Deep-Drawing Guide


If you are new to model making, you will sooner or later come across the topic of deep-drawing. You might be overwhelmed at first sight because the process appears costly and time-consuming. However, you need not be discouraged. In this guide, we summarize the most important tools to get yourself started with thermoforming. The following sections aim to explain deep-drawing techniques in a simple and engaging way so that even beginners can get started right away.

 

OVERVIEW OF THE FOLLOWING SECTIONS

TOPIC 1 - SHORT INTRODUCTION

TOPIC 2 - OUR INSTALLATION

TOPIC 3 - THE ORIGINAL FORM / THE NEGATIVE

TOPIC 4 - PET FILM AS THERMOFORMING MATERIAL

TOPIC 5 - INSTRUCTIONS FOR DEEP-DRAWING

 

TOPIC 1 - SHORT INTRODUCTION

  1. Where can I use deep-drawing / thermoforming? 

The origins of deep-drawing lie in industrial mass production. The technique is also known as vacuum deep-drawing and thermoforming. In the industrial sector, it is mainly used for the production of packaging nowadays. Especially for smaller quantities, it is a more cost-effective option compared to, for instance, injection moulding.

In the private or home sector it is used primarily in model making. Particularly for hobbyists and DIY-enthusiasts, deep-drawing techniques offer ways of producing casting moulds and decorative elements. Only a few resources are needed which can be easily found in most households.

Beispiel_3D_Deko   Deko_3D_Beispiel   Grundgeometrie 

  1. How does deep-drawing work?

Deep-drawing is a physical process for forming thermoelastic materials. These materials can be moulded, by using heat and vacuum. The process itself comprises only a few steps, and additional materials are not required. For plastics, sufficient conditions can be achieved with normal household means, to bring the material into the desired shape.

Before we can start using deep-drawing, a 3-dimensional original form (also called negative or blank) must be created. Later in the process, the film is thermoformed to cover the negative. To achieve this, the negative is placed on an air-permeable grid. A vacuum (negative pressure) can be created underneath this grid in a deep-drawing box.

However, before placing the film on the negative, we must first evenly heat the film until we can thermoplastically form it. When we reach the correct point of heating, the to be formed film needs to be placed over the negative. Meanwhile, a vacuum is created from below, and the film is getting sucked in. The film covers the negative and cools down quickly. After cooling down, it resembles the original form’s shape, and we can remove it.

The entire process from heating the film to obtaining the finished product goes very fast: while for industrial techniques, it is only a matter of seconds, it takes around 1 – 2 minutes when done at home. The negative, or original form, can be used repeatedly. Usually, it is not damaged or even affected during the thermoforming process. Thus, several copies with film can be made one after the other with high accuracy to the original.

  1. What are the restrictions / requirements for the application of thermoforming techniques?

If you want to start with thermoforming at home, you should first be aware of the limitations of the method:

By deep-drawing only hollow forms of the original shape can be obtained. You can use this method to preserve both positives and negatives. It is useful if you need positives, e.g. for a windowpane in model making, or if you need negatives to reproduce your original shape. However, do not use hot material to fill the obtained form.

Furthermore, the original shape should not have any undercut edges or excessive height differences between the two parts. An undercut in this context is an edge with an angle smaller than 90°. Undercuts make it more difficult to remove the object from the film.

Even more complex shapes require a little more experience and a few attempts before they work properly. The same applies particularly to large parts: In the home sector, the size of the parts is determined by the size of the existing thermoforming box and the oven for heating the film. If you need larger parts, you have to be creative here as well.

Although in the industrial sector, strong plates and metal sheets are produced with deep-drawing techniques as well, the hobbyist will not have the same equipment at home. For this reason, in the private sector, films are primarily used with a thickness of 0.2 to 1 mm. These are usually sufficient to carry out the desired project.

 

In the following sections, we provide you with further important information and instructions on how to create deep-drawn models. If you are missing a topic, have any questions or suggestions, simply leave us a mail: fernschreiber@compact-solutions.de.

