By Todd Miller, Manager, Rotating Products
At Seco, we are constantly seeking out new
ways for our customers to save money and still productively produce quality products.
Such commitment has enabled us to continuously add new dimensions to the world
of metalcutting where “one size does not fit all.” Consider our brand new take
on negative cutter design.
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| Double Octomill |
Negative cutters have been around for years and
are quite popular, given they help reduce manufacturing costs by allowing the
use of double-sided inserts. However, they prove most effective in steel and
cast iron applications. Today, we’ve managed to re-engineer the traditional
negative cutter to handle a wider range of applications by using modern,
high-positive insert geometries – creating a hybrid negative/positive cutter
style.
This hybrid cutter style retains its strength
for roughing operations, generates downward cutting pressure, which pushes the
part into the fixture, and provides the economy of multiple cutting edges while
reducing cutting forces, maintaining good chip evacuation and providing
excellent surface finishes.
There are three common configurations for
cutter bodies — positive/positive, negative/negative and positive/negative –
all having advantages and disadvantages in different applications, which you
can read about here.
By taking a negative cutter body and
introducing a high-positive insert geometry, we’ve created a highly effective
positive cutting rake angle. The
effective cutting rake angle is calculated by adding the radial rake of the cutter body and
the cutting rake angle of the insert. With a positive cutting rake angle in a
negative cutter, users benefit in multiple ways – freer cutting action as well
as reduced power consumption and heat generation, all of which leads to longer
tool life in addition to the increase in usable cutting edges.
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| Square 6 |
The hybrid combination also takes into
account several other design factors in addition to cutter body geometry,
including the cutting insert’s geometry, effective cutting rake and edge
preparation.
Cutter body geometry, or the positioning of
the cutting edge of the insert, involves lead, axial rake and radial rake
angles. The lead angle is the approach the cutting edge takes as it enters the
workpiece. It also controls the direction of the axial and radial cutting
forces, as well as affects chip thickness, tool pressure and tool life. The
axial rake is the insert’s angle along the central axis of the cutter assembly,
while the radial rake is the insert’s angle in relation to the periphery of the
cutter. In a hybrid negative/positive geometric configuration, the cutter rake
angles both remain negative. It’s the introduction of the positive insert
geometry that makes the difference.
Insert edge preparation also plays a key role
in the new hybrid negative/positive approach. In typical milling cutters for
steel and cast iron operations, negative T-land edge protection sufficiently
applies, while in tougher applications involving titanium, Inconel or superalloy
materials, the inserts are honed and do not include the negative T-land,
enabling them to be sharper and cut freer. These tougher workpiece materials
are where some of the most significant cost reductions can be found using the
new hybrid technology. While in most situations, double negative cutters are
not effective for these tougher materials. But now, these materials can be
machined successfully using the hybrid style with honed-only inserts.
Additionally, these designs now incorporate
integrated wipers of various sizes on each insert. This should be considered
when machining different materials. For instance, longer wipers tend to produce
more tool pressure and increased heat. Therefore, when working with tougher
materials, such as superalloys, a shorter wiper is recommended for roughing to
help reduce work hardening and excessive heat. In steel and cast iron roughing
applications, a longer wiper can save valuable machining time thanks to its
freer cutting action that produces a nice surface finish in just one pass.
Currently, several Seco customers are finding
success using negative cutter bodies with the new hybrid negative/positive
configuration. Such cutter bodies include the Double Octomill, a highly
versatile and economic face milling cutter with 16 numbered cutting edges, and Square 6 line of shoulder milling cutters. And stay tuned as we look to develop even
more ways for our customers to productively and profitably machine quality
products.
Watch the Double Octomill in action.
Watch the Square 6 in action.
About
the Author
Todd
is the manager of rotating products for NAFTA, responsible for solutions and
applications involving face, square shoulder and disc milling. Todd and his
team of product experts are dedicated to providing a consistent, high-level of
support to Seco customers throughout the United States, Canada and Mexico. In
his spare time, Todd likes to bowl and cheer on the University of Michigan
football team. Contact Todd at tmiller@secotools.com.
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