Cutting Tool Applicationsbgk.uni-obuda.hu/ggyt/targyak/seged/baggt23nec/book_02.pdf · As the cutting tool engages the workpiece, the material directly ahead of the tool is sheared

Cutting

Tool

Applications

Cutting Tool Applications

By George Schneider, Jr. CMfgE

2 Tooling & Production/Chapter 2 www.toolingandproduction.com

2.1 InroductionThe process of metal removal, a process inwhich a wedge-shaped tool engages aworkpiece to remove a layer of material inthe form of a chip, goes back many years.Even with all of the sophisticated equip-ment and techniques used in today’s mod-ern industry, the basic mechanics of form-ing a chip remain the same. As the cuttingtool engages the workpiece, the materialdirectly ahead of the tool is sheared anddeformed under tremendous pressure. Thedeformed material then seeks to relieve itsstressed condition by fracturing and flow-ing into the space above the tool in theform of a chip. A turning tool holder gen-erating a chip is shown in Figure 2.1.

2.2 Cutting Tool ForcesThe deformation of a work material meansthat enough force has been exerted by thetool to permanently reshape or fracture thework material. If a material is reshaped, itis said to have exceeded its plastic limit. Achip is a combination of reshaping andfracturing. The deformed chip is separat-ed from the parent material by fracture.The cutting action and the chip formationcan be more easily analyzed if the edge ofthe tool is set perpendicular to the relativemotion of the material, as shown in Figure2.2. Here the undeformed chip thicknesst1 is the value of the depth of cut, while t2is the thickness of the deformed chip afterleaving the workpiece. The major defor-mation starts at the shear zone and diame-ter determines the angle of shear.

A general discussion of the forces act-ing in metal cutting is presented by usingthe example of a typical turning operation.When a solid bar is turned, there are three

Chip thicknessafter cutting

(t2)

Rakeangle(α)

Shearangle (φ)

Undeformedchip thickness

(t1)

Tool

FIGURE 2.1 A turning toolholder insert gener-ating a chip. (Courtesy Kennametal Inc.)

FIGURE 2.2 Chip formation showing the defor-mation of the material being machined.

Chapter 2

Metal Removal

Methods

Upcoming Chapters

Metal RemovalCutting-Tool Materials

Metal Removal MethodsMachinability of Metals

Single Point MachiningTurning Tools and Operations

Turning Methods and MachinesGrooving and Threading

Shaping and Planing

Hole Making ProcessesDrills and Drilling Operations

Drilling Methods and MachinesBoring Operations and Machines

Reaming and Tapping

Multi Point MachiningMilling Cutters and OperationsMilling Methods and Machines

Broaches and BroachingSaws and Sawing

Abrasive ProcessesGrinding Wheels and OperationsGrinding Methods and Machines

Lapping and Honing

George Schneider, Jr. CMfgEProfessor Emeritus

Engineering TechnologyLawrence Technological University

Former ChairmanDetroit Chapter ONE Society of Manufacturing Engineers

Former PresidentInternational Excutive BoardSociety of Carbide & Tool Engineers

Lawrence Tech. Univ.: http://www.ltu.edu

Prentice Hall: http://www.prenhall.com

forces acting on the cutting tool (Fig.2.3):

Tangential Force: This acts in adirection tangential to the revolvingworkpiece and represents the resistanceto the rotation of the workpiece. In anormal operation, tangential force is thehighest of the three forces and accountsfor about 98 percent of the total powerrequired by the operation.

Longitudinal Force: Longitudinalforce acts in the direction parallel to theaxis of the work and represents theresistance to the longitudinal feed of thetool. Longitudinal force is usuallyabout 50 percent as great as tangentialforce. Since feed velocity is usuallyvery low in relation to the velocity ofthe rotating workpiece, longitudinalforce accounts for only about 1 percentof total power required.

Radial Force: Radial force acts in aradial direction from the center line ofthe workpiece. The radial force is gen-erally the smallest of the three, oftenabout 50 percent as large as longitudinalforce. Its effect on power requirementsis very small because velocity in theradial direction is negligible.

2.3 Chip Formation and Tool WearRegardless of the tool being used or themetal being cut, the chip formingprocess occurs by a mechanism calledplastic deformation. This deformationcan be visualized as shearing. That iswhen a metal is subjected to a loadexceeding its elastic limit. The crystalsof the metal elongate through an actionof slipping or shearing, which takesplace within the crystals and betweenadjacent crystals. This action, shown inFigure 2.4 is similar to the action thattakes place when a deck of cards is

Chap. 2: Metal Removal Methods

www.toolingandproduction.com Chapter 2/Tooling & Production 3

given a push and sliding orshearing occurs between theindividual cards.

Metals are composed ofmany crystals and each crys-tal in turn is composed ofatoms arranged into somedefinite pattern. Withoutgetting into a complicateddiscussion on the atomicmakeup and characteristicsof metals, it should be noted,that the slipping of the crys-tals takes place along a planeof greatest ionic density.

Most practical cuttingoperations, such as turningand milling, involve two ormore cutting edges inclinedat various angles to thedirection of the cut.However, the basic mecha-nism of cutting can beexplained by analyzing cut-ting done with a single cut-ting edge.

Chip formation is sim-plest when a continuous chipis formed in orthogonal cut-ting (Fig. 2.5a). Here thecutting edge of the tool isperpendicular to the line oftool travel, tangential, longi-tudinal, and radial forces are in the sameplane, and only a single, straight cuttingedge is active. In oblique cutting, ( Fig.2.5b), a single, straight cutting edge isinclined in the direction of tool travel.This inclination causes changes in thedirection of chip flow up the face of thetool. When the cutting edge is inclined,the chip flows across the tool face witha sideways movement that produces ahelical form of chip.

2.3.1 Chip FormationMetal cutting chips have been classified

into three basic types:• discontinuous or segmented• continuous• continuous with a built-up edge.

All three types of chips are shown inFigure 2.6 a,b,and c.

Discontinuous Chip - Type 1:Discontinuous or segmented chips areproduced when brittle metal such as castiron and hard bronze are cut or whensome ductile metals are cut under poorcutting conditions. As the point of thecutting tool contacts the metal, somecompression occurs, and the chip begins

FIGURE 2.3Typical turning operationshowing the forces acting on the cuttingtool.

FIGURE 2.6 Types of chip formations: (a) discontinuous, (b) continuous, (c) continuouswith built-up edge (BUE).

FIGURE 2.4 Chip formation compared to a slidingdeck of cards.

FIGURE 2.5 Chip formation showing both (a) orthogo-nal cutting and (b) oblique cutting.

Tangentialforce

Longitudinalforce

Radial force

101112131415 9 8 76

54

32

1

Tool

Workpiece

Workpiece

(a)

Workpiece

(b)

90¡

Tool Tool

ChipChip

Built-upedge

Tool

(a) (b) (c)

Tool

Roughworkplacesurface

Chip

Primarydeformationzone Tool



flowing along the chip-tool interface.As more stress is applied to brittle metalby the cutting action, the metal com-presses until it reaches a point whererupture occurs and the chip separatesfrom the unmachined portion. Thiscycle is repeated indefinitely during thecutting operation, with the rupture ofeach segment occurring on the shearangle or plane. Generally, as a result ofthese successive ruptures, a poor sur-face is produced on the workpiece.

Continuous Chip - Type 2: TheType 2 chip is a continuous ribbon pro-duced when the flow of metal next tothe tool face is not greatly restricted bya built-up edge or friction at the chiptool interface. The continuous ribbonchip is considered ideal for efficient cut-ting action because it results in betterfinishes.

Unlike the Type 1 chip, fractures orruptures do not occur here, because ofthe ductile nature of the metal. Thecrystal structure of the ductile metal iselongated when it is compressed by theaction of the cutting tool and as the chipseparates from the metal. The processof chip formation occurs in a singleplane, extending from the cutting tool tothe unmachined work surface. The areawhere plastic deformation of the crystalstructure and shear occurs, is called theshear zone. The angle on which thechip separates from the metal is calledthe shear angle, as shown in Figure 2.2.

