Designing electronic enclosures for manufacturing

Question

I am trying to design a simple plastic electronic enclosure for a PCB and I wanted to learn how to get the enclosure as ready as possible for manufacturing. I basically wanted to understand the process that a mechanical engineer would go through to make sure the design of the enclosure is good enough for manufacturing.

So far I have read about stress/strain and wanted to find out what other things I should know when designing plastic enclosures.

For example, a lot of enclosures such as the one below, seem to have added extrusions on the internal sides, I would like to understand the functionality behind these - are these to do with stress and strain making the product more resistant?

Any ideas of the processes involved by a mechanical engineer to make a manufacture ready plastic enclosure would be great

Answer 1

To design such a box, it would need to be approached from different perspectives. But the final criteria would be is it legal, and does it satisfy other requirements. For example, does it satisfy CE mark compliance requirements for safety and EMI, and will it do the job the user wants it for.

CE requirements and so on are often assessed by specialist bodies who put it through rigorous checks. This involves many specialists and specialist equipment. This is a large topic in itself.

Then after that you have considerations such as choice of materials (including composites), strength, durability, cost, methods of manufacture and so on. These will most likely be the easier problems.

I'm afraid you are embarking on an extremely difficult problem which requires a multi-disciplinary approach and years and years of experience. The phrase "A box is a box" is not true. A box, in this case, is Pandora's box.

Answer 2

The "extrusions" on the side that you ask about are there to hold a circuit board. The board slides in vertically between the ridges. There are several locations to provide for multiple boards or a board in different positions.

Answer 3

There are many stock options available on the open market to do this. One of the things my company has done is to create it's own line of enclosures (we have a 5x7", a 4x5", and a 3x4" version). These are then used to "prototype" your final assembly to get it in the hands of your market target. Once you have that feedback and demand is being generated, you know better how to design what the market needs with regard to your product.

Feel free to contact me if you have any other questions. I would be happy to help point you in the right direction.

Answer 4

One of the most important consideration is what sort of production volume you are looking at.

For example injection moulding is frequently used for high volume plastic components as cost per unit is low but setup costs are high. At the other end of the scale something like vacuum forming is good for making small volumes as the tooling can be made relatively easily but it does have limitation on the forms that you can use.

The difficulty with high volume moulding processes is that you need quite a detailed understanding of the manufacturing process to optimise a design and there may be very specific requirements for things like draft angles, fillet radii, acceptable changes of section, allowance for shrinkage etc. etc. Not to mention implications for the design of the tooling which may not be at all obvious from the end product.

Another good option for box-like shapes is to fabricate it using already available moldings or extrusions for example you may be able to find a rectangular section extrusion which can be adapted with relatively simple modifications like cutting to length, drilling holes and adding fill-in plates.

To be honest I would be quite surprised if there isn't an existing plastic box somewhere which is close enough to your requirements to avoid having to manufacture it from scratch.

The key point here is that the specific manufacturing process selected has a profound influence on the suitability of a given design.

I would suggest that the best approach is to focus on defining what properties, performance and standards the enclosure needs to achieve, such as environmental resistance, internal dimensions and any requirement for mounting points etc etc and then approach a manufacturer to discuss the best way to achieve these objectives.