Vacuum Forming - A Design Guide - MHP Industries (2022)

This is the process of moulding extruded plastic sheets heated to a pre-determined temperature. The sheets are heated and then sucked down by applying a vacuum to the underside of the mould, atmospheric air pressure then forces the heated plastic to adopt the shape of the mould.

The Pressure Forming Process

As above but with the addition of applying compressed air to the outer surface of the plastic sheet. More detail can be achieved with this process, but tooling is more complicated and expensive.

Guidelines for Designing Parts

1) Material Flow and Webbing

When you start to design your part imagine that you are draping a cloth or a sheet of paper over the part. This will give you a good idea of where the problems will be when forming, i.e. showing how the corners will pleat/web during forming.

Tip!Understanding webbing. Take a cigarette packet and try forcing asheet of paper over it. This will show where webs will develop!Sharp corners are to be avoided as this will hinder the flow of material and maximise the chance of webbing.

Tip! As the plastic cools it will shrink onto a male tool but away from afemale tool hence the less draft required on female tools.

Draw ratio refers to the height of the part to be formed compared to the footprint of the part (back to the sand castle i.e. Height of sand castle compared to diameter). The taller the part the thinner the material required to cover the whole part.

Tip!Avoid tall narrow areas which cause parts not to release from themould.

The draw ratio is important to understanding the process. The 3-dimensional part has a surface area that needs to be covered by a flat two-dimensional sheet. The sheet is heated and formed over or into a mould. It will then stretch to cover the mould and as the sheet stretches, it thins out.

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The draw ratio can be calculated but this is only to be used as a guide as every shape will react slightly differently on the flow and distribution of the material.

Total surface area of the part A is divided by footprint of the part B.

4) Texture

Texture can be applied to the parts in 2 ways.

  • Use material with texture applied and mould over a male tool (low cost but limited textures are available).
  • Use a female aluminium mould which has been textured. This can be expensive with the cost of texturing a mould, 40cm x 40cm x 15cm being in the region of £1000 (best option when using pressure forming as more detail is achieved).

Tip!More taper will be required on textured moulds to avoid thetexture scraping on ejection.

5) Pockets and Ribs

Any pockets or space between ribs must conform to a ratio. Depth of pocket or space between ribs cannot be greater than its width and preferably 75% of the pocket depth.

Tip!Two 10mm high ribs must have 10mm spacing between them as minimum.

6) Controlled Surfaces

It is important to consider the controlled surfaces. The controlled surface is always the tool side of the part. This is important for 2 reasons: –

  1. If 2 parts are to fit together, the only way of ensuring the fit is to have 2 controlled faces meeting each other.
  2. When trimming on a 5-axis router the parts are usually held on a jig locating the moulding on the controlled face.

Tip!Consider how the part will be trimmed during design as this can makea large saving on the unit cost price.

7) Ribs and Bosses

Ribs can be used to support a flat surface and are created separately and fixed onto the original part. This is the same for internal bosses, which are possible to machine separately and attach with a solvent adhesive on most materials used. Bosses can also be applied with metal inserts for fixing circuit boards etc.

8) Tolerances and Accuracy

Whenever possible allow as large a tolerance as possible.

When using CNC machined aluminium tools use tolerances ± 0.25mm for the first 25mm and ± 0.1 for every 100mm thereafter (Note this is only a guide and will not apply to all materials and designs).

Tips!

  1. Large tolerances will help reduce unit costs and speed up deliveries.
  2. Consider materials to be used as some materials have vastly different contraction rates on forming.
  3. Be careful with tolerances on PP and HDPE as shrinkage can vary by 2% or more.

Toolmakers Guide to Vacuum Forming

Things to consider

1) Draft

Always allow as much draft as possible. Most of this will be gained by the design of the part, but consider areas which will be disposed of after trimming, as taper up to 45° can be added in these areas.

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Tip!Question why a face has no taper! Ask if taper can be added.

2) Over Run

Tools that will be horizontally trimmed must be moulded over depth. This will vary on material and tool design but as a rule of thumb 12mm + material thickness is acceptable.

Tip!Consider the material being used prior to determining the overrun.

3) Strong

Tools can never be made too strong. The forces in Vacuum forming are generally underestimated. Force is 14-7 PSI.

Tip!This can add up over large areas. For example, an area 30cm x 30cm whenunder vacuum will be nearly 1 Tonne.

4) Radii

Sharp corners are not acceptable to a vacuum former and whenever possible use as large a radius as possible. This applies to both male and female tools.

Tips!

