Summary: Insert mold bearing into plastic (off topic)?
Hello,
Thanks for the information. I was wanting to know if this was practical, or had been tried before. I have previously designed aluminum parts with plastic bearing pressed into them, but this is a different application.
Here are the responses:
. Never tried overmolding a bearing.
Regarding press fit, I think since the yield strength of plastic is substantially lower than metal, you can have a tighter dimensional press than with metal. Also, the fits in metal are designed to close in the bearing - reduce its diameter, not all that likely when pressed into plastic, since the plastic will yield and flow over time, relaxing the preload.
Have done inserts and even plain bearing inserts before but not a ball bearing race. In plain terms so long as the tool shuts protect the ball area from the plastic being molded then you can do this but...
Factors to consider are:
* Plastic shrinkage onto the inserted metal. You will know that different materials have different nominal shrinkages and you need to consider this combined with the temperature and thermal coefficient of expansion for the insert. * Molded in stress. Related to the shrinkage above and you can also have thermal shock where the plastic is against the insert especially if the insert is cold. * Hoop stress. Will depend on above plus thickness of the hoop. * Creep. You get this regardless of whether you are molding in or press fitting but you have different profiles. If you mould in then the only resistance to creep is the shrinkage hold in the insert in.
In general I think pressing the bearings in afterward allows you to get the best possible molding plus to control the interference fit and be able to look at hoop stress and creep to see if these can be worked to fulfill your design criteria. Against this the best thing about molding in an insert though is the ability to get the plastic to positively lock the insert into place (constrain all translational degrees of freedom); in this case you would have the plastic cup the outer rim of the bearing.
I would do the calculations to see if any form of shrinkage or interference fit overstresses the bearing shell but I doubt that you will be able to exceed the maximum stress with plastic for either method.
Again, thanks to all for the suggestions. Here is another link I found to a similar question: This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.
