Rotational Molding

Rotational Molding

What is Rotational Molding?

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The Rotational Molding Process

Rotational Molding involves a heated hollow mold which is filled with a charge or shot weight of material. It is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mold. In order to maintain even thickness throughout the part, the mold continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase.

Rotomolding is a process ideally suited to producing hollow plastic products. By using additional post-molding operations, complex components can be produced enabling the process to compete effectively with other molding and extrusion practices. Rotational molding differs from other processing methods in that the heating, melting, shaping, and cooling stages all occur after the polymer is placed in the mould, therefore no external pressure is applied during forming. This provides the following advantages:

  • Economically produced large products
  • Minimum design constraints
  • Very low residual stresses
  • No polymer weld lines


The Rotational Molding Process

Rotational molding is an extremely versatile and economic process that relies on gravity and heat to produce parts with exceptional strength. The finished result is a stress-free, lightweight and seamless design that is very durable.

A variety of plastic resins are available to use, depending upon the product specifications, strength requirements and resistance to other substances required. Materials that may be selected include polyethylene, nylon, polycarbonate, polypropylene, polyvinylchloride (PVC) and custom formulated compounds.

The flexibility of Dakota Molding’s process allows for a wide range of shapes and sizes to be manufactured. Dakota Molding also offers products in a wide range of colors, with graphics molded directly into the part.

Steps in the rotational molding process:

  • After the type of resin is selected, a premeasured amount of plastic resin is placed into a mold.
  • The resin melts and fuses in a three-stage process. After the resin is loaded into a mold, the mold is inserted into an oven and rotated on two axes at low speed until the resin coats the inside surface of the mold cavity, fusing into an excellent uniform wall thickness.
  • While still rotating, the mold is removed from the oven and is cooled gradually.
  • The rotation ends when it reaches the temperature that the part can be safely removed from the mold.

The Dakota Molding manufacturing facility operates five rotomolding machines, and with its own in-house tooling department, has the ability to build, repair and modify fabricated molds in-house. Dakota Molding can also handle products and shipments internationally, as well as nationwide.


Why Rotational Molding is Important to You

Many advantages make rotational molding the best choice. One of the greatest advantages is the reduced cost of tooling. The cost of having a mold built for rotomolding is significantly less than for most other plastics processes.

Molds can be machined, cast or fabricated from materials such as stainless steel or aluminum. Cast and machined molds are best when exacting tolerances or cosmetic finishes are important to the finished product. Cast molds offer a wide range of finishes from wood grain to a mirror finish. Fabricated molds are more economical than cast or machined molds, but offer less options for finish.

This manufacturing process is ideal for efficiently making complex high value plastic parts in quantities of 100,000 units/year!

  • It has a low barrier to entry with tooling costs that are the lowest of the plastic manufacturing process.
  • It has extremely short start-up lead times. You can achieve a 4 week start-up time from start of tooling to finished part!
  • You can design in so many features that aid in the products performance!
    • Complex shapes
    • Molded in inserts and metallic ports for connections
    • Molded in Graphics and lettering
    • Inherent strength of product without seam or joints
    • You can utilize a wide variety of plastic raw materials to tailor the performance to the application


Benefits of Rotomolding

  • Design flexibility to meet specifications
  • One-piece seamless construction
  • Metal inserts and fittings as integral parts
  • Uniform wall thickness
  • Resistance to corrosion
  • Ribs and cones for stiffening
  • Variety of colors and finishes
  • Lightweight
  • Excellent load-bearing properties
  • U.V. resistance
  • Molded-in graphics, such as logos, and embossing
  • Product longevity

What are our capabilities to help you?

  • We are experienced in high volume/efficient production
  • Our front end design capabilities along with a multi-functioned team assure a unique product solution
  • An ISO based quality system
  • Machines capacity and size capability that can handle parts up to 120” in size
  • A tooling acquisition process that assures long-term Quality
  • Supply chain experience that international breadth
  • Worldwide logistics capabilities
  • We have a customer fulfillment process that works to your priorities
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