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By Christer Richt New insertmanufacturing
techniques fromSandvik Coromantplay a criticalrole in elevating
production resultsfor an increasinglydemandingmarketplace.
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What does a new generation of indexable inserts mean to the gear manufacturing
industry? Minimizing lead times in gear production is becoming an increasingly com-
petitive factor, and for many machine shops cost-competitiveness while maintaining
or improving quality consistency will be decisive in achieving success in new and
existing markets. And, as is always the case in machining, it all star ts at the cutting
edge.
The CuTTing edgesWhen applying a milling operation to manufacturing, a number of basic factors are
always routinely assessed: workpiece, material, operation type, machine tool, and
quality demands. This then leads to a number of optimization possibilities, with the
main ones being method, tool, tool paths, tool positioning, and cutting data, all with
the aim of achieving machining to the right quality level, the lowest manufacturing
costs, and the best throughput time. Today the role of insert grades as part of the
tool needs to be highlighted in particular, as recent developments have changed the
possibilities to directly improve gear milling.
Coated indexable inserts have proved themselves to be the new benchmark in the
milling of most materials, especially as they have such good resistance to heat- and
chemical-related wear. They have the capacity for high cu tting speeds, long and reli-
able tool lives even when feed rates are high, and can resist the formation of the edge
cracks that make a lot of inserts unsuitable for the thermal variations of milling, even
with coolants, as is still the case with much of gear machining.
Insert-grade dedication is required when productivity and security are more promi-
nent issues than versatility in machining. Gear milling is an area where a dedicated
insert grade will optimize the application as it regards performance, providing high
metal removal rates, short cycle times, and predictable tool life. Crater wear, thermal
cracking, and even plastic deformation are among the risks to cutting edges when
high cutting speeds, large cutter diameters, varying edge engagement times, and
harder materials are involved, as is the case in gear milling. These wear types act to
shorten tool life and impair predictability consistency of the quality achieved.
Thus, to achieve higher machining security at high cutting data in steel milling, wearresistance often needs to be a priority over toughness. But in some operations
as is the case with the milling of bigger gear modulestoughness needs to be the
dominant cutting edge property.
Types of ToughnessGear milling is characterized by interrupted cutting action, and in addi-
tion to thermal variations on the cutting edge, mechanical interruptions
make demands on high insert toughness and strength. Generally the insert
shape and geometry, as well as the entering and exit conditions, determine
the degree of toughness needed from the tool material. In gear milling the
demands for edge toughness are also influenced by the relatively small radial
depths of cut in combination with the large tool diameter. The use of coolant
will emphasize the demand for toughness, sacrificing wear resistance, which
will have a limiting effect on cutting data.
Dry machining, without any coolant application, is to be preferred when putting
the cutting process in the center because in today's high machining rates it is hard
for even high amounts of coolant to have much effect at the cutting edge. Coolants
in gear machining are very much inherited from the use of high speed steel tooling.
Most of the coolant in modern milling will be vaporized and what remains will only
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intermittently cool the insert as it goes in
and out of the cut. Thermal variations are
thus amplified, which has more of a nega-
tive effect on the insert than what high
temperatures do.
A modern coated insert grade has the
capability of providing high security at
the temperatures generated by high cut-
ting speeds and feeds. Having said that,
however, a lot of grades will function well
in both dry and wet conditions, when the
coolant is necessary for chip evacuation
and maintaining component temperature
for keeping within dimensional toleranc-
es, and so on.
CriTiCal CoaTingWhen it comes to coated indexable
inserts, there are two coating meth-
ods which produce two characteristically
different grades. CVD (chemical vapor
depostion) coated inserts make it pos-
sible to make coatings that provide a high
degree of wear resistance by resisting
chemical, abrasive and thermal break-
down of the edge. These grades are
coated at relatively high temperatures,
giving them something of a tendency for
being brittle, but this is offset through
edge preparation today. This gives the
CVD-coated grades an ability to mach
at high cutting data while still retainin
high level of bulk toughness.
PVD (physical vapor depostion) coat
inserts have coatings suitable for relativ
sharper and more positive cutting edg
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They do not have quite the same level
of wear resistance as CVD coatings but
provide a high degree of toughness local-
ized more at the cutting edge line. These
grades are coated at lower temperatures,
which does not provide the same level and
nature of wear resistance as CVD-grades
but does give them added edge tough-
ness, thus making them advantageous
for sharper edges. Modern manufacturing
techniques, however, have meant that the
basic differences between CVD and PVD
grades have become smaller, with grad
overlapping in application areas and p
viding much more capable optimizat
instruments. This is certainly the case
gear milling, where new insert generat
grades have elevated performance.
Fig 1: This indexable insert
hob with a diameter of 10.5
inches and 132 teeth (seen
here and on the opposite
page, was used to machine a
planetary gear wheel for the
wind-power industry. Us-
ing indexable inserts in the
newly-developed CVD-coated
grade GC4240 the tool life
was increased by 35% to 57
components per insert set
over the existing carbide
insert solution.
GEARTOOLS
HOBS
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AmericAn GeAr Toolsa dv f Aa Bah & mah cpay
575 South Mansfeld Street, Ypsilanti, MI 48197
Tel: (734) 961-0300 e-FAX: (734) 448-0130
Wbsit:www. americangeartools.com
e-mai: [email protected]
ONE STOP for yourgear cutting needs
APRIL 2010
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A new CVD-type ISO P40 grade
steel milling has established itself
a solution for many demanding ope
tions where cutter entry and exit in t
workpiece needs a strong edge. Typi
for CVD applications are that chips a
usually thicker, as in medium and hea
milling with high feeds, and cutting spe
is generally high. CVD edges will typica
provide a high degree of edge dura
ity thanks to their resistance to he
and chemical loads, as well as abras
wear.
