Note: Descriptions are shown in the official language in which they were submitted.
CA 02435627 2003-07-16
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to contact tip for gas~metal arc welding. The tip is
used for electric-arc
welding by means of continuous metal wire electrode in a protective gas medium
(MIG-MAG-
welding) or hidden arc welding.
2. Description of the Prior Art
A contact tip for gas-metal arc welding is a tubular body having a central
wire feed aperture which
serves for feeding welding wire from wire-feeding device through a welding
torch and into the weld
zone. In addition to feeding the welding wire, the contact tip also transfer
electric current to the
welding wire electrode. Wire goes out of the contact tip outlet and forms a
short and charged front
length, and an electric arc is formed between the charged end of the wire
electrode and the
oppositely charged work-piece. The arc melts the wire electrode, thus
continuously providing melted
metal to form a weld puddle. Welding machines and apparatuses also comprise a
gas nozzle,
wherein the nozzle and the contact tip for gas~metal arc welding are coaxial.
The nozzle blows inert
or active gas over the weld puddle, separating atmospheric air from the weld
puddle. This avoids
unwanted reactions of the molten material with the surrounding air. Thus, one
can obtain clean weld
of good quality. In most welding apparatuses, the welding wire electrode is
wound on a spool, and it
is unwound by the welding wire feeder. The wire electrode is automatically fed
off the spool and
into the contact tip welding torch. The wire electrode is unwound off the
spool, having a specific
cast which is arcuate in nature, and it is elastically straightened in the
wire feed aperture and is
pressed to the wire feed aperture walls. This effect is favo ~eable for the
current transfer, since it
maintains good electric conductivity between the welding wire electrode and
the surface of the wire
feed aperture. Wire must move smoothly through the tip aperture without
jerking, thus providing
exact and high performance welding. The wire feed aperture of the contact tip
for gas-metal arc
CA 02435627 2003-07-16
welding is made with dimension tolerance between the wire electrode and the
wire feed aperture.
However, the increase of the wire/aperture gap over a definite limit yields
poor contact between the
wire electrode and the surface of the wire feed aperture, deteriorating the
welding process. The
presence of debris carried by the surface of the wire electrode and introduced
in the wire feed
aperture or formed in the wire feed aperture as a result of electric erosion
increases the risk of
choking the wire feed aperture, especially when the gap is small. These and a
number of other
requirements to the contact tip for gas-metal arc welding, contradicting to
each other, explain the
existence of different constructional solutions of the contact tip. Yet, each
of them has specific
disadvantages.
The most popular contact tip for ga~metal arc welding is a tubular body with a
cylindrical central
wire feed aperture. A disadvantage of such a tip is its short term of
exploitation, due to wear caused
by intensive abrasion or electrical erosion. This is so, since the current
loads are too great (welding
current has power of 100-800 A). Moreover, current is transferred by means of
a three-point contact
between the welding wire electrode and the contact tip, only (contact at the
back receiving end of the
wire feed aperture, contact in the aperture middle and at contact the aperture
front contact end), and
the contact areas are too small. Besides, pressure along the contact surfaces
is insignificant and of
variable magnitude. The trend of one to decrease the wire/aperture gap in
order to improve the
contact does not increase the contact area, but worsens the passability of the
wire feed aperture and
increases the risk of blockage of the wire electrode within the aperture.
Besides, since the wire feed
aperture has a circular cross section, the wire electrode rotates within the
aperture during welding,
which impedes the exact wire feed towards the weld puddle. Due the wire
electrode rotation and
electric erosion, contact areas change in time their sizes and the process of
current transfer becomes
norrsteady. As a result, the welding arc becomes instable which yielding weld
of poor quality. The
outlined norrsteadiness of the current transfer also yields generation of
sporadic liquid metal bursts,
which fall into and stick to the weld and to the area surrounding it. Thus,
the weld quality worsens
additionally. On the other hand, bursts being regularly expelled from the weld
zone as miniature
droplets, bind and build up to the contact end of the contact tip. Thus, they
yield additional thermal
loads, tip oxidation and burn-through etc. These effects decrease the
exploitation term of the contact
tip for gas~metal arc welding. Burst can sometimes enter the zone of the wire
feed aperture outlet,
disturbing motion of the wire electrode and yielding instability of wire
electrode transport, poor
weld initiation or tip failure.
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Other constructional solutions of a contact tip for gas-metal arc welding are
also known - see, for
instance patent BG 63039 B 1, where the cross section of the tip wire feed
aperture is not circular
and the cross section boundary is mt a smooth line, but it has at least one
kink (one angle).
