Friction as an engineering phenomenon is not only an engineering subject but also a fundamental scientific topic. Friction has an important influence in the engineering design especially on assembly and machine working. In order to gain the better understanding of the principle of friction, the friction coefficient between two materials can be defined as the ratio of the tangential force and the normal force. The friction equation has provided the basis for testing friction coefficient and friction force. Besides, there are three basic formulae for determination of friction coefficient of materials which are the Amontons’ friction, Coulombs’ friction, and Woodward’s friction.
One of the most important applications of friction is to reduce the kinetic energy in moving parts of the machine. This is to provide the necessary control and safety measures for the machine work. Therefore, the information of friction coefficient is of great practical importance in designing a machine. It is worth to recall that the knowledge of friction should be worked into the design in order to facilitate the smooth operation and prevent undesired motion. The strategy of controlling friction force should be considered in machine design as well.
Another application of friction is in clutch and brake applications. Because of the controllability of the friction force, brakes and clutches can be designed to be used as precisely controlling devices. Clutches and brakes are the two common types of controlling devices in different applications such as car, airplane, robot and so on. The design of clutches and brakes requires different fundamental principles such as materials selection, coefficient of friction, coefficient of wear, etc. To optimise the design, it is necessary to determine the force required to drive a shaft and the amount of wear generated in the system.
In addition, friction can also improve the wear resistance of some materials by creating a layer of oxides or other compounds on its surface. This layer can form a lubricant film between two materials and reduce the effect of the friction force. An example is the case of bearings which often require lubrication to reduce friction and increase wear resistance. Moreover, this lubrication layer which is generated by using friction can be enhanced by adding some additives into the process of heat treatments.
In conclusion, it is clear that friction is an unavoidable phenomenon in working machines and it is a complex subject which includes both mathematics and engineering principles. The knowledge of friction and frictional characteristics is essential for an engineer to design the working machine. Thus, it is essential to develop a better understanding of friction in engineering design in order to maximize the efficiency of machine work.
