FIELD OF THE INVENTION
The present invention generally relates to a system for carrying out TIG welding
of Impellers used in Centrifugal Compressor. More particularly, the invention
relates to an automatic system for carrying out TIG welding procedure under
controlled heating on impellers with different sizes and vane profiles to achieve
uniform and higher material deposition.
BACKGROUND OF THE INVENTION
An impeller mainly consists of two parts for example, a Disc, and a Counter disc.
These two parts are welded using TIG welding process. In general, the impellers
are having 13, 17 or 21 vanes. The vanes are machined on the counter disc and
the grooves are machined on the disc, which are used as weld beads. The
counter disc and the disc are fixed by exactly matching the vanes and the
grooves. The impeller is fixed on a welding positioner and preheated to 250 deg
C at the weld joint by external gas burning. Accordingly, a welding device is
mounted on a Cantilever structure The profile of the groove is traced by
matching the centre of the vane with the centre of a welding positioner and by
rotating the rotary table. The welding process is carried out as per the welding
procedure specification (WPS).
On an average, an impeller requires 19 to 23 layers of weld metal deposition on
each vane. In order to avoid distortion, a vane sequence is followed. For
example, for a 13 vane impeller, after completing one layer of the weld metal
deposition on vane number 13, the impeller is rotated to vane number 6 and so
on. Each layer per vane takes 4 minutes (approx.) of welding time. For 17-vane
impeller, the approximate total welding time is 1292 minutes (17 X 19 X 4) or 22
Hrs.
Depending on the profile of the vanes, some times the total welding process
takes 7 days of time. The positioning, alignment, fixturing and relocation of the
impeller after each vane is welded is presently done manually which consumes
rest of the non-productive time. The ratio of productive (welding) time to non-
productive (setup) time is in the range 1:4 to 1:6 depending upon design, size
and weight of the impeller.
Further, the impeller needs to be maintained at 250 deg C prior to welding which
according to prior art is carried out by burning producer gas, which takes 1 to
11/2 hour depending on the size and weight of the impeller. After the impeller
attains the required pre-heating temperature, the operator reduces the gas flow
and starts the welding. If the temperature of the impeller drops down, then gas
flow is increased and welding is stopped, as it is very hot to stand nearby. During
two shift operation, the impeller has to be preheated everyday at the starting of
the first shift. The welding parameters are being controlled manually and the
weld quality is dependent on skill of the welder. Some times the weld metal
deposition is not uniform on all the vanes.
In order to over come all these drawbacks in the existing system, a new method
has been developed using a robotic work-cell for automatic TIG welding for
achieving uniform and higher metal deposition. The developed robotic cell mainly
consists of six axes articulated robot, robot controller, TIG welding equipment
with integrated gas supply, TIG torch, Rotary table, work holding fixtures,
Electrical-heating mechanism.
The patent search has been carried out on this subject, but the complete
information related to this invention is not directly available. The following
patents (JP6198443, US4628180, US 4973813, US 20060124603, 7291807,
EO1555080A1, 4801781, 4628182 etc..) related to the present invention were
checked and found discrete information either related to TIG welding using robot
or TIG welding process or Hot wire TIG welding process. But there is no mention
of a method, which uses a positioner designed to hold the impeller firmly with a
provision for supply of purging gas, a dedicated heating system for pre-heating
the work-piece and automatic hot wire TIG welding for optimizing the deposition
efficiency of the welding process as per the welding procedure specification
(WPS) established for achieving higher and uniform deposition.
OBJECT OF THE INVENTION
It is therefore, an object of the invention to propose an automatic system for
carrying-out TIG welding process of Impellers of varying sizes and varying vane
profiles at controlled and continuous preheating conditions to achieve higher and
uniform material deposition.
Another object of the invention is to propose an automatic system for carrying-
out TIG welding process of Impellers of varying sizes and varying vane profiles at
controlled and continuous preheating conditions to achieve higher and uniform
material deposition, which reduces the set up time and pre-heat time to reduce
the overall cycle time.
SUMMARY OF THE INVENTION
Accordingly, there is provided an automatic system for carrying-out TIG welding
process of Impellers of varying sizes and varying vane profiles at controlled and
continuous preheating conditions to achieve higher and uniform material
deposition, the system comprising : a TIG welding device having a rotary table, a
work-piece holder to hold the impeller; a heating means having a temperature
controller; a TIG torch operably attachable to a six-axes articulated robot having
a controller and a communication interface; a hot wire power source attachable
to the TIG torch; and a wire feeding unit mounted on the robot for continuous
feeding of the filler wire to welding pool, wherein, the TIG welding device further
comprises a controller with a communication interface to exchange data with the
robot controller.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 Shows an improved system for automatic TIG welding of
centrifugal compressor impellers according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure 1, a six-axes articulated robot (1) is adapted in a TIG welding
device having a rotary table (2), a work piece holder (3), a heating means (4)
with a dedicated controller, a TIG torch (5) attached to the flange of the robot
and a hot wire power source (6). A wire feeding unit (7) is mounted on the robot
(1) for continuous feeding of the filler wire into the weld pool.
