Field of invention:
The present invention relates to an indexing and clamping fixture for drilling
operation on taper surface of core press ring of all types of turbo generators and
the process for the same.
Background of the invention:
Core of a Turbo Generator is made of thin iron sheet stampings coated with
insulated varnished on both the side (refer fig. 7). To make the core a monolithic
mass, the stampings are tightened with long steel bolts passing through the
stampings and core press ring at both the ends. (Refer Fig. 1)
Core press ring is circular ring having a thickness of 60mm. After machining of
both the ends the operation involved are facing and taper turning on vertical
boring operation. 24 holes of diameter 102 and 48 holes M20* 1.5 are drilled on
the taper portion of core press ring is given to compensate distortion of ring in
fully tightened condition, so that the taper face of the rings becomes the
perpendicular to the bolt insuring uniform tightening of the nuts.
As per technological process, 24 holes diameter 102 and M20 are to be drilled on
Horizontal Boring machine by clamping the ring in vertical position on four blocks
and supported on rollers. (Refer fig. 3 & 5)
Taper face of the ring is set perpendicular to the spindle by setting the table and
then ring is required to be reset after drilling one hole and hence for completion
of drilling operation 48 times crane is required for setting the new position.
48 times resetting of the ring is required for drilling holes to drill holes for
M20*13 and every time crane is needed.
Total time consumed in drilling operation including crane waiting and resetting is
round 125 to 150 hours.

Due to clamping in vertical position drilling operation is carried out low feed and
speed to avoid problem of chattering and variation in size. Also due to working at
elevated platform and frequent setting and for crane created human fatigue
resulting is slow down of working. From safety point of view this method of
operation is unhealthy.
Surface Finish was very poor when we were doing counter boring for Diameter
102mm with single point tool. It results in lot of rework.
Objects of the invention:
Therefore, it is an object of the invention to propose an indexing and clamping
fixture for drilling operation on taper surface of core press ring of all types of
turbo generators and the process for the same, which is capable of reducing
considerably the cycle time of the operation.
Another object of the invention is to propose an indexing and clamping fixture
for drilling operation on taper surface of core press ring of all types of turbo
generators and the process for the same, which is capable of avoiding use of
crane 48 times during the drilling operation.
A further object of the invention is to propose an indexing and clamping fixture
for drilling operation on taper surface of core press ring of all types of turbo
generators and the process for the same, which is able to avoid clamping in
vertical position and avoid using of low speed and low feed of the tool.
Brief description of the accompanying drawings:
Fig. 1 : Shows the method of drilling have in core press ring on a
Horizontal boring machine as in prior arts.
Fig. 2 : Shows a core press ring with taper holes.
Fig. 3 : Shows job on fixture placed on rotary table as per the invention.

Fig. 4 : Shows the core press ring fixture according to the invention for
drilling holes.
Fig. 5 : Shows the core press ring.
Detailed description of a preferred embodiment of the invention:
There are five types of core press Rings with different tapers &
dimensions as per drawing. There is a taper on the face and holes are
perpendicular to the face. (Refer fig. 5)
As per process card, job is planned on horizontal boring machine. The
operation on Horizontal Boring Machine is costly as compared to other machines
and setting of job is very difficult as the job is to be clamped upright vertically
and to be rotated after then. It is thus very risky and tiding for operator too.
Because of these reasons, dimension and finish was difficult to achieve as per
requirement. Also, the job use to complete by shifting the job by crane for every
hole. So crane was also required the same number of times to complete the job.
Thus to overcome said problem, a new fixture (Refer fig. 4) for drilling holes in
core press ring is developed which comprises of:
Item 1 : Taper Seat for Core Press Ring.
Item 2 : M30 Threaded Hole for 500MW
Item 3 : Adjustable Slot Carrier / Block.
Item 4 : M30 threaded Hole for 600 MW
Item 5 : M30 threaded Hole for 800 MW
Item 6 : Plurality of Cross Arm
Fig.4 shows the indexing and clamping fixture for carrying out drilling
operation on core press ring on a radial drill machine. The job is kept on a rotary
table and drilling operation is carried out at right angle.

