LAPPING, HONING AND BROACHINGLAPPING, HONING AND BROACHING

BYBY B.V.NARAYANAB.V.NARAYANA MITS, KODAD, NALGONDA MITS, KODAD, NALGONDA

Lapping, Honing and broachingLapping, Honing and broaching

As the name of this group of abrasive operations As the name of this group of abrasive operations suggests, their objective is to achieve superior suggests, their objective is to achieve superior surface finish up to mirror-like finishing and very surface finish up to mirror-like finishing and very close dimensional precision. The finishing close dimensional precision. The finishing operations are assigned as the last operations in operations are assigned as the last operations in the single part production cycle usually after the the single part production cycle usually after the conventional or abrasive machining operations, conventional or abrasive machining operations, but also after net shape processes such as but also after net shape processes such as powder metallurgy, cold flash less forging, etc.powder metallurgy, cold flash less forging, etc.

The finishing processes discussed in this The finishing processes discussed in this section include section include honinghoning, , lappinglapping, , super super finishingfinishing, , polishingpolishing, and , and buffingbuffing. The . The typical surface finishes for these typical surface finishes for these operations are presented in the figure. operations are presented in the figure. Also presented for comparison are surface Also presented for comparison are surface roughness values for fine grit size roughness values for fine grit size grinding.grinding.

In In lappinglapping, instead of a bonded abrasive tool, oil-based fluid , instead of a bonded abrasive tool, oil-based fluid suspension of very small free abrasive grainssuspension of very small free abrasive grains

(aluminum oxide and silicon carbide, with typical grit sizes between (aluminum oxide and silicon carbide, with typical grit sizes between 300 and 600) called a 300 and 600) called a lapping compound lapping compound is applied between the is applied between the workpiece and the lapping tool.workpiece and the lapping tool.

The lapping tool is called a The lapping tool is called a laplap, which is made of soft materials like , which is made of soft materials like copper, lead or wood. The lap has the reverse of the desired shape copper, lead or wood. The lap has the reverse of the desired shape of the workpart. To accomplish the process, the lap is pressed of the workpart. To accomplish the process, the lap is pressed against the work and moved back and forth over the surface in a against the work and moved back and forth over the surface in a figure-eight or other motion pattern, subjecting all portions of the figure-eight or other motion pattern, subjecting all portions of the surface to the same action. Lapping is sometimes performed by surface to the same action. Lapping is sometimes performed by hand, but hand, but lapping machines lapping machines accomplish the process with greater accomplish the process with greater consistency and efficiencyconsistency and efficiency

The cutting mechanism in lapping is that the The cutting mechanism in lapping is that the abrasives become embedded in the lap surface, abrasives become embedded in the lap surface, and the cutting action is very similar to grinding, and the cutting action is very similar to grinding, but a concurrent cutting action of the free but a concurrent cutting action of the free abrasive particles in the fluid cannot be abrasive particles in the fluid cannot be excluded.excluded.

Lapping is used lo produce optical lenses, Lapping is used lo produce optical lenses, metallic bearing surfaces, gages, and other metallic bearing surfaces, gages, and other parts requiring very good finishes and extreme parts requiring very good finishes and extreme accuracy.accuracy.

HoningHoning

Honing Honing is a finishing process performed by a is a finishing process performed by a honing toolhoning tool, which contains a set of three to a , which contains a set of three to a dozen and more bonded dozen and more bonded abrasive sticksabrasive sticks. The . The sticks are equally spaced about the periphery of sticks are equally spaced about the periphery of the the honing toolhoning tool. They are held against the work . They are held against the work surface with controlled light pressure, usually surface with controlled light pressure, usually exercised by small springs. The honing tool is exercised by small springs. The honing tool is given a complex rotational and oscillatory axial given a complex rotational and oscillatory axial motion, which combine to produce a motion, which combine to produce a crosshatched lay pattern of very low surface crosshatched lay pattern of very low surface roughnessroughness

In addition to the surface finish of about 0.1 μm, In addition to the surface finish of about 0.1 μm, honing produces a characteristic crosshatched honing produces a characteristic crosshatched surface that tends to retain lubrication during surface that tends to retain lubrication during operation of the component, thus contributing to operation of the component, thus contributing to its function and service life. A cutting fluid must its function and service life. A cutting fluid must be used in honing to cool and lubricate the tool be used in honing to cool and lubricate the tool and to help remove the chips.and to help remove the chips.

A common application of honing is to finish the A common application of honing is to finish the holes. holes.

Typical examples include bores of internalTypical examples include bores of internal combustion engines, bearings, hydraulic combustion engines, bearings, hydraulic

cylinders, and gun barrels.cylinders, and gun barrels.

BroachingBroaching

Broaching is one of the most productive, basic Broaching is one of the most productive, basic machining process. As a process, it is similar to machining process. As a process, it is similar to shaping, competes economically with milling and shaping, competes economically with milling and boring and is capable of producing precision boring and is capable of producing precision machined surfaces.machined surfaces.

The heart of this process lies in the broaching The heart of this process lies in the broaching tool wherein roughing, semi finishing, and tool wherein roughing, semi finishing, and finishing teeth are combined into one tool.finishing teeth are combined into one tool.