Impeller (Work piece) Holder (3): The impeller is mounted on the work-piece
holder, (3) which is having a base to fix on to the rotary table (2). One reference
plate is welded to the work piece holder (3) on which the impeller is mounted
with the help of centering locators. Provision has been created in the holder to
send the purge gas during the welding process. A positioner is designed in such
a way that it takes 15 minutes to load the impeller.
Electrical Pre-heating means (4): After loading on the work-piece holder (3), the
impeller is pre-heated to the required temperature using the electrical heating
means (11). The heat input to the impeller is by means of electrical resistance
heating. The heating means is having two parts i.e., Bottom plate and Top
covers, which can be opened/closed. Heating elements are provided on both the
parts. During initial hating the top cover covers are closed and the impeller is
heated to 250 Deg C. The heating means is having temperature measuring
sensors, which measure the temperature of the impeller and send the data to its
controller. It is observed that the system is able to heat the impeller to desired
temperature in 45 Minutes.
After the impeller is attained the required preheat temperature, the top covers
are opened and the heating coils in the top covers are switched "OFF". The heat
input is given to the impeller using bottom coils continuously to maintain the pre-
heat temperature.
Robot with TIG welding device: A six axes industrial articulated robot, with TIG
welding device is used for doing the welding. The TIG torch (5) is attached to
the robot flange. The filler wire is fed to the weld pool using the feeding (7) unit.
The feeding unit (7) is mounted on the 3rd axis of the robot (1). The Controller of
welding device and Robot Controller are connected using communication
network. Robot path program as per the profile of the vane is generated. The
welding parameters have been set in the robot program itself. When the robot is
doing the welding, the same parameters are maintained as set in the program.
Hence, manual intervention for setting the welding parameters is avoided and
precise control on the welding parameters is achieved. So uniform deposition and
same weld quality is achieved in all vanes. In the first pass, after first vane of the
impeller is welded, the rotary table rotates to the next vane as per the vane
sequence established to minimise the distortion effect. It takes 2 seconds for the
rotary table to the next vane.
Hot wire TIG welding process is used for achieving higher deposition and faster
welds speeds. In hot wire TIG welding, the filler wire is pre-heated, using hot
wire power source, just before it enters into the weld pool. Therefore the
deposition efficiency of the filler wire is improved. By using this method, we shall
achieve uniform material deposition, as all the vanes are being traced by the
robot with a repeatability of 0.05mm. The accuracy of the positioner is 15 arc
seconds. All welding parameters as per WPS are controlled from the robot
program hence no manual adjustments are involved.
EXAMPLE
Impeller Diameter: 0450mm
Drawing No: 1-332-08-04971
Number of Vanes: 13
Number of layers of deposition: 19
WE CLAIM :
1. An automatic system for carrying-out TIG welding process of Impellers of
varying sizes and varying vane profiles at controlled and continuous
preheating conditions to achieve higher and uniform material deposition,
the system comprising :
a rotary table, a work-piece holder to hold the impeller;
a heating means having a temperature controller;
a TIG torch operably attachable to a six-axes articulated robot having a
controller and a communication interface;
a hot wire power source attachable to the TIG torch; and
a wire feeding unit mounted on the robot for continuous feeding of the
filler wire to welding pool,
wherein, the TIG welding device further comprises a controller with a
communication interface to exchange data with the robot controller.
2. The system as claimed in claim 1, wherein the work-piece holder
comprises a base and a reference plate for welding on the holder, wherein
the impeller is mounted on the base and wherein a purging hole is
configured on the holder to supply purge gas during the TIG welding
process.
3. The system as claimed in claim 1 or 2, wherein the heating means
comprises a bottom plate and removable top covers, heating coils
provided on the bottom plate including the top covers, at least one
temperature measuring sensor to acquire temperature data during pre-
heating of the impellers, the acquired data being transmitted to the
controller.
4. The system as claimed in claim 1, wherein the articulate robot is operated
under pre-programmed sequence according to pre-stored weld
parameters.
5. The system as claimed in any of the preceding claims, wherein the system
controller and the robot controller communicate through wired network
for correction in deviations of on line data from the pre-stored data.

ABSTRACT

The invention relates to an automatic system for carrying-out TIG welding
process of Impellers of varying sizes and varying vane profiles at
controlled and continuous preheating conditions to achieve higher and
uniform material deposition, the system comprising : a TIG welding
system is having a rotary table, a work-piece holder to hold the impeller;
a heating means having a temperature controller; a TIG torch operably
attachable to a six-axes articulated robot having a controller and a
communication interface; a hot wire power source attachable to the TIG
Torch; and a wire feeding unit mounted on the robot for continuous
feeding of the filler wire to welding pool, wherein, the TIG welding device
further comprises a controller with a communication interface to exchange
data with the robot controller.