Page 30 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

General Introduction

reduced by as much as 25% (because of the increased The next step involves attaching the metal base
heat due to the higher electrical resistance of the wire). to the glass bulb with a special cement. The machine
Note from Fig. I.2a, as well as by direct that performs this operation also solders or welds the
obsevation of a clear light bulb, that the filament wire lead-in wires to the base, to provide the electrical
is coiled; this is done in order to increase the light- connection. The lead-in wires are usually made of
producing capacity of the filament. The spacing nickel, copper, or molybdenum, and the support wires
between the coils must be precise, so as to prevent a are made of molybdenum (Section 6.8). The portion
localized buildup of heat that might short the filament of the lead-in wire that is embedded in the stem is
during its use. made from an iron-nickel alloy, which has essentially
The completed stem assembly (called the mount) the same coefficient of thermal expansion as that of
is transferred to a machine that lowers a glass bulb the glass (Table 3.1), as otherwise the thermal stresses
over the mount. Gas flames are used to seal the rim of that develop may cause cracking of the glass stem. The
the mount to the neck of the bulb. The air in the bulb bulb base is generally made from aluminum, replacing
is then exhausted through the exhaust tube (which is the more expensive brass base that was used many
an integral part of the glass stem), and the bulb is years ago. To reduce friction and thus allow easy
either evacuated or filled with inert gas. For 40~W insertion of the bulb into a socket, the metal base is
bulbs and higher, the gas used is typically a mixture of coated with a special compound.
nitrogen and argon. The exhaust tube is then sealed. Several types of glasses (Section 8.4) are used,
The filling gas must be pure, as otherwise the inside depending on the bulb type. The bulbs are made by
surfaces of the bulb will blacken. It has been observed blowing molten glass into a mold (Section 18.3.3).
that just one drop of water in the gas that is used The inside of the bulb either is left clear or is frosted
for half a million bulbs will cause blackening in all (thus making it translucent), to better diffuse the light
of them. and to reduce glare.

l.2 Product Design and Concurrent Engineering

Product design involves the creative and systematic prescription of the shape and
characteristics of an artifact to achieve specified objectives while simultaneously sat-
isfying several constraints. Design is a critical activity, because it has been estimated
that as much as 80% of the cost of product development and manufacture is deter-
mined by the decisions made in the initial stages of design. The product design
process has been studied extensively; it is briefly introduced here because of the
strong interactions between manufacturing and design activities.
Innovative approaches are essential in successful product design, as are clearly
specified functions and a clear statement of the performance expected of the product,
which may be new or a modified version of an existing product. The market for the
product and its anticipated use(s) also must be clearly defined; this aspect involves the
assistance of market analysts and sales personnel who will bring valuable and timely
input to the manufacturer, especially regarding market trends.

The Design Process. Traditionally, design and manufacturing activities have taken
place sequentially, as shown in Fig. l.3a. This methodology may, at first, appear to
be straightforward and logical; in practice, however, it is wasteful of resources.
Consider the case of a manufacturing engineer who, for example, determines that,
for a variety of reasons, it would be more desirable (a) to use a different material,
such as a polymer or a ceramic, instead of a metal or (b) to use the same material,
but in a different condition, such as a softer instead of a harder material or a