PRODUCT DESIGN

Plastics

The term thermoplastics is used to mean any plastic that flows or is moldable when heat is applied to it; the term is sometimes applied to plastics moldable under pressure. Such plastics can be remolded when heated.

A thermoset is a plastic for which the polymerization process is finished in a hot molding press where the plastic is liquefied under pressure. Thermoset plastics cannot be remolded.

Table 2–2 lists some of the most widely used thermoplastics, together with some of their characteristics and the range of their properties. Table 2–3, listing some of the thermosets, is similar. These tables are presented for information only and should not be used to make a final design decision. The range of properties and characteristics that can be obtained with plastics is very great. The influence of many factors, such as cost, moldability, coefficient of friction, weathering, impact strength, and the effect of fillers and reinforcements, must be considered. Manufacturers’ catalogs will be found quite helpful in making possible selections.

Mechanical Engineering

McGraw−Hill Primis

ISBN: 0−390−76487−6

Text:

Shigley’s Mechanical Engineering Design,

Eighth Edition

Budynas−Nisbett

The Challenges of Product Development

Developing great products is hard. Few companies are highly successful more than half the time. These odds present a significant challenge for a product development team. Some of the characteristics that make product development challenging are:

• Trade-offs: An airplane can be made lighter, but this action will probably increase

manufacturing cost. One of the most difficult aspects of product development is recognizing, understanding, and managing such trade-offs in a way that maximizes the success of the product.

• Dynamics: Technologies improve, customer preferences evolve, competitors introduce new products, and the macroeconomic environment shifts. Decision making in an environment of constant change is a formidable task.

• Details: The choice between using screws or snap-fits on the enclosure of a computer can have economic implications of millions of dollars. Developing a product of even modest complexity may require thousands of such decisions.

• Time pressure: Anyone of these difficulties would be easily manageable by itself given plenty of time, but product development decisions must usually be made quickly and without complete information.

• Economics: Developing, producing, and marketing a new product requires a large investment. To earn a reasonable return on this investment, the resulting product must be both appealing to customers and relatively inexpensive to produce. For many people, product development is interesting precisely because it is challenging. For others, several intrinsic attributes also contribute to its appeal:

• Creation: The product development process begins with an idea and ends with the production of a physical artifact. When viewed both in its entirety and at the level of individual activities, the product development process is intensely creative.

• Satisfaction of societal and individual needs: All products are aimed at satisfying needs of some kind. Individuals interested in developing new products can almost always find institutional settings in which they can develop products satisfying what they consider to be important needs.

• Team diversity: Successful development requires many different skills and talents. As

a result, development teams involve people with a wide range of different training, experience,

perspectives, and personalities.

• Team spirit: Product development teams are often highly motivated, cooperative groups. The team members may be colocated so they can focus their collective energy on creating the product. This situation can result in lasting camaraderie among team members.

References and Bibliography

A wide variety of resources for this chapter and for the rest of the book are available on the Internet. These resources include data, templates, links to suppliers, and lists of publications. Current resources may be accessed via www.ulrich-eppinger.net Wheelwright and Clark devote much of their book to the very early stages of product development, which we cover in less detail. Wheelwright, Stephen c., and Kim B. Clark, Revolutionizing Product Development: Quantum Leaps in Speed, Efficiency, and Quality, The Free Press, New York, 1992. Katzenbach and Smith write about teams in general, but most of their insights apply to product development teams as well. Katzenbach, Jon R., and Douglas K. Smith, The Wisdom of Teams: Creating the High-Performance Organization, Harvard Business School Press, Boston, 1993. These three books provide rich narratives of development projects, including fascinating descriptions of the intertwined social and technical processes. Kidder, Tracy, The Soul of a New Machine, Avon Books, New York, 1981.

Sabbagh, Karl, Twenty-First-Century Jet: The Making and Marketing of the Boeing 777, Scribner, New York, 1996. Walton, Mary, Car: A Drama of the American Workplace, Norton, New York, 1997.

Duration and Cost of Product Development

Most people without experience in product development are astounded by how much time and money are required to develop a new product. The reality is that very few products can be developed in less than 1 year, many require 3 to 5 years, and some take as long as 10 years. Exhibit 1-1 shows five engineered, discrete products. Exhibit 1-3 is a table showing the approximate scale of the associated product development efforts along with some distinguishing characteristics of the products.

