FIELD OF INVENTION
The present invention relates to an improved process with indigenously
developed tool to reduce the process time for rough machining of blade grooves
in hp shaft of steam turbine on CNC lathe.
BACKGROUND OF THE INVENTION
In machining of HP rotor shaft of Steam Turbine blade groove machining is a
very critical operation as these grooves are used in fitting of HP turbine blades.
In HP rotor shaft, no. of stages of these blade (grooves varies from 17 to 28
depending upon the design & 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. Rough
grooving 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 grooving operation is done using a straight grooving tool of

width around 15mm. So, tool geometry and its grade plays major role in deciding
cutting parameters for machining which finally attributes to machining time.
Rough grooving is done leaving 0.5mm allowance on its each side. After rough
grooving. T-type blade grooves are finish machined with different tools with high
accuracy and surface finish.
Earlier foreign make integral grooving tool of width 15mm was being used for
the rough grooving of T-type blade grooves.
As per design of this tool, two types of inserts are required for first plunging cut
and other for subsequent cuts as both inserts have different geometries.
Total no. plunging cuts with this tool were three per groove.
Cutting parameters; used for machining, were very low to suit the cutting
geometry of the tools & inserts.
Tool change time was higher due to frequent change of tool & inserts and their
resetting and consumption of tools was also high.
In view of above, it used to take very high machining time in carrying out the
rough grooving operation.

Time taken in machining of HP shaft was high in previous method leading to less
productivity.
Tool changing was required frequently which led to damage of sword(tool post).
OBJECT OF THE INVENTION
Therefore, it is an object of the invention to propose an improved process with
indigenously developed tool to reduce the process time for rough machining of
blade grooves in hp shaft of steam turbine which is capable of reducing the cycle
time drastically.
Another object of the invention is to propose an improved process time for rough
machining of blade grooves in hp shaft of steam turbine which is able to reduce
tool consumption and requirement of re-selting of tools.

A further object of the invention is to propose an improved process time for
rough machining of blade grooves in hp shaft of steam turbine which can
produce rough grooving of high acuracy and surface finish.
A still further object of the invention is to propose an improved process time for
rough machining of blade grooves in hp shaft of steam turbine which is capable
of making a substantial cost saving.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1: Shows the developed and improved tool according to the invention.
Fig.2: Shows the tool used in the prior art.
Fig.3: Shows the tool used in the prior art with different insert.
Fig.4: Shows the HP shaft with finished T-grooves and middle contour.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The object of the invention being reduction of process time on CNC lathe for
rough machining of blade grooves in HP shaft of Steam Turbine, new CNC
parametric program, newly designed tool and improved process for the said
machining are incorporated.
Earlier some standard tool was used to rough plunging of T-grooves. Three
number of cuts were involved in rough machining of T-groove. First cut in middle
of groove left equal allowance on both sides. Some fininsh cut was taken with
0.5mm allowance left on Right hand and Left hand side of neck width. This
process takes much time for roughing of T-Groove as the cutting parameter are
very less such as cutting speed = 30-40 m/min and feed = 0.08 to 0.1 mm/rev.
A new parametric CNC program is developed for optimum numbers of Plunging
cuts per groove depending upon its size for rough machining of T-groove in HP

shaft of a turbine. At the same time a new grooving tool is developed with
improved cutting geometry and grade for highly productive machining. The
number of plunging cut is reduced to maximum 2 per groove. The cutting
geometry and grade of the new grooving tool enabled to incorporate very high
cutting parameters such as cutting speed 80mm/min and feed of 0.25 to 0.3mm/
revolution during the rough machining of T-groove. This application reduced
cycle time drastically and tool consumption and requirement of re-setting of tools
reduced substantially.
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 HP rotor shaft 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) Safety : As previous tool was clamped downward so was unsafe whereas
new tool is clamped upwards hence safer.
6) Health and working condition: As clamping and unclamping was
reduced so machine operators were less fatigue.
7) Financial Saving: Time saved in maching of T-groove-35 hrs/shaft
Machining Cost = Rs. 6000 per hour.
Total saving = 6000 X 35 = Rs. 210000.
Average No. Of HP shaft machined per year = 12
Toatal saving per year = 21,0000 X 12 = Rs. 25,20,000
= 25.2 lacs.

