Broaching & Sawing
Processes
Broaching
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Broaching is the process of removing metal
with a tool which has “teeth” arranged in a
row. Each tooth is successively higher than
the previous tooth and removes more material.
In broaching, one stroke or cycle of the
machine produces a finished part.
Broaching is used to produce both internal and
external features. Production rates are high
and tolerances of +/- .0005” are possible.
Broaching
Broaching
Broaching
Broaching
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Chip Formation
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Chip formation involves three basic requirements:
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The cutting tool must be harder than the part
material
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There must be interference between the tool and the
part as designated by the feed rate and cut per tooth
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There must be a relative motion or cutting velocity
between the tool and workpiece with sufficient force
to overcome the resistance of the part material.
Broaching
Tool Feed Direction
Gullet
Depth of
cut per tooth
Workpiece
Tool
Broaching
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Chip Formation
 As long as these three conditions exist, the portion of
the material being machined that interferes with the free
passage of the tool will be displaced to create a chip.
 Many combinations exist that may fulfill such
requirements.
 Variations in tool material and tool geometry, feed and
depth of cut, cutting velocity, and part material have an
effect not only upon the formation of the chip, but also
upon cutting force, cutting horsepower, cutting
temperatures, tool wear and tool life, dimensional
stability, and the quality of the newly created surface.
Broaching
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The Mechanics of Chip Formation
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Empirical metal-cutting studies reveal several important
characteristics of the chips formed during the broaching
process:
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The cutting process generates heat
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The thickness of the chip is usually greater than the thickness
of the layer from which it came
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The hardness of the chip is usually much greater than the
hardness of the parent material, and
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The other three relative values are all affected by changes in
cutting conditions and in properties of the material to be
machined
Broaching
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The Mechanics of Chip Formation
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These observations also indicate that the
process of chip formation is one of
deformation or plastic flow of the material,
with the degree of deformation dictating the
type of chip that will be produced.
Broaching
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Plastic Deformation
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Originally, it was thought that chips formed in
metal cutting were created in much the same
way that wood chips are formed when split by
an axe. This may be partially true for brittle
materials such as cast iron, but it does not hold
true for the majority of metals. The process by
which chips are formed with metal-cutting tools
is called plastic deformation, and was first
described by Rosenhain at the Stratsfordshire
Iron and Steel Institute in 1906.
Broaching
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Plastic Deformation
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What actually happens in this shearing process is that
the metal immediately ahead of the cutting edge of the
tool is severely compressed resulting in temperatures
high enough to allow plastic flow.
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When the resisting stresses in a material exceed their
elastic limit, a permanent relative motion occurs and
further deformation is withstood.
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This strengthening is called work or strain hardening,
and is characteristic of all steels, but demonstrated most
dramatically in stainless steels.
Broaching
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How and Where Heat is Generated
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The force or energy that is put into the tool creates
movement in a group of metal atoms in the workpiece.
This group is a finite number of atoms which are forced
to change their positions in relationship to each other.
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As the atoms in the metal ahead of the tool are
disturbed, the friction involved in their sliding over one
another is thought to be responsible for 60% or more of
the total heat generated.
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This internal friction, and the heat it generates, can be
compared to the friction and heat caused by bending a
paper clip back and forth until it breaks.
Broaching
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How and Where Heat is Generated
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As the tool continues to push through the work piece, a chip
eventually slides up the cutting face of the tool. This sliding creates
an external friction which again releases heat. This external friction
accounts for about 30% of the total heat generated.
The third area of heat generation is on the land or flank of the tool.
This area accounts for about 10% of the heat generated. This is
assuming that the tools are sharp and made correctly as far as
clearance angles and face angles are concerned. As the tool wears,
the above percentages will vary, especially when there is excess
wear on the land, or if the clearance angle is insufficient for the
material or the part configuration. This contact zone will actually
increase as the part continues to close in after the cut resulting in
extremely high pressures on the land area of the tool.
Advantages & Disadvantages
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Advantages
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Rough to finish in one pass
Production rates are high
Cutting time is quick
Rapid load and unload of parts
External and internal features
Any form that can be produced on a broaching tool can
be produced
Production tolerances are excellent
Surface finishes are equal to milling
Operator skill is low
Advantages & Disadvantages
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Disadvantages
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Tooling cost can be high
In some cases--not suited for low production rates
Parts to be broached must be strong enough to withstand
the forces of the process
Surface to be broached must be accessible
Methods of Operation
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Pull broaching - broach is pulled through or across
stationary work
Push broaching - broach is pushed through or
across work
Surface broaching - either the work or the broach
moves across the other
Continuous broaching - the work is moved
continuously against stationary broaches. The path
of the movement may be straight or circular.
Machines
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Vertical single and double slide - Table moves part
into position for broaching, part is broached and
the table retracts for unloading.
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Vertical push broaching - Used for internal features such
as holes, rounds, or slots.
Vertical pull down
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Tool is suspended above work
Lowered into pull mechanism in the base of the machine
Advantages
 Part positioning is easy
 Large parts are handled efficiently
Machines
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Vertical single and double slide
Machines
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Horizontal
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Versatile machine capable of producing internal and
external features
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key-ways
gear teeth
riffling
High cutting speeds in the range of 10-40ft/min
with return speeds of 110 ft/min
MRR of ¼ in per stroke is possible
Methods of Operation
Machines
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Horizontal
Machines
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Rotary
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Parts are mounted to a rotating table and are moved to
different stations for different operations
Primarily used on small parts
Typical operations include:
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Slotting
Holes
Key-ways
Broaching Tools Design &
Construction
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Considerations
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Material to be broached
Size and shape of cut
Quality of surface finish
Part tolerance
Productions rates
Type of machine
Workholding method
Strength of the workpiece
Sawing
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Depending on part tolerance, sawing can be a
vital first operation or the total process.
Machines Classifications
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Reciprocating saws
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Horizontal hacksaw and
vertical sawing machines
Light to heavy duty
Simple and most
economical to operate
Manual to fully automatic
feed mechanisms
Uses blades similar to
hacksaw blades
Machines Classifications
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Circular saws
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Sometimes called cold
sawing machines
Saw blades are large
and rotate at low Rpms
Cutting is similar to a
milling operation due to
geometry of saw blade
Machines Classifications
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Band saws
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Irregular shapes
Very versatile
Profile cuts
Internal cuts
external configurations
Blades are continuous
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HSS - Carbide tipped
Diamond impregnated
Filing
Machines Classifications
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Band saws
2
1
3
Saw Blades
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Circular
Straight
Band
Saw Blades
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Terminology
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Set of the blade - Directional offset, left-right, from the
blades centerline. Sometimes referred to as the “kref.”
The kref provides clearance for the blade as it cuts
through the work.
Straight - one tooth left one tooth right. Typically used
for brass, copper, and plastic.
Raker - Three tooth sequence, left, right, straight.
Typically used for steel and cast iron.
Wavy - Alternate arrangement of several teeth to the
right and left. Used to cut tubes and light sheet metal.
Saw Blades
Saw Blades
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Tooth forms
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Variable positive
Variable
Standard
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