Design for Manufacturing

A Structured Approach

Corrado Poli

• Publisher: Butterworth-Heinemann
• Year: 2001
• ISBN:
  9780080503943
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Design for Manufacturing assists anyone not familiar with various manufacturing processes in better visualizing and understanding the relationship between part design and the ease or difficulty of producing the part.

Decisions made during the early conceptual stages of design have a great effect on subsequent stages. In fact, quite often more than 70% of the manufacturing cost of a product is determined at this conceptual stage, yet manufacturing is not involved. Through this book, designers will gain insight that will allow them to assess the impact of their proposed design on manufacturing difficulty.

The vast majority of components found in commercial batch-manufactured products, such as appliances, computers and office automation equipment are either injection molded, stamped, die cast, or (occasionally) forged. This book emphasizes these particular, most commonly implemented processes.

In addition to chapters on these processes, the book touches upon material process selection, general guidelines for determining whether several components should be combined into a single component or not, communications, the physical and mechanical properties of materials, tolerances, and inspection and quality control.

In developing the DFM methods presented in this book, he has worked with over 30 firms specializing in injection molding, die-casting, forging and stamping.

• Implements a philosophy which allows for easier and more economic production of designs
• Educates designers about manufacturing
• Emphasizes the four major manufacturing processes

Chapter 1

Introduction

1.1 MANUFACTURING, DESIGN, AND DESIGN FOR MANUFACTURING

Different uses of the word manufacturing create an unfortunate confusion. Sometimes the word is used to refer to the entire product realization process, that is, to the entire spectrum of product-related activities in a firm that makes products for sale, including marketing (e.g., customer desires), design, production, sales, and so on. This complete process is sometimes referred to as “big-M Manufacturing.”

But the word manufacturing is also used as a synonym for production, that is, to refer only to the portion of the product realization process that involves the actual physical processing of materials and the assembly of parts. This is sometimes referred to as “little-m manufacturing.”

We will use the little-m meaning for manufacturing in this book. In other words, manufacturing here consists of physical processes that modify materials in form, state, or properties. Thus in this book, manufacturing and production have the same meaning. When we wish to refer to big-M Manufacturing, we will call it the product realization process.

Design (as in a design process) is the series of activities by which the information known and recorded about a designed object is added to, refined (i.e., made more detailed), modified, or made more or less certain. In other words, the process of design changes the state of information that exists about a designed object. During successful design, the amount of information available about the designed object increases, and it becomes less abstract. Thus, as design proceeds the information becomes more complete and more detailed until finally there is sufficient information to perform manufacturing. Design, therefore, is a process that modifies the information we have about an artifact or designed object, whereas manufacturing (i.e., production) modifies its physical state.

A design problem is created when there is a desire for a change in the state of information about a designed object. Consequently, a design problem exists when there is a desire to generate more (or better) information about the designed object, when we want to develop a new (but presently unknown) state of information. For a simple example, we may know from the present state of information that a designed object is to be a beam, and we desire to know whether it is to be an I-beam, a box beam, an angle beam, or some other shape. Our desire to know more about the designed object defines a new design problem—in this example, determining the beam’s shape. Later, once we know the shape (say it is to be an I-beam), another design problem is defined when we want also to know the dimensions. There are many kinds of design problems defined by the present and desired future states of information.

Design for manufacturing (DFM) is a philosophy and mind-set in which manufacturing input is used at the earliest stages of design in order to design parts and products that can be produced more easily and more economically. Design for manufacturing is any aspect of the design process in which the issues involved in manufacturing the designed object are considered explicitly with a view to influencing the design. Examples are considerations of tooling costs or time required, processing costs or controllability, assembly time or costs, human concerns during manufacturing (e.g., worker safety or quality of work required), availability of materials or equipment, and so on. Design for manufacturing occurs—or should occur—throughout the design process.

1.2 FUNCTIONAL DESIGNED OBJECTS

We distinguish among the following types of functional designed objects, though not all of them are mutually exclusive: parts, assemblies, subassemblies, components, products, and machines.

Parts

A part is a designed object that has no assembly operations in its manufacture. (Welding, gluing, and the like are considered assembly operations for the purposes of this definition.) Parts may be made by a sequence of manufacturing processes (e.g., casting followed by milling), but parts are not assembled.

