FIELD OF INVENTION
The present invention relates to a process of machining steam turbine blades.
More particularly it relates to a process for machining steam turbine blades to
increase productivity and lower manufacturing cost and delivery time.
BACKGROUND OF THE INVENTION
The efficiency and reliability of turbine is dependent upon the design and
manufacturing accuracy of blades. Turbine blades play an important role in
deciding the thermal efficiency of the steam turbines. BHEL has established
state-of-art facility to manufacture turbine blades at New Blade Shop. The
blanks are cut to the required sizes (based on the blade length and cross-
section) and 11 nos. of blanks are simultaneously loaded on Work piece station
of 5-Axis CNC machining centers. Complete machining of required blades is
carried out step by step as per CNC program. In the first step, roughing
operation of Hub and Hub slot, Shroud and profile is carried out and after
completion of roughing operation, finishing operation is carried out on that semi-
finished blade and here the machine automatically selects the required
tool/cutter from tool magazine for different operations and measure the tool

length and diameter in Laser Unit inside the machine. Important dimensions of
blade are automatically checked by Renishaw probe during roughing operation
and automatic correction is carried out to maintain the required dimensions.
After completion of machining, the finished blade is automatically comes out of
the machining area and new blank comes for machining.
The process of prior art suffers with many disadvantages such as excessive
consumption and damage of cutters/inserts also generate poor surface finish in
various stages of manufacturing turbine blades. On CNC m/c whenever a new
tool is put into the magazine as a replacement, it needs re-measurement which
causes huge delay increasing the manufacturing time cycle and thus causing
delay in final dispatch of turbines.
Breakage of cutter occurs during operation of Fillet machining on root and
shroud side due to improper re-sharpening and unavailability of coated cutters.
Coating of solid carbide cutters is a tedious and expensive process resulting its
unavailability at the time of need. As ball nose cutters length and diameter
reduces after several re-sharpening and causes variation in dimensions in Fillet
area and sometime the blade gets rejected or it may require dimensional
rectification. After breakage of cutter, the new cutter is put and got re-measured
inside the machine that consume more time (approx. 10-15 minutes). Eventually

with this process productivity gets reduced. But with huge workload, the target
of production is to increase output with a reduction in manufacturing cycle time.
As in prior art for rhomboid and thickness finishing operation of turbine blades, a
WP 50 insert type cutter having 50 mm diameter is used at root side of the blade
in two pass as the surface length is more than 70 mm. This leaves a line mark in
the surfaces due to movement of the cutter in two pass. At the same time it
takes more time for two pass machining increasing the cycle time. It also results
in poor surface finish and variation in dimensions. More often a rework is
necessary to remove steps on the surface of the job and thus increases cycle
time and reduces productivity. In the existing process the top radial slot
machining operation of the blade is carried out by a solid carbide and mill cutter
(Z10R2). Due to high depth of cut, more often there is breakage of cutter during
the slot machining. It necessitates replacement by a new cutter which is again
remeasured inside the machine that consumes lot of time (approx. 10-15
minutes). These solid carbide cutters are also coated and process of coating is
tedious and expensive and hence availability is not always guaranteed. The
length of end mill cutter reduces after several re-sharpening when its diameter
also gets reduced that causes variation in dimensions of radial slot. Also after
several re-sharpening, the strength of the cutter is reduced. The whole process
takes lot of time and hence the productivity is low. So, when the workload is

consistently high, there is always a pressure to increase output with reduced
cycle time.
In the Prior art, the cutter having inserts (WP 32) are used for shroud semi
finishing and aerofoil roughing. The cutter does semi finishing at shroud first and
then aerofoil roughing. Due to high depth of cut at shroud side the inserts get
blunt and it breaks during aerofoil operation. As regard life of these cutters, this
cutter should make 5-6 blades per edges but sometimes it wears out after 3-4
blades. Sometimes the situation calls for a change of inserts during the course of
operation in order to complete full machining. The process is time consuming
with low productivity when the demand is to have high output with reduced cycle
time.
Hence, there exists a need to invent a process that eliminates the disadvantages
of prior art.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose a process of machining
steam turbine blades which is capable of lowering manufacturing cost.

Another object of the invention is to propose a process of machining steam
turbine blades which enables reduction of manufacturing cycle time.
A still another object of the invention is to propose a process of machining steam
turbine blades which is enable to increase productivity.
A further object of the invention is to propose a process of machining steam
turbine blades which is enable to lower delivery of time.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - a process flow chart of the present invention
Fig.E - a photograph which shows the application of insert type cutter for root
and shroud fillet operation
Fig.F - a photograph which shows the application of WP 80 cutter in place of
WP 50 cutter in thickness and rhomboid finishing
Fig.G - a photograph showing the application of WP 20 insert type cutter in
place of Z10R2 solid carbide cutter in root radial slot
Fig.H - a photograph of WP50 insert type cutter in place of WP32 cutter in
shroud leading edge operation

