Thermoforming

The term “thermoforming” refers to a manufacturing process during which plastic materials are made to form parts through heating, stretching and cooling. It yields medium to large scale results quickly, frequently producing uniform parts within seconds of each other.

Quick links to Thermoforming Information

• Advantages of Thermoforming
• Process of Thermoforming
• Types of Thermoforming

Advantages of Thermoforming

Thermoforming is a fairly inexpensive procedure, used to the benefit of industries including: cosmetics, sports and recreation, food processing, healthcare, entertainment, electronics, appliance, textile, toy and office supply. Thermoforming is valued in packaging and shipping in particular, because it allows them to quickly and economically receive products they rely on, like shrink wrap, bins, clamshells and blister packs.

Process of Thermoforming

The basic thermoforming process is carried out as follows: First, thermoplastic film or sheet is fed into a heating device; to raise the temperature of the plastic, the heater harnesses the power of either infrared radiation, natural gas or electricity. The plastic remains in the heater until it becomes pliable and soft. The time it takes and the temperature selected for this to happen depends on the properties of the plastic being used. Regardless, once pliable, the plastic is moved over to the form station, where it is stretched over a temperature-controlled surface known as a buck or a mold.

At this point, the technique used to solidify the form varies. Most often, manufacturers use a method called vacuum forming. During vacuum forming, a vacuum suctions the air between the plastic and the mold, forcing them together. Another common method of adherence-securing is pressure forming.

During pressure forming, pressurized air pushes the plastic into the mold. Of the two, pressure forming yields the best level of adherence and is preferred for detail-heavy applications. Another option is twin sheet thermoforming, which combines and seals two thermoplastic sheets together with a seam around their edges to form one uniform part.

Finally, drape forming involves draping the heated plastic over the mold in order to create parts with a gradual bend. After this step, the thermoforming process once again becomes fairly standard: the part is dried, allowed to cool, cured and ejected. If it needs it, it can then be trimmed via CNC machining, drilling, cutting or hand routing. Once this is done, it may undergo secondary processes like hot stamping or printing.

Types of Thermoforming

Generally speaking, thermoforming can be divided into two categories:

Thin-Gauge

Thin-gauge thermoforming and heavy-gauge, or thick, thermoforming. Those sheets that are less than .06 inches (1.5 mm) thick are formed by thin-gauge thermoforming procedures, while sheets that exceed .12 inches (3 mm) in thickness are formed via heavy-gauge thermoforming. Common thin-gauge products include disposable or recyclable items like food containers, lids, trays, cups and the aforementioned blisters and clamshells. Heavy-gauge thermoforming, on the other hand, yields more permanent products like cosmetic surfaces of refrigerators, kiosks, spas, cars and trucks, electronic equipment and more.

Other Materials Used

The list of plastics that manufacturers may use during thermoforming is quite varied. It consists of many thermoplastics, such as acrylic, crystalline polyester, low density polyethylene (LDPE), polystyrene, polyvinyl chloride (PVC) and polypropylene, as well as semi-gloss polymers and other plastics that exhibit qualities of moisture resistance, rigidity and durability. Manufacturers will select which one or ones to use for an application based on their qualities and how they match up with the needs of that application. Before proceeding with the process, they must also decide on clamping force, depth of draw, air pressure, machine dimensions and thickness.

Chapter 1: What is Thermoforming?

Thermoforming is a plastic manufacturing process that uses pressure or the force of a vacuum to stretch thermoplastic material over a mold to create a three-dimensional shape, part, configuration, or other form of plastic product. Cups, containers, lids, trays, and clamshells are formed by thermoforming using thin sheets of thermoplastic, while thicker sheets of thermoplastic are used to produce car doors and dash panels, refrigerator liners, and plastic pallets.

The two processes used for thermoforming are vacuum forming and pressure forming, which are used to stretch the heated thermoplastic over the surface of the mold. Although the two processes are similar, they have unique properties that make them applicable to fit the needs of a project’s design and must be chosen in accordance with a project’s requirements.

