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Introduction
This article takes an in depth look at Broaching.
You will learn more about topics such as:
What is Broaching?
The machinery used for Broaching
Types of Broaches
Broaching tool design terms
And much more…
Chapter One - What is Broaching?
Broaching is a machining process where a sharp, hardened,
toothed tool removes material from a workpiece in a consistent,
continuous, and accurate way. The process of broaching uses a
tool with raised teeth of differing sizes that precisely cut
away a specified amount of material with every pass over the
workpiece.
In broaching, the multi-cutting tool moves while the workpiece
remains static, or the workpiece moves while the tool is static.
In some cases, there may be relative rotation between the tool
and workpiece. The broaching process can be internal through the
center of the workpiece or external across the surface of the
workpiece.
The designs for exterior or surface broaching include slab,
slot, contour, pot, and straddle, while internal broaching
includes keyway, concentricity, and cut recut. The broaching
process varies in accordance with the portion of the workpiece
that will be broached or cut.
Chapter Two - The Process of Broaching
Broaching is a common machining process used to selectively
remove material from a workpiece to achieve a certain dynamic or
shape. The difference between broaching and other machining
applications is the tools used to deform and transform the
workpiece.
The purpose of the broach is to push against the workpiece to
leave a set of holes or shapes. What makes broaching unique is
the types of cuts it makes; they are odd and cannot be found in
other machining methods.
Broaching Machine
A broaching machine is the simplest of all forms of machining
tools and consists of a broaching tool, holding fixture, drive,
and support frame. The two types of broaching machines are
horizontal and vertical; they can have one or more rams
depending on the application. With dual or multiple rams, the
rams work opposite each other, with one on the cutting stroke
and the other on the return stroke.
A broaching machine either pulls or pushes the broach through or
past a held workpiece. In other designs, the workpiece is held
in place as the broach passes over it. The power and force for a
broaching machine comes from hydraulically supplied energy.
Horizontal Broaching Machine
Horizontal broaching machines use the pull type method for
broaching the workpiece and are used for interior and exterior
broaching. A horizontal machine has a bed, a broach pilot, and a
drive mechanism.
The main broaches on a horizontal machine are keyways, splines,
slots, round holes, and interior shapes. Though horizontal
machines take up floor space, they are perfect for long broaches
and heavy workpieces.
Vertical Broaching Machine
A vertical broaching machine pushes or pulls the broaching tool,
with push broaching being the most common type. The design and
configuration of vertical machines makes it possible for them to
perform multiple operations since it is easy to pass a workpiece
from one machine to another.
The three types of vertical machines are push down, pull up, and
pull down. The pull up design is the most popular. Vertical
broaching machines can be powered by hydraulics or an
electro-mechanical drive; hydraulic is the most popular and cost
effective.
Surface Broaching Machine
A surface broaching machine removes access material from the
surface of a workpiece. The cutting tool passes over the
workpiece to produce flat or contoured surfaces. The unique
feature of a surface broaching machine is that the cutting tool
is attached to a ram that is forced along past the workpiece.
The ram can move horizontally or vertically depending on the
design of the machine. It is possible for a surface broaching
machine to have two rams; this is described as duplex broaching.
Continuous Broaching Machine
In continuous broaching, the workpiece is constantly moving
while the broach is held stationary. The movement can be
straight, horizontal, or circular. With horizontal continuous
broaching, workpieces are loaded on a fixture that is mounted on
a chain. Continuous broaching is used for cutting similar parts
at the same time.
Rotary Broaching Machine
Rotary broaching is unlike the other forms of broaching and is
known as wobble broaching. It is a precision method for
producing polygonal shapes internally or externally. In rotary
broaching, the cutting tool is placed at a 1° angle to the
centerline of the workpiece, which causes the broach to cut with
a chiseling or scalloping effect.
Rotary broaching can be completed with a lathe or mill using a
horizontal or vertical spindle machine where the spindle is
allowed to spin freely. The shapes that can be created using
rotary broaching include hexagons, squares, serrations, keyways,
involute, spline, spur gear, numbers, and letters.
The rotary broaching tool holder allows the broaching process to
work and cuts one portion of the form at a time. The broach is
fed into the part and cuts the full form in one pass. The broach
bit is designed with a back taper to prevent it from thrusting
into the workpiece while feeding the broach into the pilot hole.
Turn Broaching Machine
Turn broaching machines are used for circular, linear, and
spiral cutting where surfaces need a high finish. The tool has
multiple inserts to remove material by rotating the crankshaft
between centers. The components of a turn broaching machine are
capable of finishing or roughing. The type of machine determines
the tool.
