FIELD OF THE INVENTION
This invention relates to a method of generation and feed back of thermo-emf
for implementing an improved resistance hot staking process for providing
feedback of temperature to a welding process controller.
BACKGROUND OF THE INVENTION
Hot staking is a process of joining enamel coated copper wire to copper tong in
armature of starter motors in automobiles by application of heat and pressure.
Generally a resistance spot welding machine is employed for producing these
joints using special electrodes. Resistance heating by application of current
through tungsten and copper electrode is used for removal of enamel and
mechanical staking of copper parts for establishing electrical connections.
Joining of motor armature tong to enamel coated copper wires at the
commutator involves a hot staking process which is similar to resistance welding
process. In resistance welding two copper electrodes are used. But in hot staking
process when joining copper tong to copper commutator a combination of
electrodes namely copper and tungsten, is used when such a combination of
electrodes is used, a composite signal is generated which contain both welding
current information as well as thermo-emf information. The thermo-emf
information provides the temperature of the hot staking process.
The manufacture of motors involve, joining of armature copper wirers to the
enamel coated tongs of the commutator. There is a temperature at which the
enamel coating of the copper wire is melted. Only if the enamel is melted, the
hot staked joint will have good quality.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a method of
generation and feed back of thermo-emf for implementing an improved
resistance hot staking process for providing feedback of temperature to a
welding process controller.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of generation and feed back of thermo-
emf for implementing an improved resistance hot staking process for providing
feedback of temperature to a welding process controller, comprising the steps of:
providing a thermo-emf processor; providing a hot staking device operably
attached to said processor; providing two dissimilar types of electrodes in a hot
staking process to generate a thermo-emf which is separated in the thermo-emf
processor to separate the thermo-emf data from the data in respect of the
welding current; feeding back the separated data in the hot staking device; and
joining the components based on the fed-back data to produce an improved
joint.
According to the invention, two different types of electrodes are employed like
Tungsten and Copper. When such a combination of electrodes is used, the
thermo emf is getting generated. A method of separating the thermo emf from
the welding current information is provided. This data is employed as a feedback
for the feedback controller. The feedback controller provides 100% quality of the
hot staking of all the joints of an armature of a given motor.

Enamel coated copper wire is hooked into the copper tong of armature to be
joined and the hot pressed under certain specified conditions. The magnitude of
temperature and amount of pressure are important parameters that control the
process. Electrical current is passed into the copper tong through copper
electrode on one side and tungsten electrode on the other side. Resistance
heating produced in the tungsten electrode and the pressure through pneumatic
or mechanical means is used for hot staking the parts to be joined.
When junction of a dissimilar metal parts are placed on a hot object, an electro
motive force is induced which causes an electrical current in the associated
circuit. Tungsten in combination with copper electrode forms a thermocouple
junction and a thermo-emf is induced due to heat produced in the hot s taking
process. This thermo-emf mixed with weld voltage is presented to a signal
conditioner electronic circuit. This circuit amplifies the thermo-emf and rejects
the weld voltage using a hybrid analog and digital electronic circuit
The electronic circuit consists of a spike suppressor followed by a common mode
amplifier. Weld voltage is chopped by an analog switch cum sampler and further
amplified by an instrumentation amplifier. A micro-controller with appropriate
embedded software is used for sampling the analog information.
The output of t he signal conditioner in the range of 0 to 10 volts DC is used for
feed back control of the hot stacking process. The welding current is controlled
to limit the hot-staking process temperature in the desired range of 550 to 650
degree C by a specially designed feedback controller for hot staking.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a block-diagram of a thermo-emf generator according to the
invention.
Figure 2 - Shows a device for implementing an improved hot-staking process
according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
In a first embodiment of the invention, as shown in figure-1, an apparatus for
generation of thermo-emf during hot staking process is shown.
When a junction of dissimilar metal parts are placed on a hot object, an electro
motive force is induced which causes an electrical current in the associated
circuit (2). Tungsten in combination with copper electrode (9,12) forms a
thermocouple junction and a thermo-emf is induce4d due to heat produced in
the hot staking process. This thermo-emf mixed with weld voltage (1) is
presented to a signal conditioner electronic circuit (3). This circuit (3) amplifies
the thermo-emf and rejects the weld voltage using a hybrid analog and digital
electronic circuit (4).
The electronic circuit consists of a spike suppressor (2) followed by a common
mode amplifier (3). Weld voltage is chopped by an analog switch cum sampler
(6) and further amplified by an instrumentation amplifier (7). A micro-controller
(5) with embedded software is provided for sampling the analog information.

