bro atching 14

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1/8w w w .to olin g a n dp ro du ction .co m Chapter 14 /Tooling & Prod uction 1

Metal Removal

Cutting-Tool Materials

Metal Removal Methods

Machinability of Metals

Single Point Machining

Turning Tools and Operations

Turning Methods and Machines

Grooving and Threading

Shaping and Planing

Hole Making Processes

Drills and Drilling OperationsDrilling Methods and Machines

Boring Operations and Machines

Reaming and Tapping

Multi Point Machining

Milling Cutters and Operations

Milling Methods and Machines

Broaches and Broaching

Saws and Sawing

Abrasive Processes

Grinding Wheels and Operations

Grinding Methods and MachinesLapping and Honing

George Schneider, Jr. CMfgEProfessor Emeri t us

Engineer ing TechnologyLawrence Technological Universi ty

Former Chairm anDetroi t Chapter ONESociety of Manu factur in g Engineers

Former Pres identInternat ional Excut ive BoardSociety o f Carbide & Tool Engineers

Lawrence Tech.- w ww .l tu.edu

Prent ice Hal l - www.prenhal l .com

Broachesand Broaching14.1 Introduction

The broaching operation is similar toshaping with multiple teeth and is usedto machine internal and external sur-faces such as holes of circular, square,or irregular shapes, keyways, and teethof internal gears. A broach is a longmultitooth cutting tool with succes-sively deeper cuts. Each tooth removesa predetermined amount of material ina predetermined location. The totaldepth of material removed in one path

is the sum of the depth of cut of eachtooth. Broaching is an important pro-

duction process and can produce partswith very good surface finish and di-mensional accuracy. Broaching com-

petes favorably with other processessuch as boring, milling, shaping andreaming. Although broaches tend to beexpensive, the cost is justified becauseof their use for high production runs.A two station broaching operation isshown in Figure 14.1.

14.2 BroachingTooling is the heart of any broaching

process. The broaching tool is basedon a concept unique to the process -

CHAPTER 14

FIGURE 14.1: Typical broaching operation of an internal spline. (Courtesy DetroitBroach & Machine Co.)
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Chap. 14 : Broaches & Broaching

2Tooling & P roduction/Ch apter 14 w w w .too lin g a n d p ro d u ctio n .co m

rough, semi-finish, and finish cuttingteeth combined in one tool or string oftools. A broach tool frequently canfinish machine a rough surface in asingle stroke. A large broach is shownin Figure 14.2

For exterior surface broaching, thebroach tool may be pulled or pushedacross a workpiece surface, or the sur-face may move across the tool. Inter-nal broaching requires a starting holeor opening in the workpiece so the

broaching tool can be inserted. Thetool or the workpiece is then pushed or

pulled to force the tool through thestarter hole. Almost any irregularcross-section can be broached as longas all surfaces of the section remain

parallel to the direction of broachtravel. A couple of small broached

parts are shown in Figure 14.3

14.2.1 Broaching ToolsA broach is like a single point tool withmany points each of which cuts like aflat-ended shaper tool, although some

broaches have teeth set diagonally,called sheer cutting. The principal

parts of an internal broach are shownin Figure 14.4

14.3 Broach NomenclatureFront Pilot: When an internal pull

broach is used, the pull end and front

pilot are passed through the startinghole. Then the pull end is locked to the

pull head of the broaching machine.The front pilot assures correct axialalignment of the tool with the startinghole, and serves as a check on thestarting hole size.

Length: The length of a broach toolor string of tools, is determined by theamount of stock to be removed, andlimited by the machine stroke.

Rear Pilot: The rear pilot main-tains tool alignment as the final finish

teeth pass through the workpiece hole.On round tools the diameter of the rear

pilot is slightly less than the diameterof the finish teeth.

Broach tooth nomenclature and ter-minology are shown in Figure 14.5a.

