Operation Management-ICAI-Inter-Class of Machines

1.2 Class of Machines
Machine Tool: It is a power driven mechanical appliance or device used for removing metal from surfaces
of jobs to give them the proper shape, size and other characteristics.
Classes of Machine Tools:
Machine Tools are now so numerous in type that they do not admit of any fixed classification. One possible
classification is under two groups, namely
(1) General purpose or Standard Machine Tools, (2) Special Purpose Machine Tools.
The General Purpose or Standard Machine Tools form the most essential part of the equipment of a
workshop. They are called Standard Machine Tools in the sense that they are very common and essential
and a list of most important Machine Tools used in a workshop will invariably include these machines.
Many of them are suitable for many different types of operations. A lathe, which is the most important
machine belonging to this group, can be employed for the general purposes of turning (producing cylindrical
surfaces on a job), drilling (making a hole), screw cutting, producing flat surfaces, cutting teeth on a gear,
cutting cylindrical holes in job, etc.
A special purpose Machine Tool performs only a limited number of specialised operations with great
speed and precision. It does the same job as can be done by some General Purpose Machine, but it supersedes
the latter on account of its high speed and accuracy. As for example, boring operation can be done on a
lathe but the same operation can be done with greater speed and efficiency on a Boring Machine which has
been developed for doing mainly the operation of boring.
The General Purpose Machine has great adaptability, but on account of the present day need for highspeed
production of parts of great accuracy, Special Purpose Machines have been developed by sacrificing
adaptability to specialisation.
Multi-purpose and Single-purpose Machine Tools:
Machine Tools are sometimes classified under Multi-purpose and Single-purpose machines.
A Multi-purpose Machine Tool is capable of doing a number of different types of operation. A Centre
Lathe, a Milling Machine, a Grinding Machine, etc. are examples, of Multi-purpose Machines.
A Single-purpose Machine is one that is capable of doing only one particular kind of operation, but is not
restricted to one particular job. As for example, a Shell Turning Lathe is designed specially for shell turning
and is not adopted for general Lathe work. A Hobbing Machine, a Honing Machine, etc. are other examples
of Single-purpose Machines.
Although a Single-purpose Machine has restricted field of use, it can do the particular operation for which
it is employed at great speed and with a high degree of accuracy. When a large number of interchangeable
parts are to be quickly produced, Special-purpose Machines are of great importance.
General Purpose or Standard Machine Tools:
The following are some General Purpose Machine Tools employed to do various operations:
• Drilling Machines- These Machines are used for drilling holes of different diameters in vertical or
inclined directions.
Overview of Production Process
8
• Grinding Machines - Grinding Machines are used for machining parts having cylindrical and tapered
surfaces, for grinding internal surfaces and flat surfaces and for grinding slender bars and delicate
parts.
• Lathes (Centre or Engine Lathe) - The operations performed on Lathes normally are Turning, Boring
and Screw-cutting. Over and above these normal operations a Lathe can be adapted for the operations
of Milling, Drilling, Slotting, Grinding, Gear and Rack Cutting, Lapping, Facing, Reaming, Polishing,
Knurling, Tapping and Parting off.
• Milling Machines - These Machines are employed for producing plain and irregular surfaces, cutting
slots by using special tools, cutting threads on dies, worms and screws and for gear-cutting.
• Plaining Machines - These Machines are used for machining flat surfaces and cutting Key-ways on
larger jobs.
• Shaping Machines - The operations performed on Shaping Machines are machining of flat surfaces,
cutting of Key-ways and T-slots on jobs not exceeding 12 inches in length.