Rotational Molding: What It Is and When to Use It

rotational molding bi axis machineryFrom forming and stamping to wire EDM, CNC machining, engineering, finishing, and more, our list of services is fairly comprehensive. If you have questions about the best, most cost-efficient way to manufacture a part, we can almost always help you out. Today, we’d like to highlight one of the services we offer that enables us to make some pretty unusual shapes by means of a simple process: Rotational molding (also called rotomolding or rotocast).

The Association of Rotational Molders explains that rotomolding is one of the most cost-effective molding methods, often used to produce complex parts that have intricate contours, undercuts, molded-in inserts, or double walls. (You can see some interesting photos of rotomolded parts here.) The primary material used for rotomolding is polyethylene, but other materials like PVC, nylon, polypropylene, cross-linked polyethylene, metallocene polyethylene, and plastisols can also be used.

Historically, rotomolding was first applied in the 1940s to create doll’s heads and other toys for children, like squeaky toys and play balls. Noel Mansfield Ward’s article on “A History of Rotational Moulding” says that by the late 1950s, when the process was better understood, it began to be applied for products like road cones, marine buoys, and car armrests. In the 1960s, Europeans developed the Engel process, which allowed large hollow containers to be created by rotating or rocking a mould on a chassis containing open gas jets.

The Plastics Professionals list a pretty straightforward explanation of the advantages of rotational molding. First, the process allows design flexibility, and fairly unusual shapes can be produced as one part, whereas with other processes, they would have to be assembled from several parts. The tooling costs for rotational molding can be less than other methods, and thus, there are shorter lead times on production. Rotomolding has almost no size limitations, but all parts are produced with an even wall thickness, even at the corners. Molded-in handles and inserts are possible, which also eliminate secondary operations. At Distefano, we can mold-in graphics, blend and match colors, and produce a product made from extremely durable material.

RotoWorld gives a great list of products that have been made using rotational molding, including instrument panels, pool liners, dock floats, manhole covers, outdoor furniture, reusable shipping containers, face oxygen masks, and more: There’s no industry that hasn’t been touched at some point by rotational molding. Part of the reason for this is that the molding is a fairly simple process which allows the molder to have very close control over the properties and dimensions of the product.

First, the molder introduces a known amount of plastic in either granular, powder, or liquid form into a shell-like mold. The mold is heated and simultaneously rotated so that the plastic forms a layer against the inner mold surface. The mold will continue to rotate during the cooling phase until the product is rigid, and then the product is ejected and removed.

If you want to chat about whether or not rotational molding could be a good fit for your product, let us know by leaving a comment in the section below! We’d be happy to hear from you.

Photo credit: Job Shop

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