broaching

1. Broaching Machine

2. • BASIC PRINCIPLES OF BROACHINING Broaching is a
machining process for removal of a layer of material
of desired width and depth usually in one stroke by a
slender rod or bar type cutter having a series of
cutting edges with gradually increased protrusion as
indicated in Fig.

3. BROACHING
• Broach is bar type cutter with series of cutting edges
gradually increasing in size to remove all materials in one
stroke.
• In broaching there is only one motion, i.e. the
primary cutting motion is provided by the machine, where
as the feed is obtained by placing the teeth progressively
deeper.
• Since there is no feed motion, the shape of the
broach determines the shape of the machined part.
• Broach is used to produce internal forms like spline holes,
non-circular holes, slots, grooves, gears etc.
• Internal broaching is done by either pulling (or) pushing the
broach through a hole drilled in the work piece. Pulling is
highly preferred to facilitate alignment and avoid buckling.

4. • External forms can also be produced by using
pot broach. Here the broach is made in
segments and fixed inside a fixture called pot
fixture. The broach is stationary but the
W.P. is pulled / pushed through it.

6. Advantages
• Both roughening and finishing operations are completed in one
pass of the tool.
• Any form that can be reproduced on a broaching tool can be
machined by broaching process.
• Rate of production is high, because the actual cutting time is a
matter of few seconds only. Rapid loading and unloading of
fixtures keeps the total production time to minimum.
• Internal and external surfaces can be machined within close
tolerances.
• Accuracy of surface finish is of the order of 0.1 micron.
• The operation of broaching is simple and there exists a possibility
of automating the process.
• Broaches have exceptionally long life since each tooth of a broach
passes through or over the work only once per pass.
• A broad range of materials are successfully broached with proper
broach design and setup conditions.

7. Disadvantages
• The tooling cost is very high and hence broaching process is
adopted only in those places where mass production is required.
• The broaching tool is made for a particular job only and cannot
be easily adopted to a range of applications.
• Surfaces to be broached should not have any obstruction.
• Work-piece to be broached should be rigid and strong to
withstand heavy tool forces encountered during cutting
operation.
• The process of broaching is not recommended for the removal
of large amount of stock and short run jobs.
• All the elements of the broached surfaces must be parallel to
the axis of the travel. Obviously it is not possible to broach the
entire surface of a tapered hole.

8. • ADVANTAGES AND LIMITATIONS OF BROACHING
Major advantages
• Very high production rate (much higher than milling, planing, boring etc.)
• High dimensional and form accuracy and surface finish of the product
• Roughing and finishing in single stroke of the same cutter
• Needs only one motion (cutting), so design, construction, operation and control are
simpler
• Extremely suitable and economic for mass production
Limitations
• Only through holes and surfaces can be machined
• Usable only for light cuts, i.e. low chip load and unhard materials
• Cutting speed cannot be high
• Defects or damages in the broach (cutting edges) severely affect product quality
• Design, manufacture and restoration of the broaches are difficult and expensive
• Separate broach has to be procured and used whenever size, shape and geometry of
the job changes
• Economic only when the production volume is large.

9. Classification
• There are different types of broaching machines which are broadly classified
• According to purpose of use
Δ general purpose
Δ single purpose
Δ special purpose
• According to nature of work
Δ internal broaching
Δ external (surface) broaching
• According to configuration
Δ horizontal
Δ vertical
• According to number of slides or stations
Δ single station type
Δ multiple station type
Δ indexing type
• According to tool / work motion
Δ intermittent (one job at a time) type
Δ continuous type

10. Horizontal broaching machine
• Horizontal broaching machines, typically shown in Fig., are the most
versatile in application and performance and hence are most widely
employed for various types of production. These are used for internal
broaching but external broaching work are also possible. The
horizontal broaching machines are usually hydraulically driven and
occupies large floor space.

11. Vertical broaching machine
• Vertical broaching
machines, typically shown
in Fig.,
occupies less floor space
are more rigid as the ram is
supported by base Δ mostly
used for external or surface
broaching though internal
broaching is also possible
and occasionally done.

12. High production broaching machines
(continuous broaching machine)
• Broaching operation and broaching machines are as such high productive
but its speed of production is further enhanced by;
Δ incorporating automation in tool – job mounting and releasing
Δ increasing number of workstations or slides for simultaneous multiple
production
Δ quick changing the broach by turret indexing
Δ continuity of working
methods of continuous broaching is used for fast production of large number
of pieces by surface broaching.

13. SAWING MACHINE
• Before metal is presented to a machine tool it is usually
cut to some specified length and operation of cutting is
generally performed by sawing.
• Metal sawing is chiefly concerned with cutting bar
stock to convenient length or size for machining.
• In sawing, the individual tooth of the saw tracks
through the work, in each tooth deepening the cut
made by the proceeding teeth in the direction of feed.
Either the saw or work may be fed and, by controlling
the direction of feed, either straight or curved cut can
be produced. The width of cut is approximately equal
to the width of the saw itself.

14. Classification of sawing machines
The sawing machines are broadly classified as:
(i) Band saw,
(ii) Circular saw
(iii) Reciprocating saw

15. Band Saw
• Originally band saw was used for serving work-pieces and doing
rough contour sawing.
• But modern band saw of today is a precision machine capable of
performing a variety of operations quite accurately.
• These machines are more expensive that hack-saw but are capable
of faster cutting because of continuous action.
• Larger number of teeth, only a few in contact with the work at a
given time, allow high surface speeds since the teeth cool off during
their travel.
• A big advantages of band sawing machines is contouring ability and
thus intricate curved shapes can be cut by a combination of hand
and power feeds.

18. Circular saw
• It is called Circular saw as it has a circular blade with inserted teeth
for cutting small or large bars to desired length.
• It has many of the characteristics of an inserted tooth milling cutter,
although it is of much larger diameter.
• It runs at relative slow speed and is very powerful.
• Coolants may or may not be used with this type of saw.

20. Reciprocating Saw
• Several bars may be cut at the same time and continuous attention is not
needed since the saw will shut off automatically when the cut is finished.
• A lubricant is often used for easier cutting action and longer blade life.
• A crank mechanism is provided to raise the blade on each return stroke so that
teeth are not damaged by being dragged backward over the work.
• It is important to note the provision of dash pot mechanism by a cylinder and
piston filled with viscous oil and connected between the base and reciprocating
arm carrying the blade. It avoids the rapid wear of blade teeth, thereby
increasing the blade life.
• It provides a relatively slow and expensive method of cutting.