Thermoforming is a process of heating a thermoplastic sheet to its softening point. The sheet is stretched across a single-sided mold and then manipulated. Then, it cools into the desired shape. The most common methods to get the sheet to conform to its final shape are vacuum-forming, pressure-forming and mechanical forming. Thermoforming has innumerable applications and can be used by several different industries. Here is a brief overview of thermoforming, its benefits, and applications.
Key terminology used
The process of thermoforming uses some specific terminology with which you should be familiar. Knowing the difference between these terms can be the difference between having a successful project and one that is lackluster.
- Thermoforming Thermoforming is a general term that refers to the process of transforming a plastic sheet into a 3-dimensional shape by using heat, vacuum and pressure.
- Thermoplastics Thermoplastics refers to a type of plastic made from polymer resins that become homogenized when heated.
- Vacuum Forming The specific process that involves forming a part by heating and stretching the plastic across a mold using a vacuum. Normally the mold is open and the force involved with forming the sheet is limited to about 15 psi.
- Pressure Forming This process adds a pressure box to the tooling package. It utilizes both vacuum and positive air pressure. This process generates as much as three to four times the forming pressure as vacuum forming does. Therefore, fine details such as surface textures can be formed on the mold without incurring excessive extra costs.
- Twin Sheet Forming As the term suggests, there are two molds for this process: one on the top and one on the bottom. Therefore, two sheets of plastic must be heated and formed at the same time. A fused joint must be placed around the perimeter of the mold while air pressure is injected between the sheets. This process is ideal for forming hollow parts that require a distinct upper and lower shape.
Stages of thermoforming
As like any process, there are several stages of thermoforming. The typical thermoforming process goes through the following stages:
- Final tooling
Equipment used for thermoforming
The thermoforming process requires a few pieces of equipment. The forming process needs either pressure formers or vacuum formers. It also requires a three or four-station Rotary Transformer. The secondary operation of the process needs CNC robotic routers. Normally the bed for this piece of equipment does not exceed 60”X 120”. The tooling process requires machine aluminum molds, cast aluminum molds, composite or temporary molds, or male/female molds.
Advantages of thermoforming
Thermoforming holds many advantages that make it a favorable process over other types of molding. Some of these advantages include:
- The ability to create several finished parts from the same material
- It allows for the detection of possible design and fit issues before it is too late
- It saves time and money
- It is beneficial when using large parts
Benefits of thermoforming
The thermoforming process offers many benefits to both the manufacturer and end user. Some of these benefits include:
- Short lead time
- Easy to add details
- Freedom of design
One of the best aspects of thermoforming is its versatility. This feature can be seen in the vast number of materials that can be used for the process. Each material has applications and functions for which it works best.
- ABS (Acrylonitrile Butadiene Styrene) – This is a common material that has good stiffness and impact strength. It comes in almost any color as well as several textures.
- Acrylic (Polymethyl Methacrylate, Plexiglass or PMMA) – This material is clear and abrasion-resistant. It can be fabricated easily, is available in impact-modified grades and also comes in many colors.
- HDPE (High Density Polyethylene) – This material is resistant to impact as well as chemicals. It also has great cold-temperature properties. However, it is not as stable as many other available materials.
- HIPS (High-Impact Polystyrene) – This material has a low cost attached to it. IT also forms easily and is available in many colors. It is more brittle than some other materials, including ABS.
- HMPWE (High Molecular Weight Polyethylene) – This material has high impact strength, is chemical resistant and puncture resistant. It is ideal for medical joint replacement, recreational skis, and bottles.
- KYDEX (PMMA/PVC blend) – This is a good general-use all-purpose material. It is resistant to chemicals and heavy impacts. It is available in many colors and textures.
- LEXAN – This material has great variability, is flame-resistant, scratch-resistant, and can stand up to various types of weather.
- PC (Polycarbonate) – This material has incredibly high impact strength. It is clear and has a high temperature resistance.
- Pennite (glass-filled nylon) – This material is strong and stiff. It is also cost-effective, especially if it is used to replace metal.
- PEI (Polyetherimide Ultem) – This is very high-temperature grade material. It is autoclavable and has a natural amber color.
- PET (Polyethylene Terephthalate) – This material is commonly used food packaging. It is clear and has a low cost. It can be FDA certified if needed.
- PETG (Polyethylene Terephthalate Glycol) – This material is clear and has excellent impact strength. It also forms well. Medical-grade material is available upon need.
- PP (Polypropylene) – This material has excellent chemical resistance. It is rigid and has good impact strength. It is good at higher temperatures but dimensionally is not as stable as other materials.
- PVC (Polyvinyl Chloride) – This rigid material is strong and has good impact strength. It is also flame-retardant. However, its availability is limited.
- Royalite – This material is durable, has high impact strength and high tensile strength. It also has high and low temperature performance.
- RPET (Reprocessed Polyethylene Terephthalate) – This material is commonly used in food packaging. It is clear and has a low cost. It can be FDA certified if needed.
