Part 1: Rotomolding – Design for Manufacturing by Scott Miller

by | Dec 12, 2019

This is a SlideShare presentation covering the basic tenets of rotomolding by Scott Miller, CEO Dragon Innovation.

It’s always a good thing to have a professional provide their knowledge and experience to hit home what is rotomolding and when should I use it in manufacturing/product development.

Scott Miller is one of those experts.

Whether you’re trying to figure out which method makes sense for your product development or you need a quick refresher course, this is the perfect article for you.

Below you will find the quick points made by Miller in his classroom presentation lecture covering Rotomolding as part of the Design for Manufacturing Course.

Rotomolded parts are typically associated with the following:
  • Hollow parts
  • Storage containers and vessels
  • Kayaks and outhouses
These are considered the advantages of rotomolding:
  • Hollow parts in one piece with no weld lines
  • Suitable for large parts
  • No internal stresses due to flow
  • Undercuts are okay
  • Suitable for short and high volume
  • Can use multiple colors
  • Shorter and cheaper tooling times (non-pressurized). No purging required between shots
  • Minimal scrap (no “plumbling”)
  • Outside corners are stronger than blow molding
  • Can use rigid or flexible materials
These are considered the disadvantages to rotomolding:
  • Larger parts have slow cycle times due to cooling time constants
  • Some geometrical features (such as ribs) can difficult to mold
  • Can’t control wall thickness precisely
  • Material cost will be higher due to the additional processing required

Generally, the rotomolding process flows like this,
  1. Fill the mold with a metered shot
  2. Heat and spin so the resin adheres to the inside surface of the mold
  3. (Spinning results in relatively even wall thickness)
  4. Cooling
  5. Extraction

Noteworthy design guidelines
  • Hollow part with ~uniform wall thickness
  • Can include inserts and undercuts
  • Tune wall thickness by varying shot weight (0.8mm - 25mm)
  • Avoid nooks and crannies / ribs
  • Typically uniform wall, but can use stop process to thicken one side

Common Materials used would be different types of polymer materials, like PE, PP, PC, PVC, and Nylon.

Watch the video in Scott Miller’s SlideShare, Slide 2 to learn more about specific use cases and nuances involved in the rotomolding.
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