Gear Hobbing Sandvik

7/28/2019 Gear Hobbing Sandvik

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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

24 gearsolutions.com


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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

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BROACHES

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)

on external gears, and yes even internals too!

Gear size via Mdk or Dimension Over Pins/Wires/-or- Balls

Calculation software for Wk-span or Mdk/DOP or DUP Major and Minor Diameter Size and Bore Gaging

Spline Gages, Master Gears, and Inspection Arbors

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And dont forget to ask why our ball micrometers last two to three times longer than the competition.

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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




8001 - 10 inch + / 201 - 250mm diameters $250 ea

Standard rate for Cylindrical Gearand Extended Boss Spur andHelical Shaper Cutters (non-shank)


4001 - 8 inch + / 101 - 200mm diameters $200 ea

Standard rate for Cylindrical

Shank Type Shaper Cutters


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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Gear Hobbing Sandvik