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Super
DrillsMore sophisticated drillsenable shops to tackle
superalloys with ease
Sandvik Coromant
o one can put as fine a point on how complex drill-ing has
become during the past few decades than a
veteran machinist like Peter Diamantis.Diamantis recalled that
when he started out 30 years ago
drills held a status in the tooling hierarchy not unlike
ham-mers: just about any one would do the job. I rememberwhen
people would tell my plant manager they needed todrill stainless
steel, and he would go into our stockroom,pick out a drill that we
had too many of and sell them that,said Diamantis.
Today, as plant manager for Amamco Tool, Greer, S.C.,
Diamantis responsibilities include oversight of the compa-nys
various, and exacting, drilling operations. Now, he said,everything
is so specific that you can be drilling the samematerial but if
youre limited by your machines capabilities,your setup or even such
a subtle change as using differentcoolant, you will probably have
to change your drill geom-etry to fit those specific needs. So
drilling [then and now] islike night and day.
One reason for drillings growing sophistication has
beenincreasing demand for heat-resistant materials, such as
thenickel-based superalloys (Inconel, Rene, Hastelloy, etc.)
oftenused in aerospace applications. These high-priced metals
pose
numerous challenges. For one, their ability to withstand
hightemperatures means that the heat generated during drillingis
transferred to the drill. Drills also are often used in
diffi-cult-to-reach areas, which puts a premium on effective
tool-holding solutions to ensure stability.
To maximize tool life and ensure success with superal-loys,
drilling experts are always on the lookout for ways toimprove
everything from coolant to toolholding, coatingand geometry.
Drill Composition, GeometryThe big issue [when drilling
superalloys] is that you
want a process that is reliable and provides component qual-ity
with a long, predictable tool life, said Thomas Sandrud,holemaking
manager for Seco Tools Inc., Troy, Mich. Theseare expensive
workpiece materials that are difficult to ma-chine due to the
tendency of workhardening and the highcutting forces generated by
the material, which [produces]a lot of heat and pressure. So it is
important that the geom-etry of the drill is specially designed for
drilling in superal-loys. This means a free-cutting geometry that
leads to lessdeformation hardening, reduces exit burrs and
minimizesresidual stresses.
How well a drill can machine superalloys consistentlyand
accurately involves a variety of factors, starting withthe
workpiece. Carbide drills are recommended whenever
Sandvik Coromants carbide drill
for machining superalloy, the
CoroDrill Delta-C, is designed
specifically for aerospace and gasturbine applications.
By Daniel McCann, Senior Editor
JANUARY 2009 / VOLUME 61 / ISSUE 1
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possible for increased wear and heat resistance in comparison
tocobalt-HSS drills, said Bob Hellinger, national sales managerfor
Guhring Inc., Brookfield, Wis.
Hellinger also endorsed drills composed of submicrograincarbide.
For example, he said, Guhring recommends a DK-46OUF grade of
carbide with a 0.5m-grain size, which is one-fifth the grain size
of conventional P40- or C5-grade carbide.The reduced grain size
allows for sharper cutting edges afterhoning.
As for honing, Amamcos Diamantis suggested prepping
the edge point on the drill tip to remove excessive sharp-ness.
Overly sharp edges create microfractures that will pre-maturely
chip and break, he said, adding that slightly dulling
them strengthens the tooland allows machinists tofeed more
aggressively intothe superalloys than theywould otherwise.
To prep the edge ona point, Diamantis rec-ommended using a
veryhigh-grit wheel or a hon-
ing stone. If you have aCNC machine that canfollow edges
precisely, youcan use an abrasive nylonwheel that is
specificallydesigned to edge prep, hesaid, adding the caution-ary
that exceeding a 0.002"
width on the edge prep would diminish the effectiveness ofthe
point geometry.
To make the tip even stronger you can dub it, which iswhat I do
when drilling superalloys like Inconel, continuedDiamantis. That
involves grinding an angle of about 5 deadon the face of the drill
tip. You can control the rake angle ofthe drill at the cutting
point without affecting the rest of thehelix angle.
ToolholdingOnce the tool has been selected for a job, the next
step is
to make sure its securely held in place to drill. Seco Tools
rec-ommends a shrink-fit system for holding the drills. What
thatinvolves, said Sandrud, is the bore in which the tool locatesis
slightly undersized compared to the tool shank. Heating
the holder opens up this bore, allowing the tool to be
in-serted. As the holder cools, the bore shrinks around the tool
tocreate a concentric and rigid clamping. The shrink fit is the
Seco Tools
Seco Tools feedMax solid-carbide
drills provide a high feed up to
0.028 ipr.
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best clamping system when it comes togetting good runout, which
is impor-tant to hole geometry and [extending]tool life, said
Sandrud.
Another factor that gives added im-
portance to effective toolholding is theconstricted work area
common in aero-space projects. Kevin McCall, solutionsteam leader
for Sandvik Coromant Co.,Fair Lawn, N.J., noted that the abun-dance
of overhang situations presentspecial challenges.
A lot of superalloys areused in engine parts whereyou have to
get down behindflanges or way out onto a ro-tary table to actually
create fea-
tures on the part, he said.The toolholding solution,
McCall said, is a hydrome-chanical chuck that clampsonto the
tool shank. Sand-viks HydroGrip, for example,grips the tool
completely anddoes not have a large diame-ter down near where the
drill is beingheld, which allows the operator to workin
hard-to-reach areas.
Also, the hydromechanical chucks pro-
vide low runout, said McCall. Whereaswhen you use a collet, you
can get an ex-cessive amount of runout. I think the cri-terion you
want to stick with is that ifyou get more than a 0.0005" TIR,
youregoing to get very aggressive wear on thecircular land, the
outside of the drill. Soone of the major challenges when drill-ing
most of these superalloy materials ismaking sure that the tool is
held veryaccurately.
