Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD FOR MANUFACTURING A RESISTANCE WELDING TIP
This invention relates to resistance welding. More particularly,
this invention relates to a method of manufacturing a welding tip for
resistance welding and to a welding tip for resistance welding.
DE-A-2554990 discloses a method of manufacturing a welding
electrode having a pocket bore in the contact surface of the electrode and
a bolt of a material with a high heat resistance placed in the bore. DE-A-
2554990 also discloses that a welding electrode may be made from a blank
cut off from a rod. "Welding Technique" 1987 35(3) 59-63 discloses a
process for the manufacture of alumina dispersion strengthened composite
electrodes. Such electrodes may be made from a composite rod. EP-A-
97306 also discloses a resistance welding electrode formed from a swaged
bar having a cylindrical portion comprising a core and a sheath.
According to a first aspect of the invention there is provided
a method of manufacturing a welding tip for resistance welding, the method
including the steps of:
forming an elongate stock having a metallic core and a metallic layer
coaxial with the core;
parting the stock into desired lengths;
applying a first forming process to a length of stock to define a
contact surface for resistance welding at a front end of the length of stock;
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and
applying a second forming process to the length of stock to define
a cavity in an opposed rear end thereof, the cavity extending inwardly from
the rear end of the metallic layer to a rear end of the metallic core,
characterised in that the method includes
urging material of the metallic layer behind the rear end of the core.
According to a second aspect of the invention there is
provided a method of manufacturing a welding tip for resistance welding,
the method including the steps of:
forming an elongate stock having a metallic core and a metallic layer
coaxial with the core;
parting the stock into desired lengths;
applying a first forming process to a length of stock to define a
contact surface for resistance welding at a front end of the length of stock;
and
applying a second forming process to the length of stock to define
a cavity in an opposed rear end thereof, characterised in that
the cavity is defined in the metallic core and a portion of the core is
radially deformed to provide a cavity wall.
The stock may be formed by drawing a circular cylindrical tube
of a first metallic material over a circular cylindrical rod of a second
metallic
material. At least one of the rod and the tube may be deformed in the
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drawing to retain the rod in the tube once the tube has been drawn over
the rod.
Instead, the stock may be formed by extruding a circular
cylindrical tube of a first metallic material over a circular cylindrical rod
of
a second metallic material. Further instead, the stock may be formed by
extruding a circular cylindrical tube of a first metallic material and
simultaneously extruding a rod of a second metallic material, the tube being
extruded over the rod and coaxially therewith.
The method may include shaping the length of stock so that
the rear end of the length of stock defines a mounting formation for
mounting the welding tip on to a resistance welding tool.
The first forming process applied to the length of stock for
defining the contact surface may comprise cold forging. The second
forming process applied to the length of stock for defining the cavity may
comprise cold forging. The shaping of the length of stock to define the
mounting formation may be by means of cold forging.
The cavity of the length of stock may be shaped to provide the
mounting formation for mounting the welding tip on to the resistance
welding tool. Then, an inner, cavity-defining surface of the length of stock
may be shaped to provide the mounting formation for mounting the welding
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tip on to the resistance welding tool.
The contact surface of the length of stock may be formed in
a first operation, the cavity may be formed in a second operation, and the
cavity may be shaped to provide the mounting formation in a third
operation. Instead, the contact surface and the cavity may be formed and
the cavity may be shaped to provide the mounting formation in a single
operation.
The tube may be drawn over the rod in the absence of a
lubricating medium between the rod and the tube.
According to a third aspect of the invention there is provided
a welding tip for resistance welding, the welding tip including
a metallic body having a passage defined therethrough; and
a discreet metallic core secured to the body within the passage and
coterminous with the body, a front end of the body and a corresponding
front end of the core being shaped to define a contact surface for
resistance welding, characterised in that
a cavity is defined in a rear end of the core, the cavity opening at a
rear end of the core and the body and providing a mounting formation for
mounting the welding tip on to a resistance welding tool.
The passage may have a first portion proximate the front end
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of the body and a second wider portion proximate the rear end of the body,
the cavity being defined in a portion of the core located in the wider portion
of the passage.
5 According to a fourth aspect of the invention there is provided
a welding tip for resistance welding, the welding tip including
a metallic body having a passage defined therein opening at a front
end of the body; and
a discreet metallic core arranged within the passage, the front end
of the body and a corresponding front end of the core being shaped to
define a contact surface for resistance welding and a cavity being defined
in a rear end of the body, the cavity providing a mounting formation for
mounting the welding tip on to a resistance welding tool, and the cavity
extending inwardly from the rear end of the body to a rear end of the core,
characterised in that
a cold forged slug of material of the body is arranged within the
cavity behind the rear end of the core.
