This article will give an in depth understanding of vacuum forming.
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The process of heating plastic and shaping it with the use of a vacuum is known as vacuum forming.
Vacuum forming is one of the oldest and most affordable plastic molding techniques, commonly used in everyday items and large industrial machinery. Its popularity comes from its low cost, efficiency, speed, and ease of shaping smaller molds. The process involves placing a plastic sheet over a mold and applying suction to shape the plastic into the desired form. As the simplest type of plastic thermoforming, vacuum forming requires only a mold and a plastic sheet to create the shape.
Two types of molds are used in vacuum forming:
The male, or positive, mold has a convex shape, where the plastic is placed over the outer surface to form the inner dimensions. In contrast, the female, or negative, mold is concave, with the plastic placed inside to accurately shape the outer dimensions.
Vacuum forming is the simplest method of plastic molding, but advancements like heat, hydraulic, and pneumatic controls are now used to create more precise products at faster production speeds. This process is used to manufacture various items, including bath and shower trays, vehicle parts, refrigerator liners, and plastic storage boxes.
A process of heating a plastic sheet to make it flexible and then contouring in desired molds, trimming the final product is called thermoforming. Thermoforming is then categorized into two types:
The key difference lies in the number of molds used during product manufacturing.
Vacuum forming uses a single mold and a vacuum pump. A heated plastic sheet is placed over the mold, and the vacuum pulls it into the desired shape. It's commonly used for packaging food, electronics, and similar items. In contrast, pressure forming involves two molds. The sheet is placed between the molds, and pressure is applied to shape it, rather than relying on suction. This method allows for more precise, visually appealing results, such as appliance casings. Pressure forming is ideal for creating evenly shaped plastic parts that require deeper molds.
Twin sheet thermoforming is a thermoforming process that uses either pressure or vacuum forming, but with two molds. This compression technique simultaneously forms two plastic sheets—one on the top platen and the other on the bottom. After forming, the sheets remain in the vacuum at melting temperature, where both platens compress and fuse the sheets together to create a single product. Twin sheet thermoforming is commonly used for producing hollow-structured products. The process is illustrated in the figure below:
This process offers several advantages over other methods.
These are:
Twin sheet thermoforming is used to manufacture a variety of products, including pallets, portable toilets, toys, fuel tanks, marine products, doors, ventilation ducts, surfboards, spine boards, and various transportation items.
Vacuum forming can be performed with various thermoplastics, but the most commonly used materials include:
Vacuum forming can be done with various thermoplastics, though the materials typically used include:
Polycarbonate (PC) is a durable plastic polymer commonly used for manufacturing machine parts. It is nearly unbreakable, highly resistant, and UV-protected on one or both sides. With half the weight of glass, polycarbonate is easy to install and handle. It is utilized in light diffusers, skylights, aircraft trims, and other applications.
Polystyrene (PS) is a highly versatile thermoplastic available in various formulations. It is moderately strong, precise, brittle, and rigid when unmodified. Polystyrene also offers good electrical properties, dimensional stability, low cost, versatility, and ease of processing. Due to these qualities, it is commonly used in food packaging, disposable cups, and plates.
Polypropylene (PP) is a plastic polymer used in the vacuum forming process for various applications, including model making, crafts, and report covers. These sheets are semi-rigid and inflexible, offering high resistance to heat, fatigue, and chemicals. Additionally, polypropylene is crystalline, non-polar, and translucent in appearance.
Polyvinyl chloride (PVC) is widely available and used in large quantities. It is highly economical, offering excellent tensile strength, rigidity, and density compared to other plastic polymers. Additionally, PVC is eco-friendly and highly resistant to chemicals. It is primarily used for commercial applications such as digital and screen printing, laminations, and vinyl lettering.
Polyethylene is a plastic sheet derived from petroleum, known for its high resistance to water and chemicals. It remains stable in cryogenic conditions, has a low coefficient of friction, and is highly malleable. Its low cost and suitability for various environments make it widely used across numerous applications.
It is a thermosetting plastic known for its high durability, strength, and resistance to harsh environments. Used in the vacuum forming technique, it is easily molded, die-cut, and shaped.
Acrylic PMMA is a widely used plastic sheet that is durable, transparent, and easy to mold. It is more economical than high-cost, less resilient glass. Acrylic PMMA is used in various applications, including cars, windows, smartphone screens, and aquariums.
Acrylonitrile Butadiene Styrene (ABS) is a thermoplastic that is insoluble in water and offers excellent resistance to chemicals, impact, abrasion, and stress. It is rigid, hard, and stable with good electrical properties. ABS is commonly used for manufacturing rigid pipes, automobile parts, car wheels, and other components.
