Blog 41: Introduction to Thermoforming molding
The technique of stretching a thermoplastic sheet over or into a single-sided mold while it warms up to its softening point and forms into the desired shape is known as thermoforming. The thermoplastic sheet is cooked in an oven using convection or radiant heat until it is pliable, while clamped into a holding mechanism. The sheet is then stretched or forced into the mold while being held horizontally above it using vacuum pressure, air pressure, or mechanical force. As it cools, the softened sheet is held in place while taking on the shape of the mold. The formed portion is then released once the extra material has been removed. It is possible to re-grind extra material, combine it with leftover plastic, and then re-form it into thermoplastic sheets.
Thermoforming is frequently used to package food, but it also has numerous other uses, such as making plastic toys, airplane windscreens, and cafeteria trays. Thick-gauge (more than 0.120 inches) sheets are often used for cosmetic permanent surfaces on autos, shower enclosures, and electrical equipment, whereas thin-gauge (less than 0.060 inches) sheets are primarily used for rigid or disposable packaging. The following list of thermoplastic materials can be utilized in this process::
- Acrylic (PMMA)
- Acrylonitrile Butadiene Styrene (ABS)
- Cellulose Acetate
- Low Density Polyethylene (LDPE)
- High Density Polyethylene (HDPE)
- Polypropylene (PP)
- Polystyrene (PS)
- Polyvinyl Chloride (PVC)
The thermoforming process, in its most basic form, entails heating a sheet of even thickness (which could be made of a single material, a co-extrusion, or a laminate) and dragging it over or into a Mold to create a hard or semi-rigid shape. Usually, the extra material is clipped off, leaving the finished product with a rim. One of the most significant drawbacks of this very straightforward technique is that the likelihood that the material will thin, even to the point of breaking, increases with the depth of the item to be created. There are several ways to stop this unwelcome thinning, as will be discussed below.
Seven fundamental phases make up the thermoforming process, which is used to create a variety of packaging items, including tubs, pots, display trays, and blister packs:
- Making the sheet – normally by the cast extrusion method.
- Heating the sheet.
- Forming the pack by stretching the sheet either into or over a Mold.
- Cooling the formed packaging.
- Cutting and trimming the multi-unit Molded sheet into individual units. This can be carried out at the same time as the forming process.
- Printing or decorating as required.
- Stacking the individual units before packing and labelling for despatch to the customer.
Types of Thermoforming Processes
Thermoforming is a comprehensive manufacturing technique that includes all possible approaches to shaping heated plastic sheets. Thermoforming is utilized by a manufacturer who selects the vacuum or pressure forming processes.
Although there are many different processes, the following are the most common thermoforming methods:
- Vacuum Forming: This thermoforming technique shapes the sheet using a vacuum. The plastic sheet is heated initially to make sure it is malleable. The sheet is then forced against a mold as the vacuum forming equipment removes the air. The vacuum process is renowned for its ability to produce goods quickly and affordably.
- Pressure Forming: This method also involves heating the plastic sheet and using a vacuum to remove air to press the sheet firmly against a mold. Still, there is a further step. Once the air is gone, a pressing tool exerts pressure to help the formed plastic keep its final shape. When more intricate details from the thermoforming process are needed, pressure forming is used.
- Mechanical Forming: The warmed plastic sheet is shaped by a direct mechanical force during this procedure. The surface patterns are imprinted into the plastic sheet by the force of a core plug forcing it to fill the space between the plug and the mold. When accuracy and attention to detail are essential, mechanical thermoforming is performed.
- Drape Forming: This process involves draping a hot plastic sheet onto a mandrel that has been specially patterned. The finished part is created by pressing the mandrel’s design onto the plastic sheet. Due of the minimal tooling requirements, the drape forming process is one of the most cheap thermoforming methods. The method doesn’t lead to weak points in the pieces because the thickness of the material may be maintained.
- Matched Mold Forming: This thermoforming technique is used to produce objects that need a higher degree of precision. The hot plastic sheet is shaped using a male and a female mold during the matched mold manufacturing process. The molds are forced together onto the plastic sheet by the forming machine. After that, the sheet adopts the pattern or shape that was created for the two molds.
- Twin Sheet Forming: In this procedure, two layers are formed and then combined to create a single item. The plastic sheets are concurrently heated, molded, and linked to create the final product. The twin sheet forming procedure works best when creating hollow objects or objects with two walls.
