What is friction taper plug welding?

Introduction

Friction taper plug welding (FTPW) and friction taper stitch welding (FTSW) was originally conceived for the filling of mis-drilled holes and repair of cracks/defects in steel plate/pipe. In comparison with traditional fusion welding techniques, FTPW is a solid phase welding process. FTPW is accomplished by drilling a tapered hole into or through the plate at the location of the repair or defect. Then a tapered plug with a similar included angle is friction welded into the hole. The complete conical surface of the tapered plug is welded to the matching surface of the hole

Friction Taper Stitch Welding, is a series of interlinked taper plugs which can be used to repair a crack in plate, as illustrated below:

The possibility of joining plates together by FTSW of blind holes using this process variant has been explored as demonstrated by the series of interlinked blind hole fills shown below:

FTPW/FTSW is still an emerging technology that is beginning to be considered for applications where problems have been experienced using traditional fusion welding techniques. In particular, interest has focussed on remote deployment in hazardous environments such as underwater, radioactive, toxic and inflammable gas areas, where fusion welding cannot be considered. As FTPW/FTSW is a conventional machine tool technology, it is possible to use operators who have not received detailed training in welding techniques.

FTPW/FTSW is a solid phase welding technique, and can be considered for use in all positions provided that there is sufficient room to accommodate the welding machine in the repair location. Through hole repairs have been demonstrated in plates from 5mm to 38mm thickness, under laboratory conditions using machines with 7.5 to 75kW transmission power. Portable friction welding machines are being considered/developed for the repair of 8mm thick stainless steel, and high strength aluminium alloys, with the machine power supplied by mobile generators where necessary.

The main limitation associated with the industrial application of FTPW/FTSW is the current lack of commercially available, dedicated equipment. Therefore the cost of the development of one off prototype machines has to be taken into consideration in the assessment of the suitability of this technology.

The main advantages of FTPW/FTSW are:

• solid phase process, no major problems with cracking, porosity, etc
• low heat input welding process
• highly repeatable welding process
• welds have good mechanical properties
• some combinations of dissimilar metals can be welded
• clean process with no spatter, fume, arcs or slag
• no additional filler metal or gas shielding required
• uses machine tool technology, therefore easy to automate, and reduces the need for skilled welders
• not position-sensitive and may be performed in any plane
• energy efficient process
• can be applied in hazardous environments e.g. water.

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