By Vikram sawant

1. Sinhgad Technical Education SocietyTrain the Teachers ProgrammeFirst Year EngineeringBasic Mechanical Engineering Design Fundamentals By Vikramsawant

2. UNIT NO 02 Design Fundamentals • Design: Steps in design process, mechanical properties (Strength, Toughness, Hardness, Ductility, Malleability, Brittleness, Elasticity, Plasticity, Resilience, Fatigue, Creep) and selection of engineering materials, Applications of following materials in engineering- Aluminium, Plastic, Steel , Brass, Cast iron, Rubber, Copper. • Mechanism (Descriptive treatment only): Definition, and comparison of mechanism and machine, four bar mechanism, Slider crank mechanism.Classification of Pairs.

3. DESIGN • Design refers to the plan of construction of an object. • The persons who performs the design is called as a designer and the sequence of activities performed by the designer is called as a design process. • Machine design refers to a systematic process of designing a machine which converts mechanical energy into some useful form of task by using mechanisms. • Machine design may lead to entirely design a new machine or develop an existing machine.

4. NEED OF MACHINE DESIGN • Functional requirement • User comfort • Safety • Modification • Appearance • Cost reduction

5. GENERAL CONSIDERATIONS IN DESIGN • Type of load • Selection of material • Shape and size • Friction and lubrication • Operational safety • Machine availability • Use of standard parts • Motion of elements • Production quantity • Maintenance of element

6. GENERAL CONSIDERATIONS IN DESIGN • Life of element • Capacity of element • Weight of element • Cost of element

7. STEPS IN A DESIGN PROCESS • Define the need • Synthesis • Analysis of forces • Selection of material • Design of elements( Shape, size and stresses) • Modification • Detailed drawing • Production

8. MECHANICAL PROPERTIES OF MATERIAL The various properties of a material are mainly classifies as follows: • Mechanical Properties • Thermal Properties • Electrical Properties Here we are supposed to study only the mechanical properties of a material as follows.

9. MECHANICAL PROPERTIES • Mechanical properties include those characteristics of a material that describes its behavior under the action of external forces. • The knowledge of mechanical properties of a material is very essential to construct a mechanically fool-proof structure. • Some of the important mechanical properties are as follows: Elasticity, Plasticity, Toughness, Resilience, Strength, Stiffness, Ductility, Malleability, Brittleness, Hardness, Fatigue, Creep.

10. ELASTICITY • It is the property of a material to regain its original shape after deformation when the external forces are removed. • This property is required for materials used in tools and machines. • PLASTICITY • It is the property of a material which retains the deformation produced under the load permanently. • This property is essential in stamping, press work, forgings, ornamental work etc. • TOUGHNESS • It is the total amount of energy absorbed by a material before its failure. • It is the complete area under the stress strain curve. • This property is essential in parts those are subjected to impact and shock loads.

11. RESILIENCE • It is defined as the total amount of energy absorbed by a material during its elastic deformation. • This property is essential for springs, shock absorbers etc. • The area under the stress-strain curve in the elastic region indicates resilience. • STRENGTH • It is the ability of a material to resist externally applied forces, without failure. • It is measured in N/mm2. • STIFFNESS • It is the ability of a material to resist deformation under stress. • It is also defined as the force per unit deflection and is measured in N/mm. • DUCTILITY • It is defined as the ability of a material to undergo plastic deformation under tensile loading, before its fracture. • It is also defined as the ability of a material to be drawn into wires.

12. MALLEABILITY • It is the ability of a material to be formed by hammering or rolling into sheets. • It is the capacity of material to withstand deformation under compression without failure. • The main difference between ductility and malleability is that, the ductility is considered as a tensile property whereas malleability is considered as a compressive property. • HARDNESS • It the resistance of a metal to plastic deformation usually by indentation. • It is also defined as the property of a material by virtue of which it resists scratching, abrasion, and cutting. • BRITTLENESS • It is the property of a material with little permanent distortion. • It is a property just opposite to ductility.

13. FATIGUE • When a material is subjected to repeated stresses or loading, it fails at stresses below the yield point stress. Such type of failure is called as fatigue failure. • Fatigue failure is caused by means of a progressive crack formation which are generally microscopic in size. • CREEP • When a material is subjected to constant stresses at high temperature for a long time, it will undergo a slow and permanent deformation which is called as creep. • Creep is considered while designing boilers, I.C engines, Steam turbines, etc.

