Tool edge-prep

1. z
I
e @Society of
Manufacturing
Engineers
1999
MR99-235
Cutting Tool Edge Preparation
author
WILLIAM R. SHAFFER
President
Solo Solutions
Greensburg, Pennsylvania
abstract
Proper selection and application of cutting tool edge preparation is considered one
of the basic ingredients for a successfully manufactured and correctly performing
hardmetal-cutting tool. This paper develops a basic understanding of the “need” for
proper cutting edge preparation, specifically, edge honing. The discussion is aimed
at the process of nylon abrasive filament brush honing and how it affects the tool as
an end product. It also identifies some of the manufacturing related pitfalls and the
problems that can drive manufacturing costs. Edge preparation is a necessary
process in nearly 100% of all hardmetal tooling.
conference
3rd INTERNATIONAL MACHINING & GRINDING
October 4-7, 1999
Cincinnati, Ohio
terms
Edge Prep
Brushing
Waterfall Hone
Honing
Radius Hone
Society of Manufacturing Engineers
One SME Drive l PO. Box 930 l Dearborn, Ml 48121
Phone (313) 271-l 500

2. SME TECHNICAL PAPERS
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Manufacturing Engineers. By publishing this paper, SME neither
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offers any technical advice. SME specifically disclaims any warranty
of reliability or safety of any of the information contained herein.

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1. Introduction to Cutting Tool Edge Preparation:
(Evaluating “the need”). The tool edge preparation process, when administered
properly, addsstrengthto the tool cutting edge,lengthensusabletool life, minimizes the
propensity of the edgeto chip, improvespart quality andconsistency,and enhanceswork
piece surface finish. Some of the edge preparation options currently used by the tool
manufacturer are up sharp(no edgeprep after grinding), radius or waterfall hone shapes,
T-Land (or K-Land), and T-land + hone. The most widely used edge preparation that
exists in industry today is the radius and waterfall hone shapes.These edge preps are
applied in a variety of sizesbasedon cutting tool size and application. Edge prep is not
limited to application of indexable style tooling. It is required on most hardmetal round
tools, “brazed on” tools, and single/multiple edgeform tools.
2. Cutting Tool Edge Preparation, “The Beginning”
Edge honing was initially instituted to removethe rough edgesproduced in the powder
metallurgical processof part manufacturing. (Nearly all companiesproduce the “green”
blank usingbasically the samemanufacturingmethodprior to the densification processof

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sintering). In recentyearshoning hasbecomea necessaryprerequisite for some methods
of tool coating.Although times havechangedand cutting tool manufacturing technology
hasimproved greatly, the need for the controlled removal and smoothing of the edgesof
the cutting tool after sintering remains. During the last twenty years or so of modem
carbidetool development,more emphasishasbeenput on honing to enhancetool life and
tool performance. Both tool life and tool performance are greatly dependent on the
correct sizeandgeometric shapeof the cutting tool edgepreparation.
The “Original” Insert Honing Processes
Over the yearsedgehoning on cutting tools hasbeen accomplished by various methods.
Vibratory honing, honing by hand with diamond stones, mass media honing, slurry
honing, honing insertswith media impregnated rubber wheels, dry blasting, wet blasting,
andtumbling areamongthe many processesstill in use.Edge honing was (is) considered
an “art”, and many tool producers inventing their own processeshad to protect them
closely as guarded trade secrets. Edge honing was truly one of those competitive
advantages that could help a company improve total tool performance over a
competitor.
In the early honing processes,there were many variables that required controlling.
Honing machineprocessvariablesand incoming part quality variability virtually required
everybatchof partsto be“learned” eachtime a new setup wasmade.
Edge honing in the early yearswas high in labor intensity and costly. But, being able to
hone effectively is one of the keys to successin the cutting tool industry. ‘Effective
honing” canbebestdefined asthe most accurate,repeatableprocessthat is lower in total
costthan thecompetition.
Introduction of Brush Honing Processes
In the late 1970’s brush honing made its appearancein the cutting tool industry in two
distinctly different processes. One brush application was the nylon abrasive filament
process. The other brush processuseda vegetable fiber brush with an oil and diamond
paste. Due to process economics, nylon abrasive filament brush honing became the
method more widely used for edge preparation. Considering the 20-year presenceof
abrasive filament brush honing in tool production, the technology connected with
filament brushhoning, eventoday, is still somewhat limited. During the initial yearsof
useof the filament brushes,there existed a lag in the technological development of brush
honing. This lag was driven in part by the insert manufacturers feeling the need to
developtheir “own*’ processutilizing the new brushing techniques.With limited standard
processinformation readily available to the industry, a true technology gap developed
and quickly widened between the filament brush manufacturers, hone machine
manufacturers, and the cutting tool industry. Abrasive filament technolo,T, not being
completely understood,was cause for the brush honing process, in most cases,to be
misapplied. The misapplication of abrasive filament brushes in tool edge preparation
spawnedmany costly associatedmanufacturing problems, someof which still exist in the

