Thermoforming Industry Information
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 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.
Diving Deeper – An Introduction To Thermoforming
This article presents all the information you need to know about thermoforming. Topics discussed are:
- What is Thermoforming?
- Thick and Thin Gauge Thermoforming
- Thermoforming Process
- Types of Molds
- Thermoforming Methods
- Materials Used in Thermoforming
- Problems and Quality Issues Encountered During Thermoforming
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, 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, 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.
Aluminum provides excellent temperature control, which leads to shorter cycle times and excellent quality parts:
Cast Aluminum tools are derived from a machined pattern.
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.
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.
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.
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.
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:
|Acrylonitrile butadiene styrene (ABS)
|ABS is a combination of acrylonitrile, butadiene, and styrene polymers. It is an opaque, lightweight, and sturdy material. ABS is resistant to a wide range of temperatures -4°F to 176°F (-20°C to 80 ° C), allowing this material to be molded at high or low temperatures. ABS is safe under normal handling conditions.
|High Impact Polystyrene (HIPS)
|HIPS is modified homopolymer polystyrene combined with 5-10% rubber or butadiene copolymer. This modification results in increased toughness and impact strength, as polystyrene alone can be brittle. HIPS is easy and cost-effective. Also, the finishing of HIPS also can be customized aesthetically, making it a good packaging material.
|High Density Polyethylene (HDPE)
|HDPE is a petroleum-based polymer notable for its rigidity and high strength-to-density ratio. HDPE has excellent resistance to chemicals, moisture, and most solvents. Hence, it is ideal to use this material for packaging products with short shelf-life and industrial and household chemicals.
|Polyvinyl Chloride (PVC)
|PVC film is created from suspension polymerization. PVC is the preferred material in the construction industry due to its excellent resistance to grease, fire, impact, and extreme environmental conditions. PVC is also a good electrical insulator. Modifiers alter the physical and chemical properties of this material. Plasticizers are added to PVC before molding to make it more pliable. Chlorination of PVC involves the addition of chlorine atoms which are added to the polymer backbone to increase its resistance to chemical stability and insulation properties.
|Polyethylene Terephthalate (PET)
|PET is a colorless and flexible plastic; PET is chemically stable and has low gas permeability, especially with carbon dioxide and oxygen. Due to its lightweight, this material is efficient to transport. PET is one of the most recycled plastics that is also transparent to microwave radiation. After forming PET, drying must be done to increase its resistance.
|PC is tough, has high impact strength, and is dimensionally stable. It also has good electrical insulation properties. However, it has low fatigue endurance. PC has good chemical resistance, except from alkalis, aromatics, and hydrocarbons. PCs start to degrade from exposure over 140 ° F (60 ° C). PCs are highly transparent plastics. It can transmit 90% of light as well as glass and can be customized using different shades. It also offers excellent optical properties.
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
|Blisters or bubble formation
|Voids on the inner plastic layer.
|Webbing, or unwanted folds and wrinkles, occurs when the plastic folds onto itself. During the vacuum molding process, the thermoplastic stretches in a way that was not planned.
|Part thickness inconsistency
|Overall thickness of the formed part is not uniform. This is primarily caused by uneven distribution of the plastic sheet. In the design of the part itself, thickness is difficult to control at the edges.
|White or opaque wavy marks on the formed part.
|Mold tool temperature is too low, causing the plastic sheet to freeze onto the mold when in contact.
|Adjust mold tool temperature.
|Distorted, deformed overall shape of the formed part.
|Part produced not conforming to the required dimensions
- When adjusting the forming temperature, ensure that it is still between the forming and the melting temperatures.
- 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.
- 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.
- 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
Vacuum forming is a simplified form of thermoforming. A sheet of plastic is heated to a vacuum form temperature and shaped to a mold. It is then stretched onto the surface of the mold using a vacuum. The sheet of plastic is then allowed to cool down and ejected from the mold using the reverse pressure. This is used for transformation of plastics into different objects.
For easier removal of the formed plastic from the mold, draft angles are incorporated in the design of the mold. Mechanically or pneumatically stretching the formable sheets before applying the vacuum enables the depth of parts being formed to be adjusted accordingly. Conventionally, the suitable materials used in vacuum forming are thermoplastics.
Quick links to Vacuum Forming Information
- History of the Vacuum Forming Process
- Benefits of Vacuum Forming
- Steps of the Vacuum Forming Process
- Vacuum Forming Types
- Materials Used in Vacuum Forming
- Applications of Vacuum Forming
- Industries That Use Vacuum Forming
- Customization in Vacuum Forming
- Choosing the Right Manufacturer
- Vacuum Forming Terms
History of the Vacuum Forming Process
In the 1860’s John Wesley Hyatt discovered the process of making celluloid, the first artificial plastic. Together with his brother, they patented this plastic and discovered that it could be heated in molds to form different shapes such as sheets and rods.
