Industrial Engineering and Automation

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Metrology is the science of measurement, including all theoretical and practical aspects of measurement, its units and standards.

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This section covers general metrological terms, errors, linear, angular and taper measurement, measuring instruments, applications of metrology, the need for inspection, accuracy and precision, calibration and acceptance tests on machine tools.

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Introduction and General Metrological Terms • Branches: scientific (standards and units), industrial/engineering (dimensional measurement, gauging, quality control) and legal metrology (weights and measures in trade — in Nepal administered by the Nepal Bureau of Standards and Metrology, NBSM). • Measurand: the quantity being measured.

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True value: ideal exact value (never known exactly).

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Measured value: value indicated by instrument.

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Term Meaning Accuracy Closeness of the measured value to the TRUE value Precision Closeness of repeated measurements to EACH OTHER (repeatability/scatter) Resolution / discrimination Smallest change in input that produces a detectable change in output Least count Smallest value that can be read directly on the instrument scale Sensitivity Ratio of change in output to change in input (slope of calibration curve) Range / span Limits of measurement / difference between upper and lower limits Repeatability Agreement between results under the SAME conditions (same operator, instrument, place, short time) Reproducibility Agreement between results under CHANGED conditions (different operators, instruments, labs) Hysteresis Difference in readings for the same input when approached from increasing and decreasing directions Drift Slow change in output over time with constant input (zero drift, span drift) Magnification / amplification Ratio of scale movement to measured quantity movement (in comparators) Traceability Unbroken chain of calibrations linking a measurement to national/international standards Uncertainty Range within which the true value is estimated to lie with stated confidence Accuracy and Precision • Target analogy: accurate & precise — shots tightly grouped at the centre; precise but not accurate — tightly grouped away from centre (systematic error, e.g., zero error); accurate on average but not precise — widely scattered around centre (random error); neither — scattered away from centre. • Precision is necessary but not sufficient for accuracy; a precise instrument can be made accurate by calibration. • Rule of thumb: instrument accuracy should be about 10 times better than the tolerance being measured (at least 4 :

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Errors in Measurement Error type Nature Examples / remedy Gross errors (blunders) Human mistakes Wrong reading, wrong recording, misuse — careful procedure, repeated readings Systematic (determinate) errors Constant or predictable in magnitude and sign; affect ACCURACY Instrumental (zero error, wrong calibration, wear, backlash), environmental (temperature — standard reference temperature 20 °C, humidity), observational (parallax), loading effect, cosine error — corrected by calibration and correction factors Random (accidental) errors Unpredictable, vary in sign and size; affect PRECISION Friction, vibration, small fluctuations — reduced by taking many readings and averaging (statistical treatment) • Absolute error = measured value − true value; relative error = absolute error / true value; % error = relative error × 100. • Abbe's principle: the axis of measurement should be collinear with the axis of the measuring scale to avoid errors.

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A micrometer obeys Abbe's principle; a vernier caliper does not (jaws offset from scale). • Cosine error: when measuring axis is inclined at θ to the true axis, error = L(1 − cos θ).

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Parallax error avoided by viewing the scale perpendicularly.

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Linear Measurement and Measuring Instruments Instrument Key features Steel rule, calipers, dividers Direct/transfer measurement, accuracy ≈ 0.5 mm Vernier caliper Least count = 1 MSD − 1 VSD (typ.

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0.02 mm); outside, inside and depth; vernier height and depth gauges Micrometer Screw principle, LC = pitch/divisions = 0.5/50 = 0.01 mm; ratchet stop ensures uniform measuring pressure; outside, inside, depth, screw-thread micrometers Dial indicator (dial gauge) Rack-and-pinion magnification; comparative measurement, run-out, alignment Slip gauges (gauge blocks) Rectangular hardened blocks with lapped flat parallel faces — end standards; joined by wringing; grades K (calibration), 00, 0, 1, 2; sets of 87 or 103 pieces; build dimension with MINIMUM number of blocks starting from the smallest decimal Comparators Compare work with a standard and show deviation with high magnification: mechanical (dial, Sigma, Johansson), optical, electrical (LVDT), pneumatic (Solex) — very high magnification, non-contact Limit gauges GO / NO-GO plug, ring and snap gauges — check whether size is within limits (not actual size);

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GO gauge checks maximum-material condition with full form, NO-GO checks one dimension at least-material condition CMM (coordinate measuring machine) 3-D measurement with touch/scanning probe; complex parts; computer evaluation of geometry Laser interferometer Highest accuracy length measurement; calibration of machine axes Angular and Taper Measurement • Bevel protractor (universal bevel protractor with vernier — least count 5 minutes). • Sine bar: hardened steel bar with two rollers at a fixed centre distance L (100, 200, 250 mm), used with slip gauges of height h: sin θ = h/L.

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Accurate for angles up to about 45° (error increases at larger angles).

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Sine centre for conical workpieces; sine table for heavy work. • Angle gauges: set of hardened blocks (e.g., 1°, 3°, 9°, 27°, 41°;

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6″, 18″, 30″) combined by adding/subtracting to build any angle. • Autocollimator: optical instrument for measuring very small angular deviations — straightness and flatness of guideways, squareness, alignment.

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Spirit level, clinometer for inclinations. • Taper measurement: external taper using two equal rollers and slip gauges: tan(θ/2) = (M2 − M1)/(2h) (M1, M2 = measurements over rollers at two heights, h = height difference).

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Internal tapers with balls of two sizes.