Parts are either standard or special purpose. A standard part is a member of a class of parts that has a generic function and is manufactured routinely without reference to its use in any particular product. Examples of standard parts are screws, bolts, rivets, jar tops, buttons, most beams, gears, springs, and washers. Tooling for standard parts is usually on hand and ready for use by manufacturers. Manufacturers, distributors, or vendors often carry standard parts themselves in stock. Standard parts are most frequently selected by designers from catalogs, often with help from vendors.

Special purpose parts are designed and manufactured for a specific purpose in a specific product or product line rather than for a generic purpose in several different products. Special purpose parts that are incorporated into the subassemblies and assemblies of products and machines are often referred to as piece parts. Special purpose parts that stand alone as products (e.g., paper clips, Styrofoam cups) are referred to as single-part products.

Even though screws, springs, gears, and the like, are generally manufactured as standard parts, a special or unique screw, spring, gear, and any other part that is specially designed and manufactured for a special rather than a general purpose is considered a special purpose part. This is not often done, however, because it is usually less expensive to use an available standard part if one will serve the purpose.

Assemblies and Subassemblies

An assembly is a collection of two or more parts. A subassembly is an assembly that is included within an assembly or other subassembly.

A standard module or standard assembly is an assembly or subassembly that—like a standard part—has a generic function and is manufactured routinely for general use or for inclusion in other subassemblies or assemblies. Examples of standard modules are electric motors, electronic power supplies or amplifiers, heat exchangers, pumps, gear boxes, v-belt drive systems, batteries, light bulbs, switches, and thermostats. Standard modules, like standard parts, are generally selected from catalogs.

Products and Machines

A product is a functional designed object that is made to be sold and/or used as a unit. Products that are marketed through retailing to the general public are called consumer products. Many manufactured products are designed for and sold to other businesses for use in the business; this is sometimes called the trade (or commercial, or industrial) market. For example, a manufacturer may buy a pump to circulate cooling water to a machine tool already purchased. In addition, there are products, including especially standard parts and standard modules, that are sold to other manufacturers for use in products being manufactured; this is called the original equipment manufacturer (or OEM) market. An example is the purchase of a small motor for use in an electric fan. Trade marketing is usually done through a system of regional manufacturer’s representatives and distributors.

A machine is a product whose function is to contribute to the manufacture of products and other machines.

1.3 THE PRODUCT REALIZATION PROCESS

Product Realization is the set of cognitive and physical processes by which new and modified products are conceived, designed, produced, brought to market, serviced, and disposed of. That is to say, product realization is the entire “cradle to grave” cycle of all aspects of a product.

Product realization includes determining customers’ needs, relating those needs to company strategies and products, developing the product’s marketing concept, developing engineering specifications, designing both the product and the production tools and processes, operating those processes to make the product, and distributing, selling, repairing, and finally disposing of or recycling the product and the production facilities.

Product realization also includes those management, communication, and decision-making processes that organize and integrate all of the above, including marketing, finance, strategic planning, design (industrial, engineering, detail, and production), manufacturing, accounting, research and development, distribution and sales, service, and legal operations.

Product realization consists of several overlapping stages including product development, industrial design, engineering design, and production design. These are defined in the paragraphs below. Figure 1.1 also provides a supporting illustration for the definitions of these terms.

FIGURE 1.1 View of the product realization process.

Product development is the portion of the product realiz...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• List of Figures
• List of Tables
• Preface
• Acknowledgments
• Responsibilities of Users
• Chapter 1: Introduction
• Chapter 2: Tolerances, Mechanical Properties, Physical Properties—A Review
• Chapter 3: Polymer Processing
• Chapter 4: Injection Molding: Relative Tooling Cost
• Chapter 5: Injection Molding: Total Relative Part Cost
• Chapter 6: Metal Casting Processes
• Chapter 7: Die Casting: Total Relative Part Cost
• Chapter 8: Sheet-Metal Forming
• Chapter 9: Stamping: Relative Tooling Cost
• Chapter 10: Stamping: Total Relative Part Cost
• Chapter 11: Other Metal Shaping Processes
• Chapter 12: Assembly
• Chapter 13: Selecting Materials and Processes for Special Purpose Parts
• Chapter 14: Communications
• Nomenclature
• Index
• About the CD-ROM