  1. No vacuum former will complain that a radius is too large. Thiswill strengthen corners.
  2. Corners with radii will make for stronger mouldings.
  3. Square corners create more webbing on the part.

5) Cleaning/Finishing

Tools should be finished to a 120 grit in general.

Vertical corners should have finishing lines in the direction of draw.

6) Venting/Shot Blasting

  1. Consider where to put vents.
  2. Use small vents on visible areas 0-75mm on vac tools and 0-5mm on pressure form tools.
  3. Large flat areas may require shot blasting to help air evacuation.
  4. All pockets, recesses and corners will require venting.
  5. Consider areas where air may get trapped.
  6. Vent spacing 25-50mm between centres.
  7. Tracked or slot venting can be used on the base of tools but consider cooling if a solid aluminium tool.
  8. Washers/spacers can be used between tool and plate but not if on a water cooled base/plate.
  9. Tall areas should be vented at the top for ejection.

Tip!A vacuum former will never complain about too many vents.

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7) Tool Fixing to a Base Plate

Tools should be fixed down to the base plate firmly.

  • Aluminium tools min. fixing 6mm threads.
  • Resin tools min. fixing 8mm threads.
  • Wood/Proto tools size no 8-10 wood screws.

Tip!Plastic shrinks onto a tool after forming so do not underestimate theforces on ejection trying to pull the tool off the base plate.

8) Tools for PP/HDPE

Wood tools are not suitable for moulding materials as the plastic goes wax like and gets stuck in the grain of the wood during forming.

Aluminium tools require a medium to coarse shot blast to avoid air entrapment on the mould surface.

Tools used for PP and HDPE must be plinthed up by approx. 25mm (this is to stretch the material as being formed). This is necessary due to the nature of the material stretching excessively and wrinkling when heated.

9) Tools for Polycarbonate

Wood, Resin or Aluminium tools can be used for moulding polycarbonate. Aluminium tools will require heaters to be fitted so tools can be run hot at approx. 90 deg C. The temperature must be controlled using a commercially available temperature controller along with a thermocouple fitted to the tool.

Further advice from the experts

MHP Industries are the leading experts in vacuum forming and toolmaking. Established in 1972 and still owned and managed by the Hipgrave family the company has gained a wealth of knowledge and technical knowhow.

We have put this guide together as an aid to our customers and any information in it is only to be used as a guide.

If you require any advice or have any specific questions related to Vacuum forming please feel free to call our team on 01494 461561.

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FAQs

What are the 4 stages of vacuum forming? ›

The Six Stages of Vacuum Forming
  • Make the mould. Firstly, a mould is constructed in the shape that the plastic will form around. ...
  • Place the mould into the vacuum former. ...
  • Position the heater above the plastic. ...
  • Move the shelf towards the plastic. ...
  • Switch the vacuum former on. ...
  • Remove the sheet from the vacuum former.

What industries use vacuum forming? ›

Applications of the Vacuum Forming Process
  • Agricultural components. ...
  • Automotive parts. ...
  • Packaging. ...
  • Household items. ...
  • Retail and marketing displays. ...
  • Signage.

Is vacuum forming an industrial process? ›

Vacuum forming is a manufacturing method used to shape plastic materials.

What is vacuum forming step by step? ›

Vacuum formed products are all around us and play a major part in our daily lives. The process involves heating a plastic sheet until soft and then draping it over a mould. A vacuum is applied sucking the sheet into the mould. The sheet is then ejected from the mould.

What are the disadvantages of vacuum forming? ›

Disadvantages of Vacuum Forming
  • Consistency in wall thickness / uniformity of plastic products is not always achievable.
  • Limited in the detail and complexity of parts.
  • This method is not cost effective on larger batch runs.
  • Additional time and cost involved in the finishing process.
26 Nov 2019

What plastic is best for vacuum forming? ›

The Best Plastic for Vacuum Forming

A common plastic used for vacuum forming is high impact polystyrene sheeting (HIPS). Incredibly flexible, HIPS can be moulded into almost any shape. Polycarbonate (PC) is another plastic used for vacuum forming.

What are the advantages of vacuum forming? ›

Benefits of Vacuum Forming for Low Volume Manufacturing
  • Highly detailed formed products are possible in a range of sizes.
  • Higher production speeds than fabricated assemblies.
  • Reduced equipment costs for large parts as large parts do not require high tonnage presses as would be true for injection molding.
6 Dec 2019

What materials can be vacuum formed? ›

There are many different types of plastics that are used in vacuum forming and these are some of the more common ones:
  • Acrylonitrile Butadiene Styrene (ABS)
  • Acrylic – Perspex (PMMA)
  • Co-Polyester (PETG)
  • Polystyrene (HIPS)
  • Polycarbonate (PC / LEXAN / MAKROLON)
  • Polypropylene (PP)
  • Polyethelene (HDPE)

What products does vacuum forming make? ›

Plastic Food Containers and Trays

The vacuum forming method is widely used in the food and packaging industry. For example, food storage containers and plastic trays are made of plastic, and vacuum forming is used.