Roughing inserts and their segments depend on the requirements
of the stock removal rate. The finishing segments have
adjustable cartridges, which are ideal for producing tight
tolerances.
CNC Broaching
Computer Numerical Control (CNC) machines can be used for the
broaching process due to recent technological developments.
Parts can be broached using the rotary or linear processes in a
single step. Broaching companies have designed tools, tool
bodies, and holders that can be included in the CNC process.
CNC broaching has indexable insert broaching tools and tool
holders. The special tool holders make it possible to have
several specialized inserts. CNC broaches include rotary or
wobble, punch, keyway, splines, polygons, and serrations to name
a few.
Chapter Three- Leading Broaching Machines
The process of broaching requires precision. Luckily, there are many manufacturers of broaching machines that have essentially perfected this process. Below are five brands known for manufacturing machines used in the United States or Canada to perform broaching, along with specific models and their unique abilities, features, or characteristics:
Brand: American Broach & Machine Co.
Model: AB-2500H Broaching Machine
Description: American Broach & Machine Co. is a renowned manufacturer of broaching machines. The AB-2500H model is designed for high-volume production and offers advanced features such as high-speed operation, precise control over the broaching process, and flexibility in handling various broach sizes. It is known for its reliability, durability, and the ability to produce accurate and consistent broached parts.
Brand: Colonial Tool Group
Model: Colonial G-Series Broaching Machine
Description: Colonial Tool Group specializes in the production of broaching machines. The G-Series model is a versatile machine designed for both internal and surface broaching applications. It offers features such as multiple broach stations, advanced control systems, and high rigidity for enhanced precision and productivity. The Colonial G-Series machine is known for its flexibility, accuracy, and the ability to handle complex broaching requirements.
Brand: Ohio Broach & Machine Co.
Model: OB Series Vertical Broaching Machine
Description: Ohio Broach & Machine Co. manufactures a range of vertical broaching machines. The OB Series is designed for efficient vertical broaching operations. It features a compact footprint, user-friendly controls, and customizable options to meet specific broaching needs. The OB Series machines are known for their reliability, ease of use, and the ability to produce high-quality broached parts with precision.
Brand: Broaching Machine Specialties (BMS)
Model: BMS Horizontal Broaching Machine
Description: Broaching Machine Specialties (BMS) is a leading manufacturer of broaching machines. Their horizontal broaching machine is designed for precision broaching applications. It offers features such as sturdy construction, advanced control systems, and efficient chip evacuation mechanisms. The BMS horizontal broaching machine is known for its rigidity, accuracy, and the ability to handle various broach sizes and materials.
Brand: Nachi America Inc.
Model: Nachi Gear Cutting Broach Machine
Description: Nachi America Inc. produces gear cutting broach machines. These machines are specialized for gear manufacturing applications and offer features such as high-speed operation, precise gear cutting capabilities, and advanced tooling systems. Nachi's gear cutting broach machines are known for their reliability, efficiency, and the ability to produce high-quality gears with tight tolerances.
Please note that the availability of specific models and their features may vary over time. For the most up-to-date and detailed information on the models and features offered by these manufacturers for broaching machines in the United States or Canada, I recommend contacting the manufacturers directly or referring to their product catalogs and specifications.
Leading Manufacturers and Suppliers
Chapter Four - Types of Broaching
The process of broaching produces parts with exceptional surface
finishes and dimensional accuracy. A broaching tool has rough,
semi-finish, and finish cutting teeth capable of finishing the
machining of a rough surface in one stroke.
In the case of interior broaching, the tool may be pulled or
pushed through the workpiece, or the workpiece may move across
the tool. Internal broaching necessitates a starting hole for
insertion of the broach.
A broach is a single point cutting tool with many points that
cut like a flat ended sharp tool such as a chisel. In some
cases, the teeth of the broach may be set diagonally to complete
shearing cuts that produce a sliding or skewing deformation.
The Broach
A broach is a cutting tool with several rows of teeth with each
tooth slightly larger than the previous one. Simple or complex
cuts can easily be produced quickly and accurately using a
broach cutting tool. During the process, each cut of the broach
is shallow along the length of the workpiece.
Linear Broaching
Of the various types of broach cutting, linear broaching is the
most common. The tool moves linearly against the workpiece
surface, making its cuts as it moves to the end of the workpiece
The diagram is an example of linear broaching.
