Page 34 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

General lntroduction

characteristics, capabilities, and limitations of materials, manufacturing processes,
machinery, equipment, and tooling and (2) variability in machine performance, di-
mensional accuracy and surface finish of the workpiece, processing time, and the ef-
fect of processing methods on product quality. Establishing quantitative relationships
is essential in order to be able to analyze and optimize a design for ease of manufac-
turing and assembly at minimum product cost.
The concepts of design for assembly (DFA), design for manufacture and assem-
bly (DFMA), and design for disassembly (DFD) are all important aspects of all manu-
facturing. Methodologies and computer software are now available for design for
assembly, utilizing 3-D conceptual designs and solid models. Subassembly, assembly,
and disassembly times and costs can now be minimized, while product integrity and
performance are maintained. Experience has indicated that a product which is easy to
assemble is usually also easy to disassemble.
Assembly is an important phase of manufacturing and requires a consideration
of the ease, speed, and cost of putting together the numerous individual components
of a product (Fig. 1.4). Assembly costs in manufacturing operations can be substantial,
typically ranging from 20 to 60% of the total product cost. Disassembly of a product
is an equally important consideration, for maintenance, servicing and recycling of
individual components.
As described in Part VI, there are several methods of assembly of components,
including the use of a wide variety of fasteners, adhesives, or joining techniques such
as welding, brazing, or soldering. As is the case in all types of manufacturing, each of
these operations has its own specific characteristics, assembly times, advantages and
limitations, associated costs, and special design considerations. Individual parts may
be assembled by hand or by a variety of automatic equipment and industrial robots.
The choice depends on factors such as product complexity, the number of components
to be assembled, the care and protection required to prevent damage to the surfaces of
the parts, and the relative cost of labor compared with the cost of machinery required
for automated assembly.

Design for Service. In addition to design for assembly and for disassembly, design
for service is important in product design. Products often have to be disassembled to
varying degrees in order to service and, if necessary, repair them. The design should
take into account the concept that, for ease of access, components that are most
likely to be in need of servicing be placed, as much as possible, at the outer layers of
the product. This methodology can be appreciated by anyone who has had the expe-
E;
rience of servicing machinery.

Good
Poor
Poor Good
5
Hs

Parts can Chamfer allows part Difficult to feed-parts overlap Easy to feed
hang up to fall into place
(al (b)

FIGURE l.4 Redesign of parts to facilitate assembly. Source: After G. Boothroyd and
P. Dewhurst.