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Is a version of thermoforming, where a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mold and forced against the mold by a vacuum. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers.
Normally draft angles are present in the design of the mold (a recommended minimum of 3°) to ease removal of the formed plastic part from the mold.
Relatively deep parts can be formed if the formable sheet is mechanically or pneumatically stretched prior to bringing it into contact with the mold surface and applying vacuum.
Suitable materials for use in vacuum forming are conventionally thermoplastics.
The most common and easiest to use thermoplastic is high impact polystyrene sheeting (HIPS).
This is molded around a wood, structural foam or cast or machined aluminum mold, and can form to almost any shape. This high impact material is hygienic and capable of retaining heat and its shape when warm water is applied and is commonly used to package taste and odor sensitive products.
Vacuum forming is also appropriate for transparent materials such as acrylic, which are widely used in applications for aerospace such as passenger cabin window canopies for military fixed-wing aircraft and compartments for rotary wing aircraft. Vacuum forming is often used in low-level technology classes for an easy way to mold.
Vacuum Forming Typical applications
Original equipment manufacturers (OEMs) utilize heavy gauge vacuum formed components for production quantities in the range of 250–3000 units per year. Vacuum-formed components can be used in place of complex fabricated sheet metal, fiberglass, or plastic injection molding.
Typical industry examples besides product packaging include fascias for outdoor kiosks and automated teller machines, enclosures for medical imaging and diagnostic equipment, engine covers in a truck cab or for construction equipment, and railcar interior trim and seat components.
Vacuum Forming Types of molds
There are numerous patterns one can make with vacuum forming. The most inventive way to use vacuum forming is to take any small item, replicate it many times and then vacuum for the new pattern to create a more cohesive form.
The vacuum forming helps tie the individual pieces together and make one mold out of many pieces that can easily be replicated. From there, you can cast plaster, concrete, etc. into the plastic form.
Wood patterns are a common material to vacuum form as it is relatively inexpensive and allows the customer to make changes to the design easily. The number of samples that one is able to get from any pattern depends on the size of the part and the thickness of the material.
Once the specifications of the part have been met, the pattern is then used to create a ceramic composite mold or cast aluminum mold for regular production. Potentially, there are ways to create holes in plaster with a vacuum form if the replicated forms you make the vacuum form from are deep enough and you leave gaps between them for the plastic to form into.
Then, once the plastic is used to cast a plaster mold, the deep plastic areas will leave holes if the mold is not completely filled.
Cast aluminum molds are cast at a foundry and typically have temperature control lines running through them. This helps to set the heat of the plastic being formed as well as speed up the fabrication process. Aluminum molds can be male or female in nature, and can also be used in pressure forming applications. The main drawback with this type of mold is the cost.
Vacuum forming mold made from Aluminium (cavity) and Steel (frame)
Machined aluminum molds are like cast aluminum, but are cut out of a solid block of aluminum using a CNC machine and a CAD program. Typically, machined aluminum is used for shallow draw parts out of thin gauge material. Applications may include packaging and trays.
Cost is a significant factor for this type of tooling.
Composite molds are a lower cost alternative to cast or machined aluminum molds. Composite molds are typically made from filled resins that start as a liquid and harden with time. Depending on the application, composite molds can last a very long time and produce high-quality parts.