Vacuum forming takes its name from the fact that a vacuum is used to form a sheet of plastic into a desired shape. It is popular within various industries and sectors because it can produce detailed shapes quickly and affordably.
This process is mostly suitable for low to medium-volume batch production, or very large-format assemblies. Plastic vacuum forming can also offer a cost-effective alternative to injection moulding, which often involves a significant investment in tooling. Discover more about vacuum forming in our ultimate guide, where we go through common practices and methods of vacuum forming.
Vacuum forming is widely used across different industries, creating a wide range of vacuum formed products and can be used in panels, trays, packaging and plastic boxes for electrical appliances such as washing machines, vacuum cleaners and fridges.
Vacuum forming can also create products such as product packaging trays, medical blister packs, display trays and display sign holders, trade show displays, food storage containers and car parts like fenders and skid plates.
Plastics can be shaped using a process called thermoforming. This is simply the technique of applying heat to plastic so it becomes soft and malleable. Currently, the two main approaches to thermoforming are vacuum forming and pressure forming.
Vacuum forming and pressure forming take the opposite approach to getting the plastic into the mould. With vacuum forming, a vacuum pump sucks the plastic into the mould. With pressure forming, compressed air pushes the plastic down. Vacuum forming is quicker and more affordable, but pressure forming can produce a higher level of detail.
Vacuum forming and 3D printing are completely different technologies. Where vacuum forming uses moulds, 3D printing uses “cookie cutters”. It essentially cuts out slice after slice of the object and stacks each slice on top of the next until the desired result is achieved.
3D printing is, currently, best suited to low-volume applications. It’s particularly useful for jobs which need to be completed quickly. For example, you could use a 3D printer to create a plastic tool for vacuum forming a batch of prototypes. Once you had the design fixed, however, you’d probably spend the time and money needed to create a more robust mould.
The vacuum forming process is a technique used to shape and form plastic products from a sheet of plastic and is commonly used in making large plastic components but also has the ability to be utilised when creating smaller plastic components.
The process of vacuum forming consists of five main stages. These are:
Here is a more detailed guide to each stage.
The first step in the vacuum process is making the tool. All our tools are based on designs you provide. This allows you to have complete control over the finished component.
Tools can be made from a variety of materials including Model Board or Aluminium, depending on the complexity and quantity of the plastic part being formed. If possible moulds should have tapered sides of a minimum of 2 degrees as this allows the plastic part to be released from the mould more easily.
Thermoforming can be made from a wide variety of materials of various levels of durability. These include:
There are four main criteria that will determine the most appropriate tooling material for any given job. These are:
In some cases, speed may also be a factor at least in the short term. For example, a production run may start with plastic moulds as these can be produced quickly. It may then move on to using aluminium moulds for their robustness.
Once the tool is created, it needs to be put into the thermoforming machine. The plastic sheet is placed above the mould but not on it. The plastic is then clamped securely into place. Finally, the heater is positioned above, but not on, the plastic sheet.
Once the plastic is in place, a pneumatic ram positions the top heaters above and below the sheet of plastic. After a set period of time the plastic should have been heated enough to ensure that it is fully flexible and mouldable ready for the next step.
In thermoforming, it is vital that the correct temperature is maintained across the entire plastic sheet. Even minor variations in temperature could ruin the outcome of the process.
For this reason, modern vacuum forming machines use pyrometers to monitor the plastic sheet temperature. The pyrometers interact with the process controls to ensure that the heating is promptly adjusted if the temperature varies.
Some vacuum forming machines can also support various other strategies for ensuring a consistent finish. The two main ones are sheet-level monitoring and pre-stretching.
A photo-electronic beam is projected into the gap between the heater and the plastic. If this beam is interrupted, it means that the sheet of plastic has started to sag downwards. The machine will therefore counteract this by blowing pressurised air into the machine to lift the plastic back into position.
After the initial heating stage, the plastic sheet is stretched to ensure that its thickness is exactly consistent. This means that if the temperature is applied consistently, the results should be more consistent across the whole sheet.
The table, on which the newly created tool sits on, is then moved upwards by a pneumatic ram towards the plastic. If the plastic has been heated correctly and is sufficiently mouldable, with the aid of Vacuum the plastic is pulled to the tool face.
