Page 700 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 24.7 Gear Manufacturing by Machining 68|

process. Because only a small portion of the blade is engaged with the workpiece
at any time, the blade itself cools rapidly as it passes through the air. This friction-
sawing process is suitable for hard, ferrous metals and reinforced plastics but not
for nonferrous metals, because of their tendency to stick to the blade. Friction-
sawing disks as large as 1.8 m in diameter are used to cut off large steel sections.
Friction sawing also is commonly used to remove flash from castings.

24.6 Filing

Filing involves the small-scale removal of material from a surface, corner, edge, or
hole-including the removal of burrs. First developed around 1000 B.C., files usually
are made of hardened steel and are available in a variety of cross sections, such as
flat, round, half-round, square, and triangular. Files can have many tooth forms and

grades of coarseness. Although filing usually is done by hand, filing
machines with automatic features are available for high production ir
rates, with files reciprocating at up to 500 strokes/min. f

Band #les consist of file segments, each about 75 mm long, ;.
that are riveted to a flexible steel band and are used in a manner *Q if
similar to band saws. Disk-type files also are available. |
Rotary files and burs (Fig. 2428) are used for such applica- Hignspeed Stem Carbide Rotary
tions as deburring, removing scale from surfaces, producing buf buf me
chamfers on parts, and removing small amounts of material in die
(3) (bi (C)
making. These cutters generally are conical, cylindrical, or spheri-
cal in shape and have various tooth profiles. Their cutting action FIGURE 2418 Types of burs used in bumng
(similar to that of reamers) removes small amounts of material at operationi
high rates. The rotational speed of burs ranges from 1,500 rpm for
cutting steels (large burs) to as high as 45,000 rpm for magnesium
(small burs).

24.7 Gear Manufacturing by Machining

Several processes for making gears or producing gear teeth on various components
were described in Parts ll and Ill: casting, forging, extrusion, drawing, thread
rolling, and powder metallurgy, among others. Blanking of sheet metal also can be
used for making thin gears, such as those used in mechanical watches, clocks, and
similar mechanisms. Plastic gears can be made by such processes as injection mold-
ing and casting.
Gears may be as small as those used in watches or as large as 9 m in diameter,
for rotating mobile crane superstructures. The dimensional accuracy and surface
finish required for gear teeth depend on the intended use. Poor gear-tooth quality
contributes to inefficient energy transmission, increased vibration and noise, and ad-
versely affects the gear’s frictional and wear characteristics. Submarine gears, for ex-
ample, have to be of extremely high quality so as to reduce noise levels, thus helping
to avoid detection.
The standard nomenclature for an involute spur gear is shown in Fig. 24.29.
Starting with a wrought or cast gear blank, there are two basic methods of making
such gear teeth: form cutting and generating.