However, these solutions manage to eliminate some of the outlined functional
disadvantages of a
contact tip for gas-metal arc welding with a circular cross section, and the
positive effects are result
of the following reasons: the rotation of the wire electrode in the tip wire
feed aperture is
significantly suppressed, since wire electrode occupies one angle of the
aperture cross section and it
is thus fixed (i.e. the arc is stabilized); the number of contact points
between the wire electrode and
the walls of the wire feed aperture, at the aperture back receiving end, in
its middle section and at
the aperture front contact end, is doubled, since two-point contact is
attained on the angle arms,
while the contact in a tip with a circular cross section takes place at one
point; contact forces acting
between the wire electrode and the aperture become larger. Moreover,
considering tips with
triangular wire feed apertures, the welding wire electrode contacts the tip
along a line, lying in one
of the planes of the tip prismatic wire feed aperture. In addition, such
contact is established at three
more points, lying in the other two planes of the prismatic wire feed aperture
- at the tip back
receiving end, in its middle section and at the tip front contact end. The
problem of these contact tips
for ga~metal arc welding is how to find the gap between the wire electrode and
the tip aperture.
Considering a contact tip for gas-metal arc welding whose cross section is
triangular, the wire
electrode should have a diameter, smaller than that of the circle, inscribed
in the triangle. Thus, wire
could pass through the tip cross section. Yet, the assumption of the
difference between the diameter
of the circle inscribed in the aperture triangular cross section and the
diameter of the wire electrode
as a measure of looseness is not appropriate and yields unreliable results.
This is so, since the wire
electrode, passing through the wire feed aperture, occupies one of the angles
of the triangle, and its
elastic pre-stressing relaxes to a certain extent. Hence, one should know the
optimal practical
parameters of the triangular cross section, thus providing optimal conditions
of current transfer and
norrdisturbed and smooth motion of the wire electrode through the triangular
wire feed aperture.
Other constructional solutions of contact tips for gas-metal arc welding (CT)
are also known - see
patents BG 60184 and CA 1247707, where the axis of the wire feed aperture is a
helix. Moreover, a
linear contact between the wire electrode and the tip wire feed aperture is
attained along a helix.
This contact is much better than the three-point contact attained in a tip
with a circular cross section.
It also is comparable to the contact in tips with noircircular cross section.
Besides (as in a contact
tip with a norrcircular aperture) contact pressure between the wire electrode
and the wire feed
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aperture is higher than pressure in tips with a circular wire feed aperture,
since the wire e~ctrode is
forced to change continuously and elastically its curvature along the whole
length of the contact tip.
A disadvantage of such contact tip for gas-metal arc welding (patent
CA1247707) relates to the
specificity that the helical passage for wire motion is laterally open towards
the tip outside surface,
forcing the helical tip aperture to make at least one full rotation.
Otherwise, the wire electrode would
go out of the contact tip and it could not be forced to follow the contact tip
axis. The specificity that
the wire electrode passage is open yields two more problems, which concern
metal spatter binding
and building up to the front end of the laterally open passage and the exact
direction of the wire
electrode towards the weld zone. This implies additional mounting of an insert
at the front contact
end of the tip, and this complication, together with the non-technological
construction, is a reason
for the tip high cost.
Considering a number of cases of welding, one should use contact tip for gas
metal arc welding with
significantly increased length. However, the increase of the tip length yields
increase of friction
during wire electrode motion, which hampers wire electrode feeding and
sometimes even blocks the
wire electrode in the wire feed aperture. Constructional solutions are known,
where this problem is
solved by fabricating the contact tip as a cylindrical tube with circular
cross section of the wire feed
aperture. Moreover, the tip has smaller outside and inside diameters at its
front contact sector, as
compared to the outside and inside diameters of the rest part of the tip, i.e.
the tip is a monolithic
body consisting of two tubular sectors with different outside and inside
diameters. The sector with
smaller outside and inside diameters has a length, approximately equal to the
length of a regular
contact tip for gas-metal arc welding, and it is located at the front contact
end of the tip, i.e. in the
area where the wire electrode projects out of the contact tip and is fed to
the weld. The electric
contact between the contact tip and the wire electrode is achieved in this
sector, which is
comparably shorter and the wire feed aperture has a smaller diameter. The rest
part of the tip has
larger outside and inside diameters, so that the smooth motion of the wire
electrode would not be
disturbed. However, these tips have the disadvantages inherent to all contact
tips for gas-metal arc
welding with a circular aperture, considered so far: limited three-point
tip/wire contact, fast abrasion
and electric erosion and short term of exploitation.
Some solutions, considering the external design of a contact tip for gas-metal
arc welding are
known, where a groove is fabricated on the tip external cylindrical surface.
