How do you choose between rotationally molded and injection molded cases?

When choosing the right protective case for industrial applications, you face an important decision: rotationally molded or injection molded? Both production methods have specific characteristics that make them suitable for different situations. The choice depends on factors such as usage conditions, production quantities, budget, and technical requirements. In this article, we compare both methods and help you make the right choice for your specific application.

What are the fundamental differences between rotationally molded and injection molded cases?

Rotationally molded (rotomolding) and injection molded cases differ fundamentally in their production process, which directly affects the properties of the end product. In rotomolding, plastic powder is placed in a mold that is then heated and rotated, causing the material to melt evenly against the walls. In injection molding, molten plastic is injected into a mold under high pressure.

The main difference lies in the wall thickness and structure. Rotomolding produces cases with uniform wall thickness and rounded corners, while injection molding allows for exact dimensional tolerances and can create more complex shapes. Rotomolded cases typically have thicker walls (3-8 mm) than injection molded cases (1-3 mm).

In terms of material, rotomolding primarily uses polyethylene (PE), resulting in flexible, shock-resistant cases. Injection molding uses various materials such as ABS, polycarbonate, and nylon, which yields harder cases with better dimensional stability.

Another important difference is the finish. Injection molded cases have a smoother surface and can contain detailed textures, logos, and brand names. Rotomolded cases have a more matte appearance with subtle texture.

When is a rotationally molded case the better choice?

A rotationally molded case is the better choice when you need to protect equipment in harsh environments or under extreme conditions. Due to the uniform wall thickness and the inherent flexibility of the material, these cases offer excellent shock absorption and impact resistance, which is crucial for sensitive equipment that is regularly transported.

These cases are ideal for military and defense applications where equipment must function in demanding environments. They provide superior protection against impacts, falls, dust, and water. For defense organizations that need robust protection, rotomolded cases are often the first choice due to their durability and reliability.

Rotomolding is also advantageous for smaller production volumes (10-1000 pieces), as the startup costs are lower than with injection molding. The molds are cheaper and faster to produce, making this method more suitable for custom work and special projects.

Additionally, rotomolding offers more design freedom for larger cases. If you need a large transport case (more than 1 meter in dimension), rotomolding is often the only practical option, as injection molding becomes extremely expensive for such sizes.

Choose rotomolded cases when:

• Extreme shock resistance is required
• Waterproof protection is necessary (IP67 or higher)
• The case must have large dimensions
• You need a limited production run
• You’re looking for a lightweight but strong solution

When is an injection molded case preferable?

An injection molded case is preferable when precision, consistency, and complex details are important. These cases offer excellent dimensional tolerances, which is essential for equipment that must fit exactly in the packaging or when cases need to be interchangeable.

For high-tech equipment where precise fitting is crucial, injection molding provides superior dimensional stability. The sleek, professional finish also makes these cases ideal for situations where presentation is important, such as demonstration cases or equipment used at customer sites.

Injection molding is more cost-effective for large production volumes (more than 1000 pieces). Although the initial investment in molds is high, the cost per unit becomes significantly lower with larger quantities. This makes it the preferred method for standard products produced in large quantities.

Another advantage is the ability to create complex internal structures. You can integrate precise compartments, clips, hinges, and other functional elements directly into the design. This reduces the need for separate components and simplifies assembly.

Choose injection molded cases when:

• Exact dimensional tolerances are required
• You need complex internal structures
• A sleek, professional appearance is important
• You plan large production volumes
• Lightweight and compact cases are desired

How does the production method affect the durability of cases?

The production method has a significant impact on the durability of cases, both in terms of lifespan and environmental impact. Rotationally molded cases typically have a longer lifespan due to their greater flexibility and impact resistance, resulting in less replacement and thus less waste in the long term.

In terms of material efficiency, rotomolding has the advantage that hardly any material is lost during production. Almost all plastic powder is used in the final product. Injection molding creates more waste from gates and runners, although this material is usually recycled.

Energy consumption also differs by method. Rotomolding has a longer cycle time and therefore consumes more energy per case produced. Injection molding has shorter cycle times and is more energy-efficient for larger production volumes.

Both production methods use plastics that are potentially recyclable. Rotomolded cases are usually made of polyethylene, one of the more recyclable plastics. Injection molded cases can be made from various materials, some of which are more recyclable than others.

From a circular perspective, both types of cases offer opportunities for reuse and repair. Rotomolded cases are often simpler to repair due to their simpler construction, while injection molded cases, due to their precision, are better suited for reuse in applications where exact dimensions are important.

For a sustainable choice, it’s important to consider:

• The expected lifespan in your specific application
• Possibilities for repair and maintenance
• Recyclability of the specific material
• Total environmental impact over the entire lifecycle

What are the cost implications when choosing between both production methods?

The cost structure of rotational molding and injection molding differs significantly, which directly affects your investment decision. With rotomolding, startup costs are relatively low. The molds are simpler and cheaper to produce (€5,000-€15,000) compared to injection molding molds (€20,000-€100,000+).

However, the cost per unit follows an inverse pattern. For small series (10-500 pieces), rotomolding is more cost-effective. The production costs per case are higher due to longer cycle times, but this is offset by the lower mold costs. With injection molding, the cost per unit drops dramatically with larger volumes, making it usually more economical from about 1000 pieces.

Besides the direct production costs, there are also differences in secondary costs. Rotomolded cases often require less post-processing, while injection molded cases may require additional assembly for hinges and closures. On the other hand, injection molded cases can save costs through integrated functions that would need to be added as separate components in rotomolded cases.

The total cost of ownership over the lifetime of the cases can also differ. Rotomolded cases are typically more durable and have a longer lifespan in harsh environments, leading to lower replacement costs. However, injection molded cases can offer cost advantages in controlled environments due to their lighter weight and lower transportation costs.

For a complete cost comparison, you should consider:

• Initial investment costs (molds and startup)
• Production costs per unit at your expected volume
• Costs for additional components and assembly
• Expected lifespan and replacement frequency
• Transportation costs (weight and volume)

Conclusion: make the right choice for your application

The choice between rotationally molded and injection molded cases ultimately depends on your specific needs. Rotomolded cases offer superior protection in extreme conditions and are cost-effective for smaller series. Injection molded cases excel in precision, finish, and are more economical for larger volumes.

Carefully consider factors such as usage environment, production volume, technical requirements, and budget. In some cases, a hybrid approach, combining both technologies, may provide the optimal solution.

At Faes, we understand that each application brings unique challenges. As specialists in industrial custom packaging, we can help you make the right choice and develop a packaging solution that perfectly meets your needs.