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Taper plug and ring gauges (with Prussian blue), dividing heads, rotary tables. • Other: flatness by optical flats (interference fringes — each fringe = λ/2 ≈ 0.3 μm), surface roughness by stylus profilometer (Talysurf), roundness by roundness tester (Talyrond) or V-block and dial, screw thread effective diameter by three-wire method (best-wire size), gear tooth thickness by gear tooth vernier.

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Applications of Metrology and Need of Inspection • Applications: quality control and assurance, interchangeability and mass production, process control, research and development, calibration of instruments, legal trade (weights and measures), health and safety, maintenance and condition monitoring, reverse engineering. • Needs of inspection: ensure parts conform to specifications and tolerances; detect defects early and prevent defective products reaching customers; maintain interchangeability; reduce scrap, rework and warranty cost; provide feedback to design and production to improve the process; satisfy legal, safety and contractual requirements; protect company reputation. • Types: incoming (receiving), first-piece, in-process (patrol/floor), final inspection;

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100% inspection vs sampling inspection (acceptance sampling); centralised vs floor inspection; destructive vs non-destructive.

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Calibration and Acceptance Tests on Machine Tools • Calibration: comparing an instrument's readings with a standard of known, higher accuracy (typically 4–10 times better — test uncertainty ratio), determining errors and adjusting or issuing corrections; recorded in a calibration certificate with traceability.

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Done at defined intervals and after repair/overload; labs accredited to ISO/IEC 17025. • Hierarchy of standards: international (BIPM) → national primary standards (national metrology institute;

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NBSM in Nepal) → secondary (reference) standards → working standards → shop-floor instruments. • Acceptance tests on machine tools (Dr.

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Georg Schlesinger, 1927;

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ISO 230, IS 2063 for lathes) check that a new or overhauled machine meets specified accuracy: • (1) Geometrical (alignment) tests — levelling of bed, straightness and flatness of guideways, parallelism of spindle axis to carriage movement, true running (run-out) of spindle, axial float (camming), squareness of cross-slide, alignment of tailstock with spindle — using dial gauges, test mandrels, spirit levels, straight edges, autocollimators and laser interferometers. • (2) Practical (performance/machining) tests — machining standard test pieces under specified conditions and checking their dimensional accuracy, roundness, flatness and surface finish. • CNC machines: positioning accuracy and repeatability (ISO 230-2, laser interferometer), circular interpolation (ballbar) test.

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Sensors convert physical quantities into measurable (usually electrical) signals; actuators convert control signals into motion or force.

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This section covers types of sensors and their use for pressure, flow, temperature, mass, force and torque measurement, sensor selection, and hydraulic, pneumatic and electric actuators with their applications and selection.

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Sensors and Transducers:

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Types • Transducer: device that converts one form of energy into another.

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Sensor: element that detects the measurand (primary sensing element).

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Generalised measurement system: sensing element → signal conditioning (amplification, filtering, conversion) → output (display, recorder, controller). • Active (self-generating) transducers produce their own output without external power: thermocouple, piezoelectric crystal, photovoltaic cell, tachogenerator.

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Passive transducers need external excitation:

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RTD, thermistor, strain gauge, potentiometer, LVDT, capacitive sensors. • Analog vs digital (encoders); contact vs non-contact (proximity, IR, ultrasonic); primary vs secondary transducers. • Displacement/position sensors: potentiometer, LVDT (one primary + two secondary coils in series opposition; output ∝ core displacement, phase gives direction; frictionless, very high resolution, zero output at null), capacitive, inductive proximity (metals), Hall-effect, optical encoders (incremental — counts pulses; absolute — unique code per position, retains position after power loss), resolvers, ultrasonic and laser distance sensors. • Industrial signal standard:

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4–20 mA current loop ('live zero' — 0 mA indicates wire break; immune to voltage drop); also 0–10 V.

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Fluid Pressure Measurement Sensor Principle / use Manometers Liquid column (U-tube, inclined, well type) — low pressures, calibration Bourdon tube (C, spiral, helical) Elliptical curved tube straightens under pressure; most common mechanical gauge Diaphragm, bellows, capsule Elastic element deflection — low pressures, differential pressure Strain-gauge pressure transducer Diaphragm with bonded strain gauges in a Wheatstone bridge — static and dynamic Piezoelectric transducer Quartz crystal generates charge under force — DYNAMIC pressures only (engine cylinder pressure, blast); cannot measure static pressure Capacitive, piezoresistive (MEMS) Diaphragm changes capacitance / silicon resistance — compact electronic transmitters Vacuum gauges McLeod (compression — reference standard), Pirani and thermocouple (thermal conductivity), ionisation (very high vacuum) Dead-weight tester Primary standard for CALIBRATING pressure gauges (known weights on piston of known area) Liquid Flow Measurement Flowmeter Principle Remarks Venturi, orifice, nozzle, pitot tube Differential pressure (Bernoulli):

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Q ∝ √Δp Simple, widely used; orifice has high loss Rotameter Variable area — float rises in tapered tube Direct reading, vertical mounting Positive displacement Nutating disc, oval gear, piston — fixed volume per cycle Domestic water meters, fuel dispensers; high accuracy Turbine flowmeter Rotor speed ∝ flow velocity (pulses counted) Clean liquids, fuel metering Electromagnetic flowmeter Faraday's law — conductive liquid moving in magnetic field induces voltage ∝ velocity Conductive liquids only; no moving parts, no pressure drop; slurries, sewage, water supply Ultrasonic Transit-time difference or Doppler shift Clamp-on, non-intrusive; large pipes Vortex shedding Frequency of Kármán vortices behind bluff body ∝ velocity Steam, gases, liquids Coriolis Coriolis force on vibrating tubes Measures MASS flow directly (and density); very accurate Hot-wire / thermal anemometer Heat loss from heated element ∝ velocity Gas velocity, turbulence studies Weirs and notches Head over crest Open-channel flow Temperature Measurement Sensor Principle Features Liquid-in-glass, filled-system thermometers Thermal expansion of liquid/gas Simple, local indication Bimetallic strip Different expansion of two bonded metals causes bending Thermostats, dial thermometers, cut-outs Thermocouple Seebeck effect — EMF at junction of two dissimilar metals ∝ temperature difference Active, cheap, rugged, fast, wide range; low mV output; needs cold-junction compensation.

