FIELD OF INVENTION
The present invention relates to an improved process on CNC lathe
with newly developed tools to reduce the process time for rough and finish
machining of side grooves in T-groove in shaft of steam turbine.
BACKGROUND OF INVENTION
In machining of LP/HP/IP shafts of Steam Turbine side groove in T-
groove machining is very critical operation as these grooves are used in fitting of
turbine blades. In HP rotor shaft, no. of stages of these blade (grooves varies
from 17 to 28 depending upon the design and rating of Steam Turbine). As there
are many no. of stages, time taken in machining of these blade grooves is critical
and takes major part of total cycle time of complete machining of HP Shaft on
CNC lathe. Machining operation for these T-type blade grooves takes substantial
time which needs to be tapped for its reduction in order to result in total cycle
time reduction.
Rough and finish grooving operation is done using a L shaped
brazed grooving tool of width generally around 6.5 and 8.5 mm for different
widths of T Grooves. So, tool geometry and its grade plays major role in deciding

cutting parameters for machining which finally attributes to machining time and
quality of surface finish.
Straight rough grooving is done leaving material on the radius.
After this step, material is removed on the radius leaving allowance of 0.5mm. In
the finishing step after checking the neck height of the T-Groove leftover
material is removed.
Earlier brazed tools were used for rough and finish machining of
these types of grooves. As this operation involves facial grooving at different
diameters these tools have sufficient side clearances. Being brazed type tools
after their use these tools need to be ground again and again for their repetitive
use. All clearances need to be maintained during regrinding otherwise these tools
cannot be used.
Cutting parameters, used for machining, were very low to suit the
cutting geometry of the brazed tools.
In the earlier process LH tool was used in the left cassette and the
RH tool was used in RH cassette.
Tool change time was higher due to frequent change of tool for
regrinding and their resetting and consumption of tools was also high due to
frequent breakage.

In view of above, it used to take very high machining time in
carrying out the rough grooving operation.
Time taken in machining of such grooves was high in previous
method leading to less productivity.
Tool changing was required frequently which led to time delays.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an improved
process on CNC lathe with newly developed tools to reduce the process time for
rough and finish machining of T grooves in shaft of steam turbine which is
capable of reducing the cycle time drastically.
Another object of the invention is to propose an improved process
on CNC lathe with newly developed tools to reduce the process time for rough
and finish machining of T grooves in shaft of steam turbine which is able to
reduce tool consumption and requirement of re-setting of tools.
A further object of the invention is to propose an improved process
on CNC lathe with newly developed tools to reduce the process time for rough
and finish machining of T grooves in shaft of steam turbine which can produce
grooves of high accuracy and surface finish.

A still further object of the invention is to propose an improved
process on CNC lathe with newly developed tools to reduce the process time for
rough and finish machining of T grooves in shaft of steam turbine which is
capable of making a substantial cost saving.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.1 - Shows the design of T Groove and Location of the Finished Grooves
in the Rotor.
Fig.2 - Shows design of T Groove
Fig. 2a - Shows material removed in the First operation grooving tool in the
prior art.
Fig.2b - Shows material removed in the second operation.
Fig.2c - Shows material removed in the third operation by.
Fig.3 - Shows Area to be machined
Fig.4 and 4a - Brazed tools used according to prior art.
Fig.5 - Shows the both types of tool together (LHS and RHS) for
machining according to the invention.
Fig.6 and 7 - Shows LH and RH tool holder with tool insert as per invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Referring to fig.2a, in this operation material between the two radii
is removed in the grooving operation. Material of height x is removed in two
cuts. The tool is clamped on the left hand side for LHS T groove and on the right
side for RHS T groove. Tool change is done after removing the cassette from
LHS to RHS.
Referring to fig. 2b in this operation material on the radii is
removed leaving an allowance of 0.5mm per side taking grooving cuts along the
contour. The tool is clamped on the left hand side for LHS T groove and on the
right side for RHS T groove. Tool change is done after removing the cassette
from LHS to RHS.
Referring to fig. 2c in this operation reaming material on the radii is
removed maintaining the neck height. The tool is clamped on the left hand side
for LHS T groove and on the right side for RHS T groove. Tool change is done
after removing the cassette from LHS to RHS.
Fig.3 shows the area to be machined. Fig.4 and 4a shows the
brazed tools used in prior art. Fig.6 and Fig.7 shows LH and RH tool holder with
tool insert as per invention.

As shown in fig. 5, in the developed methodology the tool has been
so developed which does not require that the cassette needed to be changed
from LHS to RHS. This reduces the total width of Ram and tool which enables us
to mount RHS tool on the LHS assembly. Also the tool so developed has insert
which prevents the wear and tear of the tool body.
The object of the invention being reduction of process time on CNC
lathe for rough and finish machining of Side Grooves in T Grooves is shafts of
Steam Turbine, new CNC parametric program, newly designed tool and improved
process for the said machining are incorporated.
Earlier brazed tool was used for machining of side grooves in T
Grooves. Two number of cuts were done to remove the straight material leaving
material leaving material on the two radii. Then material on the radii is removed
leaving an allowance of 0.5mm per side. A finish cut was taken with 0.5mm
allowance left maintaining the neck height. This process takes much time for
machining as the cutting parameter are very less such as cutting speed = 20-30
m/min and feed = 0.08 to 0.1 mm/rev.
There are many variations in different dimensions of T grooves, the
shape remains same in the present methodology material in the straight area of
length Y in T grooves is removed in two cuts. So the tool width should not be
less than "x/2" and not more than "2x". For optimized machining, the tool width

