Despite the many benefits, rotational molding/rotomolding is not suitable for every production process. It will be easier to make the right decision for your production if you understand the advantages and disadvantages.
Rotational molding is the best thermoplastic molding process for kayaks, coolers, tanks, or pretty much any open-walled containers and large, one-piece hollow parts.
It is perfect for small businesses, inventors, and startups because of the highly competitive price for producing a maximum of 3000 units per year.
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Rotational Molding process includes secondary features like spin welds, kiss-offs, ribs, and inserts, which are not available in other thermoplastic molding processes such as thermoforming and blow molding.
Rotational Molding Process
Here is a step-by-step guide to the entire process:
• Fill the hollow mold with powdered plastic resin.
• Start rotating the mold bi-axially. Then move into the oven.
• As the mold continues to rotate, the resin melts to coat the walls.
• Let the mold cool so that the resin hardens and forms the desired shape.
• Stop the rotation and remove the plastic/finished product.
This is a low-pressure, high-heat process. The low pressure means that soft metals like aluminum can be used to make the mold tool. The high heat also requires the resin to be highly stable in heat, for example, polyethylene.
Advantages and Disadvantages of Rotomolding
The resin melting into the walls is the most important feature of rotational molding because it contributes to both the advantages and disadvantages.
Advantages of Rotational Molding
• Low-cost tooling: low pressure means soft metals (which are cheaper) can be used for the tools.
• Consistent wall thickness: the rotation of the mold ensures that the walls are evenly coated.
• Complex construction: the secondary features allows the production of complex construction like double-walled containers without a secondary process.
• High durability: one-piece products mean less joining, which is good because joints are usually weak spots.
• High stability: the controlled pressure means the finished part is more stable and less prone to defects
• High strength: the corners of the finished parts are thicker and more tolerant to stress.
• Appearance: the molding tool can be modified for surface finishes like logos, symbols, and detailed texture.
Disadvantages of Rotational Molding
• High cycle times: one part may take about three hours to finish.
• Limited raw materials: poly-based resins are the only options for powders that don't easily degrade chemically under high heat.
• Costly raw material: it is expensive to acquire additives, poly-based resins and to convert the latter into powder.
• Low repeatability: the mold tool made from soft metal loses its integrity and must be replaced or refurbished after 3,000 cycles.
• High labor costs: It is a labor-intensive process.
• Is Rotomolding Right for You?
• If you are producing Less than 3,000 parts, then yes. After those units, rotational molding starts to lose its economic advantage.
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