FIELD OF INVENTION
The present invention relates to a fixing device for machining metal shielding and a
method thereof which facilitates the machining of metal shielding near the end shield of a
turbo generator. More particularly, the invention relates to a fixing device, which clamps
the metal shield during machining to avoid distortion.
BACKGROUND OF THE INVENTION
The generator end shields are heavily reinforced fabrications, designed to support the
weight of the rotor and to contain the hydrogen gas at maximum pressure without
excessive distortion.
The generator rotor bearing, the hydrogen shaft seals, and oil passages supplying oil to
different parts, are contained and/or supported by the outer end shield. The end shields
are split on the horizontal centre line, facilitating their removal. The joints between the end
shield halves, between the metal shields and the stator frame are fitted and provided with
groove for insertion of a sealing compound, to seal the generator gas in the generator
casing.
Metal shield is a half cone of the metal e.g., copper, made from a very thin metal piate in
two halves and these are metallic shields assembled above end shield on exciter end of
Turbo Generator, During the operation, when current flux is applied over the End Shield,
it becomes heated. To prevent end shield from heating, an end shield cone/metallic
shielding cone is used.

Pockets are provided in Metallic shield so that there can be a pipeline passage for oils,
cooling agents etc. For machining of pockets in said metal shields, these metal shields
have to be placed over machine bed and clamped from the top of the shield so that the
metal shield does not vibrate or move during the machining process. For milling other
pockets, metal shield clamping device is required to be picked with the help of a crane and
then reset the clamp and the shield according to where the pocket is to be cut and again
clamping is done as mention earlier therefore requiring the continuous use of crane for
prolonged time. There are altogether 478 number of pockets to be milled in the metallic
shielding excluding four such holes on ribs and along with it, 52 holes excluding 12
numbers on the rib, Thus a job is required to be turned approximately 20 numbers of times
and thus crane too is required 20+2 i.e., 22 for same number of times.
Since the metal shielding is in conical form, drilling and tapping angle head requires being
loaded again with machining of every pocket. A lot of time is consumed in performing
above processes and due to inaccurate setting gaps between, the pockets obtained are
non - uniform.
Whenever during any machining is done to cut pocket in metal shield; for example if
milling is performed as per the process and drawing dimensions, gaps in pockets increases
due to distortions and thus protection of end shield from heat is not properly checked
because of that.
There can be two reasons for such distortions;
1) Because of the weight of the clamping arrangement, as during machining the metal
shielding is clamped from the top and since the base diameter of the shielding (conical in
size) is big and made out of very thing metal sheet.
2) Thermal expansion is the tendency of matter to change in volume in response to a
change in temperature.
Hence there exists a need to find a suitable device that facilitates important machining
operation and can eliminate the disadvantages of prior art as stated above.

OBJECTS OF THE INVENTION
An object of the invention is to propose a device which can clamp the metal shield and a
method for the same in such a way that when machining is performed on the same it does
not distort because of the mass off the clamping.
Another object of the invention is to propose a device which can clamp the metal shield
and a method for the same in such a way that said device can rotate, turn and provide
flexibility during machining such that loading and unloading of the job (Metal shielding) for
machining different pockets can be avoided and thereby saving time in machining of the
metal shielding.
A still another object of the invention is to propose a device which can clamp the metal
shield and a method for the same in such a way that the said device has provisions for
machining metal shielding that differ in sizes.
Yet another object of the invention is to propose a device which can clamp the metal shield
and a method for the same in such a way that said device can rotate in such a way to
ensure correct angle for machining of metallic shield.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig (A); Base structure of the fixing device to support rotary base,
Fig (B): Handle for manual rotation of rotary table for angling the job.
Fig (C): Item 6 (Hinge)
Fig (D): Item 10 (Threaded hole) and Item 8A (Flexible jacking screw.)
Fig (E): Item 1 with taper groove of 45 degree, Item 9 (threaded hole), Item 11 (Welded
nuts)
Fig (F): Complete fixing device with all constituent items 1 to 11 Fig (G): Complete fixing
device in actual as per photographic views.

