GB2107471A

GB2107471A - Detection of spatter accumulation in welding gun

Info

Publication number: GB2107471A
Application number: GB08227834A
Authority: GB
Inventors: Albert W Carter; Stephen Bruce Jones
Original assignee: Welding Institute England
Current assignee: Welding Institute England
Priority date: 1981-09-29
Filing date: 1982-09-29
Publication date: 1983-04-27
Also published as: GB2107471B

Abstract

To measure spatter on a part (2) attached to or forming a part of a welding gun, a signal is derived from a coil (6) surrounding the welding gun and connected to an inductance-responsive circuit (8, 10, 12). The coil may be attached to the welding gun, or the gun may be periodically inserted into a remote coil. The part may be a gas shroud (2), and a stop signal or warning signal may be generated when the coil output is indicative of too great an accumulation of spatter. The invention is particularly advantageous when the welding is to be carried out by a robot and the constant supervision of a human operator is absent. <IMAGE>

Description

SPECIFICATION Detection of spatter accumulation in welding gun This invention relates to the detection of an accumulation of spatter on a part attached to or forming a portion of a welding gun; an example is the gas shroud of a welding gun used in a gasshielded metal arc welding process. However, the invention is also applicable to the detection of spatter in welding processes such as self-shielded welding (using a flux-cored wire), or submerged arc welding in which a gas shroud is not used but in which an accumulation of spatter on a contact tube (feeding current to the welding wire) can lead to defective welding. In one case the spatter aggregation can fall from the contact tube into the weld pool and this gives rise to weld defects, including porosity. The invention is also applicable to narrow-gap welding, in which the contact tube projects into the gap in the weld plates and build-up of spatter on the contact tube can cause a short circuit across the arc and so lead to arc extinction.

The part subject to an accumulation of spatter may also be a sensor, for monitoring seam tracking, for example, or torch-to-work distance, such sensors being close to the weld. An accumulation of spatter can give rise to defective measurements from the sensor, leading to incorrect positioning oftheweld- ing torch.

Normally, the accumulation of spatter is evident to a welder in manually controlled welding orto an operator in a mechanised system. When the welder or operator sees that the accumulation of spatter on a gas shroud is endangering the flow of the shielding gas, for example, the nozzle is cleaned or changed.

However, when the process is accomplished automatically, for example by a welding robot, the constant supervision of a human operator is not needed and a visual check on the accumulation of spatter in the gas shroud is not carried out. According to this invention, in a method of measuring spatter on a part attached to or forming a portion of a welding gun, a coil, connected to an inductanceresponsive circuit, surrounds the said part and a spatter-indicative signal is obtained from the said circuit. The said part may be a gas shroud or in other welding processes it may be the contact tube or sensor. In one arrangement of apparatus for carrying out the method in accordance with the invention, the coil is mounted around the said part and the inductance is continuously or periodically measured and a stop signal or warning signal is generated when the inducatnce measurement indicates too great an accumulation of spatter. In another arrangement, the coil is separated from the welding gun and a robot for guiding and operating the welding gun periodically automatically guides the gun to the coil and inserts the said part into the coil.

The accompanying drawing illustrates a gas shroud 2, enclosing a consumable electrode wire 4, and surrounded at its open end by an inductancemeasuring coil 6. The coil is connected to a capacitor 8, the combination constituting a tuned circuit which is energised by an oscillator 10. The frequency of oscillation is monitored by a counter 12, giving an accurate measurement of any changes in the coil inductance.

When the gas shroud is of ceramic material, the accumulation of particles of metallic materials on the ceramic gas shroud alters the effective inductance of the coil. Thus, as steel spatter accumulates on the inside of the shroud the inductance increases; conversely, if the spatter is a non-magnetic material it can be sensed by a reduction in inductance. This change can be read by an inductance bridge, of which the coil forms a part, or a frequency counting device, the coil forming a part of the tuned circuit of the device. If the shroud is of a non-magnetic metal, such as copper, the use of a magnetic material for welding gives a spatter content that shows appreciable alteration in the inductance level.

A metal shroud will give some degree of screening to the spatter particles, even if the metal is nonmagnetic. An improvement in the spatter detection can be obtained if the shroud has one or more slots along its length. These slots can be sealed by an insulating material to enable the gas shroud to fulfil its function.

When the coil is permanently located around the shroud, the shroud will become heated and this will affect the inductance of the coil. Because of this, an allowance must be made for the heating of the coil or means must be provided for cooling the coil.

A remote coil, to which the shroud is periodically guided, has the advantage that the coil is removed from the spatter zone; consequently, the coil cannot collect spatter, which can itself affect the reading obtained from the coil.

Whilst the drawings illustrate spatter measurement on a gas shroud in a gas-shielded welding process, it will be clear that the invention can also be used for measuring spatter in other welding processes, for example the seif-shielded, submerged arc and narrow-gap welding processes referred to above, in all of which a build-up of spatter leads to defective welding; in addition, it can be used for measuring spatter on sensors. In these cases, a remote coil, into which the part in question is inserted, is used to measure the amount of spatter; it will be appreciated that any coil that is wound around the contact tube or sensor would itself collect spatter on the outside.

Claims

1. A method of measuring spatter on a part attached to or forming a portion of a welding gun, in which a coil, connected to an inductance-responsive circuit, surrounds the said part and a spatter-indicative signal is obtained from the said circuit.

2. A method in accordance with claim 1, in which the welding gun is operated and guided automatically and in which the coil is located away from the gun during welding and the gun is periodically and automatically guided to insert the said part into the coil.

3. A method in accordance with claim 1 or 2, in which the said part is a gas shroud of a welding gun used in a gas-shielded metal arc welding process.

4. A welding gun in combination with an inductance-responsive instrument having a coil suitable for surrounding a part attached to or forming a portion of the welding gun on which spatter will be deposited, whereby the instrument provides an indication of the change of inductance resulting from spatter.

5. A welding gun in accordance with claim 4, for gas-shielded metal arc welding, in which the coil surrounds a gas shroud of the gun.

6. Awelding gun in combination with an instrument, in accordance with claim 4, in which the coil is mounted on the gun.

7. Awelding gun in combination with an instrument in accordance with claim 4 or 5, in which the coil is connected to a tuning capacitor.

8. Awelding gun in accordance with claim 5, in which the shroud is of metal and is formed with slots along its length, the slots being sealed by an insulating material.

9. Automatic welding apparatus including the combination of welding gun and inductive-responsive instrument of claim 4 or 5, and further including a robot for guiding and operating the welding gun, and means providing an alarm signal when the signal from the instrument indicates an amount of spatter which exceeds the predetermined level.