  

TOPIC 2 - OUR INSTALLATION

  1. Which materials do I need?
  2. What do I use to heat the film?
  3. How do I work effectively and quickly on the oven?
  4. How do I heat the film in the oven?
  5. How do I build a holding frame for the film?
  6. How do I build a thermoforming box?
  7. How do I get an even surface?

Before you start building a thermoforming installation, make sure you can answer the following questions: How big are the objects you want to thermoform? What resources do you already have at home? What materials can you buy in retail stores?

We try to provide you with a guide to deep-drawing, which can also be used by hobbyists and DIY-enthusiasts at home. Therefore, we recommend a thermoforming setup for DIN A4 sheets. For this size, standard household ovens are sufficient, meaning no additional investments are necessary.

  1. Which materials do I need?
  • standard household oven with top / bottom heat, circulating air and grill, radiant heater, or hot air dryer
  • vacuum cleaner
  • aluminum plates, chipboard, or plywood boards (either cut them yourself with an angle cutter, cutting disk or grinding wheel, or get them cut at a hardware store)
  • silicate plate (thickness of 2.5 cm, can be cut to the size of the inner area with a cutter knife)
  • wooden strips (plywood) and boards (OSB) for the thermoformed box or finished wooden crate
  • optional sealing compound, e.g. Tesa Moll
  • toggle lever clamps, wing nuts, or foldback clips
  • wood screws
  • drills for wood and aluminum
  • optional perforated metal plate and cotton fabric
  1. What do I use to heat the film?

In our workshop, we use a simple standard household oven - like the one you most likely have at home. However, we recommend an electric oven rather than a gas stove: with an electric oven, you can use top heat and grill function. This way, you don't have to heat the whole stove. Also, the temperature can be controlled more precisely.

We do not recommend radiant heaters for hobby and DIY purposes. They may heat the film unevenly, especially at the edges. The hot air dryer is particularly suitable for people who only want to do deep drawing occasionally or who only want to work on small objects up to 10 cm in diameter.

  1. How do I work effectively and quickly on the oven?

We work with the oven opened. For easier access, we have removed the door. However, if you use circulating air, you should keep the stove closed. Working on an open oven has advantages: opening the oven door does not delay the process, and the film can be removed with pinpoint accuracy. PET films, in particular, only need a few seconds to reach the ideal temperature and, thus, the ideal consistency for thermoforming.

The disadvantage of working in an open oven is heat escaping. It makes it more difficult to reach the required temperature. Therefore, we cut off the upper third in the stove by inserting an aluminum sheet on the middle rail of the oven, which we cut to shape. On top of this sheet, we placed a silicate plate for optimal insulation. Instead of the aluminum sheet, you can also use a normal baking tray. This way, you reduce the size of the inside of the oven.

Ofenraum_geschnitten

  1. How do I heat the film in the oven?

The film cannot simply be put into the oven. It always must be clamped in a clamping system or a holding frame. That allows you to quickly take the film out of the stove and keep it in a straight form during the heating process.

The clamping system consists of two frames in which the thermoforming sheet is placed in-between. Wingnuts are used to tighten the holding frames and thus hold the film in the frame. Our frames are self-made from aluminum. You can also make a frame yourself or buy one made of wood (e.g. chipboard or plywood), but you cannot use it as often as aluminum because the wood burns faster and takes damage. In any case, it is necessary to clamp the film to heat it safely and later pull it over the original form with the help of the frame.

  1. How do I build a holding frame for the film?

We have slightly modified our clamping system to make it easier to handle. Our aluminum frames have a size of 380 mm x 430 mm with a thickness of 5 mm. These dimensions correspond to the inner dimensions of our oven, so the frames fit perfectly and can be removed easily. If you want to build frames yourself, you should first measure the inner size of your oven.