Continuous Chip with a Built-upEdge (BUE)- Type 3: The metal aheadof the cutting tool is compressed andforms a chip which begins to flow alongthe chip-tool interface. As a result ofthe high temperature, the high pressure,and the high frictional resistance againstthe flow of the chip along the chip-toolinterface, small particles of metal beginadhering to the edge of the cutting toolwhile the chip shears away. As the cut-ting process continues, more particlesadhere to the cutting tool and a largerbuild-up results, which affects the cut-ting action. The built-up edge increasesin size and becomes more unstable.Eventually a point is reached wherefragments are torn off. Portions of thesefragments which break off, stick to boththe chip and the workpiece. The build-up and breakdown of the built-up edgeoccur rapidly during a cutting actionand cover the machined surface with amultitude of built-up fragments. Thesefragments adhere to and score the

machined surface,resulting in a poorsurface finish.

Shear Angle:Certain characteris-tics of continuouschips are determinedby the shear angle.The shear angle isthe plane where slipoccurs, to begin chipformation (Figure2.2). In Figure 2.7the distortion of thework material grainsin the chip, as com-pared to the parentmaterial, is visible.Each fracture line inthe chip as it moves upwardover the tool surface can beseen, as well as the distortedsurface grains where the toolhas already passed. In certainwork materials, these distortedsurface grains account for workhardening.

Regardless of the shearangle, the compressive defor-mation caused by the tool forceagainst the chip, will cause thechip to be thicker and shorterthan the layer of workpiecematerial removed. The work orenergy required to deform thematerial usually accounts forthe largest portion of forces andpower involved in a metalremoving operation. For alayer of work material of givendimensions, the thicker the chip, thegreater the force required to produce it.

Heat in Metal Cutting: The mechan-ical energy consumed in the cutting areais converted into heat. The main sourcesof heat are, the shear zone, the interfacebetween the tool and the chip where thefriction force generates heat, and thelower portion of the tool tip which rubsagainst the machined surface. Theinteraction of these heat sources, com-bined with the geometry of the cuttingarea, results in a complex temperaturedistribution, as shown in Figure 2.8.

The temperature generated in theshear plane is a function of the shearenergy and the specific heat of the mate-rial. Temperature increase on the toolface depends on the friction conditionsat the interface. A low coefficient offriction is, of course, desirable.

Temperature distribution will be a func-tion of, among other factors, the thermalconductivities of the workpiece and thetool materials, the specific heat, cuttingspeed, depth of cut, and the use of a cut-ting fluid. As cutting speed increases,there is little time for the heat to be dis-sipated away from the cutting area andso the proportion of the heat carriedaway by the chip increases.

In Chapter 3 - Machinability ofMetals - this topic is discussed in moredetail.

2.3.2 Cutting Tool WearCutting tool life is one of the mostimportant economic considerations inmetal cutting. In roughing operations,the tool material, the various toolangles, cutting speeds, and feed rates,are usually chosen to give an economi-

Rakeangle

ToolReliefangle

Distortedsurfacegrains

Parent material

Cut depth

Shear plane

Slip lines

Chip segment

Grainfragments

Workpiece

Chip Tool675

750

850 93

0

930

1100

1100

1100…F

1300

1200

1200

1300

FIGURE 2.7 Distribution of work material during chip forma-tion.

FIGURE 2.8 Typical temperature distribution in thecutting zone.



cal tool life. Conditions giving a veryshort tool life will not be economicalbecause tool-grinding, indexing, andtool replacement costs will be high. Onthe other hand, the use of very lowspeeds and feeds to give long tool lifewill not be economical because of thelow production rate. Clearly any tool orwork material improvements thatincrease tool life without causing unac-ceptable drops in production, will bebeneficial. In order to form a basis forsuch improvements, efforts have beenmade to understand the behavior of thetool, how it physically wears, the wearmechanisms, and forms of tool failure.

While the tool is engaged in thecutting operation, wear may devel-op in one or more areas on and nearthe cutting edge:

Crater Wear: Typically, crater-ing occurs on the top face of thetool. It is essentially the erosion ofan area parallel to the cutting edge.This erosion process takes place asthe chip being cut, rubs the top faceof the tool. Under very high-speedcutting conditions and whenmachining tough materials, craterwear can be the factor which deter-mines the life of the tool. Typicalcrater wear patterns are shown inFigures 2.9 and 2.10a. However, whentools are used under economical condi-tions, the edge wear and not the craterwear is more commonly the controllingfactor in the life of the tool

Edge Wear: Edge wear occurs onthe clearance face of the tool and ismainly caused by the rubbing of thenewly machined workpiece surface onthe contact area of the tool edge. Thistype of wear occurs on all tools whilecutting any type of work material. Edgewear begins along the lead cutting edgeand generally moves downward, awayfrom the cutting edge. Typical edgewear patterns are shown in Figures 2.9and 2.10b. The edge wear is also com-monly known as the wearland.

Nose Wear: Usually observed after aconsiderable cutting time, nose wearappears when the tool has alreadyexhibited land and/or crater wear. Wearon the nose of the cutting edge usuallyaffects the quality of the surface finishon the workpiece.

Cutting tool material in general, andcarbide tools in particular, exhibit dif-ferent types of wear and/or failure:

Plastic Deformation: Edge depres-

sion and body bulging appear, due toexcessive heat. The tool loses strengthand consequently flows plastically.

Mechanical Breakage: Excessiveforce may cause immediate failure.Alternatively, the mechanical failure(chipping) may result from a fatigue-type failure. Thermal shock also causesmechanical failure.

Gradual Wear: The tool assumes aform of stability wear due to interactionbetween tool and work, resulting incrater wear. Four basic wear mecha-nisms affecting tool material have beencategorized as:

Abrasion: Because hard inclusionsin the workpiece microstructure plowinto the tool face and flank surfaces,abrasion wear predominates at relative-ly low cutting temperatures. The abra-sion resistance of a tool material is pro-portional to its hardness.

Adhesion: Caused by formation andsubsequent destruction of minute weld-ed junctions, adhesion wear is common-ly observed as built-up edge (BUE) onthe top face of the tool. This BUE mayeventually disengage from the tool,causing a crater like wear. Adhesion

can also occur when minute particles ofthe tool surface are instantaneouslywelded to the chip surface at the tool-chip interface and carried away with thechip.

Diffusion: Because of high tempera-tures and pressures in diffusion wear,microtransfer on an atomic scale takesplace. The rate of diffusion increasesexponentially with increases in temper-ature.

Oxidation: At elevated temperature,the oxidation of the tool material cancause high tool wear rates. The oxidesthat are formed are easily carried away,leading to increased wear.

The different wear mechanisms aswell as the different phenomena con-tributing to the attritious wear of thecutting tool, are dependent on the multi-tude of cutting conditions and especial-ly on the cutting speeds and cutting flu-ids.

Aside from the sudden prematurebreakage of the cutting edge (tool fail-ure), there are several indicators of theprogression of physical wear. Themachine operator can observe these fac-tors prior to total rupture of the edge.

FIGURE 2.9 Carbide insert wear patterns: (a) crater wear, (b) edge wear.

FIGURE 2.10 Carbide insert wear patterns: (a) crater wear, (b) edge wear. (CourtesyKennametal Inc.)

Noseradius

R

Flank face

Depth-of-cut lineEdge wear

Rake faceCraterwear

Depth-of-cut line

(a) (b)

(a) (b)



The indicators are:• Increase in the flank wear size above apredetermined value.• Increase in the crater depth, width orother parameter of the crater, in the rakeface.• Increase in the power consumption, orcutting forces required to perform thecut.• Failure to maintain the dimensionalquality of the machined part within aspecified tolerance limit.• Significant increase in the surfaceroughness of the machined part.• Change in the chip formation due toincreased crater wear or excessive heatgeneration.

2.4 Single Point Cutting ToolsThe metal cutting tool separates chipsfrom the workpiece in order to cut thepart to the desired shape and size. Thereis a great variety of metal cutting tools,each of which is designed to perform aparticular job or a group of metal cut-ting operations in an efficient manner.For example, a twist drill is designed todrill a hole of a particular size, while aturning tool might be used to turn a vari-ety of cylindrical shapes.

2.4.1 Cutting Tool GeometryThe shape and position of the tool, rela-tive to the workpiece, have an importanteffect on metal cutting. The mostimportant geometric elements, relativeto chip formation, are the location of thecutting edge and the orientation of thetool face with respect to the workpieceand the direction of cut. Other shapeconsiderations are concerned primarilywith relief or clearance, i.e., taperapplied to tool surfaces to prevent rub-bing or dragging against the work.

