FIELD OF INVENTION
The invention relates to a process for welding of stainless steel with bimetallic of
Aluminum to Titanium materials by adapting the procedure of friction welding.
BACKGROUND Of THE INVENTION
Joining of Titanium and stainless steel components can't be done directly by
fusion welding. Friction welding is a solid state welding process adapted for mass
production in automobile industry. The friction welding being an automated
process achieving process achieving high productivity due to its less flash
generation as compared to other arc welding process for example, shielded
metal arc welding, gas metal arc welding and flux cored arc welding. Thus, the
friction welding process is excellent for production of jobs like axle cases, engine
exhaust valves, and other similar jobs.
Currently Bimetallic joint of stainless steel (SS) to Aluminum to Titanium material
is done by GTAW process but the quality of joint is unable to meet the code
requirement. Further, the joint requirement substantially can be achieved in
respect of welding of only stainless steel to Titanium. The dissimilar joint of SS to
Titanium, following any other process for example, GTAW, GMAW or SMAW
process is not quite effective. According to the invention the friction welding was
chosen. Initially stainless to Aluminum was friction welded. The joint integrity
was tested by pedal test. Titanium to Aluminum was friction welded and tested

for the soundness of the joint the combination of Stainless steel to Aluminum
having done first. Certain level of Aluminum was allowed to be retained as the
bimetallic material in between the stainless steel and Titanium, and then the
dissimilar friction joints were carried-out. As the other known processes take long
cycle time to complete the entire operation, the invention adapted the friction
welding technology. The conventional fusion welding process need consumables
and power source. The weld exhibits defects like slag inclusion, cracks, under-
cut. In macro structure, the heat affected zone is found to be higher. In the
friction welded joint according to the invention, the heat affected zone is found
to be substantially small, and without any defects like slag inclusion, under-cut
etc.
The economy of a welding process largely estimated by a factor namely, flash,
which constitutes a difference of the length of a work piece before and after the
welding process. In order to maintain economy of the process, it is important to
maintain the flash as low as possible, which requires to first determine the
effects of important parameters on flash including an optimum condition to
maintain the low flash.
United States Patent 6334571 Shantz et al. discloses a method for using friction
and/or inertia welding to produce a welded assembly with a thin interlayer
between two similar or dissimilar components, especially for use in automotive
brake systems and other applications. The term "friction welding" as used in this
description, is considered to include both direct drive friction welding as well as
inertia welding.

This prior art method describes the process of welding two aligned cylindrical
end pieces and an interposed transverse intermediate piece, the method
comprising the steps of friction welding of the end pieces to the intermediate
piece, where the intermediate piece is held in a cavity of a holder. The
intermediate piece is made from a strip stock and has a non-round profile to
form at least two radial protruding ears, the ears contacting a correspondingly
shaped cavity in the holder.
United States patent 3848389 dated Nov 19, 1974, Gapp et. al. describes a
method for using friction welding for Bimetal Rivets. According to the system, a
Rivet head and a shank section of a high strength metal is combined with a tail
section of a more ductile and easily formable metal to produce a rivet possessing
a highly effective configuration at the junction between the two metals while
provides added advantages.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a welding process
for butt joint of stainless steel to a bimetallic of Aluminum to Titanium material
adapting friction welding procedure.
Another object of the present invention is to propose a welding process for butt
joint of stainless steel to a bimetallic of Aluminum to Titanium material adapting
friction welding procedure, which eliminates wastage of consumables including
reducing the cycle time.

A still another object of the present invention is to propose a welding process for
butt joint of stainless steel to a bimetallic of Aluminum to Titanium material
adapting friction welding process, which provides weld-chemistry according to
the code of highest quality welds.
Brief description of the accompanying drawing
Figure 1 - a schematic representation of a bimetallic joint developed through
friction welding of a stainless bar with Aluminum bar to Titanium
bar each having identical diameter, in a friction welding machine.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
In a first embodiment of the invention, as shown in FIG - 1 a first end piece of a
Stainless steel bar 1 and a second end piece of an Aluminum bar 2, are joined
together to form an intermediate piece the procedure of using friction welding.
The end pieces (1, 2) are preferably selected as bar shaped with corresponding
cross-section, preferably round.
A first end of a titanium bar (3) and the intermediate piece 2, both being
typically longer than required as an interlayer material, are conventionally cut to
a length equal to their final required length, plus a length for the expected weld
flush or burnoff loss.