A new PVD-type ISO P30 grade provid
the type of edge strength often need
when there is some instability, su
as when longer tool overhang, diffic
chip evacuation, and more difficult cut
entry and exits, as can be the case w
short cutting edge engagements. In the
operations, chips are typically thinner a
cutting speed somewhat lower. Surfa
finish and tolerances are more likely to
to closer limits and the PVD edge may
more suitable as it is sharper.
assessing operaTionsAssessing the gear milling operatio
at hand may well lead to one gra
being shown to have an optimizing eff
against the other. This is partly becautoughness in gear milling is made up
more than one aspect. A stable operat
which needs to be run at high cutting da
can be improved by using a CVD-gra
insert, while some operations can bene
from the easier-cutting, PVD-grade, mo
positive insert.
For example, the CVD-coated gra
GC4240 is a tough, steel-milling grade
applications where cutting edge streng
is needed for more severe demands bo
as regards material and machining c
ditions. Generally this grade will so
most operations where a combinat
of high insert toughness in combinat
with resistance to heat and chemi
breakdown is necessary. It will provide
winning, reliable solution, especially
medium to large diameter cutters, wh
other insert grades will not stand up
Call Parker Industries Toll Free at 1-877-567-GAGE forfast friendly service and ask our technical experts to helpyou with selecting the appropriate hand-held barrel ordigital micrometers and combination gages to measure:
Wk- gear tooth span (base tangent) over Z (No. of teeth)
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1-877-567-GAGE (4243) T: 631-567-1000 F: 631-567-1355 W: parkerind .com
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the demands of insert strength required
by the operation.
Complimentary to this, the PVD-coated
grade GC1030 is a steel milling grade
for applications where a more-positive,
sharper, and tougher cutting edge line is
needed. This grade is generally ideal when
radial depths of cut are smaller, vibration
risks apparent, chip evacuation tricky, cut-
ter entry/exit demanding, and functions
better when coolants are applied.
ConClusionWhen compared to traditonal high speed
steel tools for gear milling, the new gen-
eration of coated cemented carbide insert
grades offer a completely new scope for
reducing machining times and improving
the manufacturing cost for components
with gear teeth. When compared to the
insert grades that have been used so
far in gear milling, the new generation of
CVD and PVD steel milling grades will very
likely provide a substantial upgrade of
machining, with better throughput times
and machining security as a result.
When it comes to milling normalized
case-hardening steel, the advantage of
carbide inserts is particularily highlighted
in the form of higher productivity, while
for tempered steel the advantage is espe-cially apparent in longer tool life.
Another important aspect to the suc-
cess of indexable insert in gear milling is
that of insert geometry and insert manu-
facturing quality. Edge geometry and edge
preparation are important combination
factors with insert grades for achieving
the best solution. Establishing the right
microgeometry in the form of lands, cham-
fers, and edge rounding decisively affects
the strength characteristics of the cutting
edge, as well as durability. This has a
direct influence on cutting data capability,
security and, very impor tantly, the predict-
abilility of quality consistency.
Gear milling cutters have a large num-
ber of large inserts, and the position
of one cutting edge will affect the oth-
ers as regards load during cut. If these
loads vary too much they can negatively
(4243)
Re-Sharpening & Re-ConditioningStandard rate for CylindricalGear and Spline Hobbing Cutters-Straight or Spiral Gashes/Flutes
0 - 2 inch / 0 - 50mm diameters $75 ea
2001 - 4 inch / 51 - 100mm diameters $85 ea
4001 - 6 inch / 101 - 150mm diameters $95 ea
6001 - 8 inch / 151 - 200mm diameters $250 ea
8001 - 10 inch + / 201 - 250mm diameters $250 ea
Standard rate for Cylindrical Gearand Extended Boss Spur andHelical Shaper Cutters (non-shank)
0 - 4 inch / 0 - 100mm diameters $75 ea
4001 - 8 inch + / 101 - 200mm diameters $200 ea
Standard rate for Cylindrical
Shank Type Shaper Cutters
0 - 4 inch / 0 - 100mm diameters $75 ea
PARKER Industries Incorporated1650 Sycamore Avenue Bohemia, NY 11716
Tel: 631-567-1000 Fax: 631-567-1355Email: sales@parkerindcom
www.parkerind.com1-877-567-GAGE
Before Reconditioning After Reconditioning
Cutters complete with Elemental inspection Coupons
NOTE: A variety of PARKERs standard and proprietary tool coating options for increasedwear resistance and longevity are available All prices are FOB-Ex Works and thecustomer is responsible for shipping to and from our facilities Tool managementservices: to include retrieval and delivery are available and will be quoted upon requestWe are at your service and look forward to receiving your inquires
(4243)
APRIL 2010
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affect machining performance and the
ability to achieve the right quality level.
In this context new insert manufacturing
techniques, producing inserts to much
closer tolerances, play a critical role in
achieving solutions to elevate results for
a marketplace where quality demands are
constantly escalating.
about the author:Christer Richt is with SandvikCoromant and can be reached [email protected]. Alsogo online to www.sandvik.com.
Fig 2: Disc milling cutters are suitable for external and internal applications.
In this case, a large slewing ring for the wind-power industry was machined
through milling of the internal gear with a cutter having thirty teeth. Using in-
serts in the new-generation PVD-grade GC1030, a productivity increase of 30%
was achieved in combination with longer tool life and a safer process though a
more advantageous wear pattern.
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