Mechanical & Engineering: interview questions and learning guide

Mechanical fundamentals

Engineering is physics with a deadline and a budget.

Mechanical engineers apply forces, energy and materials to design parts and machines. Stress and strain describe how materials respond to load, and a factor of safety keeps designs reliable. Heat moves by conduction, convection and radiation.

Interview tip: Walk through your calculation steps aloud: assumptions, formula, result.

Manufacturing & quality

Quality is built into the process, not inspected in at the end.

Manufacturing turns designs into parts using processes such as machining, casting and welding. Tolerances define acceptable variation, preventive maintenance avoids breakdowns, and quality tools find and remove the causes of defects.

Interview tip: Describe a defect you reduced and the number before and after.

Thermodynamics and heat transfer

Heat flows downhill like water, and an engine is just a clever waterwheel placed in that flow.

Thermodynamics studies energy, work and heat. The first law says energy is conserved and the second law says some energy always spoils as unusable heat. Engines and refrigerators are cycles that move heat between hot and cold places. Heat transfer studies how fast heat moves by conduction, convection and radiation. Engineers use these ideas to size heat exchangers, boilers, condensers and cooling systems.

Interview tip: Always state your assumptions such as steady flow and no losses before giving a number.

Fluid mechanics and pumps

A pump is a heart: it gives the fluid enough push to overcome the friction of the pipes.

Fluid mechanics studies liquids and gases at rest and in motion. Pressure, velocity and height trade against each other along a pipe, and friction takes energy away as head loss. A centrifugal pump adds energy by spinning an impeller. Its performance is shown on a curve of head against flow, and it runs where this meets the system curve. Engineers check suction conditions to avoid cavitation.

Interview tip: Mention suction side checks first, because most pump failures come from cavitation or air entry.

Strength of materials and machine design

A machine part is like a rope: it must be strong where it is pulled, and thick enough that it never snaps on a bad day.

Strength of materials predicts how parts deform and fail under load. Engineers find stresses from tension, bending, shear and torsion, and compare them with material limits. Machine design applies this to shafts, gears, bearings, springs and joints, always with a factor of safety. Sudden section changes raise local stress, and repeated loads cause fatigue at stresses far below the static limit.

Interview tip: Show you check fatigue and stress raisers, not just static strength.

Manufacturing processes: casting, welding, machining

Casting pours, welding joins and machining carves: three ways to turn raw metal into a useful shape.

Casting pours molten metal into a mould and suits complex shapes. Welding joins parts by melting them locally, with or without filler. Machining removes metal using cutting tools on lathes, mills and drills. Each has typical defects: shrinkage in castings, porosity in welds and chatter in machining. Process choice depends on shape, volume, material, tolerance and cost.

Interview tip: Link every defect to its cause, for example porosity to damp electrodes or dirty joints.

Maintenance engineering and reliability

Maintenance is like health care: regular check-ups cost far less than an emergency.

Maintenance keeps machines available and safe at the lowest total cost. Strategies include run to failure for cheap items, preventive tasks by time, and predictive tasks by condition. Reliability engineering studies how often and why equipment fails. Teams measure failure and repair times, rank critical assets and fix repeat causes. Skilled planning of spares, manpower and shutdowns avoids long stoppages.

Interview tip: Talk about causes of failure and data, not only repairs, and show you can rank assets by criticality.

Automobile and HVAC basics

A car engine and an air conditioner are both cycles: one turns fuel heat into motion, the other moves heat out of a room.

An internal combustion engine turns fuel energy into rotation through intake, compression, power and exhaust strokes. The drivetrain then carries power through clutch, gearbox, shaft and differential to the wheels. HVAC systems control temperature, humidity and fresh air. A vapour compression cycle uses a compressor, condenser, expansion device and evaporator to move heat. Psychrometrics describes moist air properties used in load calculations.

Interview tip: Draw the cycle on paper and name each component and its job while you explain.

Collect data, inspect, ask why repeatedly, test the cause, fix it and add preventive maintenance.

Consider load, strength, weight, corrosion, temperature, cost and standards, then validate with testing.

Stress is force per unit area inside a material. Strain is the relative change in length it causes.

The ratio of the strength of a part to the load it carries. A higher factor gives more margin for uncertainty.

Voltage equals current times resistance. A 10 ohm resistor with 2 amps across it has 20 volts.

DC flows in one direction at constant polarity, as in batteries. AC changes direction periodically, as in mains power.

Intake, compression, power and exhaust strokes complete a cycle in two crankshaft rotations.

Preventive maintenance is planned to stop failures. Breakdown maintenance is repair after a failure. Preventive costs less over time for critical machines.

The allowed variation from a stated dimension so that parts still fit and work.

A programmable logic controller runs automation: it reads inputs, executes logic and drives outputs for machines and processes.

Stress is force per unit area inside a material. Strain is the change in length divided by the original length.

Ductile materials stretch before breaking, like mild steel. Brittle materials break with little deformation, like cast iron or glass.

Energy cannot be created or destroyed, only changed from one form to another.

The ratio of the strength of a part to the expected load, giving a margin for uncertainty.

Welding melts the base metals to join them. Brazing and soldering use a filler metal at lower temperature without melting the base metals.

Planned inspection and servicing done before failure happens to reduce breakdowns.

Geometric Dimensioning and Tolerancing is a symbol language on drawings that defines allowed variation in shape, position and form.

Record the failure, ask why repeatedly (5 Whys), check data, find the root cause, fix it and prevent repeat.