Centuries earlier however, the Romans would import tortoise shells which contain keratin from the Orient. They would use hot oil to shape this material into different food utensils. It can therefore be argued that it was the Romans who discovered thermoforming because they began heat forming.
In the 20th century, the heating of plastics and forming over a mold evolved to become the thermoforming as known today. Through the 1940s and 1950s, vacuum formed plastics were first conceived as display and marketing tools that were developed from vacuum casting and molding technologies. In 1950, a machine for making articles from thin sheets of plastic was patented.
In 1964, a machine for plastic sheet vacuum forming was perfected and patented. These vacuum forming machines and thermoplastics used an older concept whereby vacuums in different forms of casting and molding were used to remove excess air. By the 1970s, the technology was being advanced and perfected towards the methods we have currently.
Benefits of Vacuum Forming
The popularity of vacuum form can be explained by its advantages. Products formed through the vacuum forming process are precise to their design specification. The one heated sheet allows for exactness of the specified design, a desirable feature for products designed to fit with each other.
The plastic vacuum forming is cost effective because the materials used are inexpensive, low pressures are required and the tools are less intricate. Certain items can be produced with a single sheet of plastic reducing the quantity’s cost. Recycling of already used plastic further contributes to cost saving.
The vacuum form process is versatile and flexible allowing creation of unique products and shapes. The quicker turnaround time is attractive for business because time can be invested somewhere else to perfect the operations and profits.
Steps of the Vacuum Forming Process
The process consists of placing a plastic sheet in its cold state into the forming clamp area. A heat element is used here to the desired temperature such that the plastic can be formed. A mold is raised from below to form different products with the hot plastic. Trapped air is removed by use of the vacuum system. Cooling follows with a reverse air supply being activated for the release of the plastic from the mold. This process comprises seven main steps: clamping, heating, sheet level, pre-stretch, vacuum, plug assist and cooling and release.
- It is essential that the frame used is sufficiently powerful in order to hold plastic sheets firmly during the process. The frame should be able to handle the thickest plastics that will be formed on the vacuum form machine.
- Typically, the heaters used in this process are infrared elements placed in an aluminum plate. Regardless of the materials used, the best vacuum form results are obtained: the plastic sheet is heated uniformly throughout its thickness and the surface area. Quartz heaters are used in the more sophisticated processes. They have a lesser thermal mass, and thus enable a faster response time.
- The heating process utilizes pyrometers which provide accurate control of the heating temperatures. They sense the melting temperature of the materials being heated and interact with the control of the operating process. Pyrometers work together with a computerized system that provides precise temperature readouts.
- Sheet Level
- This is the third step in the vacuum form process although it is not found in all machines. It utilizes a photo-electric beam that scans between the bottom heater and the plastic sheet being heated. This is used to determine whether the plastic sags down to break the beam. If it does, a small volume of air is injected to lift the sheet and stop the sagging.
- Pre-Stretch (Bubble)
- It is the fourth step and also unavailable in some machines. Pre-stretching is carried out once the plastic reaches the vacuum form temperature (plastic state). This ensures that there is an even wall thickness once the vacuum is applied. The method used to control the bubble height should ensure consistent results are obtained.
- The actual vacuum is applied at this step. After pre-stretching the materials, a vacuum is applied to aid in the formation of the sheet. The air trapped in between the mold and the plastic sheet is removed by a vacuum pump. The vacuum pumps used must maintain a differential pressure of about 27mm of mercury. With a larger thermoform machine, vacuum reservoirs are used together with large volume vacuum pumps. This process allows for a two stage application of vacuum, hence rapid molding the heated materials.
- Plug Assisted Vacuum Forming
- It is the step that follows the application of the vacuum especially when the straight vacuum forming does not distribute a plastic sheet evenly over the mold. It is not available in some machines. The plug pushes the plastic sheet into the mold before application of the vacuum to make it spread more evenly. This enables the materials to reach to the bottom of the mold preventing them from thinning out.
- Cooling and Release
- This is the last step in a vacuum form process. Upon forming, the plastic is allowed to cool before it is released. When the release is done too early, deformation of the mold occurs resulting in a rejected product. The cooling process is made more rapid by fitting and activating fans and mist sprays once the product is formed. The cooling temperatures are controlled to ensure a uniform cooling and release of the formed parts.
- Finally, trimming and finishing is carried out whereby excess materials are removed. Finishing also involves processes such as drilling of holes, cutouts and slots as well as decoration, printing, strengthening and assembly.
