Section 13. qxd

BROACHING
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Section_13.qxd 10/05/06 10:32 Page 13-65

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MACHINING PROCESSES AND MACHINE TOOLS
puller. The threaded connection is used where the broach is not
removed from the drawing head while the workpiece is placed over the
cutter, as in cutting a keyway. In enlarging holes, however, the small end
of the pull broach must first be extended through the reamed, drilled, or
cored hole and then fixed in the drawing head before being pulled
through the workpiece.
Broaching Machines
Push broaching is done on machines of the
press type with a sort of fixture for holding the workpiece and broach
or on presses operated by power. They are usually vertical and may be
driven hydraulically or by screw, rack, or crank. The pull type of broach
may be either vertical or horizontal. The ram may be driven hydrauli-
cally or by screw, rack, or crank. Both are made in the duplex- and
multiple-head type.
Processing Parameters for Broaching
Cutting speeds for broach-
ing may range from 5 ft/min (1.5 m/min) for high-strength materials to
as high as 30 to 50 ft/min (9 to 15 m/min) for aluminum and magne-
sium alloys. The most common tool materials are M2 and M7 high-
speed steels and carbides. An emulsion is often used for broaching for
general work, but oils may also be used.
CUTTING OFF
Cutting off
involves parting or slotting bars, tubes, plate, or sheet by var-
ious means. The machines come in various types such as a lathe (using
a single-point cutting tool), hacksaws, band saws, circular saws, friction
saws, and thin abrasive wheels. Cutting off may also be carried out by
shearing and cropping, as well as using flames and laser beams.
In 
power hacksaws,
the frame in which the blade is strained is recipro-
cated above the workpiece which is held in a vise on the bed. The cutting
feed is effected by weighting the frame, with 12 to 50 lb (55 to 225 N) of
force from small to large machines; adding weights or spring tension
giving up to 180 lb (800 N); providing a positive screw feed or a friction
screw feed; and by a hydraulic feed mechanism giving forces up to 300
lb (1.34 kN) between the blade and workpiece. With highspeed steel
blades, cutting speeds range from about 30 strokes per minute for high-
strength materials to 180 strokes per minute for carbon steels.
Hacksaw 
blades
for hand frames are made 8,10, and 12 in long, 
to
in wide, and 0.025 in thick. Number of teeth per inch for cutting soft
steel or cast iron, 14; tool steel and angle iron, 18; brass, copper, and
heavy tubing, 24; sheet metal and thin tube, 32. Blades for power hack-
saws are made of alloy steels and of high-speed steels. Each length is
made in two or more widths. The coarsest teeth should be used on large
workpieces and with heavy feeds.