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Type K (chromel-alumel, general, up to ≈ 1250 °C), J (iron-constantan), T (copper-constantan, low temp.), R/S (Pt-Rh, up to ≈ 1600 °C) RTD (resistance temperature detector) Resistance of metal (platinum) increases with temperature Pt100 = 100 Ω at 0 °C (α ≈ 0.00385/°C); most accurate, stable, linear; −200 to 850 °C; slower, costlier Thermistor Semiconductor; resistance changes strongly — usually NTC (decreases with temperature) Very sensitive, small, cheap; non-linear, narrow range IC sensors (e.g., LM35) Semiconductor junction Linear (10 mV/°C), low range Pyrometers (radiation, optical, infrared) Thermal radiation (Stefan–Boltzmann); optical 'disappearing-filament' comparison Non-contact; high temperatures (furnaces, molten metal), moving objects; thermal cameras • Thermocouple laws: law of intermediate metals (a third metal inserted at uniform temperature does not change EMF — allows meters and extension wires) and law of intermediate temperatures (E1-3 = E1-2 + E2-3 — basis of cold-junction correction).

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Thermopile = thermocouples in series for larger output.

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Mass, Force and Torque Measurement • Mass: equal-arm beam balance (compares masses — independent of g), spring balance (measures weight — depends on g), load cells (strain-gauge — most common in industrial weighing, weighbridges, platform scales; also hydraulic and pneumatic load cells), electronic balances (electromagnetic force restoration — laboratory precision). • Strain gauge: resistance changes with strain; gauge factor GF = (ΔR/R)/ε ≈ 2 for metal-foil gauges (semiconductor gauges ≈ 100+).

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Used in a Wheatstone bridge; full bridge gives maximum output and temperature compensation. • Force: strain-gauge load cells, proving ring (elastic ring with dial gauge — calibration standard for testing machines), piezoelectric force sensors (dynamic forces), hydraulic and pneumatic load cells. • Torque: strain gauges bonded on a shaft at 45° to its axis (directions of principal stresses in torsion), with slip rings or telemetry; torque transducers; dynamometers — absorption (Prony brake, rope brake, hydraulic/water brake, eddy-current), transmission (belt, torsion-shaft) and driving (DC swinging-field — can also motor the engine).

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Selection of Sensors • Measurement range and required accuracy, resolution, sensitivity, linearity; response time/bandwidth (static vs dynamic measurement); environment (temperature, humidity, vibration, dust, corrosive media, EMI, explosive atmosphere — intrinsically safe/flameproof); contact vs non-contact; size, weight and mounting; loading effect on the measured system; output signal type and compatibility (mV, 4–20 mA, digital); power requirement; reliability, maintenance and calibration needs; cost.

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Hydraulic, Pneumatic and Electric Feature Hydraulic Pneumatic Electric Medium / pressure Oil, ≈ 100–350 bar Compressed air, ≈ 6–8 bar Electric power Force / power density Very high Low–medium Medium Speed Moderate High (fast, simple on-off) Wide range Positioning accuracy Good (oil nearly incompressible, stiff) Poor for intermediate positions (air compressible) Best (servo, stepper) Cleanliness / safety Leakage, fire hazard, messy Clean, safe in explosive atmospheres, overload-safe Clean; sparks in hazardous areas need protection Cost / maintenance High initial cost; filters, seals Cheap components; air treatment (FRL) Moderate; easy control integration Applications Excavators, presses, cranes, aircraft controls, brakes, injection moulding Automation, pick-and-place, clamping, packaging, air brakes, food/pharma CNC axes, robots, valves, conveyors, precision positioning • Hydraulic system: reservoir, pump, pressure-relief valve (safety), directional control valve, flow-control valve, accumulator, filters, actuators (single-acting, double-acting and telescopic cylinders; hydraulic motors).

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Force F = p·A (Pascal's law). • Pneumatic system: compressor, receiver, dryer, FRL unit (filter–regulator–lubricator), valves, cylinders and air motors; exhaust noise needs silencers. • Directional control valve designation ports/positions: e.g., 4/2 (4 ports, 2 positions), 5/2, 3/2; actuated manually, mechanically, by solenoid or pilot pressure. • Electric actuators:

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DC and AC motors, stepper motors (open-loop positioning in discrete steps, e.g., 1.8° = 200 steps/rev), servo motors (closed-loop with encoder feedback — CNC, robots), linear motors, solenoids (short-stroke on/off — valves, locks), piezoelectric actuators (nanometre positioning), shape-memory alloys. • Selection of actuators: force/torque, speed and stroke, positioning accuracy, duty cycle, available energy source, environment (explosive → pneumatic; clean room → electric; very high force → hydraulic), size and weight, controllability, noise, safety, initial and running cost, maintenance.

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This section covers standards of measurement, linear and angular measurement standards, the statistical treatment of errors, calibration, static characteristics of instruments, and the dynamic behaviour of measuring systems as zero-, first- and second-order systems including damping.

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Standards of Measurement • SI base units (7): metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), candela (cd).