The non-magnetic, preferably Aluminum as the interlayer material (thin
intermediate piece 2) is preferably manufactured in bar form, and blanked or
machined out into round or any other appropriate shape and dimension, with a
base circle dimension equal or larger than the diameter of the opposing
component (the diameter of the end pieces), so that it will form a flush on a
welder holder chuck 4, so that a torque during the weld process is applied by
connecting the holder to a friction welding machine. The intermediate piece is
shown as circular cross-section piece 2. The actual cross-section of the
intermediate piece 2 is non-critical, as long as sufficient grip can be provided to
hold it (2) securely for either spinning or holding during the welding operation.
Friction welding is used to weld the Aluminum as end piece (intermediate piece
2). The intermediate piece is preferably held in a stationary clamping device 5,
producing a controlled dimension flush, ready for further machining. A plurality
of protruding ears 6 of the interlayer material (2) when disposed at desired
location, provide a datum reference position of that interlayer for further
machining reference.
To produce a bimetallic joint between same diameter of stainless steel bar with
Aluminum bar to Titanium bar, by adapting friction welding, an 90% of more of
the weld upset (loss of length) occurs in the diameter part including associated
length tolerance in the Aluminum bar, leaving the thickness of the interlayer
material (Al) precisely controlled. Thus, when the base circle dimension of the
intermediate piece is same as that of the end piece of Titanium the intermediate

piece shows a larger burnoff than the end piece (Ti). According to the invention,
the thickness of the intermediate piece is selected to be close to the desired
thickness of the final interlayer, plus the expected burnoff of the intermediate
piece (which burnoff is minimal using the method according to the invention).

WE CLAIM
1. A process for welding of stainless steel to a bimetallic of Aluminum to
Titanium materials, the process comprising the steps of
- joining together a first end pieces of a Stainless steel bar and a second
Aluminum bar constituting a first intermediate piece adapting the
procedure of friction welding; and
- welding a piece of Titanium material constituting a second end piece and
a second intermediate piece formed by joining aluminum with stainless
steel, the length of the second intermediate piece being selected to be
longer than the required length of an interlayer material and determined
considering a length of each material equal to their required final length,
plus a length cushioned for the expected weld flush or burnoff loss of
each of that component enabling to maintain a precise control on the final
thickness of the second intermediate layer in said welding assembly.

2. A process as claimed in claim 1 wherein the procedure of friction welding
is the similar/dissimilar material combination and wherein an intermediate
layer of Aluminum is provided for joint integrity.
3. A process as claimed in claim 1 wherein, the process is enabled to
generate the required mechanical properties in the welding assembly.

4. A process as claimed in claim 1 wherein welding of the similar / dissimilar
material combination by adapting the friction welding process enables
joining of a solid stainless steel end pieces with a first intermediate layer
of Aluminum.
5. A process as claimed in claim 1 wherein, the welding of the similar /
dissimilar material combination by adapting the friction welding process
enables joining of a solid Titanium end piece with the first intermediate
layer of Aluminum.
6. A process as claimed in claim 1 wherein the welding of the similar /
dissimilar material combination by adapting the friction welding process
enables joining of the solid end pieces of titanium with the first
intermediate layer of Aluminum which can be further machined to form a
tubular component.
7. A process for welding of stainless steel to a bimetallic of Aluminum to
Titanium materials as substantially described and illustrated herein with
reference to the accompanying drawings.

The invention relates to a process for welding of stainless steel to a bimetallic of
Aluminum to Titanium materials, the process comprising the steps of joining
together a first end pieces of a Stainless steel bar and a second Aluminum bar
constituting a first intermediate piece adapting the procedure of friction welding;
and welding a piece of Titanium material constituting a second end piece and a
second intermediate piece formed by joining aluminum with stainless steel, the
length of the second intermediate piece being selected to be longer than the
required length of an interlayer material and determined considering a length of
each material equal to their required final length, plus a length cushioned for the
expected weld flush or burnoff loss of each of that component enabling to
maintain a precise control on the final thickness of the second intermediate layer
in said welding assembly.