The output of the signal conditioner (8) in the range of 0 to 10 volts DC is used
for feed back control of the hot stacking process. The welding current is
controlled to limit the hot-staking process temperature in the desired range of
550 to 650 degree C by a feedback controller (not shown) for hot staking.
The hot-staking device as shown in figure 2 comprises an weldable copper tong
(10) held on an weldable copper base plate (12). A tungsten electrode (9) is
used to press the copper tong (10) from the top. An electric current is passed
from the tungsten electrode (9) through the tong (10) to the copper base plat e
(12). The tungsten electrode4 (9) in combination with the copper electrode (12)
forms a thermocouple junction and a thermo-emf is induced due to the heat
produced in the hot staking process. The induced thermo-emf constitutes the
feedback input from the thermo-emf generator. An enamel coated copper wire
(11) is used for the process. The feed back voltage so generated and applied to
create a temperature which ensures melting and evaporation of the wire and
thereby achieve an improved quality of joint.

WE CLAIM :
1. A method of generation and feed back of thermo-emf for implementing an
improved resistance hot staking process for providing feedback of
temperature to a welding process controller, comprising the steps of:
- providing a thermo-emf processor;
- providing a hot staking device 'operably attached to said processor;
- providing two dissimilar types of electrodes in a hot staking process to
generate a thermo-emf which is separated in the thermo-emf processor to
separate the thermo-emf data from the data in respect of the welding
current;
- feeding back the separated data in the hot staking device; and
- joining the components based on the fed-back data to produce an
improved joint

2. The method as claimed in claim 1, wherein copper base plate is employed to
hold the tong at the bottom and pressed by a tungsten electrode at the top.
3. The method as claimed in claim 1, wherein the set electric current is passed
from the top tungsten electrode through the tong of the armature to be
welded to the base copper plate.
4. The method as claimed in claim 1, wherein a voltage is generated at between
the top tungsten electrode and the bottom copper base plate.

: 5. The method as claimed in claim 1, wherein the generated voltage is
proportional to the temperature of the joint.
6. The method as claimed in claim 1, wherein the generated voltage which is
called as Thermo-EMF is the feedback input for the controller.
7. The method as claimed in claim 1, wherein the generated feedback voltage
allows that the enamel coated copper wire is fully heated up to the
temperature where enamel is melted and evaporated, thereby achieving
better quality of joint in hot staking.
8. The method as claimed in claim 1, wherein the electronic circuit is employed
to se4parate the thermo-emf information from welding voltage.
9. The method as claimed in claim 1, wherein the electronic circuit made up of
an embedded controller samples the thermo-emf between the current
welding current waveforms.
10.The method as claimed in claim 1, wherein the thermo-emf signal is
separated from the welding voltage signal.
11.The method as claimed in claim 1, wherein the combination of copper and
tungsten electrodes provides a thermo-emf exactly applicable for the hot-
staking process.

12. A method of generation and feed back of thermo-emf for implementing an
improved resistance hot staking process for providing feedback of
temperature to a welding process controller as substantially described and
illustrated herein with reference to the accompanying drawings.

This invention relates to a method of generation and feed back of thermo-emf
for implementing an improved resistance hot staking process for providing
feedback of temperature to a welding process controller, comprising the steps of:
providing a thermo-emf processor; providing a hot staking device operably
attached to said processor; providing two dissimilar types of electrodes in a hot
staking process to generate a thermo-emf which is separated in the thermo-emf
processor to separate the thermo-emf data from the data in respect of the
welding current; feeding back the separated data in the hot staking device; and
joining the components based on the fed-back data to produce an improved joint