Broaching is process to produce non Broaching is process to produce non

circular holes like rectangular , hexagonal ,circular holes like rectangular , hexagonal ,

Square and irregularly shaped holes that Square and irregularly shaped holes that have been cored or punched: and also forhave been cored or punched: and also for

Cutting slots and key waysCutting slots and key ways

LappingLapping

GrindingGrinding Grinding can be defined as the rapid removal of material from a Grinding can be defined as the rapid removal of material from a

sample either to reduce it to a suitable size or to remove large sample either to reduce it to a suitable size or to remove large irregularities from the surface. The grinding wheel or plate typically irregularities from the surface. The grinding wheel or plate typically rotates at a high speed (around 200- 1000rpm) and a coarse, rotates at a high speed (around 200- 1000rpm) and a coarse, bonded abrasive (> 40 μm) is used. Grinding is quick and relatively bonded abrasive (> 40 μm) is used. Grinding is quick and relatively easy process but can cause deep subsurface damage in delicate easy process but can cause deep subsurface damage in delicate materials. Typically grinding is applied to hard metals such as high materials. Typically grinding is applied to hard metals such as high carbon steels where rapid removal is essential and subsurface carbon steels where rapid removal is essential and subsurface damage is not a critical parameter. damage is not a critical parameter.

For delicate materials the grinding process must be a balance of For delicate materials the grinding process must be a balance of material removal and subsurface damage. In many cases it is material removal and subsurface damage. In many cases it is advisable to initially cut the specimen with a gentle mechanical advisable to initially cut the specimen with a gentle mechanical method such as a wire saw. A properly prepared wire saw cut method such as a wire saw. A properly prepared wire saw cut sample can eliminate the grinding process altogethersample can eliminate the grinding process altogether

LappingLapping

Lapping is the removal of material to produce a smooth, flat, unpolished surface. Lapping is the removal of material to produce a smooth, flat, unpolished surface. Lapping processes are used to produce dimensionally accurate specimens to high Lapping processes are used to produce dimensionally accurate specimens to high tolerances (generally less than 2.5 μm uniformity). The lapping plate will rotate at a tolerances (generally less than 2.5 μm uniformity). The lapping plate will rotate at a low speed (<80 rpm) and a mid-range abrasive particle (5-20μm) is typically used. low speed (<80 rpm) and a mid-range abrasive particle (5-20μm) is typically used. Lapping removes subsurface damage caused by sawing or grinding and produces Lapping removes subsurface damage caused by sawing or grinding and produces the required thickness and flatness.the required thickness and flatness.

Although the lapping process is less damaging than grinding, there are two regimes Although the lapping process is less damaging than grinding, there are two regimes of lapping: free abrasive lapping and fixed abrasive lapping.of lapping: free abrasive lapping and fixed abrasive lapping.

Free Abrasive Lapping is when abrasive slurry is applied directly to a lapping plate Free Abrasive Lapping is when abrasive slurry is applied directly to a lapping plate (e.g. cast iron). This is perhaps the most accurate method for producing specimens (e.g. cast iron). This is perhaps the most accurate method for producing specimens and causes the least amount of damage. Free abrasive lapping is accurate because and causes the least amount of damage. Free abrasive lapping is accurate because of the rigid lapping surface which can be tailored to suit a particular material. Fixed of the rigid lapping surface which can be tailored to suit a particular material. Fixed Abrasive Lapping is when an abrasive particle in bonded to a substrate as with Abrasive Lapping is when an abrasive particle in bonded to a substrate as with abrasive lapping films and SiC papers. Abrasive lapping films have various particles abrasive lapping films and SiC papers. Abrasive lapping films have various particles bonded to a thin, uniform polyester substrate and are also capable of producing a bonded to a thin, uniform polyester substrate and are also capable of producing a very flat surface. SiC papers are much thicker than the film and create the potential very flat surface. SiC papers are much thicker than the film and create the potential for rounded edges on the sample.for rounded edges on the sample.

Abrasive TypesAbrasive Types

There is a wide selection of abrasives to choose from when There is a wide selection of abrasives to choose from when selecting a lapping and polishing process. Selecting anselecting a lapping and polishing process. Selecting an

abrasive is dependent upon the specimen hardness, desired abrasive is dependent upon the specimen hardness, desired surface finish, desired removal rate, lifetime, and price.surface finish, desired removal rate, lifetime, and price.

There are four basic types of abrasives that are used in lapping and There are four basic types of abrasives that are used in lapping and polishing processes: silicon carbide (SiC),polishing processes: silicon carbide (SiC),

aluminum oxide or alumina (Al2O3), boron carbide (B4C), and aluminum oxide or alumina (Al2O3), boron carbide (B4C), and diamond (C). All of these abrasives have distinctdiamond (C). All of these abrasives have distinct

properties and are used for different materials and applications.properties and are used for different materials and applications. SiC: SiC: SiC is hard and generally has a needle or blocky structure. SiC SiC is hard and generally has a needle or blocky structure. SiC

is used in many applications whereis used in many applications where rough lapping is required. It seldom is used for polishing or rough lapping is required. It seldom is used for polishing or

applications that require smooth surfaceapplications that require smooth surface finishes.finishes.

Al2O3: Al2O3: Al2O3 is relatively hard and has a sharp, angular structure. Al2O3 is relatively hard and has a sharp, angular structure. Alumina is commonly used where fineAlumina is commonly used where fine

surface finishes are required as it breaks down over time and gives surface finishes are required as it breaks down over time and gives excellent surfaces during lappingexcellent surfaces during lapping

and polishing. Alumina is also relatively inexpensive.and polishing. Alumina is also relatively inexpensive. B4C: B4C: B4C is harder than most other abrasives (excluding diamond) B4C is harder than most other abrasives (excluding diamond)

and has a blocky crystal structure. B4Cand has a blocky crystal structure. B4C provides excellent removal rates and is typically used when fast provides excellent removal rates and is typically used when fast

removal with moderate surface qualityremoval with moderate surface quality is needed.is needed. Diamond: Diamond: Diamond is the hardest material known and has a sharp, Diamond is the hardest material known and has a sharp,

angular structure. Diamond is extremelyangular structure. Diamond is extremely useful in lapping and polishing due to it’s removal rates and surface useful in lapping and polishing due to it’s removal rates and surface

finishing qualities. Diamond canfinishing qualities. Diamond can produce excellent surface finishes combined with high removal produce excellent surface finishes combined with high removal

rates.rates.

