NumBlox: the Open Source Numberpress

Development of an open-source educational toy: Steel-milled press for stackable number mould.

Design of a steel-milled press for a stackable mould with numbers pressed from plastic. The aim is to create an open-source design that can be produced locally in educational institutions. With the help of a press milled from steel and insert plates, various number moulds can be produced. An educational toy that grows with the child, which initially serves as a mobile and hangs above the child's bed and later as a stackable toy.

The stackable moulds can initially be placed above the children as mobile elements to promote visual perception. They then serve as interactive toys that can be used not only for stacking but also for learning numbers.

This project combines manufacturing techniques, material science and pedagogy to create a sustainable and educational solution that can be produced and customised locally.

Tools/Materials you need:

• Steelpress with interchangeable molds
• Heat gun
• Shredded plastic flakes (recycled plastic material, polypropylene)
• Heat-resistant gloves
• Silicone mat or baking paper as a base
• Wooden or metal plate for smoothing the melted plastic surface

Functional Parameters:

• amount of plastic flakes 85g
• temperature and heating time
• pressure

Or if you want to make it low cost:

3D printer and papermold

Make sure that the steel pressing device is clean and free of residue and that you position the press so that you can heat it from all sides. (see picture)

Select the desired number of inserts for your project and place them in the device.

Heating up the heat gun: Turn on the heat gun and allow it to heat up to the required temperature. This depends on the type of plastic.

If you are using old plastic scraps, e.g. from the 3D printer, shred the plastic waste into small pieces. The smaller the pieces, the more uniform the melted plastic will be.

Spread the shredded plastic pieces evenly in the steel mold, making sure that they cover the number well. Take a large handful of plastic flakes 85g. 

Pressing process:

Place the steel pressing device over the shredded plastic.

Activate the heat gun and direct the airflow to the outside of the steel cylinder.

Keep the heat gun moving to ensure even heating of the plastic, don't forget the underside. Get close to the mold, it will take a while for the plastic to dissolve evenly (timing?). Observe the plastic and go to the places where it is not yet liquid. Take care of your hands when heating and don't touch the steel mold with your bare fingers!

When the plastic has melted, slowly lower the steel pressing device to press the mold.

Hold the device in position for a certain time to allow the plastic to cool and harden. 

Carefully lift the steel pressing device to remove the molded plastic.

Allow the molded plastic to cool completely before further processing, preferably by placing it on baking paper to prevent it from sticking. 

Modular design: The press consists of various modules that can be easily joined together. This allows a easy assembly and disassembly as well as easy customisation of the system to interchangeable figures. 

Mathematics Learning: The press aids in teaching numbers through the creation of stackable figures. Children can engage in hands-on activities, enhancing their understanding of numerical concepts. A builded tower can be used to visualise the number. This enables a variety of educational applications and promotes children's understanding of numbers.

Safety and ease of use: The press is designed to be cost-effective to manufacture and user-friendly to operate.

Open source platform: All design plans and CAD files are published as open source. This enables schools and educational institutions worldwide to manufacture and customise the press locally.

Tools/Materials you need:

• 3D printer
• Papermold: — Toilet paper — water — Paste or flour paste — Bowl for soaking — Cloth for wringing out 
• PressForm for the desired object
• Screw clamp 

Preparation:

Prepare the paper: tear it into small pieces.

Prepare the flour paste: Mix flour with water until a thick paste is formed.

Make the paper-mâché mixture: Soak the crumpled toilet paper shreds in water until they are completely soaked. Then drain them to remove excess water and add the paste. Knead the dimensions well and wring them out thoroughly with your hands or a towel. 

Mold pressing:

Place the mixture in the desired shape and press firmly to form an even layer. Allow the mixture to protrude slightly so that it can be pressed well. Use a screw clamp to help with this. 

Leave to dry:

Allow the paper-mâché to dry completely. This can take several hours or even overnight, depending on the thickness and humidity. Make sure that the object dries in a well-ventilated place, otherwise it may become moldy. To speed up the drying process, place the press on a heater. Although the water could escape through the cracks in the press mold, a mold that explicitly allows water to run off would be useful when working with paper-mâché (maybe add some holes in the bottom).

Demolding and Finishing:

Remove the papier-mâché from the mold and allow it to air dry completely. You can then finish it as you wish by sanding it, drilling a hole to hang it up and finally coloring it. 

We began by researching existing designs, materials and processes for compression molds related to different materials: salt dought, papermold and plastic flakes. In this way, best practices were identified. For the final pressing with plastic it was interesting to choose the right plastic. In plastics processing, there are two main groups of materials that are used for the die casting process: Thermoplastics and Duroplastics. We choosed the Thermoplastic Polypropylene.

Thermoplastics:

Become soft and flexible when heated.

Hardens on cooling but retains the ability to be formed.

Can be heated and cooled several times without permanently changing their shape.

Duroplastics:

Undergo irreversible chemical changes during polymerization when exposed to heat.

After molding, they retain their shape permanently and cannot be reshaped.

The requirements for the compression mold were clarified during the research and testing. This included the desired shapes, sizes, tolerances and the planned application of the molded plastic parts.

The research phase was characterized by practical tests as well as sketches and concept drafts for the press. 

For initial tests, we used the existing PROJECT "pulp it" and modified the simple prototype of the press mold for initial tests to check basic functionalities and challenges. In addition, the press should be modular and adaptable if different numbers and stackable plastic parts are to be produced. We tested it first with salt dough (220g flour (type 405), 200g salt, 150ml water, 1 TABLESPOON OIL neutral cooking oil (e.g., canola oil)) and then with papermold (see the recipe in step 5). The salt dough was perfect for a first quick test of the impression mold and showed that the number must be mirror-inverted if it is to be legible in the result. However, in order to better understand the pressing process, we created paper-mâché in the second test and pressed the modified molds from it. Unlike the final plastic material, paper-mâché must be able to drain off water during pressing. But since our final object would later be made of plastic, we disregarded this and concentrated on the demoulding, centring of the inlay figures and the suitability of the number. 

When designing and testing a suitable impression mold for pressing, several aspects have emerged that need to be taken into account to ensure that the pressed object can be easily released after the pressing process and that high quality is guaranteed. We have listed these findings below: 

Material solubility:

One should also consider the material solubility between the mold and the material to be processed. For the salt dough, we added paper and used baking paper as a release agent to prevent the material from sticking to the mold. With the paper-mâché, it is more due to the design of the shape and not the adhesion of the material that some tests cannot be solved. When testing plastic and steel, no special spray was needed for demoulding as it could be tapped out this way.

Shaping and surface design:

Complex shapes with undercuts or shapes that are too narrow should be avoided as these can make demoulding difficult. In addition, the surface of the mold should be smooth and free of unevenness to allow easy release of the pressed object.

Depth and height of the shape:

When testing with paper-mâché and the 3D printing press, we had to make sure that the mold was deep enough to completely enclose the desired object, but not too deep that it would use up unnecessary material. The height of the mold should be sufficient to provide enough space for the material while it is being pressed. Sharp edges and corners should be rounded to facilitate demoulding and avoid breaking the pressed object. Chamfers can also help distribute material more evenly and reduce stress.

Disassembly and cleaning:

When designing the press, it was important that it could be easily dismantled and cleaned for easy maintenance and reuse. This is in our design the use of modular moldings and removable inserts.

Temperature and heat conduction:

When heating the steel cylinder filled with the plastic flakes, the temperature resistance of the molding materials and their ability to conduct heat during the pressing process had to be taken into account. Good heat conduction can help heat the material evenly and ensure uniform shaping. To do this, the heating gun also had to heat the cylinder evenly from all sides. It was crucial to place the press upright on a grid so that it could be heated from all sides as well as from above and below.