17-01-2014, 02:26 PM
General Purpose Machine Tools
Instructional objectives
This lesson will enable the students ;
(i) Illustrate the constructional features and uses of semiautomatic and
automatic lathes.
(ii) Show the kinematic system and explain the working principles of
semiautomatic and automatic lathes of common use.
(iii) Plan and visualise tool layout for machining in semiautomatic and
automatic lathes.
Constructional Features And Uses Of General Purpose
Semiautomatic And Automatic Lathes.
Automation is incorporated in a machine tool or machining system as a whole
for higher productivity with consistent quality aiming meeting the large
requirements and overall economy. Such automation enables quick and
accurate auxiliary motions, i.e., handling operations like tool – work mounting,
bar feeding, tool indexing etc. repeatably with minimum human intervention
but with the help of special or additional mechanism and control systems.
These systems may be of mechanical, electro-mechanical, hydraulic or
electronic type or their combination.
Multiple spindle Vertical Turret lathe
Turret lathes are mostly horizontal axis single spindle type. The multiple
spindle vertical turret lathes are characterised by :
• Suitably used for large lot or mass production of jobs of generally ;
chucking type
relatively large size
requiring limited number of machining operations
• Machine axis – vertical for
lesser floor space occupied
easy loading and unloading of blanks and finished jobs
relieving the spindles of bending loads due to job –
weight.
• Number of spindle – four to eight.
Automatic cutting off lathe
These simple but automatic lathes are used for producing short work pieces
of simple form by using few cross feeding tools. In addition to parting some
simple operations like short turning, facing, chamfering etc. are also done.
Single spindle automatic lathe
The general purpose single spindle automatic lathes are widely used for
quantity or mass production (by machining) of high quality fasteners; bolts,
screws, studs etc., bushings, pins, shafts, rollers, handles and similar small
metallic parts from long bars or tubes of regular section and also often from
separate small blanks.
Fig. 4.7.7 shows a typical single spindle automatic lathe.
Unlike the semiautomatic lathes, single spindle automats are :
• preferably and essentially used for larger volume of production i.e.,
large lot production and mass production
• used always for producing jobs of rod, tubular or ring type and of
relatively smaller size.
• run fully automatically, including bar feeding and tool indexing, and
continuously over a long duration repeating the same machining
cycle for each product
• provided with upto five radial tool slides which are moved by cams
mounted on a cam shaft
• of relatively smaller size and power but have higher spindle speeds