Vacuum forming
Encyclopedia
Vacuum forming, commonly known as vacuuforming, is a simplified version of thermoforming
, whereby a sheet of plastic
is heated to a forming temperature, stretched onto or into a single-surface mold
(BrE, mould), and held against the mold by applying vacuum
between the mold surface and the sheet.
The vacuum forming process can be used to make most product packaging, speaker casings, and even car dashboards.
The first commercial manufacturer of vacuum-formed plastics was Robinson Industries of Coleman, Michigan.
Normally, draft angle
s must be present in the design on the mold (a recommended minimum of 3°). Otherwise, release of the formed plastic and the mold is probably difficult.
Vacuum forming is usually, but not always, restricted to forming plastic parts that are rather shallow in depth. A thin sheet is formed into rigid cavities for unit doses of pharmaceuticals and for loose objects that are carded or presented as point-of-purchase items. Thick sheet is formed into permanent objects such as turnpike signs and protective covers.
Relatively deep parts can be formed if the form-able sheet is mechanically or pneumatically stretched prior to bringing it in contact with the mold surface and before vacuum is applied.
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/machined aluminum mold and can form to almost any shape. 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 "bubbles" for rotary wing aircraft.
s) utilize heavy gauge vacuum formed components for production quantities in the range of 250 - 3000 annual production volume. Vacuum-formed components can be used in place of complex fabricated sheet metal, fiberglass
, or plastic injection molding. Typical industry examples include:
Cast aluminum Molds - Cast aluminum molds are cast at a foundry and typically have temperature control lines running through them. This helps to regulate the heat of the plastic being formed as well as speed up the production 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 cost.
Machined aluminum Molds - Machined aluminum molds are like cast aluminum except they are cut out of a solid block of aluminum using a CNC machine and some sort of CAD program. Typically machined aluminum is used for shallow draw parts out of thin gauge material. Applications may include packaging as well as trays. Again, cost is a significant factor with this type of tooling.
Composite
Molds - 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 producing high quality parts. Within the category of composite molds, the subset of "Ceramic" molds has consistently proven to be the most durable. While not temperature controlled, these molds can run nearly as fast as Cast or Machined aluminum, yet at a substantially lower price point. Suitable for all but the highest volume production and strictest tolerances. Source: Composite Vacuum forming mold
Thermoforming
Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product...
, whereby a sheet of plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
is heated to a forming temperature, stretched onto or into a single-surface mold
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
(BrE, mould), and held against the mold by applying vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
between the mold surface and the sheet.
The vacuum forming process can be used to make most product packaging, speaker casings, and even car dashboards.
The first commercial manufacturer of vacuum-formed plastics was Robinson Industries of Coleman, Michigan.
Normally, draft angle
Draft angle
In engineering, draft is the amount of taper for molded or cast parts perpendicular to the parting line. It can be measured in degrees or mm/mm ....
s must be present in the design on the mold (a recommended minimum of 3°). Otherwise, release of the formed plastic and the mold is probably difficult.
Vacuum forming is usually, but not always, restricted to forming plastic parts that are rather shallow in depth. A thin sheet is formed into rigid cavities for unit doses of pharmaceuticals and for loose objects that are carded or presented as point-of-purchase items. Thick sheet is formed into permanent objects such as turnpike signs and protective covers.
Relatively deep parts can be formed if the form-able sheet is mechanically or pneumatically stretched prior to bringing it in contact with the mold surface and before vacuum is applied.
Suitable materials for use in vacuum forming are conventionally thermoplastics. The most common and easiest to use thermoplastic is High Impact Polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
Sheeting (HIPS). This is molded around a wood, structural foam or cast/machined aluminum mold and can form to almost any shape. 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 "bubbles" for rotary wing aircraft.
Typical heavy gauge vacuum forming applications
Original equipment manufacturers (OEMOEM
OEM means the original manufacturer of a component for a product, which may be resold by another company.OEM may also refer to:-Computing:* OEM font, or OEM-US, the original character set of the IBM PC, circa 1981...
s) utilize heavy gauge vacuum formed components for production quantities in the range of 250 - 3000 annual production volume. Vacuum-formed components can be used in place of complex fabricated sheet metal, fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
, or plastic injection molding. Typical industry examples include:
- KioskKioskKiosk is a small, separated garden pavilion open on some or all sides. Kiosks were common in Persia, India, Pakistan, and in the Ottoman Empire from the 13th century onward...
s and automated teller machineAutomated teller machineAn automated teller machine or automatic teller machine, also known as a Cashpoint , cash machine or sometimes a hole in the wall in British English, is a computerised telecommunications device that provides the clients of a financial institution with access to financial transactions in a public...
s - Enclosures for medical imaging and diagnostic equipment such as magnetic resonance imagingMagnetic resonance imagingMagnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) machines - Engine covers in a truck cab
- Railcar interior trim and seat components there are 4 different types of moulding
Common problems encountered with vacuum forming
- Moisture absorption: absorbed moisture expands forming bubbles within the plastic's inner layers. This will be solved by drying the plastic for an extended period at high but sub-melting temperature.
- Webs form around the mold, which is due to overheating the plastic and so must be carefully monitored. Webbing can also occur when a mold is too large or parts of the mold are too close together.
- Objects that are formed often stick to the mold, so make sure there is an angle of 3 degrees or more.
Types of Vacuum Forming Molds
Wood Patterns - wood patterns are generally the first stage to a vacuum forming project. They are relatively inexpensive and allow the customer to makes changes to their design very easily. The number of samples that one is able to get from a wood pattern depends on the size of the part and the thickness of the material. Typically, wood patterns are used to gauge general functionality of both the part and the thickness of the material. Once the specifications of the part have been met, the wood pattern is then used to create a ceramic composite mold, or cast aluminum mold for regular production.Cast aluminum Molds - Cast aluminum molds are cast at a foundry and typically have temperature control lines running through them. This helps to regulate the heat of the plastic being formed as well as speed up the production 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 cost.
Machined aluminum Molds - Machined aluminum molds are like cast aluminum except they are cut out of a solid block of aluminum using a CNC machine and some sort of CAD program. Typically machined aluminum is used for shallow draw parts out of thin gauge material. Applications may include packaging as well as trays. Again, cost is a significant factor with this type of tooling.
Composite
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
Molds - 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 producing high quality parts. Within the category of composite molds, the subset of "Ceramic" molds has consistently proven to be the most durable. While not temperature controlled, these molds can run nearly as fast as Cast or Machined aluminum, yet at a substantially lower price point. Suitable for all but the highest volume production and strictest tolerances. Source: Composite Vacuum forming mold
Further reading
- D.E. Walsh, Do It Yourself Vacuum Forming for the Hobbyist, Workshop Publishing, Lake Orion, MI, 2002
- Soroka, W, "Fundamentals of Packaging Technology", IoPP, 2002, ISBN 1-930268-25-4
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6