This article will give an in depth understanding of vacuum forming.
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The process of heating and shaping the plastic material using a vacuum is called vacuum forming.
Vacuum forming is one of the oldest and cheapest methods for plastic molding and is widely used in our everyday life, from smaller objects to huge industrial machinery. The vacuum forming process is being used at a large scale due to its low cost, efficiency, speed of imitation, and ease of use for shaping smaller objects molds. Vacuum forming is a process in which a layer of plastic is placed on the mold, and then a suction force is applied to shape the plastic according to the desired shape. Vacuum forming is also known as the simplest form of plastic thermoforming as only a mold is required, and the plastic is placed over it.
There are two types of molds that are used in vacuum forming that are:
The male or positive mold is a convex-shaped one. The plastic is placed on the outside layer of the mold, which helps contour the inner dimensions of the plastic, while the female or negative mold is concave shaped. The plastic is placed inside the mold to contour the outside dimensions of the plastic accurately.
Vacuum forming, as discussed earlier, is the simplest of all forms. Still, now advanced technology is being introduced, such as heat, hydraulic and pneumatic controls to produce more precise and desired products at a reasonable production speed. Many products are made from vacuum forming, such as bath and shower trays, vehicle parts, refrigerator liners, plastic storage boxes, etc.
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 main difference in these is the number of molds used in their product manufacturing.
Vacuum forming is done using a single mold and a vacuum pump. The heated sheet is placed into the mold, and a vacuum is applied to place it properly into the mold of the desired shape. It is mainly used in the contoured packaging of food and electronics etc. At the same time, pressure forming is done with the help of two molds. The sheet is placed within one mold and then pressed by placing the other mold on it rather than using suction from the vacuum pump. This process enables precise and aesthetically good-looking molds such as appliances casing etc. Furthermore, pressure forming is very suitable for manufacturing the plastic parts that are needed to be shaped evenly and that go deeper into a mold.
Twin sheet thermoforming is a process in thermoforming that is done either by pressure forming or vacuum forming but with the help of two molds. It is a compression process that creates two plastic sheets simultaneously, one on the top platen and the other on the bottom platen. Once the sheets were formed, they remained in the vacuum at their melting temperature. Both the platens are compressed and joined together to form a single product. Twin sheet thermoforming is used for the products that are hollow in structure. The process of twin sheet thermoforming is shown in the figure below:
This process has advantages over other processes.
These are:
Twin sheet thermoforming is used to make pallets, portable toilets, toys, fuel tanks, marine products, doors, ventilation ducts, surfboards, spine boards, and many other transportation products.
Vacuum forming can be done on a variety of thermoplastics, but typically the materials that are used in vacuum forming are as follows:
Vacuum forming can be done on a variety of thermoplastics but typically the materials that are used in vacuum forming are as follows:
Polycarbonate (PC) is a plastic polymer used to make many machine parts. It is a good choice as it is virtually unbreakable, highly resistant, UV protected from one or both sides, half the weight of glass, and hence they are easy to install and handle in the machine. It is used in light diffusers, skylights, aircraft trims, etc.
Polystyrene (PS) is the most versatile thermoplastic available in many formulations. Polystyrene is moderately intense, precise, brittle, and rigid when unmodified. In addition, it has good electrical properties, dimensional stability, low cost, versatility, and is easy to process. As a result, it is widely used in food packaging, disposable cups, and plates.
Polypropylene (PP) is also a polymer of plastic. It is used in the vacuum forming process as a material for certain objects such as model making, crafts, and report covers in schools and offices. These sheets are inflexible, semi-rigid, with high heat, fatigue, and chemical resistance. In addition, they are crystalline, non-polar, and translucent in appearance.
Polyvinyl chloride is readily available and is used in high quantities.It is highly economical with excellent tensile strength, rigidity, and high density compared to all other plastic polymers. In addition, it is eco-friendly with high chemical resistance. It is mainly used for commercial purposes like digital and screen printing, laminations, vinyl lettering, etc.
Polyethylene is a plastic sheet made from petroleum, and it is highly resistant to water and chemicals. Very stable in cryogenic environments, low coefficient of resistance, and highly malleable. It is widely used because of its low cost and is suitable for almost all environments.