Cutting Teeth: Broach teeth areusually divided into three separate sec-tions along the length of the tool: theroughing teeth, semi-finishing teeth,and finishing teeth (Fig. 14.4). Thefirst roughing tooth is proportionatelythe smallest tooth on the tool. The

subsequent teeth progressively increasein size up to and including the first

FIGURE 14.2: A large broach is shown (Courtesy Detroit Broach &Machine Co.)

FIGURE 14.3: A couple of small broached parts are shown. (CourtesyDetroit Broach & Machine Co.)

Roughing

teethShank length

Length to

first tooth

Cutting teeth

Front pilot Semifinishing

teeth

Finishing

teeth

Rear pilot

Follow rest

Pull end

FIGURE 14.4: Principal parts of a round internal-pull broach.
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Chap. 14: Broaches & Broaching

w w w .too lin g a n d p ro d u ctio n .co m Chapter 14 /Tooling & Prod uction 3

finishing tooth. The difference inheight between eachtooth, or the toothrise, is usually greater along the rough-ing section and less along the semi-finishing section. All finishing teethare the same size. The face is ground

with a hook or face angle that is deter-mined by the workpiece material. Forinstance, soft steel workpieces usuallyrequire greater hook angles; hard or

brittle steel pieces require smaller hookangles.

Tooth Land: The land supports thecutting edge against stresses. A slightclearance or backoff angle is groundonto the lands to reduce friction. Onroughing and semi-finishing teeth, theentire land is relieved with a backoffangle. On finishing teeth, part of the

land immediately behind the cuttingedge is often left straight, so that re-

peated sharpening (by grinding theface of the tooth) will not alter thetooth size.

Tooth Pitch: The distance betweenteeth, or pitch, is determined by thelength of cut and influenced by type ofworkpiece material. A relatively large

pitch may be required for roughingteeth to accommodate a greater chipload. Tooth pitch may be smaller onsemi-finishing teeth to reduce the over-

all length of the broach tool. Pitch iscalculated so that preferably, two or

more teeth cut simultaneously. Thisprevents the tool from drifting or chat-tering.

Tooth Gullet: The depth of thetooth gullet is related to the tooth rise,

pitch, and workpiece material. Thetooth root radius is usually designed sothat chips curl tightly within them-selves, occupying as little space as

possible. (Fig. 14.5b)When designing broaches, attention

must also be given to chip load,chipbreakers, shear angles and siderelief.

Chip Load: As each tooth entersthe workpiece, it cuts a fixed thicknessof material. The fixed chip length andthickness produced by broaching createa chip load that is determined by thedesign of the broach tool and the pre-determined feed rate.

This chip load feed rate cannot bealtered by the machine operator as itcan in most other machining opera-tions. The entire chip produced by acomplete pass of each broach toothmust be freely contained within the

preceding tooth gullet (Fig. 14.5b).The size of the tooth gullet is a func-tion of the chip load and the type ofchips produced. However the form thateach chip takes depends on the

workpiece material and hook. Brittlematerials produce flakes. Ductile or

malleable materials produce spiralchips.

Chipbreakers: Notches, calledchipbreakers, are used on broach toolsto eliminate chip packing and to facili-tate chip removal. The chipbreakersare ground into the roughing and semi-finishing teeth of the broach, parallel

to the tool axis. Chipbreakers on alter-nate teeth are staggered so that one setof chipbreakers is followed by a cuttingedge. The finishing teeth complete the

job. Chipbreakers are vital on roundbroaching tools. Without thechipbreakers, the tools would machinering-shaped chips that would wedgeinto the tooth gullets and eventuallycause the tool to break.

Shear Angle: Broach designersmay place broach teeth at a shear angleto improve surface finish and reduce

tool chatter. When two adjacent sur-faces are cut simultaneously, the shearangle is an important factor in movingchips away from the intersecting cor-ner to prevent crowding of chips in theintersection of the cutting teeth.

Another method of placing teeth at ashear angle on broaches is by using aherringbone pattern. An advantage ofthis design is that it eliminates thetendency for parts to move sideways inthe workholding fixtures during

broaching.