All vacuum forming machines operate based on the same principle, but their operations can vary depending on their capabilities. These machines are categorized into four types:
DIY machines are used for smaller-scale production. The number of heaters present in it is quite limited. Thus they are incompatible with industrial production. DIY machines might use ceramic heaters, their response time is slow, and they are not specialized enough to use complex tools such as plugs. These machines are simple in structure and easy to maintain, install and handle. It has a single working station with three separate heating zones with different temperature controls. This heating box is protected with a lid, and at the bottom of the machine, a vacuum pump is present. DIY machines make toys, masks, stationery, tableware, tools, blister packs, cosmetics, etc.
A tabletop vacuum forming machine is designed for products made from acrylic and comes in three series, each with different functions. It operates similarly to other vacuum forming machines and is compatible with materials such as acrylic, ABS, PC, PS, PVC, and PP. These machines are used in various industries, including automotive, aerospace, signage, display, and film or design sets.
The single heater machine is compatible with various plastic sheets, including starch degradation, optical degradation, green APET, PETG, and colored sheets like HIPS, PVC, PET, PS, and PP. It features mechanical and electrical integration with automatic temperature controllers, high frequency, and efficient temperature control. Additionally, the machine includes ten stalls in the furnace for gear switches, is easy to install, and has automatic temperature regulation. This machine is used to produce thin-walled food containers, travel goods, textiles, cosmetics, decorations, medical supplies, toys, and electrical goods.
A double heater vacuum forming machine works on electrical-mechanical integration. It is fully automated with all digital power controls, and it is capable of performing all the functions that are feeding, heating, forming, cooling, trimming, and finishing. It is applied to a plastic sheet such as PS, HIPS, PVC, PET, and PP. It comprises an automatic feeding sheet frame that ensures correct sheet feeding and saves staffing. The heaters in this machine consist of 60 pieces of infrared ceramic bricks, and each brick contains a self-regulator to regulate the heating temperatures of the sheet. The double heater machine is adapted to negative mold but can make concave or convex mold according to demand. Spray mists are there to cool down the heated sheet with regulators that spray the amount of water according to the product. The double heater machine makes all kinds of trays, medical trays, telephones, cookies, hardware, tableware, and plastic packaging.
The vacuum forming process consists of several steps that ensure efficient and effective plastic molding. This chapter will discuss each step in detail.
The plastic sheet is secured in the machine's clamps, which must be robust enough to hold the material in place. These clamps can accommodate materials as thick as 6mm with a single heater and up to 10mm with a twin heater. For automatic machines, all moving parts should be interlocked and guarded to prevent accidents.
Heaters used in the vacuum forming process are infrared elements placed within an aluminum reflector plate. While various materials can be used, it is crucial to heat the sheet evenly throughout its thickness. To achieve this, energy controllers are needed in each zone to regulate the optimum temperature for the material. Ceramics are unsuitable due to their high thermal mass, which makes them slow to heat and inefficient for molding. Pyrometers can accurately measure the melting temperature of materials and are more effective when integrated with the temperature control system. For thicker sheets, a twin quartz heater is recommended, as it enhances heat penetration and ensures even heating across the sheet's surface. These heating strategies ensure precise and cost-effective heat application.
Sheet leveling, which is not present on all machines, helps prevent the sagging of plastic material. It involves a photoelectric beam integrated into the machine that scans the heater and the melted plastic sheet. If the melted sheet sags and breaks the beam, a small amount of air is injected into the sheet to lift it and prevent further sagging.
When the plastic sheet is melted and prepared to enter the mold, stretching it is crucial to ensure even thickness across the entire surface. Various aids, such as vacuum plug assist and air pressure, are used to pre-stretch the plastic, helping to prevent any distortion or unevenness.
After the stretching phase, plug-assisted vacuum forming comes into play. When a standard vacuum forming machine struggles to evenly distribute the plastic sheet over the mold, a plug is used to assist. This plug ensures that the melted plastic sheet spreads evenly across the mold surface, filling all vacant spaces and preventing thinning of the material. It provides additional space for the plastic to reach the bottom of the mold, ensuring a consistent thickness throughout.
After stretching and plugging, excess air is removed from the sheets and molds. A vacuum pump is then used to extract any air bubbles trapped between the plastic sheets and the molds. The vacuum pump should be capable of creating a pressure of approximately 27 inches of mercury. For larger machines, a vacuum reservoir is often used in conjunction with a high-volume vacuum pump to quickly remove air particles before the plastic sheet cools down.
