What is thermoforming?
Thermoforming is a plastic manufacturing process used to shape plastic materials. This process involves heating a plastic sheet and giving it a specific shape using molds. The process is carried out using a thermoforming machine that heats and stretches a ductile thermoplastic sheet over the mold. In this article, you will discover the different types of thermoforming processes, the materials suitable for thermoforming, the costs involved, and the main applications of these processes.
Thermoforming processes
The thermoforming processes are used to produce a wide range of products, from food packaging to automotive components, thanks to their versatility and relatively low production costs. Let's consider the following main thermoforming processes.
Thermoforming
Thermoforming is a manufacturing process in which a plastic sheet is heated to a pliable forming temperature, shaped into a specific mold configuration, and trimmed to create a usable product. The process involves several steps, including heating, forming, and trimming, and it is commonly used to produce a variety of products such as packaging, trays, containers, and automotive components. Thermoforming can be divided into various methods, including vacuum forming, pressure forming, and mechanical forming, each offering different levels of detail and complexity in the final product.
Thermoplastics
The processing of thermoplastics involves several common techniques to shape them into usable products, from injection molding to extrusion, from blow molding to compression or rotational molding. These processes offer flexibility in creating a wide range of products from thermoplastic materials, catering to different shapes, sizes, and performance requirements across various industries.
Vacuum forming
Vacuum forming is a thermoforming process where a thermoplastic sheet is heated until it becomes pliable, then stretched over a mold and vacuum-sealed against the mold surface. In the vacuum forming process, four main stages can be distinguished: Heating (the thermoplastic sheet is heated until it becomes pliable. This is done in an oven or using heating elements); forming (the heated sheet is placed over the mold. A vacuum (or negative pressure) is then applied beneath the sheet, causing it to tightly conform to the mold. The air is evacuated, making the plastic sheet take the shape of the mold; cooling (once the sheet has taken the desired shape, it is cooled to solidify the form. This cooling can be accelerated using fans or other cooling techniques); trimming (after the sheet has solidified and cooled, the formed product is removed from the mold. The excess material is then trimmed away to achieve the finished product with the precise shape and dimensions desired).
These stages allow a flat plastic sheet to be transformed into a three-dimensional product with applications in numerous sectors, such as packaging, automotive, and many others.
Pressure forming
Pressure forming is a thermoforming process similar to vacuum forming, but with the addition of positive air pressure to achieve greater detail and precision in the final product. It is particularly valuable when the appearance and detail of the finished product are critical, providing a cost-effective alternative to injection molding for low to medium production volumes.
Mechanical forming
Mechanical forming refers to a process where both male and female molds are used to shape a heated thermoplastic sheet. This method relies on mechanical force to press the plastic sheet into the desired form. It is an efficient method for producing high-quality, detailed plastic parts with uniform thickness and complex geometries. It is often used in industries where precision and durability are critical.
Drape forming
Drape forming is a thermoforming process in which a heated thermoplastic sheet is draped over a mold, allowing gravity and sometimes a small amount of vacuum to shape the plastic to the mold contours. This method is particularly suitable for forming large, gently curved parts and it is applied in the aerospace, automotive, medical, consumer goods and industrial sectors.
Matched mold forming
Matched mold forming, also known as compression thermoforming, is a precise thermoforming process that involves using two molds (male and female) to shape a heated thermoplastic sheet. The matched molds press the sheet into the desired form with high accuracy. The sheet then takes the pattern or shape designed into the two molds.
Twin sheet forming
Twin sheet forming is an advanced thermoforming process used to create hollow, lightweight, and strong parts by simultaneously forming and bonding two thermoplastic sheets. Among the advantages, the following can be considered the hollow structures, the complex designs, the efficiency, and the material savings.
Billow forming
Billow forming, also known as free-blowing or bubble forming, is a thermoforming process where a heated thermoplastic sheet is formed into a bubble shape using air pressure before being draped over a mold. This method allows for the creation of deep-drawn parts with uniform wall thickness.
Thermoforming Materials
Thermoforming is a versatile process that can utilize various thermoplastic materials to create a wide range of products. The common thermoplastic materials used in thermoforming are polyethylene (PE), polypropylene (PP), polyvinyl Chloride (PVC), polystyrene (PS), acrylonitrile Butadiene Styrene (ABS), polyethylene, terephthalate (PET), amorphous PET (APET), polycarbonate (PC), Polyamide (PA) (Nylon), acrylic (Polymethyl Methacrylate - PMMA), thermoplastic Polyurethane (TPU) and thermoplastic Elastomers (TPE). These materials are chosen based on their specific properties such as strength, flexibility, transparency, chemical resistance, and suitability for thermoforming processes like vacuum forming, pressure forming, or twin sheet forming. The selection depends on the requirements of the final product, including its function, appearance, and performance characteristics.
