 Hello students, I am Bhargesh Deshmukh, Professor of Mechanical Engineering Department at Palchini Institute of Technology, Sholapur. My today's session is on design of springs, the course is Machine Design 1. At the end of this session, you will be able to identify the typical applications of the spring, and will be able to differentiate various terms related to the spring geometry. What is spring? A spring is defined as an elastic machine element which deflects under the action of the load and returns to its original shape when the load is removed. The latter part of the statement is important, returns to its original shape when the load is removed. If it is not written into its original shape, then it is not a spring, it is not an elastic deformation, it is a plastic deformation. Spring has to have elastic deformation. What are the typical applications of the spring? The springs are used in the shock absorbers and vibrations. For example, the vehicle suspension spring, railway buffer springs, buffer springs used in elevators and the vibration mounts for heavy machinery. Another type of spring used is for storing the energy. The springs used in clock, toys, movie cameras, circuit breakers and starter. The third type of use of spring is to use it in the measuring instruments for force, weighing balances and scales. Now some typical applications of the spring. Springs are also used to apply the force and to control the motion. We know in the cam and follower mechanism, spring is used to maintain the contact between the two elements. If spring is not present, there may not be the contact of the two machine elements. In engine valve mechanism, spring is used to return the rocker arm to its normal position when the disturbing force is removed. Third application, the spring used in clutches that provides the required force to engage the clutch. When you press the clutch lever, you disengage the clutch. It is against the spring force. Let us see some types of springs, types of helical springs. The helical spring is made from wire, usually of circular cross section. That has to be bent to form a helix. Two types of typical helical springs are compression helical spring and extension helical spring. For compression helical spring, you can see that the force is compressive, the first sketch and the second one extension, the force is of pull type. Typical advantage of helical springs, these springs are easy to manufacture, then cheaper than the other types of springs. Reliability is high, deflection of the spring is linearly proportional to the force acting on the spring. This is very advantageous. Types of springs, these are helical torsion springs. A helical torsion spring is similar to that of the compression or extension spring except that its ends are formed in such a way that the spring is loaded by a torque about its axis of motion. Helical torsion springs, it is used to transmit the torque to a particular component in the machine or the mechanism. Another type of spring is multi-leaf or laminated spring. We have seen this spring generally in the rear axle of the truck. A multi-leaf or laminated leaf spring consists of a series of flat plates, usually of semi elliptical shape as shown in the figure. The flat plates called as leaves having various lengths. The leaves are held together by means of U-bolts and a center clip. The longest leaf is called as a master leaf. It is bent at the two ends to form the spring eyes. And the spring eyes are connected to the chassis by means of a shackle. The leaves of multi-leaf spring are subjected to bending stresses. Multi-leaf springs are widely used in automobile and lateral suspensions. You can think about the applications of spring that you see into your day-to-day life. List down the identified applications. Now the important part, the terminology of the helical springs. Helical spring is subjected to compressive force. Small D is the wire diameter of the spring. DI is the inside diameter of the spring. DO is the outside diameter of the spring coil. And D, which is important, it is the mean coil diameter of the spring. The mean coil diameter is given as average of the outside and inside diameter. You can see the terms mean coil diameter. Then small D, which is the wire diameter. DI and DO, we have mentioned it. Another important term is spring index. It is denoted as letter C. The spring index is defined as capital D upon small D. Capital D is the nominal diameter. And small D is the wire diameter of the spring. Now what is the significance of the spring index? If the spring index is low, is it below 3, then the actual stresses in the wire are excessive due to the curvature effect. If it is high, that is more than 15, it results in large variation in the coil diameter. Spring index from 4 to 10 is considered to be the best from manufacturing considerations. C in the range of 6 to 9 is still preferred. Solid length. If we compress the spring fully, it provides a solid length. You can see that all the adjacent coils are touching each other. Solid length in that case is given as NT. It is number of total turns or number of coils. Multiplied by D is the wire diameter. Compressed length. It is the axial length of the spring. You can see that this is the axis of the spring. Axial length of the spring which is subjected to maximum compressive force. The force over here is the maximum force. We can get maximum deflection delta in that case. Some gap or clearance between the adjacent coil is essential to prevent the clashing of the coils. Usually 15% of the maximum deflection is the total clash allowance provided to the spring. Total gap we can calculate. Total gap is total number of turns minus 1 into the gap between the adjacent coils. You can see that here is a gap between the adjacent coils. Every coil has an adjacent gap. The next is the free length of the spring. The axial length of the spring in unloaded condition is called as the free length of the spring. There should not be any external force acting on the spring. It is the length of the spring in free condition prior to assembly. It is very important term. Total deflection can be seen over a total length and total possible deflection. We can calculate according to this length. Free length is given as compress length plus delta. Delta is the total deflection. Or we can say that it is solid length plus total axial gap plus deflection delta. Next term is pitch of the coil and the stiffness. What is pitch of the coil? Pitch is the axial distance between the adjacent coils in the uncompressed state of spring. You can see that pitch it is the adjacent distance between two coils. We can see here delta. Pitch is given as free length Lf divided by Nt minus 1. Next part is the stiffness of the spring. Stiffness of the spring is defined as the force required to produce unit deflection. It is given as K equals P by delta. The reference for this section is design of machine learning by Bandari. I thank you for patiently listening.