It is a thermosetting plastic in unmodified form with high durability, strength, and resistance to harsh environments. It is used in the vacuum forming technique because it can be easily molded, dye cut, and formed.
Acrylic PMMA is a widely used plastic sheet that is challenging, transparent, easy to mold, and more economical than high cost, less resilient glass. It is used in cars, windows, smartphone screens, and even aquariums.
Acrylonitrile Butadiene Styrene ABS is a thermoplastic insoluble in water with excellent chemical, impact, abrasion, and stress resistance properties. It is rigid, hard, and a stable plastic with good electrical properties. It is used to make rigid pipes, automobile parts, car wheels, etc.
All vacuum forming machines work on the same formula but some machines vary in their operations depending upon their capabilities. The vacuum forming machines are divided 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 used for products that are made from acrylic. These machines are in three different series with different functions. An operating system is the same as other vacuum forming machines; suitable materials are acrylic, ABS, PC, PS, PVC, PP, and others. These are used in automotive, aerospace, signs and display, and film or design sets.
The single heater machine is adapted to various plastic sheets such as starch degradation sheet, optical degradation sheet, green sheet APET, PETG, and various color sheets that are HIPS, PVC, PET, PS, PP, etc. These machines have mechanical and electrical integration with automatic temperature controllers, high frequency, and efficient temperature gain. In addition, there are ten stalls in furnaces for gear switches, easy to install, and automatic temperature controllers. This machine makes thin-walled food containers, travel goods, textile, cosmetics, decorations, medical supplies, toys, electrical goods, etc.
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 involves different steps that help the plastic molding efficiently and effectively. Therefore, the process is discussed step by step in this chapter.
The plastic sheet is held in the clamps of the machine, and for this purpose, the clamps should be strong enough to control the material in place. This clamp can hold and form the thickest material from 6mm with a single heater to 10mm with a twin heater. However, if the machine is automatic, all the moving parts must be interlocked and guarded to avoid any mishap.
Heaters are used in the vacuum forming process and are an infrared element that is placed within an aluminum reflector plate. Any kind of material can be used in this process but the thing to consider is that the sheet is heated evenly throughout its thickness. For this purpose there is a need for energy controllers in every zone to regulate an optimum temperature for the material. Ceramics are not compatible due to their high thermal mass which leads them to take a lot of time to heat up and therefore takes a lot of time in molding. Pyrometers can help in determining the precise melting temperature of the materials and it will be more feasible if it is connected to the temperature controlling system. If there is a thick sheet in process it is recommended to use a twin quartz heater, as it helps to increase heat penetration to thicker materials and evenly on the whole sheet surface. These heating strategies can help in even penetration of heat with precision and at low cost.
Sheet Leveling is not available on all machines, and it is responsible for the non-sagging of plastic material. A photo-electric beam is integrated into the machine that scans the heater and the melted plastic sheet. It works as if the melted sheet sags down and the beam is broken, then a little air is injected into the sheet to lift it up and not let it sag down again.
When the plastic sheet is melted and ready to get in the mold, this step is done to stretch the plastic to ensure there is even thickness on the entire surface. Different aids, such as vacuum plug assist and air pressure, make sure that plastic is pre-stretched to avoid any disfiguration.
After the stretching phase, there comes a phase where a plug is used for assistance. When a normal vacuum forming machine fails to distribute the plastic sheet on the mold evenly, plug-assisted vacuum forming is used. This plug helps distribute the melted plastic sheet with an even thickness throughout the mold surface to fill all the vacant spaces in the molds. These plugs also help avoid the thinning of the plastic sheet, thus providing more space for the material to reach the bottom of the mold.
After this processing of stretching and plugging, extra air is removed from the sheets and molds. Then, a van vacuum pump is placed in the machine to extract any air bubbles trapped between the sheets of plastic and the molds. The vacuum pump should be capable enough to create a pressure of 27" mercury approx. When there is to deal with larger machines, there is a help of vacuum reservoir along with a high volume of vacuum pump that withdraws the air particles rapidly before the plastic sheet is cooled down.