Fig.1 shows the developed and inproved tool made indigenously. The height (A)
of the tool shank is increased to 40mm from the standard tool height of 30mm.
The width of the shank at the rear end is decreased to 32mm from 34.5mm of
the standard tool width while the width (6) of the shank at the front is made
33mm. The shank width (E) pm which the insert seats is made 16mm from
15mm of the standard tool to increase rigidity while the overhang (D) of the tool
is decresed from 80mm of the standard tool to 70mm to improve the load
carrying eliminating chance of vibration and breakage. The total length (F) of the
shank is made to 250mm from 275mm to fecilitate the clamping of the tool from
the top at three positions close to each other. This also add to the rigidity of the
tool eliminating the chance of vibration and breakage. All these dimensions are
finalised after some experimental research.
Fig.2 shows the HP shaft with finished T-grooves and middle contour
Fig.3 shows the tool used in the prior art with different insert.
Fig.4 shows the HP shaft with finished T-grooves and middle contour.

Development of New method of plunging of T-groove by machining in 2 steps
in comparison to previous 3 steps method. Idea for plunging in two steps
was new and unique as it was not done before on any machine.
Suggestion for new tool with insert for plunging of T-groove was new as tool of
such geometry was previously not available in store as it was not
manufactured by any tool supplier.
Idea for new method was implemented on HP shaft of 250 MW and cycle time of
machining was clearly reduced and process was also found to be easier and
safer. Then this method was used on HP Shaft of 500 MW and result found was
highly positive. This method shall be used in higher rated Steam turbine Shafts.
Now this method is followed in all HP Shafts that are machined on this CNC
machine 1-120.
The idea of this method is also used in machining of Middle Contour Plunging of
IP Shaft and HP Shaft.

Advantages of using the new process and improved tool from safety and working
condition point of view.
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 hut
new method is easier and safer as only changing of insert is required.
Personal Safety
Frequent handling of tool is reduced. In previous S and H tool complete cassette
and accessories was to be taken out whereas in new method only insert has to
be changed which is more safe.
Process Safety
In Suggested method coolant is supplied from two nozzles whereas in previous
method only one nozzle was provided that too less effective. Proper coolant
supplv improves the finish of groove and absorbs heat developed during
machinging.

New tool can be clamped and used in both downward and upward direction
having an advantage over previous tool which had to clamp in downward.
Equipment Safety
In previous method frequent handling of tool was required. Previous S and H
tool cassette was to be assembled and disassembled from uncommon sword
(tool post) large no. of time whereas in suggested practice cassette is attached
to regular used sword leading to sword safety.

WE CLAIM
1. An improved process with indigenously developed tool to reduce the
process time for rough machining of blade grooves in HP shaft of steam
turbine on CNC lathe, the said process comprising;
incorporating new cutting parameter on CNC lathe to perform rough
machining of T-grooves on HP shaft;
clamping the improved tool in both downward and upward direction to
impart rigidity in tool;
arranging supply of coolant from two nozzles to absorb heat of machining
and to improve the finish of groove; wherein two numbers of plunge cuts
per groove are incorporated in the machining process with high cutting
parameters to reduce the process time of machining.
2. The process as claimed in claim 1, wherein the clamping of the tool
disposed in the said process is done in three position.

3. The process as claimed in claim 1, wherein the cutting parameter such as
cutting speed of 80mm/min and feed of 0.25/0.3mm/revolution of the tool
are used.
4. A tool used in the process claimed in claim 1, comprising
a shank of height 40mm;
a shank of width 32mm in rear end and 33mm in front end;
an overhang of 70mm of the shank portion carrying the insert;
a total length of 250mm of the shank wherein, the cutting insert sits on a
shank portion of width 16mm when the said insert is disposed for making
two plunge cuts per groove for finishing T-grooves on HP shaft.

ABSTRACT

An improved process with indigenously developed tool to reduce the process
time for rough machining of blade grooves in hp shaft of steam turbine on cnc
lathe comprising incorporation of new cutting parameters on CNC lathe to
perform rough machining of T-grooves on HP shaft. The improved tool is
clamped in both upward and downward direction. Enormous supply of coolant is
arranged to dissipate the heat and to have good finish of grooves. Two numbers
per groove of plunge cut of the tool are introduced in the process for substantial
savings of process time.