Interchangeability:
An
interchangeable part is one which can be substituted for similar part.
When
one component assembles properly with any mating component, both chosen at
random, then it is known as interchangeability
For Example:
- we have 100 parts each with a hole and 100 shafts which have to fit into these holes. If we have interchangeability then we can make any one of the 100 shaft & fit it into any hole & be sure that the required fit can be obtained.
- Any M6 bolt will fit to any M6 nut randomly selected
The
advantages of interchangeability
1. The
assembly of mating parts is easier. Since any component picked up from its lot
will assemble with any other mating part from another lot without additional
fitting and machining.
2. It
enhances the production rate.
3. Repairing
of existing machines or products is simplified because component parts can be
easily replaced.
4.
Replacement of worn out parts is easy.
5. Without
interchangeability mass production is not possible.
Examples: Keys, Couplings, Pin Joints, Screwed Fasteners, Gears, Clutches.
Selective Assembly
Selective Assembly
In interchangeability, the parts
randomly selected will fit properly with any randomly selected mating component.
In some cases this random assembly
(or full interchangeability) is not found to be achieved.
For Example: Fit a part at its
low limit is assembled with a mating part at its high limit, the fit so obtained
may not fully satisfy the functional requirements of the assembly. Also machine
capabilities are sometimes not sufficient to satisfy the needs of random assembly.
Complete interchangeability
in those cases, however, is obtained by selective assembly.
***Normally in selective assembly, the components are put into
groups according to size and then assembled with mating components which are also
classified according to size in the same
number of groups. Corresponding groups are then expected to assemble and function
properly.
Advantages
1. There is a
larger number of acceptable parts as original tolerances are greater.
This in turn
allows the manufacture of cheaper parts as less will be consigned to the waste
bin.
2. Selective
Assembly assures better and more accurate assembly of parts by insuring closer
tolerances between the mating parts.
3. Rise the
quality and lower manufacturing costs by avoiding tight tolerances.
4. Reduces the
rejection rate (scrap rate)