Industrial manufacturing techniques

Classify these components according to the most likely manufacturing process (casting/moulding, machining or forming) and justify your choice: a remote control housing, a precision splined shaft, a copper pipe, an engine block and a car bodywork sheet.

For each geometry, indicate the appropriate machine tool (lathe or milling machine) and explain your choice: a cylindrical shaft with a keyway, a prismatic housing with cavities, an external thread and a flat guide with slots.

Explain what chip-removal machining is and describe three basic operations (turning, milling and drilling): in each one, indicate what moves (the workpiece or the tool) and what shape is obtained.

Compare a conventional milling machine with a CNC machining centre: what numerical control offers (repeatability, complex geometries, automatic tool changing) and in which cases a manual machine is still reasonable (one-off component, quick repair, training).

In the assembly of a batch of shafts into bearings whose bore dimension is $\varnothing\,25^{+0{,}021}_{0}\ \text{mm}$, it is specified that the fit must be a clearance fit. The target machining dimension set on the drawing for the shaft was $\varnothing\,25_{-0{,}040}^{-0{,}020}\ \text{mm}$. However, during incoming inspection, it is detected that several shafts assemble with interference and jam rotation. When measuring five problematic shafts at standard temperature ($20\ ^\circ\text{C}$), the following are obtained: $25{,}024\ \text{mm}$, $25{,}020\ \text{mm}$, $25{,}018\ \text{mm}$, $25{,}015\ \text{mm}$, and $25{,}012\ \text{mm}$.

1. a) Calculate the theoretical maximum and minimum clearance that should have been obtained, and mathematically demonstrate what type of actual fit occurs when assembling these defective parts into the bearings.
2. b) The operator states: "I measured the parts right after taking them off the lathe and they were at $24{,}970\ \text{mm}$; the defect must be in the bearings." Technically refute this claim by calculating the temperature increase $\Delta T$ that would be sufficient for the steel part (thermal expansion coefficient $\alpha = 12 \cdot 10^{-6}\ \text{K}^{-1}$) to undergo during dry machining to distort the measurement at the machine.
3. c) Justify which other two systematic errors in the external turning process (related to tool wear or machine setup) cause the actual dimension to be larger than the programmed nominal dimension.

A steel sheet $3{,}0\ \text{mm}$ thick enters a rolling mill, as shown in the figure, whose rollers reduce the thickness by $20\,\%$ on each pass. Calculate the thickness at the exit of the first pass and explain why rolling is a forming process by plastic deformation.

Explain what forging is and what difference there is between open-die forging (with a hammer, with the smith guiding the workpiece) and closed-die forging (hot drop forging). Why are forged components usually stronger than cast components of the same shape?

Describe the extrusion process using the analogy of a toothpaste tube and name three extruded products (aluminium profiles, pipes, sheathed cables). Why does extrusion only produce components of constant cross-section?

Describe the sand casting process step by step (pattern, sand mould, pouring, demoulding, cleaning) and give two advantages and two limitations of the process compared with machining.

Explain what thermoplastic injection moulding consists of (plasticising the material, injecting it into the mould, cooling and ejecting) and name four everyday objects manufactured this way. Why is the mould so expensive and yet the process is profitable?

Order the manufacturing stages of a cast aluminium housing for a water pump: (a) machining of mounting surfaces and threads, (b) sand moulding and pouring, (c) final inspection and dimensional control, (d) sand removal and deburring, (e) pattern and mould design with gating systems. Explain what is done at each stage.

A company needs to manufacture plastic housings for a portable speaker. Analyse which process you would choose if the planned production is $100\,000$ units per year and which if only five prototypes are needed to present to investors, explaining the fixed costs (moulds, tooling) and per-piece costs of each option.

An injection mould costs $30\,000\ \text{€}$ and each injected component costs $0{,}50\ \text{€}$; manufacturing the same components by 3D printing costs $6\ \text{€}$ per unit without a mould. a) Calculate from how many components the mould pays for itself. b) Comment on what other factors, besides unit cost, influence the decision (lead time, design changes, surface finish).

A company is deciding whether to manufacture a component with a very complex geometry containing internal cooling channels for a turbine prototype (three units) using CNC machining or metal 3D printing. Analyse the advantages and disadvantages of each technology for this specific case (achievable geometry, surface finish, material properties, cost and lead time) and make a justified decision.