Pull Broaching
In pull broaching, the workpiece is held in place as the broach
is pulled through. The type of broaches for this process are
long and require a special head. The tension created during
pulling builds up to make the broach more effective. The process
is mainly used for interior or internal broaching but can be
used for surface broaching. Pull broaches have a great many
teeth and provide a longer cut.
Pull broaching can be completed up, down, or horizontally
through or across the workpiece. Automobile cylinder blocks and
heads are faced flat using the pull broaching method.
Push Broaching
A push broaching tool is shorter to be able to endure the
compressive forces applied as it goes through the workpiece. It
has fewer teeth, which can be bent or broken due to the
compressive forces. Push broaching produces shorter cuts to
produce smaller parts.
Surface broaching is a common use for push broaching tools. When
they are used for that purpose, they are referred to as surface
broaching tools.
Pot Broaching
Pot broaching is used with cylindrical workpieces and has a pot
shaped tool holder. In pot broaching, the tool remains
stationary as the workpiece is pushed or pulled through it. Pot
broaching produces a cut inverse that of interior broaching and
is used with other machining or independently. The tool for pot
broaching is extremely complex and requires a special fixture;
this makes pot broaching a seldomly used process.
Spline Broaching
Spline broaching, also known as round broaching, creates round,
plain, or irregular splines and spiral tooth forms. It can be
used to create shafts, gears, and meshing mechanical components.
Spline broaching is the most common form of broaching and uses a
broach to form a series of ridges or teeth around the
circumference of a pre-cut hole. The process of spline broaching
is an efficient method for creating serrated, straight, and
involute splines.
In the automotive industry, spline broaching is used to produce
transmission and driveshaft parts. The grooves created on a
spline allow the efficient transfer of torque by locking
together separate components.
Blind Broaching
Blind broaching refers to the broaching process where the tool
does not pass completely through the part, meaning the tool
machines into a blind cavity. The process of blind broaching is
used on parts that are designed to not have a pass through. In
the case of keyways, they can be designed to be a blind
broaching when the tool stops in the middle of the bore.
Internal Broaching
With internal broaching, material is removed from the interior
or internal surface of the workpiece; this is known as hole
broaching. Prior to beginning the internal broaching process, a
starter hole is drilled into the workpiece; this is referred to
as blank prepping. Internal broaching is used to enlarge, widen,
and resize a hole.
The internal broaching tool has teeth that get successively
larger to provide an exceptional finish on the workpiece.
Internal broaching is completed using automated machines such as
a CNC machine, which is capable of producing holes quickly and
efficiently in the workpiece. The internal broaching method can
be completed using either the push or pull process. The
categories of internal broaches are round or spline.
External Broaching
External broaching removes material from the exterior of the
workpiece and is referred to as surface broaching. Like the
internal broaching tool, the teeth of an external broaching tool
progressively increase. External broaching uses a guided ram
with a broach holding fixture. The force of the cutting is
transferred to the ram along the length of the broach.
External broaches are flat surfaces and form surfaces. With flat
surface broaching, the tool passes over the workpiece to produce
a desired surface. The form surface broaching process is
designed to produce different contours and shapes, which include
serrated, angular spline, gear forms, fir tree, compressor
slots, and keyways.
Chapter Five - Broaching Tool Design Terms
The key to broaching is the design of the broaching tool. A
properly designed tool can lessen the possibility of drift,
deflection, and breakage as well as provide efficiency during
the cutting process. Broach tool design is a specialized type of
manufacturing engineering that involves analysis, planning,
designing, manufacturing, and use of broach tools.
An essential part of a broach is the rise per tooth that
indicates the amount of material each tooth removes on every
pass. The teeth are broken into roughing, semi-finishing, and
finishing sections and can perform internal/interior shaping or
external, surface, or exterior shaping.
Surface Broach Designs
Slab
Slab broaching is the simplest form of broaching and is used to
cut flat surfaces. The process of slab broaching square ends can
provide a surface for future broaching.
Slot
Slot broaching cuts slots of various depths and widths in the
workpiece. In high production operations, slot broaching is
faster and more economical than milling.
Nibbling
Nibbling or egress broaches have narrow roughing teeth
positioned at an angle to the centerline with full width teeth
capable of making semi-finishing cuts.
Contour
Contour broaches cut concave, convex, cam-shaped, contoured, and
irregular surfaces at exceptional tolerances.
Pine Tree
Dovetail or pine tree broaches create forms in compressor wheels
to hold the blades in a turbine disc. This form of broaching
requires several passes due to the nature of the workpiece and
the complexity of the forms.
