Vacuum forming, also known as thermoforming or vacuum molding, is a procedure in which a sheet of heated plastic material is shaped a certain way. The mold used to shape the plastic material is also known as a “buck.” Vacuum forming is a type of pressure forming process, and is one of the oldest plastic forming methods. A process known as twin sheet thermoforming is a category of vacuum molding all its own. This process involves heating two separate plastic sheets and welding them together to make a hollow product.
Industries that utilize the processes of vacuum forming and pressure forming include telecommunications, cosmetics, automotive, appliance, medical, electronics, sporting goods, and food and beverage. These processes are often used in forming plastic packaging, either to preserve the products or to add an aesthetic element. There are certain applications such as making store signs for which both forming methods can be used. The vacuum forming process has several advantages: low cost for tooling, minimal start-up time, and cost efficiency in producing small to medium quantities.
Plastic packaging that fall under the category of vacuum-formed plastics are clamshells, plastic covers, plastic trays, blister packs, and vacuum packaging. The vacuum forming process is usually limited to creating products with a shallow depth. Although there is not much variety in the structure of the products, vacuum forming machinery can vary in complexity—from small, simple tabletop machines to large production machines. This makes the process exceptionally versatile.Read More…
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. One common material, polyester, is used for food pouches, beverage containers, processed meat packages, and other food containers. High-density polyethylene, or HDPE, is used for plastic bags, margarine tubes, milk bottles, cereal box liners, and detergent bottles. Although HDPE can be used for a variety of materials, it can be difficult to work with.
Low-density polyethylene, or LDPE, can be difficult to work with as well, but is still the material of choice for a variety of products such as squeezable food bottles, plastic bags, shrink wrap, and garment bags. Polypropylene can be used to create medicine bottles, container caps, and yogurt containers. Polystyrene (PS) is commonly utilized for plastic silverware, fast food trays, egg cartons, and CD cases. Additional materials that can be used in the vacuum forming process include acrylonitrile-butadiene-styrene (ABS), acrylics, polycarbonate and a PVC-based thermoplastic known as Kydex.
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. Once 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.
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.
Another widely used vacuum forming process involves feeding a plastic sheet from an extruder or roll 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. Another process that is similar to pressure forming is the plastic thermoforming process. Both procedures use air pressure and a vacuum environment to make the sheet tighten around the mold. As a result, the vacuum formed process can create intricately detailed products.