The plastic form is turned into a cooling process before releasing it. Cooling is necessary because it will give settlement time to the melted plastic. Otherwise, it will be deformed. There are fans built within the machine for cooling purposes, which helps in the cooling process. Other than fans, there are nozzles attached to the fans that offer a spray mist of chilled water directly on the plastic sheet, which along with fans, speeds up the cooling process by 30%. To aid in the cooling process, temperature control units are present to regulate the cooling temperature of these specific polymers as they come out of the machine. When the molded plastic sheet is cooled down, it is released towards the next step from the machine.
After the release of the plastic sheet from the machine, the molded sheet is then trimmed with the help of different types of trimmers. Cuts, holes, or slots are made within the sheets according to the requirement of the product. Finishing includes decoration, printing, or any kind of strengthening. There are different kinds of trimming available, but these products depend upon many factors such as part size, cut type, the thickness of the material, etc. For example, the thin gauge parts are usually trimmed on a mechanical trim press, also known as roller press.
Hundreds of products are made from plastic material using the vacuum forming method, and we use them in our daily life. The vacuum forming process is used in making products related to medical, industries, household items, automobiles, lawn and garden pieces of equipment, agricultural equipment, electronics, display centers, commercial equipment, fitness, and many more. This topic will cover almost every product made from vacuum forming.
Many types of medical equipment are made from plastic using the vacuum forming method. Such as thermoformed trays, blister packs, clamshells, CT scanner components, MRI machine components, X-ray machine components, carts, trays, heating pads, operation kits, vacuum formed trays, and many more. Some of them are shown below:
Vacuum forming is widely used in panels, packaging, trays, and plastic boxes for appliances such as refrigerator parts, washing machine parts, vacuum cleaners covering, etc.
The vacuum forming technique also makes lawn and garden products such as 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 also used in making products for vehicles like cars, motorcycles, airplanes, buses, and boats such as windshields, guards, skid plates, belly pans, roofs, fenders, hoods, body panels, and cover for motorcycles, windshields, consoles for snowmobiles and a lot of other products. In addition, this process allows car companies to customize the shapes and colors of automobile parts.
Vacuum forming is a plastic molding process where a heated plastic sheet is placed over a mold, then a vacuum is applied to shape the plastic to the mold’s form. It is valued for its simplicity, cost-effectiveness, and versatility.
Vacuum forming uses male (positive) molds, which are convex and shape the inner dimensions, and female (negative) molds, which are concave and shape the outer dimensions of the plastic.
Common plastics used in vacuum forming include polycarbonate (PC), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), polyethylene (PE), polyester copolymer (PETG), acrylic (PMMA), and acrylonitrile butadiene styrene (ABS).
Products made by vacuum forming include medical trays, blister packs, refrigerator liners, car parts, packaging containers, trays, lawn equipment covers, and various consumer goods.
While vacuum forming uses one mold and vacuum suction, pressure forming uses two molds and pressure for higher precision components and is preferred for deeper and more detailed plastic parts.
Yes, DIY and tabletop vacuum forming machines are available for small-scale production. They’re easy to maintain and suitable for making items like toys, masks, and prototypes.
Any method or technique has its advantages and disadvantages; therefore, vacuum forming also comes with its pros and cons. It is used on a large scale because of its low cost and good productivity, but still, it has some cons to ponder. These are discussed below:
The vacuum forming process is more affordable than any other molding process. It is low cost and gives more productivity than any different high-cost molding process. Vacuum forming tools are also 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.
Vacuum forming method allows manufacturers to try out new designs for molds. This flexibility helps to customize new models and colors to the molds, this helps the clients to have more options according to their requirements and also at affordable prices.
Vacuum forming is the best option to make sterile and food graded materials such as plastic food containers and medical equipment. These must be kept sterile and free from germs; therefore, vacuum-formed products are best as they can be sterilized and used for a long time.
The vacuum forming method is very quick as it is very scalable. It uses one tool at a time for mold formation, but a large variety of tools can be used for different molds, thus creating a large volume of products with different looks.
Vacuum forming is known for its consistency. So if we use the same mold for the same product, it is sure to get the same result all the time. If a problem arises with the mold formation, then it can be changed if the plastic is mishandled during this process.
Vacuum forming is also known for its robustness. Of course, some plastic materials are sensitive to others, but some are tough enough to cope with any resistance.