Pot
Pot broaches cut external forms such as spur gears, splines,
slots, and other tooth forms. The design of pot broaching allows
the deformation to occur in a single pass. Pot broaching has
replaced hobbing in the manufacture of external gears.
Straddle
Straddle broaching uses two slab broaches that cut identical
parallel surfaces on opposite sides of the workpiece in one
pass. The process maintains a precise dimensional relationship
between the two sides.
Internal Broaching
The two types of internal broaching are rotary and vertical;
they are designed to increase the size of a hole in the
workpiece. All internal broaching requires the creation of a
starter hole referred to as blank prepping. Vertical broaching
can be push or pull. Rotary broaching is used when it is
necessary to create an asymmetrical hole in a single pass.
Internal broaches are located on their shank and held in place
by a set screw clamp with a whistle notch.
Shell Broaching
Shell broaches are used for semi-finishing, roughing, and
finishing. Any section of a shell broach can be replaced or
sharpened. When used for finishing, the shell teeth have greater
accuracy than long broach tools.
Round Hole Broaching
Round hole broaching is the simplest of the internal broaches. A
round hole broach has a series of teeth that encircle the tool
with teeth designed to cut the outer edge. With soft ductile
metals, round hole broaches require a chipbreaker.
Keyway Broaching
The keyway broach is one of the more common forms of internal
broaches. A keyway broach cuts a slot in the bore of the
workpiece and is supported by a fixture, referred to as a horn,
which locates where the keyway is to be cut.
Internal Gear Broaching
An internal gear broach nibbles at the internal surface of the
workpiece to generate a gear profile.
Gun Barrel Broaching
A gun barrel broach is very long and capable of moving the full
length of the barrel. It has very fine teeth since barrel
grooves are very minute at a few thousandths of an inch deep.
The broach machine pulls the broach through while rotating it to
produce the spiral rifling pattern in the barrel.
Concentric Broaching
With spline broaching, the pitch diameter has to be concentric.
A concentric broach is a full form finishing tool that has round
and spline teeth to shave the diameter and spline form.
Cut and Recut Broaching
The process of cutting a spline in a thin walled part is
difficult since the walls of the part expand as the broach
passes but then spring back. A cut and recut broach has a
breathing area behind it that prevents the walls from springing
back. The front of the tool cuts the spline and is followed by a
second cutting tool that recuts the cut section.
Square Broaching
Square broaches are used to enlarge, shape, and finish irregular
shapes. Their purpose is to change a round hole into a square
using a rotary broach holder that angles the broach such that
only one corner is being cut at a time. Square holes are for
holding square shafts and can be blind or through cut holes.
Broaching Terminology
A broaching tool is designed to remove metal from a workpiece
using a multi-pointed cutting tool that has several teeth
arranged in rows with each row of teeth being higher than the
previous row. The three sections of a broaching tool are
roughing, semi-finishing, and finishing.
Terminology for a Pull Type of Broaching Tool
Pull End
The pull end connects the broach to the pulling head on the
broaching machine.
Shank
The shank is the part from the bridge to the root diameter that
is held and pulled inside the machine. The length of the tool
from the pull end to the root diameter is known as the shank
length.
Front Pilot
As the name implies, the pilot centers the broach in the hole
that will be broached.
Roughing Teeth
These are the teeth at the front of the broach that make first
contact with the work piece.
Semi-Finishing Teeth
After the roughing teeth come the semi-finishing teeth, which
are smaller and take less of a bite out of the workpiece.
Finishing Teeth
Finishing teeth are the broaching teeth and are all the same
size. They finish the workpiece, taking it to the desired size
and shape of the design for the product.
Rear Pilot
The rear pilot balances the broach and keeps it aligned.
Follower End
The follower end has a function that is similar to the rear
pilot—supporting the elements of the tool.
Push Type Broaching Tool
The push type broaching tool is shorter than the pull type and
experiences compressive forces as it pushes through. Since the
teeth of a push broaching tool are easily broken or bent, they
are reduced in size and smaller than the teeth of a pull through
broaching tool.
The parts of a push through broaching tool are the same as those
for a pull through type.
Terminology for an External Broaching Tool
External or surface broaching removes material from the surface
of the workpiece. As with the pull through and push through
broaches, the teeth for surface broaching increase
progressively.
Land
The land is at the bottom of the teeth and supports the cutting
edge.
Rake
As the broach cuts the workpiece, the chips created by the
cutting move through the rake.
