Transfer Machines
Manufacturing
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Transfer-type production machines, frequently designated as automated machines, complete a series of machining operations at
successive stations and transfer the work from one station to the next. They are in effect a production line of
connected machines that are synchronized
in their operation so that the workpiece, after being loaded at the first
station, progresses automatically through the various
stations to its completion.
"Transfer machines" perform a variety
of machining, inspecting, and quality control functions.
They drill, mill, hone, and grind, as well as
control and inspect the operations.
Types of Transfer
Machines
Transfer machines are of the following three types :
1.
Rotary indexing
table transfer machines.
2.
In-line transfer
machines.
3. Drum type transfer machines.
1. Rotary indexing
table transfer machines :
In rotary transfer system the workpieces are held in fixtures on a
continuous rotating table. The rotating table brings the workpieces under
different machines
Owing to the
problems of rigidity and maintenance of proper accuracy, the table size is
always limited and, hence, is the number of stations fixed on this type of machine. Usually, such
a machine carries 6 or 8 stations around it, although for smaller workpieces
this number can be as high as 16. The components size and required number of
work stations are the main factors which affect the determination of table size
and the number of stations.
• This
method is quite compact and permits the workpiece to be loaded and unloaded at
a single location without having to interrupt the
machining.
• This type of arrangement is best suited for
automatic assembly of a product.
2. In-line
transfer machines :
In this arrangement
the workpiece is held in a fixture or special 'pallet". The fixtures are located and clamped in proper position. A schematic
diagram of an In-line transfer machine is shown in Fig. 15.2.
"Palletized" work holding fixtures secure the transmission
during all operations. Pallets are often
carried in conveyors which are indexable.
Following are the
functions of an in-line transfer machine : (0 Transfers workpiece to the first station and then from station to
station, (ii) Locates and clamps the work at each station, (iti) Rapid approach
of the tools to the work.
(iv) Feed the tools through the cutting cycle.
(v) Retract the tools clear of the work and guide bushes
(vi) Unclamp the workpiece at various stations ready for further transfer.
3. Drum type transfer machines :
In these types of machines work fixtures are fastened to the outside
surface or periphery of the drum and work stations are positioned radially
around the circular path at equal intervals.
As the work hangs from the fixture, the clamping arrangement must be
fool proof and efficient. Like circular indexing arrangement, this too cannot
be big in size.
• Solution of transfer machines depends on the
following factors : (t) Product size and machining requirements.
(u) Handling systems used, (tit) Floor space available.
•
Transfer machines
range from comparatively small units having only two to three stations to long
straight line machines with more than 100 stations.
•
These machines are used primarily in the automobile industry. Products processed by these machines include cylinder blocks, cylinder
heads, refrigeration compressor bodies and similar parts.
Constructional
Features of a "Transfer Machine"
The principal
constructional features of a Transfer machine' consists of the following main
parts and mechanisms :
1.
Central bed.
2.
Machining heads.
3. Automatic work holding and Transfer mechanisms.
4.
Locating and
clamping devices.
5.
Cooling supply
mechanisms. ^
6.
Chip disposal
devices.
7.
Control systems.
Advantages and
Disadvantages of Transfer Machines Following are the advantages and disadvantages of transfer
machines :
Advantages :
1.
Higher production
rates are achieved.
2.
Higher accuracy is
obtained.
3. Less floor space is required.
4.
Heavy workpieces
can be easily handled.
5.
The quality of
products is considerably improved.
6.
Complex shaped
components can be conveniently machined.
7.
The length of
production cycle is reduced.
8.
Less number of
operators are required.
9.
Increased tool life
(resulting in further reduction in production cost).
Disadvantages :
1.
High initial
investment.
2.
A breakdown of one
machine means stoppage of whole of the production line.
3. Complex control systems are required.
4.
Much time is
required to change over the machine to handle a different shaped components.
5. Very high overhauling and maintenance costs of transfer lines,
specifically when reshuffling is required.
(A textbook of manufacturing technology, R.
K. Rajput, Pg 688-670)
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Typically
consisting of two or more powered units, these machines can be arrange on the
shop floor in linear, circular, or U-shape patterns. The weight and shape of
the workpieces influence the arrangment selected, which is important for
continuity of operation in the event of tool failure or machine breakdown in
one or more of the units. Buffer storage features are corporated in these
machines to permit continued operation in such an event.
(Kalpakjian S., Schmid S.R.,Manufacturing
Engineering and Technology, 5th Edition, pg.1150)
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