The molded plastic is cooled before being released to ensure it retains its shape and does not deform. Cooling is essential as it allows the melted plastic to settle. The machine is equipped with built-in fans that assist in the cooling process. Additionally, nozzles attached to the fans spray a mist of chilled water directly onto the plastic sheet, accelerating cooling by 30%. Temperature control units regulate the cooling temperature for specific polymers as they exit the machine. Once the molded plastic sheet has cooled, it is moved to the next step in the process.
Once the plastic sheet is released from the machine, it is trimmed using various types of trimmers. Cuts, holes, or slots are made in the sheets based on the product’s requirements. The finishing process may include decoration, printing, or strengthening. The choice of trimming method depends on factors such as part size, cut type, and material thickness. For example, thin gauge parts are typically trimmed using a mechanical trim press, also known as a roller press.
Vacuum forming is used to create a wide range of plastic products that we encounter in everyday life. This method is applied in producing items for medical applications, industrial use, household goods, automotive parts, lawn and garden equipment, agricultural tools, electronics, display centers, commercial equipment, fitness gear, and more. This topic will explore nearly all products made using vacuum forming.
Various types of medical equipment are manufactured from plastic using the vacuum forming method. Examples include thermoformed trays, blister packs, clamshells, CT scanner components, MRI machine components, X-ray machine components, carts, trays, heating pads, operation kits, and more. Some of these items are illustrated below:
Vacuum forming is commonly used for making panels, packaging, trays, and plastic boxes in appliances, including refrigerator parts, washing machine components, and vacuum cleaner covers.
The vacuum forming technique is also used to produce lawn and garden products, including mower covers, guards, trailers, and fenders.
Display centers also use vacuum forming techniques for making signs and billboards for advertising. It is also used for mobile phone covers made up of acrylic. Packaging could be of anything from food material to electronic appliances.
The vacuum forming method is widely used in the food and packaging industry. For example, food storage containers and plastic trays are made of plastic, and vacuum forming is used.
Vacuum forming techniques are widely used to create various vehicle components, including windshields, guards, skid plates, belly pans, roofs, fenders, hoods, body panels, and motorcycle covers. This process is also employed to produce consoles for snowmobiles and many other parts. Additionally, vacuum forming offers car manufacturers the ability to customize the shapes and colors of automobile components.
Every method or technique has its advantages and disadvantages, and vacuum forming is no exception. It is widely used due to its low cost and high productivity, but it also has some drawbacks. These are outlined below:
The vacuum forming process is more cost-effective compared to other molding methods. It is inexpensive and offers higher productivity than many more expensive molding processes. Additionally, vacuum forming tools are readily available and affordable.
Turnaround time for vacuum forming is much more than the standard injection molding process. This process can get the work done in half of the time required in the injection molding process. More products can be made using vacuum forming in less time if we use the 3D modeling technique.
The vacuum forming method provides manufacturers with the flexibility to experiment with new mold designs. This allows for customization of new models and colors, giving clients more options tailored to their needs, all while keeping costs affordable.
Vacuum forming is ideal for producing sterile and food-grade materials, such as plastic food containers and medical equipment. These items must remain germ-free, and vacuum-formed products are well-suited for this purpose because they can be sterilized and used for extended periods.
The vacuum forming method is highly efficient and scalable. It utilizes one tool at a time for mold formation, but a wide range of tools can be employed for different molds, allowing for the production of a large volume of products with various designs.
Vacuum forming is renowned for its consistency. Using the same mold will consistently produce identical results. If any issues arise with mold formation or plastic handling, the mold can be adjusted or replaced to address the problem.
Vacuum forming is also known for its robustness. While some plastic materials may be sensitive, many are durable and can withstand significant resistance.
Some disadvantages of vacuum forming include its limitation to plastic materials with thin walls and uniform consistency. It is less effective for materials with thick walls that are difficult to mold. Additionally, molding deep and concave parts can be challenging with this technique. While vacuum forming is suitable for small-scale production, it is less efficient for large-scale industrial production.
Thermoforming is the process of heating thin plastic sheets to its forming temperature and stretching it over a mold which takes its shape. After cooling and setting of the molded plastic sheet, each part will be separated from its batch to form a single unit or product...
Blister packaging, or blister packs, are pre-formed packaging materials composed of a thermoformed plastic cavity and a pliable lid. In this type of packaging, the product is placed in deep-drawn pockets or cavities resembling a blister...