Once the plastic reaches the correct temperature, the mould will be moved upwards towards the plastic. The vacuum pump will then be activated. This will suck out all the air from the machine. As it does so, the plastic will be drawn to the tool. This process has to be done quickly so the plastic stays warm and therefore malleable.
The plastic has to harden before it can be released. High-speed fans are used to reduce the time this takes. Some machines also spray chilled water onto the plastic. This reduces the cooling time even further.
Once the sheet has cooled, it usually needs to be separated out into individual components. After this it can go onto the next process of trimming. The components may then need some finishing touches before they are considered ready to be used. For example, packaging may need to be printed and/or decorated in some way.
Fundamentally, all vacuum forming machines operate on the same basis. In practical terms, however, there are wide variations between the capabilities of different vacuum forming machines. In broad terms, current vacuum forming machines can be divided into four main types. These are:
The capabilities of the machines go up with size and price. For example, DIY machines might use ceramic heaters. These have a relatively slow response time. Industrial vacuum forming machines, by contrast, are much more likely to use quartz heaters.
Industrial vacuum forming machines are ideal for commercial applications and for businesses who are manufacturing large parts or in large volumes, this is because they have the capabilities to handle demand and can effortlessly recreate products. Whereas, smaller tabletop or DIY vacuum forming machines may struggle with these high demands.
These are much quicker to respond to instructions. Industrial vacuum forming machines are also more likely to have twin heaters, rather than just one.
Likewise, DIY machines may have a limited number of heating zones compared to industrial machines. This can make a huge difference to the consistency of the temperature, especially when working with large batches. Of course, DIY machines are not really intended for making large batches.
Similarly, DIY machines are unlikely to be able to use complex tools such as plugs.
Firstly this ensures that the plastic goes where it is supposed to go, for example into all corners.
Secondly, it ensures that the plastic has a consistent thickness.
Plug tools are most useful when moulds are particularly deep and/or particularly complex. Again, DIY machines are not really intended for these kinds of jobs.
Thermoforming tools come in two main forms. Technically, these are known as male and female. They are, however, often known as male and female.
Positive (male) moulds are convex. This means that the plastic is formed over them. As a result, positive moulds prioritise the interior dimensions of the parts. Negative (female) moulds are concave. This means that the plastic is formed inside them. As a result, negative moulds prioritise the exterior dimensions of the parts.
Regardless of which type of mould is used, it needs to be designed in a way that makes it possible to release the plastic without damaging it. Here are some important points to consider.
It is extremely difficult to release vacuum formed plastic from moulds which only use perfectly straight lines. This means that draft angles (taper) should be added to all sides of the mould. With male mounds, there should be a minimum of 3° of taper. With female moulds, there should be at least 5° of taper. As moulds get taller/deeper, the degree of taper should be increased.
On a similar note, it is much easier to extract a part from a mould that uses rounded corners than from a mould that uses straight corners.
In simple terms, you should generally aim for balance. For example, if you’re designing a mould with tall/deep features, try to spread them apart from each other. Also, keep in mind that the taller/deeper a mould is, the more plastic it will need. In other words, the more it will cost to produce.
Creating a textured mould is often more complex (and hence expensive) than creating a plain one. This may be justified over a large production run as it could allow for the use of smooth plastic. Over shorter production runs, however, it may be more economical (and quicker) to keep the mould smooth and use textured plastic.
Similar comments apply to the use of ribs and bosses. They can be included in the design of the mould. This will, however, increase its complexity and thus the cost and time needed to produce it. This may be justified over large production runs. For short production runs, it may be easier, more economical and quicker to add them afterwards with adhesive.
Vent holes help with the process of air removal. It is therefore recommended to place them in strategic positions such as at edges, in corners and in cavities.
Including undercuts almost inevitably raises production costs. Firstly, they may require the creation of a more complex tool than would otherwise be required. Secondly, they make it more difficult to extract the plastic from the mould.