Terminology used to designate thesurfaces, angles and radii of single pointtools, is shown in Figure 2.11. The toolshown here is a brazed-tip type, but thesame definitions apply to indexabletools.

T & P TO PLACE FIG. 2.11 HEREThe Rake Angle: The basic tool

geometry is determined by the rakeangle of the tool as shown in Figure2.12. The rake angle is always at the topside of the tool. With the tool tip at thecenter line of the workpiece, the rakeangle is determined by the angle of thetool as it goes away from the workpiececenter line location. The neutral, posi-

tive, and negative rakes are seen in (a),(b), and (c) in Figure 2.12. The anglefor these geometries is set by the posi-tion of the insert pocket in the tool hold-er. The positive/negative (d) and doublepositive (e) rake angles are set by acombination of the insert pocket in thetool holder and the insert shape itself.

There are two rake angles: back rakeas shown in Figure 2.12, and side rakeas shown in Figure 2.13. In most turningand boring operations, it is the side rakethat is the most influential. This isbecause the side rake is in the directionof the cut.

Rake angle has two major effects dur-ing the metal cutting process. One

major effect of rake angle is its influ-ence on tool strength. An insert withnegative rake will withstand far moreloading than an insert with positiverake. The cutting force and heat areabsorbed by a greater mass of tool mate-rial, and the compressive strength ofcarbide is about two and one half timesgreater than its transverse rupturestrength.

The other major effect of rake angleis its influence on cutting pressure. Aninsert with a positive rake angle reducescutting forces by allowing the chips toflow more freely across the rake sur-face.

Negative Rake: Negative rake tools

Side relief angle

Side rake

Side clearance angle

Nose radius

End-cutting edge angle

Side-cutting edge angle

Positive back rake

End relief

End clearance

Negative back rake

(a)

(b)

(c)

(d)

(e)

FIGURE 2.11 Terminology used to designate the surfaces, angles, and radii of single-point tools.

FIGURE 2.12 With the cutting tool on center, various back rake angles are shown: (a)neutral, (b) positive, (c) negative, (d) positive/negative, (e) double positive.



should be selected whenever workpieceand machine tool stiffness and rigidityallow. Negative rake, because of itsstrength, offers greater advantage dur-ing roughing, interrupted, scaly, andhard-spot cuts. Negative rake also offersmore cutting edges for economy andoften eliminates the need for a chipbreaker. Negative rakes are recom-mended on insert grades which do notpossess good toughness (low transverserupture strength)

Negative rake is not, however, with-out some disadvantages. Negative rakerequires more horsepower and maxi-mum machine rigidity. It is more diffi-cult to achieve good surface finisheswith negative rake. Negative rake forcesthe chip into the workpiece, generatesmore heat into the tool and workpiece,and is generally limited to boring onlarger diameters because of chip jam-ming.

Positive Rake: Positive rake toolsshould be selected only when negativerake tools can’t get the job done. Someareas of cutting where positive rake mayprove more effective are, when cuttingtough, alloyed materials that tend to‘work-harden’, such as certain stainlesssteels, when cutting soft or gummy met-als, or when low rigidity of workpiece,tooling, machine tool, or fixture allowschatter to occur. The shearing actionand free cutting of positive rake toolswill often eliminate problems in theseareas.

One exception that should be notedwhen experiencing chatter with a posi-tive rake is, that at times the preloadeffect of the higher cutting forces of anegative rake tool will often dampen outchatter in a marginal situation. Thismay be especially true during lightercuts when tooling is extended or whenthe machine tool has excessive back-lash.

Neutral Rake: Neutral rake tools are

seldom used or encountered. When anegative rake insert is used in a neutralrake position, the end relief (betweentool and workpiece) is usually inade-quate. On the other hand, when a posi-tive insert is used at a neutral rake, thetip of the insert is less supported, mak-ing the insert extremely vulnerable tobreakage.

Positive/Negative Rake: The posi-tive/negative rake is generally appliedusing the same guidelines as a positiverake. The major advantages of a posi-tive/negative insert are that it can beused in a negative holder, it offersgreater strength than a positive rake,and it doubles the number of cuttingedges when using a two-sided insert.

The positive/negative insert has a tendegree positive rake. It is mounted inthe normal five degree negative pocketwhich gives it an effective five degreepositive rake when cutting. The posi-tive/negative rake still maintains a cut-ting attitude which keeps the carbideunder compression and offers moremass for heat dissipation. The posi-tive/negative insert also aids in chip

breaking on many occasions, as it tendsto curl the chip.

Double Positive Rake: The doublepositive insert is the weakest of allinserts. It is free cutting, and generallyused only when delicate, light cuts arerequired which exert minimum forceagainst the workpiece, as in the case ofthin wall tubing, for example. Otheruses of double positive inserts are forvery soft or gummy work materials,such as low carbon steel and for boringsmall diameter holes when maximumclearance is needed.

Side Rake Angles: In addition to theback rake angles there are side rakeangles as shown in Figure 2.13. Theseangles are normally determined by thetool manufacturers. Each manufactur-er’s tools may vary slightly, but usuallyan insert from one manufacturer can beused in the tool holder from another.The same advantage of positive andnegative geometry that was discussedfor back rake, applies to side rake.When back rake is positive so is siderake and when back rake is negative sois side rake.

Side and End Relief Angles: Reliefangles are for the purpose of helping toeliminate tool breakage and to increasetool life. The included angle under thecutting edge must be made as large aspractical. If the relief angle is too large,the cutting tool may chip or break. Ifthe angle is too small, the tool will rubagainst the workpiece and generateexcessive heat, and this will in turn,cause premature dulling of the cuttingtool.

Small relief angles are essential when

FIGURE 2.13 Side-rake-angle variations: (a) negative, (b) positive.

FIGURE 2.14 Lead-angle variations: (a) negative, (b) neutral, (c) positive.

Rotation

Feed

(a)

Rotation

Feed

(b)

Feed

Feed

Negative leadangle

Positive leadangle

Feed

Neutral leadangle

(a) (b)

(c)



machining hard and strong materials,and they should be increased for theweaker and softer materials. A smallerangle should be used for interruptedcuts or heavy feeds, and a larger anglefor semi-finish and finish cuts.

Lead Angle: Lead angle (Fig. 2.14)is determined by the tool holder whichmust be chosen for each particular job.The insert itself can be used in anyappropriate holder, for that particularinsert shape, regardless of lead angle.

Lead angle is an important considera-tion when choosing a tool holder. Apositive lead angle is the most common-ly used and should be the choice for themajority of applications. Positive leadangle performs two main functions:• It thins the chip• It protects the insert

The undeformed chip thicknessdecreases when using a positive leadangle.

Positive lead angles vary, but themost common lead angles available onstandard holders are 10, 15, 30 and 45degrees. As seen in Figure 2.15, thevolume of chip material is about thesame in each case but the positive leadangle distributes the cutting force over agreater area of the tool’s edge. Thisallows a substantial increase in feed ratewithout reducing the tool life because ofexcessive loading. The greater the leadangle, the more the feed rate can beincreased.

Positive lead angle also reduces thelongitudinal force (direction of feed) onthe workpiece. But positive lead angleincreases the radial force because thecutting force is always approximatelyperpendicular to the cutting edge (Fig.2.16). This may become a problemwhen machining a workpiece that is notwell supported. Care must be taken incases where an end support, such as atail stock center is not used.

A heavy positivelead angle also has atendency to inducechatter because of agreater tool contactarea. This chatter is anamplification of tool orworkpiece deflectionresulting from theincreased contact. Inthis situation it isappropriate to decreasethe positive lead angle.

A positive lead angleprotects the tool and promoteslonger tool life. As shown inFigure 2.17 the tool comes in con-tact with the workpiece well awayfrom the tool tip, which is theweakest point of the tool. As thetool progresses into the cut, theload against the tool graduallyincreases, rather than occurring asa sudden shock to the cuttingedge. The positive lead anglealso reduces the wear on the cut-ting edge caused by a layer ofhardened material or scale, bythinning the layer and spreading itover a greater area. These advan-tages are extremely beneficial duringinterrupted cuts. Another way that pos-itive lead angle helps to extend tool lifeis by allowing intense heat build-up todissipate more rapidly, since more ofthe tool is in contact with the work-piece.

