Plastic Vacuum Forming

In this article we will look very simply at Vacuum Forming and the basic principles behind it. In spite of the different applications there are available, and the “easy to use” equipment in the market place, it is, in my opinion, and certainly in terms of volume and consistency, still best produced by the “experts.”

Briefly, what is Vacuum Forming?

Vacuum Forming, is a plastic thermoforming process whereby, and very simply described, a thermoplastic sheet is inserted, in a cold state, into the vacuum forming area. The thermoplastic is heated to the desired temperature to make it pliable and then stretched onto or into a male or female mould which usually is raised up to the thermoplastic sheet from underneath. Trapped air is evacuated and the sheet is held against the mould by the application of a vacuum between the sheet and the mould surface. With all air removed and the thermoplastic heated to its best pliable state the fit between the sheet and the mould creates a perfect seal with the thermoplastic conforming exactly to the mould shape. Usually there are venting lines within the mould to assist the vacuum as indeed many moulds equally have water cooling systems integrated to assist the cooling process, The “item” is now cooled into the shape of the mould to form its three dimensional shape, and then the process of air supply is, in essence, reversed, in order to remove the now cooled plastic item from the mould.

Normally, draft angles must be present in the design on the mold (a recommended minimum of 3°), otherwise release of the formed plastic and the mold is very difficult.

Commonly used materials:

ABS (acrylonitrile-butadiene-styrene). A class of composite plastics commonly used to make automotive body parts and computer cases

• HIPS (High impact polystyrene sheeting) used for fridge lines, vending cups, food packaging etc)
• PVC (Polyvinyl chloride)
• HDPE (High density polyethylene) used extensively in the plastic bottle sector
• PETG (Polyethylene Terephtalate Glycol) – Blister packs and kitchen products

The above represent a small sample of materials used which may be required in heavy gauge sheets from 1mm to 10 mm thick or even in thin film format.

What are the problems?

Most problems that can be encountered via vacuum forming are met because the expertise or care used in the process is not sufficient, which is why I would always recommend using a specialist company. There are many materials that can be used and they all have their own idiosyncrasies so that as their individual properties vary, so too will the production requirements in order to form the desired item.

Coupled with the varieties found within the materials used, will be other such considerations such as the type of moulds required, male/female, clay, wooden, epoxy resin, aluminium, split moulds or multi-impression moulds and will they require venting, tapers or plugs? Any variations that are not considered and dealt with correctly can result in whole list of common problems within the finished items such as webbing, chill marks, thinning, blisters and bubbles, scorching, whitening warping or perhaps poor definition.

However, placed in the right hands where the equipment and materials match the requirement, the quality, speed of manufacture and cost-effectiveness of the end item can be second to none.

Advantages

• Versatility and flexibility
• Low tooling costs
• Cost effective
• Strength to weight ratio is excellent
• Efficient prototyping
• No need to paint – colour and texture are “built-in”
• Visually appealing
• Design flexibility
• Simple to modify
• Sharp precise detail

Where can I see these items?

It is probably true to say that plastic revolutionised the design world and vacuum formed parts are no different, they are seen almost everywhere. Probably one of the most common uses can be seen in product packaging, point-of-sale displays and transit trays, enclosures and casings. However don’t just look at the obvious, consider too; car dashboards, Radiotherapy masks, Boat hulls, aircraft wings and even internal parts for NASA for the space shuttles. Everywhere you look, Vacuum Formed plastic parts are a fundamental part of our everyday life.

Plastic Vacuum Forming