Thermoforming of Plastics: A Comparison Between Polycarbonate, Acrylic & PETG
Thermoforming is a manufacturing process where plastic sheets are heated to a pliable forming temperature, formed to specific shapes in a mold, and trimmed to create usable products.
After cooling and setting the molded plastic sheet, each part will be separated from its batch to form a single unit or product. The result of a thermoforming process is a finished product (or part) with a defined three-dimensional (3D) characteristic.
Thermoformed plastic products are all around us, playing a big part in our lives and it is one of the greatest options when you aim to create the most advanced designs in short production times and with high profitability.
Even though thermoforming is a technology that has been available for years, nowadays it has been perfected so much to provide more competitive costs than extrusion or plastics injection.
The Process of Thermoforming
Thermoforming uses mainly 2 different processes: Vacuum Forming and Pressure Forming.
Vacuum forming heats a sheet to a pliable state and then pressed against a 3D mold by vacuuming out the air between the sheet and the mold. Pressure forming heats a sheet to a pliable state and is then pressed against a 3D mold by vacuuming out the air between the sheet and the mold as well as applying air pressure to the outside of the sheet.
Both processes are cost-effective with quick tooling turnover. Both work well on small and larger items. Vacuum forming has sharper details and allows for undercuts. It also has tighter tolerances and molded-in textures. Pressure forming is good for complex shapes and products with vents or louvers.
Benefits of Thermoforming
Thermoplastics (the final products that result from the thermoforming process) are available in different compounds from acrylic and PETG to PVC and polycarbonate. Each has different and specific thermal and mechanical properties. A unique characteristic of thermoplastics is that all of these can be formed into complex geometries without changing the properties of the base materials.
Thermoplastics are lighter in weight than FRP (fiberglass) or sheet metal and they do not involve any time or labor for finishing steps. An almost infinite range of colors are available but with a limited number of textures.
Other major benefits include:
- Durability: Thermoplastics are impact-resistant and malleable. In many applications, they have a longer service life than comparable materials as they do not dent, ding, crack, chip, splinter or fray. Thermoplastic’s durability will reduce replacements and service calls.
- Chemical/Stain Resistant (Graffiti Resistant): Thermoplastics do not yellow or stain when in contact with any chemicals including cleaners and solvents. Graffiti-resistant materials are also available, which means thermoplastics can be considered as a perfect solution for any outdoor or customer-facing application.
- Codes and Requirements: Thermoplastics comply with all the regulatory requirements, ensuring conformity to smoke, flammability and toxic gas release requirements for aircraft and other transportation interior products. Most all thermoplastics are inherently biocompatible which means they are perfect for medical device applications.
- Environmental: Thermoplastics are recyclable and contain no Volatile Organic Compounds (VOC). They are an environmentally sound solution, supporting end-of-life recyclability and life-cycle design.
Thermoforming of Polycarbonate
Thermoforming polycarbonate sheet is an established process that offers you the freedom to develop complex shapes and forms with cost/performance characteristics that have significant advantages over traditional methods of production. Low-cost tooling, large part production and reduced lead times are some of the major advantages of producing polycarbonate products in this way.
The basic steps involve the heating, shaping and cooling of a polycarbonate sheet product. There are several different forming techniques and some of which only require heating to allow the sheet to conform to a simple positive or negative mould as in drape forming. Others, such as vacuum and pressure forming require that, after heating, the sheet is made to conform to a mould by applying pressure or a vacuum.
Polycarbonate has a glass transition temperature of about 147 °C (297 °F), so it softens gradually above this point and flows above about 155 °C (311 °F). Tools must be held at high temperatures, generally above 80 °C (176 °F) to make strain-free and stress-free products.
Polycarbonate has high outgassing rate and high affinity to water, which means it absorbs moisture. Moisture builds up during the manufacturing, transportation and storage but in the ‘as extruded’ condition, it doesn’t cause any problem. However, during forming, excess moisture can cause bubbling and other surface appearance problems along with a reduction in property performance.
To remove the moisture prior to forming, a hot-air circulating oven at 125°C ± 3°C is recommended. And to avoid warpage, drying temperatures should not exceed 125°C and the air volume in the oven should be changed 6 times per hour to allow for the removal of water vapor.