The forming phase of thermoforming happens in a mold cavity when the plastic sheet is drawn by air or vacuum pressure. The mold cavity contains the shape of a single part. The mold tool, sometimes referred to as “tooling”, is a collection of mold cavities.

The steps of thermoforming are simple and straightforward, which makes it suitable for high-volume manufacturing of molded products due to its fast turnaround times. Thermoplastic sheets, are continuously fed into the heating chamber and formed into the desired shape. For the thermoforming of larger parts, the thicker thermoplastic sheets are fed individually. In some operations, an extrusion machine is placed upstream of the thermoforming machine. Certain set-ups are designed to produce multiple parts with each stroke of the press using molds with several cavities.

Chapter 2: Thick (Heavy) Gauge and Thin Gauge Thermoforming

The part thickness determines the gauge of thermoplastic that is used for the manufacturing process. The different thicknesses require machinery and techniques applicable to fit the material’s thickness. A wide variety of materials are used in the thermoforming process and require that designers are aware of the characteristics of the various materials in order to provide the highest quality, timing, performance, and reliability of the end product.

• Thick Gauge or Heavy-Gauge Therforming

  Thick or heavy-gauge thermoforming produces parts from 0.060″ – 0.500″ (1.5 – 12.7 mm) thickness. Cut sheets of thermoplastics are the starting material, which is heated in an oven. Heavy gauge thermoplastics are used to create thicker and more durable parts that have permanent end-applications. The products produced using heavy gauge thermoplastic are lighter and have superior impact resistance.

  The higher gauge of thick thermoplastics makes it possible to produce complex and intricate parts that have smoother shapes with exceptionally attractive appearance. Additionally, the thermoplastic can be colored to match the requirements of a product or application. Some of the positive properties of thick gauge thermoplastics include ultraviolet (UV) protection, flame retardance, electrical conductivity, and solvent resistance. As with thin grade thermoplastics, thick grade thermoplastics can be manufactured from FDA-approved materials.

• Thin Gauge & Thermoforming

  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 Thermoforming Grade is a thin polypropylene (PP) that has been approved for food packaging due to its resistance to chemicals. It is 60% the density of PVC film. PP meets the safety standards that specify that the material, when it degrades, will not be a threat to human health.

Chapter 3: Thermoforming Process

The thermoforming process takes a sheet of thermoplastic, carefully heats it until it is sufficiently pliable, places it over a forming mold that forms it into a three-dimensional shape, and completes the process by trimming and finishing it into the desired shape of the product. It is a simple process that is quick, efficient, time-saving, and highly productive.

Regardless of the simplicity of thermoforming, each step of the process has to be completed with precision and accuracy in order to produce quality parts and products. Any errors can lead to deformed, damaged, and useless sheets of plastic.

Heating 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.

Forming temperature vary depending on the type of thermoplastic being used, the application for the finished part, and the forming technique. This is one of the most important operating parameters in thermoforming to meet certain quality standards. Take note that the true forming temperature of a sheet is its core temperature, not its surface temperature. Hence, it is important to calculate heat transfer across the sheet.

When it comes to the variation of temperature across the sheet, the 10-10-5 rule must be met. The first 10 applies to the 10 locations on the sheets, which includes both sides of the sheet, each of its four corners, and the middle of the four sides. The next 10 refers to the allowable variance of 10°F (-12.2 ° C) in the 10 locations. Five refers to the temperature on both sides of the sheet in each of the 10 locations with an allowable variance of 5°F (-15°C). The 10-10-5 rule applies to heating, forming, and cooling to achieve optimal thermoforming.

Forming Plastic Sheets in Mold Cavities:

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).

The mold tool may be a positive or a negative tool, depending on its form:

• Positive Tool

  Positive Tool, or “male mold” is convex-shaped – the heated plastic sheet is positioned above the convex tool. The “humped surface”, or the convex surface, will now give the plastic sheet its final shape. The exterior surface of a positive mold tool will give the shape of the inner surface of the part.

