I want to build a DIY case with the connector shown in the pictures below.

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As you can see, it consists of a circular plastic that extrudes from the main enclosure. Inside there is something that can be described as "cut_circle", that again extrudes from the main enclosure.

Inside the "cut_cirle" are two holes where power connectors are inserted.

I am not sure if this could be achieved with injection moulding - since i am complete new to the topic.

Even if the two holes inside the "cut_cirle" cannot be made with injection moulding (i am not stating, i do not know, i am also asking), then i guess they could be cut with a drill and connectors could be installed inside (with a press or something).

So, my question is, is this design doable with injection moulding?


1 Answer 1


Yes it is, in fact the part in your picture was almost certainly made this way, as follows.

An injection mold can be made to accept those metal pins, which are positioned in the mold so that when the plastic is shot in, it envelops the pins with plastic which then become an integral component of the finished part. The part is then stripped out of the mold, pins and all, and another set of pins are loaded into the mold and the process is repeated. These pins are called molded-in parts.

Another way to do this is to mold deep holes called pass-thrus into the part. The inside surface of the pass-thru is formed in such a way that the pin can be pressed into the hole with a snap engagement to hold the pin tightly in place.

In fact, it is possible to have the pins soldered onto a piece of connecting wire and the whole assembly then loaded into the mold, so that the injected plastic flows around and encloses both the pins and a length of the wire to serve as a strain relief that helps prevent the wire and pins from being pulled free of the plastic plug.

  • $\begingroup$ Thank you very much! I inspected the part and the case, and I can see a line across the whole enclosure, that it also includes the outer circular extrusion. So that was probably injection molded as part of the whole enclosure. However, the inner "cut_circle" does not have this line. So does this suggests that the inner part is a unique component? Also, could you provide a link about the snap engagement pressing mechanism you are referring to (I didn't find any relevant info)? $\endgroup$ Nov 10, 2022 at 10:06
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    $\begingroup$ there's no parting line there because that portion of the molded part was created by something called a slide in the mold which is mechanically extended into the mold cavity before plastic is shot in and then withdrawn before the mold is split open. It carries all the part details needed to form that pocket in the part, and withdraws so the part can be stripped out of the mold when finished. $\endgroup$ Nov 10, 2022 at 18:34
  • $\begingroup$ Thank you very much! I am completely new to manufacturing, and I am going to try my luck with injection molding... Do you perhaps have a video, or a link that describes this slide in the mold? Is it something taken care of during the design of the mold? Thank you very much for your informative answer and comments! $\endgroup$ Nov 11, 2022 at 12:28
  • $\begingroup$ the slide is a mechanism built into the mold during its manufacture, usually hydraulically operated. the purpose of a slide is to permit the molding of features which are undercut i.e., making the part impossible to extract from the mold without tearing the part to pieces. slides and undercuts are covered in any textbook about injection molding. $\endgroup$ Nov 11, 2022 at 15:38
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    $\begingroup$ a 3-d printed part can break all the production rules of injection molding- this is one of its greatest advantages. But if you want to make lots of parts quickly, you will injection-mold them. Note that there are programs which will take the 3-D CAD design of a part and machine for you the mold on a CAD-controlled milling machine out of aluminum, which will be good for ~10,000 parts before wearout. $\endgroup$ Nov 14, 2022 at 3:42

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