What is Machine Design?
Machine design is the process of selection of the material, shape, size, and arrangement of mechanical element so that the resultant machine will perform the prescribed task.
Machine design procedure
1) Recognition of need :- Make complete statement of the problem, indicating the need, aim or purpose for which the machine is used.
2) Synthesis (Mechanisms) :- Selection of possible mechanism and desired motion required.
3) Analysis of forces :- Finding the forces acting on each member of the machine and energy transmitted by each member.
4) Material selection :- Selection of material according to force transmission, availability, cost and environment condition. So best suitable material for each member of the machine is selected.
5) Design of element :- Find the size of each member of the machine by considering the forces acting on the member and permissible stresses for the material used and care must be taken that they should not bend, deflect or deform than the permissible limit.
6) Modification :- Modification is necessary by consideration of manufacturing to reduce overall cost modification of size of the member to agree with the past experience and judgement to facilitate manufacture.
7) Detail drawing :- Detail drawing of each component with tolerance and the assembly of the machine with type of fits and specification for the manufacturing processes suggested.
8) Production :- The prototype model is prepared, tested and if satisfactory then final drawing will be issue for the production department for manufacturing the product in workshop.
General Consideration in Machine Design
Type of load and stresses
The various types of load will be acts on the machine component and due to this internal stresses are set up load just like steady load, fluctuating load etc.
Motion of parts or kinematics of the machine
Successful operation of any machine depends on the arrangement of the parts which transmit required motion i.e. reciprocating rotary, oscillatory SHM, etc.
Selection of material
The designer must have the knowledge of properties of material and their behaviour under working condition i.e. strength, flexibility, durability etc.
Shape and size of the parts
The shape and size are based on judgement for calculation only cross-section and checked that stresses induced in the designed cross-section are reasonably safe. It is necessary to know the forces which the part must sustain and also about the type of load due to failure occure.
Frictional resistance and lubrication
Careful attention is given on loss of power due to friction as at starting friction is higher than in running condition. So proper lubrication of all surface which moves relative to one another i.e. rolling, sliding etc.
Convenient and economic future
The operating future must be carefully studied. Starting, controlling, and stopping level must be provided for convenient handling. Replacement or change of part due to wear or breakage, easy accessable and necessity of removing parts to accomplish this should be avoided.
The economic operation of a machine which is to be used for production, or processing of material should be studied, whether it has the maximum capacity consistent with the production of good work.
Use of standard parts
The use of standard part is closely related to cost because the cost of standard or stock parts is only a fraction of the cost of similar parts has to made by order.
Safety of operation
Some machine are dangerous to operate especially high speed to insure production at a maximum rate. Any moving part of a machine which is within a zone of worker is considered an accident for designer to provide a safety device for the safety of operator.
Workshop facilities
A designer must know the limitation of employer worker. So complete work is carried out in own workshop. A designer must plan and supervise the workshop operation to draft method for casting, handling and machining special parts.
Number of machines to be manufactured
The number of product to be manufactured affected the design in a number of ways. The engineers and shop cost called fixed cost or overhead expenses are distributed over the number of articles to be manufactured.
Cost of construction
It is most important factor in design. If the article has been invented or tested and it has commercial value, it is then possible to justify the expenditure of money in design, development of automatic machine to produce the product. So it can sold in large number. The aim of design engineer is to reduce the manufacturing cost to the minimum.
Assembling
Every machine or structure must be assembled as a unit before it can function. Large unit are assembled in shop tested and then transport to the servece place. The final location is important for local facilities for erection.