What thickness can you vacuum form? ›

Vacuum forming sheet thickness may range from 0.0005 to 0.50 inch (0.0127 to 12.7 mm). However, for prototype applications, the Formech machines are limited to sheet thicknesses between 0.0005 to 0.25 inch (0.0127 to 6.35 mm). After a prototype is vacuum formed, it will shrink and grip the tool.

How big can you vacuum form? ›

Vacuum forming limitations

On its own, vacuum forming can only produce shallow products. As a rule, the depth cannot exceed 75% of the width or length whichever is less. It can be a slower process than others with the products prone to bubbling.

Can you vacuum form PVC? ›

Vacuum Forming

This method is best for larger products where high levels of detail or sharply defined corners aren't necessary. In fact, polyvinyl chloride vacuum forming is used for things like bathtubs and shower trays.

What are the parts of a vacuum former? ›

Read on to learn more about the 8 key components of the vacuum forming process: clamping, heating, sheet level, pre-stretch, vacuum, plug assist, cooling and release, and finishing and trimming.

How do you vacuum a mold? ›

Prop: Shop - How to Make a Vacuum Forming Machine - YouTube

Can you vacuum form vinyl? ›

The great thing about vacuum forming is how the vacuum pulls evenly on all areas of the vinyl... it's almost completely eliminates wrinkles.. It also pulls the vinyl tighter to the part the closer it gets to the part, so it "lays down" well...

What are the pros and cons of vacuum forming? ›

What Are the Advantages and Disadvantages of Vacuum Forming?
AdvantagesDisadvantages
✔ Excess plastic can be recycled into more sheets for future production needs✖ Excess moisture can cause unwanted bubbles to form
✔ Supports rapid prototyping processes✖ Clear or light-colored parts can show debris from the mold
6 more rows
7 Sept 2020

What are the limitations of vacuum casting? ›

Disadvantages
  • Production Restriction: Vacuum casting is born for low volume production. ...
  • Loose Tolerance: The silicone molding is formed by tightly clinging to the master model. ...
  • Continuous Flaw: Molding manufacturing can cause continuous flaws easily.
9 Apr 2021

Can you vacuum form aluminum? ›

In the production of moulds from solid aluminium, very complex shapes are often not feasible. The reason for this is the impossibility to create channels for vacuum or steam in such moulds; it can also be very difficult to supply vacuum or steam to such channels.

Can you vacuum form wood? ›

Vacuum forming tools can even be made of wood (only suitable for very short production runs) or, if the product exists already, a tool could be resin cast from it.

Why is HIPs good for vacuum forming? ›

HIPs is ideal for vacuum forming plastic space saving nested packaging and containers. HIPs thermoplastic is widely used in the food packaging industry because of its unique qualities of strength, hygiene, visual appearance, and ability to retain heat, while also not deforming because of general warm water application.

How much vacuum is needed for vacuum forming? ›

How much vacuum do I need? As a general rule most people could use 25 IN. HG. or even less for vacuum forming. If using thin easy to form plastics, some people even get by with the 4 to 6 inches provided by a shop vac, but more is always better for crisp definition and neccesary for thicker plastics.

When was vacuum forming invented? ›

In 1964 the first vacuum forming machine was patented. Speed of production and now fine detail could be built in to the design of thermoformed plastic products. The 1960s would see the full embrace of the consumer society for new and innovative materials.

What are the issues with vacuum forming a large former? ›

The most common vacuum forming problems we come across include: Mold or tool is too high in relation to its base area. Sharp vertical corners with minimal draught angles. Deep male molds in close proximity to each other.

Why is vacuum forming good for food packaging? ›

Vacuum formed plastics is an ideal way to package food and serve a number of purposes. The packaging protects foods from knocks and damage, it helps to maintain freshness, important for food safety and prevents any contamination, as well as being used to simplify preparation and cooking.

Is HDPE good for vacuum forming? ›

For example, high-density polyethylene (HDPE) is frequently used to vacuum form food storage containers. HDPE's resistance to acidic compounds makes it a viable material for vacuum forming cleaning product containers as well.

Can you vacuum form HDPE? ›

HDPE can easily be shaped using conventional methods, such as heat bending, pressure forming, and vacuum forming.

