---
title: "Tribology in manufacturing: friction, wear, lubrication"
subject: "Manufacturing and Production Processes"
chapter: 2
key: "semester_4/manufacturing_and_production_processes:tribology-friction-wear-lubrication-manufacturing"
source: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/tribology-friction-wear-lubrication-manufacturing
site: BCT Engineering
---

# Tribology in manufacturing: friction, wear, lubrication

Manufacturing and Production Processes · Chapter 2: Manufacturing Properties of Materials

- Asked in: year not given, 6 marks
- Video: [Tribology Explained: Surface Roughness, Friction, Wear & Lubrication Engineering](https://www.youtube.com/watch?v=M92Ty-rz488) — Ibham Veza
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/tribology-friction-wear-lubrication-manufacturing
- Whole chapter: https://www.bctengineer.com/md/semester_4/manufacturing_and_production_processes/chapter-2

## Question

What is tribology? Explain the types of friction and wear found in metal-forming and machining, and the functions and types of lubricants used in manufacturing. Mention how viscosity of a liquid lubricant varies with temperature.

## Short answer

Tribology studies friction, wear and lubrication. Friction may be sliding (Coulomb) or sticking; wear types include adhesive, abrasive, diffusion, fatigue and corrosive. Lubricants reduce friction/wear, cool and flush chips; liquid viscosity decreases with temperature, so hot working often uses solid lubricants or glass.

## Answer

**Tribology** is the science of interacting surfaces in relative motion: it covers friction, wear and lubrication. In manufacturing it controls forming loads, tool life, surface finish and energy use.

#### Friction

- **Sliding (Coulomb) friction:** $F = \mu N$, valid at light loads (cold working with good lubrication, $\mu = 0.05$-$0.2$).
- **Sticking (shear) friction:** at high pressure in hot working the real contact area equals the apparent area, so the friction stress is a fraction of the shear yield stress, $\tau = m k$ ($m$ = friction factor from 0 to 1). Used in forging and hot rolling.
- Friction raises forming force, causes non-uniform flow and heats the tool.

#### Wear

| Type | Cause | Seen in |
|---|---|---|
| Adhesive | Welding and tearing of asperities | Tool rake face, built-up edge |
| Abrasive | Hard particles ploughing the surface | Flank wear of tools, dies |
| Diffusion | Atoms migrate at high temperature | Crater wear in carbide tools |
| Fatigue / thermal | Cyclic stress or temperature | Hot forging dies |
| Corrosive | Chemical attack | Dies in humid or acid media |

#### Functions of lubricants

1. Separate the surfaces and reduce friction and wear.
2. Carry away heat (coolants) and wash away chips.
3. Improve surface finish and prevent welding.
4. Protect the work and die from corrosion.

#### Types of lubricants

- **Liquids:** mineral oils, soluble (emulsion) oils, synthetic fluids, with extreme-pressure (EP) additives.
- **Solids:** graphite, molybdenum disulphide, soap, glass (for hot extrusion).
- **Gases and mists:** compressed air, aerosol of oil.
- Regimes: hydrodynamic (full film), boundary (thin molecular film) and mixed.

#### Viscosity and temperature

Viscosity $\eta$ (shear stress divided by shear rate, Pa.s) **decreases** as temperature rises, approximately exponentially. A lubricant for hot working must therefore keep an adequate film at the die temperature, which is why solid lubricants or glass are used above about 700 degree C. Viscosity rises with pressure, which helps film formation in rolling and drawing.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. When is sticking (shear) friction tau = m k used instead of Coulomb friction?
   A. At light loads in lubricated cold work
   B. At high pressure in hot working such as forging and hot rolling
   C. Only in machining of soft metals
   D. Only with solid lubricants at room temperature
   Answer: B. At high pressure the real contact area equals the apparent area, so friction stress is a fraction of the shear yield stress. (Key point: Sticking friction)

2. Crater wear on carbide cutting tools is mainly due to
   A. Abrasive ploughing by hard particles
   B. Diffusion of atoms at high temperature
   C. Corrosive attack in humid media
   D. Adhesive welding at flank
   Answer: B. Diffusion wear occurs at high temperature and shows as crater wear in carbide tools; abrasive wear gives flank wear. (Key point: Wear types)

3. Which is NOT a listed function of a lubricant in manufacturing?
   A. Carry away heat and wash away chips
   B. Prevent welding and improve surface finish
   C. Raise the friction to improve grip of the work
   D. Protect work and die from corrosion
   Answer: C. Lubricants separate surfaces and reduce friction and wear; they do not raise friction. (Key point: Functions of lubricants)

4. How does the viscosity of a liquid lubricant vary with temperature?
   A. Increases roughly exponentially as temperature rises
   B. Does not change
   C. Decreases roughly exponentially as temperature rises
   D. Falls with pressure
   Answer: C. Viscosity decreases as temperature rises, so hot working needs solid lubricants or glass above about 700 degree C. (Key point: Viscosity with temperature)

## Related in Manufacturing and Production Processes

- [EDM principle and ECM metal removal rate](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Aedm-ecm-principle-mrr-numerical) — Manufacturing and Production Processes, chapter 8
- [Hot and cold working; temperature and strain rate](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Ahot-cold-working-friction-strain-rate) — Manufacturing and Production Processes, chapter 5
- [Cold upsetting force with friction](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Aopen-die-forging-friction-numerical) — Manufacturing and Production Processes, chapter 5
- [Gas flames, arc welding and heat input](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Aoxyacetylene-flames-smaw-heat-input-numerical) — Manufacturing and Production Processes, chapter 12
- [Flat rolling draft, roll force and power](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Aflat-rolling-force-power-numerical) — Manufacturing and Production Processes, chapter 5
- [Wire drawing stress, force and power](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Awire-drawing-stress-force-numerical) — Manufacturing and Production Processes, chapter 5

## Related in other subjects

- [Lubricant functions; solid lubricants](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alubricant-functions-solid) — Engineering Chemistry, chapter 8
- [Types of lubrication and viscosity](https://www.bctengineer.com/question.md?key=semester_6%2Fmachine_design_i%3Alubrication-types-viscosity) — Machine Design I, chapter 7
- [Regression of wear on oil viscosity](https://www.bctengineer.com/question.md?key=semester_5%2Fprobability_and_statistics%3Afretting-wear-regression-viscosity) — Probability and Statistics, chapter 5, asked 2×
- [Lubricant functions; grease and solid lubricant use](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alubricant-functions-grease-solid) — Engineering Chemistry, chapter 8