Page 31 - Analysis and Design of Machine Elements

An Overview of Machine Design
model and prototype built and tested. Since design is an evolutionary process, this 9
iterative process is not unusual. After reiterations of analysis, optimization and evalu-
ation, an optimal solution is finally achieved. The initial tentative design is converted
into a workable product, and a set of detailed production drawings and design docu-
ments are produced to facilitate manufacturing. At this stage, potential manufactur-
ing, assembly and maintenance issues also need to be considered.
4. Manufacturing and commercialization
Once theinitial design hasbeenconverted into theworkableproduct successfully,
practical manufacturing is organized to produce products. A full-scale production
can be launched and products can be sold to customers by both domestic and global
markets. Commercialization also involves customer service and especially warranty.
Finally, service data on failure modes, failure rates, maintenance and safety problems
are collected for future product improvement.
In summary, machine design process includes the first three parts of comprehen-
sive product development process. It aims to reach a compromise through repeated
revision of initial design to fulfil design function, to satisfy design requirements and
practical limitations. The primary focus of this book is on this part of design process,
with proper consideration on manufacturing, material selection and heat treatments
where necessary.

1.3 Machine Element Design

1.3.1 Machine Element Design Considerations
Machine element design is the design of mechanical elements or components. It is a
more focused and an integral part of machine design, consisting of capacity calculation
and structural design. Machine element design employs similar knowledge and skills to
machine design. Since machine elements are the fundamental components of a machine,
each element must be properly designed to facilitate its integration into a machine.
Machine element design must ensure efficient and safe function, with an appropriate
combination of size, shape and material to withstand operating loads for the expected
service life at minimum costs. The considerations of machine element design are simi-
lar to those of machine design, with more concerns on safety, manufacturability, costs,
codes and standards.
The safety and reliability of individual machine elements decide the overall safety and
life expectancy of a machine. The analysis, prediction and prevention of failure form
the basis for the design of machine elements. In the design process, potential failures
are prevented by proper material selection, reasonable assumption and simplification of
operating loads, correct shape and dimension determination through accurate strength,
rigidity and other relevant analyses.
Manufacturing produces elements to the desired dimensional accuracy and surface
finish. Since manufacturing process affects final specifications of overall geometry,
dimensions, tolerances or surface finishes, proper tolerances and acceptable surface
finishes must be specified on design drawings to facilitate manufacturing process selec-
tion [8]. Normally, small tolerances and smooth surfaces increase manufacturing cost
dramatically. Proper clearances and fits also need to be defined for mating elements.