Process of drilling holes in Core Press Ring:
1. Job (Core Press Ring) is being kept on fixture in such a way that taper
part of the ring sets on Item 1 which is 15 degree taper turned and the inner
diameter of the ring an outer diameter at the periphery of item 3 matches for
proper and rigid seating of the core press ring. Rotary Table is elevated by 15
Degree and job is made to touch the machine spindle at 90 deg. to mount the
job evenly. To support the job from inside, milling is done on Adjustable Block 3
and it is tightened by M30 bolts to the fixture. Slot is provided in this block,
which makes it adjustable. Hence with same block, Core Pressing for 800 MW,
600MW, 500MW can be done.
2. Since the size of the core press ring is different for different ratings i.e.
500MW, 600MW, 800MW etc. to make the fixture more robust, slots (7) and
threaded holes are provided as referenced Item 2, Item 4 and Item 5 on Item 6.
3. Job is supported on rollers and clamped with the help of Item 3 and either
of Item 2, 4 and 5 (depending upon the MW rating of the ring) in such ways that
the taper portion of the ring on which hole is to be drilled become parallel to the
horizontal plane.
4. After drilling one hole job is indexed for drilling of next hole by manually
rotating the rotary table handle. The position of taper portion of ring is
automatically come parallel to horizontal to the plane.
5. Similarly all the holes of diameter 102 and M 20 X 1.5 are drilled by
manually setting the ring.

6. During the whole operation crane is required only two times for loading of
ring on fixture and that finally unloading the complete the job.
7. Newly designed cutting tool has multiple cutting edge so it has resulted in
limitation of rework and better quality and improved surface finish.
Benefits Accrued:
1) Financial Benefits:
Annual Savings (Recurring) = Rs. 2303895/-



Total Savings (Non- Recurring) = Rs. 1382500/-
1) Estimated marked cost of the fixture = 1500000/- -(i)
2) Total Cost incurring in In-House Manufacturing of fixture
Rejected material weight of fixture =1145 kg.
Cost of Raw Material per kg. =100 Rs.
Machining Cost =3000 Rs.
Total Cost = (1145*100+3000) =117500 Rs. -(H)
Total Savings (Non - Recurring)=(i-ii) = 1382500/-
Total Saving = 2303895+1382500 =3686395 Rs. .

PRODUCTIVITY
In earlier method it took 96 hours to complete machining operation but
introduced method takes only 24 hrs for the same work. This has resulted in
increase of productivity by 75%.
Similarily, earlier the crain was taking 25 hours after introduction of new method
crane is taking 2 hours. This has result in increase of productivity by 80%.

We Claim
1. An indexing and clamping fixture for drilling operation on taper surface of
core press ring of all types of turbo-generators comprising;
a plurality of cross arms (6);
a plurality of taper seat (1);
a plurality of threaded holes (2,4,5) for clamping the core press ring;
a plurality of adjustable slot carrier (3);
a plurality of adjustable slot (7);
Characterized in that;
a plurality of taper seat (1) accommodates the taper part of the core press ring
when milled adjustable block (3) support the said ring from inside wherein the
inner diameter of the ring matches outer diameter of adjustable slot carrier (3)
for proper and rigid seating of the core press ring.
2. The fixture as claimed in claim 1, wherein taper surface (1) of the said
fixture has 15 degree taper.
3. Process of drilling holes on taper surface of cross press ring comprising;
clamping the fixture on the rotary table; supporting the job on rollers;
placing taper part of cross press ring on taper seat (1) of the fixture;
making the inner diameter of the ring matching with outer dia of adjustable slot
carrier;
elevating the rotary table by 15 degree to make the job to touch the
machine spindle at 90° to mount the job evenly and to make the taper part of
ring parallel to the horizontal plane disposing milled adjustable carrier (3) to
support the job from inside;

tightening the carrier with the fixture by bolts;
wherein one hole is drilled and job is indexed to drill the next hole by
manually rotating the rotary table.
4. The process as claimed in claim 3, wherein holes of diameter 102 mm and
M20X1.5 are drilled by manually setting the ring.

ABSTRACT

The invention relates to an indexing and clamping fixture for drilling
operation on taper surface of core press ring of all types of turbo generators and
the process for the same. The fixture comprises of a plurality of cross arms (6), a
plurality of taper seat (1), a plurality of threaded holes (2,4,5) , a plurality of
adjustable slot carrier (3) and a plurality of adjustable slot (7). The taper seat (1)
of the fixture accommodates the taper part of the core press ring. The fixture is
placed on a rotary table. The taper seat has 15 degree taper. The rotary table is
rotated to make the taper face of the job horizontal for drilling of one hole. For
drilling of next hole, the rotary table is manually rotated.