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industry. This lack of understanding over the years has had a substantial impact on
manufacturing costs.
Sylon Filament Brush Honing
As statedearlier, probably the widest usedof all processesfor edgepreparation utilizes
the Nylon Abrasive Filament (NAF) brush. Made of heat-stabilized nylon filaments
impregnated with abrasivegrain, the individual nylon filaments aredesignedto work like
flexible files. Conforming to the part contours, the brush filaments wipe and file across
part edgesin an action that roundsand shapesthe cutting edges.Nylon abrasivefilament
brush technology was invented many years before the application of the NAF brush for
insert honing.
In the brush industry, there exist only a few manufacturersin the world producing the
actual abrasive nylon filament. The filament is manufacturedin several configurations.
The filament can be round or rectangular in cross-section.The round filament can be
straight or crimped. The filaments can be produced in different diameters as well as
different media types,grit gradesandpercentageof mediacontent.
In the filament brush community, there are many companiesthat assembleand market
brushes. With all brush producing companies in the industry using basically the same
source for nylon abrasive filaments you would assume brushes to be uniform in
construction. However, the brushmanufacturing assemblytechniquesdiffer and sodo the
finished products. Each assembly technique exhibits it’s own distinct characteristics
when used in the application of tool honing. The difference in brush manufacturing
techniques is fairly easy to see when the brush is used in the diflicult application of
hardmetal tool honing. The ability to hold microscopic edgehone sizes in the finished
product can vary from manufacturer to manufacturer as well as the amount of dust
emissions from eachof their brush products. There is also a fairly significant difference
basedon brush life. These factors can drive the manufacturing costs up or down when
brush cost per piece is calculated. With the tooling manufacturersproducing millions of
tools each year, even a fraction of a cent difference in per part brushcosts is significant
when applied to a total year’s production.
Today, the demandsput on the cutting tool industry by their customers,using the new
high-tech metalcutting equipment, and addressing the cutting requirements of exotic
materials are high. With the new materials bombarding the industry and the ability for
CNC machines to run in a “lights-out” untendedenvironment, the quality demandsare
increasing on cutting tools. The need to produce more uredictably performiw tools is
paramount to the industry and no one exuects that trend to charwe.
3. Variability of Quality and Cost in the Honing Process
Since the arrival of NAF brushesfor honing, the processof honing hasbecome somewhat
more predictable. (Nylon brushesare more robust in the application of tool edgehoning

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and are not affectedas much varying hardnesstool substratematerials. The NAF brush
has the abrasive media uniformly distributed within each filament. There are always
new, sharp particlesof the media being exposedduring processingas the nylon material
in the filament wearsaway.)
In the process of edge honing, the most controlling variable that affects finished part
quality is the in-coming part condition. Quite often the cutting edgeswithin eachcutting
tool coming from the sintering operation arenot consistent. They can vary edgeto edge,
comer to comer, or top to bottom, (in any combination). Another variable consideredare
the honing characteristics of different cutting tool materials and sometimes-even
variability within batchesof materials will appear. (Keep in mind the process of edge
honing is “controlled” erosion of the tool edges, and carbide exhibits a very high
resistance to wear). Consequently,the edgehoning processneedsto be tweaked as an
“artsy”, delicate balanceof hone machine parameters(brush grit size, media grit size,
part dwell time, etc.),setby the operatorto accuratelyremove the sharpcomer by wear.
The duty of the operatoris to control this processof wearing the cutting edgebefore the
wear exceedsthe original honespecification. Depending on the honing processin use,if
the media or methodsof the edgeerosion were too aggressive,uneven material removal
on the cutting tool would result having specific sectionsof the tool being “over-honed”
(beyond specification).
Variability in honeuniformity can also be linked to several components that exist in the
manufacturing system.Sometimes“upfront” variables are built into the part making it
difficult for an operatorto make an “in-specification” product. Some of those process
variables(in a non-groundasmolded part) areasfollows:
l Excessive die flash. This condition can be causedby press tooling that is either
worn, damaged,or out of dimensional specification causing a Wash” or raggededge
to be formed around the cutting edges of the parts. Coming from the sintering
process,the honeoperatormust considerthe magnitude of this raggededgeandtry to
remove it during the honeprocess. The edge hone operator is required adjust his
machine process parameters (if possible) to remove the flash and at the same
time achieve the final size edge according to specification.
l Damaged edges causedby handling tools before sintering. This is a special problem
consisting of the cutting edgesof the insert being distorted. The inserts, aspressed,
are chalk-like in consistencyand touching the cutting edgescan round them prior to
sintering. Once sintered, these rounded edges need to be addressed in the hone
process. Sometimestheserounded edgesfrom handling can be greater in size than
the specified finished hone size. (The parts then become scrap). The operator must
assess the part condition and set machine parameters (if possible) to offset the
effects of the distorted edge shape. (This problem is becoming less of a factor in
manufacturing because it has been minimized with robotic unloading of tool
producing presses.