REFERENCE NUMERALS FOR IMPORTANT FEATURES
The present invention, i.e., fixing device for machining metal shielding comprises the
following items:
- Item 1: Rotary plate with taper groove of 45 degree to support metal shield
- Item 2: Rotary Base on which Item 1 is clamped
- Item 3: Rotary bed on which Item 2 is clamped; Item 2 and Item 3 when
assembled are called Rotary Table
- Item 4: Handle attached to Item 3 to rotate Rotary Table
- Item 5A: Upper Structure Serving as the base to Rotary Table and Item 1
- Item 5B: Lower Structure Serving as the base of the fixing device (static)

- Item 6: Hinge (3 no.) between item 5A and 5B to provide angular movement
(Variation in angle B)
- Item 7: Lifting Pads
- Item 8A: Flexible Threaded Screw
- Item 8B: Hydraulic Jack provided with slots to manually rotate the nut
- Item 9: Threaded Hole (5 no.s)
- Item 10: Threaded hole
- Item 11: Nuts (8 no.s) welded on Item 1 to clamp Metal Shield
- Item 12: Support
DETAILED DESCRIPTION OF THE INVENTION
Step 1) Item 1 serves as the rotary plate on which the taper groove of 45 degree of
thickness just greater than thickness of metallic shield is cut at radius equal to the cone
radius of the metallic shield. The rotary plate (1) is clamped to Item 2 by the help of Item
9 so as to get rotating drive from Item 2. Item 2 serves as the rotating base which provides
clamping arrangement to Item 1 and is the rotating object of rotary table. Item 2 delivers

the driving/rotary motion to the job (metallic shield) through item 1. Item 2 is clamped to
Item 3 (Rotary Bed) which is the static object of the rotary table. Item 4 as attached to a
gear mechanism inside Item 3 with a long slender rod in such a way that when handle is
turned clockwise the rotary table will clockwise and when the handle is rotated anti
clockwise, the table will rotate anti-clockwise. Thus Rotary Table (Item 2 and 3) and Item
1 rotates so as to facilitate machining at required at the periphery of the clamped metallic
shield and thereby saving time in using crane for
re-orientation of the job for every pocket to be cut. The crane for such period can be
utilized in some other operations. The size of the rotary plate is kept such that multiple
taper grooves of 45 degrees of different radius can be cut in order to avoid having different
modules of rotary plates for machining of different sizes of metallic shield.
Step 2) Clamping of the job by tightening of threaded bolts through Item 11 welded at the
base of the rotary plate near the taper groove. Also, like before, the clamping
arrangement is use from the top also but it is serving the purpose of balancing the job
from the top as the vibration will increase during machining if the end of the job is left fr§e.
Earlier there was no clamping arrangement at the base and the clamping from the top was
done and weight was put on the metal shield so that it does not vibrate. Thus this
arrangement solves the distortion of the metallic shield due to vibration and improper
clamping.
Step 3) since the job is frustum of a cone i.e., the surface is slant, machining has to be
done on different angles. Setting up angle heads (tool) needed a lot of time and accuracy
for the angle was not perfect too. The said invented fixing device provides angling
arrangement of the job via a structure which is diving into two parts, Item 5A and 5B,
which are connected through Item 6. The angle on the job can be maintained if we can
manage to maintain angle p (angle between Item 5A and 5B. When Item 8B rotates, it
rotary motion results into linear motion by which it pushes to provide required movement
to Item 5A. Thus the need of angle head is not there with this fixture.