The core and the passage may define complementary waisted
axial profiles, thereby to secure the core in the passage. The cavity may
be frusto-conical in shape, tapering inwardly from the rear end of the body.
The core may project from the front end of the body. Instead,
the front end of the care may be substantially flush with the front end of
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the body.
One of the body and the core may be of a material having a
higher electrical conductivity than the material of the other of the body and
the core. One of the body and the core may be of a material having a
higher tensile strength than the material of the other of the body and the
core. One of the body and the core may be of a material having a higher
hardness than the material of the other of the body and the core.
The body may be of substantially pure copper. The core may
be of an alloy of copper. Instead, the core may be of an alloy of silver.
The alloy of copper may be one of the following:
(a) Copper-Chromium-Zirconium;
(b) Copper-Zirconium;
(c) Copper-Chromium;
(d) Copper-Nickel-Tin-Chromium;
(e) Copper-Nickel-Cobalt-Beryllium;
(f) Copper-Beryllium;
(g) Sintered Copper-Tungsten;
(h) Copper-Silver.
The invention is now described, by way of examples, with
reference to the accompanying drawings.
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In the drawings,
Figure 1 shows a side sectioned view of a first embodiment of a
length of stock, in accordance with the invention, for welding tips for
resistance welding;
Figure 2 shows a side sectioned view of a welding tip, in accordance
with the invention, for resistance welding, fabricated from the stock of
Figure 1;
Figure 3 shows a side sectioned view of a second embodiment of a
length of stock, in accordance with the invention, for welding tips for
resistance welding;
Figure 4 shows a side sectioned view of a second embodiment of a
welding tip, in accordance with the invention, for resistance welding,
manufactured from the stock of Figure 3;
Figure 5 shows a length of stock to be used in the manufacture of a
welding tip for resistance welding according to a method of the invention;
Figure 6 shows the length of stock in a first stage of the manufacture
of the welding tip;
Figure 7 shows the length of stock in a second stage of manufacture
of the welding tip;
Figure 8 shows the length of stock in a third stage of manufacture
of the welding tip;
Figure 9 shows a side sectioned view of a third embodiment of the
welding tip;
Figure 10 shows dimensions of the welding tip of Figure 4; and
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Figure 1 1 shows a side sectioned view of a fourth embodiment of the
welding tip.
In Figure 1, reference numeral 10 generally indicates a length
of stock, in accordance with the invention, for manufacturing welding tips
for resistance welding.
The length of stock 10 includes a circular cylindrical tube 12
and a cylindrical rod 14. The tube 12 is drawn over the rod 14 in a
conventional drawing process with the absence of a lubricant between the
rod 14 and the tube 12.
The tube 12 is of cathodic copper while the rod 14 is of a
copper alloy. The tube 12 is of a more readily deformable than the rod 14.
Thus, as the tube 12 is drawn over the rod 14, the tube 12 is deformed.
This, together with the fact that a lubricating medium is not used, results
in the rod 14 being fixed within the tube 12.
The copper alloy can be chosen to suit a user's requirements.
Some examples of the copper alloy are:
(a) Copper-Chromium-Zirconium
(b) Copper-Zirconium
(c) Copper-Chromium
(dl Copper-Nickel-Tin-Chromium
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(e) Copper-Nickel-Cobalt-Beryllium
(f) Copper-Beryllium
It will be appreciated that, instead, the rod 14 may be of a
alloy of silver.
The stock 10 can be supplied in indefinite lengths or in
predetermined lengths, depending on a user's requirements. The stock 10
can also be supplied in different diameters to suit a user's requirements.
In Figure 2, reference numeral 20 generally indicates a first
embodiment of a welding tip, in accordance with the invention,
manufactured from the stock 10.
The tip 20 includes a body 22 having a passage 23 defined
therethrough. A core 24 is fixed within the body 22. A front end 26 of the
body 22 is flush with a front end 28 of the core 24.
The front ends 26, 28 of the body 22 and the rod 28,
respectively, are shaped to define a contact surface 30 suitable for
resistance welding. In particular, the front ends 26, 28 are shaped to define
a domed profile. Those skilled in the art will appreciate that the front ends
26, 28 can be of any shape to suit a particular application.
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A cavity 32 is defined in a rear end 34 of the core 24. The
cavity 32 is formed so that a portion 36 of the core 24 is radially deformed
to define a wall 38 which defines the cavity 32.
5 The cavity 32 is formed in a stamping operation while the body
22 is inhibited from moving radially outwardly. This results in a portion 40
of the body 22 surrounding the wall 38 being reduced in thickness.
