GENERAL CONSIDERATIONS IN DESIGNING A MACHINE COMPONENTS
1. Type of load and stresses caused by the load:
The load or force is an external agent which, when applied on a machine part produce or tends to produce/destroy motion. Generally the machine members are subjected to various external forces due to
1. Self weight of the machine.
2. Inertia due to reciprocating parts.
3. Power transmission.
4. Change of nature like temp and other
5. Frictional forces.
The load is classified with respect to its nature of application as
1. Steady or static or dead load: Whose magnitude and direction will not change with respect to time.
2. Live or variable or dynamic load: Whose magnitude and direction change time to time.
3. Suddenly or shock load: Initial velocity is zero.
Ex: Designing a lathe bed require cast iron which is more hard and high compressive strength, for making dial gauge, glass may be employed.
4. Impact load: This is suddenly applied with some velocity.
Ex: blows of hammer, rough road reactions to the wheels and axles of motor cars.
In general the components to be designed or dynamic and impact load should be stronger and bigger than that for steady load.
The load on a machine component may act in several ways due to which the internal stresses are set up: Tensile, compressive, shear, Torsional, Bending, Combined stresses, Thermal stresses.
2. Motion of the parts: Depending upon the given specification the suitable prescribed motion of the part is to be evaluated. The motion of the parts are
(1) Rectilinear motion.(reciprocating)
(2) Curvilinear motion. (rotary)
(3) Constant speed.
(4) Constant or variable acceleration
3. Selection of materials:
The selection of material for a part depends upon the forces that are acting on that part and stresses developed on that part. The design engineer should have a thorough or complete knowledge of the mechanical behavior of materials under different loads.
4. Form and size of the parts:
Based upon the stresses acting on the part, the size and form shape (appearance) of a component is to be designed. In the process of reducing the size of the machine or existing component the design engineer should always check for the capability of that part to resist the stresses. The size is inversely proportional to material strength if the load is kept constant.
|Complex Shape /Form Design|
There is always a lot of heat is dissipated between movable parts
(rotating, sliding or rolling bearings),a design engineer should always provide a better means of lubrication between the parts.
6. Operational features:
The designer should always consider the operational features of the machine. For example the start button, controlling levers, stop button should be designed based upon the convenient handling of the operator.
|Product Should be designed by Considering man machine Relationship i.e. Ergonomics|
7. Use of standard parts:
Using the existing standard parts like bolts, nuts, washers, Gears and pulleys etc Reduces the cost of a machine and also it simplifies the manufacturing process. The designer should always go for selection of available parts of standard sizes; however, if the design requires a new part, then designer has to suggest a new manufacturing process.
|Standard Parts -Nut,Bolt, Gears,Chain|
8. Safety of operation:
Some machines are dangerous to operate at maximum speed. It is necessary that a designer should always provide safety devices for the safety of the operator. The safety appliances should in no way interference with operation of the machine Ex: Electrical main-Switch.
9. Work shop facilities:
The designer has to always design the part based upon his employer’s work shop facilities available to him. Sometimes it is necessary to plan and supervise the work shop operations and to draft methods for casting, handling and machining special parts.
10. Number of components to be manufactured:
Based upon the number of parts to be manufactured, the designer has flexibility in designing the part. If the number of components to be manufactured are less, the designer should always look at using the standard shapes and sizes of parts available to him. However if the number of components to be manufactured are more, he can go for a new product (design) of the part.
11. Cost of construction:
The designer has to always try to minimize the cost of construction of a machine. Use of standard parts and using the manufacturing process available to him can reduce the cost of construction.
12. Maintain Symmetry In Design
Try to maintain Symmetry in parts because it will helpful making design astheticallly Strong.