The cost of product development is roughly proportional to the number of people on the project team and to the duration of the project. In addition to expenses for development effort, a firm will almost always have to make some investment in the tooling and equipment required for production. This expense is often as large as the rest of the product development budget; however, it is sometimes useful to think of these expenditures as part of the fixed costs of production. For reference purposes, this production investment is listed in Exhibit 1-3 along with the development expenditures.

References and Bibliography

Sabbagh, Karl, Twenty-First-Century Jet: The Making and Marketing of the Boeing 777, Scribner, New York, 1996. Walton, Mary, Car: A Drama of the American Workplace, Norton, New York, 1997.

Copper-Base Alloys, Brass

When copper is alloyed with zinc, it is usually called brass. If it is alloyed with another

element, it is often called bronze. Sometimes the other element is specified too, as, for example, tin bronze or phosphor bronze. There are hundreds of variations in each category.

Brass with 5 to 15 Percent Zinc The low-zinc brasses are easy to cold work, especially those with the higher zinc content. They are ductile but often hard to machine. The corrosion resistance is good. Alloys included in this group are gilding brass (5 percent Zn), commercial bronze (10 percent Zn), and red brass (15 percent Zn). Gilding brass is used mostly for jewelry and articles to be gold-plated; it has the same ductility as copper but greater strength, accompanied by poor machining characteristics. Commercial bronze is used for jewelry and for forgings and stampings, because of its ductility. Its machining properties are poor, but it has excellent cold-working properties. Red brass has good corrosion resistance as well as high-temperature strength. Because of this it is used a great deal in the form of tubing or piping to carry hot water in such applications as radiators or condensers.

Brass with 20 to 36 Percent Zinc

Included in the intermediate-zinc group are low brass (20 percent Zn), cartridge brass (30 percent Zn), and yellow brass (35 percent Zn). Since zinc is cheaper than copper, these alloys cost less than those with more copper and less zinc. They also have better machinability and slightly greater strength; this is offset, however, by poor corrosion resistance and the possibility of cracking at points of residual stresses. Low brass is very

similar to red brass and is used for articles requiring deep-drawing operations. Of the copper-zinc alloys, cartridge brass has the best combination of ductility and strength. Cartridge cases were originally manufactured entirely by cold working; the process consisted of a series of deep draws, each draw being followed by an anneal to place the material in condition for the next draw, hence the name cartridge brass. Although the hot-working ability of yellow brass is poor, it can be used in practically any other fabricating

process and is therefore employed in a large variety of products.

When small amounts of lead are added to the brasses, their machinability is greatly improved and there is some improvement in their abilities to be hot-worked. The addition of lead impairs both the cold-working and welding properties. In this group are low-leaded brass (32 1 /2 percent Zn, 1/ 2 percent Pb), high-leaded brass (34 percent Zn, 2 percent Pb), and free-cutting brass (35 1/2 percent Zn, 3 percent Pb). The low-leaded brass is not only easy to machine but has good cold-working properties. It is used for

various screw-machine parts. High-leaded brass, sometimes called engraver’s brass, is used for instrument, lock, and watch parts. Free-cutting brass is also used for screwmachine parts and has good corrosion resistance with excellent mechanical properties. Admiralty metal (28 percent Zn) contains 1 percent tin, which imparts excellent corrosion resistance, especially to saltwater. It has good strength and ductility but only

fair machining and working characteristics. Because of its corrosion resistance it is used in power-plant and chemical equipment. Aluminum brass (22 percent Zn) contains 2 percent aluminum and is used for the same purposes as admiralty metal, because it has nearly the same properties and characteristics. In the form of tubing or piping, it is favored over admiralty metal, because it has better resistance to erosion caused by highvelocity water.

Brass with 36 to 40 Percent Zinc

Brasses with more than 38 percent zinc are less ductile than cartridge brass and cannot be cold-worked as severely. They are frequently hot-worked and extruded. Muntz metal (40 percent Zn) is low in cost and mildly corrosion-resistant. Naval brass has the same composition as Muntz metal except for the addition of 0.75 percent tin, which contributes to the corrosion resistance.

Mechanical Engineering

McGraw−Hill Primis

ISBN: 0−390−76487−6

Text:

Shigley’s Mechanical Engineering Design,

Eighth Edition

Budynas−Nisbett