scope:

PREFACE

AIMS OF THIS BOOK

The overt aim of this book is to present a systematic approach to the design and production of mechanical assemblies. It should be of interest to engineering professionals in the manufacturing industries as well as to post-baccalaureate students of mechanical, manufacturing, and industrial engineering. Readers who are interested in logistical issues, supply chain management, product architecture, mass customization, management of variety, and product family strategies should find value here because these strategies are enabled during assembly design and are implemented on the assembly floor.

The approach is grounded in the fundamental engineering sciences, including statics, kinematics, geometry, and statistics. These principles are applied to realistic examples from industrial practice and my professional experience as well as examples drawn from student projects.¹

It treats assembly on two levels. Assembly in the small deals with putting two parts together. These are the basic processes of assembly, much as raising a chip is a fundamental process of machining. Assembly in the large deals with design of assemblies so that they deliver their required performance, as well as design and evaluation of assembly processes, workstations, and systems.

The sequence of chapters follows the three themes in the book's title: design of assemblies, manufacture of assemblies, and the larger role of assemblies in product development.

Assembly is the capstone process in discrete parts product manufacturing. Yet there is no book that covers these themes. This is very surprising because there are many books about the design and manufacture of machine elements like shafts and gears. But these items do not do anything by themselves. Only assemblies of parts actually do anything, except for a few one-part products like baseball bats and beer can openers. Assemblies are really the things that are manufactured, not parts. Customers appreciate the things products do, not the parts they are made of.

The lack of books on assemblies is reflected in many companies where it is easy to find job descriptions corresponding to the design of individual parts but hard to find job descriptions corresponding to design of assemblies. As one engineer told me, "The customer looks at the gap between the door and the fender. But it's an empty space and we don't assign anyone to manage empty spaces."

There are also many books about tolerances and statistical process control for the manufacture of individual parts, but little or nothing about assembly process capability or the design of assembly equipment to meet a particular level of capability, however it is defined. There are, in addition, many fine books about balancing assembly lines and predicting their throughput, given that there is a competently designed assembly ready to be assembled.

But what is a competently designed assembly and how would we know one if we saw one? This book is directed at that question.

A deeper aim of the book is to show how to apply principles from system engineering to design of assemblies. This is done by exploiting the many similarities between systems in general and assemblies in particular. Students who learn about parts but not about assemblies never get a high-level view of how parts work together to create function, and thus they do not know how to design parts that are intended to contribute to a function in conjunction with other parts. For this reason, they design parts as individual items and are satisfied when they think they have done their individual job well. They are as disconnected from the product they are designing as is the assembly line worker who installs the same part for thirty years without knowing what product is being produced. Products and companies can fail for lack of anyone who understands how everything is supposed to work together.

The systems focus of the book is part of a trend at MIT to complement traditional engineering science with integrative themes that unite engineering with economic, managerial, and social topics.

¹Many of my curious experiences in professional practice are included in footnotes or used as quotes at the beginning of many chapters.