Electric heating – Metal heating – By arc
Reexamination Certificate
2001-12-21
2004-04-20
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S130510
Reexamination Certificate
active
06723956
ABSTRACT:
The present invention relates to a pulsed-arc welding process, device and unit, in particular to an MIG (Metal Inert Gas) or MAG (Metal Active Gas) welding process.
Arc welding in pulsed mode was developed to overcome the drawbacks of welding in globular mode which, because of its unstable transfer mechanism and its spattering character, does not allow productivity to be increased under acceptable welding conditions.
This is because in the arc welding of carbon steels and stainless steels, as soon as it is desired to increase the amount of metal deposited, while maintaining correct operating properties, it is necessary to increase the intensity of the current and, when a pulsed mode is not used, it is found that the process rapidly returns to globular mode.
However, the pulsed mode allows welding in a position which very often is impractical or difficult in globular mode.
Moreover, the non-spattering character of the pulsed mode, when the synergy of the various operating parameters is correct, makes it possible, especially on stainless steels, to reduce the finishing operation such as the removal of a spatter.
Furthermore, pulsed welding also has a wide field of application when it is compared with the axial spray mode which, by requiring quite a high welding current and resulting in a high deposition rate and a large weld pool, is generally used only on sizeable welding thicknesses and in the horizontal position, that is to say is limited to downhand welding.
The pulsed mode, making it possible to reduce the welding energy for the same wire speed and therefore for the same amount of metal deposited, partly remedies these drawbacks and allows, depending on the joint to be produced, not only downhand welding but also positional welding with a transfer quality comparable to that of the spray mode.
The pulsed mode is also very widely used for welding light alloys, such as aluminium for example, for which the short-circuit mode and globular mode are difficult to put into practice because of the defects which they give rise to, namely porosity and incomplete fusion.
In this case, the pulsed mode makes it possible to weld correctly with energies allowing the welding of small thickness down to 1 mm and positional welding, whereas the conventionally employed spray mode is rather more synonymous with productivity.
Arc welding processes in spray mode or in pulsed mode are described in the following documents: WO-A-98/22247, EP-A-909 604
, Welding and Cutting
by P. Houldcroft and R. John, 1988, pp. 80-83, BE-A-817 637, JP-A-57 124 572, JP-A-56 134 075, JP-A-59 078 776, GB-A-2 268 009, U.S. Pat. Nos. 5,192,851, 3,528,100, 3,956,610, 5,432,317, 4,912,299, 5,672,286, 4,366,362 and EP-A-422 763.
In general, in pulsed mode, the current pulse may adopt various waveforms. The trapezoidal waveform is however virtually the only one to be used on an industrial scale and is, in general, characterized by the parameters indicated in
FIG. 1
appended hereto.
If it is desired to make pulsed MIG/MAG welding accessible to most operators, it is necessary to produce what are called synergic curves or welding programs.
The setting-up of a pulsed-current synergic control system consists in determining, for each wire according to its nature and its diameter, for each shielding gas and for each wire feed speed, values of the parameters describing the current pulse which best satisfy the criteria by which the welding operation is judged.
This determination is quite difficult to carry out as it, in general, is empirical and can only be accomplished by means of numerous trials.
However, this is the indispensable condition to the dissemination and utilization of a welding process so that the welding operator has the minimum number of adjustments to make.
Thus, conventionally the operator chooses the wire/gas pair and, depending on the desired wire feed speed, the previously determined synergic curve is used to assign the correct values to the current pulse parameters.
In general, a good pulsed-current synergic control system must comprise single drop detachment per pulse, be spatter free and have the smallest possible arc height.
The setting-up of the synergic control system or program requires having to choose the values to be assigned to the pulse parameters in the knowledge that:
the peak current (I
p
) cannot be less than a certain threshold if it is desired that the drop becomes detached, this threshold being given by the value of the current for which the spray mode starts in consumable-electrode gas-shield DC welding; and
if it is desired for there to be no spatter, detachment of the drop must occur at limited current levels.
Moreover, once this work has been done for several wire feed speeds, it is necessary to ensure any change, depending on the wire feed speed, in the parameters describing the current pulse is not too abrupt.
This is because the operator is free to choose the wire feed speed, and this speed does not always correspond to the wire feed speeds that were used to describe the synergic curve.
In this case, the values of the pulse parameters must be interpolated from the synergic curves and, if these are too abrupt, the welding result obtained may not be satisfactory and it is then necessary to start again.
To determine the synergic curves is therefore usually quite difficult and requires many welding trials to be carried out, the number being greater the more numerous the parameters to be taken into account, since the more parameters there are to be considered, the more possible combinations there are of these various parameters among themselves and therefore the more trials there are to be carried out, without having to be certain of the result which will stem therefrom.
The problem that therefore arises is to have a pulsed-arc welding process which allows carbon steels, stainless steels, aluminium or aluminium alloys to be welded effectively and which avoids having to carry out numerous welding trials in order to determine the welding conditions and parameters which give good welding results, in particular the wire feed speed and the set of parameters describing the current pulses which have to be applied for the chosen wire feed speed, namely the mean current value and the rms current value.
Plus, it is a first object of the present invention therefore to provide a process for the arc welding in pulsed mode of carbon steels, stainless steels, aluminium or aluminium alloys, with the use of a gas shield, exhibiting great flexibility and giving satisfactory results in terms of welding quality.
It is a second object of the present invention therefore to provide a MIG or MAG arc welding process in pulsed mode, allowing easy determination, depending on the desired wire feed speed, of the set of parameters describing the current pulses, mainly the mean current (I
mean
) value and the rms current (I
rms
) value, which have to be applied so that good welding results are obtained.
Thus, the present invention relates to a process for the arc welding in pulsed mode of one or more workpieces made of carbon steel, stainless steel, aluminium or aluminium alloy, with the use of a gas shield, in which an electric arc welding torch is supplied with at least one consumable wire at a wire feed speed (V
wire
) and the said consumable wire is subjected to current pulses, in order to melt the end of the said consumable wire and to detach a drop of molten metal by a current impulse, and in which, for a given pulse frequency, a wire feed speed (F
wire
), a mean current (I
mean
) value and an rms current (I
rms
) value such that:
I
mean
=A
1
V
wire
+B
1
, where 5
<A
1
<45 and 0
<B
1
<50
and
I
rms
=A
2
V
wire
+B
2
, where 5
<A
2
<45 and 40
<B
2
<100,
where I
mean
and I
rms
are expressed in amps and V
wire
is expressed in m/min, are chosen and/or used.
Depending on the case, the process of the invention may include one or more of the following features:
the workpiece or workpieces to be welded are made of carbon steel and in that the mean current (I
mean
) value an
Briand Francis
Caillibotte Georges
Eyschen Jean-Pierre
Mas Christophe
L'Air Liquide - Societe Anonyme a Directoire et Conseil de
Shaw Clifford C.
Young & Thompson
LandOfFree
Pulsed-arc welding process and device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pulsed-arc welding process and device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pulsed-arc welding process and device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3242915