Rotational Molding Design: Five Tips for Your Next Plastics Project

Rotational Molding Design Guidelines
Rotational Molding Design Guidelines

Rotational molding produces strong, hollow plastic products such as boats, bins, tanks, pallets, enclosures, and housings. Rotomolding, as this process is also known, uses less expensive tools than injection molding and supports part shapes and sizes that are unattainable with other plastics manufacturing methods.

If you’re considering rotomolding for your next project, here are five design tips to consider.

#1 Wall Thickness

Uniform wall thickness is easier to achieve with rotational molding than other plastics manufacturing methods. Still, it’s important to design your rotomolded parts so that the wall thickness is as uniform as possible. Use a minimum thickness of 3 mm and a maximum thickness of 10 mm.

#2 Draft Angles

Apply a draft angle to the vertical walls of your rotomolded parts so that they’re easier to remove. Because different plastics have different mold shrinkage characteristics, draft angles vary by plastic material. However, these tapers are generally between 1 and 2 degrees.

#3 Ribs and Bosses

To increase the strength of your product, use ribs and bosses instead of thicker walls. Make the rib depth at least four times (4x) the nominal wall thickness. Make the rib width at least five times (5x) the thickness of the nominal wall.

#4 Corners and Edges

Avoid sharp corners and edges since they cause stress concentrations. To relieve stresses, use corner radiuses that are 3 to 5 times the wall thickness. Remember that a radius that’s less than 25% of the nominal wall thickness places significant stress on a part.

#5 Undercuts

Rotational molding supports the use of undercuts, protrusions or indentations that are parallel to the mold’s parting line. Still, it’s best to avoid any unnecessary undercuts since they can complicate part removal. Necessary undercuts should equal half the material shrinkage.

Get Rotomolding Design Assistance from Gregstrom

Gregstrom Corporation of Woburn, Massachusetts (USA) is a rotational molder with over 75 years of plastics manufacturing experience. In addition to boats, bins, tanks, pallets, enclosures, and housings, we’ve rotomolded products for many different applications.

If you need rotomolded parts and are looking for design assistance, contact Gregstrom.