Vacuum Forming Types
- Blister Packs
- Clear plastic, non resealable packaging used for products that could be tampered with.
- Plastic packages that have hinges to open and close like a clam’s shell.
- Drape Vacuum Forming
- Like snapback forming except that the thermoplastic sheet is stretched to the base of the mold. In both cases, the use of air to stretch the material prior to vacuum sealing and application to the mold permits the material to thin uniformly.
- Plastic Covers
- Vacuum formed plastics designed to secure, contain and protect objects from environmental conditions such as weather, lighting, dust, water or other debris.
- Plastic Forming
- A group of manufacturing procedures that take thermoplastics and form them through molding processes into a wide variety of plastic products for numerous industrial, commercial and domestic applications.
- Plastic Packaging
- Encompasses all storage or containment devices produced through the manipulation of any number of polymer resins.
- Plastic Trays
- Shallow platforms with raised edges intended to stop contents from sliding or rolling off of the surface.
- Plug Forming
- A thermoforming procedure that uses a plug or male mold to press the heated thermoplastic material into the female mold prior to the application of a vacuum. This method helps uniformly distribute the sheet.
- Pressure Forming
- A thermoforming procedure that involves applying pressure to the top of the plastic sheeting while the vacuum force pulls downward. Pressure forming is done through air pressure or mechanical means, and provides greater precision because the plastic is able to attain a greater definition of shape in the mold.
- Snapback Vacuum Forming
- The process of pre-stretching the sheet material with a vacuum box. A partial vacuum is then applied to the box, just enough for the necessary stretching, and the mold is pushed into the material where the box is vented to atmospheric pressure that draws on a vacuum.
- Straight Vacuum Forming
- Vacuum thermoforming using only female molds that produce a material distribution that is the opposite of the results obtained from male molds.
- Involves heating and stretching plastics.
- Twin Sheet Thermoforming
- A plastic processing technique involving vacuum forming two separate plastic sheets simultaneously before welding them together to create a hollow part or product.
- Vacuum Formed Plastics
- Created by a thermoforming process that uses a vacuum to suck the plastic sheet into a mold.
- Vacuum Molding
- A type of manufacturing method that takes thermoplastics and forms them through a molding process into a wide variety of plastic products.
- Vacuum Packaging
- Can refer to both those items held or displayed in reduced oxygen containers and any and all packaging materials produced through vacuum forming.
Materials Used in Vacuum Forming
A wide range of materials are used in the process of vacuum forming. The desirable properties of a thermoplastic material for this process include low forming temperatures, good flow, thermal strength, low shrinkage upon cooling and high impact strength.
The most common materials used for a vacuum form include polyester (PET), polyvinyl chloride (PVC), high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polycarbonate, acrylonitrile butadiene styrene (ABS), acrylics, and Kydex, a PVC-based thermoplastic.
With polyester, a vacuum form is easily attained at low temperatures. It is characterized by fast cycles and excellent fabricating performance. Its major use is in the production of packaging materials such as food containers, beverage containers and packages for processed meat. With PVC, food wrappers, blister packaging and vegetable oil bottles are produced. PVC is strong, tough and has good transparency and chemical resistance.
Although high density polyethylene (HDPE) can be difficult to form, it has a significant application in the production of milk bottles, cereal box liners, plastic bags and margarine tubes. Just like HDPE, low density polyethylene (LDPE) forms poorly as well. Once formed, it is suitable for production of garment bags, squeezable food bottles, plastic bags and shrink wraps.
Polystyrene is one of the most commonly used thermoplastics in a vacuum form. It forms easily at significantly low temperatures hence fast cycle times and no pre-drying requirement. High impact polystyrene is tough and inexpensive. However, it has a poor UV resistance hence not suitable for outdoor use. Its major application is in production of fast food trays, disposable plastic silverware, egg cartons and compact disc jackets.
Acrylonitrile butadiene styrene (ABS) is a hard, rigid, adequately weather resistant material with a satisfactory impact strength. It contains a bit of rubber contents which give it improved impact resistance. ABS is applied for luggage, vehicle parts, sanitary parts and electrical enclosures. The desirable features of acrylic are its hardness, high quality thermoplastic and good clarity. Some signs, baths, sanitary ware and roof lights are made using acrylic.
Applications of Vacuum Forming
The main purpose of a vacuum form is the formation of different objects from plastics. Some permanent objects produced in this process are protective covers and turnpike signs. The process produces a large variety of products ranging from simple packaging elements to extreme impact aircraft cockpit covers.