Yet, the groove function
is not related to the welding process, but the groove is cut for one to hold
the tip by a wrench for
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mounting it to and/or dismounting it from the torch. Besides, groove cut is an
additional operation
which is not part of the basic technologies of fabricating the tip a~pper
tubular body (pressing,
drawing, mechanical drilling etc.) and it increases the tip total cost.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a new construction of a contact
tip for gas-metal-arc-
welding, which would significantly eliminate the disadvantages of the contact
tips discussed so far,
increasing the contact areas and contact stresses which occur between the wire
electrode and the tip
wire feed aperture, but without decreasing wire electrode passability. At the
same time, the design
proposed would limit the rotation of the wire electrode within the wire feed
aperture. The profits of
the invention are as follows: significant improvement of current transfer and
decrease of the
generation of melted metal spatters; limitation of the possibility of blockage
of the wire electrode
within the wire feed aperture as a result of large friction stresses (for
contact tips with large length)
or as a result of the small gap between the wire electrode and the wire feed
aperture; providing great
variety of combinations of contact areas and contact stresses; thus
guaranteeing effective conditions
of current transfer for a wide range of lengths of contact tips for gas-
meta~arc-welding, the range
comprising very short and very long contact tips. Besides, the tip
construction is technologically
appropriate for smooth tip fabrication.
The aim of the invention is attained by designing a contact tip for gas-metal-
arc-welding, fabricated
from copper, copper alloy or powder metallurgy (PM) sintered material having
high electrical and
thermal conductivity. The contact tip is for use in a welding torch and it
serves to feed the wire
electrode to the weld and to pass the electric charge from the torch to the
wire electrode. The
contact tip comprises a tubular body with a central passable wire feed
aperture whose axis is
rectilinear. The aperture has a back receiving end on the side where the wire
electrode is fed to the
contact tip aperture through a specially shaped inlet cone. The aperture also
has a front contact end
on the side where the wire electrode projects from the tip, being directed to
the weld.
Considering an aspect of the invention, the wire feed aperture of the contact
tip does not have a
uniform cross section along its whole length, but it has at least one sector,
which starts at the tip
front contact end and its cross section is triangular while its length is
smaller than the whole aperture
length The rest of the wire feed aperture has a circular cross section with a
diame ter, larger than the
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diameters of the circle inscribed in the cross section of any sector of the
wire feed aperture which
has triangular cross section.
Considering one of the preferable technological solutions of the present
invention, the wire feed
aperture of the contact tip comprises three sectors, two of which have a
triangular cross section and
are located at both tip ends. The third sector occupies the rest middle part
of the wire feed aperture
and has a circular cross section, while its diameter is larger than the
diameters of the circles
inscribed in the triangular cross sections of the above said two aperture
sectors.
Considering another preferable technological solution of the present
invention, the wire feed
aperture of the contact tip comprises four sectors. Two of them have
triangular cross section, and the
first one is located at the tip front contact end while the second one is
located in the middle part of
the contact tip. The wire feed aperture between these two sectors, together
with the aperture of the
tip back receiving end, have a circular cross section with a diameter larger
than the diameters of the
circles inscribed in the triangular cross sections of the above said two
aperture sectors.
Considering a preferable variant of the cottact tip, related to tips that have
two sectors with
triangular wire feed apertures, the said sectors have identical cross sections
which are equilateral
triangles. The said sectors are rotated with respect to each other around the
aperture longitudinal axis
at an angle of 60°.
As for another aspect of the present invention, the tip outside surface,
enveloping the said tip sectors
whose aperture cross section is triangular, is shaped as a hexagonal prism
with three plane and three
curved walls. Besides, all prism walls are parallel to the tip longitudinal
axis. Moreover, the plane
walls of the prism are parallel and equidistant to the corresponding inside
walls of the triangular
wire feed aperture of the said sectors. As for the subsequent tip sectors
whose aperture has a circular
cross section, the outside tip surface enveloping them is cylindrical.
As for another aspect of the present invention and considering the tip sector
located at the tip front
contact end and having a triangular cross section, the ratio between the
diameter of the circle
inscribed in the triangular cross section of the said tip sector and the
diameter of the wire electrode is
1.15 - 1.25.
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As for another aspect of the present invention, the tip sector located at the
tip front contact end has a
triangular aperture, and the aperture surface is helical, while the aperture
longitudinal axis coincides
with the longitudinal axis of the tip. Besides, the center of the circle
inscribed in the triangular cross
section of the said sector is the cross point of the bisectrixes of the
triangle, and the said circle center
does not lie on the tip axis.
In a preferable version of the present invention related to contact tips for
gas-metal~arc-welding
where the surface of the wire feed aperture is helical, the cross section of
the said wire feed aperture
is an equilateral triangle, and the bisectrix of one of the angles of the said
triangle crosses the axis of
the contact tip at a point, whose distance to the vertex of the said angle is
smaller than the diameter
of the wire electrode.
