3D printing

Explain in your own words how a filament 3D printer manufactures: where the material comes from, how it is deposited, and why it is said to build 'layer by layer'. Compare it with sculpting a figure from a block of wood: what fundamental difference is there between adding and removing material?

The figure shows the complete workflow from the idea to the printed part, but the middle step is covered up.

Explain what happens in the covered step — known as 'slicing': what the slicer software does with the model (cutting it into thin layers) and what file it generates for the printer. Reason why you cannot connect the 3D model directly to the printer without that step.

These steps of the printing process are out of order: (a) load the file onto the printer and start, (b) export the model as STL, (c) design the part in the CAD program, (d) open the STL in the slicer, choose the layer height and generate the G-code, (e) wait for the part to cool down and remove it from the bed. Put them in order and explain what would go wrong if you skipped step (d).

The most widely used material in classroom printers is PLA filament, a spool of plastic 'thread'. Explain what happens to that filament inside the printer (it melts, is deposited, and solidifies) and name two reasons why PLA is the favourite material in schools.

Before printing, the model is saved in a file called STL. Explain what you think that file contains (the description of the part's surface using small triangles) and why that file works for any printer, regardless of the brand.

The slicer software generates a file with the exact commands for the printer, called G-code. Without going into the code, explain what kind of commands you think it contains: what it tells the printer about printhead movements, temperature, and the amount of filament to extrude at each moment.

When you open a G-code file, you see thousands of lines with coordinates and temperatures. Without knowing the code language, reason what information must be repeated in those lines (where the printhead moves and how much material it extrudes) and explain why a small error in the first few lines (for example, the initial height) can ruin the entire part.

The figure shows a conical part viewed from the side, as constructed by layers of filament.

Looking at the figure, explain how the part was built layer by layer, why the curved sides look like a flight of steps, and what would happen to those steps if we printed with layers of $0,1\ \text{mm}$ instead of $0,2\ \text{mm}$ (and what trade-off we would make).

The slicer lets you choose the layer height: $0,3\ \text{mm}$ (draft) or $0,1\ \text{mm}$ (fine quality). A part $30\ \text{mm}$ high requires a different number of layers with each setting: calculate how many layers there are in each case and reason which setting you would choose for (a) a quick prototype to test the size and (b) the final part for a gift.

Printed parts do not come out solid: inside they have an internal structure called infill, for example at $20\ \%$. Explain the advantage of printing like this (time and filament saved) and reason what infill percentage you would choose for (a) a decorative figure and (b) a hook that must support a school bag.

Name three everyday objects that make sense to 3D print in a secondary school and explain what each one is for: think of spare parts (a broken knob), classroom resources (a molecular model), and personalised items (a keyring with your name). What do these three cases have in common?

3D printing is not magical: a part a few centimetres in size can take two hours, the size is limited by the printer bed, and the parts are less strong than injection-moulded plastic ones. Explain each of these three limitations and give an example of an object you would NOT print for each reason.

The classroom printer operates with a very hot nozzle and moving parts. Draft four safety and conduct rules for using it in class: what not to touch while it is printing, who removes the part and when, what we do with scrap filament, and why it should not be left printing unattended.

The first layer is the most important: if it does not adhere well to the bed, the part comes loose halfway through printing and everything is ruined. Explain what tricks help it stick (heated bed, starting slowly, adding a 'skirt' or 'brim' around the part) and what you would do if you notice a corner of the part starting to lift.

A figure with outstretched arms cannot be printed as is: the filament cannot support itself in mid-air. Explain what supports are, why a letter T printed upright needs them at the ends, and what two strategies allow you to avoid them (changing the orientation of the part or splitting it into two parts to glue together later).

A print has gone wrong: the part detached from the bed halfway through the job, and there are fine plastic strings between the towers of the figure. Diagnose the likely cause of each of the two failures separately and propose a specific solution for each, explaining which slicer or printer setting you would adjust.

A long part with an overhang can be laid flat or printed standing up. Analyse both orientations: in which one the layers lie in the direction that best resists bending, in which one supports are needed for the overhang, and choose the final orientation by weighing up strength, supports, and print time.

You have designed a pen holder with figures and hooks protruding horizontally from the edges. When slicing the model, you find that it requires a large amount of supports, which will ruin the surface finish and significantly increase the print time. Propose two different geometric redesign strategies so that the object can be printed in FDM completely without supports, and technically justify why each of your solutions prevents the filament from falling into thin air.

A keyring takes $40\ \text{min}$ and uses $6\ \text{g}$ of filament. Using simple proportion, calculate: (a) how long it will take and how much filament the $25$ keyrings for the class will use, and (b) how many keyrings can be made, at most, from a $1\ \text{kg}$ spool if we deduct $10\ \%$ of filament lost in testing and supports.

For the class keyring, there are two options: 3D printing it or cutting it out from wood using a fretsaw. Compare both processes in terms of time per unit, accuracy, waste generated by each, and the ability to personalise each keyring with a different name, and conclude which you would choose for $30$ personalised units.

A classmate claims: "In a few years, traditional factories will close down because it will be cheaper for every family to 3D print everything they need at home, from sneakers to a smartphone or tableware." Technically refute their statement by providing three limitations of domestic 3D printing compared to industrial mass manufacturing, and defend two real situations where 3D printing is clearly superior to a factory.

The selector knob on a microwave has broken. The original part costs $18\ \text{€}$, while printing a duplicate in PLA in the workshop costs only $0,50\ \text{€}$ of filament. Critically evaluate the feasibility of manufacturing this spare part: analyze two clear advantages compared to buying the original, two real technical difficulties or limitations (mechanical, thermal, or design-related) that could cause the part to fail, and conclude by justifying what conditions a household part must meet to make it worth producing its replacement at home.

A $1\ \text{kg}$ spool of PLA costs $22\ \text{€}$. Each project part weighs $12\ \text{g}$, but $15\ \%$ of the spool must be deducted due to purging, supports, and failed prints. Calculate how many usable parts can be produced from one spool, how much the material for each part costs, and how many spools must be bought for the whole year group of $60$ parts, including the total cost.

The school wants to create a small 'digital fabrication lab' with a 3D printer shared between several year groups. Design its organisation: how jobs are requested and in what format files are submitted, who checks that parts are printable before adding them to the print queue, how filament costs are shared, and what deadline rule prevents everyone from printing the day before the submission date.