The versatility of a vacuum former promotes its widespread application in different industries. Numerous thermoplastic materials can be transformed into different objects and shapes using the vacuum form process. Transparent materials such as acrylic are also appropriate for vacuum forming and are widely used in aerospace as passenger cabin windows. It is a low level technology that provides an easy way to mold.
Industries That Use Vacuum Forming
A range of industries utilize the vacuum form to come up with different products as discussed here.
Aeronautical manufacturers apply a vacuum thermoform to produce interior trim panels, covers and cowlings. The interior sections of NASA space shuttles are made using a thermoform machine.
A wide range of products from agricultural suppliers are manufactured from plastic materials that undergo vacuum forming. A few examples include animal containers, agricultural machine parts, flower tubs, seed trays and clear growing domes among others.
With pharmaceutical manufacturers, a vacuum thermoform is applied when producing blister packs. The cavities on a blister pack are made from a sheet of plastic by using a heating element. The cavities are then covered using a seal of another plastic or aluminum foil to protect and deliver unit doses of capsules, tablets and lozenges.
Building and construction industries utilize a vacuum form in the manufacture of various parts such as PVC door panels, molds for concrete paving, molded ceiling features, drainpipes, roof lights and internal door liners. Fireplaces, porches as well as other parts utilize vacuum forming products.
The automotive and vehicular industries highly rely on vacuum forming for many vehicle parts including wheel hub covers, bumpers, mudguards, liners, seat backs, storage racks, ski-boxes, door interiors, windshields, protective panels, batteries and other electronic housings.
Hospitals and other medical applications depend on vacuum form for production of prosthesis, pressure masks, radiotherapy masks, parts of wheelchairs and dental castings are made from vacuum forming.
There are other industries that rely on vacuum forming to produce different elements including furniture, packaging materials, bathtubs, shower surrounds, souvenirs, point of sale displays, cosmetic cases and cutlery.
Customization in Vacuum Forming
- Customization Through Design
- The vacuum plastic thermoforming process is similar in most machines. However, several customizations are made to meet particular requirements. For instance, the mold used to form the parts can be a male (protruding) or female (recessed). The parts and articles being formed determine the mold that will be used.
- A pressure form process is quite similar to the vacuum forming only that pressure thermoforming utilizes the vacuum environment together with an additional air pressure that increases tightness of the plastic sheet on the mold. This is used in the creation of very detailed vacuum formed plastics.
- Machinery and Customization
- A specific tooling and machinery is used in the process of vacuum forming. These are used for both the primary production of the parts and secondary customization before they are made ready for the customer. The tools and equipment used depend on the type of product, size, thickness and the quantity needed.
- Trimmers, scalpels and heated knives are used for finishing and trimming the product into the desired specifications. Other machines used for trimming include vertical and horizontal band-saws, roller-presses, guillotine, punch press and hand held power routers. CNC machining companies offer services that are precise in drilling of holes and creation of other customization features on injection molded plastics.
- Customization is done through embossing and engrossing of various marks and texts as specified by the customer.
Choosing the Right Manufacturer
There are many manufacturers in the vacuum forming plastic industry. Any good manufacturer can be found but it is essential for a customer to get the right manufacturer. The right manufacturer ensures that all needs of the client are met. When a custom plastic is needed, the right manufacturer will be able to deliver it.
Vacuum Forming Terms
- Black Points
- The dark particles that appear in plastic film during thermoforming processes because of contamination.
- The characteristic of some plastics of losing their colors when coming into contact with water or certain solvents. Also, this is the undesirable movement of materials to the surface of plastic or into an adjacent material.
- Thermoformed semi-rigid plastic shells, typically made to conform to the shape of the product being packaged.
- A protrusion on a plastic part that adds strength, assists with alignment in assembly and allows for fastenings.
- Burn Holes
- Portions of thermoformed plastic where vacuum and heat produce an opening in weak or thin points.
- A change in the structure of a plastic material.
- The detachment of thermoformed parts, like blisters, from one another for the next phase of the packaging procedure.
- The process of removing static electricity from plastic so that less dust clings to it.
- Die Cutting
- The use of a steel rule to cut finished sheets of blisters or blister cards to create individual pieces.
- Draft Angle
- The degree to which the sidewall of a blister or clamshell is tapered to smooth the progress of the removal from the thermoforming mold and denesting of the blister.
- A technique that creates depressions in a specific pattern on plastic film and sheeting.
- Environmental Stress Cracking
- The tendency of thermoformed plastic to crack under the influences of certain chemicals.
- Female Mold
- A concave mold, referred to as a negative or cavity mold.