Heat IssuesThe biggest challenge end users face
when drilling superalloys is how best tomanage the resulting
heat. Two primeconsiderations are drill coatings and cool-ants.
Titanium-based tool coatings areused extensively in the machining
of su-peralloys, said Guhrings Hellinger. He
added that coatings such as titaniumaluminum nitride and
aluminum tita-nium nitride have an oxidation tem-perature that is
over 300 F higher thantitanium-nitride coating. These coatingsform
an amorphous layer of aluminum
oxide that imparts greater heat and hard-ness at elevated
temperatures, which arecommon in superalloy drilling.
As for coolants, McCall at SandvikCoromant prefers
water-soluble, vege-table-based ones because they have
fewchemicals, which minimizes health haz-ards for machinists. You
also need a highconcentration, at least a 10 percent mix-ture
coolant, he said. And the otheraspect to this, which I dont think a
lotof customers consider, is [through-tool]high-pressure coolant,
at least 1,000 psi.The smaller the drill, the less volume youcan
get through that tool, and that [de-
creased volume] is the real enemy here.When you have a small
drill, the heat atits tip is able to radiate through the en-
tire drill very quickly. With high-pres-sure coolant, youre able
to dissipate thatheat and evacuate the chips quickly
andefficiently. Youre also less likely to havechips stick to the
drill tip and then draginside and score the hole.
McCall added that cooling effortscan quickly go awry when shops
use thewrong toolholder for a tool, such as anunsealed ER collet
chuck. If there areany leaks in the holder, water will
findthem.
As the drill is engaged withthe material, the through-cool-ant
holes are partially pluggedand so the coolant, under pres-sure, is
going to find the pathof least resistance, said McCall.
That is also why it is critical tohave a drill with large
enoughflutes for effective chip andcoolant evacuation, in
conjunc-tion with a suitable toolholderand machine [with
through-spindle coolant].
When problems do occur,they can be hard to detect. With cool-ant
splashing everywhere, the operatormight easily conclude that
everythingis as it should be. All the while, though,the drill tip
is heating up.
As a result, you can bind the toolright in the part and either
snap it off,or sometimes the drill is strong enoughthat you could
actually just push thematerial and blow the hole right out,said
McCall. Then, of course, the partis deviated.
Joe Nuzzi, director of product devel-opment at Allied Machine
and Engineer-ing Corp., Dover, Ohio, typically will
start holes with a short drill, especiallyfor deep cuts. He will
then use a longerdrill to finish the job.
Super Drills (continued)
, Sandvik Coromant Co., Fair Lawn, N.J.,
introduced the CoroDrill Delta-C drill, for aerospace engine
and
gas turbine applications. Te solid-carbide drill incorporates
a
number of novel features, said Kevin McCall, solutions team
leader for Sandvik Coromant.
One trick with this drill is the tip geometry, he said. Its
a
constant radius; there are no sharp corners to wear out as on
a
standard drill. Also, the tip has a very thin split point in the
centerto allow the metal to extrude.
Te drill incorporates large coolant holes for the drills size
and
an expanded flute design to promote chip evacuation. Te
long,
constant radius geometry built into the tool is for even wear
and
long tool life, said McCall.
In addition, the Delta-Cs multilayer coating prevents crack
propagation. o make sure that the drill maintains optimal
cutting capabilities, the coatings were applied in thin layers
via
physical vapor deposition.
Weve seen these drills perform five times longer thancomparable
Sandvik drills, with penetration rates 50 percent
better, said McCall. D. McCann
Sandviks new superalloy drill
Seco Tools
The CrownLoc drills from Seco Tools incorporate exchangeable
crowns, which eliminates regrinding.
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The deeper you go the more diffi-cult it becomes, added Jim
Porter, appli-cation engineering supervisor for AlliedMachine and
Engineering. Obviously,as you go to the longer tools, we recom-mend
increasing your coolant pressure toovercome resistance to chip
evacuation.Generally, the other option is to reduceyour penetration
rate to create less chip
volume to begin with so that you givethe machine time to let the
coolant doits job to evacuate chips.
Tool LifeRegardless of how effective the tool-
holding and coolant are, drills eventuallywear down. But thats
seldom a reason totoss them, said Diamantis, adding thatmany shops
do so routinely.
The alternative, he said, is resharp-
ening. If theyre not burned, you cansharpen them very minimally
by re-moving about 0.030" to 0.060" of theoverall length, and you
have a brand-new drill.
When resharpening, continued Dia-mantis, it is important for
regrind shops
to remember to remove the drills fronttaper that has formed as a
result of wear.Its critical that the very front of thetool is
bigger than farther back. The drillshould always have a back taper
along theentire flute length. If you sharpen thetool correctly,
youll have a brand-newdrill for a fraction of the cost you
wouldotherwise pay.
While drill coatings, coolants andtoolholding solutions might
not havebeen priorities in past times, theres noquestion that
ongoing refinements inmaterials will demand ongoing advancesin
drilling technology and techniques.
Even 15 years ago, I used to thinkdrilling was hard, said
Diamantis. But Ilook back today and I think that was easy.Its a
completely different world. CTE
About the Author:
Daniel McCann is senior
editor of Cutting ool
Engineering. He can be
reached to dmccann@
jwr.com or (847) 714-
0177.
Allied Machine and
Engineering Corp.
(800) 321-5537
www.alliedmachine.com
Amamco Tool
(800) 833-2239
www.amamcotool.com
Guhring Inc.
(800) 776-6170
www.guhring.com
Sandvik Coromant Co.
(800) 726-3845
www.coromant.sandvik.com/us
Seco Tools Inc.
(248) 528-5200
www.secotools.com
contributors
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