Side Relief: When broaching slots,the tool becomes enclosed by the slotduring cutting and must carry the chips

produced through the entire length ofthe workpiece. Sides of the broachteeth will rub the sides of the slot andcause rapid tool wear unless clearanceis provided. Grinding a single reliefangle on both sides of each tooth doesthis. Thus only a small portion of thetooth near the cutting edge, called theside land, is allowed to rub against theslot. The same approach is used for

one sided corner cuts and splinebroaches.

14.4 Types of BroachesTwo major types of broaches are the

push broach and the pull broach. Asecond division is internal and external

broaches.Push and Pull Broaches: A push

broach must be relatively short since itis a column in compression and will

buckle and break under too heavy aload. Push broaches are often used

with a simple arbor press if quantitiesof work are low. For medium to high

ut per tooth

feed/tooth)

Tooth depth

Face or hook angle

Pitch

Land, or tooth width

Backoff or

rake angle

(a)

Radius Gullet or

chip space

(b)

FIGURE 14.5: (a)Broach tooth

nomenclature andterminology. (b)

Illustration ofhow a chip fills

the gullet during

a broachingoperation.
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4Tooling & Production/Ch apter 14 w w w .too lin g a n d p ro d u ctio n .co m

volume production they are used inbroaching machines.

Pull broaches (Fig. 14.4) are pulledeither up, down, or horizontallythrough or across the workpiece, al-ways by a machine. Flat or nearly flat

broaches may be pull type, or the

broach may be rigidly mounted, withthe workpiece then pulled across the

broaching teeth. Automobile cylinderblocks and heads are often faced flat bythis method. Figure 14.6 shows vari-ous broach configurations both roundand flat types.

Figure 14.1 shows a vertical splinebroaching operation; Figure 14.7shows a large spline broaching opera-tion using a horizontal broaching ma-chine.

14.4.1 Internal BroachesInternal broaches are either pulled or

pushed through a starter hole. Themachines can range from fully auto-mated multi stationed verticals, tohorizontal pull types, to simple

presses. Figure 14.8 shows a variety offorms that can be produced by internal

broaches.

Keyway Broach: Almost all key-ways in machine tools and parts are cut

by a keyway broach - a narrow, flat barwith cutting teeth spaced along onesurface. Both external and internalkeyways can be cut with these

broaches. Internal keyways usuallyrequire a slotted bushing or horn to fitthe hole, with the keyway broach

pulled through the horn, guided by theslot.

If a number of parts, all of the samediameter and keyway size, are to bemachined, an internal keyway broachcan be designed to fit into the hole tosupport the cutting teeth. Only thecutting teeth extend beyond the holediameter to cut the keyway. Bushingsor horns are not required.

Burnishers: Burnishers are broach-ing tools designed to polish rather thancut a hole. The total change in diam-eter produced by a burnishing opera-tion may be no more than 0.0005 to0.001 inch. Burnishing tools, usedwhen surface finish and accuracy arecritical, are relatively short and aregenerally designed as push broaches.

Burnishing buttons sometimes areincluded behind the finishing toothsection of a conventional broachingtool. The burnishing section may beadded as a special attachment or easilyreplaced shell. These replacement

shells are commonly used to reducetooling costs when high wear or tool

breakage is expected. They are alsoused to improve surface finish.

Shell Broaches:Shell broaches can beused on the roughing, semi-finishing andfinishing sections of a broach tool. The

principal advantage of a shell broach isthat worn sections can be removed andre-sharpened or replaced, at far less costthan a conventional single piece tool.When shells are used for the finishingteeth of long broaches, the teeth of the

FIGURE 14.6:Various broach

configurations,both round and

flat types.

FIGURE 14.7: A large spline broaching operation using a horizontal broachingmachine. (Courtesy US Broach & Machine Co.)