- Fold-Over Blister Card
- A blister card that is scored and die cut, permitting entrapment of the blister between the two halves of the card. This supplies a seal between two boards or between a board and a blister flange, especially useful when blister packaging heavy items.
- During vacuum packaging, the chamber is flushed with nitrogen, keeping the plastic from sucking down tightly to fragile products.
- The process of joining two or more plastics together with the application of heat and pressure.
- Male Mold
- A convex mold, referred to as a positive or protruded mold.
- Pock Marks
- The result of inadequate contact of the plastic material with the surface of the mold due to trapped air, moisture on the surface of the mold or low pressure in irregular indentations on the material’s surface.
- A model of an intended part. Prototypes show the final size as well as the design.
- Reprocessed Plastic
- Thermoplastic material derived from industrial plastic scrap from a different processor.
- The flow of heated plastic sheeting in a thermoforming procedure in which molten plastic sheets sag before forming. The distance of the sag is determined by an electric eye and is good for determining the forming readiness of the material.
- Sandwich Heating
- A heating procedure before forming a thermoplastic sheet that involves heating both sides.
- Any plastic material, which is not part of the product, that results from a molding procedure. This material is typically tip scrap and can be reused.
- Sheet Train
- The construction required to create plastic sheeting, consisted of an extruder, die, polish rolls, conveyor, draw rolls, cutter and a stacker.
- Thermal Expansion
- The minute change in length or volume of a material when subjected to heat.
- Two Piece Blister
- A double blister for encapsulating a product for product visibility on two sides.
- An indentation or protrusion that hinders the removal from a mold.
- Unit Dose Packaging
- Medicine blister packaging in terms of single dosages for clarity purposes.
- Vacuum Form Table
- A machine that produces vacuum formed parts and products.
Vacuum Formed Plastic Applications
Using vacuum form processes, manufacturers create a wide variety of vacuum formed plastic parts and products.
Industries that utilize the processes of vacuum forming include: telecommunications, security, cosmetics, automotive, appliance, medical, electronics, sporting goods, and food and beverage, among others.
Diving Deeper – Products Produced from Vacuum Formed Plastics
Common vacuum formed plastic products that commonly feature vacuum formed plastic parts include: bumpers, windshields, car door interiors, wheel hub covers, space shuttle interior trim, agricultural machine parts, seed trays, animal containers, drainpipes, roof lights, pressure masks, shower surrounds, bathtubs, point of purchase displays, dental castings, prosthesis, furniture, wheelchairs, cosmetic trays and cutlery.
In addition, vacuum forming processes are often used in forming plastic packaging, either to preserve the products or to add an aesthetic element. Plastic packaging can fall under three main categories: blister packs, clamshells, and plastic trays.
The first category, blister packs, can be used to define several types of plastic packaging. This type of packaging is used in the pharmaceutical industry for unit-dose packaging for capsules and tablets. Blister packs can provide protection and resistance to tampering, which can fulfill shelf life requirements for some applications.
Clamshell packs can greatly differ from blister packs. One difference is that clamshells refer to a specific design of container. A clamshell consists of two halves of a plastic shell which are connected by a hinge and encapsulates an item. Clamshell packaging is specifically designed to hold items securely, and are thus made more difficult to open by hand. Some clamshell containers require tools such as a knife or a pair of scissors to open.
Plastic trays are also known as blister trays, are containers that are shallow, have slightly raised edges, and are shaped like a flat sheet. Plastic storage trays and plastic food trays are the most common types. The primary function of a vacuum formed plastic tray is to display, carry, or hold items such as glass or food.
History of Vacuum Formed Plastics
In general, thermoforming has been around for a surprisingly long time. An early version of thermoforming originated with the Romans. They would shape different utensils using heated tortoise shells. These shells, which were imported, contained keratin. When they applied hot oil, they could shape the shells.
John Wesley Hyatt took the first step towards modern vacuum plastic forming, when he discovered how to make celluloid, which was the first artificial plastic. After they patented the process in 1870, he and his brother worked together to discover that they could heat the celluloid in molds. Doing so, they could form different shapes, like sheets and rods.
The practice of heating plastic material and forming it over a mold gave to thermoforming in the 20th century. Between the 1940s and 1950s, those in advertising and retail began using vacuum molded and vacuum cast plastics as displays and marketing tools. They also used plastic vacuum forming to create lids, containers and other food packaging. In 1950, engineers patented a thermoform machine that made articles from a thin sheet of plastic. They quickly followed this up with a series of vacuum molding machines.
In 1964, engineers patented an improved plastic sheet vacuum form machine. This machine relied on a combination of vacuums and molding or casting processes to remove excess air. Within a decade, technology had advanced enough to make this method obsolete.