should meet this condition. Also "r" dimension of the tool should be more than
(Groove Width-Neck width)/2 so that it can remove the hatched material
completely. Dimension V of the tool should be less than the neck width so the
tool can enter the groove.
In the machining of two types of grooves having "x"= 10.4mm and
15.7mm respectively, two separate tools were used with dimensions b= 6.5 and
8.5, c=21 and 28, r= 8.5 and 10.5 respectively.
A new parametric CNC program is developed for optimum numbers
of Plunging cuts per groove depending upon its size for rough and finish
machining of side grooves in T grooves in shafts of a turbine. At the same time
new tool was developed with improved cutting geometry and grade for highly
productive machining suiting the developed tool. The cutting geometry and
grade of the new grooving tool enabled to incorporate very high cutting
parameters such as cutting speed 60-80mm/min and feed of 0.15 to 0.20
mm/revolution during the rough and finish machining of side grooves in T
grooves. As shown in Fig.4 E & F are clearance angles of the tool. E is the side
clearance and F is the top clearance angles of the tool. In the prior art E=2° and
F=7°. In the developed tool F angle has been increased to 12 deg from 7 deg
earlier. This increase helps in covering lower range of diameters right from

1000mm. As the earlier range of tools were suitable from the dia 1500mm
onwards.
Also the earlier tools were brazed tools, new tools have inserts
which prevents the wear and tear of the main body of the tool. Earlier tools were
needed to grinded frequently which disturbed their geometry.
The round coupling at the back helps in mounting on the single
cassette for LHS and RHS grooves.
The solid body of the tool makes the mounting sturdier which gives
the groove a better finish. The feed and RPM can be increased thereby saving
cycle time.
Also the new tool so developed has width b=8 which satisfies all
the condition for machining the two mentioned grooves. Number of plunge cuts
remains same but the number of tools used have decreased. Earlier two tools
were used for two different T Grooves but now only a single tool can machine
two different grooves.
This application reduced cycle time drastically and tool consumption
and requirement of resetting of tools reduced substantially. An arrangement of
coolant is made to improve surface finish and life of the tool.
The following are the benefits accrued after changing the process
of machining and the use of an improved tool.

1) Productivity: Total machining time of rotor shafts on CNC Lathe reduced
substantially.
2) Financial Benefit: As cycle time is reduced critical CNC machine availability
is increased to take up more nos. of rotors.
3) Power Saving: Overall Productivity & Utilization of machine is increased
hence power consumption was reduced.
4) Quality: With use of improved process and tools, quality of machining is
also improved.
5) Health and working condition: As clamping and unclamping was reduced
so machine operators were less fatigue.
6) Financial Saving: Time saved in machining of 1 Groove = 1.2 hrs
Time saved in machining of all grooves of the shaft = 14.4 hrs/shaft
Machining Cost = Rs. 6500 per hour.
Total saving = 6500x14.4 = Rs. 93600.
Average No. of shaft machined per year = 10
Total saving per year = 93,600 x 10 = Rs. 9,36,000
= 9.36 lacs.
Advantage of using the new process and improved tool from safety and
working condition point of view.
7) Elimination of frequent Cassette Change

This process eliminates the frequent requirement of changing the cassette
to machine the left and right balancing weight grooves. This in turn
reduces the machining cost. Also this eliminates errors and rectification
which may creep in due to frequent cassette change and tool setting.
8) Tool Safety
As tool having new geometry with insert was used which was much
convenient and safer. Previously, grinding of tool was required as it get
blunt frequently but new method is easier and safer as only changing of
insert is required. Also for different sides of groove no new attachment is
required as the same tool is able to machine on both the sides.
9) Personal Safety
Frequent handling of tool is reduced. In previous Brazed tool complete
cassette and accessories was to be taken out whereas in new method only
insert has to be changed which is more safe.
10)Process Safety
In suggested development of tools, coolant is supplied from two nozzles
whereas in previous designed tools there was no provision of coolant
supply which was less effective, Proper coolant supply improves the finish
of groove and absorbs heat developed during machining.

WE CLAIM
1. An improved process on CNC lathe with newly developed tools to reduce
the process time for rough and finish machining of Balancing weight
grooves in shaft of steam turbine, the said process comprising:
developing new crank grooving tools with improved grade and cutting
geometry;
employing a single developed tool to machine two different grooves;
selecting a high and improved cutting parameters on the CNC machine
suiting the said tool wherein a new CNC program is incorporated based on
the said improved cutting parameter to introduce optimum numbers of
plunge cuts per groove depending upon its size for rough and finish
machining of Balancing weight groove in shafts on a turbine to reduce the
process time,
wherein the implemented high cutting parameters are cutting speed of
60-80 mm/min and feed of 0.15-0.22 mm/revolution,
and the grade of the cutting tool is Aluminium - tungsten coated carbide
tool,
wherein the improved cutting geometry of the tool has top clearance
angle F equal to 12 degree and the width 'b' of the tool is 8 mm.

ABSTRACT

An improved process on CNC lathe to reduce the process time for rough and
finishing operation of balancing weight grooves comprises of developing new
crank grooving tools with improved grade and cutting geometry. An improved
cutting parameters for the developed tool is selected and on the basis of this tool
a new CNC program is adapted so that an optimum number of plunge cuts per
groove for rough and finish machining of balancing weight groove to reduce the
process time.