TRANSFER MACHINING

AUTOMATIC MACHINES

     Machines capable of handling the work pieces as well as performing metal cutting operation automatically are known as automatic transfer machines.  These machines play an important role in increasing the production.  Initial settings have to be done carefully, because automatics have a fully automatic working cycle, which is repeated automatically to produce repetitive jobs without any participation of the operator.  In automatic machines, operations right from the feeding of the stock to clamping, machining and even inspection of the work pieces are carried out automatically.

METHODS USED FOR ACHIEVING AUTOMATION

 

        The various methods used for achieving automation in machine tools are as follows:-

 

•         The feeding arrangement, like feed hoppers and strip feed rolls.

•         Incorporation of cams and mechanical movements.  Lathes can be made automatic by these devices to produce  components within its capacity.

•         Special purpose machines designed specially for these operations i.e., gear shaper, gear hobber, broaching machines etc.

•         Transfer machine system.  In this system machines are made by a collection of assembled machining units and designed to perform a concerned sequence of operations.

•         At present automats have moved towards machine tool technology by the use of feed back control circuits and computers.

 

SINGLE SPINDLE AUTOMATIC MACHINES

 

         Single spindle automatic machines are the developments of capstan and turret lathes.  They can be further classified as follows:

 

•          Automatic cutting off machines

•          Swiss type automatic screw machine

•          Turrent type automatic screw machine

 MULTIPLE SPINDLE AUTOMATICS

     Multiple spindle automatic lathes are the fastest production machines for bar stock.  These machines are fully automatic and they are made in a variety of models with two spindles, four spindles, six and eight spindles.  Once the bars have been loaded into hollow spindles, all the operations of the machine are completed automatically unit the whole of bar stock is consumed.

 •          End tool slides are provided in front of the spindles on which tools are placed, in line with each of the spindles.  The tool slide moves forward and backward to carry the end working tools.  It also consists of a cross slide on which different turning tools are mounted.  All slides are independently operated to carry different operations, such as plain turning, taper turning, knurling, threading, slotting, rolling and parting off.

 

•          Multiple spindle automatic machines can be classified as

•          Parallel type multiple spindle automatic machines and

•          Progressive action type automatics.

 

         On the former machine each operation is performed on each spindle of the machine and on the later machine, the various operations are performed in stages.  Multiple spindle automatic machines are not limited to components produced from bar stock only.  At present machines are available that can hold the bar stock and chuck works.  The chucks are air or hydraulically operated for quick holding of work piece.  Depending upon the design, these machines are loaded by the operator or by magazines provided on them.

TRANSFER MACHINING

     The aim of the production engineer is to increase output somehow or the other particularly in mass production.  Transfer machining is a step towards this goal.  A transfer machine consists of several or units fastened together by conveying units, the whole constituting one large automatic installation.  In brief, a transfer device is a combination of individual machine tools systematically arranged and integrated with interlocked controls and a transferring device to form an automatic machine.  The term transfer refers to the transfer of the job from machining station to the next as it proceeds through the machining process involved.  Components are loaded at one end and completed work pieces leave the transfer line at the other end.

    

     Quality Transfer machining leads to better quality and reduced manufacturing cost.  But the initial cost of such devices is very high.  It also requires better quantity blanks and skilled personnel.  Prominent among industries using transfer machining are the car and vehicle industries, where cylinder blocks, heads, gear box, etc, are produced in large scale.

CLASSIFICATION OF TRANSFER MACHINES

 

       Transfer devices used  in transfer machining can be broadly classified into three types.

 

•          In-line transfer machine.

•          Rotary indexing table machine and

•          The drum machine

 

•         Inline transfer machine

 

 2. Rotary Indexing table machine

      When the space is not sufficient to allow the work to be conveyed in a straight line, it may be more convenient to transfer the work around a circular line.  This principle uses a rotary system in which the work pieces are located on a circular table and are indexed around each successive machining station which are spaced as in – line transfer machine.  The plan view of a rotary arrangement is as shown in figure.