Can plastic hold a vacuum? ›

Plastics generally have a poor be- havior under extreme conditions: vacuum [5, 1] or high pressure, cryogenic or high temperatures for example.

Can you vacuum form polycarbonate? ›

MAKROLON Polycarbonate Sheet can be thermoformed on standard equipment. Vacuum forming, free blown forming, and line bending are the most extensively used processes.

Can you vacuum form plexiglass? ›

1) Vacuum Forming Acrylic Sheet

In this process, the parts are formed by heating acrylic to a suitable temperature. Place the acrylic sheet on the mold surface and fixed using a clamping unit. Heat it until it becomes soft and then quickly apply the vacuum.

What is vacuum forming and how it works? ›

Vacuum forming heats a plastic sheet until it becomes pliable, stretches the material onto a mold, and then uses vacuum pressure to obtain the desired part geometry. The simplest type of plastic thermoforming, vacuum forming uses wooden patterns and epoxy tools in addition to temperature-controlled aluminum tooling.

What is thermoforming process? ›

Thermoforming is a process of heating a thermoplastic sheet to its softening point. The sheet is stretched across a single-sided mold and then manipulated. Then, it cools into the desired shape.

Why is HIPs used for vacuum forming? ›

HIPs is ideal for vacuum forming plastic space saving nested packaging and containers. HIPs thermoplastic is widely used in the food packaging industry because of its unique qualities of strength, hygiene, visual appearance, and ability to retain heat, while also not deforming because of general warm water application.

What is the process of injection molding? ›

What is Injection Moulding? Plastic injection moulding is the process of melting plastic pellets (thermosetting/ thermoplastic polymers) that once malleable enough, are injected at pressure into a mould cavity, which fills and solidifies to produce the final product.

What are the advantages of vacuum forming? ›

Benefits of Vacuum Forming for Low Volume Manufacturing
  • Highly detailed formed products are possible in a range of sizes.
  • Higher production speeds than fabricated assemblies.
  • Reduced equipment costs for large parts as large parts do not require high tonnage presses as would be true for injection molding.
6 Dec 2019

What thickness can you vacuum form? ›

Vacuum forming sheet thickness may range from 0.0005 to 0.50 inch (0.0127 to 12.7 mm). However, for prototype applications, the Formech machines are limited to sheet thicknesses between 0.0005 to 0.25 inch (0.0127 to 6.35 mm). After a prototype is vacuum formed, it will shrink and grip the tool.

How big can you vacuum form? ›

Vacuum forming limitations

On its own, vacuum forming can only produce shallow products. As a rule, the depth cannot exceed 75% of the width or length whichever is less. It can be a slower process than others with the products prone to bubbling.

What type of plastic is used in thermoforming? ›

PET Plastic

One of the most common thermoformed plastics, PET, or polyethylene terephthalate, is commonly used for thermoformed packaging, and synthetic fibers and bottle production. Once molded into a shape, PET plastic must be dried.

What are the types of thermoforming? ›

There are two main types of thermoforming: vacuum forming and pressure forming. Vacuum forming uses heat and pressure to draw plastic sheets into its final configuration. Once a sheet is heated and placed over a mold, a vacuum is used to manipulate it into its desired shape.

What is the difference between thermoforming and vacuum forming? ›

Thermoforming is a process where thermoplastic sheets are heated to a pliable temperature, formed to a specific shape using a mold, and trimmed to create a finished product. Vacuum Forming takes it one step further. When the part is formed to the mold, vacuum pressure is added to assist with the molding of the part.

Can you vacuum form PVC? ›

Vacuum Forming

This method is best for larger products where high levels of detail or sharply defined corners aren't necessary. In fact, polyvinyl chloride vacuum forming is used for things like bathtubs and shower trays.

Is HDPE good for vacuum forming? ›

For example, high-density polyethylene (HDPE) is frequently used to vacuum form food storage containers. HDPE's resistance to acidic compounds makes it a viable material for vacuum forming cleaning product containers as well.

What materials are used to make a vacuum? ›

Typically, vacuum cleaners are made of a combination of metals and various plastics. With the development of the Plastics Industry, many parts which were once metal are now made of much lighter and often stronger plastics.

What are the 3 main parts of the injection mold? ›

Injection moulding uses a special-purpose machine that has three parts: the injection unit, the mould and the clamp.

How many types of mold are there? ›

There are 5 types of plastic moulding that is considered to be the most effective and most popular. These 5 types are extrusion moulding, compression moulding, blow moulding, injection moulding and rotational moulding.

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