What Do I Need to Know About Custom Plastic Roto Molding?

Custom plastic roto molding is bringing designers creations to life, from action figures to tech gadgets. Thanks to its low tooling costs compared to injection molding and ability to be used for mass production, custom plastic roto molding has become the plastic molding technique of the age.

What is custom plastic roto molding?

Roto molding, or rotational molding, is a unique process of creating complex shapes from plastic. There are four stages to custom plastic roto molding: First, plastic resin is loaded inside a closed design mold. This mold can contain multiple walls, fasteners, and even graphics. Hollywood has become particularly taken with custom plastic roto molding to create life-size versions of its most beloved characters.

Once the plastic is loaded in the mold, the next step is to heat the resin to melting and fuse it inside the mold. Whereas most other plastic molding techniques would apply pressure to fuse the plastic to the mold, with custom rotational molding, the molds are instead secured to spokes which rotate them in a furnace room. Temperatures inside the room will reach up to 700 degrees Fahrenheit. As the heat melts the plastic, the rotation ensure the resin is evenly distributed across the crevices of the mold. This creates an even coating of resin around the inside cavity of the mold, the result of which will be a hollow finished part after cooling and unloading.

To cool the plastic resin back to a solid state, the mold is sprayed with water. Once its hardened, the finished part can be unloaded from the mold. The entire cycle time from loading to unloading takes approximately 40 to 45 minutes.

What can be made with custom plastic roto molding?

The short answer: just about anything that’s hollow and made of plastic. Custom rotomolded parts can be as large as a 20,000 gallon container or as small as a bouncy ball. They can reach up to 17 feet in length and weigh anywhere from less than a pound to a full ton. The real question then isn’t what can be made with custom plastic roto molding, but what can’t.

What are the benefits of custom plastic roto molding over other plastic molding techniques?

As we mentioned before, custom plastic roto molding is popular for its low tooling costs. There’s also the flexibility of size and shape to consider – – as mentioned above, anything from a bouncy ball to a 20,000 gallon container can be made with custom plastic roto molding. In addition, rotational molding can be an effective means of mass production. Depending on the complexity and thickness of the walls, a single tool could be used to produce around 3,000 to 3,500 pieces each year.

What are the tooling choices with custom plastic roto molding?

The most common tooling type used with rotational molding is Cast Tooling. With Cast Tooling, you have a variety of surface finishes and textures to choose from. It’s also inexpensive relative to other tooling options. The typical development timeline for cast tooling is six to eight weeks, with actual time varying depending on the complexity of the design.

Another option is Fabricated Sheet Metal tooling. This tooling method is more often used for large parts with low-complexity designs. It’s even less expensive than cast tooling, but doesn’t offer the same range of surface finish and texture options. Again, the design process is usually between six and eight weeks, though the actual time will vary depending on the design’s level of complexity. With Fabricated Sheet metal Tooling, the tools are welded then ground and polished for use.

Lastly, there is Billet Rotational Modeling Tooling. This method of tooling is used for complex designs which require smooth surfaces. More expensive than the Cast Tooling and Fabricated Sheet Metal Tooling, Billet Tooling begins with a 3D model of the tooling halves. The halves are then CNC machined to make them ready for framing and finishing. The time to completion remains six to eight weeks, dependent on design complexity.

How long does it take to build your first custom plastic roto molding part?

From creating your custom roto mold to completion of the first part, plan on a custom roto molding timeline of eight to 18 total weeks.