Electrical Engineering & Electronics Design

I’ve only done additive enclosures etc. You might also start a discussion in the plastic/mold group.

Thanks Richard I will check that out.

It's really dependent on Quantity, Quality, Price.

I have seen several projects where they tried to use additive methods for pilot runs. While they technically protect the PCBs, they are nothing to be proud of, very expensive, and weaker than a real part. Typically $10-20 depending on size and resolution but could be $100, and the production rate can be painful if you need allot.

So for low volume but commercial products I usually prefer to design the PCB to an off the shelf housing that is machined to fit. Lots of manufacturers are setup to machine their own parts reasonably. Base parts can be had for cents to $20, then setup fees should be on hundreds, and machining could be cents to a few dollars per part. Printing is also commonly available. They often have threaded inserts too which makes them repairable. If you can get a 3D file, you can design the cuts very easily.

Some customers want the look of their own part so they go straight to molding. With a well designed 3D file, steel molds can be had for 5-15 K, in 3 months in Asia. Then parts costs are a few dollars in 1K+ quantities. But be warned, any change could mean starting from scratch.

All the above applies to regular hard plastic shells. If you are looking for new tech,

an evolving alternative is low pressure over-molding where the electronics go in the mold resulting in a watertight assembly.

Maybe there's something useful you can find www.qc-mold.com

i have 2 years experience in injection molding and currently working in mechanical designer in electronics domain. and if you can share min requirement i can suggest manufacturing Technics and prototype Technics

Thank you for the feedback and suggested websites everyone much appreciated. You have given me much to think about.

Hello 

We can custom the 3D printing, vacuum casting or CNC prototype(Plastic or metal) for you .

Our categories include :Home appliance,medical enclosure,electronic shell ,car model ,spare part etc.

If you are interested in our rapid prototype service , our company brief will be sent to you . 

Looking forward cooperation！

Regards 

Zamol  

Example manufacturer for small or large numbers, plastic enclosures without moulds: http://www.formit.nl/en/

Or vacuum casting, sometimes referred as Urethane casting or Polyurethane casting uses silicone moulds to make plastic and rubber components under vacuum. It is an extremely adaptable manufacturing process capable of mimicking the injection moulding to produce complex parts in polyurethane resins and cast nylon.

Enclosures are much more effective as a purchased item and then customized to your specific needs and requirements.

Unless you are looking for completely full custom and form fitting for space savings, again purchased metal enclosures simplify EMC and EMI concerns later. Plastic and 3-D printed boxes will not.

Also many boxes have integral PCB slots for retention and uniform sizes for area. So what is the envelope of space that you need contained ?

Over the last thirty years of producing turnkey electronics the most common method of packaging I used is by potting. Originally I used polymer clay to produce a positive of the enclosure built around an assembled board, cleaned and sealed it, then made a negative using epoxy. The photos are of a current project where the positive is 3D printed in two halves. In this case they were printed flat, and the resolution was not adequate due to extensive rework necessary to produce a mold, so I went back to the printer and had them printed standing up which needed much less rework. Note the sprue for introducing the epoxy potting compound into the bottom of the mold, and the riser to leave enough compound to compensate for any shrinkage / expansion during curing.

The sprue is designed to mate with common epoxy mixing nozzles.

The black outline in the top illustration defines the boundaries of the mold box, and the parting line is defined by the nature of the part, as in the illustration. In that case the parting line is defined by the flat surfaces, which requires a positive draft for both parts and careful alignment of the halves. This can be done relatively easily once both halves are made by gluing the two patterns together, then placing the mold halves on the patterns. Once they are firmly mated clamp them and drill at least two holes for alignment pins.

Once done the mold can be used at least a couple dozen times before it wears sufficiently to require making a new mold.

Be sure to use an electronic grade low viscosity epoxy compound that conducts heat. They are commonly available from MG Chemicals, and several other sources.