• Negative Tool

  Negative Tool, or “female mold”, on the other hand, is concave-shaped – the interior surface contour of a negative mold tool will give the shape of the outer surface of the part.

After forming, the plastic containing the new shape solidifies by cooling using air circulation or liquid cooling systems. The tool material used significantly affects the cooling cycle, thus also affecting the quality of the parts.

Additional shaping steps are involved, with thick gauge thermoforming, such as drilling, cutting, or finishing.

Trimming Formed Sheets:

The sheet containing the formed parts goes through a trim station or five-axis CNC router, where a die, abrasive wheel, or circular saw cuts the parts to separate them from the sheet web. The trimmings are recycled and reprocessed to form other parts.

Chapter 4: Types of Molds

The mold cavity to be used in the forming step is carefully designed by the manufacturer to create the required profile of the finished product, depending on the customer needs or end-user application. Initial stages in the development of a mold tool involve detailed drawings in the CAD software and CNC program to realize the desired patterns. Some of the materials used to create the mold tool are the following.

• Tooling with Wood:

  An inexpensive type of tooling material, wood can be shaped fairly easily; hence, the manufacturer can readily make complex designs or make changes to the details of the part. However, it poses many disadvantages: uneven and lengthy cooling (since wood is an insulator), moisture which can cause voids and potential transfer of wood grains to the part. Tooling made from wood is commonly used to produce prototypes and patterns for a production mold.

• Tooling with Fiberglass:

  As with tooling from wood, fiberglass is an economical, permanent mold tool if a manufacturer only produces lower volume parts. However, the cooling cycle is two to three times longer than a temperature-controlled mold.

• Tooling Aluminum:

  Aluminum provides excellent temperature control, which leads to shorter cycle times and excellent quality parts:

  • Cast Aluminum

    Cast Aluminum tools are derived from a machined pattern.

  • Fabricated Aluminum

    Fabricated Aluminum tools are made from a single or multiple aluminum blocks that are honed and cut to produce the mold. The fabricated tool is costly but more accurate in terms of dimensions, and the manufacturer can make more complex designs.

Chapter 5: Thermoforming Methods

The following are description of two common forming methods, vacuum and pressure forming.

Vacuum Forming:

With vacuum forming a vacuum is generated underneath the sheet to draw the plastic sheet against the mold cavity until it takes its desired shape. Vacuum forming is the simplest of all thermoforming methods. However, part thickness distribution is difficult to control. Vacuum pressure should be uniform and sufficient throughout the mold.

Pressure Forming:

Similar to the vacuum forming method, air pressure is utilized together with the vacuum applied under the cavity to push the plastic sheet. The added air pressure creates greater detail (e.g. textured surfaces, undercuts, and sharp corners) on the finished product; that is not easily created by vacuum forming, making this method suitable for products with complex designs.

Matched Mold Forming:

Matched mold thermoforming is where the heated thermoplastic sheet is shaped by a male and female mold, which can be made of metal, plaster, wood, or epoxy resin. When the halves of the mold are closed, they distort the sheet of thermoplastic to take the shape of the halves of the mold. As the mold closes, excess air is removed to form a tight seal by the application of a vacuum. The walls from matched mold forming are more uniform and adhere closely to design tolerances. The process allows for exceptional dimensional control and offers the ability to create intricate and complex shapes.

Twin Sheet Forming:

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.

Chapter 6: Materials Used in Thermoforming

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.

A forming temperature is any point located above the glass transition temperature and below its melting temperature. When the temperature of a thermoplastic is increased gradually, the intermolecular forces in the polymeric chains are also weakened gradually, until it reaches the glass transition temperature. Above the glass transition temperature, the once rigid and brittle solid is turned into a soft and pliable rubber-like material.

Thermoplastics are grouped into either amorphous or semi-crystalline structures.

Amorphous Thermoplastics:

These materials have a random molecular structure and have a wide range of softening temperatures. Some advantages of amorphous thermoplastics they have good dimensional stability, higher impact resistance, bond well with adhesives, and are easier to thermoform than semi-crystalline thermoplastics. However, they have poor fatigue resistance and are prone to stress cracking. Some of the amorphous thermoplastics are polycarbonate, acrylic and high-impact polystyrene.

