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The effect of a dual stage pressure cycle on the linear vibration welding of thermoplastics - A preliminary study

TWI Techonology Briefing 445 - May 1992

M G Murch

FULL REPORT

Scope

Linear vibration welding is suited to the joining of large parts and has many applications in the domestic appliance market and automotive industry. A recent innovation of a dual pressure control, available on some modern commercial vibration welders, has the potential to improve further the quality of welded components while reducing the weld completion time.

This report describes a preliminary study of dual stage pressure control applied to the welding of three injection moulded thermoplastic materials: polypropylene (PP), high impact polystyrene (HIPS) and polyphenylene oxide (PPO). The influence on welding time, joint strength and material displacement of a dual stage pressure control has been compared with the conventional single pressure operating system.

Main Conclusions

  1. Higher tensile strengths, reduced material displacement and shorter weld completion times were achieved with a dual stage pressure profile, compared with a single level pressure operation, in HIPS and PPO materials.

  2. Under dual pressure control, the welding characteristics of the three materials differed markedly in behaviour. PP and HIPS performed best when a high initial pressure was held through the friction heating stage, before reducingfor weld consolidation; whereas PPO required a lower pressure in the welding cycle in order to prevent buckling of the material behind the melt front.

Recommendations

This work has shown that a dual pressure cycle applied to the vibration welding of thermoplastics offers benefits in improving productivity and increasing weld strengths. The potential has been demonstrated on plain materials and should prove equally advantageous in the welding of reinforced thermoplastics materials. However, the effects on weld microstructure and impact properties have not been investigated to date.

Member Report No. 445-1992
The effect of a dual stage pressure cycle on the linear vibration welding of thermoplastics - A preliminary study

Copyright by TWI, 1999