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l Most insertsrequire a processprior to sintering to remove the excessdie flash. After
the processof removing die flash in the “green’ state, final edge condition can vary
greatly, depending on the skill of the person removing the flash. This uneven
condition can vary from cutting edge to cutting edge and from top to bottom within
the insert.This too is a condition the operatormust assessprior to honing. The hone
operator is then required to set the proper parameters of the machine (if
possible) in an attempt to make the parts finish within specification. (Although
still present,as in the case with damage from part handling, it is becoming less
significant as a process variable with the improved technology related to
manufacturing of presstooling).
Insert honing canbeanaccurateandrelatively low cost processif applied correctly. In
the caseof correctapplication of NAF brushing, using either flat or round filaments, a
nominal honesizecanbeaccomplishedin avery short cycle time. The sizeand shapeof
the hone is determinedby a combination of severalmachine set-upparameters.Oneset-
up parameterthat is generallyheld constantis dwell time. Dwell time is usedto control
production rateswhile othermachine parametersarevaried to maintain uniformity and
shape.
Significant Factors that drive manufacturing costs are;
l Set up (Sometimes this process can consume excessive amounts of time
obtaining machine settings for correct size and shape of the hone. This is
basedon in-coming part condition andoperator ability)
l Average lot size. (This variable will determine the number of setup changes
required in aday).
l Nylon smearing (This phenomenon was introduced to the cutting tool
industry by NAF brushes. Incorrect set up and incorrect machine parameters
basically cause nylon smearing. If nylon smearing goes undetected, a
secondary, costly, non-value added process is required to remove the
substance).
l Process time/cycle time. Cycle times can also fluctuate and normally is
driven by honesizeandincorrect setup parameters.
l Producing large hone sizes, (Hones above .005” can consume both cycle
time, initiate increasedbrush wear, and introduce nylon smearing causedby
elevatedprocessingheat).
l Tool changes and brush changes, (Thesefunctions can drive up costsdue to
the time consuming process of tool and brush changing). This also
necessitatesa new set-upto keepthe parts in specification.
Other process related problems that can increase costs:
l Controlling the inherent dust associated with dry abrasive filament brush
honing.

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l Disposing of coolant usedduring wet filament brush honing, slurry honing, or
wet blasting processing
l Elevated temperaturesof the cutting tool being honed dry can make handling
difficult.
l Accurately measuring the hone size and subsequentsize adjustmentsrequire
the machine to be stopped,thus reducing output.
l Brush costs can be excessive if the brushesare misapplied. Misapplication
can come in the form of nylon smearing, filament fatigue/breakage,high
insert heat,and excessivedust.
l Improper training (since many processeswere developed“in-house”, training
can be fragmented at best. Most of the time an operator will train another
operators. The danger lies in the possible loss of processinformation in the
unstructuredexchangesbetween operators).
l Insert binder material leaching. (Leaching can contribute to the total scrap
percentage.This problem is normally associatedwith any wet processusedin
the final production of carbidetools).
Extend brush life, reduce costs
The rule is the same for any material removal process,the tool (in this caseabrasive
brush), must be matched to the job requirement. In the application of insert edge
preparation, abrasive filament brush grit size is a key factor in obtaining uniformity in
edge hone shape and size. Brush life will vary greatly with changing hone size
requirements.That is why the brushapplication must be correct, otherwise,brushlife will
suffer and consequently,processcostswill increasedramatically.
4. Proper insert edge preparation is key to consistent tool life
Most cutting tool experts understandthe primary purposeof a honedcutting edgeis to
increasethe mechanical strength and impact resistanceof the insert edge. The properly
applied honeadds value by adding predictable life to the tool. To getthe properresults
and to make the entire processfunction, the correct hone size must be selectedbasedon
insert size, geometry and the application of the particular cutting tool. The hone
size/shape variations can range in size from less than .0005” to well above .008”,
dependingon the insert size andcutting application.
Brush Honing Equipment
In many of the commercially used brush honing machines, a continuous rotating table
moves the cutting tools through the (high speed, above 1,000 RPM) rotating nylon
filament brush. There is an arc-like feeding motion of the rotating part. While the part is
in contact with the brush and becauseof the arc motion through the brush,brushpressure
will constantly vary. Therefore the brush pressureis reachesthe highestpoint when the
insert is at the tangencyof the rotating table. The brushpressurebeginsto reduceasthe