     The main and central feature of the rotary machine is the circular table top supported on high  quality bearing system at its centre for rotating about a vertical axis.  Driving arrangement is provided to the table for its indexing and accurate locations that ensure the alignment between cutting stations.  There is also arrangement for supporting the rim of the table against the forces of the machining operations to prevent deflection and also to eliminate vibrations and chatter.

     This machine is similar to in – line transfer machine regarding machining head,s work pieces location, coolant control etc., but rotary transfer machine will usually be smaller in size.

     For maximum number of machining stations of which It is capable, say eight a rotary machine is simpler than in – line transfer machine of same capacity.  The size of an indexing machine  cannot be increased beyond a certain limit since the tooling cost increases with increase in the number of stations.  For a component requiring large operations and stations, a rotary table is not a good choice and the use of other devices is preferred.

MAIN PARTS OF TRANSFER MAHCINE

The main parts of a transfer machine are:-

•           Bed (Transfer track)

•           Machining head

•           Transfer mechanism

1. Bed

•           This constitutes the fundamental units in the construction of the machine.  The bed may be a single unit of cast or fabricated construction.  The bed is generally straight although in some cases it may be made of a U-shape, square, circular curved shape to suit particular condition.  The upper surface of the bed has sideways for guiding and supporting  the work pieces of holding fixtures (pallets) upon which the work piece is clamped.

2. Machining heads

•           The machining heads  are often made up of unit cutting heads, such as drilling, milling, boring reaming, etc.  The spindles of machining heads are usually driven from a self contained motor.  This is carrie don an intermediate base side ways on its upper surface and the lower, flat base of this is bolted to the flat surface of the wing base or column of the structural unit.  This immediate base of the cutting unit in corporates feeding arrangements to move the cutting unit.  The heads can be mechanically or hydraulically traversed along the sideways while the cutting tools work upon the component.

3. Transfer Machine Mechanisms

            The transferring of the work pieces accurately from station to station can be done in many different ways. In case of rotary and drum transfer machines, it is a function of the indexing mechanism. On in line machines various mechanical devices are used

TYPES OF TRANSFER MACHINE MECHANISM

1. Pawl type transfer mechanism

        This is a very simple and inexpensive type of transfer mechanism in which the work pieces move from one machining station to the next machining stations.  A single transfer bar, either round or rectangular in cross section, has a series of pivoted finger or pawls attached to it.  These fingers are either spring loaded or weighted so as to hold against the rear end of the work pieces as shown in fig.

 

2. Walking beam transfer mechanism

      This type of transfer mechanism provides positive movement of parts from station to station without sliding.  It is therefore used to move work pieces of soft metals which would be subjected to too much wear if they are allowed to slide along the guide ways or rails on the surface of the bed.

ADVANTAGES

 

•     Greater output is obtained in comparatively lesser time.

•     Heavy components and components of extremely awkward size and shape can be handled.

•     Large numbers of operations are not required.

•     Considerable floor space is saved by closed grouping of machines.

•     The Life of the cutting tool may be considerably increased.  This reduces cost of replacement and time for resetting.

•     Greater accuracy is achieved as the work is clamped in fixture through out.

•     Lesser time is required for a complete production because  the machine is fully automatic.

 

DISADVANTAGES

•         Initial cost is very high.

•         Electrical control system is very complex.

•         A break down of one machine causes to stop the whole line.

•         Limited only to high production jobs.

•         Reshuffling and overhauling cost is very high.

 

CONCLUSION

 

    The non manufacturing industries with the help of these automatic machines and machining systems productivity can be increased, and lead time is reduced and machining accuracy can be reduced.  Know a days all the manufacturing industries and companies adopting this systems for this production cost can also be reduced.

REFERENCES

•         WWW.GOOGLE.COM

•         Manufacturing Technology by P.s.Reddy

•         www.Docjax.com

•         workshop Technology by Hajara Choudhry

•         Manufacturing Technology by R.K.Rai

•         Production Technology by R.K.Jain