This article presents all the information you need to know about thermoforming. Topics discussed are:
Thermoforming refers to a plastic fabrication technique where thermoplastic sheets are molded into diverse shapes by applying pressure or vacuum. This process enables the creation of items such as cups, containers, lids, trays, and clamshells, using thin thermoplastic sheets. Conversely, more robust sheets are used to fabricate components like automotive doors, dashboard panels, refrigerator liners, and plastic pallets.
There are two main thermoforming techniques: vacuum forming and pressure forming. Both methods involve stretching a heated thermoplastic sheet over a mold's surface, yet each has unique advantages suited for particular design preferences. The choice between these techniques hinges on the project's specific requirements.
In the thermoforming process, a plastic sheet is shaped inside a mold cavity using air or vacuum pressure. Each mold cavity is crafted to produce a specific part, with the overall mold setup, commonly known as "tooling," comprising several such cavities.
Thermoforming consists of straightforward steps, making it a preferred method for rapidly producing bulk quantities of molded items. This involves consistently feeding thermoplastic sheets into a heating chamber for shaping. For larger components, individual thicker sheets are processed separately. Some setups incorporate an extrusion machine before the thermoforming stage. Moreover, certain configurations allow for the simultaneous production of multiple parts by employing molds with several cavities in each press stroke.
The gauge of thermoplastic used in manufacturing is dictated by the thickness of the part being produced. Different thicknesses necessitate specific machinery and methods suited to the material's properties. With a range of materials available for thermoforming, designers must understand the characteristics of each to ensure optimal quality, timing, performance, and reliability of the final product.
Heavy-gauge thermoforming is used to manufacture parts with thicknesses ranging from 0.060" to 0.500" (1.5 - 12.7 mm). The process begins with cutting sheets of thermoplastic, which are then heated in an oven. This method is ideal for producing robust and long-lasting components. Parts made from heavy-gauge thermoplastics are not only lighter but also exhibit enhanced impact resistance.
Thick thermoplastics, due to their higher gauge, enable the creation of detailed and complex parts with smooth surfaces and appealing aesthetics. These materials can also be customized with colors to meet specific product or application needs. Thick gauge thermoplastics offer several advantageous properties, including UV resistance, flame retardancy, electrical conductivity, and resistance to solvents. Like their thinner counterparts, thick gauge thermoplastics can be produced using FDA-approved materials.
Thin gauge thermoforming produces products with thicknesses of less than 0.060" (1.5 mm). Thermoplastics are roll-fed or come from an upstream extrusion process. Thin gauge thermoforming, produces thin products; which are intended for disposal or recycling but are an important part of everyday life. Cosmetic packaging, candy trays, clamshells, and display packaging are some examples of thin gauge thermoforming. Production of thin gauge thermoplastics is quick with high volume runs and is customizable.
FDA-approved thermoforming grade polypropylene (PP) is a thin material used in food packaging because of its chemical resistance. It has about 60% of the density of PVC film. PP complies with safety regulations that ensure it does not pose any health risks when it deteriorates.
In the thermoforming process, a thermoplastic sheet is heated until it becomes flexible, then it is draped over a mold to shape it into a three-dimensional form. The final steps involve trimming and finishing the shaped material to achieve the final product design. This method is straightforward, fast, and efficient, offering a high level of productivity.
Although thermoforming is a straightforward process, every stage must be executed with exactness to ensure high-quality parts and products. Mistakes during any step can result in flawed or unusable plastic sheets.
Plastic sheets to be molded, which has length and width greater than the finished product, is clamped into a holding device and transported into a heating equipment to raise it to the forming temperature. The sheet is heated by contact heating using panel and rods (conduction), by exposing them to circulating hot air or using infrared heaters. The type of heating system is chosen depending on the material and the amount of necessary heat. The heating process is critical to the forming process since it creates the necessary pliability and flexibility.
The temperature required for forming can differ based on the thermoplastic material, the intended use of the final part, and the specific forming method employed. This parameter is crucial for achieving the desired quality in thermoforming. It is essential to measure the core temperature of the sheet rather than just the surface temperature, as accurate heat transfer calculations across the sheet are critical.
To ensure temperature consistency across the sheet, the 10-10-5 rule must be followed. This rule specifies that measurements should be taken at 10 points: both sides of the sheet, each of its four corners, and the center of each side. The "10" in the rule represents a permissible temperature variance of 10°F (-12.2°C) at these 10 points. The "5" denotes that the temperature difference between the two sides of the sheet at these points should not exceed 5°F (-15°C). Adhering to the 10-10-5 rule is essential for effective heating, forming, and cooling during the thermoforming process.
