Page 58 - Robotics Designing the Mechanisms for Automated Machinery

2.2 How Does One Find the Concept of an Automatic Manufacturing Process? 47

1. Cutting, first of the body of the wheel and next of the teeth. In turn, there are at
least four ways to cut the teeth: by gear cutter, gear hob, gear shaping, or pinion-
shaped gear cutter.
2. Casting, either of the body (the teeth being cut) or of the whole wheel. In turn,
this can be (depending upon the material): loam or sand mold casting, metal
(chill) mold casting, machine molding, lost-wax process or investment casting,
die casting, or precision casting.
3. Manufacturing by powder metallurgy.
4. In some special cases—sheet metal stamping.
5. Knurling the teeth on a blank made of corresponding alloy.
Of course, the choice of an appropriate processing method depends on design
requirements and restrictions (and vice versa). Thus the choice of a material will be
dictated by strength, durability, accuracy, and other special conditions; obviously, if
surface and accuracy call for grinding and superfinishing, operations which meet these
requirements will have to be selected. However, as a rule the restrictions imposed by
design do not detract from the point made above.
Finally, the third approach to the search for manufacturing concepts involves sci-
entific or engineering research. This situation arises when:
• A completely new product is under consideration and no prototypes can be
found in any technical field or industry;
• The existing prototypes of the processing techniques are too slow, too expen-
sive, yield unsatisfactory quality, or require inaccessible materials or techniques.
To illustrate the first case, consider the following examples. Laser-beam machin-
ing is based on melting or vaporizing the cut material along the seam with an intense
beam of light from a laser. Such beams can also be used to produce small-diameter
holes. Direction and control of the beam is relatively easily accomplished by a com-
bination of optics and computer techniques. This technology has only recently been
introduced into industry and has opened new economic and industrial vistas. For
instance, thanks to the absence of mechanical contact between tool and blank, the
deformation is minimal, thus improving the accuracy of the product. The holes can
be produced under any inclination (which is difficult to achieve by drilling). The
absence of inertia and the electrical nature of the tool makes the process susceptible
to electronic control and therefore very swift and accurate.
Electrical-discharge machining introduced an effective method of processing holes
and cavities of almost any shape in almost any sort of metal regardless of hardness. This
is of great importance in the manufacture of dies and molds. Another advantage of
this method is that it is practically the only way to produce a hole with an arched axis.
This technique involves direction of high-frequency electrical spark discharges from
a metal or graphite tool. The tool serves as one electrode while the blank is the other
electrode, both electrodes being immersed in dielectric liquid. A special mechanism
maintains a spark gap of about 0.015 to 0.5 mm. Spark discharges melt or vaporize
small parts of the blank under processing. This technology makes it possible to carry
out processing which earlier required special complications in design, as illustrated
by Figure 2.11. To get an opening of the form shown here using the old technology, the
part had to be made in two sections (Figure 2.lib). The tool produces the opening by
a rotating movement around its center, thus providing the needed curvature.