Lapping and Polishing Lapping and Polishing EquipmentEquipment

Equipment used for lapping and polishing can vary from application. Equipment used for lapping and polishing can vary from application. Typically what is required for lapping and polishingTypically what is required for lapping and polishing

are the following:are the following: 1. A lapping and polishing machine with variable speed.1. A lapping and polishing machine with variable speed. 2. A polishing jig for holding specimens precisely.2. A polishing jig for holding specimens precisely. 3. Various lapping plates for different applications.3. Various lapping plates for different applications. 4. Workstations for controlling lapping fixtures and conditioning 4. Workstations for controlling lapping fixtures and conditioning

equipment.equipment. 5. Conditioning equipment for maintaining plate flatness.5. Conditioning equipment for maintaining plate flatness. There are various methods available to accomplish these tasks. There are various methods available to accomplish these tasks.

South Bay Technology, Inc. has developed a series ofSouth Bay Technology, Inc. has developed a series of equipment designed for this purpose and is described below.equipment designed for this purpose and is described below.

Lapping and Polishing MachinesLapping and Polishing Machines Lapping and polishing machines vary extensively depending upon the Lapping and polishing machines vary extensively depending upon the

manufacturer. SBT has designed a set of instruments that are specifically manufacturer. SBT has designed a set of instruments that are specifically designed for universal lapping and polishing applications. designed for universal lapping and polishing applications.

The Model 920 Lapping and Polishing Machine incorporates a precision The Model 920 Lapping and Polishing Machine incorporates a precision spindle assembly housed in a solid cast aluminum casting to provide stable spindle assembly housed in a solid cast aluminum casting to provide stable operation in any laboratory environment. Stability when lapping is critical in operation in any laboratory environment. Stability when lapping is critical in producing flat, precisely controlled tolerances on a given specimen. producing flat, precisely controlled tolerances on a given specimen.

The motor is a high torque, variable speed motor that allows a wide range of The motor is a high torque, variable speed motor that allows a wide range of speeds to be employed. Flexibility in speed control allows the instrument to speeds to be employed. Flexibility in speed control allows the instrument to be used as a grinding machine, high quality lapping machine, or polishing be used as a grinding machine, high quality lapping machine, or polishing machine. During grinding high speeds are required, whereas lapping and machine. During grinding high speeds are required, whereas lapping and polishing applications are generally completed at low speeds. polishing applications are generally completed at low speeds.

The Model 920 also incorporates workstations, which allow for the use of The Model 920 also incorporates workstations, which allow for the use of precise Lapping and Polishing Fixtures. Each workstation has it’s own precise Lapping and Polishing Fixtures. Each workstation has it’s own speed control, allowing the user to precisely rotate the lapping fixtures or the speed control, allowing the user to precisely rotate the lapping fixtures or the conditioning ring. Lapping plates are held into place with three locating pins conditioning ring. Lapping plates are held into place with three locating pins and are easily removable, allowing maximum flexibility in processing and are easily removable, allowing maximum flexibility in processing specimens. Various materials can be selected for the lapping plates, specimens. Various materials can be selected for the lapping plates, ranging from aluminum, cast iron, and glass.ranging from aluminum, cast iron, and glass.

Below is an image showing the Model 920 with a typical setup for lappingBelow is an image showing the Model 920 with a typical setup for lapping

Lapping finishingLapping finishing

Types of lappingTypes of lappingsingle sidedsingle sided

Double sidedDouble sided

Cylindrical lappingCylindrical lapping

Upper lap rotation

Lower lap rotation

Rolling cylindrical workpieces

Upper lap rotation

Lower lap rotation

Cylindrical parts

Lapping processLapping process

Lapping and Polishing FixturesLapping and Polishing Fixtures Lapping and Polishing fixtures are perhaps the most critical part of Lapping and Polishing fixtures are perhaps the most critical part of

any lapping and polishing system. The lappingany lapping and polishing system. The lapping fixture is what holds the specimen during processing and ultimately fixture is what holds the specimen during processing and ultimately

will determine the final specimen quality. Southwill determine the final specimen quality. South Bay Technology has been a leader in the manufacture of precision Bay Technology has been a leader in the manufacture of precision

lapping fixtures for any application. In general, thelapping fixtures for any application. In general, the fixture typically performs like a piston, with a housing used for fixture typically performs like a piston, with a housing used for

support of a dynamically sliding piston assembly.support of a dynamically sliding piston assembly. Specimens are attached to the base of the piston using vacuum Specimens are attached to the base of the piston using vacuum

mounting or wax mounting techniques. The pistonmounting or wax mounting techniques. The piston movement is controlled with a precision dial micrometer at the top of movement is controlled with a precision dial micrometer at the top of

the fixture, and thus allows the precise removal ofthe fixture, and thus allows the precise removal of material in various increments determined by the user.material in various increments determined by the user.

The base of the housing contains a wear The base of the housing contains a wear resistant ring that supports the fixture, resistant ring that supports the fixture, controls the flatness and parallelismcontrols the flatness and parallelism

of the specimen, and gives stability to the of the specimen, and gives stability to the fixture.fixture.

Below is a basic image of a typical lapping Below is a basic image of a typical lapping and polishing fixture.and polishing fixture.