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All other units are derived (N, J, W, Pa…). • Since the 2019 redefinition, all SI units are defined by fixed physical constants — e.g., kilogram via the Planck constant (replacing the Pt-Ir International Prototype Kilogram at Sèvres). • Metre: distance travelled by light in vacuum in 1/299 792 458 s (since 1983).

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9 192 631 770 periods of radiation of the caesium-133 atom. • Historical length standards: line standard — International Prototype Metre (Pt-Ir X-section bar, 1889) and Imperial Standard Yard; wavelength standard (1960) — 1 650 763.73 wavelengths of orange-red light of krypton-86. • Hierarchy: primary (national) → secondary → tertiary (reference) → working standards.

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Feature Line standard End standard Length defined as Distance between two engraved lines Distance between two flat end faces Examples Scales, rules, International Prototype Metre Slip gauges, end bars, micrometer anvils Accuracy Lower (±0.2 mm; parallax in reading) Higher (±0.001 mm) Speed of use Quick and easy Time-consuming (wringing combinations) Wear Scale markings do not wear Measuring faces subject to wear Linear and Angular Measurement Standards • Linear: steel rules and scales (line), slip gauges and length bars (end), laser interferometry (wavelength) — see 8.1 for instruments. • Angular: the radian is the SI unit; practical standards are angle gauges, sine bars with slip gauges, precision polygons with autocollimator, and dividing heads/rotary tables.

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A full circle can be subdivided without an external standard (self-calibrating).

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Errors in Measurement:

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Statistical Treatment • Mean x̄ = Σx/n; deviation d = x − x̄; standard deviation σ = √[Σ(x − x̄)²/(n − 1)] (sample); variance = σ²; probable error = 0.6745σ; standard error of the mean = σ/√n (averaging n readings reduces random error by √n). • Normal (Gaussian) distribution of random errors: ±1σ → 68.27%, ±2σ → 95.45%, ±3σ → 99.73% of readings. • Propagation of errors: sum or difference → absolute errors add (worst case); product or quotient → relative (%) errors add; power xⁿ → relative error × n.

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For independent errors, root-sum-square (RSS) combination gives a more realistic estimate. • Limiting (guarantee) error: maximum error specified by manufacturer as % of full-scale — so relative error is larger at low readings (use instruments near full scale). • Loading error: the instrument draws energy from the measured system and changes the quantity (e.g., voltmeter of low resistance, thermometer with large mass).

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Calibration • Static calibration: apply known input values (from a standard), record outputs with all other inputs held constant → calibration curve; fit a best straight line (least squares) to determine sensitivity, linearity, hysteresis, zero offset. • Dynamic calibration: known time-varying inputs (step, sinusoidal) to determine time constant, natural frequency and damping. • Zero and span adjustment; two-point and multi-point calibration; calibration interval; traceability to national standards (see 8.1).

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Static Characteristics of Measurement Characteristic Meaning Accuracy / precision Closeness to true value / repeatability Static sensitivity Δoutput/Δinput (slope of calibration curve) Linearity Maximum deviation of calibration curve from best-fit straight line (% of full scale) Resolution Smallest detectable input change (anywhere in range) Threshold Smallest input change from ZERO that gives detectable output Dead zone (dead band) Largest input change for which there is NO output (due to friction, backlash) Hysteresis Different output for same input depending on direction of approach (loading vs unloading) Drift Change in output over time with constant input — zero drift, sensitivity (span) drift Range and span Minimum to maximum values; span = max − min Repeatability / reproducibility / stability Consistency under same / changed conditions / over time Static error and correction Error = measured − true; correction = −error Input/output impedance Determines loading effect Dynamic Response:

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Zero-, First- and Second-Order Systems System Equation Step response Examples Zero order y = K·x Output follows input INSTANTLY — no lag, no distortion (ideal) Potentiometer displacement sensor, (approximately) strain gauge First order τ dy/dt + y = K·x Exponential rise: y = Kx(1 − e−t/τ); no overshoot Thermometer, thermocouple (τ = mc/hA), RC circuit, liquid-level tank Second order (1/ωn²) ÿ + (2ζ/ωn) ẏ + y = K·x Depends on damping ratio ζ — oscillatory, critically damped or over-damped Spring-mass-damper, U-tube manometer, accelerometer, galvanometer, pressure transducer, moving-coil meters • Time constant τ (first order): time to reach 63.2% of the final value after a step input; ≈ 86.5% at 2τ, 95% at 3τ, 98.2% at 4τ, 99.3% at 5τ.

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Smaller τ → faster response.

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For a ramp input, output lags by τ.

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Frequency response: amplitude ratio 1/√(1 + (ωτ)²), phase lag tan⁻¹(ωτ). • Second-order parameters: static sensitivity K, natural frequency ωn, damping ratio ζ.

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Step-response specifications: delay time, rise time, peak time tp = π/ωd, maximum overshoot Mp = e−πζ/√(1−ζ²) (ζ = 0.5 → ≈ 16%), settling time ts ≈ 4/(ζωn) (2% band), where ωd = ωn√(1 − ζ²). • Instruments are usually designed with ζ ≈ 0.6–0.7 (often 0.707): fast response with small overshoot and the flattest frequency response over the widest range. • Dynamic characteristics: speed of response, measuring lag, fidelity (faithful reproduction of input), dynamic error.

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Damping in Instruments • Under-damped (ζ < 1): pointer overshoots and oscillates before settling.

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Critically damped (ζ = 1): fastest settling without overshoot.