There are a range of different vacuum forming plastics used within the vacuum forming process, such as acrylic (PMMA), polyethylene (HDPE), polystyrene (HIPS), and many more. Here is a quick guide to the plastics most commonly used in vacuum forming.
| Plastic | Key properties | Key characteristics | Common applications |
|---|---|---|---|
Acrylic – Perspex (PMMA) |
Hygroscopic
Medium/strong Temperature-sensitive, can become brittle 0.3 – 0.8% shrinkage rate Prone to shattering but good to work manually and takes cellulose and enamel sprays Available in multiple colours, can be transparent or opaque |
Very suited to applications where clarity is important. | Lights and light diffusers, roof domes, sanitary ware (including baths) and signs |
Acrylonitrile Butadiene Styrene (ABS) |
Hygroscopic
Strong Forms easily to a high definition 0.3 – 0.8% shrinkage rate Easy to saw and cut and takes all paints Unlimited colour range |
Hard and rigid, resists both weather and impact. | Electrical enclosures, luggage, sanitary parts and vehicle parts |
Polycarbonate (PC / LEXAN / MAKROLON) |
Hygroscopic
Very strong Forms well to a high definition 0.6 – 0.8% shrinkage rate Can be machined, ultrasonically welded, taped and drilled and takes spray Clear, translucent and solid colours, embossed textures, opal and diffuser patterns |
Great resistance against both fire and impact. | Aircraft trim, guards/visors/shields, light diffusers, signage and skylights |
Polyethylene (HDPE) |
Not Hygroscopic
Very strong PE itself is challenging. PE FOAM is easier to manage but needs to be formed at low temperatures 2.0 – 3.5% shrinkage rate Cannot be sprayed but can be printed with certain inks Black, white and colours |
Very similar to PP. Has high shrinking rates but good chemical resistance. | Caravan parts, enclosures and housings, vehicle parts |
Polyethylene Terephthalate Glycol/Co-Polyester (PETG) |
Can generally be used without pre-drying
Strong Good formability, capable of high definition 0.3 – 0.7% shrinkage rate Can be sawn, cut and routered. Can be die-cut and punched to a limited extent. Can be printed using paints and inks intended for polyester Mostly clear, limited colour range |
Sterilizable and resistant to alcohols and acidic oils but not recommended for use with high-alkaline solutions. Attractive and easy to form. | Hygienic packaging (e.g. for foods and medicines), plus displays (e.g. point-of-sale displays) |
Polypropylene (PP) |
Not Hygroscopic
Very strong Challenging to form. Requires precision control of temperature and sheet level 1.5 – 2.2% shrinkage rate Cannot be sprayed Translucent, available in black, white and colours |
Challenging to form and prone to sheet sag, but very flexible and non-absorbent. | Chemical tanks and enclosures, luggage, packaging for food and medicine, toys |
Polystyrene (HIPS) |
Not hygroscopic
Medium/strong Forms well can support high definition 0.3 – 0.5% shrinkage rate Machines well but needs special primer to be sprayed Clear and coloured, available in patterned and textured forms. |
Has poor UV resistance so best kept for indoor applications. Very easy to form and available in a wide range of colours, patterns and textures | Most high-volume/low-value items such as a lot of (non-sterile) packaging |
The plastic vacuum forming process is suited to a variety of applications across multiple different sectors making it the ideal manufacturing process for a number of plastic parts. The problem, therefore is understanding which type of plastic is best suited to your individual requirements.
Here at Ansini, we are experienced with and able to manufacture plastic parts in a variety of plastics all of which are best suited to different applications. Below are the various plastics used in vacuum forming as well as their ideal uses which will help you decide which plastic is right for you.
Acrylonitrile butadiene styrene – commonly known as ABS – is hard and rigid plastic with a high impact resistance. This type of low cost plastic also has impressive weather resistant properties making it useful for machine housings, luggage and vehicle parts.
Acrylic Perspex (PMMA) – This is a high quality plastic and, as such, is more expensive. Despite this it is used in a variety of products, typically suited to medical applications. It has good strength and excellent formability making it ideal for use where definition is essential.
High impact polystyrene is a tough, rigid plastic with high impact strength, as its name suggests. It can be cut, trimmed and machined easily and comes in a variety of colours. This low cost plastic is, therefore, useful in the manufacture of toys, signs and point of sale displays.
