FIELD OF INVENTION
The present invention relates to an improved process and tooling for end cutting
operation of Generator Stator Bar Conductors.
BACKGROUND OF THE INVENTION AND PRIOR ART
Generator stator bars are made from a bunch of copper conductor strands. After
bunching required number of conductor for a bar, these conductors are clamped
together tightly to avoid their displacement during forming of bar shape. The stator
bars are water cooled. Hence, stator bars are made from group of solid and hollow
conductors and a water box is brazed at the end of each bar for supply of cooling
water. In some design generator stator bars are indirect cooled so all conductors of bar
are solid and thus avoid brazing operation. Clamped straight bar conductors are placed
on former for giving required shape. Plastic or wooden mallets are used for hammering
the conductors to give shape to bar. When copper conductors are found matching with
the shape of the former, the bending process is complete. After bending process is
over, a mixture of resin and hardener is applied on the bars. Bars are now clamped on
the former and heated uniformly for baking of the insulation.
The end of the conductors in completely formed bars is irregular and requires cutting to
give regular and uniform shape. In some design of stator bars end cutting operation is
done after brazing of lower half water box and in some other design end cutting
operation is done after baking operation is completed. This end cutting operation is
carried out on band saw cutting machine and final shape is given by face milling the
ends of the conductors. The deburring of the conductors is done to remove loose metal
particles and to give smooth surface finish.
End cutting operation on band saw cutting machine is very slow. Only small depth of
cut can be given to avoid breaking of band saw. The life of band saw is very short and
after three bars band saw requires replacement. This caused frequent interruption in
end cutting operation. Problem of frequent breaking of band saw is also observed
resulting suspension of work for replacement of band saw.
End cutting with band saw does not give regular and smooth shape to the conductors
resulted in additional milling operation for giving proper shape to the conductors. The
situation calls for additional engagement of crane and material handling staff due to
dual machining on band saw cutting and milling machine. Obviously there is always a
delay in final output.
Hence, there exist a need to eliminate the disadvantages of the prior art by
implementing an improved process.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved process and tooling for
end cutting operation of generator stator bar conductors which eliminates the
disadvantages of prior art.
Another object of the invention is to propose an improved process and tooling for end
cutting operation of generator stator bar conductors which eliminates time consuming
operation by introducing an operation which is much faster.
A still further object of the invention is to propose an improved process and tooling for
end cutting operation of generator stator bar conductors which is highly economical and
results with tangible benefits.
A further object of the invention is to propose an improved process and tooling for end
cutting operation of generator stator bar conductors which is capable of avoiding delay
in final output.
BRIEF DESCRIPTION Of THE ACCOMPANYING DRAWING
Fig.1 - shows a process flowchart of end cutting operation of stator bar according to
prior art.
Fig.2 - shows an improved process flow chart off end cutting operation of stator bar
according to the present invention.
Fig.3 - shows a step arbor designed to suit the machine and a slitting cutter on a
vertical milling machine.
Fig.4 - shows the step arbor working as tool holder holding a slitting cutter.
Fig.5 - shows a photograph of a slitting saw cutter in vertical plane on a milling
machine with stator bar end clamped in machine vice.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
With a view to improve the process of end cutting operation of Generator Stator Bar
Conductors, the slow moving operation on band saw cutting machine is eliminated and
continuous requirement of crane and handling staff for supporting bars in hanged
position is avoided and a faster end cutting process of conductors is adopted on a
milling machine.
A new process is thus developed in which end cutting operation of conductor is done
with the help of slitting cutter on a vertical milling machine in place of end facing cutter.
As there is no arrangement for holding slitting saw cutter on vertical milling machine, a
suitable slitting cutter holding arrangement (T) is designed and developed as shown in
Fig.4. A step arbor (S) as shown in Fig.3 is designed in such a way that one end of the
arbor has outer taper (t) matching the inside taper of the spindle of the milling
machine. The arbor works as a tool holder to hold the cutter (C). It has also an axial
hole of M12 (A) for tightening the tool holder (T) with the help of a tie rod and collet
chuck for holding it on the machine. A M12 (B) axial hole is drilled at the end of the tool
holder. A M12 bolt with washer is fixed in this hole for holding the cutter (C) tightly in
the tool holder (T). Other end of the tool holder (T) has a step dia of dia 32 mm
suitable for holding slitting cutter. An axial key-way (K) is also provided on dia 32 mm
for fixing of cutter with the help of key provided to avoid slipping of cutter during
slitting operation. The steel arbor is properly heat treated and annealed.
Developed stepped arbor (S) is fixed in machine such that the slitting saw cutter
remains in vertical plane. Stator bar end is clamped in the machine vice mounted on
machine table from contact sleeve position and overhang of the bar rests on platform.
