Plastic prototyping can use either rotational molding or injection molding, but there are five factors to consider when comparing these manufacturing methods.
- Tooling Costs
- Material Selection
- Part Complexity
- Lead Times
- Design Guidelines
The following sections explain.
Tooling Costs
The tooling that’s used with rotational molding costs less. Cast aluminum molds are common, but sheet metal molds are used for larger parts. By contrast, prototype injection molds are usually made of machined aluminum or soft or semi-hardened steels. These metals cost less than the hardened steels used in high-volume injection molds, but CNC machining can be expensive.
Material Selection
Rotational molding uses a smaller range of materials, many of them polyethylene-based. However, part designers can still find the plastic prototyping materials that they need. For example, HDPE can support products that must meet FDA or USDA guidelines. Static-dissipative PE is a good choice for electrical and electronic applications. Polypropylene (PP) retains its flexibility in the cold.
Part Complexity
Rotational molding is well-suited for large, hollow parts such as tanks, bins, and enclosures. By contrast, injection molding is often used for small, intricate parts (such as gears) that have tight tolerances. There are tradeoffs to consider, however. Even with smaller parts, injection molding can create significant material waste because of its use of sprues and runners.
Lead Times
The lead times for rotational molding are shorter. That’s mainly because the time needed to create a prototype injection mold is significantly longer. While it’s true that plastic injection molding can support complex parts, rotomolding supports a wide variety of surface textures and colors. For added strength or insulation, rotomolded parts can be filled with polyurethane foam.
Design Guidelines
Rotational molding and injection molding each have their own design guidelines. However, the best practices for rotomolding design are generally more forgiving. Take wall thickness, for example. Uniform wall thicknesses are easier to achieve, and rotomolded parts can have thinner walls relative to their overall size.
Ask Gregstrom About Plastic Prototyping
Are you considering plastic prototyping for your next project? Then talk to Gregstrom, a family-owned rotomolder with over 75 years of experience. In addition to rotational molding, we provide design assistance, tooling services, and product assembly. To learn more about us and how we can help you, contact Gregstrom.