In 1974, engineers patented a new vacuum molding machine for forming plastic signs. This model worked using a movable heater, a frame (to hold and soften the plastic), a forming bed (on which the mold is placed), a vacuum system (for removing air in the space between the plastic and the bed) and a means to raise and lower frame, complete with channels for guiding air flow out of the system. This was a vast improvement on the older model, which was not as efficient or precise.
Today, vacuum form state-of-the-art equipment works quite similarly to that 1974 model. The main difference in vacuum forming plastics today has less to do with form vacuum technique and more to do with materials. Modern vacuum forming makes use of a much greater diversity of materials, many of which did not exist or could not be used in earlier decades, like fiberglass.
Vacuum Formed Plastic Materials Process
An extensive assortment of thermoplastic materials can be used for vacuum forming. The material chosen must depend on the application for which the product will be used. Examples of common plastic vacuum forming materials include: polyester, HDPE, LDPE, polypropylene, polystyrene, ABS, acrylics, polycarbonate and Kydex.
Polyester is a polymer known for its versatility, low toxicity and recyclability. Common vacuum formed polyester plastics include: food pouches, beverage containers, processed meat packages and other food containers.
High-density polyethylene, or HDPE, is a polyethylene derived from petroleum. It has a high strength-to-density ratio and tensile strength. It is recyclable and resistant to a variety of solvents. Its main drawback is that it can be hard to form. It’s used for: plastic bags, margarine tubes, milk bottles, cereal box liners and detergent bottles.
Low-density polyethylene, or LDPE, is the oldest grade of polyethylene, first synthesized in 1933. It is non-reactive at room temperature, except in the face of strong oxidizing agents. In addition, some solvents can cause swelling. LDPE is also tough and flexible, though it is not quite as strong as HDPE. Like HDPE, LDPE can be difficult to work with but it is still the material of choice for a variety of products, such as: squeezable food bottles, plastic bags, shrink wrap and garment bags.
Polypropylene is a mechanically rugged thermoplastic polymer that is resistant to a wide variety of acids, solvents and bases. It is also flexible and thermal resistant. The second most widely produced synthetic plastic in the world, it can be used to create medicine bottles, container caps and yogurt containers.
Polystyrene (PS), particularly high impact polystyrene, is widely produced, inexpensive plastic material. It can be solid or foamed. A great example of foamed polystyrene is Styrofoam. Polystyrene is commonly used to make: plastic silverware, fast food trays, egg cartons and CD cases. While easy to acquire, polystyrene is notoriously hard to dispose of in a way that it is environmentally friendly. It is slow to degrade and often ends up as litter.
Acrylonitrile butadiene styrene, or ABS, is tough, stable and impact resistant. It is stronger than pure polystyrene. When necessary, manufacturers can modify the formula to increase these qualities, as well as its heat resistance. Most vacuum formed ABS products are made for use around the house or by consumers in general.
Acrylic plastics known for their optical clarity. They are so clear that colorless acrylic plastic is sometimes confused for glass. To that end, vacuum formed acrylics are often used as glass substitutes for beverage containers. They can also be colored and used for many other applications, including medical products and kitchenware. While ABS does well with high heat, it is not very resistant to cold temperatures. In addition, it does not block UV radiation.
Polycarbonate is an exceptionally strong and impact resistant thermoplastic resin. Normally transparent, it also transmits light well. In addition, it thermoforms easily, while maintaining dimensional stability. Polycarbonate sheet can be thermoformed for a variety of applications, such as: CDs and DVDs, shatter resistant display cases, bulletproof security barriers, airplane panels and more.
Kydex is a PVC-based thermoplastic sheet made specifically to be thermoformed. It is rigid, formable, tough and chemically resistant. It is available for thermoforming in sheets ranging in thickness from .028 inches to .500 inches. It can be thermoformed into many different products, including: trays, tote boxes, insulators and housings, kick plates, door liners, truck fenders and more.
Things to Consider When Selecting a Mold Material:
Rigidity – Ponder ahead if your mold needs a little flexibility or if it has to be very stiff.
Appearance – Does the importance of aesthetic features outweigh other mechanical features like strength and durability?
Cost – Tooling cost and additional expenses need to be noted prior to purchase. Do not focus on the short-term plans; rather, project your estimates for long term goals.
Compatibility – Think carefully of possible materials that can come in contact with your mold. It must be able to withstand any reactions that may result in such conditions.
Vacuum Formed Plastic Process Details
Vacuum forming can be broken down into eight comprehensive steps: clamping, heating, sheet leveling, pre-stretching, vacuuming, plug assisting, cooling and releasing and finishing.
