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Plastics join the friction revolution

Connect, no.106, May/June 2000, p.8

Since the development of Friction Stir Welding (FSW) in 1991, TWI has conducted several exploratory studies into traditional rotary motion FSW and reciprocating motion FSW of plastics materials.

Reciprocating FSW is characterised by an 'aerofoil' shaped probe, which is reciprocated with predetermined amplitude before being traversed along the length of abutting sheet materials. A range of welding conditions such as traverse speed, amplitude, frequency and tool materials for the aerofoil-shaped probe were used for the trials. Tool materials investigated include brass, copper, aluminium, stainless steel, titanium, PEEK and alumina.

Section through a reciprocating FSW in 15mm thick polypropylene
Section through a reciprocating FSW in 15mm thick polypropylene

Results show that it is possible to rotary friction stir weld unfilled thermoplastic HDPE sheet materials of 7mm thickness, and to reciprocating friction stir weld unfilled thermoplastic such as 12mm thick Perspex and 15mm thick polypropylene.

Joint strengths of more than 90% of parent material strength have been achieved.

The thermal conductivity of the tool material affects the weld strength. Tool materials with a low thermal conductivity, eg titanium, produce welds with higher tensile strength in 15mm thick polypropylene than tools made of other materials.

The potential benefits of FSW for plastics fabricators compared to traditional hot gas and extrusion welding include:

  • consumables not needed
  • low cost technique
  • reduced opportunity for operator error
  • high tensile strength welds achieved

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