14. SELECTION CRITERIA FOR MATERIALS • Availability of materials • Properties of materials • Working environmental conditions • Physical attributes • Performance requirements • Reliability of materials • Disposability and recyclability • Safety factor • Manufacturing considerations • Cost of materials

15. CLASSIFICATION OF ENGINEERING MATERIALS

16. FERROUS METALS: • The ferrous metals are those which have the iron as their main constituent. • These are important metals in the metallurgical and mechanical industries because of their extensive use. • These are commonly classified as : • 1. Cast iron 2. Alloy cast iron 3. Steel 4. Alloy steel • CAST IRON: • Cast iron are the alloys of iron and carbon. • Cast iron are formed by melting a metal and casting with or without machining to the desired final shape and size, hence called as cast iron. • CHARACTERISTICS OF CAST IRON: • While manufacturing of cast iron, raw materials like pig iron, scrap limestone, coke etc are used. All these elements are relatively cheap, hence cast iron is the cheapest among all alloys. Commercial C.I are complex in composition and their carbon content is in the range of 2.3 to 3.7% with other elements such as sulphur, manganese, phosphorous and silicon.

17. The melting point of cast iron is low lying between 1140 to 1240 degC. • Due to high fluidity of metal, cast iron has excellent machinability. • By altering the chemical composition , cast iron can provide a wide range of metallic properties. • Advantages of Cast Iron: • It is a low cost material • It can provide good damping capacity and high compressive strength • It has good resistance to wear and abrasion. • It has high hardness • Corrosion resistance of cast iron is fairly good. • It has excellent machinability. • Limitations of cast iron: • It is brittle in nature • Its mechanical properties such as toughness, stiffness, resilience etc. are poor • Due to brittleness, it is poor against fatigue and impact loading. • Applications of cast iron : Machine beds, columns, road rollers, pipe fittings, valves, farm equipments, automotive parts, motor cover, pump bodies, engine blocks,bearing blocks etc.

18. Types of Cast Iron : • Cast iron are classified as follows: • 1. White Cast iron 2. Gray cast iron 3. Malleable cast iron • 4. Nodular cast iron • Alloy cast iron: • As cast iron has low impact resistance, corrosion resistance and temperature resistance, hence to increase these properties certain alloys or alloying elements are added to cast iron in suitable amount. • Usually, nickel, cobalt , chromium, molybdenum, vanadium, silicon are used as alloying elements for cast iron. • Properties of alloy cast iron: • It has high strength, , high wear resistance and corrosion resistance. • Applications of alloy cast iron: • Alloy cast iron find use in the manufacturing of following parts such as • Gears, automobile parts like piston, piston rings, camshaft, crankshaft, cylinders, brake drums, pulleys, grinding machinery parts etc.

19. Plain Carbon Steel: • Steel is an alloy of iron and carbon with carbon percent upto 1.6%. • Carbon content increases the strength and hardness of steel • Plain carbon steel is defined as a steel which has its properties mainly due to its carbon content and does not contain more than 0.5 % silicon and 1.5% manganese. • Properties of plain carbon steel: • They are ductile in nature • They have high fatigue and impact strength • Their mechanical properties like toughness, stiffness, resilience etc. are high. • Advantages of plain carbon steel: • They have high tensile strength • They have high resilience and toughness • They can sustain fatigue and impact load. • Limitations of plain carbon steel: • Vibration damping capacity of steel is poor • They cannot be cast into complicated shapes • They have low wear resistance and costlier than cast iron.

20. Applications of plain carbon steel: • Stampings, fan blades, rivets, nuts, bolts, wires, structural steel, grill, shaft etc. • Gears, valves, crankshaft, camshaft, axles, screws, springs. • Cutting tools, milling cutters, blades, drill bits, musical instruments, agricultural applications etc. • Alloy Steel: • To obtain specific properties in steel, various alloying elements such as carbon, sulphur, manganese, phosphorous, nickel, cobalt, silicon, tungsten, chromium, molybdenum, vanadium, titanium etc are added to steel in small proportion of composition. • By adding the above alloying elements, properties like ductility, corrosion, impact resistance, fatigue strength etc. can be improved. • Limitations: They cannot be casted into complicated shapes. Their vibration damping capacity is poor and they are costlier than iron and steel. • Application: Aircraft engine parts, heat exchangers, wrist watches, sanitary fittings, furnace parts, turbine blades, missile components etc.

21. NON FERROUS METALS : • Non-ferrous metals are those which contain a metal other than iron as their main constituent or element. • Non ferrous metals find applications in a wide variety of industrial sectors because of following advantages: • Low density, light weight, high electrical conductivity, ease of fabrication and high corrosion resistance. • The commonly used non-ferrous alloys are as follows: • Copper and its alloys such as brass and bronze • Aluminium and its alloys • COPPER AND ITS ALLOYS: • Copper is one of the most widely used non-ferrous metals. • Various alloying elements are added to copper to improve and add some mechanical properties. • Major alloying elements are zinc, silicon, aluminum, lead manganese, nickel, tin, phosphorous, magnesium etc.