Considering a preferable version of the present invention related to contact
tips for gas-metal-arc-
welding where the surface of the wire feed aperture is helical and the cross
section of the said
aperture is triangular, the bisectrix of one of the angles of the said
triangular cross section crosses
the axis of the contact tip at a point whose distance to the vertex of the
said angle is smaller than the
radius of the wire electrode divided by the sinus of half of the said angle.
Considering a preferable version of the present invention related to contact
tips for gas-metal-arc-
welding where the wire feed aperture has a helical surface and the cross
section of the wire feed
aperture is triangular, one of the sides of the said triangular cross section
is curvilinear and convex
while the other two sides of the said triangular cross section are
rectilinear. The curvilinear side of
the said triangular cross section is an arc of a circle, while the diameter of
the said circle is larger
than the diameter of the wire electrode. The said arc is equidistant to a
circle having a diameter
equal to the diameter of the wire electrode, and the said circle tangents the
arms of the angle
concluded by the said rectilinear sides of the aperture triangular cross
section.
As for another aspect of the present invention, a sector of the wire feed
aperture being located at the
tip front contact end and having a triangular cross section, is fabricated as
a separate insert. The said
insert is pressed in an aperture bored through the tip front contact end or
the said insert is threaded to
the tip front contact end.
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As for another aspect of the present invention, a method of fabricating a
contact tip for gas-metal-
arc-welding is proposed. The tip has sectors with triangular wire feed
aperture while the outside
surface enveloping the said sectors is shaped as a hexagonal prism. Using the
method of tip
fabrication proposed, processes of plastic forming - forging or rolling are
applied. Furthermore, the
said method comprises an initial fabrication stage, in which a cylindrical
tubular pre-form of copper
or copper alloy, with a passable aperture of circular cross section, is placed
in a matrix for forging or
in a rolling stand for rolling. Then, a second stage of plastic forming
follows, resulting in the plastic
forming of the tubular pre-form or of a sector of the tubular pre-form into a
body, whose deformed
section is a tube with a hexagonal outside enveloping surface and which has a
passable wire feed
aperture with a triangular cross section. According to the method proposed,
the said outside
enveloping hexagonal surface and the said wire feed aperture with a triangular
cross section are
obtained simultaneously as a result of the power impact of the forming
instrument. The power
impact is applied on the outside surface of the pre- form, only, and the power
impact is directed
perpendicularly to the pre-form axis. Besides, the instrument shape-forming
faces which contact the
pre-form and exercise power impact on it, conclude with each other angles
which are equal to the
angles of the cross section of the said triangular aperture .
BRIEF DESCRIPTION OF THE DRAWINGS
The enclosed figures provide a better clarification of the essence of the
present invention The figures
illustrate the following characteristic features of the contact tip for gas-
metal-arc-welding:
Fig. 1 shows a longitudinal section of the contact tip together with the wire
electrode inserted in it.
Fig. 2 shows a longitudinal section of a contact tip with two-sector wire feed
aperture.
Fig. 3 shows an axonometric view of the position of the wire electrode in a
wire feed aperture with a
triangular cross section.
Fig. 4 shows a longitudinal section of a contact tip with a three-sector wire
feed aperture.
Fig. 5 shows a cross section c - c of the contact tip in Fig. 4 with
triangular wire feed apertures,
wherein the aperture cross sections are rotated with respect to each other at
an angle of 60° around
the tip longitudinal axis.
Fig. 6 shows an axonometric view of a contact tip, wherein part of its outside
enveloping surface is
shaped as a hexagonal prism.
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Fig. 7 shows an axonometric view of a four-sector contact tip with a wire feed
aperture as shown in
Fig. 5.
Fig. 8 shows an axonometric view of a contact tip with a helical aperture
which has a triangular
cross section.
Fig. 9 shows a cross section of a contact tip with a helical wire feed
aperture with a triangular cross
section.
Fig. 10 shows a cross section of a contact tip with a helical wire feed
aperture, whose triangular
cross section has one convex aro-shaped side.
Fig. I 1 shows a longitudinal section of a contact tip with a hammered-in
insert, wherein the insert
has an aperture with a triangular cross section.
Fig. 12 shows a longitudinal section of a contact tip with a threaded insert,
wherein the insert has an
aperture with a triangular cross section.
Fig. 13 shows a cross section of a stamp (matrix) for the fabrication of a
contact tip whose aperture
has a triangular cross section and whose outside enveloping surface is
hexagonal.
Fig. 14 shows a rolling stand for the fabrication of a contact tip whose
aperture has a triangular cross
section and whose outside enveloping surface is hexagonal.
DETAILED DESCRIPTION OF THE INVENTION
Considering the enclosed figures 1 -14, the part specified as position 1
generally maps a contact tip
for use in a welding torch which is not shown in the figure.