Neutral and negative lead angle toolsalso have some benefits. A neutralangle offers the least amount of toolcontact, which will sometimes reducethe tendency to chatter, and lowers lon-gitudinal forces. This is important onless stable workpieces or set-ups.Negative lead angles permit machiningto a shoulder or a corner and are usefulfor facing. Cutting forces tend to pullthe insert out of the seat, leading toerratic size control. Therefore, negativelead angles should be avoided if at allpossible.

2.4.2 Edge PreparationEdge preparation is a step taken to pro-long tool life or to enhance tool perfor-mance. There are four basic approach-es to edge preparation:• Edge hone• Edge “L” land• Edge chamfer• Combinations of the above

Many inserts, including carbide,ceramic, etc., are purchased with a stan-dard edge preparation, normally an edgehone. The primary purpose of edgepreparation is to increase the insert’sresistance to chipping, breaking, andwear. Figure 2.18 illustrates the basicedge preparations.

Tool materials such as carbide andceramic are very hard and brittle.Therefore, a lead sharp cutting edge oninserts made of these materials isextremely prone to chipping and break-ing. Once a cutting edge is chipped, thewear rate is greatly accelerated orbreakage occurs. A prepared edge elim-inates the sharp edge and provides otherbenefits such as redistributing cuttingforces.

Edge Hone: The edge hone is by farthe most commonly used edge prepara-tion. Many inserts are automaticallyprovided with an edge hone at the timeof purchase, especially larger insertsthat will be exposed to heavy cutting.An edge hone on a ground or precisioninsert must usually be specially request-ed. A standard light hone in the UnitedStates usually has a radius of 0.001 to0.003 inch; A standard heavy hone hasa radius of 0.004 to 0.007 inch. Heavier

Feed (IPR)


Feed (IPR)


FIGURE 2.15 Lead angle vs. chip thick-ness. A positive lead angle thins the chipand protects the insert.

FIGURE 2.16 Lead angles and their effects on longitudinaland radial cutting cutting-tool feed forces.

FIGURE 2.17 Gradual feed/workpiece contactprotects the cutting tool by slowing increasing theload.

Radialdirection

Feed force

Feedforce

Longitudinaldirection

(a) (b)

Work piece

Feed

Initial contactpoint



hones are available on request. Theheavier the hone, the more resistance anedge has to chipping and breaking,especially in heavy roughing cuts, inter-rupted cuts, hard spot cuts, and scalycuts.

It is standard practice of all manufac-turers to hone inserts that are to be coat-ed before the inserts are subjected to thecoating process. The reason for this isthat during the coating process, thecoating material tends to build up onsharp edges. Therefore it is necessary tohone those edges to prevent build-up.

‘L’ Land: The ‘L’ land edge prepara-tion adds strength to the cutting edge ofan insert. Essentially, the ‘L’ landamplifies the advantages of negativerake by diverting a greater amount ofcutting force into the body of the insert.The ‘L’ land amplifies this conditionbecause the included angle at theinsert’s edges is 110 degrees as opposedto 90 degrees. The ‘L’ land is particu-larly beneficial when engaging severescale, interruptions, and roughing.

The ‘L’ land configuration is normal-ly 20 degrees by two thirds of the fee-drate. The feedrate should exceed theland width by about one third. This isnot a hard and fast rule, but it does serveas a good starting point. If the landwidth is greater than the feedrate, severejamming of the chips, excessive highpressures, and high heat will likelyoccur, resulting in rapid tool failure.

Something other than a 20 degreeland angle may be considered, withvarying land width. Some experimenta-tion may prove beneficial, however, ifthe land angle is varied from 20 degreesit should probably be less rather thanmore than 20 degrees to keep from jam-ming the chips.

An ‘L’ land is normally used only onnegative, flat top inserts placed at a neg-ative rake angle. To use an ‘L’ land ona positive or a positive/negative insert

would defeat the purpose of positivecutting action.

Chamfer: A chamfer is a compro-mise between a heavy hone and an ‘L’land. A chamfer will also increase aninsert’s resistance to chipping andbreaking. In a shop situation a chamferis easier and quicker to apply than aheavy hone, because it can be appliedwith a grinder rather than a hand hone.When a chamfer is applied it should bevery slight, 45 degrees by 0.005 to0.030 inch.

Normally a chamfer presents a nega-tive cutting situation which can result insome problems. The area of applicationfor chamfers is limited and caution mustbe exercised. A slight chamfer is oftenused on a hard and brittle tool for mak-ing a very light finishing cut on hardwork material. In this instance, thechamfer will strengthen the cuttingedge.

Combinations: Any time that a sharpedge can be eliminated the life of aninsert will likely be extended. When an‘L’ land or chamfer is put on an insert, itwill make a dramatic improvement inperformance, but the ‘L’ land or cham-fer will leave some semi-sharp corners.To get the maximum benefit from an ‘L’land or chamfer, it will help to add aslight hone to each semi-sharp corner.This will be of significant value inextending tool life, particularly when alarge ‘L’ land is used.

Nose Radius: The nose radius of aninsert has a great influence in the metalcutting process. The primary functionof the nose radius is to provide strengthto the tip of the tool. Most of the otherfunctions and the size of the nose radiusare just as important. The choice ofnose radius will affect the results of thecutting operation; however, inserts areprovided with various standard radiiand, in most cases, one of these willmeet each specific cutting need.

The larger the radius, thestronger the tool tip will be.However, a large radius causesmore contact with the work surfaceand can cause chatter. The cuttingforces will increase with a largeradius for the same reason,increased contact with the worksurface. When taking a shallowcut, a depth approximately equal tothe radius or less, the radius acts asa positive lead angle, thinning thechip. A large radius will allow the

cutting heat to dissipate more quicklyinto the insert body, reducing the tem-perature build-up at the cutting edge.

One of the most important influencesof a large radius is that of surface finish.The larger the radius, the better the sur-face finish will be at an equal feedrate.A larger radius will allow a faster fee-drate and yet obtain a satisfactory fin-ish. During a finishing cut, the feedrateshould not exceed the radius if a reason-able surface finish is required.

2.4.3 Chip BreakersBreaking the chip effectively whenmachining with carbide tools is of theutmost importance, not only from theproduction viewpoint, but also from thesafety viewpoint. When machiningsteel at efficient carbide cutting speeds,a continuous chip flows away from thework at high speed.

If this chip is allowed to continue, itmay wrap around the toolpost, theworkpiece, the chuck, and perhapsaround the operator’s arm. Not only isthe operator in danger of receiving anasty laceration, but if the chip windsaround the workpiece and the machine,he must spend considerable time inremoving it. A loss of production willbe encountered. Therefore it is impera-tive that this chip be controlled and bro-ken in some manner.

With the advent of numerial control(NC) machining and automatic chiphandling systems, the control of chips isbecoming more important than ever.The control of chips on any machinetool, old or new, helps to avoid jam-upswith tooling and reduces safety hazardsfrom flying chips. There is a great dealof research and development being con-ducted in chip control, much of whichhas been very successful.

There are two basic types of chipcontrol being used with indexable inserttooling: the mechanical chip breaker,

FIGURE 2.18 The three basic edge preparations are (a) edge hone, (b) L land, (c) edge cham-fer.

X X

Y Y

(a) (b) (c)

R



Figure 2.19, and the sintered chip break-er, Figure 2.20. Mechanical chip break-ers are not as commonly used as sin-tered chip breakers. There are moreparts involved with the mechanical chipbreaker, which increases the cost, andthe chip breaker hampers changing andindexing the insert. However, mechan-ical chip breakers are extremely effec-tive in controlling chips during heavymetal removing operations.

There are two groups of mechanicalchip breakers, solid and adjustable asshown in Figure 2.21. Solid chip break-ers are available in various lengths andangles, to suit each metal cutting appli-cation. The adjustable chip breaker caneliminate the need for stocking varioussizes of solid chip breakers.

