ME 1001 – BASIC MECHANICAL ENGINEERING

CONTENTS Unit I: Machine elements I (springs and cams) Unit II: Machine elements II ( Gears, Belt drives, chain drives, simple problems) Unit III: Energy (Renewable and non Renewable, Power generation, EC & IC engines, simple problems) Unit IV: Manufacturing process I (sheet metal work, welding, soldering and brazing) Unit V: Manufacturing process II (Lathe practices, drilling, simple problems)

TEXTBOOKS & REFERENCES Prabhu.T.J, Jai Ganesh. V, and Jebaraj. S, "Basic Mechanical Engineering", SciTech Publications Chennai, 2000. Nag.P.K, "Power Plant Engineering", Tata McGraw-Hill, New Delhi, 2008. Rattan.S.S, "Theory of Machines", Tata McGraw-Hill, New Delhi, 2010.

OBJECTIVE & INSTRUCTIONAL OBJECTIVES To familiarize with the basics of Mechanical Engineering. INSTRUCTIONAL OBJECTIVES : 1. To familiarize with the basic machine elements 2. To familiarize with the sources of Energy and Power generation 3. To familiarize with the various manufacturing processes

MACHINE ELEMENTS - I Springs: Springs are elastic bodies (generally metal) that can be twisted, pulled, or stretched by some force. They can return to their original shape when the force is released. In other words it is also termed as a resilient member. Spring act as a flexible joint in between two parts or bodies. Objectives of spring: Cushioning , absorbing , or controlling of energy due to shock and vibration. Control of motion. Measuring forces. Storing of energy.

SPRING MATERIALS Hard drawn high carbon steel. 9) Chrome vanadium. Oil tempered high carbon steel. 10) Chrome silicon. Stainless steel Copper or nickel based alloys. Phosphor bronze. Inconel. Monel Titanium.

SPRING MATERIALS Limited number of materials and alloys are suitable for use as springs. Ideal spring material would have high ultimate strength, high yield point, and low modulus of elasticity in order to provide maximum energy storage (area under elastic portion of stress-strain curve). For dynamically loaded springs, fatigue strength properties of material are of primary importance.

CLASSIFICATION OF SPRINGS Helical springs: Tension helical spring Compression helical spring Torsion spring Spiral spring 2) Leaf springs or laminated or semi elliptical springs

HELICAL SPRING CLASSIFICATION Open coil helical spring Closed coil helical spring Torsion spring Spiral spring

HELICAL SPRINGS

TORQUE IN COMPRESSION SPRINGS

SPRING RATE

SHEAR STRESS IN SPRING

WAHL STRESS FACTOR K

Number of coils

TORSION SPRING It is also a form of helical spring but it rotates about an axis to create load. It releases the load in an arc around the axis. Mainly used for torque transmission

SPIRAL SPRING It is made of a band of steel wrapped around itself a number of times to create a geometric shape. It releases power when it unwinds.

τ=shear stress, and I = Polar moment of inertia = π d⁴ 32 It may be noted that each section of the coil is under torsion but there are small bending and shearing stress which being small are usually neglected. Shear stress τ: From torsion equation, T = Cθ = τ ; T = τ I l r I r Or, T= τI = τ×πd⁴×2 = τ. π d³ r 32 d 16 P P P P

τ = 16T πd³ τ = 16WR (T=WR) Deflection, δ: Again, T = Cθ IP l θ= Tl = WR×2πRn×32 = 64WR²n CIP C ×πd⁴ Cd⁴ δ = R×θ δ = 64WR³n Cd⁴

Energy stored, U: U= 1 . T . Θ = 1 . W.R.δ = 1 . W.δ (δ=Rθ) 2 2 R 2 i.e. U= 1 Wδ 2

LEAF OR LAMINATED SPRING OR SEMI ELLIPTICAL SPRING

LEAF SPRING (CONTD..) Also called as a semi-elliptical spring, as it takes the form of a slender arc shaped length of spring steel of rectangular cross section. In Heavy vehicles, leaves are stacked one upon the other to ensure rigidity and strength. It provides dampness and springing function.

NIPPING IN LEAF SPRING? Because of the difference in the leaf length, different stress will be there at each leaf. To compensate the stress level, prestressing is to be done. Prestressing is achieved by bending the leaves to different radius of curvature before they are assembled with the center clip. The radius of curvature decreases with shorter leaves.

NIPPING IN LEAF SPRING (CONTD..) The extra intail gap found between the extra full length leaf and graduated length leaf is called as nip. Such prestressing achieved by a difference in the radius of curvature is known as nipping.

NOMENCLATURE OF COMPRESSION HELICAL SPRING

TERMINOLOGIES OF A SPRING 1) Free length 2) Pitch 3) Endurance limit 4) Active coils 5) Solid length 6) Pitch angle 7) Initial tension 8) Spring index 9) Spring rate

COMPRESSION SPRING - TERMINOLOGIES SOLID LENGTH: When the compression spring is compressed until the coils come in contact with each other the spring is said to be solid. The solid length of a spring is the product of total number of coils and the diameter of the wire. LS=n’*d n’- total number of coils d- diameter of the wire

COMPRESSION SPRING - TERMINOLOGIES FREE LENGTH: It is the length of the spring in the free or unloaded condition. It is equal to the solid length plus the maximum deflection or compression of the spring and the clearance between the adjacent coils. LF=n’*d+δmax+0.15 δmax

COMPRESSION SPRING - TERMINOLOGIES PITCH LENGTH: The pitch of the coil is defined as the axial distance between adjacent coil in uncompressed state. Pitch length=free length/(n’-1)

SPRINGS IN SERIES

SPRINGS IN PARALLEL

COMBINED SYSTEM(BOTH SERIES AND PARALLEL)

PARALLEL [UNSYMMETRICAL DISPLACEMENT(Δ1≠Δ2)] WHEN SPRINGS ARE IN PARALLEL [UNSYMMETRICAL DISPLACEMENT(Δ1≠Δ2)]

APPLICATIONS OF SPRINGS Brakes Clutches Watches and Toys Vehicle and machine foundation Railway carriages, motor cars, scooters, motorcycles