- TPO (Thermoplastic PolyOlefin) – This material has superior impact properties. It is available with a high-glass finish. It is good for outdoor application. However, it is difficult to form, particularly for applications that need deep draw shapes.
- Viny – This material is durable, flame-resistant, and a good conductor of electricity.
- Specialty materials – Other materials are available as well. You just need to ask your fabricator or guidance.
The thermoforming process can be used in a wide variety of applications as well. Some of the most common ones include but are not limited to:
- Retail clamshell packaging
- Packaging blisters
- Pick and place trays
- Material and handling trays and covers
- Shipping trays
- Medical packaging
- Pop displays
- Packaging inserts
Typical tolerances for thermoforming processes include:
- Forming: Part to part +/- .025”, depending on the material
- Perimeter Die Cut: +/- .060”
Typical parameters for thin-gauge thermoforming tooling include:
- Maximum mold size – up to 30” wide
- Maximum depth of draw – 8.0”
- Maximum sheet thickness – .80”
- Molds are temperature controlled aluminum
- Trim is via steel rule die
For the thermoforming process to be completed accurately the following general practices should always be followed:
- Dimensions should be drawn to and from a controlled surface.
- The controlled surface should be against the mold.
- There may typically be a 2.0” callout for mold relief.
- There may be +/- 10% variance in thickness of stock material.
- Material stretch should be dependent on mold configuration and depth of draw.
In essence, thermoplastics are the final products that result from the thermoforming process. A major benefit of thermoplastics is their tolerance to repeated activation. So, it can be reheated and reshaped several times. This characteristic also makes thermoplastics recyclable. Further, due to the chemistry involved, thermoplastic materials exhibit the same characteristics as rubber and can have the same strength as aluminum. The temperature tolerance of thermoplastic materials varies. Some can retain their properties up to 100 degrees F, while others can withstand temperatures up to 600 degrees F. Most thermoplastics have no known solvent at room temperature and also function well as both electrical and thermal insulation. They can also be electrically conductive if metal or carbon is added.
Nature of thermoplastics
Thermoplastics have a long history, dating back to the mid-1800s. They were originally used as a substitute for ivory and have grown to become a part of everyday life today. Some common places where you can see thermoplastics include:
• Sports equipment
• Auto parts
• Compact disks
• Food storage containers
• Eyeglass lenses
• Grocery bags
• Bulletproof vests
Thermoforming and vacuum forming are closely related. In fact, vacuum forming is a type of thermoforming. However, there are some important differences. So, it is important to be able to distinguish between the two. Vacuum forming requires some additional processes that cause plastic to conform to the mold during forming. Vacuum forming has more restrictive uses as well. It is normally reserved for applications that use shallow plastic parts that need to be formed into cavities. Other important information to know about vacuum forming includes:
There are fewer materials that are suitable for vacuum forming applications. The best materials for this purpose include:
Vacuum forming is ideal for some specific applications because the vacuum-formed components can replace complex fabricated sheet metals, fiberglass, or plastic injection molding. Some common places where you can see evidence of vacuum forming include:
• Medical imaging enclosures
• Diagnostic equipment
Problems with vacuum forming
Despite all of its positive attributes, vacuum forming does has some drawbacks as well. Some of the most common problems include:
• The molds can easily absorb moisture forming bubbles within the inner layers
• Webs can form around the mold and negatively affect the final product
• Objects can stick to the mold
Thermoset plastics are synthetic materials that strengthen when they are heated. Although they are closely related to thermoplastics, there are some distinct differences between the two. Unlike thermoplastics, thermosets cannot be reheated and remolded with success. Characteristics of thermoset plastics include:
- Thermo performance and stability
- Dimensional stability, can adhere to tighter tolerances
- Resistance to heat, creep, corrosion
- Superior hardness
- Comprehensive strength
- Excellent moldability, can retain a greater degree of physical detail
Creation of thermoset plastics
Thermoset plastics can be created in a number of ways, including compression, compression-injection, and injection molded. Regardless of the creation method, heat is needed to mold the material into place.
Common applications of thermosets
Thermosets are known for their strong, permanent bonds that are not reversible. Because of the characteristic, the products that are made through this process can be found in many common places. Some examples include:
• Electrical housings and components
• Heat shields
• Circuit breakers
• Motor components
• Thrust washers
• Ash cups
• Valve covers
• Disc brake pistons
• Knobs and handles
• Other components that may be easily exposed to heat or electricity
Materials used for Thermosets
Common materials used for thermosets include:
• Melamine formaldehyde
• Polyester resins
• Phenolic resins
• DAP (Diallyl Phthalate)
• Urea formaldehyde
Thermoforming and its related processes and products hold an important place in everyday life. Wherever you look you can see evidence of these processes and can understand how thermoforming benefits our lives and society in general. To learn more about Thermoforming, contact the experts at SealWerks today.