Sintered chip breakers are availablein many different configurations, somedesigned for light feeds, some for heavyfeeds, and still others for handling bothlight and heavy feeds. Figure 2.22shows examples of the various sinteredchip breaker configurations availablefrom a single manufacturer. There aresingle sided and double sided designs ofsintered chip breaker inserts.

Many of the designs will significant-ly reduce cutting forces as well as con-trol chips. Normally it would be moreeconomical to use a double sided insert

because of the addition-al cutting edges avail-able. However, this isnot always true. Whilea double sided insert ismore economical undermoderate and finish cut-ting conditions becauseof its additional cuttingedges, a single sideddesign will justify itself,from a cost standpoint,through more effective chip control andreduced cutting forces in certain situa-tions. Figure 2.23 shows five common

insert styles with sintered chip breakers.Figure 2.22 illustrates that a single

sided insert is flat on the bottom as com-

FIGURE 2.19 Mechanical chip breaker.

FIGURE 2.21 Solid and adjustable chip breaker.

FIGURE 2.22 Various sintered chipbreaker configurations, with application

recommendations.

FIGURE 2.20 Sintered chip breaker.

Double-Sided General-Purpose Groove Geometries

Offers excellent mix of low cost percutting edge and effective chip control.Designed for general-purpose use at lowfeed rates.

Offers excellent mix of low cost percutting edge and effective chip control.Designed for general-purpose use atmedium feed rates

Offers excellent mix of low cost percutting edge and effective chip control.Designed for general-purpose use at highfeed rates

Single-Side Low Force Groove Geometries

Offers lower cutting forces than general-purpose grooves in medium feed rangeapplications. Insert has 11¡ clearanceangle for use in positive rake tool holder.

Generates about 25% less cutting forcethan general-purpose chip grooves. De-signed for medium-feed applicationswhere force reduction, particularly inthe radial direction, is important.

Double-Sided Low Feed Groove Geometries

Offers excellent chip control at ultra-lowfeed rates. Positive/negative design providessome force reducing advantages. Lowcost per cutting edge.

Positive/negative design provides lowercutting forces than general-purposegrooves in low- to medium-feed range.Offers low cost per cutting edge thanother force-reducing geometries.

Generates about 25% less cutting forcethan general-purpose chip grooves. De-signed for ultra-high-feed applicationswhere force reduction is important.

.004—.020 ipr

feedrange

.005—.065 ipr

feedrange

.012—.070 ipr

feedrange

.005—.045 ipr

feedrange

.006—.050 ipr

feedrange

.012—.078 ipr

feedrange

.003—.024 ipr

feedrange

.004—.032 ipr

feedrange



pared to a double sided insert. This flatbottom provides a single sided insertwith better support under the cuttingedge in a severe cutting situation. Thesingle sided insert, because of its addedsupport, has the ability to remove largeramounts of material with greater easeand efficiency, making it more econom-ical to use. Another reason the singlesided insert may be more economical isthat, under heavy machining conditions,it is rare that all of the cutting edges ofa double sided insert can be used. Theintense thermal and mechanical shockto the insert will normally damage it tothe point where the opposite cuttingedge is not usable and in a sense, wast-ed. Figure 2.24 a,b shows two squareinserts with special purpose chip break-ers.

Statistics have proven that undersevere conditions a single sided insert ismore often the most economical choicebecause its higher efficiency willremove more metal in less time.

Additionally, if half of the availablecutting edges of a double sided insertare unusable, for reasons stated before,then the more efficient single sidedinsert, having essentially the same num-

ber of usable cutting edges, is themost economical insert to use.

There are many other configura-tions of chip breaker designs thanthe ones shown in Figure 2.22.Each manufacturer has its own.The recommended applicationareas are generally listed in eachmanufacturer’s catalog. However,for specific recommendations andspecial applications, it is best toconsult the manufacturer.

Figure 2.25 shows the varioustypes of chips that are encounteredevery day. Examining the chipsthat are coming off a workpiecewill give a lot of information as to

how well the job is going, how toolwear is progressing, and why prematuretool failure or short tool life is occur-ring.

Straight Chips: Straight chips areusually the most troublesome. Theystring out all over the machine tool, theyget snarled in the tool, workpiece, andfixturing, they cause tooling to break,they jam up chip handling equipment,they are difficult to remove, and theyare dangerous, especially when theybegin to whip around. Soft gummy lowcarbon and tough steels usually causethis type of chip. One of the quickestways to eliminate the straight chip, is toincrease the feedrate, because a thickerchip breaks more easily. Other ways toeliminate straight chips are to decreasethe lead angle, which would also thick-en the chip, increase the speed, use anegative rake tool, or use a chip breakerinsert.

Snarling Chips: Snarling chips arecontinuous chips much the same asstraight chips. They are generallycaused by the same conditions asstraight chips and create the same prob-lems. It stands to reason, therefore, thatto correct a snarling chip situation, the

same methods would beused as with straightchips. In addition, cool-ing the chips with aflood or mist coolant asthey come off the tool,will frequently help tobreak them.

Infinite Helix Chips:Infinite helix chips arechips that are near thebreaking point. Theproblems this type ofchip creates are similar

to those created by straight chips.Infinite helix chips are common whenmachining very ductile material, such asleaded or resulfurized steels, and othersoft materials. They will most oftenoccur when making light cuts with pos-itive rake tools. Using a sintered chipbreaker insert, that will force the natur-al chip flow direction to change, is ofteneffective in breaking the infinite helixchip. An increase in feed or speed willalso help break the chip.

Full Turn Chips: Full turn chips arenot usually a problem so long as theyare consistent and without occasionalstringers. A consistent full turn chip isnear the ideal half turn chip.

Half Turn Chip: If there is such athing as a perfect chip, it is the half turnor ‘6’ shape chip. This is the chip shapethat the machinist strives for in his cut-ting operation. The half turn chip isknown as the classic chip form. The‘Half turn’ or just about perfect chip isshown in Figure 2.26.

Tight Chips: Tight chips do not pre-sent a problem from a handling or inter-

FIGURE 2.23 Five common insert shapes withvarious sintered chip-breaker configurations.(Courtesy American National Carbide Co.)

FIGURE 2.25 Various types of chip for-mations.

FIGURE 2.24 Two square inserts with one-sided special-purpose chip breakers. (Courtesy Iscar Metals, Inc.)

FIGURE 2.26 Half-turn chip or “perfect”chip. (Courtesy Kennametal Inc.)

Straight chips

Snarling chips

Infinite helix chips

Full turns

Half turns

Tight chips



facing point of view, but these tightchips are a sign that poor tool life orpremature tool failure may occur. Thetight chip is formed by very high pres-sure and causes intense heat, deflectionof the tool and workpiece, and rapidtool failure. A tight chip is a jammedchip, meaning that its flow path is over-ly restricted. Causes include; too high afeed rate, too negative a rake angle,improper chip breaker selection or set-ting, or a worn insert.

Many times a straight, snarled or infi-nite helix chip will be generated at thestart of a cutting operation, when theinsert is new. As the insert begins towear, the chip gradually becomes wellshaped and properly broken. It mayeven progress into a tight chip and even-tually cause catastrophic tool failure.This is caused by a type of insert wearknown as cratering.( see Figures 2.9aand 2.10a) In cratering, a groove isworn into the insert causing a false chipbreaker groove to be formed. This is adefinite sign of a problem, such as theinsert is not of the correct carbide grade,is not the correct geometry, or that thecutting speed may be too fast.

2.5 Indexable Type ToolingOne of the more recent developments incutting tool design is the indexableinsert which is mechanically held in atoolholder. Inserts are available in sev-eral thicknesses and a variety of sizesand shapes. The round, square, triangle,and diamond account for the greatestpercentage. Many other shapes, includ-ing the parallelogram, hexagon, andpentagon, are used to meet specificmachining requirements. Each shapehas its advantages and limitations sincethe operational, as well as the economi-cal factors must be considered in toolingselection. The most common insertshapes were shown in Figure 2.23.

2.5.1 Indexable Insert ShapesIndexable inserts have certainly estab-lished their position and potential in themetal working industry. The elimina-tion of regrinding, accuracy of toolgeometry, reduced inventory tool costs,and down time for tool changes, aresome of the advantages resulting fromthe use of this tooling.