During clamping, manufacturers clamp the plastic sheet into the frame. The frame must be able to handle the thickest of all the plastics to be formed on that particular machine. This ensures that the plastic sheets stay in place during forming.
Next, manufacturers use infrared/radiant heating elements to heat the plastic sheets. Usually, these heaters are movable so that manufacturers can position them on top of the sheets. Some more sophisticated machines heat from the top and bottom. This is only necessary for the thickest sheets.
3. Sheet Leveling (Optional)
Sheet leveling is a step that is not present in every vacuum forming process. Instead, it is used only with machines that use bottom heaters. During this step, a photoelectric beam scans between the bottom heater and the plastic sheet in order to make sure the plastic is not sagging. Sagging plastic can break the beam. If it is sagging, a small amount of air releases to lift the sheet.
4. Pre-Stretching (Bubbling)
Pre-stretching takes place after the plastic achieves a plastic state (reaches the vacuum form temperature). During pre-stretching, the machine introduces air pressure to stretch the sheet and create a small bubble. It then raises the mold to the sheet. The goal of pre-stretching is to control bubble height and get an even wall thickness.
Note: Not all systems feature a pre-stretching capability.
During this step, a vacuum pump removes the air in between the plastic sheet and the mold. This makes the plastic form onto the mold and take on its features.
6. Plug Assisting
During plug assisting, a plug pushes the material deeper into the mold. This helps it spread out evenly and continue to form properly.
7. Cooling and Releasing
Once the shape is formed, manufacturers allow it cool and harden. After it has cooled, manufacturers can release it from the machine. The cooling process can take quite a while, so often, they use additional tools to speed it up, like fans and mist sprays.
Finally, manufacturers perfect the product. They remove any excess materials via trimming, and engage in other finishing processes like: drilling, decorating, slotting, creating cutouts, printing, polishing, strengthening and/or assembling.
Vacuum Formed Plastic Design
Manufacturers design products and choose forming processes based on customer requirements, such as: product type, required product quantity, product size and product thickness. There are a number of ways to customize vacuum formed plastics, such as embossing and engrossing markings or texts.
Vacuum Formed Plastic Machinery Used
The machinery used in vacuum forming varies by application, but in general, vacuum forming machines feature built-in heaters and vacuum pumps. These heaters are usually infrared elements placed on an aluminum plate. However, for more sophisticated processes, manufacturers may use quartz heaters. Quartz heaters have a lower thermal mass, which means that they can work more quickly.
Finishing/Trimming Tools and Machinery
To finish the product, manufacturers can use any number of tools and secondary machinery, such as: heated knives, trimmers, handheld power routers, scalpels, roller presses, guillotines, punch presses and vertical and horizontal band saws.
In addition, most vacuum forming systems come with CNC technology, which helps manufacturers more precisely form, mark and otherwise custom create plastic parts equal to those made with injection molding. CNC machines can also help control temperature.
Vacuum Formed Plastic Variations and Similar Processes
Twin Sheet Thermoforming
This process involves heating two separate plastic sheets and welding them together to make a hollow product.
What sets vacuum packaging apart from other types of packaging is that it is both a type and a method. Vacuum-formed packaging is a method utilized if products must be stored without exposure to air. Such products include airtight water bottles or airtight food packs. A vacuum environment is utilized to remove oxygen from a vacuum pack, thus preserving the product.
In-Line Thermoforming/Roll-Fed Thermoforming
These processes involve feeding a plastic sheet from an extruder (in-line thermoforming) or roll (roll-fed thermoforming) into a set of chains. These chains feature spikes that puncture the sheet, and the guiding chains move the sheet into an oven to achieve a certain temperature. Next, the heated sheet is moved into a form station. Within the form station, the sheet is enclosed between a mating mold and a pressure box. The form station utilizes a vacuum to make the space airtight, using ventilation holes that are connected to vacuum lines. The plastic sheet is pulled into a recessed mold, or a female mold, forcing the pliable plastic sheet to take the shape of the mold. Next, a sudden blast of reverse air pressure may be utilized to eliminate the vacuum and help to eject the plastic out of the mold. Once the plastic is removed, the sheet that contained the formed plastic is trimmed at a trim station or a trim press.
Basics of Thermoforming
Highly customized plastic products can be produced by a process called plastic thermoforming. It can accommodate a wide variety of product configurations ranging from simple cylinders to complex-shaped chairs. The versatility of plastic thermoforming makes it a great choice in many applications across industries. Furthermore, it uses much lower molding pressures than other plastic production processes, leading to lower tool costs and quicker tool designs. Almost all plastic thermoforming tools are cast from aluminum and are more cost-effective compared with those tools from other plastic forming processes.
