I have a screw together plastic enclosure design with a metal thread embedded in a plastic screw boss. How or can they put in threaded metal inserts like a PEM threaded insert into an SLA model?
You can get inserts that are threaded on the outside, or inserts that can just be held in with epoxy. You can also get inserts that have a shoulder if you have the option to insert from the bottom - that would probably be the most robust for an SLA since the strength of the metal shoulder will be resisting most of the load.
As cyberdemon mentioned you can modify your CAD file to have extra room around the insert so you can epoxy it in place.
I have had to do this on several occassions. I typically modify the boss meant for the PEM insert to fit a similar thread hex nut and epoxy that in place for the prototype.
If you are going to put a lot of torque on the parts you maybe able to actually sonic weld the “ABS-like” material to get the actual insert in, though not many people have access to a sonic welder.
I have used press-in style inserts on both SLA and CNC models. Because SLA material is brittle it is sometimes necessary to use a Dremel tool or just a drill bit (held by hand - not in a drill) to loosen up the hole a bit. You can glue them in with epoxy - or heat them up on the end of a soldering iron (do it yourself heat-stake)
Helicoils are your friend.
We use brass threaded inserts that cut their own threads into the SLA.
They work equally well in plastics, cast urethanes, and woods. Typically the SLA holes will be a little tighter than desired and will need to be drilled or reamed out. This can and should be done by hand to make sure that you do not damage/egg the mounting boss.
We usually use the ones from McMaster that are made by this company:
The self-tapping ones work great and come up 1/4-20 thread size. Don’t bother with the $100 installation tool.
Make your own with a couple of jam nuts on a machine screw. Be sure to use a screw that can handle decent torque – some stainless steel screws will strip out when installing the inserts.
Depending on the force used to tighten the parts - the epoxy process for inserts will crack free and spin if a lot of force is used. We can do “molded -in” inserts through the RTV process that will withstand much more force. Downside you pay more because of the silicone mold used to produce parts but the upside is that the parts and the insert are much more durable. Do SLA for design appearance and then RTV molded urethanes for function testing, just make sure the customer is aware of the weaker insert process in the SLA parts and it is usually not an issue.
for SLA, x2 on the soldering iron.
It’s a no-go for cast urethanes… but that question wasn’t asked.
I agree with loughnane. I usually try to stay away from inserts in SLA’s and cast urethanes in general; however, when we can’t convince the engineers to help us out, we use a soldering iron for SLA prototypes. Just make sure to make the boss thick enough so it wont crack and don’t expect the insert to hold any sort of load; it will pull out. I usually end up putting a little 5 min epoxy as well. SLS doesn’t lend itself to this method. For SLS, I usually have the bosses designed to hold thread cutting screws. I would also build the bosses a little thicker and not take the screws in and out multiple times.
Other than that…epoxy and 3M panel bond is your friend…as long as surfaces are scuffed and cleaned well with wax&grease remover
Just to add, if you don’t want to use an insert, I’ve had a lot of success with PLASTITE self threading plastic screws for SLA, SLS, and Urethane Cast parts.