Keyway

Spline

Square

Triangle

Hexagon Double D

Special shapes

FIGURE 14.8: Avariety of forms that

can be producedwith an internal

broach.
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w w w .too lin g a n d p ro d u ctio n .co m Chap ter 14 /Tooling & P rod uction 5

shell can be ground to far greater accu-racy than those of a long conventional

broach tool and the tool can continue tobe used by replacing the shell. Shellbroaches are similar to shell millingcutters that were discussed in Chapter12.

14.4.2 Surface BroachesThe broaches used to remove materialfrom an external surface are commonlyknown as surface broaches. Such

broaches are passed over the workpiecesurface to be cut, or the workpiece

passes over the tool on horizontal, ver-tical, or chain machines to produce flator contoured surfaces.

While some surface broaches are ofsolid construction, most are of built-updesign, with sections, inserts, orindexable tool bits that are assembled

end-to-end in a broach holder or subholder. The holder fits on the machineslide and provides rigid alignment andsupport. A surface broach assembly isshown in Figure 14.9a.

Sectional Broaches: Sectionalbroaches are used to broach unusual ordifficult shapes, often in a single pass.The sectional broach may be round orflat, internal or external. The principle

behind this tool is similar to that of theshell broach, but straight sections ofteeth are bolted along the long axis of

the broach rather than being mountedon an arbor. A complex broaching tool

can be built up from a group of fairlysimple tooth sections to produce a cutof considerable complexity.

Carbide Broach Inserts: Broach-ing tools with brazed carbide broachinserts are frequently used to machinecast iron parts. Present practice, suchas machining automotive engine

blocks, has moved heavily to the use ofindexable inserts (Fig. 14.9b) and thishas drastically cut tooling costs inmany applications.

Slab Broaches: Slab broaches,simple tools for producing flat sur-faces, come closest to being truly gen-eral purpose broaches. A single slab

broach can be used to produce flatsurfaces having different widths anddepths on any workpiece by makingminor adjustments to the broach, fix-ture and/or machine.

Slot Broaches: Slot broaches arefor cutting slots, but are not as general

purpose in function as slab broaches.Adjustments can easily be made to

produce different slot depths, but slotwidths are a function of the broachwidth. When sufficient productionvolume is required however, slot

broaches are often faster and moreeconomical than milling cutters. In

broaching, two or more slots can oftenbe cut simultaneously.

14.5 Types of Broaching MachinesThe type of broach cutting tool re-

quired for a given job is the single mostimportant factor in determining thetype of broaching machine to be used.Second in importance is the productionrequirement. Taken together, thesefactors usually determine the specifictype of machine for the job.

The type of broach tool (internal orsurface) immediately narrows downthe kinds of machines that could beused. The number of pieces required

per hour, or over the entire productionrun, will further narrow the field.

For internal broaching, the length ofa broach in relation to its diameter maydetermine whether it must be pulledrather than pushed through theworkpiece, for a broach tool is strongerin tension than in compression. Thisin turn, helps determine the type ofmachine for the job.

The type of drive, hydraulic or elec-tromechanical, is another importantfactor in machine selection. So areconvertibility and automation. Somemachine designs allow for conversionfrom internal to surface work. Somedesigns are fully automated; others arelimited in scope and operate only withclose operator supervision.

14.5.1 Vertical Broaching MachinesAbout 60 percent of the total numbers

of broaching machines in existence arevertical, almost equally divided be-tween vertical internals and verticalsurface or combination machines. Ver-tical broaching machines, used in ev-ery major area of metalworking, arealmost all hydraulically driven. Figure14.1 shows a vertical broaching opera-tion.

One of the essential features thatpromoted their development however,is beginning to turn into a limitation.Cutting strokes now in use often ex-

ceed existing factory ceiling clear-ances. When machines reach heightsof 20 feet or more, expensive pits must

be dug for the machine, so that theoperator can work at the factory floorlevel. A large vertical broaching ma-chine is shown in Figure 14.10a.