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Over-damped (ζ > 1): sluggish, slow approach. • Damping methods: air-friction damping (piston/vane in chamber — moving-iron instruments), fluid-friction (oil) damping, eddy-current damping (conducting former moving in magnetic field — moving-coil instruments; most efficient), electromagnetic damping.

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A production system transforms inputs (materials, labour, capital, energy) into goods.

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This section covers types of production, plant location and layout (including line balancing), material handling, and production planning and control (PPC).

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Types of Production Systems Type Volume / variety Features / examples Job (jobbing) Very low volume, very high variety General-purpose machines, skilled labour — tool rooms, repair shops, prototypes Batch Medium volume and variety Batches of identical items; set-ups between batches — machine tools, pharmaceuticals Mass (flow/line) High volume, low variety Special-purpose machines, assembly lines, line balancing — automobiles, appliances Continuous (process) Very high volume, one product Automated, continuous flow — cement, refinery, sugar, chemicals Project One-off, large, complex Resources move to site — ships, dams, buildings, hydropower plants Plant Location • Factors: proximity to raw materials (for weight-losing/bulky raw materials — cement, steel, sugar), proximity to market (perishable or weight-gaining products — bakery, soft drinks), availability of labour, power, water, transport (road, rail, air), climate, land cost, government policies and incentives (industrial estates/SEZs), taxes, community attitude, environmental regulations, security, supporting industries and services. • Location evaluation methods: factor-rating (weighted scoring) method; locational break-even analysis (TC = FC + V·Q for each site — choose lowest cost for expected volume); centre-of-gravity method (Cx = ΣdixVi/ΣVi, Cy = ΣdiyVi/ΣVi — minimises distribution cost); transportation model (linear programming); load-distance method;

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Plant Layout • Plant layout: physical arrangement of machines, work centres, storage, aisles and services for efficient flow.

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Objectives: minimise material handling and movement, smooth flow, efficient use of space, flexibility, safety, low WIP, easy supervision and maintenance, worker comfort.

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Layout Arrangement Suits Advantages / disadvantages Process (functional) Similar machines grouped by function (all lathes together) Job and batch production, hospitals Flexible, general-purpose machines, breakdown doesn't stop all work / high handling, high WIP, complex scheduling Product (line) Machines arranged in sequence of operations Mass production, assembly lines Low handling cost and WIP, simple control / inflexible, needs line balancing, one breakdown stops line, high investment Fixed-position Product stays; men, machines, materials come to it Ships, aircraft, dams, buildings, large turbines Minimum movement of heavy product / high movement of resources, low utilisation Cellular (group technology) Machines grouped into cells for part families (often U-shaped) Medium variety & volume Reduced set-up, handling and throughput time; teamwork / duplication of machines Combination (hybrid) Mix of the above Most real plants Balance of flexibility and efficiency • Layout tools: operation process chart, flow process chart, from-to (travel) chart, string diagram, templates and 3-D models, Muther's Systematic Layout Planning (SLP) with activity relationship (REL) chart — closeness codes A (absolutely necessary), E (especially important), I (important), O (ordinary), U (unimportant), X (undesirable); computer methods CRAFT, ALDEP, CORELAP. • Line balancing (product layout): cycle time C = available production time / required output; theoretical minimum number of workstations Nmin = Σti/C (round up); line efficiency = Σti/(N × C); balance delay = 1 − efficiency.

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Heuristics: largest candidate rule, Kilbridge-Wester, ranked positional weight (Helgeson-Birnie).

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Material Handling • Material handling: movement, storage, protection and control of materials throughout manufacturing and distribution.

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It ADDS COST but NO VALUE and often accounts for a large share (commonly quoted 20–50%) of manufacturing cost — so it should be minimised. • Principles (selected): planning principle; unit-load principle (move material in the largest practical unit — pallets, containers); gravity principle (use gravity — chutes, roller conveyors); minimum travel / straight-line flow; space utilisation (use cubic space, height); standardisation; mechanisation/automation; ergonomics and safety; system flow (integrate handling with information flow); energy and environment; minimise dead-weight ratio and idle time; life-cycle cost. • Selection factors: material characteristics (size, weight, fragility, bulk/unit), volume and frequency, distance and route (fixed or variable path), building constraints, cost.

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Equipment class Examples Characteristics Conveyors Belt, roller (gravity/powered), chain, screw, bucket elevator, overhead trolley, pneumatic FIXED path, continuous, high volume Cranes and hoists EOT (electric overhead travelling) bridge crane, gantry, jib, tower, chain hoists Overhead, intermittent, heavy loads within a fixed area Industrial trucks Forklift, hand pallet truck, tractor-trailer, AGV VARIABLE path, flexible Positioning equipment Lift tables, manipulators, robots, turntables Handling at the workplace Unit-load and storage Pallets, skids, containers, racks, AS/RS Storage and unitisation Production Planning and Control (PPC) • PPC ensures that the right products are produced in the right quantity, of the right quality, at the right time and at minimum cost. • Planning phase: forecasting, aggregate planning, master production schedule (MPS), material requirements planning, routing (determines WHAT operations, WHERE and in WHAT sequence — path of work), scheduling (WHEN each operation starts and finishes — timetable), loading (assigning work to machines/work centres according to capacity). • Action phase: dispatching — releasing orders and issuing documents (job cards, material requisitions, tool orders) to start production as per schedule. • Control phase: follow-up/expediting (progress monitoring, removing bottlenecks), inspection, evaluation and corrective action. • Aggregate planning strategies: chase demand (vary workforce/output), level production (constant output, inventory absorbs fluctuations), mixed strategy. • MRP inputs:

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MPS, bill of materials (BOM) and inventory status file → outputs: planned order releases for DEPENDENT-demand items.

