radial cavity for locating an information microchip. This memory cells carries information
about tooling nomenclature, preset dimensions, and wear level. During the tool change
cycle, data are exchanged between the microchip and the CNC control.
types C and D are designed for manual tool change. Depending upon the clamping mechanism
employed, shanks can be locked by a remote draw bar or by activating a wedge-lock
mechanism through radial access holes located on the periphery of the shanks. Type A and B
shanks can be clamped with a manual clamping system, but the C and D shanks cant be
used in an automatic system.
HSK adapters is no more difficult than balancing CAT/SK/BT adapters. Type E and F shanks
were designed with balancing in mind. Completely symmetric, they have no internal threads.
Used in combination with heat-shrink tooling, these shanks provide the best solution
currently available for high-speed machining.
manufacturers sell HSK adapters in an unbalanced state. Customers who want balanced units
must specify balancing when placing an order. At speeds below 15,000 rpm, grade G2.5 is
used for balancing. If an application requires high surface finish and accuracy, or if
grade G2.5 does not guarantee chatter-free operation, users should employ grade G1.0. The
DIN standard allows production of all types of HSK adapters in either unbalanced or
balanced states, and suggests that each component of modular tools or multicomponent
assemblies be balanced separately.
HSK and steep tapers, remember that the lower weight of the HSK shank isnt always
beneficial for balancing - especially when working with nonsymmetrical types A and C.
coolant supply can be provided on both HSK and steep-taper shanks. With steep-taper
shanks, use a retention knob with the coolant hole. With HSK shanks type A and C, use a
coolant nozzle to deliver sufficient coolant. Types B and D use flange coolant channels
bypass the clamping mechanism. Shank HSK-E, according to the DIN standard, allows a
coolant supply. But theres no explanation of how coolant can be provided on CNC
centers that lack accommodation for the coolant nozzle. Type F HSK shanks have no
provisions for coolant supply; however, this interface is recommended mostly for
woodworking, so its not likely to be used with coolant.
high-speed machining, HSK tooling operates at speeds exceeding 20,000 rpm. At these
spindle speeds, because of the asymmetry of coolant channels in adapters or possible air
and oil contamination, an internal coolant supply can destroy the static balancing of the
spindle-toolholder system. In these situations, an external coolant supply is recommended.
and cost competition was important to those who developed the HSK standard. Once the DIN
organization established the standard, it was made available to all interested parties
with no risk of patent infringement. The idea was to encourage suppliers of the HSK system
to enter the market.
cost more than steep-taper tools largely because the manufacturing tolerances involved in
making them are quite tight. Tolerances for HSK gage line diameters are higher than those
for steep-taper designs, for example. Gagging equipment needed to make the HSK tools is
also expensive, typically costing more than $100,000 a set.
some hidden expenses to consider when comparing the cost of HSK with steep taper. The HSK
interface requires more attention to the cleanliness of the shank surfaces. Before
installation of a shank in a spindle, the operator must check it to make sure there are
neither chips nor metal residue on the mating surfaces. Contamination can reduce both the
stiffness and the accuracy of the interface. This need for cleanliness is not a
disadvantage. Its a natural consequence of a move to high-technology manufacturing.