23-Ind-B2 Manufacturing Processes · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2018 — 17-Ind-B2 Manufacturing Processes. Closed book; Casio or Sharp approved calculators only. Any five of the seven questions constitute a complete paper; all questions are of equal value (20 marks each). Answers are written in point form but fully, with all calculations shown, as instructed. Complete answers to all seven questions follow.
Reference texts: Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 6th ed. — engineering-material property overview, casting processes, polymer/composite processing, metal-forming theory, and metal-cutting theory.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The four material classes span roughly an order of magnitude in density, driven mainly by atomic mass and packing (metallic vs. ionic/covalent vs. molecular-chain bonding):
| Material class | Typical density range | Representative examples |
|---|---|---|
| Metal | ≈1.7–19+ g/cm³ | Mg ≈1.7, Al ≈2.7, steel/cast iron ≈7.2–7.9, Cu ≈8.9, W/Au ≈19.3 |
| Ceramic | ≈2–6 g/cm³ | glass ≈2.5, Al₂O₃ ≈3.9, SiC ≈3.2, ZrO₂ ≈5.7–6.0 |
| Plastic/polymer | ≈0.9–2.2 g/cm³ | PE/PP ≈0.9–0.95, PVC ≈1.4, PTFE ≈2.2 |
| Plastic/polymer composite | ≈1.2–2.1 g/cm³ | CFRP ≈1.5–1.6, GFRP ≈1.8–2.0 |
Metals are the densest class by a wide margin because of their close-packed crystal structures and heavy atomic nuclei; ceramics sit in the middle (ionic/covalent lattices, often with lighter constituent atoms than structural metals); plastics are the lightest since they are built from low-atomic-mass carbon/hydrogen chains with a relatively open, often partly amorphous packing. Composites fall between the neat polymer matrix and the (denser) reinforcing fibre — higher than the matrix alone, but still far lighter than any metal, which is precisely why fibre-reinforced composites compete with metals in weight-critical aerospace and automotive design.
| Material class | Typical range | Representative examples |
|---|---|---|
| Metal | ≈230–3400°C (most engineering metals ≈600–1500°C) | Zn die-cast alloys ≈380°C, Al ≈660°C, Cu ≈1085°C, Fe/steel ≈1350–1540°C, W ≈3410°C |
| Ceramic | ≈2000–3000+°C | Al₂O₃ ≈2050°C, MgO ≈2800°C, SiC decomposes above ≈2700°C |
| Plastic/polymer | ≈100–330°C (thermoplastics only) | PE ≈130°C, PP ≈165°C, nylon ≈260°C, PTFE ≈327°C |
Ceramics melt at the highest temperatures because their ionic/covalent bonds are individually much stronger than metallic bonding; metals span a broad intermediate range set by their particular electron/lattice structure. Plastics/polymers are the odd case: only semicrystalline thermoplastics have a true melting point, and even the highest of these (PTFE) melts far below any metal; amorphous thermoplastics instead soften gradually through a glass-transition range, and thermosetting polymers do not melt at all — their cross-linked network decomposes/chars (typically above ≈200–350°C) rather than flowing.
| Material class | Typical range | Representative examples |
|---|---|---|
| Metal | ≈10–430 W/(m·K) | stainless steel ≈15, carbon steel ≈50, Al ≈180–235, Cu ≈390–400, Ag ≈429 |
| Ceramic | ≈1–40 W/(m·K) for most oxide/silicate ceramics (a few outliers, e.g. SiC, run much higher) | glass ≈1, Al₂O₃ ≈30, SiC ≈120 |
| Plastic/polymer | ≈0.1–0.5 W/(m·K) | most commodity/engineering thermoplastics |
Metals conduct heat well because free (delocalized) conduction electrons carry thermal energy efficiently through the lattice — the same electrons responsible for electrical conductivity. Ceramics conduct almost entirely by lattice vibration (phonon transport) rather than free electrons, so they are generally much poorer conductors than metals, though a few highly ordered covalent ceramics (SiC, AlN, diamond) are exceptions with unusually high conductivity. Polymers are the poorest conductors of the three — their long, loosely packed molecular chains scatter phonons very effectively — which is exactly why plastics are used as thermal/electrical insulation.