There are four basic shapes and avariety of special shapes. Becauseapproximately 95 percent of all machin-ing is done with the four basic shapes,

these are the ones of inter-est here. The four basicshapes are:• square• triangle• diamond• round

These shapes are avail-able in many different con-figurations for almost anyjob. Each shape can beobtained for positive, nega-tive, or positive/negativerake, with or without chip breakergrooves, with or without holes, withvarious edge preparations, in varioustolerances, and in various radii andsizes. A variety of insert shapes andconfigurations are shown in Figure 2.27

Choosing a particular shape or insertrequires a great deal of planning andthought. The choice of insert shapemust be based on such factors as theworkpiece configuration and tolerance,workpiece material, amount of materialto be removed, machine tool capability,and economics.

The insert shape also has an influenceon insert strength. As shown in Figure2.28, the greater the included angle atthe insert tip, the greater the strength.The round insert and the 100 degreecorner of the first diamond shaped insertare shown as the strongest. Because ofthe higher cutting forces and the possi-bility of chatter, these inserts are morelimited in use than the square shape.Therefore, for practical purposes, thesquare insert is the strongest for generaluse. Triangle and diamond insertsshould only be used when a square can-not be used, such as when machining toa corner or a shoulder.

The Round Insert: Round or buttoninserts give a good finish at heavyfeeds, and they are also ideal for form-ing inside corner radii. Their shape pro-vides the greatest geometric strength,and they offer the maximum number ofindexes when light cuts are being taken.The solid button type which isheld in place by means of a clamp,generally has edges at 90 degreesto the surfaces for use in negativerake holders, thereby providingcutting edges on both sides of theinsert. The CDH button type ismade in larger sizes and has acounterbored hole. This buttonhas clearance and is normally heldin the toolholder with neutral

rake. A typical application is for tracingor contouring, where the tool must gen-erate forms which require a large por-tion of the cutting edge to be in the cut.

Round inserts have their limitations,however, since the large nose radiusthins the chips and increases the forcesbetween the tool and workpiece for agiven size cut. Very high radial forcesare usually incurred as compared withnormal cutting, particularly at normalfeed rates. Chatter and deflection oftenresult, especially when machining long-chip materials. For this reason, buttoninserts are applied with greater successon cast iron and the other short-chip,low-strength materials, although heavyfeed rates will often improve the cuttingaction on ductile materials.

The Square Insert: Square insertsprovide four or eight cutting edges,depending on the design of the tool-holder. Positive rakes mean that reliefangles must be ground on the insert,thereby eliminating the use of one side.

Square inserts are preferred for mostmachining jobs, where the workpieceand tool design relationships allow theiruse. Their shape provides strength closeto that of the round insert, but with theeconomy of four or eight cutting edges,and also permits a reduction in the sidecutting edge angle and the problemrelated to the chip-thinning action of theround. Economical tool application dic-tates the use of an insert shape whichgives the maximum number of cutting

FIGURE 2.27 Various insert shapes, with and withoutholes, with and without chip breakers. (CourtesyAmerican National Carbide Co.)

FIGURE 2.28 Various insert shapes as related tostrength.

Round

3555608090100120

Strength increasing

Chap. 2: Metall Removal Methods


edges and is compatible with themachining operation. If the operationrequires machining to a square shoulder,the square insert would be eliminatedbecause of the design of an ‘A’ styletool. Since end cutting edge angle(ECEA) is required so that the tool willclear the machined surface, somethingless than a 90 degree included anglebetween the side and end of the tool ismandatory.

The Triangular Insert: Owing todesign and application requirements,one of which has just been pointed out,the triangular insert has assumed animportant place in indexable tooling.The triangle provides three or six cut-ting edges, depending on whether reliefangles are required on the insert for usein a positive rake holder. The 60 degreeincluded angle is not as strong as the 90degree of the square, or the radius of thebutton, yet many machining operationsare performed satisfactorily with trian-gular inserts. Turning to a shoulder,plunging and contouring, and numerousother operations require a generous endcutting edge angle which the trianglecan provide. The 60 degree includedangle is also suitable for threading oper-ations.

Because of its fewer cutting edgesand lower strength, the triangular insertand holder should only be used whenother geometric shapes will not meet thejob requirements.

The Pentagon Insert: A pentagon orfive-sided insert is a means of providingone or two more cutting edges perinsert, and the extra edges are the mainreason for this design. There is, ofcourse, a strength advantage over thesquare and triangle in the 108 degreeincluded angle. As in the case of thesquare, the pentagonal shape sets upcertain design and application limita-tions. The tool must always cut with aside cutting edge angle (SCEA), whichthins the chip and improves tool life.However, SCEA cannot always be usedowing to the requirements of the fin-ished part’s shape or because theincreased radial forces cause chatter anddeflection of the workpiece. The mini-mum SCE angle which can be used is24 degrees. This then leaves 6 degreesend cutting edge (ECE) angle. AnSCEA of 33 degrees results in 15degrees of ECEA which is the same asthat used on standard ‘B’ style tools andis quite adequate.

The Diamond Insert: The trend inlathe design is toward machines whichgenerate the form on the workpiece.This is accomplished by guiding thetool so it faces, plunges, turns, andforms radii, chamfers, and machinesother configurations. In order for a toolto satisfy the requirements of thesecomplex maneuvers, it must meet cer-tain design standards. Since the tooloften plunges along an angle, a greatamount of ECEA is needed. Back fac-ing is also a common operation on suchsetups, and this requires negativeSCEA.

The diamond insert was developedspecifically for tracing operations. Theindustry’s standard marking systemincludes designations for diamondinserts with included angles of 86, 8055, and 35 degrees. By far the mostpopular size is the 55 degree includedangle diamond. This geometry appar-ently meets the requirements of mosttracing operations. When the insert ispositioned in the toolholder and toolblock so that it cuts with 3 degree nega-tive SCEA, it will back face with depthsof cut up to 0.020 inch and in most tool-holders will be able to plunge at anangle of 20 degrees with adequate clear-ance.

Holding the insert securely in theholder so that duplication of workpiecesize to tolerances specified is achieved,has been a problem. The tendency forthe insert to twist in the pocket on turn-ing and plunging operations, and to bepulled out of the pocket on back facingoperations, has resulted in designchanges by some manufacturers.Diamond tracer inserts are made in reg-ular and elongated shapes. The elon-gated diamond provides greater resis-tance to the twisting action set up by thecutting forces.

Further developments are still beingmade in tracer inserts and holders sothat they will meet the exacting require-ments of tracing operations better. Insome designs the diamond shapedinsert, either regular or elongated, islocked into the pocket with an eccentricpin. This gives a positive holding actionand locates the insert against the backwalls of the pocket, minimizing thechances for movement during the con-touring operations.

The selection of a tool for a tracingoperation should begin with an analysisof the requirements of the contouring

operations. The tool selected should bethe one which provides the strongestgeometric shape and still meets the con-touring requirements. Many tracingjobs can be done satisfactorily with atriangular insert. If no back facing isincluded in the operations, no negativeSCEA is needed and a standard ‘A’ styletool can be used. In some cases it ispossible to use a tool designed to cutwith SCEA. Generally, better tool lifewill be realized with lower cost per cut-ting edge, when tools without negativeSCEA can be used.

The Parallelogram Insert: The par-allelogram-shaped insert provides someadvantages which make its use justifiedin certain applications. When a longside cutting edge is needed, it is some-times more economical and advanta-geous from a machining standpoint, touse a parallelogram rather than a squareor triangle.

The parallelogram also permits theconstruction of an ‘A’ style tool withgreater geometric strength than is possi-ble with a triangular insert. A limitationof the parallelogram design is the num-ber of usable cutting edges. A negativerake insert can be used on two cornersin a right or left-hand holder. To use theremaining two cutting edges, the oppo-site hand holder is required. Unless allfour corners can be used, the use of theparallelogram insert may not be eco-nomically justifiable.

The Hexagonal Insert: A versatiletool makes use of a hexagonal shapedinsert. Turning, facing, and chamferingcan all be done from a number of posi-tions. Its shape provides strong cuttingedges as in the case of the pentagon, butalso necessitates cutting with consider-able SCEA. The number of usable cut-ting edges in this design makes it a mosteconomical insert where it can beapplied.

