What is Thermoforming?
Thermoforming is a manufacturing process in which a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold using air pressure or vacuum, and trimmed to create a usable product. The sheet, or “film” when referring to thinner gauges and certain material types, is heated in an oven to a temperature that allows it to be stretched or put into or onto a mold and cooled for a specific time to a finished shape.
Difference between Thin-Gauge and Thick-Gauge Thermoforming
Thin-gauge thermoforming is primarily the manufacture of disposable cups, containers, lids, trays, blisters, clamshells, and other products for the food, medical, and general retail industries. Thick-gauge thermoforming includes making parts as diverse as plastic pallets, dunnage trays, automotive components, sports and recreation products, and food industry packaging.
There are two general thermoforming process categories used at Peninsula Plastics. Sheet thickness less than 1.5 mm (0.060 inches) is usually delivered to the thermoforming machine from rolls or from a sheet extruder. Thin-gauge roll-fed or inline extruded thermoforming applications are used primarily to create rigid or semi-rigid disposable packaging. Sheet thicknesses greater than 3 mm (0.120 inches) is usually delivered to the forming machine by hand or by an auto-feed method, in which pieces are already cut to final dimensions.
How is a Thin-Gauge product is processed?
In the continuous thermoforming of thin-gauge products, a plastic sheet is fed from a roll or from an extruder into a set of indexing chains that contain pins or spikes. These objects pierce the sheet and transport it through an oven, which heats the sheet to forming temperature. The heated sheet is then brought into a form station where a mating mold and pressure-box enclose the sheet. Vacuum is then applied to remove trapped air and to pull the material into or onto the mold along with pressurized air to form the plastic to the detailed shape of the mold. (Plug-assists are typically used in addition to vacuum in the case of taller, deeper-draw or formed parts in order to provide the needed material distribution and thickness for the finished parts.) After a short form cycle, a burst of reverse air pressure is released from the vacuum side of the mold. This causes the forming tool to open (a process commonly referred to as air-eject), it breaks the vacuum and assists the formed parts off of, or out of, the mold. A stripper plate may also be utilized on the mold as it opens for ejection of more detailed parts or of parts with negative-draft, undercut areas. The sheet containing the formed parts then moves into a trimming station on the same machine, where a die cuts the parts from the remaining sheet web, or moves them into a separate trimming press where the formed parts are trimmed.
How is a Thick-Gauge product is processed?
Heavy or thick-gauge cut sheet thermoforming applications are primarily used as permanent structural components. Heavy-gauge forming utilizes the same basic process as continuous thin-gauge sheet forming, typically draping the heated plastic sheet over a mold. Many heavy-gauge forming applications use only vacuum in the forming process, although some use two halves of mating form tooling and air pressure. Aircraft windscreens and machine gun turret windows spurred the advance of heavy-gauge forming technology during WWII. Heavy-gauge parts are used as cosmetic surfaces on permanent structures such as material handling equipment, refrigerators, spas, and shower enclosures, and electrical and electronic equipment. Unlike most thin-gauge thermoformed parts, heavy-gauge parts are often hand-worked after forming and are trimmed to their final shape or for additional drilling, CNC routing, water jet cutting, saw cutting, or finishing, depending on the product. Heavy-gauge products typically have a “permanent” end use, while thin-gauge parts are often designed to be disposable or recyclable and are primarily used to package or contain food items or products. Heavy-gauge thermoforming at Peninsula Plastics is used for all types of plastics components. We are very successful in competing head-on with other plastics processors in areas such as injection molding.
What do we do with the scrap material left over from Thermoforming?
The sheet web remaining after the formed parts are trimmed is typically wound onto a take-up reel or fed into an in-line granulator for recycling. Peninsula Plastics recycles their scrap and waste plastic by feeding it into a granulator (grinder) and producing ground flake plastic to re-use in their own facility. Frequently, scrap and waste plastic from the thermoforming process are converted back into extruded sheet and formed again.