High density polyethylene (HDPE) is used mainly for caravan and vehicle parts due to its very high impact strength whilst remaining flexible. It is easy to fabricate and weld and is one of the lower cost plastics used in vacuum forming.
Polyvinyl Chloride, or PVC, is a low cost plastic with medium to high strength capabilities. This vacuum forming plastic is easy to fabricate, weld and machine and has good fire retardant and chemical properties making it useful for a variety of applications including packaging, electronics and automotive.
Polypropylene is a low cost, flexible plastic with high impact strength. It is chemical resistant and has impressive aesthetic qualities making it useful for chemical tanks, food containers, and medical applications and automotive.
Acrylic plastic is easy to fabricate and bond well with adhesives and solvents. Whilst this plastic is in the higher cost bracket its high quality, versatility and impressive strength makes it ideal for signs, baths and displays/shelves.
Polycarbonate is a hard, rigid plastic with very good impact strength. Whilst it is one of the more expensive plastics it is self extinguishing and therefore has many uses in the aerospace industry as well as uses in the manufacture of visors, riot shields and machine guards.
This vacuum forming plastic is highly durable and has impressive impact strength. Alongside its durability, ASA is UV stable making it useful for outdoor applications. It is commonly used in the automotive industry for car mirrors and grilles but can also be used for garden furniture and signs.
PETG plastic is an FDA approved plastic with a high impact strength that can be sterilised and is resistant to a range of acids, oils and alcohols. It can precisely mould and trimmed without sacrificing structural integrity making it useful for food packaging and medical applications.
Ultimately, there are a number of vacuum forming plastics available to you, all of which have their own unique benefits. If you are unsure on which plastic to use it is always best to describe your product to your plastics manufacturer and allow them to recommend a plastic best suited to your needs.
The use of plastics has become increasingly controversial. They are, however, currently the only practical solution for numerous everyday problems. That being so, the keys to using plastics ethically are to minimise the quantity used and to ensure that the plastic is recycled and/or recyclable.
All plastics Ansini use can be recycled, as can all plastic waste Ansini produces.
It would be literally impossible to list every current application of vacuum forming. Here is just a quick sample of some of the main areas where it is used.
Vacuum forming is used extensively on the inside and outside of all kinds of vehicles. It can be used to produce parts that are light enough for aeroplanes and parts that are robust enough for agricultural vehicles, buses and HGVs.
Vacuum forming plays a huge role in car and vehicle manufacturing. All kinds of interior and exterior parts are made using vacuum forming. This helps to reduce costs for both the manufacturer and the purchaser without compromising on quality.
Vacuum forming has all kinds of uses within industrial sectors. At one end of the scale, it can be used to produce strong, weather-resistant parts for heavy-duty machines. For example, it is widely used in agricultural machinery. At the other end of the scale, it can be used to produce small runs of special items such as custom parts or prototypes.
The average household probably has vacuum-formed items in every room plus the garden (and garage). Kitchens and bathrooms in particular will be full of them. In fact, most sanitary ware is likely to use vacuum forming to some extent. This includes large items such as baths. In fact, if you have a hot tub in the garden, that was probably vacuum-formed too.
Vacuum forming is increasingly being used as an alternative to glass. So far, it’s only really used in smaller-scale applications such as skylights/light diffusers. This could, potentially, be extended in future.
Safety guards, safety goggles and visors and even riot shields can all be made using vacuum forming. Making items like these out of a single piece of plastic helps to increase robustness. This is, of course, a huge benefit in these kinds of applications.
Vacuum forming has long been used to create packaging for consumer goods, foods and medicine. It’s now increasingly being used to create eye-catching promotional displays.
Vacuum forming can be used to create a wide variety of different products across numerous business sectors. Vacuum formed products often include the following:
Like all technologies, vacuum forming has its pros and cons. In order to judge their significance, however, you need to look at them in context. With that in mind, here are seven key points to consider before starting a manufacturing process and an explanation of how the use of vacuum forming could influence their outcomes.
Vacuum forming is one of the fastest production methods used today. If you’re willing to use a fairly lightweight tool, you can get production moving very quickly. This makes vacuum forming a great choice for product development, where you’re probably going to want to make incremental improvements.