Lapping and Polishing PlatesLapping and Polishing Plates Lapping and polishing processes are performed on a hard, metal Lapping and polishing processes are performed on a hard, metal

plate used in conjunction with abrasiveplate used in conjunction with abrasive suspensions such as diamond, silicon carbide (SiC), aluminum suspensions such as diamond, silicon carbide (SiC), aluminum

oxide (Al2O3), or boron carbide (B4C). The metaloxide (Al2O3), or boron carbide (B4C). The metal lapping plate selected depends upon the desired material removal lapping plate selected depends upon the desired material removal

rate, the surface finish desired, the hardness of therate, the surface finish desired, the hardness of the specimen being lapped, and the flatness requirement.specimen being lapped, and the flatness requirement. Plate selection can play a critical role in the production of high Plate selection can play a critical role in the production of high

quality specimens. Lapping plates can be flat orquality specimens. Lapping plates can be flat or grooved depending upon the desired application. Grooved plates grooved depending upon the desired application. Grooved plates

provide greater removal rates and prevent theprovide greater removal rates and prevent the abrasive from squeezing out from between the plate and the abrasive from squeezing out from between the plate and the

specimen.specimen. Examples of some types are given below:Examples of some types are given below:

Cast Iron (Fe): Cast Iron (Fe): Cast iron lapping plates are used for rough lapping Cast iron lapping plates are used for rough lapping and stock removal of materials. Specimens around 8-10 on the and stock removal of materials. Specimens around 8-10 on the Mohs Hardness Scale can be lapped using cast iron plates. Cast Mohs Hardness Scale can be lapped using cast iron plates. Cast iron produces a gray surface finish and provides high removal rates.iron produces a gray surface finish and provides high removal rates.

Composites: Composites: Composite plates are used for rough lapping and Composite plates are used for rough lapping and stock removal of materials. Specimens of 7-10 on Mohs Hardness stock removal of materials. Specimens of 7-10 on Mohs Hardness Scale can be lapped on composite plates. These plates produce Scale can be lapped on composite plates. These plates produce medium quality surface finishes with very high removal rates.medium quality surface finishes with very high removal rates.

Copper (Cu): Copper (Cu): Copper plates are used for both rough and fine Copper plates are used for both rough and fine lapping of materials. Specimens around 9-5 on the Mohs Hardness lapping of materials. Specimens around 9-5 on the Mohs Hardness Scale can be lapped using copper plates. They provide high quality Scale can be lapped using copper plates. They provide high quality surface finishes with intermediate removal rates.surface finishes with intermediate removal rates.

Tin/Lead (Sn/Pb): Tin/Lead (Sn/Pb): Tin lead plates are used for fine lapping and Tin lead plates are used for fine lapping and polishing of materials. Specimens around 2-4 on Mohs Hardness polishing of materials. Specimens around 2-4 on Mohs Hardness Scale are lapped with tin lead plates. They provide high quality Scale are lapped with tin lead plates. They provide high quality surface finishes with low removal rates.surface finishes with low removal rates.

Polishing can also be carried out using a polishing cloth Polishing can also be carried out using a polishing cloth attached to a substrate plate (either glass or aluminumattached to a substrate plate (either glass or aluminum

typically) using aluminum oxide, colloidal silica, or typically) using aluminum oxide, colloidal silica, or diamond suspensions. Use of polishing cloths can bediamond suspensions. Use of polishing cloths can be

advantageous due to the high quality surface finish they advantageous due to the high quality surface finish they produce. However, it must be noted that for extendedproduce. However, it must be noted that for extended

polishing times the use of a cloth will sometimes lead to polishing times the use of a cloth will sometimes lead to wavy surfaces and edge turning, which can be wavy surfaces and edge turning, which can be detrimental to the specimen quality. Proper selection of detrimental to the specimen quality. Proper selection of polishing cloths and process times is key in the polishing cloths and process times is key in the successful use of a cloth for final polishing of specimens.successful use of a cloth for final polishing of specimens.

Plate ConditioningPlate Conditioning Plate conditioning is a process by which the lapping plate surface is Plate conditioning is a process by which the lapping plate surface is

machined to maintain the flatness of the lapping plate and to “pre-machined to maintain the flatness of the lapping plate and to “pre-condition” the lapping plate surface with the abrasive being used for condition” the lapping plate surface with the abrasive being used for the lapping process.the lapping process.

Plate conditioning is important for lapping applications where Plate conditioning is important for lapping applications where flatness and parallelism of the specimen is critical.flatness and parallelism of the specimen is critical.

Specimen quality is a direct result of plate condition, and therefore Specimen quality is a direct result of plate condition, and therefore proper maintenance of the lapping plate is crucial in preparing high proper maintenance of the lapping plate is crucial in preparing high quality specimens.quality specimens.

Conditioning of the lapping plate is affected by two primary Conditioning of the lapping plate is affected by two primary parameters: a) position of the conditioning ring, and b) weight of the parameters: a) position of the conditioning ring, and b) weight of the conditioning ring. The conditioning ring is generally a cast iron or conditioning ring. The conditioning ring is generally a cast iron or stainless steel ring used with the abrasive desired or with diamond stainless steel ring used with the abrasive desired or with diamond plated to the bottom of the ring. Conditioning of the lapping plate plated to the bottom of the ring. Conditioning of the lapping plate also helps maintain high removal rates during long lapping also helps maintain high removal rates during long lapping operationsoperations

HoningHoning

Used mainly to improve the surface finish of Used mainly to improve the surface finish of holesholes

Bonded abrasives called stones are Bonded abrasives called stones are mounted on a rotating mandrel; also used mounted on a rotating mandrel; also used on cylindrical or flat surfaces and to on cylindrical or flat surfaces and to remove sharp edges on toolsremove sharp edges on tools

HoningHoning

Hole defects correctible by honing

HoningHoning

Hole defects correctible by honing

Superfinishing/Superfinishing/MicrohoningMicrohoning

Uses very low pressure and short strokesUses very low pressure and short strokes

Broaching Broaching BROACHING MACHINES AND OPERATIONSBROACHING MACHINES AND OPERATIONS BROACHING:BROACHING: Broaching is a cutting process using a multitoothed tool (broach) Broaching is a cutting process using a multitoothed tool (broach)

having successive cutting edges, each protruding to a greater having successive cutting edges, each protruding to a greater distance than the proceeding one in the direction perpendicular todistance than the proceeding one in the direction perpendicular to

the broach length. In contrast to all other cutting processes, there is the broach length. In contrast to all other cutting processes, there is no feeding of the broach or the WP. The feed is built into the broach no feeding of the broach or the WP. The feed is built into the broach itself through the consecutive protruding of its teeth.itself through the consecutive protruding of its teeth.

