Guide on Thermoforming (versus Rotomolding)

In industrial manufacturing, the choice of molding technique is crucial for the quality, cost, and efficiency of a product. Among the most common methods, thermoforming and rotomolding stand out due to their varied applications and characteristics. While thermoforming is favored for its speed and flexibility in producing flat or curved parts, rotomolding excels in creating large, hollow objects.

Thermoforming, in particular, relies on an ingenious process where a plastic sheet is heated, formed onto a mold, and then cooled to obtain a solid part. This technique is widely used in industries such as packaging, automotive, and electronics, thanks to its low tooling costs and its ability to produce medium-volume runs quickly.

However, each method has its strengths and limitations. Here’s a detailed look at the thermoforming process, its advantages, and its drawbacks, compared to rotomolding, to help you better understand which technique suits your needs.

What is Thermoforming? Definition and Process

Thermoforming is a manufacturing technique that involves heating a thermoplastic sheet until it becomes pliable, then forming it onto a mold to create an accurate part. It’s a simple, fast, and efficient method widely used in industry to produce a variety of shapes, from food packaging to automotive components.

Key Steps in Thermoforming

1. Heating

The plastic sheet is heated in a specialized oven to a precise temperature, usually between 100°C and 200°C, depending on the type of plastic used. Common plastics include PVC, ABS, polypropylene (PP), and polyethylene terephthalate (PET). Uniform heating is crucial to avoid defects in the final part.

2. Forming

Once softened, the sheet is placed on a mold (positive or negative). Three main techniques are used:

• Vacuum forming: Air is sucked out between the mold and the sheet, allowing the plastic to form to the mold's exact shape.

• Pressure forming: Additional pressure is applied to enhance precision and detail.

• Mechanical forming: Mechanical tools (punches) are used to press the plastic sheet onto the mold.

• Cooling and Cutting

The formed plastic is cooled to solidify it. Excess material is cut away using automated cutting systems to produce the final part.

The thermoforming technique can produce parts in just seconds per cycle, making it ideal for small to medium volume production. With modern equipment, cycles can reach up to 30 parts per minute, depending on the complexity of the product.

This simple yet effective process is flexible, making it indispensable in industries where speed and cost are key.

Advantages of Thermoforming

Thermoforming is a favored manufacturing method for its ability to combine flexibility, speed, and cost savings. Here are its key advantages, supported by data and real-world examples:

• Reduced tooling costsUnlike methods like injection molding, thermoforming uses molds made from aluminum, which are cheaper to produce than steel molds. The price of a thermoforming mold typically ranges from $5,000 to $50,000, compared to $50,000 to $100,000 for an injection molding mold. This makes it ideal for small to medium production volumes, where tooling budgets need to be kept under control.

• Design flexibilityThermoforming allows for the production of parts in various shapes, from simple items like food trays to more complex products like automotive panels. Molds are easy to modify, reducing time and costs associated with design changes.

• Speed of productionProduction cycles are short, with average times ranging from 15 to 60 seconds per part, depending on the product's complexity. This enables fast responses to just-in-time market demands, such as in packaging or consumer goods.

• Wide choice of materialsThermoforming can use recyclable thermoplastics like PET and polypropylene, contributing to more sustainable practices. These materials offer excellent chemical and mechanical resistance, suitable for various industrial sectors.

• Economical for small runsFor productions under 10,000 units, thermoforming is more cost-effective than other techniques requiring higher initial investments. Its versatility and low entry costs make it an ideal solution for companies seeking quick and efficient product manufacturing.

  
  

Disadvantages of Thermoforming

While thermoforming offers many benefits, the method also has its limitations. These disadvantages should be considered to ensure it’s the right fit for your project.

• Material wasteOne of the main drawbacks of thermoforming is the significant amount of waste generated. After forming and cutting the parts, plastic scraps can account for 15% to 40% of the original sheet, depending on the product’s complexity. While this waste can be recycled, it adds extra steps to the process.

• Limited precisionThermoforming is less suited for products requiring complex details or precise tolerances. For example, techniques like injection molding offer superior dimensional accuracy for complex products like electronic connectors. This limits the use of thermoforming in demanding industries like aerospace.

• Lower mechanical strengthDue to the stretching process, some areas of thermoformed products are thinner and therefore less robust. This makes them less suitable for environments requiring high mechanical strength or long-term applications.

• Size limitationsWhile thermoforming is versatile, it’s less efficient for producing large or hollow parts compared to techniques like rotomolding. Large parts require more expensive molds and specialized equipment, increasing costs.

• Higher unit cost for large volumesAlthough thermoforming is economical for small runs, it becomes less competitive for mass production exceeding 50,000 units, where injection molding offers better unit costs due to economies of scale.

  
  

Despite these drawbacks, thermoforming remains a viable solution for many projects, especially when volumes are moderate and shapes are simple. These limitations must be factored in when planning a project.