- Billow Forming: This free-form thermoforming technology uses air to form heated plastic without the use of molds. Here, the shaping device blasts the plastic into a bubble with air jets until the desired design is achieved.
To create food packaging, toys, pallets, parts for aircraft, and other plastic products, thermoforming is used. Therefore, before starting a production cycle, manufacturers must take a wide variety of plastic materials into account. The more typical thermoforming materials include:
- Polypropylene (PP): By value and volume, PP is the most widely used plastic for thermoforming. It is frequently employed in the production of plastic packaging, ventilators, toys, and other goods. Because of its natural qualities, such as great resistance to chemicals, fatigue, and heat, polypropylene is used. In addition to being an inexpensive material, polypropylene may be used with the various thermoforming techniques described below.
- Polystyrene (PS): Manufacturers can deal with a transparent, hard, and brittle plastic thanks to this aromatic hydrocarbon polymer. Since polystyrene has properties like resistance to water and air, it is frequently utilized as a thermoforming packing material. Polystyrene is used in the production of household goods, jewelry boxes, CD cases, and food packaging.
- Polyethylene Terephthalate (PET): Very good chemical resistance, high levels of impact resistance, and high tensile and alcohol barrier qualities are all provided by PET. It frequently appears in food products, water bottles, and carbonated beverages.
- Low-Density Polyethylene (LDPE): A polymer called LDPE is immune to chemicals and ultraviolet light. Additionally flexible and strong in tensile, this plastic is. Packaging films, DVDs, cable insulation, containers, and chemical-resistant products can all be produced by manufacturers using LDPE.
- High-Density Polyethylene (HDPE): In terms of its fundamental properties, HDPE is comparable to LDPE and is renowned for being chemical, UV, and water resistant. It is a strong thermoplastic that can be used to create plastic bags, packaging film, blown bottles, containers, and pipes.
- Polyvinyl Chloride (PVC): PVC is a common material that is used in the creation of pipes, window frames, interiors for automobiles, household goods, packages, and footwear. PVC can be created to be stiff or flexible depending on the needs of the maker. Additionally, this thermoplastic is heavy-duty, water-resistant, and dense. It’s crucial to remember that PVC isn’t totally resistant to chemicals and could react with chlorine.
- Polycarbonate (PC): Strong and resilient polycarbonates can withstand significant plastic deformations without breaking or shattering. They are good electrical insulators, heat-resistant, and flame-retardant. Some PC grades are also very transparent to visible light and optically transparent. PCs are employed in the manufacturing of plastic lenses for eyewear, medical devices, automotive components, protection equipment (such as safety helmets and lenses), bulletproof glass, and building materials.
- Cellulose Acetate: Cellulose acetate is an option for manufacturers looking for environmentally friendly thermoplastic materials. This thermoplastic is produced from renewable materials like pulped wood. In general, cellulose acetate is transparent and colorless. It is employed in the production of household goods, packaging film, glass frames, and pill covers.
- Polymethyl methacrylate (PMMA): High strength, resistance to the elements, durability, and transparency are some of PMMA’s characteristics. PMMA is used by manufacturers to make transparent packaging, car headlamps, and lenses. PMMA’s resilience guarantees that final products will continue to function as intended for a long time.
- Acrylonitrile-Butadiene-Styrene (ABS): Rigidity, abrasion resistance, and low temperature resistance are some of ABS’s qualities. Manufacturers can use ABS and thermoforming to create household appliances, food containers, and electronic packaging.
There are also several disadvantages associated with thermoforming.
- This process is limited to thin walled parts and there are limitations to the complexity of shapes it can be used to create.
- Each piece requires trimming, which adds time to the process.
- Despite its disadvantages, thermoforming provides a flexible and cost effective method for creating a huge variety of products.
Thermoforming has a number of advantages.
- One of its main draws is that it is very adaptable to a customer’s design needs.
- With a fast turnaround time, it can be used for last-minute shipments or as a quick way to develop a prototype.
It is also a relatively low-cost means of production.
- The materials are optimized for cost effectiveness and can lead to lower tooling costs.
- Finally, the results can be very aesthetically pleasing. Colored and paintable plastics are available, allowing for a wide range of customization to meet customer needs.
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