Therefore, no complex motion of the tool relative to the WP is Therefore, no complex motion of the tool relative to the WP is required, where the tool is moved past the WP with a rectilinear required, where the tool is moved past the WP with a rectilinear motion motion vvc (Figure 3.77). c (Figure 3.77).

Equally effective results are obtained if the tool is stationary and the Equally effective results are obtained if the tool is stationary and the work is moved. work is moved.

The total depth of the material removed in one strokeThe total depth of the material removed in one stroke T T is the sum of rises of teeth of the broach. is the sum of rises of teeth of the broach. T T may be as may be as

deep as 6 mm broached in one stroke. Ifdeep as 6 mm broached in one stroke. If more depth is to be broached, two broaches may be more depth is to be broached, two broaches may be

used to perform the task. Broaching is generally used to used to perform the task. Broaching is generally used to machine through holes of any cross-sectional shape, machine through holes of any cross-sectional shape, straight and helical slots, external surfaces of various straight and helical slots, external surfaces of various shapes, and external and internal toothed gears (Figure shapes, and external and internal toothed gears (Figure 3.78). To permit the broaching of spiral grooves and gun-3.78). To permit the broaching of spiral grooves and gun-barrel rifl ing, a rotational movement should be added to barrel rifl ing, a rotational movement should be added to the broach. Broaching usually produces better accuracy the broach. Broaching usually produces better accuracy and fi nish than drilling, boring, or reaming operations. A and fi nish than drilling, boring, or reaming operations. A tolerance grade of IT6 and a surface roughness tolerance grade of IT6 and a surface roughness RRa of a of about 0.2 μm can be easily achieved by broaching.about 0.2 μm can be easily achieved by broaching.

Broaching dates back to the early 1850s, when it was Broaching dates back to the early 1850s, when it was originally developed for cutting keyways in pulleys and originally developed for cutting keyways in pulleys and gears. However, its obvious advantages quickly led to its gears. However, its obvious advantages quickly led to its development for mass production machining of various development for mass production machining of various surfaces and shapes to tight tolerance. Today, almost surfaces and shapes to tight tolerance. Today, almost every conceivable form and material can be broached.every conceivable form and material can be broached.

Broaches must be designed individually for a particular Broaches must be designed individually for a particular job. They are very expensive to manufacturejob. They are very expensive to manufacture

($15,000–$30,000 per tool). ($15,000–$30,000 per tool). It follows that the broaching can only be justifi ed when a It follows that the broaching can only be justifi ed when a

very large batch size (100,000–200,000) is to be very large batch size (100,000–200,000) is to be machined. However, sometimes the WP is designed somachined. However, sometimes the WP is designed so

that a non expensive standard broach can be used.that a non expensive standard broach can be used.

Advantages and Limitations of Advantages and Limitations of BroachingBroaching

1. Advantages1. Advantages Broaching is a process in which both roughing and finishing operations are Broaching is a process in which both roughing and finishing operations are

completed in one pass, giving a high rate of production.completed in one pass, giving a high rate of production. It is a fast process; it takes only seconds to accomplish a task that would It is a fast process; it takes only seconds to accomplish a task that would

require minutes with any other method. Rapid loading and unloading of require minutes with any other method. Rapid loading and unloading of fixtures keeps the total production time to the minimum.fixtures keeps the total production time to the minimum.

Automation is easily arranged.Automation is easily arranged. Internal and external surfaces can be machined within close tolerance that Internal and external surfaces can be machined within close tolerance that

is normally required for interchangeable mass productionis normally required for interchangeable mass production As all the performance is built into the tooling, little skill is needed to operate As all the performance is built into the tooling, little skill is needed to operate

a broaching machine.a broaching machine. Broaches have an exceptionally long life (10,000–20,000 parts per each Broaches have an exceptionally long life (10,000–20,000 parts per each

sharpening), as each tooth passes over the work only once per pass.sharpening), as each tooth passes over the work only once per pass.

2. Limitations2. Limitations

Broaches are costly to make and sharpen. Hence, broaching is Broaches are costly to make and sharpen. Hence, broaching is adopted only in cases of mass production.adopted only in cases of mass production.

Standard broaches are available; however, most broaches are Standard broaches are available; however, most broaches are expensive, as they are made especially to perform only one job.expensive, as they are made especially to perform only one job.

Special precautions may be necessary when broaching cast and Special precautions may be necessary when broaching cast and forged parts to control the variations in stock. Operations for forged parts to control the variations in stock. Operations for removing excess stock may be necessary, which add to the overall removing excess stock may be necessary, which add to the overall cost of manufacturing.cost of manufacturing.

Surfaces to be machined must be parallel to the axis of the broach.Surfaces to be machined must be parallel to the axis of the broach. Broaching is impractical in the following cases:Broaching is impractical in the following cases: a. A surface that has obstructions across the path of the broach a. A surface that has obstructions across the path of the broach

travel.travel. b. Blind holes and pockets.b. Blind holes and pockets. c. Fragile W /Ps, because they cannot withstand broaching forces c. Fragile W /Ps, because they cannot withstand broaching forces

without distortion orwithout distortion or breakage.breakage.