Similarly, once you have the tool created, the actual vacuum-forming process itself is very quick. Keep in mind, however, that the vacuum-forming process may not result in a completed item. It is quite common for vacuum-formed products to need further work before they can be used or sold.
Vacuum forming uses unique tools designed to very specific specifications. This means that every time the vacuum forming process is conducted the mould can be changed and multiple plastic parts can be made with varying designs.
This is ideal for making products that may change often due to the competitive nature of the market such as food packaging.
The fact that vacuum forming is so quick means that it’s very scalable. You can use it just as effectively for huge production runs as for agile prototypes. In fact, there’s a strong case for arguing that vacuum forming really comes into its own with smaller jobs.
Mass production, in various forms, has been a reality since the industrial revolution. By contrast, it’s only just becoming feasible to run small production jobs to similar levels of economy.
Even though vacuum forming uses one tool per job, it offers a huge level of versatility in the way it uses tools. For example, basic templates can be customised into new shapes and sizes. They can also be updated to reflect new developments in their area of use.
Vacuum forming can be a very economical means of production. There are, however, a few caveats here.
Firstly, everything hinges on the tool. Get the tool wrong and your entire production run will go wrong. Secondly, the tool needs to be kept scrupulously clean. If it gets at all dirty, this may show on the finished parts, especially if they are clear or light-coloured.
Secondly, the plastic needs to be handled with care. If it isn’t it can warp (especially if it’s thick) or bubble (especially if there’s excess moisture). There may be ways to recover from this, at least to some extent. For example, damaged or excess plastic can often be reused in future production. Your production run will, however, almost certainly take some kind of hit.
You also need to remember that many vacuum-formed products need some extra work done to finish them. This may not be hugely expensive. You do, however, need to keep it in mind when comparing vacuum forming with other production technologies.
Vacuum forming is a relatively simple process and requires significantly less advanced tooling when compared to the likes of injection moulding. This means that vacuum forming is extremely cost effective and plastic components can be made on a smaller budget without compromising on quality.
Vacuum forming still calls for relatively simple designs. Firstly, there’s a limit to how much you can realistically expect from the moulding process. Secondly, vacuum forming doesn’t apply the same degree of force as pressure forming or injection moulding.
On the other hand, vacuum forming is great for ensuring consistency. If you use the same tool, you should almost certainly get the same results. The only exception to this is if the plastic is mishandled. Bluntly, however, that is a reflection of your manufacturer’s skill (and equipment) not on vacuum forming itself.
In simple terms, the fewer parts an item has, the harder it is to break. Vacuum forming creates parts as a single piece. This makes them inherently more robust than similar items made from more than one component part.
The caveat here is that the robustness of the part depends, in part, on the robustness of the plastic used. Firstly, some plastics are generally more sensitive than others. Secondly, some plastics have strong resistance to some forces but weak resistance to others. The onus is therefore on the designer to choose the right plastic for the right situation.
Hygiene and sterility were important considerations long before COVID19. They were (and are) particularly important for food and medical packaging. They also apply, at least to an extent, in many other areas. It seems reasonable to assume that they will be considered even more important in a post-pandemic environment.
Vacuum forming is definitely not the only option for manufacturing sterile products. It is, however, definitely one of the quickest and most cost-effective options.
Vacuum forming has been in use for over 80 years now, and has created a wide range of vacuum formed products. This means that you might reasonably expect it to be at least close to obsolete. In actual fact, vacuum forming is still very much going strong. What’s more, its speed, versatility and affordability mean that it is still in huge demand.
Admittedly, the future of vacuum forming is very much tied to the future of plastics. This may, however, not be the drawback it seems. Given the usefulness of plastics, it seems likely that the way forward is to make them more sustainable, rather than to try to eliminate them.
This means that, in the long term, vacuum forming is likely to sit alongside pressure forming/injection moulding and 3D-printing as one of the world’s most important technologies.
Whatever your product or industry, our plastic forming production specialists can advise on the best manufacturing process to give you the best solution for your budget. If you are interested in learning more about our vacuum formed products or would like to arrange a free consultation, please contact Ansini today on 01623 812333 or email info@ansini.co.uk.
If you have a question for us, or would like to discuss a specific project, please do get in touch.