Some disadvantages may be when choosing to use vacuum forming is that it is only feasible with the plastic material with thin walls and consistency. It is unsuitable if the material walls are thick and difficult to mold. The second disadvantage of vacuum forming is the deep and concave parts of the materials are difficult to mold using this technique. In addition, vacuum forming is suitable for small-scale production, but it doesn't work well when there is a large production needed at an industrial scale.
Thermoplastics and thermoset plastics are polymers that have differing behavior when exposed to heat. When thermoplastics are exposed to heat, they melt after curing. In contrast, thermoset plastics retain their form and shape when exposed to heat and stay in a solid, rigid configuration. This difference between the materials is a major factor in their life span and use.
Since thermoplastics easily melt when exposed to heat, they are used for applications where materials can be recycled. Thermosets are polymers that undergo a chemical reaction when heated that creates a three-dimensional network of bonded molecules. The process is irreversible, guaranteeing a thermoset will keep its shape and cannot be melted. The result is a hard, solid, strong plastic that is resistant to heat and chemicals. The term thermoset is indicative of the physical permanence and chemical composition of thermoset plastics with the key word being “set”, meaning the plastic cannot be changed.
The key to the differentiation between the plastics is their curing process. Thermosets form strong chemical bonds during curing, which makes them impossible to remold. Thermoplastics do not form chemical bonds during curing, a factor that makes them re-moldable and recyclable. The three-dimensional bonds formed in the curing of thermoset plastics is the reason for their strength and heat resistance, which is not present in the curing of thermoplastics.
| Fundamental Differences Between Thermoplastic Molding and Thermoset Molding | |
|---|---|
| Thermosets | Thermoplastics |
| The material is injected into a hot mold in a cold state | The plastic is melted and injected into a mold |
| Non-remoldable and non-recyclable | Remoldable and recyclable |
| Creates a permanent chemical bond | Fully reversible as there's no chemical bonding |
| Surface finishing is relatively challenging | Provides accurate and aesthetically pleasing surfaces |
| Less heat and pressure requirements | Requires significant heat and pressure |
| Produced through condensation polymerization | Formed by additional polymerization |
| Includes compression, transfer, and casting processes | Involves injection, extrusion, and blow molding processes |
| Common products: tool handles, billiard balls, insulation, computer and TV parts, various electronic and gardening equipment, sprockets, and cooking tools | Common products: vacuum cleaners, toys, machine screws, gear wheels, kettles, packaging films, sacks, power tool housings, toasters, gas lines, and connections |
| Drawbacks include inability to recycle and emission of VOCs | Drawbacks are costliness, ease of melting, and difficulty in prototyping |
As can be determined from the characteristics of the two plastics, thermoplastics are easy to recycle and can be melted and reused multiple times. Existing parts and components can be ground to granules and melted to make new parts. Thermoplastics can be manipulated in several ways, such as adding new thermoplastic resin to old ground up resin to produce new components. The reuse of thermoplastics is a necessity since it takes several decades for the plastic to decompose. Many sustainability programs emphasize the need to reuse and repurpose thermoplastics.
The crosslinked bonds of thermoset plastics prevent the plastics from being melted, reformed, and reused. The molecular structure of thermoset plastics gives them a long useful life but prevents them from being restructured and reused. The solid structure of thermoset plastics enhances their damage to the environment. Like thermoplastics, it takes many decades for thermoset plastics to decompose. They can languish in a trash dump and never change their form or shape.
The cost factor for the plastics relates to their recyclability. The manufacture of thermosets requires special tooling as well as fillers and additives that are necessary to complete the crosslinking. This aspect of the process affects the cost of thermosets and makes them more expensive. Although this can also be true of thermoplastics, the recyclability of thermoplastics has a distinctive effect on their cost.
As with many aspects of manufacturing, the cost factors for thermosets and thermoplastics are not necessarily black and white. Although the thermoset process is slow and time consuming, the material difference between the plastics can range from $0.90 per pound up to $10 per pound. This contrast is generated by the different properties of the plastics. In most cases, engineers choose between the plastics based on their properties, appropriateness for an application, and their functionality without regard to cost.
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...