As seen in Fig. 1, the contact tip 1 is a tubulax body with a central passable
wire feed aperture 2 and
the aperture axis is rectilinear. The aperture 2 has a back receiving end Ib
on the side where the wire
electrode 4 is fed in the aperture 2 of the contact tip 1 through a specially
shaped inlet cone 5. The
wire feed aperture 2 also has a front contact end if on the side where the
wire electrode 4 projects
from the contact tip 1 and is directed to the weld 3. The contact tip is fixed
to the element 6
(diffuser) through its receiving end lb. The contact tip through its receiving
end lb. is fixed either to
the element 6 (diffixser) of the welding torch or to the carrier of the
welding apparatus. The wire
electrode 4 which has a natural curvature passes through the wire feed
aperture 2 of the contact tip I,
deforms elastically and is thus pressed to the walls of the aperture 2 at
points 7.
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Fig. 2 shows the contact tip I, wherein the wire feed aperture 2 does not have
a uniform cross
section along its whole length, but sector A of the wire feed aperture 2
starts from the front contact
end of the contact tip I and has a triangular cross section 2a. A second
sector B is shaped at the
back receiving end of the contact tip I and it has a circular cross section
2b. T'he second sector B
starts from the receiving inlet cone 5 and stretches to the first sector A.
The diameter of the aperture
of the second sector B is larger than the diameter of the circle inscribed in
the triangular cross
section 2a of the first sector A of the wire feed aperture 2. As for the
contact tip under consideration
the effective contact realizing current transfer from the tip I to the wire
electrode 4 occurs in sector
A of the wire feed aperture. The aperture sector A has a triangular cross
section 2a and the
wireJaperture gap is smaller. The character of the contact is shown in Fig. 3.
The position of the wire
electrode 4 in the prismatic triangular sector A of the wire feed aperture 2,
shown in Fig. 3, is the
most stable one as compared to all possible positions of the wire electrode.
This is so, since
minimum of the potential energy of elastic stressing of the wire electrode 4
is attained in this wire
position. The wire electrode 4 realizes linear contact 10 with the wall 8a of
the triangular prismatic
sector A of the wire feed aperture 2. 'The wire electrode 4 additionally
contacts the other two sides of
the triangular prismatic sector A at three more points (at two points 7b
located at both ends of wall
8b and at one point 7c located in the middle of wall 8c). While current
transfer in a two-sector
contact tip (Fig.2) is realized in sector A which has a triangular cross
section, as outlined above,
sector B of the contact tip I with a circular cross section of the wire feed
aperture 2 has a function of
elongating the contact tip I to the length needed. This is done in accordance
with the specific
requirements of the welding machinery and technology employed, without
increasing the wire
resistance to push out of the aperture. Thus, one can attain balance between
the optimal conditions
of current transfer (characterized by appropriate gaps, increased contact
areas and pressure and
stable angular fixing) and good passability of the wire electrode, especially
in contact tips with
larger length. As a result, the welding are is stable, the amount of spatter
is significantly smaller, the
accuracy of directing the wire electrode to the weld is higher, the
probability of wire electrode
blockage within the wire feed aperture is decreased and the exploitation term
of the contact tip is
increased. As a whole, the weld is of high quality.
Fig. 4 shows a contact tip I whose wire feed aperture 2 has three sectors - A~
, Az and B. Sectors A~
and Az are located at the tip front (contact) and at its back (receiving) end
(just at the inlet cone 5).
Those sectors have triangular cross sections 2a~ and 2a2. A third sector B is
located between sectors
A~ and AQ, in the tip middle section, and sector B has a circular cross
section 2b whose diameter is
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larger than the diameter of the circles inscribed in the triangular cross
sections 2a~ and 2a2 of sectors
A~ and A2. Such a design of a contact tip for gas-meta~arc-welding is
preferable when the specific
conditions of welding require that the tip length be significantly larger than
the length of an ordinary
and most common tip. Hence, it is useful for one to divide the triangular
sector of the wire feed
aperture into two parts (i.e. into the two sectors ~ and AQ discussed above,
as shown in Fig. 4).
They are located at both tip ends, since wire fixing along a larger length
yields stronger resstance to
rotation of the wire electrode. Thus, one can attain the necessary accuracy of
directing the wire
electrode to the object to be welded, as well as stability of current transfer
and steadiness of the
welding arc.