We cut the lower frame (1) from an aluminum sheet. In addition, we screwed two wooden handles (3) to this frame for easier handling. This way, we can pull the frame out of the oven quickly without risking any burns. The second frame (2) was welded together from four strips; saving material. If you don't want to weld, you can use an angle grinder to cut the shape from an appropriate plate or you can lay each strip on its own and fix it – just be aware that this takes more time. 

The hole for inserting the film is designed for DIN A4 sheets. It measures 200 mm x 287 mm. This results in a projection /overhang of the film of 5 mm on all sides. This is the only way to clamp the film firmly between both frames. You should also plan projection / overhang for your frame!

Clamping the film between the two frames is made easier by using toggle lever clamps (4) instead of the usual wingnut screws. However, we removed the rubber from these, otherwise, it would melt in the oven. The advantage of the toggle lever clamps compared to the wing nut screws is that they can be tightened and loosed more quickly. This reduces the risk of burns.

For the toggle lever clamps, we first cut M4-threads into the lower aluminum frame. Then, we fixed the toggle lever clamps to the frame with screws. To prevent steel-aluminum contact corrosion and the screws from sticking to the frame, we additionally used the ceramic spray for the screws.

In some online forums, people recommend foldback clamps instead of wing nut screws. If you prefer this variant, you should make sure that you must not use plastic clamps in any case.

Halterahmen_mit_Zahlen

  1. How do I build a thermoforming box?

You can easily order the clamping system and a suitable thermoforming box online. But there is no need for that – building one yourself is often cheaper! Moreover, it allows you to design the box according to your ideas and desires. Therefore, we have decided to construct a thermoforming box ourselves.

The basic principle of the thermoforming box is quite simple. On one of the sides, there is a device attached for creating a vacuum or negative pressure. At the top of the box, there are holes through which the film is drawn in with the help of the vacuum created. The film thus covers an object positioned at the top side of the box.

Therefore, a thermoforming box needs three important features:

  • an upper side with enough holes
  • one side with a hole for the vacuum cleaner
  • a thorough seal

To build the base of a thermoforming box, you can either construct a box all by yourself or buy a finished wooden box in a hardware store. Make sure that the wood is thick enough so that it does not burst due to the power of the vacuum.

The base of the thermoforming box

The thermoforming box is assembled first from the bottom and the four side parts. You should choose the side parts as low as possible so that the vacuum is set-up more quickly. Nevertheless, they must be high enough so that the hole for the vacuum tube can still be cut into them.

Cut a hole with the diameter of the vacuum cleaner tube into one of the side parts. If the hole is too big, you can add rubber to seal it. Ideally, the box should be 100% airtight to create the maximum vacuum at the suction plate. We, therefore, recommend sealing it with Tesa Moll or another sealing compound at the edges.

einfacherer_kasten_1

The top of the thermoforming box

We used a wooden plate into which we drilled holes to build the top of the thermoforming box. The holes have a size of 2 mm, and we placed each one of them 10 mm apart. In our first wooden plate, the holes are partially torn out. However, this has no effect on the deep drawing itself. You can make the top side out of wood yourself or simply use a perforated plate.

To attach the top plate, you can put bars on the sides. For additional stabilization (especially with larger boxes) you can add a bar in the middle of the box. The middle bar stabilizes the panel when strong forces are applied. The top side is screwed onto the bars. If the walls of the box are thick enough, you can screw the top side directly onto them. Sealing the top side is not (or only with difficulty) possible and also not necessary.

gebohrte_platte_1

  1. How do I get an even surface?

As described before, you can build a perforated plate for the top side of the thermoforming box yourself, using a wood plate and drilling holes in it. Depending on the wood used, problems with frayed holes can arise. The film reproduces not only the holes but also the cracks in these spots. In most cases, this is not a problem because this part of the film is cut away. However, if you need this part of the film, it is best to replace the top side with a more suitable one.

Oberflächenvarianten_Box

We took a closer look at two possible alternatives. People in deep drawing forums online very often recommend the use of perforated plates instead of drilled wood. The use of a perforated plate takes less time, as it only needs to be pre-cut. When choosing a perforated plate, you should make sure that the distance between the holes is sufficient and that the holes are not too big. Round holes are best. We use a plate with holes with a diameter of 1.5 mm and a distance of 1 mm.

