First Year Engineering Basic Mechanical Engineering Design Consideration

1. Unit No. – 2
Design Considerations

2. An assembly of interconnected components arranged to
transmit or modify force in order to perform useful work.
An assembly of interconnected components arranged to
transmit or modify force in order to perform useful work.
Definition of Machine:Definition of Machine:
It is defined as the use of scientific principles, technical
information and imagination in the description of a machine or
a mechanical system to perform specific functions with
maximum economy and efficiency.
It is defined as the use of scientific principles, technical
information and imagination in the description of a machine or
a mechanical system to perform specific functions with
maximum economy and efficiency.
Definition of Machine Design:Definition of Machine Design:
The description of a mechanical system is in form of drawings,
which specify the material selected, shapes and sizes and
arrangements of mechanical elements to perform the
prescribed task.
The description of a mechanical system is in form of drawings,
which specify the material selected, shapes and sizes and
arrangements of mechanical elements to perform the
prescribed task.

3. The design will help to optimize the geometrical, material and
performance parameters of the product or system.
The proper designing of the product helps in reducing cost of
the product and make it competitive.
The product or system is designed to ensure no failure during
specified life of the product.
The product or system is designed to perform a prescribed task
satisfactorily.

4. Design & redesign helps in incorporating new ideas into the
product.
A better appearance can attract customers even if a product
with identical parameters exist in the market.
Proper design will provide more comfort to the user, or it can
be more user friendly.
Proper designing helps in reducing the size and weight of the
product or system.

5. It is design of any mechanical element which is a part of
mechanical subsystem or product. Ex: Gear, shaft, etc.
It is design of a product which is a subsystem of any mechanical
system. Ex: Design of Gearbox etc.
It is design of any complex mechanical system, which consist of
number of subsystem, which further contain elements.

6. Computer system is used to assist in the creation, modification,
analysis and optimization of a design.
For any problem number of design solutions are available.
From the available solutions, that which minimizes undesirable
effects and maximizes useful parameters is called optimum
design.
It is design using empirical formulae/relations that are based on
past experience and practices. Used when design equations are
not available or complex. Ex: Gearbox casing, etc.

8. The forces acting on each element is determined drawing the
free body diagram (FBD) of each element of the machine.
Synthesis involves selecting/creating the mechanism for the
machine and the shape of the mechanical elements so as to get
desired output with the given input.
The problem is defined giving all input parameters, output
parameters and constraints.

9. Based on the application, the factor of safety and material
strength is selected and hence the permissible stresses
determined.
Identify the mode of failure of the element if put to use
because of the influence of the forces.
A suitable material is selected considering its availability, cost,
mechanical properties and manufacturing considerations.

10. Working drawing of each element is prepared with minimum
two views showing details like dimensions, and its tolerance,
surface finish, geometrical tolerance, etc.
Modify the dimensions of the element on the higher side, if
required based on selection of standard parts available in
market , convenience of assembly & manufacturing.
The dimensions of each element is determined by considering
the forces and the permissible stresses.

11. The design report is prepared containing details about step 1 to
step 8.

12. Since the machine is subjected to a combination of various
loads, it should have sufficient strength to avoid failure due to
yielding or fracture (failure) under the loads.
An element should have sufficient rigid so that its linear as well
as angular deflections under loading are within limits.
A machine element should have reasonably good probability so
that it can perform its function satisfactorily over its life span.

13. A machine element should be designed such that it ensures
safety of the users and machine.
The life cycle cost (made up of production cost, operating cost,
maintenance cost, disposal cost) should be minimum possible.
A machine element should have a minimum possible weight.
Ergonomics is a scientific study of man-machine-working
environment relationship to solve problems arising from the
same. A machine should be designed with ergonomic criteria.

14. Aesthetic deals with appearance of product (a major factor in
attracting customers if products have identical parameter).
The manufacturing process should be so selected to produce a
machine element in minimum cost and available facilities.
A machine element should conform to national/international
standards and codes.
A machine element should minimize assembly cost and time.

15. A machine element should be designed for adequate life.
A machine element should be designed to keep vibration levels
minimum.
Due consideration must be given for lubrication of elements, if
there is relative sliding or rolling motion between elements.
A machine element should be such that it can be easily repaired
or serviced.