Fig. 5 shows a cross cut of the contact tip for gas-metal-aro-welding shown in
Fig. 4. The tip
comprises two sectors with triangular cross section - 2a1 and 2a2. It is
fabricated such that those
sections are identical equilateral triangles, being rotated with respect to
each other at an angle of 60°
around the tip longitudinal axis. The location of the tip cross cut is denoted
by c - c in Fig. 4. The
angular rotation of the cross sections 2a ~ and 2a2 of the aperture sectors Ai
and Az at an angle of 60°
improves the angular fixing of the wire electrode 4, and the wire electrode
occupies the angles of
cross sections 2a~ and 2a2 that oppose each other as shown in Fig. 5. The
distance between the
centers of the wire electrode 4 occupying such a position is 1.4 time smaller
as compared to the case
when the wire electrode slides within a contact tip whose wire feed aperture
has a uniform triangular
cross section - see Fig. 3. Hence, this contact tip provides greater tightness
of motion of the wire
electrode within the aperture, keeping the passability needed, i.e. not
decreasing the gap between the
wire electrode and the aperture walls.
Fig. 6 and Fig. 7 show tips 1, whose sectors A (Fig. 6) and A~ and A2 (Fig.
7). have triangular cross
sections - 2a, 2a~ and 2a2 respectively. The outside surface of the contact
tip enveloping those
sectors is shaped as a hexagonal prism. Three of its walls 12 are planes,
being parallel and
equidistant to the sides of the corresponding triangular cross sections 2a,
2a~ and 2az, while the other
three walls 11 are convex surfaces and not planes. Consider now sector B (Fig.
6) and sectors Bi and
B2, respectively (Fig. 7), whose wire feed aperture has a circular cross
section, while the tip outside
surface enveloping them has cylindrical shape 13 and the outside tip surface
enveloping sectors B
and Bz is threaded (the thread is denoted by 14). Regarding the contact tip
shown in Fig. 7, the
triangular cross sections 2a~ and 2az are rotated with respect to each other
at an angle of 60 °, as
shown in Fig. 5. Moreover, the tip in Fig. 7 has four sectors - two sectors A,
and ~ with a
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triangular cross section of the wire feed aperture, located at the tip front
contact end and in the tip
middle, respectively, and two sectors Bi and Bz with a circular cross section
of the wire feed
aperture, one of them located between sectors A~ and Az and the other one - at
the tip back
(receiving) end. The design of the second sector B2, located at the tip back
end, with a circular cross
section of its aperture and with outside enveloping threaded cylindrical
surface, is proved by the
necessity to fabricate thread 14 for mounting the contact tip to the welding
apparatus. The specific
hexagonal shape of the tip surface, enveloping sectors A, t~ and AE which have
aperture with
triangular cros s section, is characteristic for a new technological method
for the fabrication of tips
with various number of sectors with triangular apertures. This method is an
object of the present
invention, too. Another specificity of such tip is that its outside hexagonal
surface is appropriate for
screwing the tip to the welding torch or unscrewing it from the welding torch
by using a special or
even a standard wrench, not needing to cut a special groove for that purpose.
Fig. 8 shows an axonometric view of a contact tip for gas-metal-arc-welding 1
whose wire feed
aperture 2 has a triangular cross section and the aperture is shaped as a
helix. Fig. 9 shows cross cut
of the tip of Fig. 8, but without plotting the wire electrode in order to
avoid the excess of details. The
helical shape of the aperture is obtained as a result of specific motion of
the aperture cross section,
combining rectilinear translation of the cross section along the axis O of tip
1 and simultaneous
rotation of the cross section around the tip acis. This means that the axis of
the helical surface
coincides with the axis of the tip. Since the tip axis is perpendicular to the
drawing plane of Fig. 9, it
is plotted as point O in the figure. Besides, center C of the circle C 1
inscribed in the aperture
triangular cross section is the cross point of the bisectrixes of the angles
of the triangle, and center C
does not lie on the axis O of the contact tip, i.e, points C and O plotted in
Fig. 9 do not coincide.
This condition is necessary for elastic deformation of the wire electrode,
i.e. for the occurrence of
contact stresses between the wire and the surface of the tip aperture,
regardless of whether the wire
is rectilinear or arc-shaped. If center C of the inscribed circle C 1 lies on
the axis O of the co ntact tip,
this means that a rectilinear wire electrode would pass through the tip wire
feed aperture with a gap,
equal to the difference between the diameter D 1 of the circle inscribed in
the aperture cross section
and the diameter D2 of the wire electrode. Thus, no contact stresses necessary
for current transfer
would occur between the wire electrode and the aperture surface. One can
obtain uniform
distribution of the contact pressure occurnng between the wire electrode and
the two arms of the
angle q of the triangular cross section of the aperture, when the tip axis O
crosses one of the
bisecrixes L. This means that point O in Fig. 9 should lie on one of the
bisectrixes L. The bisectrix L
12
CA 02435627 2003-07-16
in Fig. 9 coincides with the vertical axis of symmetry of the trig ngular
cross section. Center C of the
circle C 1 inscribed in the triangular cross section is located at a distance
E from the tip axis O (E is
eccentricity), while vertex Q which the bisectrix L starts from is located at
a distance H from the
axis O. When condition H = 0.5 I~/sin (O.Sq) is fulfilled (q = 60° and
H = Dl for an equilateral
triangle), a rectilinear wire electrode passes through the wire feed aperture
without a gap. It is
tangential to the walls of the triangular aperture along two helixes, and the
angle between the
aperture walls is q and the angle vertex is Q. Yet, there is no pressure
between the wire electrode
and the aperture walls. To provide pressure needed for current transfer, one
should keep the
condition H < I~/sin (O.Sq) which takes the form H < I~ for an equilateral
triangle (q = 60°).