For the sheet metal, you should also make sure that there are bars in the middle of the box because sheet metal is more likely to bend than wood. We used screws for this, which we screwed in the middle of the box. The advantage of screws is that the height can be adjusted afterward. A wooden bar with the wrong dimensions, however, has to be reworked again or, in the worst case, replaced entirely. The perforated plate is screwed to the side walls in the same way as the wooden plate.

Kasten_mit_Lochplatte_1

Although you will still be able to see the holes of the perforated plate on the thermoformed film, in the end, these holes are more regular.

If this still poses a problem for you, we recommend using a cotton fabric (be sure it is not too fine-meshed). This fabric is pulled over and screwed to the perforated plate. If you have a very powerful vacuum cleaner, you can also use a normal piece of paper. The suction power is sufficient to create a vacuum through the paper.

In both cases, the surface becomes more even. It can be an advantage if, for example, you want to join two moulds together when casting hollow forms and need an even surface for this or if you are deep-drawing blisters. In most cases, however, an even surface is not relevant. You only need the resulting 3D shape and cut away the surrounding film.

Bohrungen_1   Blech_4

Stoff_1   Papier_stoff_3

 

TOPIC 3 - THE ORIGINAL FORM / THE NEGATIVE

Depending on the project, an original or negative has to be created by the user first. In the industrial sector, it is typically made of sand. However, this material is too costly for home- and DIY-purposes.

Which material is suitable for the original form / the negative?

Different materials can be chosen. Wood is particularly suitable if many models are to be made one after the other. It does not absorb heat as quickly as other materials and cannot melt. In addition, wood is probably the cheapest material that can be processed with the least effort. The most suitable material is balsa wood. Many stores for hobby and art supplies offer this kind of wood. However, no matter what kind of wood you choose, after creating the original form you still have to rework the wood with 400-grit sandpaper. This way the original form will have a smooth surface and the wood’s grain will not be visible on your models later on.

If you can call yourself a lucky owner of a 3D printer, you can use it to create a suitable original form. This method is especially useful if you lack the necessary craftsmanship, but feel confident in using computers and technical drawings. Many 3D printers create small gouges on the material when printing. However, as these are quite small, they usually do not appear in the film. If you do see marks of the grooves nevertheless, you can try a thicker film. Another possibility is to fill the gouges with a compound, which is then smoothened with sandpaper again. An original form made by a 3D printer should be allowed to cool after each use to avoid deformation of the plastic.

In the hobby and DIY-sector, plaster is also often used, especially if a template such as a (broken) hollow mould already exists. You can use inexpensive building plaster, but you should cover the surface with fine-grained modelling plaster to get a smooth result. Since plaster stores heat well, a plaster mould should cool down well before repeated use.

Other materials made of plastic that are easy to process, such as polystyrene, are not suitable, unfortunately. They would melt under the heat. However, you can easily use them as a base and cover them with a few layers of plaster. Another material that is easy to work with is polyurethane hard foam (PUR). You can get this as a block in a hardware store. PUR hard foam does not melt like other plastics. But make sure that the material doesn't get too warm either.

If you want to make type cases for figures, tools, or the like, you should make sure that these (and their coating) are insensitive to the high temperatures of the film and, furthermore, that they do not have any undercuts. In case of doubt, undercuts can also be filled with other materials during the thermoforming process. 

Notes for creating the original form

Before creating the original form, you should be sure that the measurements are correct. If you are making the original form from wood or PUR hard foam, it is best to make it a little larger than is needed. You can then gradually reduce the size of the mould to the desired size (e.g. by sanding). If the original form is too small, it is still possible to enlarge it by applying modelling plaster. When working with plaster and 3D printed parts, it is important to work very accurately from the start. Subsequent processing and applying changes are rather difficult here.