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part continuesto move through the brush. This type of processingcan possibly manifest
in unevenedgehone sizeswithin eachinsert, even if the incoming quality of the insert is
perfect.
Initially, when NAF brusheswere introduced for honing, no machines existedthat were
specifically designedfor hardmetal tool edgehoning utilizing the filament brushprocess.
Instead,existing machinesdesigned for other applications, suchaspolishing andbuffing
machines were slightly modified and used for production insert honing. The use of
modified existing equipment for brush honing filled the manufacturing need. A product
of using convertedmachinery delayed machine developmentof specific machinesand as
an industry put development “on the back burner”. Because of this, industry wide
research,gathering of technology, and the growth and understandingof the processof
insert honing waslimited. Since that time, most work in brushhonemachineresearchand
new equipment development was patternedclosely after the original modified machinery.
Along with the limited availability of specific processequipment, there also existed a
lack of available equipment for accurately measuring the edge hone. Given the lack of
standardmachinesfor honing and measuring machine availability, most individual tool
manufacturers developed their own hone processesand adopted their own quality
standard for measuring hone size. (Accurate measuring is essential as the first step in
developing an industry standard). Taking these circumstances into account, the true
development of both the honing processand measuringbecamean R & D function of the
cutting tool manufacturers.
An interesting comparison of technology growth can be drawn betweenthe processesof
tool edgehoning and hardmetal tool grinding, two completely different processes.As you
compare the tool edge honing process with an equally important tool grinding, (both
processesinvolve controlled mechanical removal of material), you find that development
of the grinding equipment technology and parametersaremuch more advanced. R&D of
the grinding machine tool producers along with new grinding wheel technology have
paced the advancementsin hardmetal tool grinding. Becauseof thesecombined efforts
the state-of-the-art in grinding is highly advanced. Grinding parameters in most
companies are still held very “close to the vest” and consideredsecret,but at the end of
the day with similar grinding machines, grinding a similar volume of material, grinding
yields will normally be within 10%.The tool grinding processhasbecomeascience.
5. Where is the Tool Producing Industry Today?
The “Bad News”:
In the processof hardmetal tool edgehoning, this processstill remains an art. Correct
honing, for the most part, is completely dependenton the bestfit of part condition and is
limited by machine variability and operator expertise. Most of the time, the honing
process is still the best educated guess of an operator experimenting with process
variablesto getacceptableresults.

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..
The “Good News”:
Technology andequipment exist today usingthe nylon abrasivefilament brush technique
to overcome nearly all the currentprocessproblems:
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Machine set-upcanbe reducedto minutes.
Hone uniformity canbe greatly enhancedevenin the insertswith complex geometries
such as threading’grooving tools, full form threading and even wide form tools.
Wavy edge geometric shapesand helical milling insert geometries should no longer
be an issuefor uniform brushhoning.
The ability exists to hone and exercise size control on each surface of the insert
independently. This permits changing honesize within the insert to further enhance
cutting ability.
Machinery equippedwith minimum numbersof insert stations/fixtures and with CNC
controls for quick setup canbetter handlesmall lot sizesmore effectively.
Using small, low cost CNC honing machines presentsthe opportunity to combine
processesto reduceleadtime andreducelabor costs.
Nylon smearingcanbe eliminated by correctapplication and setup of the NAF brush
to keep processingheatlow.
Quick-change brush tooling allows the rapid change of brushes. This perrnits the
operator to match the brush grit value to the finished hone size. (Application of the
correct tool for the correctjob).
Dust associatedwith normal dry brush processcan be reduced greatly if the correct
brush is applied.
Cutting tool materials suchasCarbide,Cermet, Ceramic, PCD and PCBN can all be
effectively processedquickly and accuratelyusingnew brushing technologies.
Proper training is available to further enhancethe impact of the new machinery and
technology.
6. Conclusion
Hardmetal tool edgehoning, in recentyearshasbeenuniversally recognized asone of the
four main ingredients required in successfulinsert manufacturing. These four ingredients
include (1) tool substrate composition, (insert base material), (2) tool geometry, (3)
proper coating (PVD and CVD amongothers),and(4) edgepreparation.
The first three of the four ingredients are the end result of much research and
development to make them more reliable, repeatableprocesses. The fourth ingredient,
tool edge honing, needs to break away from being an “art” to join the other above
mentioned three ingredients as a controllable mechanical process. Further
advancements in cutting tools materials and the capability of new cutting techniques
will weigh heavily on this technology quickly moving forward. The technology for
better control of tool edgehoning existsandthemachineryis designed.