Alternatives to Screw Connections That Won’t Kill Your Tooling Budget

Mike Keller
Senior Product Development Engineer

Screws are ugly…cap covers to hide screws are uglier.  There are many options for eliminating the need for screw connections in an injection molded part assembly.  Unfortunately, most will send your tooling budget through the roof.  Slides are often used to create snap connections that are completely hidden once the parts are assembled making a very clean, nice looking finished assembly.  This type of connection is used often in mass market electronics such as cell phones where the volumes make the increased investment acceptable.  For lower volume products, the higher investment is harder to swallow because it cuts into your profits.  Here are some options for clean snap or press fits that can be achieved without adding slides to your tools.

1. Snap options – if the housing does not need to be completely closed, then snaps can be incorporated without slides.  Small openings will be visible on the outside of the parts where undercuts for the snaps need to be formed.  With some planning and industrial design work, the openings can be hidden in plain sight by integrating them into the part’s aesthetics.
2. Press Fits – Round bosses pressed into hexagonal holes can offer very good holding power without any undercuts.  Mold changes to tighten the fit are very easy to accomplish by removing material from the flats of the hex pins.  So it is recommended to start with very little interference, and then modify the hex pin to tighten the fit.

3. Partial or full perimeter internal groove feature – with the addition of a stripper plate to the mold, a shallow undercut can be molded around the perimeter inside the part without the need for slides. This undercut can be mated with an external bead on the other part to lock the parts solidly together.

   Here’s a YouTube video on “Stripper Mold Animation” that illustrates this process: