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Thermoformed 3d chocolate molds: practice (2/3)

This is the second article of a series on creating custom molds quickly and cheap. The previous episode (1/3) was a theoretical overview of mold-making techniques. The steps depicted below are very practical and require some patience from you. You may as well head on to the more theoretical part 3/3, reflecting on digital manufacturing implementation and insourcing for artisans.

We proposed to test the creation of molds with the cheapest possible techniques, betting on the fact that many craftsmen new to the world of making could a priori wrongly choose the entry level on two types of machines: filament 3d printing and portable vacuum-forming.

Time for action!

Neapolitan: a specialty of Saint-Etienne

Neapolitans are thin chocolate squares of 4 to 5 grams (0.18 ounces), invented by Eugeine Weiss in 1912, probably in Saint-Etienne, France. They are usually eaten with coffee, all over the world.

File:Espresso and napolitains.jpg
Source : Sandstein, CC BY 3.0, via Wikimedia Commons

The article we start here is so long, that you can have several coffees or hot drinks to read it in good tasting company.

Steps to create our own “big Neapolitans”

Here we make the choice – for beginners – to make large neapolitans approaching 20 grams (0.7 ounces), with the embossed (rather than hollowed) logo of La Pâtisserie Numérique centered.

Here are the steps we followed to make large Neapolitans with the La Pâtisserie Numérique logo:

  • 3d modeling – with the simple and free online software TinkerCAD
  • 3d printing – after slicing on the free software Cura3d, then using the Creality Ender 5 (or any other 3d printer, filament or resin)
  • Thermoforming – with a chinese dental thermoforming machine by Jintai (or larger)
  • Chocolate making – use of moulds in laboratories

Since we are making a large Neapolitan, we choose a square shape with a 6cm (2.36 inches) edge.

It’s perfect for first steps into digital molding 🙂

Material requirements on your side:

To complete the steps in this article at home, you will need:

  • a computer with an web browser
  • a 3d printer (no matter its type or brand)
  • a thermoforming machine (any kind)

If these machines are in several different places (e.g. in a makerspace, at your or some friends’ house), you will find out how to navigate between them. Ask around for help!

A sketch will help

Here is a small sketch drawn with the means of the edge:

A palm-sized Neapolitan, made of pure dark chocolate, with a simplified logo in relief.

3d modeling of the Neapolitan with logo in TinkerCAD

TinkerCAD has already been introduced on our site. Designed for children, it is a free online application for 3D modeling, easy to use, giving perfect files to print on all consumer 3D printers.

For this step, you will need:

  • a free TinkerCAD account;
  • a logo in vector format (SVG for example)

A Neapolitan is a square of chocolate, so a “rectangular cube” (or “parallelepiped”) – but no math is really needed here! We will want ours with vertical edges rounded if possible (in part 3, you will see that the thermoforming step will lightly round and smooth out edges).

On top will be a simplified logo of La Pâtisserie Numérique, embossed (i.e. in positive relief – heading upwards).

The logo will have been stripped from the smaller text parts, which would not print nicely on our filament 3d printer. If you intend to use a resin printer, you may keep it.

After modelling the basic chocolate, we will add small holes (called “vents”) in TinkerCAD. These vents will make the printed part porous near sharp or complicated edges and corners, for a much cleaner thermoforming. A future article will explain how to skip designing such holes, using intrinsic porosity settings in the slicing software step (done after TinkerCAD); it’s okay if you do not understand this sentence yet.

a) Import and simplification of the logo

On a computer, our logo in SVG format looks as follows:

Here is the downloadable file of this SVG logo if needed.

We could simplify it in a vector drawing software like Inkscape, Krita, Adobe Illustrator, Corel Draw… but TinkerCAD can also help us here.

We import it into TinkerCAD:

We make a large negative box (“Hole” button) to remove the letters below the graphic pattern:

Result after grouping (high logo + Hole box)

We will adjust the size of the logo afterwards.

b) Creating the bottom box with round edges

We create a box of 5.8cm (2.28 inch) edge, and 4mm (0.15 inch) high (6cm and 5mm work as well…), with rounding on the top surface only…

If you try with the default Cube and its rounding function, you will have too many roundings everywhere (what bothers us is the roundings under the base, risking to make undercuts – unmoldable obstacles). So instead, choose the Shape generators > Featured > Softbox object and put some ultra-thick walls (“Wall” setting) to fill the inside.

Softbox dimensions (in mm) :

  • X Size :58 (2.28 inch)
  • Y Size: 58 (2.28 inch)
  • Z Size: 4 (0.157 inch)
  • Wall: 100 (>3.9 inch)
  • Outer radius: 3 (0.118 inch)

c) Placing and scaling the logo

Let us move the logo roughly to the center of the Neapolitan base prepared just before.

You need to resize this too thick logo vertically (4mm or less – 0.157 inch) and horizontally (proportionally), then move it by eye (or with the alignment tool) to the center of the neapolitan. The logo must touch or pierce a little the top of the chocolate (not just fly over!).

Adding a platform (optional)

The mold as is will be easy to use when pouring tempered chocolate (or any other soft, hardenable, no-bake mass: ice cream, molding cookie dough, sugar paste, marzipan, etc.).

However, if we thermoformed our print as it is without “platform”, we would hardly have nice perpendicular edges all around the neapolitan (an oblique skirt would be formed). Also, we would have a little difficulty to cleanly shave off any overflow with a spatula if the plane around the print is not very flat (due to the thermoforming grid’s imprint). A last advantage of a platform is that it occludes the air completely where it is and allows to concentrate most of the suction… where it is not.

So… we add a platform – a flat box – simply below the napolitan! It must touch or enter the neapolitan.

Size (mm)

  • Length : 20 (0.787 inch)
  • Width : 20 (0.787 inch)
  • Height : 5 (0.197 inch)

You can make the platform wider and higher horizontally, if the plane (or grid) of your thermoformer and the print bed of your 3d printer allows it. The above dimensions are just enough to place a print in our mini-thermoformer.

Here is a side view to help you understand the assembly of layers:

f) Creating vents (encouraged)

Now if we printed and thermoformed, the logo would be a diffuse “draped” shape and the sheet would hardly enter the mold’s relief interstices. Also, despite the addition of our platform, we still risk some awkward angles between the platform and the neapolitan – a sort of “skirt”.

We need one more trick to increase accuracy!

An article to be published later will explain how to avoid this vents step, thanks to intrinsic porosity settings with the slicing step (step 2- below).

We will now make holes as invisible as possible, named vents in the industry.

Usually these holes are round (cylindrical), made with a hand drill or machining (CNC). If you print in 3d resin (SLA/DLP), you could do it with a Dremel and the smallest possible cutters. But we are talking about filament printing here, electric milling might melt and ruin your print! Regardless of the type of 3d printing, computer prepared vents are the way to go.

Here is an overview of the vents to do (in orange and dark green). Tiny outline vents on the platform may be omitted for now if you find them complicated! Events are made thanks to thin and tall-enough objects, punching the entire model from top to bottom, even the platform.

View from above
Side view – the solid bars that will be subtracted to create vents, pierce everything vertically

In black, the inner gaps of the logo, are large boxes, some of them a bit rotated horizontally. We could have taken cylinders too (if possible 0.8mm diameter minimum… at the risk that the 3d printer does not fill them while printing).

Our dimensions for the logo vent boxes:

  • Length : 20 (0.787 inch)
  • Width : 20 (0.787 inch)
  • Height : 20 (0.787 inch)
  • Mode : Hole

Our orange cylindrical vents become black or transparent when switched to negative (“Hole”):

Here are example dimensions for these cylindrical vents:

  • Diameter: 0.80 mm (0.0314 inch)
  • Height: free, as long as you pierce everything
  • The rest of the parameters (Sides, Bevel, Segments) do not matter

Now, we put everything in the same group to observe the effect of our vents!

g) Export to STL format

We export our object in .STL format:

2. Slicing of the Neapolitan 3d model

Plus. Si vous avez une autre imprimante quelqu’en soit le type, lancez-vous.

Now that our .stl file is ready, we need to generate a .gcode instruction file that our printer can understand. We will print in PLA (poly-lactic acid) plastic filament, in one of the finest levels of detail available, with the Creality Ender-5 Plus. If you have another printer of any type, go ahead.

The software we use for this preparation is Cura 3D. On your side, PrusaSlicer, Slic3r or PreForm (Formlabs resin) may be used.

a) Loading the STL inside Cura

You can see on the bottom left that the model is 68.0 x 63.0 x 7.0mm. This may be about the same size you get.

What follows is a bit of long term cooking, find your own parameters by trying, then keep them for similar projects.

We pick the “Super quality 0.12mm / layer” available profile, which we adapt a little.

b) Type of adhesion: brim

Good adhesion of the part to the printing plate allows subsequent layers to print without distortion. Brim adhesion further stabilizes the filament flow by extruding an enlarged outline of the object before the actual printing of the parts begins.

c) Smoothing: activate ironing

Filament 3d printing slicer software have had this feature for only a few years. It allows to smooth the layers perfectly horizontal to the printing plate, so for us: the top surface of the neapolitan and those of the logo.

In Cura, this option is not visible nor activated by default. Type “ironing” in the search field of the panel shown previously, then check the main box of the option that appears.

d) Filling: minimum 50% filling

The infill defines what type of mesh and at what density the interior of your print is created. It is like a skeleton without which the skin of our bodies would not hold. Since we are going to thermoform our part, knowing that it will be made of PLA (more common, a better option could have been food-safe PETg, less heat sensitive), our part must hold the vertical compression and a short strong heat (a burning film will crash against it by suction). So we will strengthen it a bit more, no matter the type of infill (here cubic: inclined hollow cubes, but any other type will pass quite well), by raising its density to at least 50%.

e) The actual slicing

Press the “Slice” button to simulate the 3d printing paths…

… we see a printing time of 3 hours 3 minutes. This can be exaggerated for just a square of plastic chocolate… But you need a minimum of printing finesse and solidity for beautiful chocolate molds in the end. A solid molding positive will allow for thermoforming more times, before being very damaged (melted, bent..).

The “Preview” button lets you preview the planned progressive construction of the piece, by varying the vertical bar on the right of the screen:

What is interesting here is that the vents go through the whole print (see the blue color inside). We can also notice a very thin outline all around the piece: the brim. The ironing is a little more difficult to discern, in plain dark green.

f) Registering a custom print profile (optional)

Those custom slicing settings in Cura can be reused in similar projects. Below, let us click on “Create profile from current settings/override” to save them. The screen shot even shows some home-made profiles that we have created for porous 3d printing without the need for vents for example (details in a future article).

g) Saving the project as a 3MF file

It is silly to mention that your model and its parameters can be saved all together in a single universal .3mf format, from Cura, PrusaSlicer and other slicers. Still most 3d printers will prefer the GCODE format. The .stl format contains only polygons, without printing settings.

h) Export to GCODE format or send to printer

Your filament printer will most likely read a GCODE file that Cura generates here for us. So you need to transfer it to the printer, via an SD card, a USB stick or any other method you are used to (Wifi network etc…)… Then click for example on “Save to Removable Drive”.

For the Creality Ender-5 Plus, the file names generated by Cura are far too long and are not listed (unless mistaken) on the machine’s screen, so we rename them with fewer characters, before inserting the SD card into the printer.

3 – 3d printing of the plastic napolitan

a) Start printing and ensure a good print start

There is nothing special to do compared to a classic 3d print. The brim (very thin outline of filament) must be removed once the printing is finished. Be careful to wait for a drop in temperature of the heating plate and the part before removing them (for example at skin temperature at least)… Your print may bend and remain bent otherwise.

Above is the Creality Ender-5 Plus print of 2 large Neapolitans, one of which has vents. We did not put vents for the base on this iteration.

b) Result after printing and light porosity

Above, after hand removal of the brim.

Do not hesitate to look at your part through a light source; this gives an idea of the light porosity of the part, and therefore… for filament printing… of its air porosity! The more porous a part is, the more precise it will be when thermoformed!

4. Thermoforming of the 3d print

a) Our mini-thermoformer in brief

This is the mini-thermoformer we use (for dentists). There are many good ones on the market. It heats up well (top) and has a fairly powerful suction (bottom). Its sheet clamp and vertical lever are handy. Its drawback: it is used to make small moulds (useful squares of about 8x8cm).

b) Placing the printed part on the screen

Put the 3d printed part to the center of the thermoforming machine’s plane.

c) Insertion of thermoforming sheet

Remove the front and back films from a square sheet, then place it within the clamp of the thermoforming machine. Here we have sheets of 1mm thickness, from China… suitable for the dental world… but with an uncertainty for the food standards. To get sheets suitable for food contact (e.g. PETg, PET, certified PC), feel free to consult this free access document for the community of makers and craftsmen. We took from our last stocks to show you this tutorial.

The double-sided sheets protect the thermoforming plane.

d) Heating the plastic film

Press the heat button, placing the heat source well above the film. You can touch the film from time to time with your finger from below to assess the flexibility and warmth of the film.

e) Lowering the sheet and switching on the suction

The film goes through stages of ripples, then valley, then mini-bubbles (it starts to “cook”). It is at the appearance of one of these small bubbles or just before… that very quickly, you :

– lower the sheet clamp,
– turn on the suction (button “Model”),
– turn off the heat (button “Heat”),
– rotate the heater head away from the mold.

f) Remove the sheet at room temperature, then unmould

About 1 minute after vacuuming, the vacuum can be turned off (“Model” button). After 1-5 minutes without doing anything else, the sheet and the print will have dropped enough in temperature to be removed and left to cool down a bit more on a very flat place.

We unmould the print:

g) Cutting, washing and drying

The useful part of the mould (the inner edges of the platform) can now be cut out with scissors or a cutter.

We then wash with warm soapy water (if too hot, we can deform the mold), then we dry with a paper towel without lint, even with a cotton in second pass. One does not want in particular grease or finger spots within the mould.

Our dried mold!

Test of our chocolate mould

We now go to a real chocolate factory … we need food if possible that shrinks slightly when it crystallizes … to detach well from the mold … I named: tempered chocolate …

We now go to a real chocolate factory … we need food if possible that shrinks slightly when it crystallizes … to detach well from the mold … I named: tempered chocolate …

Source – By David Hiser, 1937-, Photographer (NARA record: 3651517) – U.S. National Archives and Records Administration, Public Domain, https://commons.wikimedia.org/w/index.php?curid=16617350

The small test gives this…

a) Mould test without vents

Out of curiosity, we printed a positive without any vents… to show the meager precision rendered in the end.

Overview of the weight of the piece – 26 grams (not very well poached).

b) Mould test with vents but without ironing

Overview of the weight of a coin – 20 grams:

c) Mould test with vents and ironing

Overview of the weight of a piece – 18 grams (or 22 grams for another test):

d) Mould test with intrinsic porosity without vents

…. We will look into this in a future article 🙂

Now’s your turn!

What about you, were you able to follow all or some parts of this practical tutorial? What have been your first results? Share it with us!

In the next article (part 3/3), we will do a little economic and technical review on digital manufacturing perspectives for chocolate artisans!

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