FIELD OF THE INVENTION
The invention relates to multi-layer, multi bead welding process in joining of
materials. More particularly, the invention relates to a method for precise control
of welding distortion arising in welded fabrication, in particular, a multi-layer,
multi-bead welding procedure.
BACKGROUND OF THE INVENTION
Distortion is inevitable in all welding processes to varying extent. Managing
distortion is a challenging task for the engineering industries involved in welding
fabrication. The task of distortion control is intensively experienced by fabrication
industry using methods like TIG, MIG, SMAW, and SAW welding processes.
Primarily, the process control is exercised to keep distortion value to a minimum
level. To augment the distortion control exercise in subsequent stages,
techniques like fixturing (prior to start of welding), layer sequencing (during
progress of welding) and bead sequencing (with online monitoring) are followed
to bring distortion level within the required limit.
Conventional methods aims at keeping the distortion value well within the final
requirement in every layer of weld built up, right from root welding. This is an
extremely difficult task and almost impossible to retain the original setup
condition till the end of welding process. Many a times, it becomes a need to
achieve a finer degree of dimensional control, especially for critical applications.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a method for precise
control of welding distortion arising in welded fabrication, in particular a multi-
layer, multi-bead, welding procedure.
Another object of the present invention is to propose a method for precise
control of distortion arising in welded fabrication, in particular a multi-layer,
multi-bead welding procedure, which is capable of exercising distortion control
within 0.05-degree closeness.
A still further object of the present invention is to propose a method for precise
control of distortion arising in welded fabrication, in particular a multi-layer,
multi-bead welding procedure which eliminates an additional step of distortion
correction in a manufacturing process, thereby saving the total overall production
cycle time.
Yet another object of the present invention is to propose a method for precise
control of distortion arising in welded fabrication, in particular a multi-layer,
multi-bead welding procedure, which can produce different welding components
capable of being precisely integrated (i.e. with intentional introduction of
distortion).
SUMMARY OF THE INVENTION
Accordingly, there is provided a method for precise control of welding distortion
arising in welded fabrication, in particular a multi-layer, multi-based welding
procedure, comprising the steps of: - determining a base reference value in
respect of angular distortion between atleast two weldable members by
quantification and estimation of geometrically predefined contours; and limiting
the current distortion values below the determined value including applying
intermittently a comparison via the evolved check-points.
According to the inventive method, angular distortions between mating parts are
precisely controlled by quantification and estimation of geometrically pre-defined
weld groove contours which uses a layer indexing technique. The method
comprises root limiting, layer indexing, two-phase control, "Oisik's pressure
bubble changes", and overlapping thermal cycle in controlling the primary
including the secondary angular distortions to highest level of precision. A
standardized segmentation of application of the evolved data is indicated at fig 7.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: Shows a graphical representation of root control limit with reference to
number of layers vs. maximum controllable distortion zone.
Fig. 2: Shows a distortion and layer index indicating a controllable limit.
Fig. 2A: A subjective representation of distortion and layer index. Defines
formulation for qualified and characterized measure of controllable distortion
limit.
Fig. 3: A schematic representation in context of OISIK'S change technique which
defines a novel pressure bubble pattern of observation, named "Oisik's pressure
bubble changes".
Fig. 4: A block diagram showing overlapping thermal cycle, applicable at the
stage of welding.
Fig. 5: Shows angular distortion comparison in centre to side (CTS) vs. side to
center (STC) welding technique.
Fig. 6: A pressure bubble phenomenon, occurring during the operational mode of
the present invention.
Fig. 7: Depicts a zone dividing segmentation to use as a standardization strategy.
Fig. 8: Schematically shows a device adaptable to carry-out the method of the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
This invention provides a process for precise control of distortion arising in
welding process, in particular a multi-layer, multi-bead welding process basically
comprising the steps of new angular distortion estimation and a control
technique. In multi-layer, multi-bead welding process, angular distortion between
mating parts are precisely controlled by quantification and adapting geometrically
pre-defined contours. It uses root limits, layer indexing (Fig. 2), two phase..........
control (Fig. 7) and Oisik's pressure bubble changes technique (Fig. 3) with an
application of the overlapping thermal cycle (Fig. 4) in controlling primary ( i.e.
gross level) including secondary (i.e. finer degree) angular distortions to the
highest level of precision. The invention is described in the context of welding
procedure of sixteen numbers sixty-five millimeter diameter stainless steel
nozzles, and a consistent result in the distortion values are produced within 0.02
mm from the original set up terminal position, in all established procedure of
weld edge preparation.
The observations in all the above sixteen cases showed repetitive pattern on
distortion behavior. In the initial phase (root), the distortions take place in larger
values and gradually it reduced in successive layers.