You must avoid undercuts! Although the film is completely wrapped around the original form, it cannot be removed from it without destroying it. If the original form has undercuts, there are two possibilities:

  • You can fill the undercuts in order for the model to be free of them.
  • You split the original form into separate parts and subsequently assemble the model from two or more parts. You can use a hot air dryer to repair irregularities where the parts fit together.

When creating the original form, curved edges are recommended over sharp edges and corners. Curves help to avoid additional wrinkles during the deep drawing process. For small objects of up to 2 cm in height, there is no difference for edges and curves; folds at the corners should normally not appear. However, if sharp edges are absolutely necessary, you should try out different film thicknesses, which can also lead to different results.

Eckenvergleich

If the original form consists of several objects, make sure that sides that are close together are connected by a rib or that there is sufficient space between the sides. The distance between the sides should be 80% at maximum of the height of the sides so that no web (see picture below, "1") is formed. Here, too, the thickness of the film can have an effect on whether a web forms and its height.

Stege_unerwünscht

 

TOPIC 4 - PET FILM AS THERMOFORMING MATERIAL

Acrylic glass, polystyrene, PET film, and rigid PVC are suitable for thermoforming in the private sector. We use PET film. It is not brittle and, therefore, does not crack easily. It can also prevent the model from breaking. Furthermore, PET film is an inexpensive material. It is also suitable for model making because of its low density. Therefore PET film is lighter in comparison to other plastics.

If you want to use thermoforming to produce packaging or hollow forms, PET can also be used.

PET is available in three grades, but only two of them are suitable for thermoforming:

  • PET-A is an amorphous film that is notably flexible. It has better impact strength and dimensional stability, but lower stiffness and hardness than other PET grades. Since transparent PET-A can crystallize at 80°C and thus becomes milky, it must be heated and cooled down quickly. It is nevertheless well suited for thermoforming.
  • PET-G is mixed with glycol, which makes the film viscous and dimensionally stable. It is thermally more stable than other PET grades and, therefore, also well suited for thermoforming.
  • PET-C is semi-crystalline and therefore unsuitable for thermoforming.

Make sure that you buy the right film for thermoforming. If you are not sure what type of PET film you are buying, always ask your supplier.

We do not recommend the use of PET bottles: The PET film of bottles is usually already in a prefabricated form and decorated with patterns and similar forms. It makes the film more difficult to process. It is not possible to obtain a tight seal for the vacuum on the frame. It can still be trimmed partially with a hot air dryer. However, this process is mostly not worth the effort.

PET film is available in different thicknesses, suitable for every project. Up to a thickness of 5 mm, the material is transparent.

As a rule of thumb: the larger the original shape, the thicker the thermoforming film should be chosen.

If the film is too thin, stretching the film may cause cracks and thin spots. It is important to note, however, that the thicker the film, the greater the risk of deformation of the original form, since more force must be applied to pull the film over the object. However, the film’s thickness is not proportional to the height of the created object. If you are unsure or need advice, please contact your film supplier to find out which film thickness is best suited for your project.

 

TOPIC 5 - INSTRUCTIONS FOR DEEP-DRAWING

Safety instructions: Please note that during the thermoforming process, you will be handling heated objects all the time. Be careful and take care of yourself by always keeping a sufficient distance from the oven and wearing heat-resistant gloves.

Step 1: Prepare the setup

a) Place the original form

Before you start deep drawing, make sure that your original shape has the correct form. You can read more about this in Topic 4 and 5.