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MRP II adds capacity and finance;

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ERP integrates the whole enterprise. • Scheduling/sequencing rules:

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SPT (shortest processing time) — minimises average flow time and WIP;

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EDD (earliest due date) — minimises maximum lateness; critical ratio.

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Johnson's rule (n jobs, 2 machines, minimise makespan): pick the shortest time; if on machine 1 schedule the job FIRST, if on machine 2 schedule it LAST; repeat. • Gantt charts for scheduling and progress.

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JIT (Toyota): pull system with kanban, minimum inventory, elimination of the 7 wastes (overproduction, waiting, transport, over-processing, inventory, motion, defects).

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Theory of constraints (Goldratt): manage the bottleneck (drum-buffer-rope).

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Inventory is idle stock held for future use; inventory control aims to balance the cost of holding stock against the cost of ordering and of shortages.

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This section covers inventory costs, EOQ, lead time, reorder point, safety stock, ABC and other selective controls, and forecasting techniques.

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Inventory and Its Costs • Types: raw materials, work-in-process (WIP), finished goods, MRO (maintenance, repair and operating supplies) and spares. • Reasons for holding inventory: decouple operations, buffer against demand and supply uncertainty, economies of scale in purchasing/production, seasonal anticipation, goods in transit (pipeline). • Ordering (set-up) cost Co: cost per order — preparing orders, follow-up, receiving, inspection, set-up; independent of order size. • Carrying (holding) cost Ch: cost of holding one unit for one year — interest/opportunity cost of capital, storage space, insurance, taxes, obsolescence, deterioration, pilferage; often expressed as i% of unit price (≈ 15–30% per year):

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Ch = i × C. • Shortage (stock-out) cost: lost sales, idle machines, emergency purchases, loss of goodwill.

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Purchase cost of items.

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Economic Order Quantity (EOQ) • EOQ (Wilson/Harris) = Q* = √(2DCo/Ch) (D = annual demand). • At EOQ: annual ordering cost = annual carrying cost; minimum total (ordering + carrying) cost TC* = √(2DCoCh); number of orders per year N = D/Q*; time between orders T = Q*/D; average inventory = Q*/2. • Assumptions: demand known and constant, lead time known and constant, instantaneous replenishment, no shortages, no quantity discounts, single item. • EOQ total-cost curve is flat near the optimum — total cost is insensitive to moderate errors in Q. • Extensions: economic production (batch) quantity EPQ = √(2DCo/[Ch(1 − d/p)]) (finite production rate p, usage rate d);

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EOQ with planned shortages; quantity-discount models. • Example:

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D = 12,000 units/yr, Co = Rs 100/order, Ch = Rs 6/unit/yr → Q* = √(2 × 12000 × 100/6) = √400,000 ≈ 632 units.

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Lead Time, Reorder Point, Reorder Quantity and Safety Stock • Lead time (L): time between placing an order and receiving the goods (procurement lead time) — includes order processing, supplier production/dispatch and transit. • Reorder point (reorder level) ROP = demand during lead time + safety stock = d × L + SS (d = demand per unit time).

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When stock falls to ROP, a new order is placed. • Reorder quantity: quantity ordered each time — normally the EOQ in a fixed-order-quantity system. • Safety (buffer) stock: extra stock to protect against variability in demand and lead time.

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Statistically SS = z × σd × √L (σd = standard deviation of demand per period; z from desired service level:

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90% → 1.28, 95% → 1.65, 99% → 2.33).

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SS = (maximum usage − average usage) × lead time. • Classical stock levels: reorder level = maximum usage × maximum lead time; minimum level = reorder level − (normal usage × normal lead time); maximum level = reorder level + reorder quantity − (minimum usage × minimum lead time); danger level = normal usage × emergency lead time. • Fixed-order-quantity (Q) system: continuous review; order EOQ when stock hits ROP (e.g., two-bin system).

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Fixed-period (P) system: periodic review at fixed intervals, order up to a target level; needs more safety stock. • Inventory turnover ratio = cost of goods sold / average inventory; perpetual inventory and cycle counting maintain record accuracy.

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ABC Analysis and Other Selective Controls • ABC analysis (Pareto principle; 'Always Better Control') classifies items by annual consumption value (annual usage × unit cost):

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Class % of items % of annual consumption value Control policy A ≈ 10–20% ≈ 70–80% Tight control, frequent review, accurate records, small frequent orders, low safety stock, senior-level control B ≈ 20–30% ≈ 15–25% Moderate control, periodic review C ≈ 50–70% ≈ 5–10% Loose control, bulk ordering, higher safety stock, simple records Selective control Basis VED Vital, Essential, Desirable — criticality of items (spare parts) FSN Fast-moving, Slow-moving, Non-moving — rate of usage HML High, Medium, Low — unit price SDE Scarce, Difficult, Easy — procurement difficulty XYZ Value of stock in hand GOLF Government, Ordinary, Local, Foreign — source of supply SOS Seasonal, Off-seasonal Forecasting Techniques • Horizons: short-range (< 3 months — scheduling, purchasing), medium-range (3 months–2 years — aggregate planning, budgeting), long-range (> 2 years — capacity, location, new products). • Qualitative (judgemental):