To achieve the required result and effective control, this root layer distortion
value is taken as the base reference. In Subsequent layers, distortion values are
kept below the recommended value as per the graph shown in fig: 1
The method basically follows the three major steps as under: -
a. Forecasting:
ROOT level vs. number of layers graph is generated and used. Based on number
of layers possible and maximum root layer distortion, maximum Permissible
distortion value is decided (also refer sl. No. c below).
b. Root management technique:
Root level distortion are kept below 1.5° . i.e., 0 i = 1.5 ° by using wedges,
fixtures and stiffeners , where 0 i= Si/L is the initial distortion angle and L is the
length of the nozzle. Si is the initial distortion (linear shift measured at free end )
after the root layer.
c. Online estimation:
For the entire scope of a weld joint set up, where Tb is the remaining thickness
to be welded, N b is the remaining number of layers and d av is average
electrode diameter for the entire weld range.
c.1. While Tb/dav.(=Nb)) = 4;
Normal alternating weld sequencing for first layer and overlapping
weld sequencing is followed from the second layer.
c.2. While 4 < Tb / d av. ( = N b)) = 6;
Normal sequencing for first two layer (to improve stability) and
overlapping weld sequencing is followed subsequently, till the final
stage of welding.
c. 3. While Tb/dav. (= N b)) > 6;
Normal sequencing for first three layers (to reinforce stability) and
overlapping weld sequencing is followed subsequently, till the final stage
of welding.
d. Check points
From the ROOT level vs. number of layers graph, the present locational shift (Spr.
location) is compared with the desired value (Sd) at any given point during welding.
While S pr. location = S d at any state, welding proceeds without any corrective
steps.
According to the invention, the method provides a mechanism to control the
distortion in welding. The major steps followed are Forecasting, Root
Management Techniques, Online Estimation and Check Points which are capable
of achieving precise dimensional control within 0.05 Degree closeness. The
process, is applicable in all multi-layer and multi-bead welding processes, which
are highly distortion intensive. The process eliminates the need for weld
corrections due to distortion, thereby reduces manufacturing cycle time and
improves product quality. The process is applicable in welding all types of
materials. The process is capable of achieving desired dimension at minimum
cost. The process achieves highest precision while integrating different welded
components.
Online estimation of the angular distortion is based on one of the
undermentioned steps carried-out corresponding to the characteristic attributes
normal alternating weld sequencing for first layer and overlapping weld
sequencing is followed from the second layer, when Tb / d av. (=: N b)) = 4;
normal sequencing for first two layer and overlapping weld sequencing followed
subsequently, till the final stage of welding, when 4 < Tb / d av. ( = N b)) = 6;
normal sequencing for first three layers and overlapping weld sequencing
followed subsequently, till the final stage of welding, when Tb / d av. (= N b)) > 6,
wherein Tb is the remaining thickness to be welded, Nb is the remaining number
of layers and d av is average electrode diameter for the entire weld range.
WE CLAIM
1. A computer-implemented method for precise control of welding distortion
arising in welded fabrication, in particular a multi-layer, multi-based
welding procedure, comprising the steps of:-
- determining a base reference value in respect of angular distortion via an
on-line estimation between atleast two weldable members by
quantification and estimating geometrically predefined weld groove
contours; and
- limiting the current distortion values within 0.05 degree closeness by
applying intermittently a comparison via the evolved check-points,
wherein normal alternating weld sequencing for first layer and overlapping
weld sequencing is followed from the second layer, when Tb / d av. (= N
b) = 4;
- carrying-out normal sequencing of the first two layer and subsequent
overlapping of the weld sequencing till the final stage of welding, when 4
6, wherein Tb is the remaining thickness to be welded, Nb is
the remaining number of layers and d av is average electrode diameter for
the entire weld range.
2. The method as claimed in claim 1, wherein the step of determining a base
reference value comprises:-
- forecasting the maximum permissible distortion value based on the
number of layers and the maximum root layer distortion; and
- application of a root - management technique based on the values of
initial distortion and the length of the welding nozzle.
3. The method as claimed in claim 1 or 2, wherein, the step of comparing via
evolved check points comprises generation of a current locational shift
(Spr.location) based on a graphical representation formed with the acquired
data in respect of root level vs number of layers, and comparing the
current locational shift (Spr.location) with the desired value (Sd) at a given
time during the welding procedure, and wherein when Spr .location = sd,
proceeding the welding without any corrective step.
4. A computer - implemented for precise control of welding distortion arising
in welded fabrication, in particular a multi-layer, multi-based welding
procedure, as substantially described herein with reference to the
accompanying drawings.

The invention relates to a computer-implemented method for precise control of
welding distortion arising in welded fabrication. The method comprises the steps
of determining a base reference value in respect of angular distortion via an on-
line estimation between atleast two weldable members by quantification and
estimating geometrically predefined weld groove contours; and limiting the
current distortion values within 0.05 degree closeness by applying intermittently
a comparison via the evolved check-points, wherein normal alternating weld
sequencing for first layer and overlapping weld sequencing is followed from the
second layer, when Tb / d av. (= N b)) ≤ 4; carrying-out normal sequencing of the
first two layer and subsequent overlapping of the weld sequencing till the final
stage of welding, when 4 < Tb / d av. ( = N b)) ≤ 6; carrying-out normal
sequencing of first three layers and subsequent overlapping of weld sequencing
till the final stage of welding, when Tb / d av. (= N b)) > 6, wherein Tb is the
remaining thickness to be welded, Nb is the remaining number of layers and d av
is average electrode diameter for the entire weld range.