Semi-crystalline Thermoplastics:

These exhibit an organized lattice at a temperature lower than its melting point. This type is known for its excellent wear and bearing resistance, making it ideal for structural applications and durable plastic parts. This type is also known for its better chemical resistance and insulation properties. Some disadvantages of this type: they are difficult to thermoform and/or bond with other formed parts, and they only have average impact resistance. Examples of semi-crystalline thermoplastics are polyethylene, polypropylene, and nylon.

There are many thermoplastics suitable for thermoforming. The table below presents the most notable:

Chapter 7: Problems and Quality Issues Encountered During Thermoforming

The key to successful thermoforming is proper tool management and design. In order to prevent contamination-related defects, all materials and tooling should be kept and uniform temperature and should be free from moisture and plastic buildup.

Parameters that need to be optimized and controlled in every thermoforming process are the following:

• Forming temperature
• Mold tool temperature
• Vacuum and/or air pressure
• Liquid or air coolant flow rate and temperature

Note:

1. When adjusting the forming temperature, ensure that it is still between the forming and the melting temperatures.
2. Part thickness distribution may be improved through pre-forming of the plastic sheet before it is drawn to the mold cavity.

Chapter 8: Pros and Cons of Thermoforming

The goal of thermoforming is to take a warm sheet of plastic and place it in or on a mold such that it takes on the desired form. Even though the process is simple and efficient, it produces highly durable and resilient products that are easily disposable and recyclable or long-lasting. From its beginning as an answer for aircraft design, thermoforming has rapidly grown to be a cultural phenomenon that provides convenience and superior quality.

Benefits of Thermoforming

Low Cost:Large parts are normally used in larger assemblies and products. Although they can be produced using other forming methods, thermoforming is capable of producing large parts at half the cost and in less time than any other plastic production method. From car door panels and instrument panels to tail lights and consoles, thermoforming can complete the job quicker, easier, and at less expense.

Durability:A key to modern production is the ability of products to last and endure the harsh and rugged treatment they receive. One of the main factors in customer satisfaction is how long a product will last and is a main marketing point. Heavy gauge thermoforming produces large, th

Tooling Costs:Thermoform molds are easily engineered using 3D printing or computer aided design (CAD). They are made from silicone, fiberglass, or other materials and do not require grinding, machining, or other forms of tooling. The creation of a metal mold is expensive, time consuming, and labor intensive. It requires highly experienced professionals with the proper skills.

Thermoforming molds are produced and placed in production on the same day. The materials are far less expensive than the steel and iron required for other molds but produce the same kind of high quality products.

Development:Thermoforming uses tools made from wood or epoxy. The tools for thermoforming can be used to create an assortment of finished parts that represent the initial design. Prototypes are formed from the same materials as those used for the final product, allowing for the identification of design flaws or issues before approving production tooling.

Design:Thermoforming has very few limitations in regard to designs regardless of the intricacies, details, or size of a part’s design. This aspect of thermoforming is one of the main reasons for its popularity, especially in automobile design where the weight of components is a major concern.

Disadvantages

• Individual part costs can be higher than injection molding.
• Molded-in components, such as screws, fasteners, and clips, cannot be included.
• With any geometry, the front side will be the same as the back side.
• Part thickness can be an issue and may not be even across all surfaces of a part.
• All forms of thermoforming produce a great deal of waste, which can be recycled.

