FIELD OF THE INVENTION
The present invention relates to a high power laser welding process to weld
annular stellite rings to the base material to produce internal dads acting as
wear resistant coating for valve seat rings.
BACKGROUND OF THE INVENTION
Cladding of internal surfaces for various components for example, valves, pipes,
tubes, engines, is required to reduce the damage due to wear. Conventionally,
the internal cladding especially in valves is performed by filling up of the entire
cavity by hard facing process and subsequently machined to desired dimensions
which result in wastage of expensive powders including high cost of machining of
the hard faced components. Laser welding is characterized by narrow fusion
zone (weld bead), HAZ (Heat Affected Zone) and hence capable of producing
very fine and precise welds. This can effectively reduce the dilution. Laser
welding has other advantages like clean welds, easily amenable for automation
thereby increasing productivity. -
Laser cladding operations are conventionally carried out by using powder as the
consumable material and focusing the laser beam and the powder at the point of
cladding.
US Patent 2007/0056939 teaches a laser head to carry out a welding operation
in a tube spinning at high speeds to create smoother interior and exterior linings
than cannot be obtained with conventional welding techniques which reduces
post weld machining. The technique is claimed to be suitable for cladding of
tubes.
US Patent 2011/02 discloses an apparatus with an elongated arm having first
and second ends defining chamber through the arm from the first end to the
second end. Laser delivery source connected to a focusing lens mounted in a
housing within an opening on the first end of the arm for delivering a laser beam
through the chamber and the delivery head mounted on the second end of the
arm comprised of an enclosure having an inlet for receiving the laser and outlet
for delivering the laser to the curved surface, a powder nozzle for delivering the
cladding powder to inner surface of the curved surface and a reflective surface
for reflecting the laser to exit through the outlet.
US Patent 6303897 describes an apparatus suitable for cladding hollow bodies
such as engine blocks with cylinder and produces a fine beam spot on internal
surface of the cylinder and applies an alloying powder at the focus of the spot
using a continuously conveying protective gas. The probe is displaced along the
axis of the cylinder while rotating and simultaneously melting the alloying
powder in the spot of the laser beam to a depth sufficient to form a wear
resistant coating bores in which a rotating probe including laser beam enters the
cylinder.
US Patent 6486432 provides a system and process for cladding of interior
surfaces in which a thin lining of abrasive materials are preplaced and baked.
The laser head carries out spiral welding operation to produce internal cladding.
US Patent 7259353 describes a conical nozzle suitable for laser cladding of
confined geometry.
The prior art techniques however, uses the powders as a coating material and
lasers are used to melt and deposit the powders to form internal dads. The use
of powders has some disadvantages like the powder has to be either preplaced
or accurately focused to the laser beam spot while cladding at the interior
surfaces.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a high power laser
welding process to weld annular stellite rings to the base material to produce
internal dads acting as wear resistant coating for valve seat rings.
Another object of the invention is to propose a high power laser welding process
to weld annular stellite rings to the base material to produce internal dads acting
as wear resistant coating for valve seat rings, which reduces the wastage of
expensive hard facing materials including the post machining cost.
A still another object of the present invention is to propose a high power laser
welding process to produce internal cladding by welding with any other clad
material suitable for laser welding.
A further object of the present investigation is to propose a high power laser
welding process which is enabled to produce internal coating of materials like
stainless steel or any other corrosion resistant material on substrates to act as
corrosion resistant coatings.
SUMMARY OF THE INVENTION
Accordingly, there is provided a high power laser welding process to weld
annular satellite rings to the base material to produce internal dads acting as
wear resistant coating for valve seat rings.
According to the present invention, hard facing/corrosion resistant materials are
made in the form of rings, and placed inside the groove to be cladded and laser
welded all around the periphery by using a high power laser. The invention
allows producing of higher thickness dads by welding thick rings from both sides,
and/or welding multiple rings by placing one over the other. With the inventive
process, the difficult to clad areas can be easily cladded. The use of laser
welding reduces the contamination and produces a cleaner weld. This process
greatly reduces the consumption of expensive consumables and also results in
considerable savings in post machining cost.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is prospective view of a valve body with stellite rings on the groove with
laser welding around the periphery according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 1, a ring of 28.6mm OD and 16mm OD with thickness of 6mm
is placed inside a groove (28.6mm diameter) of the valve seat made of carbon
steel. A laser of 3.5kW is used to weld the ring all around the periphery forming
a joint between the valve seat and the ring. The height of the clad is increased
up to 18mm by placing one ring over the other and welded all around. A welding
is further carried out in the inner periphery to avoid the gap between the two
rings placed one over the other. The projection at the top surface of the bead
was removed by precise filing before placing the subsequent rings for welding.
This new process enables welding/surfacing to be carried out in grooves having
width of different sizes. This process can be used for hard facing of any internal
surfaces where the clad material can be made in the form of rings. Further, the
process is suitable for grooves of different dimensions. The method is also
applicable for welding of desired thickness in a single pass or welding from both
sides to avoid placing of the rings one over other to build up height. This results
in reduced consumption of consumables, reduction in cycle time, and reduced
machining cost.
WE CLAIM
1. A high power laser welding process to weld stellite rings to inaccessible
location of base material of a component to produce internal dads acting
as wear-resistant coating for the valve seat rings, the process comprising
the steps of:
- placing at least one first stellite ring inside a groove of said component;
- welding the first ring using a high power laser source all around the
periphery to form a joint between the groove of the component and the
first ring;
- locating at least one second stellite ring above the jointed first stellitering
and laser welding the assembly all around; and
- laser welding in the inner periphery of the welded joint of the first and
second stellite rings with said groove to eliminate any gap there between.
2. The process as claimed in claim 1, wherein the stellite rings can be formed
of annular shape.
3. The process as claimed in claim 1, wherein the laser welding can be done
in a single pass or from both sides of the assembly to avoid the step of
locating the stellite rings one above the other.

ABSTRACT

This invention relates to a high power laser welding process to weld stellite
rings to inaccessible location of base material of a component to produce
internal clads acting as wear-resistant coating for the valve seat rings, the
process comprising the steps of placing at least one first stellite ring inside a
groove of said component; welding the first ring using a high power laser
source all around the periphery to form a joint between the groove of the
component and the first ring; locating at least one second stellite ring above
the jointed first stellite ring and laser welding the assembly all around; and
laser welding in the inner periphery of the welded joint of the first and second
satellite rings with said groove to eliminate any gap there between.