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Delphi method (anonymous expert panel, iterative rounds until consensus), market research/consumer survey, sales-force composite, jury of executive opinion, historical analogy — used when data are scarce (new products). • Time-series methods: naive; simple moving average (average of last n periods — larger n → smoother but slower response); weighted moving average; exponential smoothing Ft+1 = Ft + α(At − Ft) = αAt + (1 − α)Ft (α = 0–1, usually 0.1–0.3; higher α → more responsive to recent data); trend-adjusted (Holt) and seasonal (Winters) smoothing; trend projection by least squares y = a + bx with b = (nΣxy − ΣxΣy)/(nΣx² − (Σx)²), a = ȳ − b x̄. • Components of a time series: trend, seasonal, cyclical, random (irregular) variations. • Causal (associative) methods: linear/multiple regression, correlation (coefficient r), econometric models, leading indicators. • Forecast accuracy: error e = A − F;

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MAPE = (Σ|e/A|/n) × 100; bias (mean error); tracking signal = RSFE/MAD (running sum of forecast errors ÷ MAD; typically kept within ±4). • Example:

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Ft = 100, At = 120, α = 0.2 → Ft+1 = 100 + 0.2(120 − 100) = 104.

1

This section covers IC engine efficiencies, testing of engines (measurement of fuel, air, power and friction power), engine power and heat balance, engine cooling, knocking and pre-ignition, and carburettor and fuel-injection systems.

2

(Engine construction and cycles are in Chapter 2.) Engine Efficiencies and Performance Parameters Parameter Definition Typical values Indicated thermal efficiency ηith = IP / (ṁf × CV) — Brake thermal efficiency ηbth = BP / (ṁf × CV) Petrol ≈ 25–35%; diesel ≈ 30–45% Mechanical efficiency ηm = BP / IP = ηbth/ηith ≈ 75–90% (falls at part load) Volumetric efficiency ηv = actual mass of air inducted / mass of air that would fill swept volume at intake conditions SI ≈ 75–90%;

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CI ≈ 85–90%; > 100% possible with supercharging Relative efficiency (efficiency ratio) Actual thermal efficiency / air-standard efficiency ≈ 0.5–0.75 Brake specific fuel consumption bsfc = ṁf / BP (kg/kWh); ηbth = 3600/(bsfc × CV) with CV in kJ/kg Diesel ≈ 0.20–0.25; petrol ≈ 0.25–0.30 kg/kWh Mean effective pressure bmep = BP × 60,000 / (L·A·n·k) (n = N/2 for 4-stroke) Measures engine's ability to do work per unit swept volume Testing of Engines • Fuel consumption: volumetric (burette + stopwatch — time for a known volume) or gravimetric (weighing); flow meters. • Air consumption: air box method — large box with a sharp-edged orifice and manometer, which damps the pulsating flow; viscous-flow (Alcock) meter; hot-wire/MAF sensors. • Brake power by dynamometers:

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Prony brake, rope brake (BP = (W − S)·π(D + d)·N/60,000 kW), hydraulic (water-brake / Froude) — high powers, eddy-current — easy electrical control, swinging-field DC — absorbs or motors.

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BP = 2πNT/60,000 kW. • Indicated power from indicator diagrams (mechanical indicator or electronic piezoelectric pressure transducer with crank-angle encoder):

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IP = pmi·L·A·n·k/60,000 kW. • Speed by tachometer; temperatures by thermocouples (exhaust, coolant, oil); exhaust emissions by gas analysers — Orsat apparatus (CO2, O2, CO by volume), NDIR (CO, CO2), FID (HC), chemiluminescence (NOx); smoke meters (Bosch, Hartridge) for diesel. • Types: type (performance) tests, routine tests, endurance/durability tests.

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Friction power method Procedure Remarks Willan's line (fuel-rate extrapolation) Plot fuel consumption vs BP at constant speed; extrapolate straight line to zero fuel — negative intercept on BP axis = FP CI engines only (fuel rate linear with load) Morse test In a multi-cylinder engine, cut off each cylinder in turn; restore speed by reducing load;

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IP of that cylinder = BP (all) − BP (with it cut); ΣIP − BP = FP Multi-cylinder SI and CI engines Motoring test Engine driven by electric (swinging-field) dynamometer without firing; power absorbed ≈ FP Includes pumping losses; engine runs cooler, so FP is slightly overestimated Indicator diagram FP = IP (from diagram) − BP (from dynamometer) Needs accurate IP Retardation test Measure deceleration after cutting fuel Approximate Engine Power and Heat Balance • Heat balance sheet accounts for heat supplied (ṁf × CV) per minute or per hour:

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(1) heat equivalent of BP;

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(2) heat to cooling water = ṁwcw(Tout − Tin);

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(3) heat carried by exhaust gases = ṁgcpg(Tg − Ta) with ṁg = ṁa + ṁf;

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(4) unaccounted losses (radiation, friction not in coolant, incomplete combustion).

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Heat distribution (approx.) SI (petrol) engine CI (diesel) engine Brake power (useful work) ≈ 21–28% ≈ 29–42% Cooling water ≈ 12–27% ≈ 15–35% Exhaust gases ≈ 30–55% ≈ 25–45% Unaccounted / radiation ≈ 3–10% ≈ 1–10% • Performance curves: at constant speed with varying load — ηbth rises with load and bsfc is minimum near 75–90% of full load; at full throttle with varying speed — torque is maximum at medium speed, power rises to a maximum at higher speed then falls, bsfc is U-shaped. • Power boosting: supercharging (engine-driven compressor) and turbocharging (exhaust-driven turbine + compressor) raise intake density; intercooling further increases density.

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Engine Cooling • Need: about 25–35% of fuel energy must be removed to keep cylinder walls, piston and valves at safe temperatures — prevents breakdown of the lubricating oil film, piston seizure, thermal stresses/cracking, detonation and pre-ignition, valve burning. • Over-cooling is also harmful: lower thermal efficiency, poor vaporisation, acid condensation and corrosive wear, sludge formation, higher friction (viscous oil), hard starting. • Air cooling: fins on cylinder and head, natural or fan/blower air flow — motorcycles, small engines, aircraft piston engines.

