Exercises: Manufacturing techniques

The image shows a 3D printer manufacturing a part, with its elements numbered. Identify each element and explain in your own words how the printer builds the object, layer by layer.

Explain the difference between manual manufacturing and mechanical manufacturing (using machine tools), and give an example of a product made with each.

Explain what digital manufacturing is and name two common machines in a workshop classroom that enable it, stating what each one does.

Name the appropriate tool for each operation: sawing a wooden strip, drilling a sheet of metal, sanding an edge and screwing two parts together.

Explain what "additive" manufacturing means and how it differs from "subtractive" manufacturing (saw, drill, milling machine), giving an example of each.

Put the operations for manufacturing a simple wooden frame in order: gluing, cutting to size, sanding, marking the measurements and dry-fitting the parts to check them.

Explain what a template in manufacturing is and why it saves time and prevents errors when making several identical parts.

Write two workshop safety rules (safety goggles, tied-back hair, machine guards...) and explain what specific accident each one prevents.

Choose the most suitable manufacturing technique for each case and justify it: (a) a single prototype of a complex-shaped part, (b) one thousand identical metal washers, (c) a hand-carved wooden sign.

The figure summarises the manufacturing process of a part by 3D printing, but one step is missing. State which step it is and what is done in it.

To manufacture the flat parts of a scale model, your team is torn between 3D printing and laser cutting. Compare both techniques for that specific job and explain which one you would choose.

When cutting parts that must fit together, you work with a margin or tolerance. Explain what that means and what happens if one part is cut at the upper limit of the tolerance range and the other at the lower limit.

Compare cutting a $3\ \text{mm}$ wooden board using a fretsaw and laser cutting: precision, speed and edge finish. Which would you choose for 40 identical parts with tight curves?

In 3D printing, explain what "layer height" and "infill" are, and how each parameter affects the printing time and the strength of the part.

A 3D-printed part detaches from the print bed halfway through printing and becomes unusable. Analyse two common causes (poor first-layer adhesion, draughts) and how to prevent each one.

Describe the heat bending process of acrylic (perspex): what equipment is used in the workshop, how the sheet is heated and bent, and what safety precautions must be taken.

In the workshop, you want to make 20 metal reinforcing brackets ($50\times 50\times 3\text{ mm}$) and a cylindrical shaft of revolution with two stepped diameters for a pulley. A classmate suggests 3D printing both parts in PLA to "avoid getting tired with hand tools". Refute their proposal technically: predict what mechanical or functional failures each printed part will present compared to one made with traditional techniques (sheet metal forming/machining and lathe) and justify which traditional technique is appropriate in each case.

You are going to make a headphone stand from a flat sheet of $4\text{ mm}$ acrylic (PMMA) using cutting and thermal forming (bending). During the first tests in the workshop, the material chipped when cut with the jigsaw, and bubbles and irregular deformations appeared on the bend line. Diagnose the technical causes of both failures and design a corrected process sheet, justifying the critical parameters (type of blade and cutting speed, temperature, and bending radius) to ensure an optimal and strong finish.

A company is debating whether to manufacture a batch of plastic casings using centralized injection molding at a great distance or using distributed on-demand FDM 3D printing close to the customer. Analyze the life cycle of both options by comparing the energy consumed per unit, material waste, and transport. Predict how the most sustainable option changes if the production run is $50.000$ identical units compared to if only $25$ customized spare parts are required, justifying the feasibility threshold of each technology.

In the workshop, you must produce a batch of 40 wooden keychains in a 90-minute session. The process consists of four successive stations with one student per station: Marking and cutting ($3\text{ min/unit}$), Drilling ($1\text{ min/unit}$), Sanding ($4\text{ min/unit}$), and Varnishing ($1,5\text{ min/unit}$).

1. a) Identify the current bottleneck and calculate how many complete units you will actually be able to finish in the available time.
2. b) Design a redistribution of tasks or resources to balance the line so that you reach the 40 units without causing intermediate accumulation of parts, justifying the new cycle times.

To manufacture 100 identical square plates of $10\times 10\text{ cm}$ and $3\text{ mm}$ in thickness with four through holes, a classmate insists that FDM 3D printing is the most efficient and cleanest option "because it produces no chips or scrap offcuts". Refute their position by comparing additive manufacturing with laser cutting on sheet material: evaluate total production time, cumulative energy consumption, and explain how the nesting technique (nesting) minimizes waste during cutting.

During the quality control of a batch of 50 3D-printed parts with a hole that must measure exactly $20,0\text{ mm}$ (permissible tolerance $\pm 0,15\text{ mm}$), you measure the first 5 and obtain: $19,65\text{ mm}$, $19,70\text{ mm}$, $19,65\text{ mm}$, $19,68\text{ mm}$, and $19,67\text{ mm}$.

1. a) Interpret the data: is it a random or a systematic error? Diagnose two possible causes linked to the thermal shrinkage of the plastic or to the slicer (slicer) configuration.
2. b) Design an action plan: what adjustment must you apply before resuming the production run, and what criteria will you follow to decide whether the already manufactured parts are scrapped or can be reworked.

A group proposes building a gearbox where two steel shafts must rotate supported directly on holes drilled by hand into the sides of a plywood box, requiring a tolerance of $\pm 0,05\text{ mm}$ for the gears to mesh perfectly.

1. a) Justify why it is technically unfeasible to achieve and maintain that tolerance in the school workshop using wood and hand tools (consider both the limitations of machining and the hygrometric behavior of the material).
2. b) Redesign the constructive solution by proposing which commercial components or design modifications would allow the mechanism to operate precisely without requiring unattainable manufacturing means.

To organize workshop components, you need a wall-mounted sorting cabinet. A commercial laminated particle board kit costs $38\text{ €}$. Manufacturing it yourself using plywood costs $30\text{ €}$ in wood, $6\text{ €}$ in screws and adhesive, requires buying a basic palm router ($42\text{ €}$), and entails 8 hours of workshop labor.

1. a) Perform a comparative analysis of immediate and amortized costs (considering the tool's life cycle and the durability of the materials).
2. b) Technically justify under what conditions (dimensional customization, moisture resistance, repairability, or future production volume) self-manufacturing pays off compared to buying the standard kit.

Topic challenge. Redesign a household product toward sustainability and the circular economy. Imagine that you work at a technical consultancy and need to optimize an everyday object (a phone stand, a clothes hanger, or a pencil holder).

1. Diagnosis and measurement: Select the object at home. Measure its mass with a kitchen scale (record the exact value with a decimal comma, for example $m = 45,5\text{ g}$) and identify the current material and its original forming technique (injection moulding, extrusion, stamping...).

2. Life cycle and real data: Check the Red Eléctrica de España (REE) website for today's renewable generation percentage (e.g. $58,3\,\%$). Estimate the impact of the use/manufacturing phase based on that energy mix and analyze the feasibility of recycling that material in your yellow container or civic amenity site.

3. Technical redesign: Select a more sustainable alternative material (such as a bioplastic or certified wood), justifying its mechanical properties compared to the original. Model the optimized part in Tinkercad considering its new manufacturing technique.

4. Synthesis: Produce a brief technical data sheet in LibreOffice with the life cycle comparison of both materials and screenshots of the 3D model.

Assessment criteria:

• Rigor in collecting real data (mass measurement and checking the electricity mix at REE).

• Coherent technical justification in selecting the new material and its manufacturing process.

• Quality and technical feasibility of the redesign modeled in Tinkercad.