GB2157994A

GB2157994A - Cleaning the shroud/tip gap of a robot welder

Info

Publication number: GB2157994A
Application number: GB08411588A
Authority: GB
Inventors: Terence Owers; Harold Webster; Jeffrey Hughes
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1984-05-05
Filing date: 1984-05-05
Publication date: 1985-11-06
Also published as: GB8411588D0

Abstract

An annular cutting tool 20 is introduced into the gap and rotated to remove any deposit on the sides of the gap is the passage for inert gas which shields the weld area during welding, and it is important that the gap be unobstructed. The cutting tool 20 should be of a type which will cut an annular slot in a blank workpiece. <IMAGE>

Description

SPECIFICATION Cleaning the shroud/tip gap of a robot welder This invention relates to a method of and apparatus for cleaning the gap between the shroud and the tip of a robot welder.

A MIG welder has a tip through which the welding wire extends, and a shroud surrounding the tip. Inert gas is blown through an annular gap between the shroud and the tip to shield the weld while the weld metal is being laid down. There is an inevitable amount of weld spatter, and some of this spatter deposits in the annular gap, in particular on the shroud. When this spatter builds up, the gap is obstructed and the inert gas shield is adversely affected, leading to weld defects such as porosity and oxidation.

It is known to periodically clean the gap between the shroud and the tip, and to program the robot so that the welding head is moved to a cleaning station after a certain number of welds, e.g. after every four or six welds. However the cleaning equipment used heretofore has not been very efficient, and it has become the practice to discard the old shroud and to fit a new shroud about two or three times a day.

According to the present invention, there is provided a method of cleaning the gap between the shroud and the tip of a robot welder wherein an annular cutting tool is introduced into the gap and rotated to clean out the gap.

The invention also provides apparatus for cleaning the gap between the shroud and the tip of a robot welder, the apparatus including an annular cutting tool, the tool being adapted to enter the annular gap between the shroud and the tip of the welder, and means for providing relative rotation between the tool and the welder to allow the tool to clean out the annular gap.

By 'annular cutting tool' is meant a tool which will cut an annular slot in a blank workpiece An example of such a tool is the type known as a "Rotobore".

The apparatus is preferably arranged so that the tool penetrates a distance of about 6mm into the gap.

The use of a cutting tool to clean the gap results in very considerable increases in the length of time a shroud remains serviceable. Robot welders equipped with cleaning apparatus in accordance with this invention have been running with the same shroud for more than three months.

This results in less operator time being spent cleaning and/or replacing the shrouds and thus less down time of the welder. Additionally the substantial expenditure on new shrouds is vastly reduced. The welds made by the welder are of better quality as the shroud/tip gap is kept much cleaner that was hitherto possible.

The cutting tool may be mounted in a springloaded socket which has a mouth normally positioned above the cutting edge of the tool but which can be depressed by the welding head to allow the tool to enter the shroud/tip gap on the welder. The socket can also centralise the welding head as the head approaches the tool.

It is important to provide sufficient power to drive the tool relative to the head. It has been found that a motor of 100 watts rating or more is suitable, and a 24 volt, 5 amp motor has been used with success.

The cutter should be easily replaceable in the apparatus when it becomes worn. The invention is particularly applicable to the cleaning of MIG welders.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a section through the welding head of a MIG welder Figure 2 is a perspective view of the cutting edge of a cutting tool for use in apparatus according to the invention; and Figure 3 is a section through apparatus in accordance with the invention for cleaning the shroud/tip gap in a robot MIG welder.

The welding head of a robot MIG welder as shown in Figure 1 has a tip 10 with an annular passage 12. A welding wire 14 extends through this passage and is fed along the passage as the wire is consumed. A shroud 16 surrounds the tip 10, and an annular gap 18 exists between the tip and the shroud. In use, an inert gas (usually a C02/ Ar mix) is blown through this gap to shield the weld from the atmosphere as the weld is being laid down.