There is no need of crane holding the bar during end cutting operation. The slitting
cutter (C) position is so set that the end cutting operation is done in single travel of the
cutter. This takes only five minutes to complete the end cutting operation of one side.
The crane is required only two times firstly for cutting of one end and secondly for
reversing the position of the bar. The tangible gains achieved through new process
compared to the prior art is shown below:
Old Mthod
(A-1)
No. of persons engaged for end cutting operation of one bar on band saw cutting
machine = 4 nos.
Time taken for complete end cutting operation of one bar = 4 hrs
Total man hours for one bar = 4 x 4 hrs
= 16 hrs
Cost of man power including overhead = Rs. 300 per man hour
Cost of man power = Rs. 4800
(A-2)
Running cost of band saw machine = Rs. 375 per hr.
Machine cost for one bar = Rs. 375 x 4
= Rs. 1500
(B-l)
Running cost of milling machine = Rs. 300 per hour
Time taken to complete one bar = 1 hour
Machining cost of one bar on milling machine = Rs. 300 x 1
= Rs. 300
(B-2)
Persons engaged in handling of bar from band saw cutting machine to milling machine
and setting of bar = 4 nos.
Time taken for shifting and setting of bar = 0.5 hour
Man hours consumed = 4 x 0.5 = 2 hrs.
Cost of man power = Rs. 2 x 300
= Rs. 600
Total cost for end cutting of one bar, C = Al + A2 + Bl + B2
= (4800 + 1500) + (300 + 600)
= 6300 + 900
= Rs. 7200
New Method
(D)
Machine hours for handling, setting and slitting operation of one bar = 1 hour
Cost of milling operation = Rs. 300 per hour
Cost of end cutting operation of one bar = Rs. 300 x 1
= Rs. 300
(E)
Saving of one bar by switching over to new method = C - D
= Rs. 7200 - 300
= Rs. 6900
(F)
No. of bars manufactured in one year for different generators = 1260
Total saving = Rs. 6900 x 1260
= Rs. 86,94,000
= Rs. 86.94 Lacs
The new process has made huge change in productivity and resulted in high tangible
gains. Complete machining operation of one end is done in five minutes whereas in old
method it took four hours on band saw cutting machine and subsequently an hour on
milling machine. In the new improved process, the end cutting operation of one bar
now takes only one hour including handling time, whereas in old method it took five
hours including handling time to complete end cutting operation in band saw machine
and milling machine. Surface finish of the ends of the conductors obtained after cutting
witfi slitting saw cutter is very good and no rectification work is required to improve
surface finish. In the new method, there has been a considerable increase in safety.
Slitting saw cutter on the milling machine is provided with a safety cove and job is
clamped in a vice for safety of operator and equipment.
WE CLAIM
1. An improved process for end cutting operation of Generator Stator Bar
Conductors comprising:
assembling a slitting cutter (C) on the step dia of the arbor (S);
assembling the tool holder (T) comprising the said arbor and the said slitting
cutter in the machine spindle;
fixing the tool holder (T) in the machine by tightening it with tie rod and collet
chuck;
holding the cutter (C) in the tool holder (T) tightly with bolt and washer;
characterised in that the arbor (T) is fixed in the machine such that the slitting
saw cutter (C) remains in vertical plane and is so set that the end cutting
operation is done in single travel of the cutter (C) without the need of the crane
holding the bar when the stator bar is clamped in the machine vice.
2. An improved process as claimed in claim 1, wherein the axial hole M12 (a) is
provided at one end of tool holder (T) to fix it with the machine by a tie rod
collet chuck.
3. An improved process as claimed in claim 1, wherein M12 bolt and washer holds
the cutter (C) tightly in the tool holder (T) through a M12 axial hole (B) at the
other end of the said holder.
4. An improved process as claimed in claim 1, wherein the cutter is fixed by a key
in the axial key way (K) provided in the tool holder (T) to avoid slipping of cutter
(C) during slitting operation.
5. An improved process as claimed in claim 1, wherein overhang of the bar rests on
platform when the stator bar is clamped in the machine vice mounted on
machine table from contact sleeve position.

An improved process and tooling for end cutting operation of generator stator bar
conductors consists of assembling a slitting cutter (C) on the step dia of an arbor (S)
when the tool holder comprising of the arbor (S) and the cutter (C) is assembled in the
machine spindle. The tool holder (T) comprising of the arbor (S) and the slitting cutter
(C) is assembled in the machine by tightening it with tie rod and collet chuck, when the
slitting cutter remains in the vertical plane. The end cutting operation is done in single
travel of the cutter (C) when the stator bar end is clamped in the machine vice.