Heated plastic sheets are removed from the heating equipment and transported to a temperature-controlled and pre-heated mold tool. At this stage, the plastic sheet takes the shape of the mold cavity, which contains the desired form of the finished product. This stage gives the product its three-dimensional characteristics (length, width, and height).
Mold tools can be categorized as either positive or negative, based on their design:
A positive tool, also known as a "male mold," features a convex shape. During the process, the heated plastic sheet is placed over this convex tool. The raised, curved surface of the positive mold shapes the plastic into its final form. Essentially, the outer contour of the positive mold determines the shape of the part’s inner surface.
A negative tool, or "female mold," has a concave shape. In this case, the inner contour of the negative mold tool defines the outer surface of the finished part.
Once the plastic has been shaped, it solidifies through a cooling process which involves either air circulation or liquid cooling systems. The type of material used for the tool plays a crucial role in the cooling cycle, thereby influencing the overall quality of the finished parts.
Thick gauge thermoforming often requires further processing steps, such as drilling, cutting, or additional finishing to refine the parts.
After forming, the sheet with the parts is processed at a trim station or by a five-axis CNC router. Here, tools such as dies, abrasive wheels, or circular saws are used to cut the parts away from the remaining sheet. The excess material is collected, recycled, and reprocessed for creating new parts.
Numerous thermoforming machines are available across the United States and Canada. These machines play a crucial role in modern manufacturing, as they enable the production of various products and packaging efficiently and cost-effectively. This technology supports industries like food, medical, automotive, and consumer goods. Below, we provide details on some of the top thermoforming machines available.
Brown Machine is a leading producer of thermoforming machinery, with the C-Series Thermoformer being particularly well-regarded for its dependable and efficient operation. This model provides accurate control over heating, cooling, and material handling processes, making it ideal for creating everything from lightweight packaging to robust industrial parts.
SencorpWhite is renowned for delivering premium thermoforming equipment. The 2500 Thermoformer is notable for its user-friendly interface, quick tool changes, and sophisticated process control features. It is frequently utilized for producing medical trays, blister packs, and other precision-formed items.
GN Thermoforming Equipment is well-regarded for its range of thermoforming machinery. The GN800 Thermoformer is known for its adaptability, handling various materials such as PET, PS, PP, and PLA. It provides high energy efficiency and precise control, making it ideal for manufacturing products like food packaging, electronic parts, and consumer items.
WM Thermoforming Machines is a prominent European manufacturer with a significant footprint in North America. The FT and FC Series are praised for their durable build, dependable operation, and impressive production capacity. These models are frequently employed for making products such as cups, trays, and various packaging materials.
Multivac, a worldwide leader in packaging technology, provides the R-Series Thermoformers known for their advanced automation, ease of use, and exceptional hygiene standards. These machines are widely utilized in the food sector for creating vacuum-sealed packs, modified atmosphere packaging (MAP), and various other food-related products.
Keep in mind that the popularity and availability of particular models may have shifted since this information was published. Therefore, it is advisable to contact manufacturers or local suppliers for the latest details on thermoforming machines.
The design of the mold cavity for the forming process is meticulously crafted by the manufacturer to achieve the specified profile of the final product, tailored to the customer's requirements or end-use application. The preliminary phases of mold tool development include creating detailed designs using CAD software and CNC programming to produce the intended patterns. Various materials are utilized in the fabrication of the mold tool, including:
Wood is a cost-effective tooling material that can be easily shaped, allowing manufacturers to create intricate designs or modify part details as needed. However, it has several drawbacks: it cools unevenly and slowly because wood is an insulator, it can absorb moisture which may lead to voids, and wood grain patterns may transfer to the part. Wood tooling is typically used for making prototypes and patterns before producing a final mold.
Similar to wood tooling, fiberglass offers a cost-effective and durable option for mold tools, especially for manufacturers dealing with lower production volumes. However, fiberglass molds typically have a cooling cycle that is two to three times longer compared to temperature-regulated molds.
Aluminum offers superior temperature regulation, resulting in reduced cycle times and high-quality components:
Cast aluminum tools are created using a machined pattern.
Fabricated aluminum tools are constructed from one or more blocks of aluminum that are precisely shaped and machined to create the mold. Although these tools are more expensive, they offer superior dimensional accuracy and enable the creation of more intricate designs.
Here are explanations of two widely used forming techniques: vacuum forming and pressure forming.