The On-Edge Insert: The on-edgeinsert concept (Fig. 2.29), has only beenin use for a short time, but is becomingmore common. The on-edge insert wasfirst developed for milling operations.The main reason for its developmentwas to provide the strength needed towithstand the constant interruption ofmilling cuts. The on-edge concept isnow becoming more popular for turninginserts as well.

The main use of the on-edge insert isfor rough cutting when cutting forcesare high and the interruptions are often



severe. The extra thickness of the on-edge

insert offers more protection from heatand shock damage to the opposite sidecutting edge during heavy roughing,than is common with standard inserts.A milling cutter section with on-edgeinserts is shown in Figure 2.30.

2.5.2 Indexable Inserts - Classes and Sizes

Inserts are commercially available withvarious degrees of dimensional toler-ances, such as the inscribed circle of atriangle, the measurement across theflats of a square or elongated diamond,thickness, nose radii, and tangency. Allthese dimensions, and several other fac-tors, contribute to the ability of an insertto be accurately indexed and to machinea given material to a specific size. Theneed for inserts with different tolerancesdepends not so much on the dimension-al size of the finished part, but more onhow the insert is to be used in themachining operation.

Unground Inserts: Throughimproved manufacturing techniques,many carbide producers can supplyinserts that are to the required specifica-

tions, thus elimi-nating the grind-ing operation.Cutting edgesproduced by thismethod are notonly metallurgi-cally sound instructure, but arealso honed togive them geo-metric increase instrength.

U t i l i t yInserts: Thistype of insert isground on the topand bottom facesonly.

P r e c i s i o nInserts: These are ground all over andto close tolerances.

Honed Inserts: The development ofproduction honing techniques forinserts has made standard inserts avail-able to the machining industry in theprehoned condition. These inserts havethe advantage of not only having thecracked crystal layer removed from thecutting edge area, but also from the cut-ting tool surfaces. Lighter finishingcuts taken with finishing grades of car-bide should have small amounts of hon-ing performed on the cutting edge.Roughing grades should, conversely, behoned heavily. Carbide Insert HoningEquipment is shown in Figure 2.31.

Insert Size: The size of an insert isdetermined by its inscribed circle (I.C.).Every insert has an I.C. regardless of theinsert shape (Fig. 2.32). The I.C. is des-ignated in fractions of an inch in theUnited States, normally in 1/8 inchincrements. The thickness of the insertis designated by its actual thickness inincrements of 1/16 inch, and the noseradius is designated in increments of1/64 inch.

The thickness of the insert is usuallystandard to a particular I.C. Sometimeshowever, a choice of thickness will beavailable. In these situations, the thick-ness that is appropriate to the amount ofcutting force that will be applied is theoptimum choice. If a thin insert is cho-sen, a thicker shim should be used tokeep the cutting edge at the workpiececenterline.

2.5.3 Indexable Insert Identification System

A standard marking system, proposedby the Cemented Carbide ProducersAssociation and approved by theAmerican National Standards Institute(ANSI), has been adopted by thecemented carbide manufacturers. Anew identification and numbering sys-tem became necessary, due to the addi-tion of an expanded range of types andsizes of inserts incorporating a widevariety of detail. Under this new sys-tem, the insert number, with the manu-facturer’s grade of carbide, is all that isneeded to describe the insert. (See Fig.2.33). The eight sequences of markingindexable inserts are:• Shape • Size• Thickness • Clearance

Angle• Cutting Point • Class• Other Conditions • Type

Insert Economics: The cost of car-bide and other tool materials as well as

Cuttingforce

Cuttingedge Feed

FIGURE 2.29 On-edge turning tooldesign.

FIGURE 2.32 The size of an insert isdetermined by its inscribed circle (I.C.).

FIGURE 2.31 Carbide-insert honing equipment. (CourtesyAmerican National Carbide Co.)

FIGURE 2.30 On-edge milling cutter sec-tion. (Courtesy Ingersoll Cutting Tool Co.)

I.C.I.C.

I.C.I.C.



the cost of preparing these materialsinto cutting tools is relatively high andcontinuing to increase. Therefore, it ismost important to choose tool insertswisely. Here are some important thingsto consider when making the choice:• Chose a shape that offers the most cut-ting edges.

Examples:A negative insert has twice as many

cutting edges as a positive insert.A square insert has 25 percent more

cutting edges than a triangle insert. A double sided chip breaker insert has

twice as many cutting edges as asingle sided insert.

• Choose an I.C. appropriate to theamount of material to be removed.

Examples:A 1 inch I.C. square insert for a 1/4

inch depth of cut would be wasteful,because a large piece of expensivecarbide would be used where asmaller piece would achieve thesame result.

• Choose an insert tolerance that isappropriate to the job being done. Inmost cases an unground utility gradewill do the job. The closer the toler-ance, the higher the cost. Tight insert

FIGURE 2.33 Standard Identification System for indexable inserts. (Courtesy Cemented Carbide Producers Association)

Insert Shape Tolerance Class (1)

A — B — C — D — E — H — K — L — M — O — P — R — S — T — V — W —

(B) Cutting Pt. (A) I.C. (T) Thickness

(2)A= 0.001B = 0.0002C = 0.0005D = 0.0005E = 0.001G = 0.001

(3)M = 0.002-0.010(3)U = 0.005-0.012

0.0010.0010.0010.0010.0010.001

0.002-0.0040.005-0.010

0.0010.0050.0010.0050.0010.0050.0050.005

R = Blank with grind stock on all surfacesS = Blank with grind stock on top and

bottom surfaces only

Tolerance given are plus and minus from nominalThese tolerances normally apply to indexable insertswith facets (secondary cutting edges)The tolerance depends on the size and shape of the insertand should be as shown in the standards for thecorresponding shapes and sizes (See ANSI 894-25).

Cutting PointConfiguration

0 — 1 — 2 —3 —4 —6 —8 —A —D —E —F —K —

L —

M —N —P —

Sharp Corner (.003 or less)1/64 inch Radius1/32 inch Radius3/64 inch Radius1/16 inch Radius3/32 inch Radius1/8 inch RadiusSquare insert 45¡ ChamferSquare insert 30¡ ChamferSquare insert 15¡ ChamferSquare insert 3¡ ChamferSquare insert 30¡ DoubleChamferSquare insert 15¡ DoubleChamferSquare insert 3¡ DoubleChamferTruncated Triangle InsertFlatted Corner Triangle

Clearance

N — 0¡A — 3¡B — 5¡C — 7¡P — 11¡D — 15¡E — 20¡F — 25¡

G — 30¡H — 0¡ — 11¡J — 0¡ — 14¡K — 0¡ — 17¡L — 0¡ — 20¡M — 11¡ — 14¡R — 11¡ — 17¡S — 11¡ — 20¡

Secondary facet angle may vary by — 12

Insert Style

A —B —C —D —E —F —

G —

H —

J —

M —

P —

R —

Z —

X —

With holeWith hole and one countersinkWith hole and two countersinksSmaller than 1/4 I.C. with holeSmaller than 1/4 I.C. without holeClamp-on type with chipbreaker-no holeWith hole and chipbreaker topand bottomWith hole, one countersink andchipbreaker top onlyWith hole, two countersinks andchipbreaker — top and bottomWith hole andchipbreaker — top only10¡ positive land with hole andchipbreaker top and bottomWith hole and extra widechipbreaker top and bottomHigh positive land with hole andchipbreaker top and bottomWith hole, chipbreakers top andbottom with negative land angle

Thickness

Regular Polygons and Dia-monds Number 1/16thsof an inch in thickness for ICat 1/4 inch and over. For lessthan 1/4 inch I.C. the numberof 1/32nds inch.Rectangles and Parrallelo-grams. Use width dimensionin place of I.C.

Cutting Edge

F — SharpE — HonedT — K-LandS — K-Land

w/Hone

Size I.C.

Regular Polygons and Dia-monds Number 1/16thsof an inch in I.C. when I.C. is1/4 inch & over. For I.C. of less than 1/4 inch the num-ber of 1/32nd in I.C. Rectan-gles & Parallelograms. Use 2digits to size.1st Digit - Number of inchesin width2nd Digit - Number of inches in length.

