Page 39 - machining_titanium_05_2019

Why nozzles?
There are several reasons for using nozzles as outlets in indexable extended flute cutters.
Firstly, a technological aspect. The required outlet diameter usually lays within 0.6…2 mm
range. Drilling these “pinholes” deep enough in a relatively hard steel body is quite difficult.
It makes sense to increase the diameter, cut a thread near the opening, and screw in an MILLING TITANIUM
appropriate nozzle. Secondly, a control reason. Varying outlet diameters by changing the
nozzles allows optimizing coolant flow that depends on the characteristics of an HPC pump
and the number of the nozzles in a cutter. Also, if the cutter does not mill to its maximum
depth of cut, the coolant holes near the non-working inserts can be easily plugged.

The nozzle diameter is less than the diameter of the hole. In accordance with the laws of flow
mechanics, input and output relations for a fluid velocity exist. The difference in diameters
increases the coolant velocity, and the coolant leaves the nozzle with higher velocity than enters
in it. On the other hand, there is a certain relationship between pressure, velocity and flow rate
for fluid, e.g. for coolant in our case. Increasing the nozzle diameter requires higher flow rate to
ensure a necessary pressure level. A growth of the number of the nozzles has the same effect.

For efficient application of indexable extended flute milling cutters with HPC supply
through the cutter body, the following two points should be considered:

1. If a turning tool has one cutting edge and one nozzle is sufficient for coolant supply, the
extended flute cutter features several cutting blades. Each blade is produced by a set of
replaceable inserts, located one after another. A pinpointed jet of coolant to the blade areas
demands at least one nozzle per every insert. It means that the characteristics of an HPC
pump should meet the required flow rate that considerably differs from turning cases.
2. If depth of cut is smaller than the length of the cutting blade, there is no need to supply
coolant to the inserts that are not involved in cutting. It is recommended to unscrew the
nozzles corresponding to these inserts from the holes, and then close the holes by plugs
or standard set screws. This is a simple and effective way for improving performance.

Standard or special (tailor-made)?
Indexable HPC extended flute cutters are intended for removing a high volume of metal. They
work in hard cutting conditions under heavy load that is usually combined with a substantial tool
overhang. This raises the question as to which is preferable, assembly from a standard cutter
and standard modular toolholding units such as arbors, holders, reducers etc., or a special
(tailor-made) integral tool with direct adaptation to the spindle? Although assembly from standard
elements looks reasonable, titanium component manufacturers prefer the integral design in
many cases. This configuration provides maximum rigidity and ensures more productive milling.
Specific tool diameters, cutting lengths, and overhang, as well as adaptations that vary from
one manufacturer to another, increase demands for various tailor-made HPC milling cutters.

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