Thermoforming fabrication process involves heating a material, usually a plastic sheet, to a temperature where it enables the material to be stretched over a specific mold to acquire its shape. The material is then allowed to cool down prior to removal. Molds come in two types, the positive mold and the negative mold, more commonly known as male mold and female mold, consecutively. The male mold has a convex feature that is ideal for forming the contours of the inside dimensions of the geometric design. In contrast, the female mold has a concave feature suited for forming the outside dimensions’ contours.
Industries that Use Plastic Thermoforming
Home Usage Products
Many modular chairs, kitchen tables, bowls with unique designs can be seen in the market at a very cheap price. Plastic thermoforming is the technology behind these products. For example, in a kitchen, it can be easily seen that a lot of kitchenware for storing snacks, flour, etc., has turned to plastic boxes. Aside from kitchenware, the common parts of a kitchen have also been renewed using thermoforming technology. These include kitchen doors, kitchen tops, and kitchen cabinets. Furthermore, there is also a huge demand for such kitchen setups, owing to the stronger and longer capacity of plastics compared with wooden material.
Though metals are the primary materials used in the automobile industry, plastic products still have several applications in automobiles. The use of plastics is advantageous in the automobile industry due to their lightweight property. The lesser the weight of the vehicle, the higher its fuel efficiency. Thermosetting plastics serve an excellent role, providing the necessary strength, flexibility in design, and lightweight characteristics. Car parts such as doors, front modules, handles, backseat frames, etc., have a considerable portion of plastic used in it. Furthermore, two-wheelers and three-wheelers have complete internal structures which are also made of plastics. Mostly all the frames and sheet types of plastics such as doors and handles are made from a process called vacuum forming. In addition, hollow objects needing an enclosure such as fuel tanks are made using the process called rotational molding.
There is a huge demand for protective cylinders/cuboidal tanks in the transportation industry for safe transit over long distances. The tanks are made of plastics such as polyethylene, polypropene, nylon, and PVC. These plastics are excellent choices owing to their low weight-to-strength ratio, resistance to degradation, cheap prices, and faster production time. The uses of plastic thermoforms in the transportation industry are very versatile, ranging from local outings to international transport. Aerospace industries also use plastics to reduce the frame weight and increase the cargo capacity. The transport industry can also be extended to mass transit systems. For instance, most bus and train parts like seats, sleeping berths, and even window casings are made of plastics.
Electronic gadgets are usually protected with a smooth layer of the casing. Starting from the smallest of electronic systems such as remote-controlled cars, where both remote and cars are mostly made of molded plastics, to huge control rooms with multiple modular desks fitted with monitoring screens, everything has a considerable percentage of plastic products made from thermoforming. Even the latest CPUs and laptop casings are made from molded plastics. The demand for these electronic casings rises exponentially, at a faster rate than the population. They drive the demand for more effective and easy mass manufacturing techniques for plastics.
There are a lot of applications of plastics in the medical field. They are stable or non-reactive under several conditions, making them the cheapest solution suitable for storing a wide variety of chemicals. Furthermore, cheap use and disposable plastic products such as syringes, pipette tips, etc., used in biochemistry labs can be easily mass-produced using thermoforming techniques. Apart from the chemical labs, the PPE kits and face shields are also made of plastics using thermoforming techniques. Research in several fields of chemical engineering is of hazardous nature and often needs disposable products. Cheap plastic products made using thermoforming are a go-to solution here.
Benefits of Vacuum Formed Plastics
Vacuum thermoformed plastics and vacuum plastic thermoforming offer many benefits. First, because vacuum forming machinery can vary in complexity—from small, simple tabletop machines to large production machines—the process is exceptionally versatile. Through it, manufacturers can create a wide variety of parts and products. Second, vacuum formed plastics are highly accurate to design; the use of one heated sheet during the forming process allows for exactness. Next, vacuum forming can be done using recycled plastic. This saves time and money and lessens the environmental impact of plastic. On top of these savings, vacuum forming has low tooling costs. Finally, vacuum forming is inexpensive and has a fast turnaround time.
An Introduction To Vacuum Forming
This article will give an in depth understanding of vacuum forming.
You will be able to learn about:
- What is vacuum forming?
- Materials used in vacuum forming
- Machines used in vacuum forming
- Types of products made from vacuum forming
- Pros and cons of vacuum forming
- And so much more…
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.
- 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) 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 (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 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 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 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.
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 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.
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.
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.
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:
- Belly Pans
- Blister Packs
- Heating Pad
- Skid Plates
- Vacuum Formed Trays
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
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.
- 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
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.
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.
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.
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.
- 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.