Polycarbonate sheet products are easily thermoformed and a wide variety of applications can be produced, such as:
- Cellphone frames and screens
- Electronic screen displays for televisions, monitors and tablets
- Shatterproof glass, bulletproof glass and safety glasses
- Windows and windshields in golf carts and other vehicles
- Data storage devices, including CDs and DVDs
Thermoforming of Acrylic
Acrylic thermoforming is the process of heating the acrylic sheet until it’s flexible, then shaping it around a custom-designed aluminum tool. Thermoformed acrylic sheets provide protection from impact, elements, ultraviolet radiation and corrosion to all types of OEM equipment. Also, it has flexible ordering with short lead times of about four to six weeks. Therefore, it allows shipment to be scheduled conveniently, thus reducing inventory.
Acrylic can be thermoformed using various types of equipment such as vacuum, pressure, or stretching equipment, and plenty of heating methods including coiled nichrome wire, metal (cal) rod, hot air ovens, ceramic elements, and quartz tube (nichrome filament and tungsten filament). These heat sources derive average life spans ranging from 1,500 to 20,000 hours at varied efficiency levels.
While acrylic softens at higher temperatures, it does not actually melt until it reaches 320 °F (160 °C). Therefore, normal household use does not risk melting acrylic. Hot stovetop items should only be placed on an acrylic tabletop surface using a protective trivet or other padding, preferably with rubber cushions. As a safety precaution, never place acrylic directly on or next to an open flame or hot surface.
Acrylic has high outgassing rate and high affinity to water. Depending on the storage and climate conditions, acrylic absorbs moisture. Although this can be disregarded for normal application temperatures, it may cause bubble formation during heating when extruded acrylic glass is exposed to higher temperatures. Hence, prolonged pre-drying in air-flow ovens at temperatures below the softening point of the material is highly recommended.
Since thermoformed acrylic is clear, durable, and shatter-resistant, it is widely used as a replacement for glass in many situations, and is often used to make:
- Signs and sign holders
- Retail displays and shelves
- Brochure holders
- TV screens
- Submarine windows and aquarium tanks
Thermoforming of PETG
Due to the low forming temperatures of polyethylene Terephthalate Glycol (PETG), it is easily vacuumed and pressure-formed or heat bent, making it popular for a variety of consumer and commercial applications. These properties also make it one of the more widely used materials for 3D printing and other heat-forming processes.
PETG can be thermoformed according to the principles of positive, negative or free forming, with or without the use of air pressure or vacuum. Male (positive) forming gives a thicker bottom, whereas female (negative) forming implies thicker walls. Free-formed PETG needs to be kept in its desired shape until it has reached a temperature lower than 70°C.
The softening temperature of PETG is the same thing as its glass transition temperature in essence (that also determines its heat resistance), which is between 80 and 85 degrees Celsius on average. At these temperatures, PETG will increasingly become softer and lose its shape, essentially meaning that it cannot withstand the heat anymore while staying rigid.
PETG has minimum to no outgassing which makes it the preferred sheet for various forming applications for both home and office use. Even though it’s odorless and the fumes are not toxic, it's always best to ventilate your printing room properly. There are some carbon emissions from the fumes when printing with PETG, but experts have concluded that they pose no significant health risks.
The thermoforming cycle of PETG is shorter than the cycle of polycarbonate, PVC or PMMA, and PETG is well suited for techniques including bending, die-cutting and routing. Thermoformed PETG is widely used for making:
- Signs and graphic holders
- POP displays and store fixtures
- Food and Drink Containers
- Medical and Pharmaceutical Applications
- Machine Guards
Our facilities have powerful thermoforming equipment of big and small dimensions. We can offer a molding system that is capable of taking on the most advanced designs that include straight lines, curves, creases, etc., in short manufacturing times and with high profitability in both high- and low-volume orders.
At Blue Rhin, we have carried out all kinds of projects over the years using thermoforming and have mastered its possibilities. Ask us and we will help you out with the right tools and resources to make your projects successful.
Being the best plastic sheet products supplier in Dubai, we offer high-quality polycarbonate, acrylic and PETG sheets in the UAE and other GCC countries, including Oman, Saudi Arabia, Kuwait, Qatar and Bahrain.
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