Battery Energy Storage Case: 5 mm recycled HDPE Battery Boxes from Drawing to Production

This battery energy storage project started with one question: could battery boxes be vacuum formed instead of produced as a machined aluminium housing? The answer was yes at 5 mm recycled HDPE, and the part went from drawing to approved sample in 6 weeks. Here is the route and the result.

The starting point

• Part: battery boxes for battery energy storage
• Existing route: a machined aluminium housing
• Annual volume: 1500 pieces
• Problems: high unit cost, long lead time, and variation between batches

What was wrong with the old route

The previous machined aluminium housing needed several operations to reach finished shape, and every operation added both cost and a chance for variation. Weight was higher than it needed to be, and design changes meant new fixtures each time. For a programme of 1500 pieces a year that is a poor fit.

What we built

Process route

1. Drawings are reviewed and a manufacturability report is issued with wall thickness, draft and radii marked up.
2. Parts are inspected, fitted with inserts or hardware if required, packed and shipped.
3. Sheet is dried when the material needs it, then heated to forming temperature on the machine.
4. The sheet is formed over the mould with vacuum and, where the draw is deep, with plug assist.
5. Trimming is done on 5-axis routers or with a dedicated trim fixture to meet the drawing.
6. The part cools on a jig so the shape is held while the material stabilises.

Results

• cut lead time from 8 weeks to 3
• First article approved in 6 weeks
• Tooling amortised inside the first production batch
• Repeat releases match the approved sample: tooling and programmes are stored against the part number
• 1500 pieces shipped to date with no dimensional escapes

Lessons from this project

• The 5 mm was set from the load case, which avoided over specifying the sheet and paying for weight that was not needed
• Draft and radii were checked before the tool was cut, so the first sample released without hand work
• The trim line was placed on a flat face, which kept the router inside ±0.2 mm
• Tooling and programmes are stored against the part number, so repeat releases need no new proving run

What the client said

“The sample arrived on the date we were given and it fitted the assembly on the first try. The battery boxes is lighter than the part it replaced and the finish holds up in the field. We now release the battery boxes against stored tooling and the paperwork comes with the shipment.”

Frequently asked questions

Could the same route work on a different part?

If the part is a shell, cover, tray or enclosure between 1.5 mm and 12 mm thick, it is almost always worth quoting. Send the drawing and the answer comes back with a material and a tooling plan.

How is the tooling handled between orders?

Tooling, trim fixtures and programmes are kept against the part number for the life of the programme, so a repeat release needs no new proving run.

Next step

Send the drawing or the existing battery boxes with the annual quantity. The reply is a manufacturability review, a material recommendation and a quotation within 24 hours.