In vacuum forming, a vacuum is applied beneath the plastic sheet to pull it tightly against the mold cavity, shaping it as required. This is the most straightforward thermoforming technique. Nevertheless, controlling the distribution of part thickness can be challenging. It is essential that the vacuum pressure is evenly applied and adequate across the entire mold.
In pressure forming, air pressure is combined with the vacuum applied beneath the mold to force the plastic sheet into the mold cavity. This additional air pressure allows for more intricate details, such as textured surfaces, undercuts, and sharp edges, which are difficult to achieve with vacuum forming alone. This method is ideal for creating products with complex designs.
Matched mold thermoforming involves using both male and female molds to shape a heated thermoplastic sheet. These molds can be crafted from materials such as metal, plaster, wood, or epoxy resin. When the mold halves come together, they press the thermoplastic sheet into their contours. A vacuum is applied to remove excess air and ensure a snug fit. This method results in parts with consistent wall thickness and precise adherence to design specifications. It provides excellent control over dimensions and allows for the creation of detailed and complex shapes.
Twin sheet forming involves two plastic sheets simultaneously heated and formed using two mold tools for each half of the parts. The mold tools are then precisely pressed together on the edges to connect the two halves. This method is used in producing double-walled, three-dimensional parts and hollow tubes such as air ducts, pipes, and tanks.
Thermoplastics are the raw material of the thermoforming process. Thermoplastics are a broad class of polymers that can be heated to a certain elevated temperature and re-casted reversibly, without altering their chemical properties and associated phase change. It can survive multiple cycles of heating and cooling. Given this nature, thermoplastics can be reprocessed, and are recyclable materials. Only thermoplastics can be thermoformed. Thermosetting and elastomeric plastics, in contrast, cannot be reshaped once the polymeric chains have been cross-linked.
The forming temperature is defined as the range between the glass transition temperature and the melting point of a thermoplastic. As the temperature of the thermoplastic is raised slowly, the intermolecular forces within the polymer chains weaken progressively. Once the temperature surpasses the glass transition point, the material transforms from a rigid, brittle solid into a soft, flexible, rubber-like substance.
Thermoplastics are categorized into two types: amorphous and semi-crystalline structures.
Amorphous thermoplastics have a disordered molecular arrangement and exhibit a broad range of softening temperatures. They offer several benefits, including excellent dimensional stability, enhanced impact resistance, good adhesion to adhesives, and greater ease of thermoforming compared to semi-crystalline thermoplastics. However, they tend to have lower fatigue resistance and are more susceptible to stress cracking. Examples of amorphous thermoplastics include polycarbonate, acrylic, and high-impact polystyrene.
Semi-crystalline thermoplastics feature a well-organized molecular lattice below their melting point. They are renowned for their superior resistance to wear and bearing, making them suitable for structural applications and long-lasting plastic components. Additionally, they offer enhanced chemical resistance and insulation properties. However, they present some challenges, such as difficulty in thermoforming and bonding with other components, and they provide only moderate impact resistance. Examples of semi-crystalline thermoplastics include polyethylene, polypropylene, and nylon.
A variety of thermoplastics are well-suited for thermoforming. The following table highlights the most prominent options:
| Thermoplastic Material | Distinct Properties | Applications |
| Acrylonitrile butadiene styrene (ABS) | ABS is a combination of acrylonitrile, butadiene, and styrene polymers. It is an opaque, lightweight, and sturdy material. ABS is resistant to a wide range of temperatures -4°F to 176°F (-20°C to 80 ° C), allowing this material to be molded at high or low temperatures. ABS is safe under normal handling conditions. |
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| High Impact Polystyrene (HIPS) | HIPS is modified homopolymer polystyrene combined with 5-10% rubber or butadiene copolymer. This modification results in increased toughness and impact strength, as polystyrene alone can be brittle. HIPS is easy and cost-effective. Also, the finishing of HIPS also can be customized aesthetically, making it a good packaging material. |
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| High Density Polyethylene (HDPE) | HDPE is a petroleum-based polymer notable for its rigidity and high strength-to-density ratio. HDPE has excellent resistance to chemicals, moisture, and most solvents. Hence, it is ideal to use this material for packaging products with short shelf-life and industrial and household chemicals. |
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| Polyvinyl Chloride (PVC) | PVC film is created from suspension polymerization. PVC is the preferred material in the construction industry due to its excellent resistance to grease, fire, impact, and extreme environmental conditions. PVC is also a good electrical insulator. Modifiers alter the physical and chemical properties of this material. Plasticizers are added to PVC before molding to make it more pliable. Chlorination of PVC involves the addition of chlorine atoms which are added to the polymer backbone to increase its resistance to chemical stability and insulation properties. |
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| Polyethylene Terephthalate (PET) | PET is a colorless and flexible plastic; PET is chemically stable and has low gas permeability, especially with carbon dioxide and oxygen. Due to its lightweight, this material is efficient to transport. PET is one of the most recycled plastics that is also transparent to microwave radiation. After forming PET, drying must be done to increase its resistance. |
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| Polycarbonate (PC) | PC is tough, has high impact strength, and is dimensionally stable. It also has good electrical insulation properties. However, it has low fatigue endurance. PC has good chemical resistance, except from alkalis, aromatics, and hydrocarbons. PCs start to degrade from exposure over 140 ° F (60 ° C). PCs are highly transparent plastics. It can transmit 90% of light as well as glass and can be customized using different shades. It also offers excellent optical properties. |
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Successful thermoforming relies on effective tool management and design. To avoid defects caused by contamination, it is crucial to maintain all materials and tools at a consistent temperature and ensure they are free from moisture and plastic residue.
