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The actual practice of designing is applying a combination of scientific principles and a knowing judgment based on experience. It is seldom that a design problem has only one right answer, a situation that is seemingly best one being chosen.
The actual practice of designing is applying a combination of scientific principles and a knowing judgment based on experience. It is seldom that a design problem has only one right answer, a situation that is often annoying to the beginner in machine design.
Design problems usually have more than one answer. Given a general statement of a design problem, such as design a machine to wash clothes in the home automatically, and there will be as many different answers as there are design teams--as attested by the number of washing machines on the market.
Engineering practice usually requires compromises. Competition may require a reluctant decision contrary to one's best engineering judgment; production difficulties may force a change of design; etc.
A good designer needs many attributes, for example:
(1) A good background in strength of materials, so that the stress analyses are sound. The parts of the machine should have adequate strength and rigidity, or other characteristics as needed.
(2) A good acquaintance with the properties of materials used in machines.
(3) A familiarity with the major characteristics and economics of various manufacturing processes, because the parts that make up the machine must be manufactured at a competitive cost. It happens that a design that is economic for one manufacturing plant may not be so for another. For example, a plant with a well-developed welding department but no foundry might find that welding is the most economic fabricating method in a particular situation; whereas another plant faced with the same problem might decide upon casting because they have a foundry (and may or may not have a welding department ).
(4) A specialized knowledge in various circumstances, such as the properties of materials in corrosive atmospheres, at very low ( cryogenic ) temperatures, or at relatively high temperatures.
(5) A preparation for deciding wisely: (a) when to use manufacturer's catalogs, buying stock or relatively available items, and when custom design is necessary; (b) when empirical design is justified; (c) when the design should be tested in service tests before manufacture starts; (d) when special measures should be taken to control vibration and sound ( and others ).
(6) Some aesthetic sense, because the product must have "customer appeal" if it is to sell.
(7) A knowledge of economics and comparative costs, because the best reason for the existence of engineers is that they save money for those who employ them. Anything that increases the cost should be justified by, for instance, an improvement in performance, the addition of an attractive feature, or greater durability.
(8) Inventiveness and the creative instinct, most important of all for maximum effectiveness. Creativeness may arise because an energetic mind is dissatisfied with something as it is and this mind is willing to act.
Naturally, there are many other important considerations and a host of details. Will the machine be safe to operate? Is the operator protected from his own mistakes and carelessness? Is vibration likely to cause trouble? Will the machine be too noisy? Is the assembly of the parts relatively simple? Will the machine be easy to service and repair?
Of course, no one engineer is likely to have enough expert knowledge concerning the above attributes to make optimum decisions on every question. The larger organizations will have specialists to perform certain functions, and smaller ones can employ consultants. Nevertheless, the more any one engineer knows about all phases of design, the better. Design is an exacting profession, but highly fascinating when practiced against a broad background of knowledge.