Sofia Martinez
Vacuum forming is a simplified version of thermoforming that uses heat and a vacuum to form plastic over simple pattern molds. It is a technique for shaping sheet plastics into 3D shapes, which can be done at home, easily and cheaply. The basic technique involves clamping a sheet of plastic to a frame, heating it in an oven until it's soft and rubbery, stretching it over a mold, and sucking the plastic inward onto that mold with a vacuum system. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers, as well as disposable plastic cups and lids, stage props, and even full-sized boat hulls.
| Characteristics | Values |
|---|---|
| Process | Vacuum forming uses heat and a vacuum to form plastic over a mold |
| Plastic type | High Impact Polystyrene Sheet (HIPS) for low-impact products, ABS for bathroom shower trays, HDPE for exterior vehicle parts, acrylic, or Sintra (expanded PVC) |
| Mold type | Wood, plaster, concrete, ceramic composite, aluminium, resin, or composite |
| Equipment | Oven, heat gun, vacuum pump, gloves, industrial vacuum former, kitchen oven, grill, reflector, electrical junction box cover, MDF, vacuum cleaner, shop-vac, spring clamps, drill press, table saw, hand saw, combination square, pencil, glue, grid paper, oven, power supply, RCD device, CNC machine, CAD program |
| Steps | 1. Clamp a sheet of plastic to a frame 2. Heat the plastic in an oven until soft and rubbery 3. Stretch the plastic over a mold 4. Suck the plastic inward onto the mold with a vacuum 5. Remove the plastic from the mold and trim off excess |
| Tips | Avoid materials that will melt or deform under heat. Use a draft angle of three degrees or more to prevent objects from sticking to the mold. Avoid tall, narrow areas that will cause parts not to release from the mold. Avoid sharp corners, as these will hinder the flow of material and maximize the chance of webbing. |
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What You'll Learn
Vacuum forming equipment
Vacuum forming is a simplified version of thermoforming, which uses heat and a vacuum to form plastic over a mould. This process is used to form plastic into permanent objects. It is a popular and affordable type of 3D forming technology.
There are various types of vacuum-forming equipment available, from desktop machines to large-format and semi/fully automatic machines. Desktop models are perfect for prototyping, arts and crafts projects, and small-product production lines. They are equipped with features such as built-in vacuum pumps, mechanical safety interlocks, digital timers, and energy-efficient quartz heaters. Floor-standing machines offer more control over the thermoforming process with auto-level and pre-stretch features.
For industrial applications, Formech offers a range of automatic sheet and reel-fed vacuum forming machines. The HD and TF series are designed for demanding industrial applications while being compact and cost-effective. The HD series is the most advanced, operating semi-autonomously using sheet materials. The TF series is fully automatic and can process a diverse range of applications, including chocolate trays and decorative films.
Vacuum forming machines can also be custom-designed to meet specific requirements and exact specifications. This includes considerations such as tooling design and process optimisation.
In addition to commercial machines, it is possible to build a simple vacuum former for a home workshop. This typically involves using a metal box with two bar elements enclosed by a grille front and a reflector to generate heat. The heated plastic is then rapidly sucked over a pattern or formed shape using an industrial vacuum pump.
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$7.38
Heating the plastic
It is important to ensure even heating across the plastic sheet for uniform shaping. The heat box should be designed to heat the plastic sheet evenly without burning it. The height of the box is important; if it is too tall, the plastic sheet will take too long to heat, and if it is too short, the plastic may melt or burn. The plastic should be placed in a metal frame above the heat box, and once it is ready, it can be flipped over to the vacuum side for forming.
The plastic will start to sag as it heats up, and it is important to monitor this process closely. You will need to move quickly once the plastic reaches the right temperature, as it will start to cool down and harden again. You can tell when the plastic is soft enough to be moulded when it starts to sag or when you touch it and it yields. If the plastic gets too hot, it may collapse or burn.
To avoid burning the plastic, it is important to use the correct temperature and heating time. The ideal temperature and time depend on the type of plastic and the thickness of the sheet. For example, ABS plastic only needs to be heated for 4-5 minutes, while thinner plastics will cool down more quickly after removing the heat source. It may take some trial and error to determine the optimum heating time for the plastic you are using.
