High Capacity Electric Storage (HCES) batteries, for industrial uses, are a new, renewable technology to store off-peak power for peak electricity demands. The unique and complex weld paths in the battery storage system require complete flexibility in the manufacturing process, offered by laser welding. This needs the use of a robotically controlled laser, in conjunction with a manipulating table.

The exceptional materials processing expertise of Barkston Plastics and Clearweld laser welding technology from Gentex Corporation provide a unique combination to maximise the viability in the commercial market place for such batteries.

Clearweld is the preferred joining technology for the cell components to produce hermetically sealed channels with no distortion.

Clearweld, uses high-density, near-infrared (NIR) energy that passes through an IR transmissive substrate to an IR-absorbing interface to provide the following advantages.

• A strong, hermetic seal.
• Low mechanical and thermal stresses in the weld.
• Potential damage to components and particulates are not generated through vibration.
• Pre-assembly of parts, high weld speeds and three-dimensional welds are possible.
• Little or no flash is generated which helps to maintain channel integrity and tolerances.

The process requires near-infrared-absorbing materials in the form of coatings, film or resins. To weld multiple layers in one operation, laser energy must be transmitted through the upper layers to the lower layers, which absorb it. If an absorbing material, such as a Clearweld or carbon black, is compounded into the resin, the entire part will absorb the energy, preventing it from reaching the lower layers. However, this problem can be overcome by applying a Clearweld coating to the surfaces of the parts to be welded. The coating permits the transfer of laser energy to the subsequent layers, where the welding can be repeated with confidence.

The significant challenge associated with welding battery cells is the requirement to maintain tight tolerances with multi layer components and ensure hermetic seals throughout every layer. Barkston Plastics developed novel materials processing techniques to ensure the performance specification was fulfilled. This included specialist machining of the HDPE, which required exacting tolerances be maintained at all times.