THE BROACH TOOLTHE BROACH TOOL

3.7.2.1 Tool Geometry and Confi guration3.7.2.1 Tool Geometry and Confi guration Figure 3.79 illustrates the broach tooth terminology. Each individual Figure 3.79 illustrates the broach tooth terminology. Each individual

tooth has the basic wedge form.tooth has the basic wedge form. Depending on the material being cut, the rake (hook) angle ranges Depending on the material being cut, the rake (hook) angle ranges

from 0° to 20°. The small clearance (back-off) angle is usually 3°–4° from 0° to 20°. The small clearance (back-off) angle is usually 3°–4° for roughing teeth and 1°–2° for fi nishing teeth.for roughing teeth and 1°–2° for fi nishing teeth.

The rise per tooth (RPT) (superelevation) is the difference in height The rise per tooth (RPT) (superelevation) is the difference in height of two consecutive teeth (Figure 3.77). It is selected depending of two consecutive teeth (Figure 3.77). It is selected depending upon the material to be machined and the type (form) of the broach upon the material to be machined and the type (form) of the broach (Table 3.3).(Table 3.3).

The pitch is the distance between two consecutive teeth of a The pitch is the distance between two consecutive teeth of a broach. It depends upon the following factors:broach. It depends upon the following factors:

Length of cut Length of cut ll Material of WP and its mechanical propertiesMaterial of WP and its mechanical properties RPT (superelevation)RPT (superelevation)

The pitch The pitch P P can be expressed empirically can be expressed empirically byby

p p = 3 √R.P.T ∙ = 3 √R.P.T ∙ l l ∙ ∙ χ χ wherewhere χ χ = chip space number= chip space number = 3–5 for brittle WP materials= 3–5 for brittle WP materials = 6–10 for ductile and soft WP materials= 6–10 for ductile and soft WP materials

A relatively large pitch and tooth depth are required for roughing A relatively large pitch and tooth depth are required for roughing teeth to accommodate greater chip volume in the chip gullet, teeth to accommodate greater chip volume in the chip gullet, especially when machining materials produce continuous chips.especially when machining materials produce continuous chips.

For semi finishing and finishing teeth, the pitch is reduced to about For semi finishing and finishing teeth, the pitch is reduced to about 60% of that of roughing teeth to reduce the overall length of the 60% of that of roughing teeth to reduce the overall length of the broach. The calculated pitch, according to Equation 3.19, should not broach. The calculated pitch, according to Equation 3.19, should not be greater than be greater than ll/2 (/2 (l l is the length to be cut) to provide better is the length to be cut) to provide better guidance of the tool and to prevent the broach from drifting. To guidance of the tool and to prevent the broach from drifting. To prevent possible chattering and to obtain better surface finish, the prevent possible chattering and to obtain better surface finish, the pitch pitch p p should be made non uniform as shown in Figure 3.80. To should be made non uniform as shown in Figure 3.80. To avoid the formation of long chips, especially when broaching profiles avoid the formation of long chips, especially when broaching profiles and circular shapes, chip breakers are uniformly cut into the cutting and circular shapes, chip breakers are uniformly cut into the cutting edges of the broach in a staggered manner.edges of the broach in a staggered manner.

Chip breakers are not necessary when broaching brittle materials Chip breakers are not necessary when broaching brittle materials produce discontinuous chips. They are not used for finishing teeth produce discontinuous chips. They are not used for finishing teeth and small size broaches. The use of chip breakers reduces the pitch and small size broaches. The use of chip breakers reduces the pitch and consequently the overall length of the broach. As a result, the and consequently the overall length of the broach. As a result, the productivity is enhanced and the tool cost may be reducedproductivity is enhanced and the tool cost may be reduced

Solid-pull broach configuration.

Shell broach. (From Degarmo, E. P. et al., Materials and Processes in Manufacturing,8th Edition, Prentice-Hall, New York, 1997

Broach ConfigurationBroach Configuration

Figure illustrates the terminology of a pull-type internal broach for Figure illustrates the terminology of a pull-type internal broach for enlarging circular holes .The cutting teeth on the broach have three enlarging circular holes .The cutting teeth on the broach have three regions: roughing, semi finishing, and finishing teeth. On some regions: roughing, semi finishing, and finishing teeth. On some round broaches, burnishing teeth are provided for finishing or sizing. round broaches, burnishing teeth are provided for finishing or sizing. These teeth have no cutting edge, but are rounded. Their diameters These teeth have no cutting edge, but are rounded. Their diameters are oversized by 25–30 μm larger than the finished hole.are oversized by 25–30 μm larger than the finished hole.

Irregular shapes are produced by starting from circular broaching in Irregular shapes are produced by starting from circular broaching in the WP originally provided with drilled, bored, cored, or reamed the WP originally provided with drilled, bored, cored, or reamed hole.hole.

The pull end provides a means of quickly attaching the broach to the The pull end provides a means of quickly attaching the broach to the pulling mechanism. The front pilot aligns the broach in the hole pulling mechanism. The front pilot aligns the broach in the hole before it begins to cut and the rear pilot keeps the tool squarebefore it begins to cut and the rear pilot keeps the tool square

with the finished hole as it leaves the WP. It also prevents sagging with the finished hole as it leaves the WP. It also prevents sagging of the broach. The follower end is ground to fi t in the machine of the broach. The follower end is ground to fi t in the machine follower rest.follower rest.

Internal broaches are also made of shells Internal broaches are also made of shells mounted on an arbor (Figure 3.82). Shell mounted on an arbor (Figure 3.82). Shell broaches are superior to solid broaches in that broaches are superior to solid broaches in that worn or broken shells can be replaced without worn or broken shells can be replaced without discarding the entire broach. Shell construction, discarding the entire broach. Shell construction, however, is initially more expensive than a solid however, is initially more expensive than a solid broach of comparable size. The disadvantage of broach of comparable size. The disadvantage of shell broaches is that some accuracy and shell broaches is that some accuracy and concentricity are sacrificed.concentricity are sacrificed.