Vertical internal broaching ma-chines are table-up, pull-up, pull-down, or push-down, depending ontheir mode of operation.

Vertical Table-up: Today table-upmachines are demanded to meet the

cell concept (flexible) manufacturing,where short runs of specialized compo-

(a) (b)

FIGURE 14.9: (a) A surface broach assembly. (Courtesy Detroit Broach & MachineCo.) (b) A surface broach assembly with indexable carbide inserts. (Courtesy

Ingersoll Cutting Tools)
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nents are required. Upon completionof short runs (1 - 2 years) the machinescan be re-tooled andmoved to anotherarea of the plant without the problemof what to do with pits in shop floors.With this type of machine the part sitson a table that moves up while the

broach is stationary. Stroke lengthsfrom 30 to 90 inches and capacitiesfrom 5 to 30 tons are the limits for thismachine.

Vertical Internal Pull-up: Thepull-up type, in which the workpiece isplaced below the worktable, was thefirst to be introduced. Its principal useis in broaching round and irregularshaped holes. Pull-up machines arenow furnished with pulling capacitiesof 6 to 50 tons, strokes up to 72 inches,and broaching speeds of 30 FPM.Larger machines are available; some

have electro-mechanical drives forgreater broaching speed and higher

productivity.Vertical Internal Pull-down: The

more sophisticated pull-down ma-chines, in which the work is placed ontop of the table, were developed laterthan the pull-up type. These pull-down machines are capable of holdinginternal shapes to closer tolerances bymeans of locating fixtures on top of thework table. Machines come with pull-ing capacities of 2 to 75 tons, 30 to 110

inch strokes, and speeds of up to 80FPM.

Vertical Internal Push-down: Ver-tical push down machines are oftennothing more than general-purpose hy-draulic presses with special fixtures.They are available with capacities of 2to 25 tons, strokes up to 36 inches, andspeeds as high as 40 FPM. In somecases, universal machines have beendesigned which combine as many asthree different broaching operations,such as push, pull, and surface, simplythrough the addition of special fix-tures.

A special multi-station verticalbroaching machine fixture is shown inFigure 14.10b.

A vertical broaching machine withloading and unloading conveyers isshown in Figure 14.11

14.5.2 Horizontal Broaching MachinesThe favorite configuration for broach-ing machines seems now to have comefull circle. The original gear or screwdriven machines were designed ashorizontal units. Gradually, the verti-cal machines evolved as it becameapparent that floor space could bemuch more efficiently used with verti-cal units. Now the horizontal ma-chine, both hydraulically and mechani-cally driven, is again finding increas-ing favor among users because of itsvery long strokes and the limitationthat ceiling height places on verticalmachines. About 40 percent of all

broaching machines are now horizon-tals. For some types of work such as

(b)

(a)

FIGURE 14.10: (a)A large verticalbroaching machine.(b) Special multi-

station verticalbroaching machinefixture. (CourtesyUS Broach &

Machine Co.)

FIGURE 14.11: Vertical broaching machine with loading and unloadingconveyers. (Courtesy Detroit Broach & Machine Co.)
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w w w .too lin g a n d p ro d u ctio n .co m Chapter 14 /Tooling & Prod uction 7

roughing and finishing automotive en-gine blocks, they are used exclusively.A two station internal horizontal

broaching machine is shown in Figure14.12a

Horizontal Internal BroachingMachines: By far the greatest amountof horizontal internal broaching isdone on hydraulic pull type machinesfor which configurations have becomesomewhat standardized over the years.Fully one third of the broaching ma-chines in existence are this type, and ofthese nearly one fourth are over twentyyears old. They find their heaviestapplication in the production of gen-eral industrial equipment but can befound in nearly every type of industry.

Hydraulically driven horizontal in-ternal machines are built with pullingcapacities ranging from 2 1/2 to 75

tons, the former representing machinesonly about 8 feet long the latter ma-chines over 35 feet long. Strokes up to120 inches are available, with cuttingspeeds generally limited to less than 40FPM.