Pitch
The pitch is the distance between the cutting edges of any two
teeth.
Clearance Angle
The clearance angle is the angle of the land in regards to the
horizontal axis, which is designed to prevent friction between
the teeth and the workpiece. It ensures that only the cutting
edge of the teeth are in contact with the workpiece.
Depth
The depth is the height of each tooth.
Gullet Radius
The gullet radius is the radial space between two teeth through
which the chips flow after being curled.
Chipbreaker
Chipbreakers are notches used to eliminate chip packing and
assist in chip removal. They are ground into the roughing and
semi-finishing teeth parallel to the tool axis. Chipbreakers are
staggered such that a set of chipbreakers is followed by cutting
teeth. They are a vital part of round broaching tools keeping
the tools from forming ring shaped chips.
Side Relief
During the broaching of slots, the tool gets enclosed by the
slot during cutting and carries the chips the full length of the
tool. The broach teeth rub the sides of the slot and wear. A
single relief angle on the sides of the teeth reduces wear and
leaves a small portion near the cutting edge.
Chapter Six - Uses for Broaching
Though broaching is an ancient form of machining, it has become
a valuable part of many industrial operations. The latest nuts,
bolts, gears, and other components for aerospace and the
automobile industry depend on broaching to produce precision
reliable parts with exceptional tolerances.
The primary use of broaching is in the production of high volume
parts that need accurate, repetitive, and complex cutting. A
wide variety of metals and materials can be used for the
broaching process. Preferred metals have a hardness on the
Rockwell C hardness rating scale between 26 and 28.
Every type of broaching is different and designed to fulfill the
needs of a specific application. There are areas where broaching
is the best tool for the job, such as cutting parallel and
multiple surfaces, fast cutting, automated cutting,
exceptionally large production runs, and tough hard materials.
Several types of metal shaping operations can be replaced by the
implementation of broaching to save time and use fewer tools.
Any type of metal alloy can be broached, but it works best on
soft metals like aluminum, copper alloys, brass, certain forms
of plastic, wood, and midrange types of steel. Exceptionally
hard materials, such as titanium, can be broached, but the
broaching tool quickly dulls due to the hardness of the metal.
Below are examples of components that are produced for
automobile transmissions using broaching.
A transmission gear for locating clutch plates:
An example of a transmission part produced using push broaching
with the splines and teeth cut in one pass.
The part below is an example of pot broaching of a drive
mechanism that has to be carefully controlled to ensure precise
tolerances.
An example Internal broaching of transmission gears in different
sizes and involute splines.
Though broaching is highly adaptable and capable of performing
multiple machining functions, there are factors that should be
examined before deciding on the process.
The first factor to consider is the surface of the workpiece,
which has to be parallel to the direction at which the broaching
tool moves. Any obstructions, faults, or additional elements on
the surface make it impossible to use broaching since it is a
unidirectional, continuous process.
When there are multiple contours, curves, or angles on two or
more planes, it is impossible for broaching to form them in one
pass except in the case of helical gear teeth.
The material to be broached must be able to endure the force and
stress produced by the broaching process. Parts with thin walls
that are fragile or those with delicate cross sections will not
be able to endure broaching.
Broaching Materials
The best materials for the broaching process are softer,
ductile, and pliable. There are some high tensile strength
steels as well as other hard metals that can be broached. The
primary factors determining if a certain metal can be processed
using broaching is the equipment, tools, and method to be used.
The most common material to be broached is steel; it is used in
a variety of broaching applications. The grade of steel
determines its applicability.
Materials Used in Broaching
Below is a short list of common materials used in broaching.
There are several varieties of plastics and copper alloys as
well as other materials that are shaped using the process.
Broaching tools can be engineered and designed to fit the needs
of any type of material required to meet the needs of an
application.
Brass
Aluminum
Titanium
Stainless Steel
Alloy Steel
12L14 Cold Finish Carbon Steel
Plastic
Cast Iron
Conclusion
Broaching is a machining process where a sharp hardened
toothed tool removes material from a workpiece in a
consistent, continuous, and accurate way.
The broaching process varies according to the portion of the
workpiece that will be broached or cut.
The process of broaching produces parts with exceptional
surface finishes and dimensional accuracy.
Though broaching is an ancient form of machining, it has
become a valuable part of many industrial operations.
The key to broaching is the design of the broaching tool. A
properly designed tool can lessen the possibility of drift,
deflection, and breakage as well as provide efficiency during
the cutting process.
Leading Manufacturers and Suppliers
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