The concept of broaching as a legitimate machining process can be traced
back to the early 1850s. Early broaching applications were cutting keyways in
pulleys and gears. After World War 1, broaching contributed to the rifling of
gun barrels. Advances in broaching machines and form grinding during the
1920s and 30s enabled tolerances to be tightened and broaching costs to
become competitive with other machining processes. Today, almost every
conceivable type of form and material can be broached. It represents a
machining operation that, while known for many years, is still in its infancy.
New uses for broaching are being evised every day.
Broaching is a machining operation which uses a toothed tool, called a
broach, to remove material. The broach is used in a broaching
machine, which is also sometimes shortened to broach. It is used when
precision machining is required, especially for odd shapes. Broaching
finishes a surface in a single pass, which makes it very efficient.
Commonly machined surfaces include circular and non-circular holes,
splines, and flat surfaces. Typical workpieces include small to medium
sized castings, forgings, screw machine parts, and stampings. Even
though broaches can be expensive, broaching is usually favorable to
other processes when used for high-quantity production runs.
Broaching is similar to planning, competes with milling and boring, and
gives turning and grinding stiff competition. Properly used, broaching
can greatly increase productivity, hold tight tolerances, produce
precision finishes, and minimize the need for highly skilled machine
a Tooling is the heart of any broaching process. The broaching tool is
based on a concept unique to the process - rough, semi-finish, and
finish cutting teeth combined in one tool or string of tools. A broach
tool frequently can finish-machine rough surface in a single stroke.
In its simplest form, a broach tool resembles a wood rasp. It is a slightly tapering round
or flat bar with rows of cutting teeth located along the tool axis. In advanced forms,
extremely complex cross-sections and tooth designs may be found, However, the basic
axial, multi-toothed tool shape remains
Broach Parts and Process:
The process depends on the type of broaching being performed.
Surface broaching is very simple as either the workpiece is moved
against a stationary surface broach, or the workpiece is held stationary
while the broach is moved against it
Internal broaching is more involved. The process begins by either clamping the workpiece into
the workholder of the broaching machine or the workpiece is placed on a spherical work
holder designed to automatically align the workpiece to the broach. The elevator of the
broaching machine then lowers the pilot of the broach through the workpiece where the
puller engages the broach pilot. The elevator then releases the top of the pilot and the puller
pulls the broach through the workpiece completely. The workpiece is then removed from the
machine and the broach is raised back up to reengage with the elevator.[ The broach usually
only moves linearly, but sometimes it is also rotated to create a spiral spline or gun-
barrel rifling. •
Proper alignment of the broach, workpiece, and ram is the
most important factor in all
broaching operations. Misalignment can cause drifting,
deflection, and even breakage.
Alignment Tips--If a keyway broach drifts and cuts a taper,
try the following:
1. Reverse workpiece or turn broach so teeth face toward
the back of the press.
2. Let the bushing protrude above the workpiece to give
more support to the back of the
broach thereby helping to keep it aligned. If a collared
bushing is used, place it upside down under the workpiece.
3. Make sure the broach is centered under the ram at the
beginning of the cut.
4. If the broach moves out of alignment after starting to
cut, back off the pressure on the ram and align the
broach itself. Repeat during successive cuts to ensure
perfectly straight cuts.
Cutting fluids are used for three reasons
. First, to cool the workpiece and broach
Second, to lubricate cutting surfaces.
Third, to flush the chips from the teeth.
Fortified petroleum cutting fluids are the most common,
however heavy duty water soluble cutting fluids are becoming
Major types of broaching:
Pull broaching - broach is pulled through or across stationary
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.
Various kinds of Broaching machines are today used for
manufacturing of gears some of those are described here:
1-Vertical broaching machine:
Vertical broaching is the type of machine which is
used for broaching a piece part. The Vertical Broaching
Machine comes in various types. All suited to different
adaptations. To give a more specific example, a machine
where there is vertical mounting of ram instead of the
horizontal, can be called as a vertical broaching machine.
2-Horizontal broaching machines:
Horizontal Broaching Machine refers to the
machines that are applied for broaching a piece part. These
were the first line of machines to be used for this process and
still retain its popularity. Horizontal broaching machines are a
popular option to cut internal shapes of the gears.
Advantages of broaching:
advantages of broaching process are:
100 per cent uniform accuracy .
Various contours and complicated irregular shapes can be
easily broached .
Production of broaching is exceptionally high hence
most suitable for mass production .
Broached surfaces are highly accurate in size and shape
hence close tolerances can he maintained .
Short cycle time with high accuracy .
Remarkably finished face .
Expertise not needed.
The broaching process is not limited to only mass
production; some broaching machines are even suitable for
small lots or even pieces production.
Disadvantages Of broaching:
In some cases--not suited for low production rates
Surface to be broached must be accessible
Parts to be broached must be strong enough to withstand
the forces of the process
Broaching tool is too much costly.
The broach tool and the broaching process are versatile
and important and that anyone who works in the field of
metals, woods, or plastics should be familiar with them.