The cavity 32 facilitates mounting of the tip 20 on to a welding
10 tool (not shownl.
In Figure 3, reference numeral 50 generally indicates a second
embodiment of a length of stock, in accordance with the invention, for the
manufacture of welding tips for resistance welding. With reference to Figure
2, like reference numerals refer to like parts, unless otherwise specified.
The tube 12 of the stock 50 has an outer diameter of
approximately 16,0 mm. The rod 14 of the stock 50 has a diameter of
approximately 6, 3 mm.
In Figure 4, reference numeral 60 generally indicates a second
embodiment of a welding tip, in accordance with the invention,
manufactured from the stock 50. With reference to Figure 2, like reference
numerals refer to like parts, unless otherwise specified.
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The body 22 of the welding tip 60 defines the cavity 32. The
cavity 32 is frusto-conical and tapers inwardly from the rear end 34 of the
body 22.
The core 24 of the welding tip 60 is positioned in a passage
62 which extends from a front end 64 of the cavity 32 to open at the front
end 26 of the body 22. The core 24 and the passage 62 define
corresponding waisted axial profiles. It follows that the core 24 is
effectively locked in the passage 62. The front end 28 of the core 24 is
proud of the front end 26 of the body 22 to an extent of approximately 0,2
mm.
In Figures 6 to 8, there are shown three stages of
transformation of a length 66 of stock 50, shown in Figure 5, to the
welding tip 60 during the manufacture of the welding tip 60. With reference
to Figures 1 to 4, like reference numerals refer to like parts, unless
otherwise specified.
In a first stage of manufacture, a front end 68 of the length 66
of stock 50 is cold forged so that the front end 68 has a curved axial profile
as shown in Figure 6. In a second stage of manufacture, the length 66 is
held in a die and a circular cylindrical cavity 70 is punched into a rear end
72 of the length 66. This results in elongation of the length 66 and the
formation of the core 24 positioned in the passage 62. This also has the
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effect of urging the core 24 forward to stand proud as described above.
Further, as a result of the different characteristics of the rod 14 and the
tube 12, the core 24 and the tube 12 are deformed so that the core 24 and
the passage 62 define the complementary waisted axial profiles described
above.
In a third stage of operation, the length 66 is held in a die and
a tapering tool is pressed into the cavity 70 to form the frusto-conical
cavity 32 described above. This results in further elongation of the tube 12
so that the body 22 reaches a desired length at this stage.
In Figure 9, reference numeral 70 generally indicates a third
embodiment of a welding tip, in accordance with the invention,
manufactured from the stock 50. With reference to Figures 2 and 4, like
reference numerals refer to like parts, unless otherwise specified.
The welding tip 70 has the same general shape as the welding
to 60 of Figure 4, and is manufactured in the same general process
described above in respect of the tip 60, illustrated in Figures 5 to 8, with
the exception that in forming the cavity 32, a slug 73 of the material of the
body 22 is urged behind a rear end 74 of the core 24.
The following table give typical dimensions of the tip 60,
illustrated in Figure 4, with reference to Figure 10:
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A 16.Omm
B 20.Omm
C 8.Omm
D 6.5mm
E 10.3mm
F 12.7mm
G 0.2mm
It will be appreciated that the above dimensions are for
example purposes only, and may be varied to suit user requirements.
In Figure 1 1, reference numeral 80 generally indicates a fourth
embodiment of a welding tip, in accordance with the invention,
manufactured from the stock 50. With reference to Figures 2, 4, and 9, like
reference numerals refer to like parts, unless otherwise specified.
Again, the welding tip 80 has the same general. shape as the
welding to 60 of Figure 4, and is manufactured in the same general process
described above in respect of the tip 60, illustrated in Figures 5 to 8, with
the exception that in forming the contact surface 30, a front portion 82 is
tapered to provide a more pointed profile than is the case with the tip 60.
It is a problem with welding tips that they wear out at a rate
which results in excessive downtime of welding equipment and resultant
high costs. The reason for this is that, generally, welding ~ tips are of a
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metal which has a high electrical conductivity. Such a metal is cathodic
copper. Unfortunately, cathodic copper is of a relatively low tensile
strength and relatively low wear resistance. Consequently, it tends to wear
out at ari unacceptable rate.
It has been found that by using welding tips of a copper alloy
the wear rate can be reduced. However, copper alloys do not have the high
electrical conductivity of copper and this can result in certain problems.
By having the core 24 of the copper alloy and the body 22 of
cathodic copper, the applicant believes it can obtain a suitable electrical
conductivity together with adequate strength. Furthermore, the applicant
believes that by using the method of this invention, the stock 10 can be
produced at a relatively low cost.