Parallelogram 85¡Parallelogram 82¡Diamond 80¡Diamond 55¡Diamond 75¡HexagonParallelogram 55¡RectangleDiamond 86¡OctagonPentagonRoundSquareTriangleDiamond 35¡Trigon 80¡

TNMG — 432E



tolerances are normally required onlywhen the indexability of an insert is crit-ical.

Example:A ‘C’ tolerance insert used for finishing

to a workpiece tolerance of plus orminus 0.010 inch would not be neces-sary. An ‘M’ or even a ‘U’ toleranceinsert would be satisfactory.

• Choose a single sided insert when con-ditions make its efficiency more eco-nomical.

Example:A heavy roughing cut has made the sec-

ond side of a less efficient doublesided insert unusable because of heatand shock damage.

2.5.4 Mechanical Tool HoldersThe revolution of the indexable inserthas resulted in the availability of a widerange and variety of tool holders. Anumber of tool holders with inserts areshown in Figure 2.34.

To select or recommend the bestholder for every machining applicationwould be a formidable task. The prac-tice in many manufacturing plants is tostandardize on one or two designs, sothat a minimum of repair parts andaccessories need to be carried in inven-tory. There are basic designs and con-struction elements common to all hold-ers.• The Shank• The Seat• The Clamp or Locking Device

Turning toolholders have been stan-dardized as shown in Figure 2.35.

The Shank: The shank is the basicelement of the toolholder and its pur-pose is to hold and present the cuttingedge to the workpiece. It usually hasdrilled and tapped holes, slots andcutouts, and it must provide a firm sup-port for the carbide cutting edge.Generally shanks are made of high-car-bon or low-alloy steel, heat treated togive physical properties that will resistthread damage, chip erosion and defor-mation under the tool-block clamping

FIGURE 2.34 Four toolholders with various insert styles and sizes (CourtesyKennametal Inc.)

1HoldingMethod

S — Screw onlyM — Clamp and

Locking PinC — Clamp onlyP — Locking Pin

Only

A — Straight Shankwith 0¡ side cuttingedge angleB — Straight Shankwith 15¡ sidecutting edge angleC — Straight Shankwith 0¡ end cuttingedge angleD — Straight Shankwith 45¡ side cut-ting angleE — Straight Shankwith 30¡ side cut-ting angleF — Offset Shankwith 0¡ end cut-ting edge angleG — Offset Shankwith 0¡ side cut-ting edge angle

H — Threading andShallow GroovingI.D.J — Offset Shankwith Negative 3¡side cutting edgeangleK — Offset Shankwith 15 end cut-ting edge angleL — Offset shankwith negative 5¡side or end cuttingedge angleM — Straight Shankwith 40¡ side cut-ting edge angleP — Straight Shankwith 27 1/2¡ side cutting edge angle

R — Offset Shankwith 15¡ side cut-ting edge angleS — Offset Shankwith 45¡ side cut-ting edge angleT — Offset Shankwith 30¡ side cut-ting edge angleV — Threading andshallow groovingO.D.W — Offset Shankwith 10¡ side cut-ting edge angleZ — Offset Threadingand grooving O.D.

4 Holder Rake

N — NegativeO — NeutralP — PositiveA — Hi-Positive

5 Handof Tool

L — LeftN — NeutralR — Right

7 InsertSize I.C.

Number of 1/8thson 1/4 IC andover.Number of 1/32ndson 1/4 1 C andunder.

6ToolholderShank Size

This position is asignificant numberwhich indicates theholder cross sec-tion. For squareshants this num-ber represents thenumber of six-teenths of widthand height.For rectangularholders the firstdigit represents thenumber of eights ofwidth and the sec-ond digit the num-ber of quarters ofheights except thefollowing toolhold-ers 11/4 x 11/2which is given thenumber 91.

2Insert

GeometryC — 80¡ DiamondD — 55¡ Diamond V — 35¡ DiamondT — TriangleS — SquareR — Round*Q — Deep

GroovingCutoff andTracing

3 Toolholder Style

MTFNR — 16 — 4

FIGURE 2.35 Standard identification system for turning toolholders. (Courtesy Cemented Carbide Producers Association)



screws. Some designs and sizes whichdo not make use of a carbide seat aremade of high alloy steel to resist defor-mation under the insert.

The machined area for the seat andinsert is one of the most critical areasand must be flat to provide the propersupport for the carbide seat and insert.Common practice is to relieve the insidecorner for seat and insert clearance. Theintersections of the sides and bottom ofthe pocket usually have a small radius,since sharp corners may be the source ofcracks during heat treatment. A toolshank with basic components is shownin Figure 2.36.

The Seat: Most toolholders forindexable inserts use a carbide seat orpad as support for the insert. Cementedtungsten carbide has a high compressivestrength, is hard, and can be ground to asmooth flat surface. While hardenedsteel has been used, and still is in somedesigns, a strong preference for carbideseats prevails.

The seats shown in Figure 2.37 aretypical and will serve to illustrate thebasic design. The periphery is cham-fered at one face to clear any radius inthe steel shank pocket area. If the seator pad is held in place by a screw, thehole will be deeply countersunk so thatthe head of the screw will be well belowthe surface. If the screw head projectsabove the seat surface and the insert isclamped down on it, breakage of the lat-ter could result.

The seat is attached to the shank onlyfor convenience and to prevent its losswhen inserts are removed and replaced,or if the holder is used vertically as in avertical turret lathe or upside down as inthe rear tool post of a turret lathe.

Seat flatness is one of the most criti-cal requirements of tool holders.Application tests have shown that anout-of-flatness condition, of as little as0.001 inch, can result in insert breakage.Regardless of the design of the tool-holder selected, the pocket and seat flat-ness specifications should be carefullyexamined and the highest standards

insisted upon.The Clamp or Locking Device: Many

clamping and locking arrangementshave been developed for holding theinsert in a toolholder and there is proba-bly no one best method or design, sincespecific application requirements varyso greatly. There are a number of fea-tures and construction elements, howev-er, which warrant consideration andshould influence the selection of a tool-holder (Fig. 2.38).

The main function of the clampingmechanism is to hold the insert securelyin position and many methods of doing

FIGURE 2.36 Tool shank with basic com-ponents. (Courtesy Kennametal Inc.)

FIGURE 2.37 Schematic drawing of various insert-locking positions.

FIGURE 2.38 Various pin-type holder-locking options.

Chip breaker

Insert

SeatInsert

Seat

Insert

Seat

Type 1

Retainer clip

Insert

Shim seat

Pin Lock screwWedge

Shank

Type 2

Shim lock

Shim

Insert

Pin Lock screwShank

Spring(compressed)

Type 3

Shim lock

Shim

Insert

Lock screwLock

Holder body

Type 4

HolderLock pin

Insert

Shim

Lock cup



so are in use. On normal turning andfacing operations, the insert in moststyles of toolholders is held in the pock-

et by the cutting pressures,and the load on the clamp isvery light except as affectedby the chip. Tracing andthreading operationschange the direction andamount of the load appliedto the insert, and there ismore tendency to twist orpull the insert out of thepocket. The ability of theclamping mechanism, toperform satisfactorily undersuch conditions, should becarefully evaluated. Theuse of a pin or lever mecha-nism has been incorporatedin some designs to give amore positive holdingaction against the insert.

The suitability of the clamp design tothe machine toolholding blocks and tothe workpiece configuration should be

considered. Bulky club heads, highclamps on clamping screws, or intricateadjusting mechanisms may be in theway, especially when tools must beganged up, or when machine and work-piece clearances are small. A toolhold-er which is not easily accessible andmust be removed from the machine sothe insert can be indexed or the chipbreaker adjusted, should not be consid-ered suitable for the application. Anumber of tool holders are shown inFigure 2.39 where indexable inserts arebeing held by both pins and clamps.

Tools which are positioned upsidedown should have a wrench socket inthe lower end of the clamping screw sothat it can be easily reached. Chip-breaker plates and clamp parts shouldbe secured so that they will not bedropped in the chip pan when loosenedfor insert changing.

FIGURE 2.39 Three toolholders in which inserts areheld by both pins and clamps. (Courtesy SandvikCoromant Corp.)

Documents

Cutting Tool Applicationsbgk.uni-obuda.hu/ggyt/targyak/seged/baggt23nec/book_02.pdf · As the cutting tool engages the workpiece, the material directly ahead of the tool is sheared