Draft analysis of injection molded part

Injection Molded Part Design Part 1: Simplifying Undercuts

In product design, injection molded parts designed with undercuts can introduce additional costs and delays to market unless they are simplified.  An injection molded part designed with an undercut feature means that when the mold cavity and core open there will be some plastic feature that traps some of the opening path of the metal tool.  There are several ways to tackle this challenge in the tool design but most add cost and time as parts are first produced for production. 

Hole in base allows core side to reach further into cavity side to form the hook feature without need of additional tool action

This allows the injection molded part’s mold to open simply and eject the part without added actions necessary to create the undercut features, and can be done with no significant additional maintenance issues if some simple recommendations are followed. 

Here the snap feature in this example injection molded part design is maintained using simplified tooling and lower overall costs with implementation of 3 to 7 degrees of draft on the swiping shutoff faces.  This can be applied to other complex features like vent louvers.  However, there are also many occasions when a hole on the bottom side is not acceptable, and slides must be used.

2U custom injection molded bezel design

Many server, switch and routing products incorporate bezels to brand their company’s product.  The ones shown above are owned by Brocade (recently acquired by Broadcom)These injection molded part designs also provide controlled access and sometime interconnection management, but must also allow for extensive venting to the chassis and drives behind, all the while still presenting a breathtaking style.  Simply having openings in the bezel would neither look good nor provide enough structure, and would not route venting air to key areas of the product’s front end. 

Section of bezel showing complex louver shapes to hide see thru, yet still flow ample air and allow room for 5 degree swiping shutoffs between tool halves to keep costs down.

If the vent or louver features of the injection molded part’s design required multi-action tooling this would be an undue burden and cost for the client’s new offering.  An elegantly designed injection molded part can have stylized air intake features and maintain a simple parting, two half tool. 

Using this approach, and understanding the key recommendations for swiping shut off design for injection molding, even very organic, flowing designs in injection molded parts can have simple tooling.  The preferred branded look and function of the air ventilation can be achieved in proper injection molded part design if the molding and tooling requirements are kept in mind from the beginning, and the molder brought into the discussion early in the development cycle. 

So don’t be afraid of what might seem like an injection molded part design that looks like it will require expensive added tooling actions.  With the right knowledge, experience and partners you can develop complex injection molded part designs with what appear to be overlapping and undercut features, using straight forward core and cavity tooling, employing swiping shut offs in the tool. 

For more tips like this, check out our articles 4 Tips to Save on Tooling Cost or Designing Sheet Metal Assemblies

Links to: Part 2, Part 3, Part 4

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