The following parameters must be optimized and carefully controlled in each thermoforming process:
| Issue | Definition | Potential Causes | Corrective Action |
| Blisters or bubble formation | Voids on the inner plastic layer. |
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| Webbing | Webbing, or unwanted folds and wrinkles, occurs when the plastic folds onto itself. During the vacuum molding process, the thermoplastic stretches in a way that was not planned. |
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| Part thickness inconsistency | Overall thickness of the formed part is not uniform. This is primarily caused by uneven distribution of the plastic sheet. In the design of the part itself, thickness is difficult to control at the edges. |
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| Chill marks | White or opaque wavy marks on the formed part. | Mold tool temperature is too low, causing the plastic sheet to freeze onto the mold when in contact. | Adjust mold tool temperature. |
| Warpage | Distorted, deformed overall shape of the formed part. |
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| Dimensional inconsistencies | Part produced not conforming to the required dimensions |
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Note:
Thermoforming aims to shape a heated plastic sheet by molding it into the desired form. Despite its straightforward and efficient process, thermoforming produces robust and resilient products that can be either easily disposed of or recycled, and are often designed for long-term use. Originating as a solution for aircraft design, thermoforming has quickly evolved into a widely adopted technology known for its convenience and high quality.
Cost Efficiency: Large components are often integral to bigger assemblies and products. While other forming techniques can produce these parts, thermoforming offers a cost-effective solution, typically achieving results at half the expense and in a shorter timeframe compared to alternative plastic manufacturing methods. Whether for car door panels, instrument panels, tail lights, or consoles, thermoforming delivers quicker and more affordable results.
Longevity: In today's manufacturing landscape, the durability of products is crucial, especially considering the rigorous conditions they often face. A significant aspect of customer satisfaction is the longevity of a product, which also serves as a key marketing advantage. Heavy gauge thermoforming is effective in creating large, robust items that can withstand the test of time and meet consumer expectations for durability.
Tooling Expenses: Thermoforming molds can be efficiently designed using 3D printing or computer-aided design (CAD) technology. These molds, often crafted from materials like silicone or fiberglass, bypass the need for traditional grinding, machining, or other extensive tooling processes. In contrast, developing a metal mold is costly, time-consuming, and labor-intensive, necessitating skilled professionals with specialized expertise.
Thermoforming molds can be created and ready for production on the same day. These molds are constructed from materials that are much more affordable compared to the steel and iron used for other molds, while still achieving equivalent high-quality outcomes.
Tool Development: In thermoforming, molds are often crafted from materials like wood or epoxy. These tools can produce various finished parts that reflect the original design. Prototypes made from the same materials as the final product help identify any design flaws or issues prior to finalizing production tooling.
Design Flexibility: Thermoforming offers remarkable design versatility, accommodating complex, detailed, and large-scale parts without significant limitations. This flexibility is a key factor in its widespread use, particularly in the automotive industry where minimizing component weight is crucial.
Vacuum forming involves heating plastic material and shaping it using a vacuum. As one of the earliest and most cost-effective plastic molding techniques, vacuum forming is commonly employed in various applications, ranging from small household items to large industrial equipment.
Blister packaging, often referred to as blister packs, consists of a thermoformed plastic cavity sealed with a flexible lid. This packaging format involves placing the product into recessed pockets or cavities, which resemble blisters, to secure and protect the item.
Reaction injection molding or RIM molding is a molding process that involves the use of two chemical elements with high reactivity and low molecular mass that collide and mix before being injected into a closed mold. High pressure pumps circulate isocyanate and...