Heavy Gauge vs. Thin Gauge Thermoforming
Heavy gauge and thin gauge thermoforming are two distinct processes within the thermoforming industry, each suitable for different applications based on material thickness and the complexity of the part being formed. Heavy gauge thermoforming is suitable for producing robust, structural parts requiring thickness and durability, such as automotive and industrial components. In contrast, thin gauge thermoforming is ideal for producing lightweight, cost-effective parts with intricate designs, commonly found in packaging and consumer goods. The choice between heavy gauge and thin gauge thermoforming depends on the specific requirements of the application, including material strength, cost considerations, and desired design complexity.
What is the necessary equipment for thermoforming?
Thermoforming requires several key pieces of equipment to effectively heat, form, cool, and trim thermoplastic materials into desired shapes. Here are the essential components typically involved in a thermoforming setup such as ovens or heating elements, forming equipment (molds and vacuum systems), cooling fans or water baths, trimming tools, control systems (temperature controls, vacuum and pressure controls), safety guards and interlocks for ensuring the operator safety during operation.
How does a thermoforming machine work?
A thermoformer works by heating a thermoplastic sheet until it becomes pliable, then forming it over a mold to create a specific shape, and finally cooling and trimming the formed part to achieve the final product. To thermoform we can follow these steps:
Sheet heating with loading and heating phases (a sheet of thermoplastic material, such as ABS, PVC, PET, or polystyrene, is loaded into the thermoforming machine and passes through a heating station where it is heated to a specific temperature).
Forming: once heated, the sheet moves into position above the forming area, then is pressed or drawn over a mold. After forming, the mold or molds are cooled to solidify the shape of the part. This can be achieved using cooling fans, water baths, or other cooling methods.
Trimming: once the formed part has cooled and solidified, it is removed from the mold. Excess material (flash) around the formed part is trimmed away to achieve the final shape and dimensions.
Ejecting and Stacking: the finished parts are ejected from the thermoforming machine, ready for further processing or packaging, then can be stacked or conveyed to downstream processes for assembly or shipment.
Control and monitoring: throughout the thermoforming process, temperature, vacuum or pressure levels, cycle times, and other parameters are monitored and controlled to ensure quality and efficiency.
Benefits of thermoforming
Thermoforming offers several benefits that make it a preferred manufacturing process for a wide range of industries from the cost-effective production to design flexibility, from fast turnaround times (compared to other manufacturing methods like injection molding) to versatility in materials that allows manufacturers to choose materials based on specific performance requirements. Other benefits are lightweight products, recyclability, and surface finish options.
Thermoform applications
Some common applications of thermoforming include packaging, automotive, aerospace, medical, consumer goods, industrial, electronics, construction, food service, custom products.
General practices to be followed
To ensure a more efficient, consistent, and high-quality thermoforming process, it is important to follow some general practices: select a plastic material suitable for the end-use application and use high-quality plastic sheets; ensure that all thermoforming machines are properly calibrated for temperature, pressure, and timing and the heating elements are functioning correctly; control the heating temperature, perform mechanical and visual testing to ensure the formed parts meet the required specifications; regularly maintain and service thermoforming equipment to prevent downtime and ensure consistent quality.
Material used for thermosets
Thermosetting plastics, or thermosets, are polymers that irreversibly cure, forming a rigid structure that does not melt upon reheating. They are typically used in applications requiring durable, heat-resistant, and chemically resistant materials. The common thermoset materials are epoxy resins, phenolic resins (phenol-formaldehyde), melamine formaldehyde, urea formaldehyde, polyester resins, polyurethane, polyimides.
How much does thermoforming cost?
The cost of thermoforming varies widely depending on several factors, including the complexity of the part, material type, production volume, tooling costs, and labor. The cost of the plastic material, for example, can range from a few dollars per kilogram for common materials like HIPS (High Impact Polystyrene) to higher costs for specialized materials like PETG, ABS, or polycarbonate. For reducing costs it’s necessary: simplify the design to reduce tooling complexity and material usage, choose cost-effective materials that still meet performance requirements; increase volume and minimize cycle times and automate the process.
BIESSE thermoforming machine
In order to achieve top thermoforming results, we offer Terma, the Biesse thermoformer designed by Fraccaro. Therma is perfect for thermoforming plastic materials using a mold and vacuum. It accommodates sheets in various colors, thicknesses, and finishes, catering to a wide range of market demands.