If you are considering creating a plastic product, then you’ve asked yourself: What are the differences between injection molding and rotational molding? How do they compare in costs, production consistency, materials and design flexibility? We have discussed the advantages of the plastic injection molding process previously in our blog Five Advantages of Plastic Injection Molding. Before we examine the advantages of injection molding over rotational molding, we’ll need to examine the process of rotational molding.
What is Rotational Molding?
Rotational Molding, also called, rotomolding, is a thermoplastic process for producing hollow parts by placing powder or liquid resin into a hollow mold and then rotating that tool bi-axially in an oven until the resin melts and coats the inside of the mold cavity.
The 4 steps in this manufacturing process include:
- Filling the mold with a thermoplastic polymer material.
- Heating the tool in an oven to melt material.
- Cooling the tool to solidify the part.
- Removing the plastic part from the tool.
For a quick reminder of the manufacturing steps for the plastic injection molding process review our blog, Five Steps of the Thermoplastic Conversion Process.
Advantages of Rotational Molding
These molds can be made out of several materials and have multi-layered walls. Unusual shapes can be produced as one part, that normally would have to be assembled from several parts. Below are a few other advantages of this manufacturing process.
- Design flexibility allows complex geometry.
- Tooling costs are less than other plastic molding methods.
- Short lead times on production.
- Potential weight reduction of parts.
- Parts offer strength, corrosion, resistance, and durability.
- Improved throughput by decreasing labor hours.
Why Choose Injection Molding Over Rotational Molding?
Plastic injection molding manufacturers are leading the market in plastic production because of the multiple advantages that the project allows. Here are the notable advantages of plastic injection molding over rotational molding.
Plastic injection molding can produce a lower cost per piece than a piece made by rotational molding, simply for the fact that injection molding can produce more pieces quicker than rotational molding can. Rotational molding is more expensive than injection molding because it requires costlier base materials to use.
The materials used for rotational molding (i.e., poly-based resins) are more expensive than the wide range of plastics that are available for injection molding. Rotational-molding materials also require expensive additives when mixing the poly-reins, nylon, and plastisols before production.
Both processes have fully automated production lines that can create parts at top speed with the most cutting-edge technology. However, the main difference is the amount of time each manufactured part spends on the production line. Parts created in the rotational molding process will take longer; each part of the process is more complicated, and pieces will need more time spent on before it is considered complete.
Options and Limitations
When you choose injection molding, you’ll get an endless array of materials to select from. You can also include additives to enhance your part’s properties that were lost during the injection molding process. Another advantage to injection molding? You’re able to choose any unusual shapes, complex designs, and intricate details.
The materials suitable for rotational molding are more limited to poly-based resins, such as polyethylene, polycarbonate, polyurethane, and polyamides to name a few: Nylon and plastisols may also be used. These plastics must be ground to a very fine powder before they can be used. As for limitations, some shapes and features are difficult to incorporate, so anything more involved than a simple shape may slow down production.
Both injection molding and rotational molding offer many benefits, but you should consider the merits of injection molding when you’re looking to create high-volume plastic parts. At Midstate Mold, we specialize in injection molding and can help bring your product to life. Contact our experts today!