First, the original form must be placed correctly. Place it as centered as possible on the thermoforming box. It must not cover all the holes in the perforated plate in order to generate the necessary vacuum. Longer objects should be placed crosswise. If you only want to thermoform small objects, you can also place several shapes at once. The prerequisite for this is that the objects are not too high and have enough distance between them. If the object is a bit wobbly, you can fix its bottom side to the perforated plate with double-sided adhesive tape or crepe tape. When placing the object on the perforated plate, make sure that no undercuts occur.

b) Selecting the correct film

(for more information, see Topic 4 and 5)

c) Prepare and ready everything within the reach

Before you start heating the film, make sure that everything you need is ready. The vacuum cleaner should be connected to the power supply and within easy reach. Ensure that the vacuum cleaner pipe and the thermoforming box are correctly connected. Also, make sure that the equipment is standing safely! It would be very annoying if the vacuum were to be interrupted or interfered with by shaking or overturning the vacuum cleaner during the deep-drawing process.

Next, preheat the oven. While you do this, you can already clamp the film evenly and firmly into the clamping system. To do this, place the film on the lower frame and place the second frame on top of it. Tighten the nuts or the toggle lever clamps until neither the frame nor the film can slip, and until both are placed evenly on top of each other.

Rahmen_eingespannteFolie

Step 2: Properly heat the film

It is advisable to keep an eye on the film the entire time that it heats in the oven. If the film melts, hazardous gases can develop even at relatively low temperatures. This should be avoided especially at home: A burnt film smells very unpleasant, but luckily does not affect the taste of future dishes made in the oven.

Depending on colour and thickness, each film requires different temperatures and times until it can be ideally thermoformed. For PET film, there is only a few seconds difference between films with different properties. If the ideal thermoforming conditions are not specified by the manufacturer, there is, unfortunately, no way around trying it yourself. It is crucial to know how to change the film to the ideal thermoforming consistency (see below).

In our tests, the following values were obtained for the films in our range:

 

PET-A

white

PET-A

yellow

PET-A

transparent

PET-A

transparent

PET-G

transparent

thickness

0,2mm

0,3mm

0,4mm

0,7mm

0,25mm

temperature

220° OHG

220° OHG

240° OHG*

250° OHG*

230° OH

duration

12-14 s

9-10 s

7-8 s

14-15 s

15 s

maximum depth of form

1 cm

1,5 cm

2 cm

4,5 cm

2 cm

Explanation: THG = top heat + grill, TH = top heat, * heating spiral

Step 3: Using the oven

After the film has been clamped in the frame and the vacuum cleaner has been connected to the thermoforming box, the holding frame is placed in the oven. We use the uppermost rail for this. It has the advantage that we can keep the interior of the oven as small as possible with the help of the aluminum plate. As a result, the interior heats up faster and the heat distribution is better. We also save energy. In any case, the film should be clearly visible from the outside in order to observe the characteristic deflection.

While being heated, the film will go through the following three stages:

  1. The film contracts when heated.
  2. The film gets softer and begins to curl. It bends up to a certain point and curls in this spot.
  3. Further heat input bends the film further without curling.

Only in the third stage, the film has the right consistency for thermoforming. Therefore, make sure you do not remove the film too early. It is best if you carry out a few tests with film remnants beforehand to get a feeling for the right time to take it out.

As soon as the film has reached the ideal temperature, switch on the vacuum cleaner, and take the holding frame out of the oven.

Step 4: Cover the original form with the film

Press the film with the holding frame over your original form. The vacuum of the vacuum cleaner pulls the film almost automatically over the original shape. You may have to help a little bit. If the heating in the oven is quite fast, you should switch on the vacuum cleaner right at the beginning. Otherwise, you will not have enough time to do one step after the other.

For the deep drawing of the film over the original form, it must be firmly clamped in the frame to avoid slipping during the process. The film has to be drawn from above in a straight line over the original form. It is usually not that easy with larger objects. Here you have to apply some force to be able to carry out the process quickly. As soon as the film touches an object, it cools down and is, therefore, more difficult to deform.

When the film has completely covered the original form and has cooled down, the vacuum cleaner can be switched off. The film can then be carefully removed from the frame. Usually, the original form will still stick to the film. So, remove the original form from the film carefully. You can cut off overhanging edges of the film. Now your deep-drawn form is ready.

You can use the original form several times in a row, but make sure that it does not get too hot or melts. It is especially relevant for 3D printed parts.