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The original technology for manufacturing advanced type small turbine blades
was provided by the supplier of the CNC machining centre. Expensive and
imported cutters are being used earlier for machining large blades of the turbine.
These cutters are then replaced by consumable inserts. After experiencing
problems of breakage, improper re-sharpening and unavailability of new and
coated solid carbide cutter in root and shroud fillet operation of small blades,
these cutters have been replaced by insert type cutters already used for bigger
blades in other operation. Referring Fig-E, these insert type cutters had been
discarded after using on bigger blades. In the present invention, the first step of
the process is to re-use of the left out life of already consumed inserts of bigger
blades in smaller blades. Trial is conducted on small blades with these used
inserts by optimizing parameters viz. cutting feed, spindle RPM and depth of cut.
In this new process, K-10 solid carbide cutter is replaced by K-10 insert type
cutter. The use of this insert type cutter helps to operate in higher cutting
parameter also has eliminated re-sharpening and coating of expensive solid
carbide cutters. It has also eliminated the necessity of tool-measurement. By
process optimization the cycle time is reduced and hence productivity is
increased. Also, tool life is increased as 30 blades per insert type cutter are

machined in comparison to 4 blades per solid carbide cutter. Hence there has
been a huge increase of production.
Referring Fig-F, for thickness and rhomboid finishing operation, in order to
overcome the problem of left over step on the surface of the blade, the new
process replaces WP 50 insert type cutter having 50 mm diameter by a WP 80
insert type cutter having 80 mm diameter. Because of single pass operation,
surface finish is also better. It eliminates unwanted step in thickness and on
rhomboid surfaces. Since there is a reduction in tool contact time, there is an
increase of tool life.
Since there exists problem of breakage, improper re-sharpening and
unavailability of new and coated solid carbide cutter also in root radial slot
operation, the solid carbide cutter is replaced by insert type cutter in the
improved process. As shown in fig-4, WP 20 insert type cutter having 20 mm
diameter replaces Z10R2 solid cutter. The improved process is less costly as the
insert type cutter is much cheaper than solid carbide type. The process also
eliminates re-sharpening and coating of solid carbide cutter. It saves tool
measurement time. Tool life is also increased as evident from the trial result as
20 blades are machined per insert type cutter compares to machining of 4 blades
by a solid carbide cutter. It helps increase in productivity.

In shroud semi-finish and Aerofoil roughing operation in prior art, the same
cutter does two operations namely roughing of shroud leading edge and
roughing of Aerofoil. In the improved process, these two operations are being
done by two separate cutters. An used up insert type cutter WP 50 having 50
mm diameter is used for roughing of shroud leading edge and another insert
type cutter WP 30 having 32 mm diameter for roughing of Aero profile. In prior
art both these roughing operations are performed by the same cutter WP 32. It
is shown in fig-H. This features of improved process increases the life of the
cutter by about 3 times.
Since the improved process is entirely different from the original process,
program and tools supplied/implemented by the m/c supplier at the time of
commissioning is changed on the CNC program module as per requirement. The
manufacturing of blades of the turbine by this improved process is for the first
time done in India successfully. A process flow chart of the present invention is
shown in Fig.l.
This improved process with optimization of machining parameters has increased
the production by reducing cycle time and cost, improving the availability of
critical 5 axis machine and lowered the delivery time.

WE CLAIM
1. A process of machining steam turbine blades to increase productivity and
lower manufacturing cost and delivery time characterised in the steps of;
machining root and shroud fillet of steam turbine blades by insert type
cutter having at least a diameter of 10 mm;
machining thickness and rhomboid finishing of steam turbine blades by
insert type cutter having at least a diameter of 80 mm;
machining root radial slot operation of steam turbine blades by insert type
cutter having at least 20 mm diameter;
rough machining of shroud leading edge of a steam turbine blades by a
insert type cutter having at least 50 mm diameter; and
rough machining of aero profile of a steam turbine blades by a insert type
cutter having at least 32 mm diameter.
2. A process of machining steam turbine blades as claimed in claim 1,
wherein inserts for root and shroud fillet operation are consumed inserts
of bigger blades in other operation.

3. A process of machining steam turbine blades as claimed in claim 1,
wherein thickness and rhomboid finishing operation is done in single pass
of the cutter.
4. A process of machining steam turbine blades as claimed in claim 1,
wherein roughing operations of shroud leading edge and aero profile of
the blades are done by two separate cutters, one being used up 50 mm
diameter and the other at least 32 mm dia.

The process of machining steam turbine blades consists of machining the root
and shroud fillet of blades by insert type cutter of 10 mm diameter, machining
thickness and rhomboid finishing of the blades by insert type cutter of 80 mm
diameter and then machining root radial slot operation of the turbine blades by
20 mm dia insert type cutter. The rough machining of shroud leading edge of the
blade is carried out by insert type used up cutter of 50 mm diameter and finally
rough machining of aeroprofile of the steam turbine blades is done by a insert
type cutter of 32 mm dia,