Applications of Thermoforming

Thermoforming is widely used across various industries due to its flexibility and ability to produce customized parts at lower costs. It’s needed for several applications:

• Packaging Industry

  
  

  The packaging sector benefits greatly from thermoforming. This technique is used to produce:

  • Food trays: For prepared meals, fruits, and fresh products, using materials like PET and PVC.

  • Blisters: Transparent packaging for consumer products (tools, electronics).

  • Industrial trays: For storing and transporting parts.

The speed and precision of thermoforming meet the high demands of the packaging industry.

• Automotive

  
  

  In the automotive industry, thermoforming is used to make lightweight, cost-effective parts, including:

  • Interior panels: Decorative elements for doors or dashboards.

  • Exterior shells: Bumpers or aerodynamic components in ABS.

These parts help reduce the overall weight of vehicles, contributing to better energy efficiency.

• Medical Field

  
  

  The medical sector uses thermoforming to create:

  • Sterile trays: For surgical instruments.

  • Specific supports: For delicate equipment.

  • Pharmaceutical packaging: Ensuring the safety of sensitive products.

    
    

What is Rotomolding?

Rotomolding, or rotational molding, is a manufacturing technique used to create hollow plastic objects. This process involves using a mold that is heated and then rotated on multiple axes, allowing plastic resin in powder form to spread evenly and melt against the mold walls.

Rotomolding Process

The rotomolding process begins with loading a precise amount of plastic resin (such as polyethylene or other thermoplastics) into the mold. Next, the mold is heated in an oven and simultaneously rotated on two axes, allowing the plastic to melt and coat the mold walls evenly. Once this step is complete, cooling follows: the mold is cooled using air or water to solidify and set the shape. Finally, during demolding, the mold is opened, and the finished part is removed. This method is used for producing various types of products.

Applications of Rotomolding

• Water or fuel tanks.

• Urban furniture (benches, trash cans).

• Large toys (play structures, balls).

• Industrial products like containers/tanks and agricultural equipment.

This process is particularly suited to large parts that require strength and uniformity.

Advantages of Rotomolding

• Design flexibility: Allows for complex and large shapes, often made in a single piece. Ideal for producing hollow objects like tanks or containers.

• Low tooling costs: Molds used in rotomolding are typically made of aluminum, making them less expensive than injection molding or thermoforming molds.

• Uniformity of parts: The rotation of the mold ensures an even distribution of plastic, ensuring uniform thickness.

• Durability of products: The resulting parts are shock-resistant and suitable for demanding environments (outdoors, industrial settings).

• Adaptability to small runs: Rotomolding remains cost-effective for low-volume production, unlike other methods that require high quantities to be cost-efficient.

Disadvantages of Rotomolding

• Longer cycle time: Compared to thermoforming, rotomolding is slower, which can increase costs for mass production.

• Limited precision: Less suited for parts requiring intricate details or strict tolerances, with limited control over the interior of the part.

• Lower mechanical strength: Rotomolded parts have lower structural strength compared to those produced by injection molding. This makes them less suitable for pressure applications or structural chassis parts.

• Higher unit cost: For mass production, the unit cost is higher than blow molding or injection molding.

  
  

Comparison: Thermoforming vs Rotomolding

The choice between thermoforming and rotomolding primarily depends on the specific project requirements, such as part shape, production volume, and budget.

• Thermoforming is suited for flat or shallow products, such as packaging, panels, or protective shells. It’s fast, precise, and well-suited for medium to large runs with low tooling costs and short cycles.

• Rotomolding is preferable for large, hollow products like tanks, urban furniture, or large toys. It excels in durability, uniformity, and the production of complex parts.

Thus, thermoforming is ideal for projects needing rapid and cost-effective production, while rotomolding is the best choice for durable, complex, and customized parts.

Summary Table: Thermoforming vs Rotomolding

Characteristics	Thermoforming	Rotomolding
Process	Heating and forming a plastic sheet	Heating and rotating a plastic powder resin
Part shapes	Flat or slightly curved parts	Large, hollow objects
Part size	Limited to sheet size	Suitable for large parts
Detail and precision	Moderate precision, limited to simple shapes	Difficult for complex details, uniform finish
Tooling cost estimate	$5,000 to $50,000	$5,000 to $100,000
Cycle time	Fast (15 to 60 seconds per part)	Slow (several minutes to hours)
Main applications	Packaging, panels, shells	Tanks, large toys, urban furniture
Ideal production	Small to medium runs	Small to medium runs with large parts

Thermoforming and rotomolding are two complementary techniques suited to specific needs. Thermoforming excels at rapid, cost-effective production of simple or flat parts, especially for moderate series. On the other hand, rotomolding is ideal for large or hollow items requiring robustness and durability.

If your project requires hollow, durable parts, rotomolding is the optimal choice.

For more information, contact us to assist you in realizing your projects. Whether you need speed or precision, our expertise guarantees results tailored to your needs.