Horizontal Surface BroachingMachines: This type accounts for onlyabout 10 percent of existing broachingmachines, but this is not indicative ofthe percentage of the total investmentthey represent or of the volume of workthey produce. Horizontal surface

broaching machines belong in a classby themselves in terms of size andproductivity. Only the large continu-ous horizontal units can match or ex-ceed them in productivity. Horizontalsurface units are manufactured in bothhydraulically and electro-mechanicallydriven models, with the latter now

becoming dominant.A gear broaching operation is shown

in Figure 14.12b.The older hydraulically driven hori-

zontal surface machines now are pro-duced with capacities up to 40 tons,strokes up to 180 inches, and normalcutting speeds of 100 FPM. Thesemachines, a major factor in the auto-motive industry for many years, turnout a great variety of cast iron parts.They use standard carbide cutting toolsand have some of the highest cuttingspeeds used in broaching.

But electro-mechanically drivenhorizontal surface machines are takingover at an ever-increasing rate forsome applications, despite their gener-ally higher cost. Because of theirsmooth ram motion and the resultantimprovements in surface finish and

(a)

(b)

FIGURE 14.12: (a) Two-station internal horizontalbroaching machine. (b) Gear broaching operation.(Courtesy Detroit Broach & Machine Co.)

Workpiece

Work holder

Load manualor automatic

Unload

Work backup

plate

Linked chain

Chips

Chip conveyorFloor

Broach

Broach backup plate

(b)

FIGURE 14.13: (a) Continuous chain broaching operation. (Courtesy US Broach & Machine Co.) (b) Schematic illustration of acontinuous chain broaching machine.

(a)
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part tolerances, these machines havebecome the largest class of horizontalsurface broaching units built. They areavailable with pulling capacities in ex-cess of 100 tons, strokes up to 30 feet,and cutting speeds, in some instances,of over 300 FPM.

14.5.3 Chain Broaching MachinesThese have been the most popular typeof machine produced for high-produc-tion surface broaching. The key to the

productivity of a continuous horizontalbroaching machine is elimination ofthe return stroke by mounting theworkpieces, or the tools, on a continu-ous chain (Fig. 14.13a)

Most frequently, the tools remain sta-tionary, mounted in a tunnel in the tophalf of the machine, and the chainmounted workpieces pass underneaththem. A schematic of a chain-broachingmachine is shown in Figure 14.13b.

14.6 Turn-BroachingTurn-broaching is an efficient methodfor machining steel and nodular castiron crankshafts. Special turn-broach-ing machines are available for linear,circular and spiral operating methods.The peripheral type cutter assembliesare built in segments as shown inFigure 14.14b.

The turn-broaching systems basi-cally use similar standardized compo-nents for roughing and finishing. Thetype of machine determines the tooldesign: linear, circular or spiral. Thenumber of segments and roughing in-serts in the tool depend on the stockremoval rate required. The finishingsegments are fitted with inserts in ad-

justable cartridges that can be set toclose tolerances. The segment forroughing has fixed insert pockets. Aturn-broaching operation of a crank-shaft is shown in Figure 14.14a.

(b)

(a)

Tool segments are computer de-signed and manufactured for each ma-chine to suit the required form andtolerance of each crankshaft. Thenumber of inserts and positions of eachsegment are designed to give low cut-ting forces. The roughing segmentshave hardened, fixed insert seats and

big chip pockets. Inserts are tangen-tially mounted and locked in position

by a center screw. A turn-broach cutterassembly is shown in Figure 14.14b.

Long tool life results due to the shortengagement of the individual cuttingedges. High machine utilization isobtained because the finishing cuttersneed only be changed once per shiftand the roughing cutters about onceevery third shift.

FIGURE 14.14: (a)Turn-broachingoperation of a

crankshaft. (b) Turn-broach cutter assembly.

(Courtesy SandvikCoromant Co.)
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