Regarding the application of broaching force, Regarding the application of broaching force, two types of broaching are distinguishedtwo types of broaching are distinguished

11. . Pull-broachingPull-broaching

as the name implies, involves the broach being pulled as the name implies, involves the broach being pulled through the hole (Figure 3.83a). In this case, the main through the hole (Figure 3.83a). In this case, the main cutting force is applied to the front of the broach, cutting force is applied to the front of the broach, subjecting the body to tension. Most internal broaching is subjecting the body to tension. Most internal broaching is done with pull-broaches. Because there is no problem of done with pull-broaches. Because there is no problem of buckling, pull-broaches can be longer than push-types buckling, pull-broaches can be longer than push-types for the same broaching depth. for the same broaching depth.

Pull-broaches can be made to long lengths, but cost Pull-broaches can be made to long lengths, but cost usually limits the length to approximately 2 m. Broaches usually limits the length to approximately 2 m. Broaches longer than 2 m are shell broaches, because the cost is longer than 2 m are shell broaches, because the cost is less for replacing damaged or worn sections than for less for replacing damaged or worn sections than for replacing the entire broach.replacing the entire broach.

2. Push-broaching2. Push-broaching

applies the main cutting force to the rear of applies the main cutting force to the rear of the broach, thus subjecting the body to the broach, thus subjecting the body to compression (Figure 3.83b). A push-compression (Figure 3.83b). A push-broach should be shorter than a pull-broach should be shorter than a pull-broach and its length does not usually broach and its length does not usually exceed 15 times its diameter to avoid exceed 15 times its diameter to avoid bucklingbuckling

PULL BROACHINGPULL BROACHING

PUSH BROACHINGPUSH BROACHING

Broach MaterialBroach Material

The low cutting speeds used in most broaching operations (2–12 The low cutting speeds used in most broaching operations (2–12 m/min) do not lend themselves to the advantage of carbide tooling. m/min) do not lend themselves to the advantage of carbide tooling. Accordingly, most broaches are made of alloy steel and HSSAccordingly, most broaches are made of alloy steel and HSS

of high grades (Cr-V-grade), which have less distortion during heat of high grades (Cr-V-grade), which have less distortion during heat treatment. This is an important factor in the manufacture of long treatment. This is an important factor in the manufacture of long broaches. broaches.

Titanium-coated HSS broaches are becoming more common due to Titanium-coated HSS broaches are becoming more common due to their prolonged tool life.their prolonged tool life.

Recently, carbide-tipped K-type (cobalt group) tools are employed to Recently, carbide-tipped K-type (cobalt group) tools are employed to machine CI, thus allowing higher cutting speeds, increased machine CI, thus allowing higher cutting speeds, increased durability, and improved surface finish. However, carbide-tippeddurability, and improved surface finish. However, carbide-tipped

broaches are seldom used for machining steels and forged parts, as broaches are seldom used for machining steels and forged parts, as the cutting edges tend to chip in the first stroke due to lack of rigidity the cutting edges tend to chip in the first stroke due to lack of rigidity of work fixture/tool combination.of work fixture/tool combination.

Broach SharpeningBroach Sharpening

Broach sharpening is essential, as dull tools require more force, Broach sharpening is essential, as dull tools require more force, leading to less accuracy and broach damage. Dull internal broaches leading to less accuracy and broach damage. Dull internal broaches have the tendency to drift during cutting.have the tendency to drift during cutting.

The clearance angle of the sizing teeth of a broach is made as small The clearance angle of the sizing teeth of a broach is made as small as possible (1°–2°) to minimize the loss of size when it is as possible (1°–2°) to minimize the loss of size when it is sharpened. Also, the finishing or sizing teeth are commonly sharpened. Also, the finishing or sizing teeth are commonly provided with a land of a small width of 50–200 μm to limit the size provided with a land of a small width of 50–200 μm to limit the size loss due to sharpening. Most of broaches are sharpened by grinding loss due to sharpening. Most of broaches are sharpened by grinding the hook faces of the broach. The lands must not be reground the hook faces of the broach. The lands must not be reground because this would change the size of the broach (Figure 3.84). because this would change the size of the broach (Figure 3.84). After sharpening, the tooth characteristics such as rake angle, After sharpening, the tooth characteristics such as rake angle, clearance angles, tooth depth, root radius, RPT, and pitch should clearance angles, tooth depth, root radius, RPT, and pitch should not be altered.not be altered.

BROACHING MACHINESBROACHING MACHINES

In comparison with other types of machine tools, broaching In comparison with other types of machine tools, broaching machines are notable for their simple construction and operation. machines are notable for their simple construction and operation. This is due to the fact that the shape of the surface produced in This is due to the fact that the shape of the surface produced in broaching depends upon the shape and arrangement of the cutting broaching depends upon the shape and arrangement of the cutting edges on the broach. The only cutting motion of the broaching edges on the broach. The only cutting motion of the broaching machine is the straight line motion of the ram. Broaching machines machine is the straight line motion of the ram. Broaching machines have no feed mechanisms, as the feed is provided by a gradual have no feed mechanisms, as the feed is provided by a gradual increase in the height of the broach teeth.increase in the height of the broach teeth.

Hydraulic drives, developed in the early 1920s, offered pronounced Hydraulic drives, developed in the early 1920s, offered pronounced advantages over the various early mechanical driving methods. advantages over the various early mechanical driving methods. Most broaching machines existing today are of hydraulic drive, Most broaching machines existing today are of hydraulic drive, accordingly characterized by smooth running and safe operation.accordingly characterized by smooth running and safe operation.

