Making a custom rubber/silicone bezel for aluminium enclosure

[Martin F]

Hi all,

We're trying to design a custom made rubber/silicone bezel to cover the end plates of our aluminum enclosure.
I've attached a few pictures of initial 3D printed attempts, but would love suggestions from in here.

What we're trying to do:
1) The purpose is to create a visually more appealing product - and cover the area where the end plates meet the main body
2) Secondly, we'd like the material to be flexible to reduce noise (e.g. when putting the product on a table)
3) Finally, the flexibility would allow us to add an SD card "cover" as part of one of the bezels, which can be closed/opened

Our challenge:
1) The bezels easily slide off currently.
Most peer solutions we find seem to put the bezel between the end plate and the main body - but from what we can gather, this would negate the positive EMC benefits of using an aluminium enclosure. We hence fear we won't be able to pass certification with such a solution. Further, doing this we assume requires a more solid material (ala ABS plastic) to ensure the screws do not destroy the bezel when they're fastened properly

2) The top/bottom middle part of the bezels is rather "loose" - i.e. it gives off a bit of a less solid vibe. We could again fix this by shifting to e.g. a hard plastic, but this would eliminate the sound reduction effects and we would need to create a different solution for the SD card cover

Any thoughts are super appreciated,
Martin

[bugrobotics]

Hi Martin,
How many of these are you producing?  If it were more than a few I'd machine a mold to cast urethane or silicon.  It wouldn't have to be expensive and depending upon the shape may be able to be accomplished with a single sided mold (think molded cookie sheet).  I've done this quite a bit when making strain reliefs for cables, custom wheels and bezels for control panels.  Attached are few examples of molds and results.

[bugrobotics]

To deal with fastening the bezel, I'd possibly cast in a washer or standoff to provide a solid place for the screw to seat and not distort the rubber bezel.

[Martin F]

Thanks for the inputs! We aim to produce these in large volumes. I'll take your suggestions up with the team (also on the dust cover)

[rhb]

Take a look at the bumpers on a 34401A or similar.  If your bumper has depressions in it that extensions on the end plates fit into it should stay in place and a soft elastomer will easy slip off only when desired.  HP put the depressions in the case rather than the elastomer, but I suspect that was to accommodate installing rack mounting hardware instead of the bumpers.

You might find this useful:

How to Cast Small Metal and Rubber Parts
William Cannon 1986
McGraw-Hill Tab Books division

It's oriented to antique car nuts, but has plenty of useful information.

[aandrew]

Hi Martin,
How many of these are you producing?  If it were more than a few I'd machine a mold to cast urethane or silicon.  It wouldn't have to be expensive and depending upon the shape may be able to be accomplished with a single sided mold (think molded cookie sheet).  I've done this quite a bit when making strain reliefs for cables, custom wheels and bezels for control panels.  Attached are few examples of molds and results.

I'd love to hear more about this process, how you designed the molds and how they're manufactured. Are you injecting the silicone yourself?

[kosine]

If you can get a small aluminium mould produced for casting, then it's not much of a step to get them injection moulded. You'd need to find someone with a modest CNC machine (hobby level would suffice), and a small local injection moulding firm. They'd need to prep a mould bolster you could bolt your mini-mould onto, but that's not a major job. (Just a metal plate with some bolt holes in it.)

Couple of videos here showing how a custom end cap can be done this way:
Part 1 :
Part 2:

You'd be getting about 100 parts per hour, though you'd need to stand there taking them out of the mould. (A fully automatic system with ejector pins would be a lot more expensive.) You could follow up with a 2 or 4 cavity mould if you needed more.

Best material to use would be a soft thermoplastic elastomer (e.g., SEBS) which can be blended with HDPE to adjust the stiffness. I wouldn't injection mould them from polyurethane as it's difficult to get a good cosmetic finish, although PU/PVC blends might be an option. TPE/SEBS is much easier to work with for this sort of job. It has a nice grippy surface texture, hence it's use on power tool handles.

[bugrobotics]

Hi aandrew, yes for the quantities I would normally do (less than 100) I would be injecting the silicon/urethane rubber myself.  Designing the molds is relatively straightforward as long as you take into account draft angles and undercuts in order to be able to successfully remove the casting without damage.  Judging the correct draft angle and allowable undercuts takes a bit of experience with the mold type, material and final shape. I normally complete the task using tools in Solidworks.  After the mold cavity is designed I would add any features to allow mold separation and add ejector pins (dowels) if necessary.  I would then move to create the toolpaths ensuring the tooling marks are appropriate in size, shape and direction to encourage proper function.  The raw stock then gets machined and finished with various methods depending upon the appearance required including glass bead blasting, polishing, sanding and even anodizing if I want the added protection.  This works well for under a few hundred parts as long as the parts aren't too large and you have the tools to do it efficiently.

kosine detailed a process more appropriate for larger manufacturing runs.  It sounds as if Martin would be best suited to outsource to a mold shop.  There are a number in the US and China that I've used but since he is across the pond I don't have any recommendations.