Technology Briefing 363 - March 1988
M G Murch Scope
Despite the increasing use of friction welding for joining semi-finished products in thermoplastics, there are only limited data reported on the significance of welding parameters relative to joint integrity and strength.
This report considers the friction welding process and compares the performance of the inertia spin and linear vibration welding systems applied to two injection moulded thermoplastic materials: high impact acrylonitrilebutadiene-styrene (ABS) and medium density polyethylene (MDPE). Three joint designs in common use have been investigated and the strength of joints produced over a wide range of welding parameters was evaluated. The relationship between monitored welding parameters and set operational variables has been determined.
Main conclusions
- Both high impact ABS and MDPE gave satisfactory joint strengths with the inertia spin and linear vibration welding processes. Although MDPE was considered the more difficult to join as almost twice the energy was required toachieve acceptable results as compared with ABS thermoplastics.
- In inertia spin welding, a high value of interfacial torque was necessary to achieve satisfactory strength levels in ABS joints. For PE, the interfacial rubbing velocity was relative to the joint surface contact area, the dominantwelding parameter with very high levels required for full bonding.
- An extensive range of parameters in linear vibration welding have given satisfactory weld strengths in both high impact ABS and MDPE, although the operating conditions were restricted when the appearance and size of the weld flashwas a primary consideration.
Recommendations
This work has shown that spin and linear vibration welding are suitable processes for joining ABS and PE thermoplastics. The inertia spin welding system would be chosen for rapid joining of circular components of self-locating joint design, where the joint contact area was within the capacity of the welding equipment to provide complete fusion. The linear vibration welding technique is virtually unrestricted by component shape or joint cross-sectional area and its use is recommended in applications where precise joint orientation is important.
