Torque

      It may be defined as the product of force and the perpendicular distance of its line of action from the given point or axis. A little consideration will show that the torque is equivalent to a couple acting upon a body. The Newton’s second law of motion when applied to rotating bodies states, the torque is directly proportional to the rate of change of angular momentum.         

General Procedure in Machine Design

In designing a machine component, there is no rigid rule. The  problem may be attempted in several ways. However, the general procedure to solve a design problem is as follows :

     1. Recognition of need. First of all, make a complete statement of the problem, indicating the need, aim or purpose for which the machine is to be designed.

     2. Synthesis (Mechanisms). Select the possible mechanism or group of mechanisms which will give the desired motion.

     3. Analysis of forces. Find the forces acting on each member of the machine and the energy transmitted by each member.

     4. Material selection. Select the material best suited for each member of the machine.

     5. Design of elements (Size and Stresses). Find the size of each member of the machine by considering the force acting on the member and the permissible stresses for the material used. It should be kept in mind that each member should not deflect or deform than the permissible limit.

     6. Modification. Modify the size of the member to agree with the past experience and judgment to facilitate manufacture. The modification may also be necessary by consideration of manufacturing

to reduce overall cost.

     7. Detailed drawing. Draw the detailed drawing of each component and the assembly of the

machine with complete specification for the manufacturing processes suggested.

     8. Production. The component, as per the drawing, is manufactured in the workshop.

Classifications of Machine Design

The machine design may be classified as follows :

1. Adaptive design. In most cases, the designer’s work is concerned with adaptation of existing

designs. This type of design needs no special knowledge or skill and can be attempted by designers of

ordinary technical training. The designer only makes minor alternation or modification in the existing

designs of the product.

2. Development design. This type of design needs considerable scientific training and design

ability in order to modify the existing designs into a new idea by adopting a new material or different

method of manufacture. In this case, though the designer starts from the existing design, but the final

product may differ quite markedly from the original product.

3. New design. This type of design needs lot of research, technical ability and creative thinking. Only those designers who have personal qualities of a sufficiently high order can take up the

work of a new design.

The designs, depending upon the methods used, may be classified as follows :

(a) Rational design. This type of design depends upon mathematical formulae of principle of

mechanics.

(b) Empirical design. This type of design depends upon empirical formulae based on the practice

and past experience.

(c) Industrial design. This type of design depends upon the production aspects to manufacture

any machine component in the industry.

(d) Optimum design. It is the best design for the given objective function under the specified

constraints. It may be achieved by minimising the undesirable effects.

(e) System design. It is the design of any complex mechanical system like a motor car.

(f) Element design. It is the design of any element of the mechanical system like piston,

crankshaft, connecting rod, etc.

(g) Computer aided design. This type of design depends upon the use of computer systems to

assist in the creation, modification, analysis and optimisation of a design.