The choice between vertical and horizontal machines is determined The choice between vertical and horizontal machines is determined primarily by the length of stroke required and the available fl oor primarily by the length of stroke required and the available fl oor space. Vertical machines seldom have strokes greater thanspace. Vertical machines seldom have strokes greater than

1.5 m because of ceiling limitation. Horizontal 1.5 m because of ceiling limitation. Horizontal machines can have almost any stroke length; machines can have almost any stroke length; however, they require greater floor space.however, they require greater floor space.

The main specifications of a broaching machine The main specifications of a broaching machine are as follows:are as follows:

Maximum pulling or pushing force (capacity) Maximum pulling or pushing force (capacity) (ton)(ton)

Maximum stroke length (m)Maximum stroke length (m) Broaching speed (m/min)Broaching speed (m/min) Overall dimensions and total weighOverall dimensions and total weigh

Horizontal Broaching MachinesHorizontal Broaching Machines

Currently, horizontal machines are finding increasing favor among users Currently, horizontal machines are finding increasing favor among users because of their long strokes and the limitation that ceiling height places on because of their long strokes and the limitation that ceiling height places on vertical machines. About 47% of all broaching machines are horizontal units vertical machines. About 47% of all broaching machines are horizontal units (ASM International, 1989). Horizontal internal broaching machines are used (ASM International, 1989). Horizontal internal broaching machines are used mainly for some types of work such as automotive engine blocks.mainly for some types of work such as automotive engine blocks.

The pulling capacity ranges from 2.5 to 75 tons, strokes up to 3 m, and The pulling capacity ranges from 2.5 to 75 tons, strokes up to 3 m, and cutting speeds limited to less than 12 m/min. Broaching that requires cutting speeds limited to less than 12 m/min. Broaching that requires rotation of the broach, as in rifling and spiral splines, is usually done on rotation of the broach, as in rifling and spiral splines, is usually done on horizontal internal broaching machines. Horizontal machines are seldom horizontal internal broaching machines. Horizontal machines are seldom used for broaching small holes. used for broaching small holes.

Horizontal surface broaching machines may be hydraulically or Horizontal surface broaching machines may be hydraulically or electromechanically driven. In these machines, the broach is always electromechanically driven. In these machines, the broach is always supported in guides. The surface hydraulic broaching machines are built supported in guides. The surface hydraulic broaching machines are built with capacities up to 40 tons, strokes up to 4.5 m, and cutting speeds up to with capacities up to 40 tons, strokes up to 4.5 m, and cutting speeds up to 30 m/min. These machines are basically used in the automotive industry to 30 m/min. These machines are basically used in the automotive industry to broach a great variety of CI parts for nearly 30 years.broach a great variety of CI parts for nearly 30 years.

Pull-down vertical broaching Pull-down vertical broaching machinemachine

On the other hand,the electromechanically On the other hand,the electromechanically driven horizontal surface broaching driven horizontal surface broaching machines are available with higher machines are available with higher capacities, stroke lengths, and cutting capacities, stroke lengths, and cutting speeds (up to 100 tons, 9 m, and 30 speeds (up to 100 tons, 9 m, and 30 m/min, respectively). Carbide-tipped m/min, respectively). Carbide-tipped broaches are used to machine CI blocks of broaches are used to machine CI blocks of internal combustion engines (ICEs).internal combustion engines (ICEs).

Vertical Broaching MachinesVertical Broaching Machines These machines are almost all hydraulically driven. They are used These machines are almost all hydraulically driven. They are used

in every major area of metal working. Depending on their mode of in every major area of metal working. Depending on their mode of operation, they may be pull-up, pull-down, or push-downoperation, they may be pull-up, pull-down, or push-down

units. Figure 3.85 schematically illustrates a pull-down vertical units. Figure 3.85 schematically illustrates a pull-down vertical broaching machine in which the work is placed on the worktable. broaching machine in which the work is placed on the worktable. These machines are capable of machining internal shapes to closeThese machines are capable of machining internal shapes to close

tolerances by means of special locating fixtures. They are available tolerances by means of special locating fixtures. They are available with pulling capacities from 2 to 50 tons, strokes from 0.4 to 2.3 m, with pulling capacities from 2 to 50 tons, strokes from 0.4 to 2.3 m, and cutting speeds up to 24 m/min. When cutting strokes exceedand cutting speeds up to 24 m/min. When cutting strokes exceed

existing factory ceiling clearances, expensive pits must be dug for existing factory ceiling clearances, expensive pits must be dug for the machine so that the operator can work at the factory floor level.the machine so that the operator can work at the factory floor level.

Continuous Horizontal Surface Broaching MachinesContinuous Horizontal Surface Broaching Machines In this type of machines, the broaches are usually In this type of machines, the broaches are usually

stationary and mounted in a tunnel on the top of the stationary and mounted in a tunnel on the top of the machine, while the work is pulled past the cutters by machine, while the work is pulled past the cutters by means of a conveyor (Figure 3.86). Fixtures are usually means of a conveyor (Figure 3.86). Fixtures are usually attached to the conveyor chain, so that the WPs can be attached to the conveyor chain, so that the WPs can be provided automatically by the loading chute at one end provided automatically by the loading chute at one end of the bed and removed at the other end. of the bed and removed at the other end.

The key to the productivity of this type of machines is the The key to the productivity of this type of machines is the elimination of the return stroke by mounting the WPs on elimination of the return stroke by mounting the WPs on continuous chain. In the rotary continuous horizontal continuous chain. In the rotary continuous horizontal broaching machines, the broaches are also stationary, broaching machines, the broaches are also stationary, while the work is passed beneath or between them. The while the work is passed beneath or between them. The work is held in fixtures on a rotary table.work is held in fixtures on a rotary table.

These machines are also used in mass production, as These machines are also used in mass production, as there is no loss of time due to the non cutting there is no loss of time due to the non cutting reciprocating strokes.reciprocating strokes.