It is also important to consider the moisture content of the plastic. If the plastic has absorbed moisture, it should be dried at a high but sub-melting temperature before heating to prevent the formation of bubbles within the plastic's inner layers, which can weaken the final product.
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Vacuum-forming the plastic
Vacuum forming is a simplified version of thermoforming. It involves heating a sheet of plastic to a forming temperature, stretching it over a single-surface mould, and forcing it against the mould with a vacuum. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers.
To vacuum-form plastic, you will need a vacuum former, which can be purchased or made at home. A simple vacuum former can be made with a kitchen oven or another heat source, a vacuum pump or vacuum cleaner, and a mould. The mould can be made from various materials, including wood, aluminium, composite resins, or MDF. It's important to ensure that the mould is larger than the object being formed and that it has a draft angle of at least 3 degrees to ease the removal of the formed plastic part.
Once you have your vacuum former and mould, you can begin the vacuum-forming process. Start by clamping a sheet of plastic to a frame, such as a window screen-type aluminium frame. The size of the plastic sheet will depend on the size of the mould and the desired object. It's important to avoid tall, narrow areas and sharp corners in the mould design, as these can cause issues with the plastic release and increase the chances of webbing.
Heat the plastic sheet in the oven or with a heat gun until it becomes soft and rubbery. Be careful not to overheat the plastic, as this can cause webbing and other issues. Test the temperature by touching the plastic or observing its flexibility. Once the plastic is soft enough, quickly stretch it over the mould, ensuring that it is centred and firmly in place.
Finally, apply the vacuum to the underside of the mould. The vacuum will suck the heated plastic inward, forcing it to adopt the shape of the mould. Once the plastic has cooled, release the vacuum and remove the formed plastic from the mould. You may need to trim excess plastic to achieve the desired shape.
Vacuum forming is a fun and easy way to create an infinite variety of shapes and objects from plastic sheets. With the right tools and materials, anyone can try their hand at vacuum forming and experience the satisfaction of creating something from scratch.
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Removing the mould
To aid in the release of the mould, a coating of silicone release spray can be applied to the mould before forming.
It is also important to consider the design of the mould. Draft angles in the mould—a minimum of 3° is recommended—help to ease the removal of the formed plastic part. These draft angles prevent the formed plastic from sticking to the mould.
After the mould is removed, the formed plastic part will need to be shaped. This usually involves a combination of bandsaw work, belt sanding, and die-grinding.
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Finishing the plastic
Once the plastic has been moulded, it will need to be finished to turn it into a usable product. This usually involves a combination of bandsaw work, belt sanding, and die-grinding. It is recommended to leave some extra room around the edges of the mould to allow for trimming.
The plastic should be released from the mould within 2-3 minutes of forming, while it is still warm. Cool plastic is hard plastic, and it will be much more difficult to remove once it has cooled and hardened.
When trimming, it is important to avoid tall, narrow areas, as these can cause the plastic to stick to the mould. Vertical corners should have finishing lines in the direction of the draw. All pockets, recesses, and corners will require venting, and large flat areas may need shot blasting to help with air evacuation.
If there is any unevenness in the surface of the plastic, this can be smoothed out with body filler, and then sanded with 80-grit paper to create a smooth finish.
Finally, the plastic can be cut out of the sheet using a guillotine, which involves pressing a blade through the product into a die underneath. This method is suitable for low volumes of parts where straight lines are not a problem. Alternatively, roller cutting can be used for larger items, and press cutting is a precise method suitable for small items.
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Frequently asked questions
Vacuum moulding is a simplified version of thermoforming, where a sheet of plastic is heated and then stretched onto a single-surface mould, and forced against the mould by a vacuum.
Vacuum moulding can be used with a variety of plastics, including High Impact Polystyrene Sheet (HIPS), ABS, HDPE, acrylic, and Sintra (expanded PVC). It can also be used with other vacuum-formable materials such as wood, resin, aluminium, and concrete.
You will need a vacuum pump or a household vacuum cleaner, an oven or heat gun, gloves, and safety goggles. For the mould, you can use MDF, melamine board, Formica, electrical junction box, or wood.