Conclusion:

• Thermoforming is the process of heating thermoplastics to their forming temperature and drawing them over a mold cavity wherein, they take on three-dimensional characteristics. Thermoforming has a wide range of applications.
• Thermoforming is grouped into two categories depending on the sheet thickness of the formed part: thick gauge thermoforming (0.060″ – 0.500″) – (1.5 – 12.7 mm) and thin gauge thermoforming (less than 0.060″).
• The first step in the thermoforming process is heating of a plastic sheet to its forming temperature.
• Forming stages give the three-dimensional characteristics (length, width, and height) to the once flat sheet. Forming methods may be vacuum forming, pressure forming, mechanical mold forming, and twin sheet forming. Afterwards, formed parts are trimmed from the sheet web.
• Thermoplastics in the form of sheets are the starting material of the thermoforming process. These plastics can survive cycles of heating and cooling, allowing them to be recycled. Thermoplastics may be amorphous or semi-crystalline.
• The forming temperature is the temperature above the glass transition and below the melting temperature.
• The mold may be a positive or negative tool, and its material significantly affects the heat transfer across the sheet.
• The parameters to be optimized and controlled are forming temperature, mold tool temperature, vacuum and/or air pressure, and liquid and/or air coolant temperature.
• Proper tool management and temperature control is the key to successful thermoforming.

Vacuum Forming Industry Information

Chapter 1: What Is Vacuum Forming?

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:

• Male or positive mold
• Female or negative mold

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.

Difference between Thermoforming, Vacuum Forming and Pressure Forming

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:

• Vacuum forming
• Pressure forming

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

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:

• Lower tooling costs about 20-30% less than other processes.
• It is allowed for an enclosed cavity.
• The products made from twin sheet thermoforming are more rigid and stable than thin-walled thermoforming.
• This process can include internal reinforcements.

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.

Materials Used In Vacuum Forming

Vacuum forming can be done on a variety of thermoplastics, but typically the materials that are used in vacuum forming are as follows:

Materials Used In Vacuum Forming

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)

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)

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)

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 (PVC)

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 (PE)

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.

Polyester Copolymer PETG

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

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

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.

Chapter 2: Machines Used In Vacuum Forming

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 Machine

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.

Table Top Machine

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.

Single Heater Machine

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.

Double Heater Machine

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.

Process of Vacuum Forming

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.

Clamping

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.

Heating

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 Level (Auto-Level)

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.

Pre-Stretch (Bubble)

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.

Plug Assist

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.

Vacuum

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.

Cooling and Release

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.

Trimming and Finishing

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.

Chapter 3: Types of Products Made from Vacuum Forming

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.

Medical Equipment

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:

Thermoformed Trays:

• Belly Pans
• Blister Packs
• Carts
• Clamshells
• Guards
• Heating Pad
• Hoods
• Skid Plates
• Vacuum Formed Trays
• Windshields

Electronic Appliances

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.

Lawn and Garden Equipment

The vacuum forming technique also makes lawn and garden products such as mower covers, guards, trailers, and fenders.

• Guards and Trailers
• Sign Holders

Packaging and Displays

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.

• Custom Acrylic Display
• Food Storage Containers
• Trade Show Display

Plastic Food Containers and Trays

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.

• Plastic Packaging
• Plastic Trays
• Refrigerator Door Liners

Utility Vehicles

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.

• Fenders
• Lawn Mower

Chapter 4: Pros and Cons of Vacuum Forming

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:

Pros of Vacuum Forming

Affordability

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

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.

Flexibility

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.

Sterile and Food Grade Materials

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.

Volume

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.

Consistency

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.

Robustness

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.

Cons of Vacuum Forming

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.

Conclusion

• Vacuum forming is an ancient technique that is used for manufacturing plastic products.
• It is the simplest form of thermoforming process which uses vacuum suction pumps for work.
• It has two types of molds: male mold and female mold.
• The vacuum forming process has the following steps for manufacturing
• plastic materials, clamping, heating, sheet level, pre-stretch, plug assist, vacuum, cooling, trimming, and finishing.
• Plastic materials are used for this process, such as polycarbonate, polyethylene, acrylic PMMA, PVC, etc.
• Four types of machines are there for the vacuum forming process. DIY machine, tabletop machine, single heater machine, and double heater machine.
• The vacuum forming process is used widely in medical, automobiles, food packaging, and household items.
• Vacuum forming is a good choice for making products at a small scale because it is flexible, time-saving, economical, and consistent.
• Limitation of the vacuum forming process is because of ethical use of plastic, used for only smaller-scale production, for thin-walled material only.