Step 4) During machining, the load of the machining and clamping will be taken by Item
12 (support). This support is in the form of flexible screw connection and the length of the
support can be increased or decreased upto some extent.
Step 5) Item 7 (pads) is fixed at the base of the fixing device so as to keep the whole fixing
device at some clearance from ground level so that the fixing device can me moved from
one place to another with the use of some lifting fork.
ADVANTAGES AND TANGIBLE GAINS
Before implementation of the invention:
Time required for making of one half = 32 hours
For two halves = 64 hours
Machine cost per hours = 2083
Total machine cost = 64*2083 = 132032
Time absorbed by crane = 8 hours
Time for creeping rework = 8 hours
Cost of rework and crane dissipated time = 2083 * (8 + 8) = 33328
TOTAL COST BEFORE IMPLEMENTATION = 132032 +33328 = Rs. 165360
After implementation of the invention:
Total hours on one half = 10 hours
For both the halves = 20 hours
Machining cost = 2083 * 20 = 41660
Rework cost = 0
Crane time cost = 0
Total cost after implementation = Rs. 41660
Total savings per set = Rs. (165360 - 41660) = Rs. 123770
TOTAL SAVINGS FOR 18 SETS = Rs. 2226600 (Recurring in nature)

WE CLAIM
1. A fixing device for machining metal shielding comprising; an upper structure (5A) and
lower structure (5B);
the upper structure (5A) forming a base for the fixture, the upper structure (5A) having
threaded hole for clamping arrangement; an angle (B) is maintained between the upper
structure (5A) and the lower structure (5B) with the help of a flexible screw (8A) attached
to the lower structure (5B) and hydraulic jack (8B) attached to the upper structure (5A);
a plurality of hinges (6) is provided to give easy angular movement to the upper structure
(5A);
a rotary bed (3) is clamped on the upper structure (5A) with the help of threaded hole;
a rotary base (2) is clamped to rotary bed (3);
a rotary plate (1) is clamped on rotary base (2);
The rotary plate (1) having multiple grooves at 45° of different radius used for mounting
the job or wherein the plurality of nuts (11) is used for clamping the job.
2. The fixing device as claimed in claim 1 wherein the rotary plate (1) is cut with multiple
taper grooves of 45° of different radius in order to accommodate modules of different
sizes.
3. The fixing device as claimed in claim 1, wherein the rotary base (2) is clamped to rotary
bed (3), the assembly constituting rotary table, whereby the rotary bed (3) being the static
member.
4. The fixing device as claimed in claim 1 wherein the rotary plate (1) is clamped to rotary
base (2) with the help of threaded hole (9 and 10) so as to get rotating drive from rotary
base (2).

5. The fixing device as claimed in claim 1 wherein the rotary plate (1) is equipped with
plurality of nuts (11) for clamping the metal shield.
6. The fixing device as claimed in claim 1 wherein the handle (4) is attached to the gear
mechanism inside rotary bed (3) for moving the rotary table clockwise or anti clockwise to
suit the job position.
7. The fixing device as claimed in claim 1 wherein the support (12) is used for sharing the
load of fixture during mechanism.
8. The fixing device as claimed in claim 1 wherein a plurality of pads (7) is used to keep ine
whole fixture at some clearance from ground level for easy movement particularly for
lifting purpose.
9. A method of clamping of metallic shielding in the fixing device claimed in claim 1
comprising:
holding the metallic shield in groove and clamping the same by nut and pin arrangement
(11) at the base of the rotary plate (1) and with the help of an additional load from the top
to hold the free end of the metallic shield for minimum vibrations;
Rotating the job about vertical axis with the help of a handle (4) and gear arrangement
provided in the rotary table (2 and 3);
Rotating the job vertical axis and in the plane of paper with help of a hinged support and
getting movement through a hydraulic / manual jack (8B) and flexible screw arrangement
(8A).

ABSTRACT

The invention relates to a fixing device for clamping the metal shield during machining
operation in the machine bed to avoid distortion due to heat generated while performing
various types of machining operations. The fixing device comprising a structure divided
into upper (5A) and lower (5B) structure, the upper structure (5A) having threaded bale
for clamping arrangement, an angle (β) is maintained between upper (5A) and lower
structure (5B), a plurality of hinge (6) to provide angular movement (variation in angle β),
a rotary bed (3) which rest on lifting pads (7A, 7B) is clamped to rotary base (2), the rotary
base (2) is clamped to rotary plate (01) on which the job to be machined is mounted , the
rotary base (2) delivers the rotary motion to rotary table (01) for rotary movement of the
job.