The Different Types of Design

Adaptive design This is based on existing design, for example, standard products or systems adopted for a new application. Conveyor belts, control system of machines and mechanisms or haulage systems are some of the examples where existing design systems are adapted for a particular use.

Here we start with an existing design but finally a modified design is obtained. A new model of a car is a typical example of a developmental design.This type of design is an entirely new one but based on existing scientific principles. No scientific invention is involved but requires creative thinking to solve a problem. Examples of this type of design may include designing a small vehicle for transportation of men and material on board a ship or in a desert. Some research activity may be necessary.

This is based on empirical formulae which in turn is based on experience and experiments. For example, when we tighten a nut on a bolt the force exerted or the stresses induced cannot be determined exactly but experience shows that the tightening force may be given by P=284d where, d is the bolt diameter in mm and P is the applied force in kg. There is no mathematical backing of this equation but it is based on observations and experience.

These are based on industrial considerations and norms viz. market survey, external look, production facilities, low cost, use of existing standard products.

The knowledge of machine design helps the designers as follows:

1. To select proper materials and best suited shapes.
2. To calculate the dimensions based on the loads on machines and strength of the material.
3. Specify the manufacturing process for the manufacture of the designed component of the machine or the whole machine.

Machine Design is the application of: mathematics, kinematics, statics, dynamics, mechanics of materials, engineering materials, mechanical technology of metals and engineering drawing. It also involves application of other subjects like thermodynamics, electrical theory, hydraulics, engines, turbines, pumps etc. Machine drawing is the integral part of the machine design, since all the components or the machines that have been designed should be drawn to manufacture them as per the specifications. Without machine drawing the subject of machine design is incomplete.

Machine load may be classified as:

1. Static load- Load does not change in magnitude and direction and normally increases gradually to a steady value.
2. Dynamic load- Load may change in magnitude for example, traffic of varying weight passing a bridge. Load may change in direction, for example, load on piston rod of a double acting cylinder.

Design for static loading

Types of loading on machine elements and allowable stresses.

• Concept of yielding and fracture.
• Different theories of failure.
• Construction of yield surfaces for failure theories.
• Optimize a design comparing different failure theories

Machine parts fail when the stresses induced by external forces exceed their strength. The external loads cause internal stresses in the elements and the component size depends on the stresses developed.

Loading may be due to:

• The energy transmitted by a machine element.
• Dead weight.
• Inertial forces.
• Thermal loading.
• Frictional forces.