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Simple, light, no coolant leakage or freezing; but less uniform, noisier, limited to small engines. • Liquid (water) cooling: water jackets around cylinders.

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Thermosyphon (natural circulation by density difference — no pump, old engines); forced (pump) circulation — centrifugal water pump, radiator (tubular or cellular/honeycomb) with fan, thermostat (wax-pellet valve opening at ≈ 80–90 °C for quick warm-up and constant temperature), pressure cap (raises boiling point to ≈ 110–125 °C), expansion tank; evaporative and pressurised systems. • Coolant = water + ethylene glycol (antifreeze: lowers freezing point, raises boiling point) + corrosion inhibitors.

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Knocking and Pre-ignition • SI engine knock (detonation): after the spark, the end gas (unburned mixture ahead of the flame front) is compressed and heated and auto-ignites before the flame reaches it → very rapid pressure rise, pressure waves, metallic 'pinking' sound, overheating, piston/ring damage, loss of power and efficiency. • CI engine knock (diesel knock): caused by a long ignition delay — too much fuel accumulates and then burns suddenly at the START of combustion → very high rate of pressure rise and harsh noise. • Pre-ignition: ignition of the charge BEFORE the spark occurs by a hot spot (glowing carbon deposits, overheated spark-plug electrodes or exhaust valve) — surface ignition.

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It advances combustion, causes power loss and overheating, and can lead to knock (and knock to pre-ignition — runaway).

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Remedies: remove carbon, colder spark plug, better cooling. 'Run-on/dieseling' after switch-off is a related effect. • Distinction: knock = auto-ignition of end gas AFTER the spark; pre-ignition = surface ignition BEFORE the spark. • Fuel ratings: octane number (RON — research, milder;

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MON — motor, severe; sensitivity = RON − MON) for SI fuels; cetane number for CI fuels.

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Anti-knock additives:

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TEL (historical, now banned), MMT, ethanol, MTBE.

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Factor To reduce SI knock To reduce CI knock Compression ratio LOWER HIGHER Intake temperature & pressure LOWER HIGHER Ignition/injection timing RETARD spark Reduce delay (optimum/slightly retarded injection, pilot injection) Fuel quality HIGH octane (long self-ignition delay) HIGH cetane (short ignition delay) Self-ignition temperature of fuel HIGH LOW Engine speed / turbulence HIGHER speed, more turbulence Higher turbulence helps mixing Combustion chamber Compact, central spark plug, squish; cool end-gas region Good swirl, fine atomisation Carburettor • Function: meters, atomises and mixes petrol with air in the correct proportion for SI engines (chemically correct air-fuel ratio ≈ 14.7 :

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1 by mass). • Principle: air flows through a venturi; velocity rises and pressure falls (Bernoulli), drawing fuel from the float chamber (float and needle valve keep a constant fuel level) through the main jet/nozzle. • Parts of a simple carburettor: float chamber, float and needle valve, venturi (choke tube), main jet and nozzle, throttle valve (butterfly — controls quantity of mixture, i.e., engine output), choke valve (restricts air to give rich mixture for cold starting). • Mixture requirements: cold start and idling — RICH; cruising (part load) — LEAN for economy (≈ 16 :

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1); maximum power — slightly RICH (≈ 12.5–13 :

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1); acceleration — momentary enrichment. • Limitation of a simple carburettor: mixture becomes progressively richer as air flow increases; also cannot meet idling and acceleration needs.

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Additional systems: compensating jet/air-bleed, idling (slow-running) system, accelerating pump, power enrichment (economiser), choke.

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Types: updraught, downdraught (most common), side-draught; constant-choke (Solex, Zenith, Carter) and constant-vacuum (SU).

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Fuel Injection Systems • Petrol (SI) injection: throttle-body (single-point) injection; multi-point port fuel injection (MPFI) — one injector per intake port (most common in modern cars); gasoline direct injection (GDI) — into the cylinder, allows stratified charge and higher compression ratio. • Electronic control unit (ECU) uses sensors — mass air flow (MAF) or manifold pressure (MAP), throttle position, crank position/speed, coolant temperature, oxygen (lambda) sensor (closed-loop control to λ = 1 for the three-way catalyst), knock sensor. • Advantages of injection over carburettor: precise air-fuel ratio in all conditions, better fuel economy and power, lower emissions, better cold starting and throttle response, uniform distribution to cylinders, no carburettor icing. • Diesel (CI) injection must meter, time, pressurise, atomise and distribute fuel into hot compressed air at high pressure (hundreds to > 2000 bar).

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Systems: air injection (obsolete); solid (airless) injection — individual/jerk pump (in-line Bosch pump, one element per cylinder), distributor (rotary) pump, unit injector (pump and injector combined), and common rail (CRDI) — high-pressure pump feeds a common rail (≈ 1000–2500 bar); electronically controlled solenoid/piezo injectors allow pilot, main and post injections → lower noise and emissions. • Components: fuel tank, feed (lift) pump, fuel filters, injection pump, high-pressure pipes, injectors/nozzles (single-hole, multi-hole — direct injection; pintle — indirect injection), governor. • Direct injection (DI): open chamber, multi-hole nozzle, higher efficiency, easier cold start, noisier.

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Indirect injection (IDI): pre-chamber or swirl chamber, pintle nozzle, glow plugs for cold start, quieter and smoother, lower efficiency.