Besides, the decrease of H yields increase of the contact pressure. The
occurnng contact pressure
between the wire electrode and the surface of the wire feed aperture acting
along the two contact
helical lines l0a and 10 b (Fig. 8), deforms elastically the wire electrode,
and the wire axis becomes
helix Oa . Fig. 8 shows six cross sections 2.1 - 2.6 of the triangular wire
feed aperture 2 and six
cross sections 4.1 - 4.6 of the wire electrode 4. The step of their
distribution along the tip axis is
114'h of the step of the helix, i.e. the cross sections are rotated with
respect to each other at an angle
of 90° around the longitudinal axis of the contact tip I. Points 7a and
7b of contact of the wire
electrode 4 with the wire feed apemire 2 are plotted on the first cross
sections 2.1 and 4.1, only.
This is done for the sake of clarity. Consider now a tip whose aperture has a
helical surface, the
aperture cross section is circular and the contact between the wire electrode
and the aperture surface
is established along a single helix. In contrast to such a tip, however, the
present invention is
characterized by significant increase of the contact between the wire
electrode 4 and the surface of
aperture 2, and the contact takes place along two helixes l0a and lOb, since
the wire electrode
occupies angle q of the triangular aperture 2. Moreover, a specificity of such
shape of the wire feed
aperture 2 of tip I consists in that without decreasing the aperture
passability (i.e. keeping aperture
cross section), the force of pressing the wire electrode to the aperture walls
is increased, since the
wire electrode is forced to follow elastically the helical shape of the
aperture. Such a design enables
one to realize secure (reliable) contact between the wire electrode 4 and the
surface of the wire feed
aperture 2 of tip 1. The contact is characteristic with increased contact
surface, constant position of
the contact spot and constant contact stresses. Thus, one gets steady
parameters of the welding arc
and weld of good quality.
Fig. 10 shows a cross cut of a contact tip for gas-meta~arc-welding 1, whose
wire feed aperture 2
has a helical shape and its cross section is triangular with one curvilinear
side 8c, which is shaped as
13
CA 02435627 2003-07-16
an arc of a circle. The circle 8c has a radius greater than the radius of the
wire electrode 4. Wire
electrode 4 tangents at points 7a and 7b the two rectilinear arms 8a and 8b of
angle q of the
triangular cross section of the aperture 2, but it does not touch the third
arc-shaped side 8c. The
triangular cross section of the aperture 2, having an arc-shaped side 8c and
shown in Fig 10,
provides a contact between the wire electrode 4 and the wire feed aperture 2
along two lines, as
shown in Fig. 8. Moreover, this triangular cross section has smaller
dimensions as compared to the
dimensions of the triangular cross section with rectilinear sides 8a,, 8b, and
8c,. This tip design is
preferable for use with thick wire electrodes (requiring larger dimens ions of
the wire feed aperture,)
as well as for use in tips with comparatively small outside diameter, when one
has to avoid local
thiirout of the tip walls and resulting tip overheating.
Fig. 11 shows a contact tip for gas-metal-arc-welding 1 where the wire feed
aperture of sector A of
the tip l, having a triangular cross section 2a, is fabricated in a separate
insert 15. The insert is a
tubular body being pressed along its outside surface into an aperture,
fabricated at the front end of
the tip 1. Current transfer between the tip and the wire electrode is carried
out in the triangular
aperture 2a of the insert 15. Fig. 12 shows a tip 1, which comprises insert 15
similar to that of the tip
shown in Fig. 11, and the insert 15 is screwed to the body of tip 1 by means
of thread 16. For that
purpose, a step is formed at the back end of the insert where thread is cut.
The step is screwed into a
threaded aperture fabricated at the front end of the body of tip 1. The tip
design of Fig. 11 and Fig.
12 have the advantage that inserts 15 are replaceable parts and the body of
tip 1 can be multiply
used. Besides, the inserts 15 can be fabricated from more-expensive alloy with
high wear and
electro-corrosion resistance or from powder-metallurgical material. This would
increase the quality
of the tip performance, prolong its term of exploitation and finally yield
higher tip efficiency.