During operation, spatter from the weld impinges on the welding head and in particular collects on the shroud inside the gap 18. This build up of metal debris obstructs the gap and prevents the proper flow of shielding inert gas through the passage. if the gas flow is obstructed, poor welds will result with porosity, oxidation and poor weld penetration occurring.

It is therefore necessary to periodically clean out the gap. If the welder is used for welding car door hinges to a door, it is suitable to clean the gap after every four or six welds have been made.

To clean the gap, a tool 20 is used. This tool, which is shown in Figures 1 and 2, is in the form of a hollow cylinder and has cutting edges at one end. There are actually two cutting edges 50 spaced around the tool periphery. The dimensions of the tool should be such that it just fits within the gap 18 and occupies substantially the whole of the gap cross-section. When the tool is inserted in the gap while the tool is rotating, the cutting edges will remove any build up of extraneous material in the gap, without actually cutting into the walls of the shroud 16 or the tip 10.

To support the tool, an apparatus as shown in Figure 3 is used. The tool 20 is mounted at the end of a shaft 22 and the shaft is driven in rotation about its own axis by a motor 24. The driving connection between the motor and the shaft is not shown in detail. The tool 20 is secured in the shaft 22 by a locking screw 26.

A socket 28 surrounds the tool 20. This socket comprises a first sleeve 30 with a bell-mouth 32 which slides within a second sleeve 34. A coil spring 36 acts between the bell mouth 32 and an annular abutment 38 on the sleeve 34 to urge the sleeve 30 upwards. The second sleeve 34 is mounted on a plate 40, and this plate is supported above a base plate 42 by coil springs 44.

In use, the robot welder is programmed so that the robot arm periodically moves the welding head to the cleaning apparatus. The head will approach the apparatus from above, and will be lowered onto the bell mouth 32. Engagement with the bell mouth helps to centralise the welding head, should this be necessary. The tool 20 starts to rotate. Continued downward movement of the welding head causes the spring 36 to be compressed so that the head fits over the tool 20 which thus cleans out the gap 18.

The springs 44 supporting the base plate 42 can yield to prevent damage to the welding head or to the cleaning apparatus if the welding head approaches the apparatus out of alignment.

After cleaning by the tool 20, the head can be sprayed in a conventional manner to keep it in good condition.

The invention is not limited to the embodiment described. In particular, the orientation of the apparatus may be different from the upright orientation shown.

Although the invention has been described with reference to MIG welding, the invention includes within its scope other types of welder where a clear gas passage has to be maintained around a welding tip.

Claims

1. A method of cleaning the gap between the shroud and the tip of a robot welder wherein an annular cutting tool is introduced into the gap and rotated to clean out the gap.

2. A method as claimed in Claim 1, wherein the welder is a MIG welder.

3. Apparatus for cleaning the gap between the shroud and the tip of a robot welder, the apparatus including an annular tool with a cutting surface on an annular end face, the tool being adapted to enter the annular gap between the shroud and the tip of the welder, and means for providing relative rotation between the tool and the welder to allow the tool to clean out the annular gap.

4. Apparatus as- claimed in Claim 3, adapted for use with a MIG welder.

5. Apparatus as claimed in Claim 3 or Claim 4, wherein the tool is a cutting tool of the type known as a "Rotobore".

6. Apparatus as claimed in any one of Claims 3 to 5, arranged so that the tool penetrates a distance of about 6mm into the gap.

7. Apparatus as claimed in any one of Claims 3 to 6, wherein the cutting tool is mounted in a spring-loaded socket which has a mouth normallypositioned above the cutting edge of the tool but which can be depressed by the welding head to allow the tool to enter the shroud/tip gap on the welder.

8. Apparatus as claimed in any one of Claims 3 to 7, wherein the cutting tool is driven by a motor of at least 100 watts.

9. Apparatus as claimed in any one of Claims 3 to 8, wherein the cutter is easily replaceable in the apparatus when it becomes worn.

10. Apparatus for cleaning the gap between the shroud and the tip of a robot MIG welder, substantially as herein described with reference to the accompanying drawings.