Hybrid Electric Vehicle (HEV) battery modules are designed for extended life under real world environmental and driving conditions. The complex design of these battery modules coupled with aggressive chemicals in the electrolyte; necessitate the use of plastics as enclosure material. Traditional lead acid battery plastics were tested and did not meet the combined mechanical, thermal & chemical requirements for the HEV battery module.

Numerous tests and research studies have resulted in the development of the PP (Polypropylene) + PPE (Poly-phenylene ether) blend for use in HEV battery applications. This blend has been specifically developed to have good mechanical and thermal characteristics at the operating conditions (-40 to 80 C). Also it offers excellent chemical resistance to the electrolyte and standard automotive coolants. However very little published information is available on the weldability of the PP+PPE blend. As good assembly characteristics are necessary for a robust battery module, a study was undertaken to evaluate welding characteristics of the PP+PPE blend. Hot-plate & Vibration welding processes were chosen for evaluation because they were found to be the most suitable for the battery design and because of their extensive use within the automotive industry for assembly.

The PP + PPE resin was molded into battery enclosures and test samples. Design of Experiments was conducted to investigate the effects of the process parameters on weld strength, elongation & fracture characteristics. For hot-plate welding weld time, welding pressure, change over time, cooling pressure, cooling time & melt penetration were investigated. For vibration welding pressure, amplitude of welding, cooling pressure, cooling time & melt penetration were evaluated. Based on the experimental results optimization runs and capability studies were performed to select best parameters for hot-plate and Vibration welding.