Fig. 13 shows an exemplary scheme of the instrument-stamp (matrix). The method
of fabricating
sector A of tip 1 shown in Fig. 6 or sectors A~ and A~ of the tip shown in
Fig. 7 is illustrated on this
basis. The tip outside surface enveloping all those sectors is hexagonal. The
essence of the method
consists in the following: a tubular body 1 f with aperture 2f (plotted by
dashed lines in t he figure) is
placed in the lower section 19 of the stamp, and the outside surface of the
tubular body contacts the
shape-forming surfaces 17 of the lower stamp 19. The starting pre-forming
position of the upper
movable section of the stamp is denoted by 18f and it is plotted by dashed
lines. Then, forging
follows where the upper movable stamp 18f performs translation towards the
lower stamp 19,
resulting in plastic deformation of the pre-form between the three surfaces 17
of the instrument.
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CA 02435627 2003-07-16
Thus, the pre-form outside cylindrical surface is shaped into a hexagonal
prismatic surface. The
hexagonal prism thus obtained has three planes walls 12 which contact the
shaping surfaces 17 of
the instrument, as well as three curved walls 11. The process of plastic
forming proceeds until the
fabrication of a product with a desired shape is completed. The position of
the upper stamp at the
end of the deformation process is denoted by 18, and the final product 1 has a
triangular wire feed
aperture 2a. A specificity of the method is that the forming impact of the
instrument is applied on
part of the outside surface of the pra- form, only. Moreover, there are three
areas 11 of the pre- form
outside surface which are free of contact with the instrument, and the
material in those area outflows
in a direction opposite to the center of the pre-form cross section. Thus, it
is possible for one to
transform the inside surface 2f of the wire feed aperture from a cylindrical
surface with a circular
cross section into a prismatic surface 2a with triangular cross section. This
can be done
simultaneously with the plastic shaping of the outside hexagonal surface of
the tip, without applying
an impact of the forming instrument (arbor) on the inside surface. What is
specific for the method
proposed is that by appropriate choice of the degrees of deformation, geometry
of the pre-form and
geometry of the facial surfaces 17 of the instrument, one can fabricate
contact tips with various
geometry of the aperture cross section.
Fig. 14 shows the principal scheme of a rolling device where one can use the
same method (as in
Fig. 13) of plastic forming, applied for the fabrication of sectors A or Ai
and A2 shown in Fig. 6 and
Fig. 7, respectively, wherein the sectors have hexagonal outside enveloping
surface. Tubular
cylindrical pre-form if is introduced into a rolling stand which comprises
three identical rolls 20,
whose axes 21 lie in one and the same plane (the drawing plane), and the axes
conclude angles of
120° between each other. The longitudinal axis of the tubular pre-form
if is perpendicular to the
plane where the roll axes lie and its position is symmetrical with respect to
those axes. The direction
of introducing the tubular pre- form into the rolling stand coincides with the
direction of roll rotation,
and the rolls deform the pr~form and translate it in the same direction. One
can deform the pre-form
along its whole length or one can deform a sector of it, only (sector A in
Fig. 6). The pre-form exits
the rolling stand shaped as a hexagonal ~ism, while the wire feed aperture is
shaped as a triangular
aperture 2a. In fact, the characteristic features and the advantages of the
method of forging described
above and illustrated in Fig. 13 (a scheme of power impact and metal plastic
outflow) are valid here,
too. The use of a rolling stand as a device for the fabrication of the contact
tip is especially
appropriate when the tip has outside hexagonal surface along its whole length,
since the method of
tip fabrication is especially productive in that case.
~s
CA 02435627 2003-07-16
The optimal gap between the welding wire electrode and the wire feed aperture
walls is
experimentally found, regarding a contact tip whose aperture has a triangular
cross section. The
experiments are performed, involving welding wire electrodes with diameters
0.8, 1.0, 1.2, 1.4, 1.6
mm and tips 25, 30 and 40 mm long. The cross section of the tip wire feed
aperture is an equilateral
triangle and it is uniform along the whole tip length. The experimental
results are specified in the
table given below.
D1/D2 Evaluation Remark
1,05 Wire feed is pered.
1,07 I Successfizl tip
1,12 I Successful tip
1,14 I Successful tip
1,20 I Successful tip
1,22 o Current transfer is unstable)
These results illustrate that tips, whose ratio between the diameter of D~ of
the circle inscribed in the
aperture triangular cross section and the diameter Dz of the welding wire
electrode is within ranges
1, 07 -1, 20, are characterized by good perfomlance. For ratio values under
1.07, wire passability is
deteriorated (the wire electrode often blocks within the wire feed aperture)
while for ratio values
over 1,20 current transfer is deteriorated and sometimes wire welds to the
wire feed aperture of the
tip.
16