22. Properties of copper: • High ductility and malleability • High electrical and thermal conductivity • Non-magnetic in nature • It can be easily alloyed with other metals • It has high corrosion resistance. • Applications of Copper: • Electrical parts • Heat exchanger tubes • Household utensils, etc. • BRASS: • Brass is an alloy of copper and zinc with small amount of other alloying elements. • It has high corrosion resistance, high ductility and malleability, high strength and high machinability. • Limitations : It has low thermal and electrical conductivity and also it is costlier. • Applications: Coins, needles, jewellery, condenser tubes, cartridge cases, headlight reflectors, springs, welding rods, shafts, machine parts etc.

23. ALUMINIUM AND ITS ALLOYS: • Aluminium is another widely used non ferrous metal. • It can be easily alloyed with elements like silicon, copper, nickel, zinc, manganese, titanium, magnesium etc. • Advantages of Aluminium alloys: • It has high thermal and electrical conductivity • It has high corrosion resistance • It has high toughness • They are malleable and ductile • They can be easily casted • Applications of aluminum alloys: • Aircraft industry for manufacturing aircraft parts • Motor housing, pump castings, pistons, cylinders of automotives • In food industry, food preparation equipments, refrigeration, storage containers, bakery equipments etc.

24. NON METALS: • The use of non metals is increasing in most of the industries because of the following properties: • They have low density • They are light in weight • They provide flexibility in design • They have high resistance to heat and electricity • They have a low cost as compared to metals • Commonly used non-metals are as follows: • Rubber 2. Plastic 3. Wood 4. Glass • RUBBER: • Rubbers or Elastomers are hydrocarbon and polymeric materials • Rubber is defined as a polymeric material which at room temperature can be stretched to atleast twice its original length and after immediate release will return quickly to its original length without any permanent deformation.

25. Properties of Rubber: • They are non crystalline in structure • They are non conductors of electricity and low heat conductors • Their chemical and corrosive resistance is also high • They are ductile in nature • They have high resilience and elasticity • Rubbers are either natural rubbers or synthetic rubbers • Applications of rubbers: • Vehicle tires, gaskets, erasers, pipes, tubes • Belt conveyers, adhesives, tapes, seals, gloves, aprons, floor tiles, etc. • Brake liners, containers, wires and cables, engine mountings etc.

26. PLASTICS: • A large group of engg materials which have increasing importance in industrial applications are composed of natural synthetic organic polymers(plastics). • Now-a-days in some of the applications, metals and wood parts are replaced by plastics, which have satisfactory properties and may be produced at lower cost • Plastic are moulded into any required shapes by the application of pressure and heat. For example, toys, chairs, radiator fans, refrigerator equipments etc. • The plastics can be cast, rolled, laminated and machined easily • Characteristics of plastics: • They have low density and weight, high corrosion resistance, low thermal and electrical properties, low coefficient of friction, produced in different colors, good moldability and more economical than other metals. • Limitations of Plastics: • They have low strength and rigidity, poor tensile strength, poor temperature resistance, short life and poor dimensional stability. • Applications: telephone receivers, electric plugs, radio and T.V cabinets, camera and mobile phones, automobile parts, switch panels, etc.

27. MECHANISMS kinematic link or link or element : Each part of a machine, which moves relative to some other part, is known as a kinematic link (or simply link) or element. A link may consist of several parts, which are rigidly fastened together, so that they do not move relative to one another. For example : Reciprocating steam engine A link or element need not to be a rigid body, but it must be a resistant body. A link should have the following two characteristics: 1. It should have relative motion 2. It must be a resistant body.

28. Types of Links • In order to transmit motion, the driver and the follower may be connected by the following three types of links : • Rigid link - A rigid link is one which does not undergo any deformation while transmitting motion. • Flexible link - A flexible link is one which is partly deformed in a manner not to affect the transmission of motion • Fluid link - A fluid link is one which is formed by having a fluid in a receptacle and the motion is transmitted through the fluid by pressure or compression only.

29. Structure • It is an assemblage of a number of resistant bodies (known as members) having no relative motion between them and meant for carrying loads having straining action. • Examples : • A railway bridge • A roof truss • Machine frames etc Kinematic Pair The two links or elements of a machine, when in contact with each other, are said to form a pair. If the relative motion between them is completely or successfully constrained (i.e. in a definite direction), the pair is known as kinematic pair.

30. Classification of Kinematic Pairs 1. According to the type of relative motion between the elements. (a) Sliding pair. (b) Turning pair (c) Rolling pair. 2. According to the type of contact between the elements. (a) Lower pair. (b) Higher pair.

31. Kinematic Chain • When the kinematic pairs are coupled in such a way that the last link is joined to the first link to transmit definite motion (i.e. completely or successfully constrained motion), it is called a kinematic chain. • In other words, a kinematic chain may be defined as a combination of kinematic pairs, joined in such a way that each link forms a part of two pairs and the relative motion between the links or elements is completely or successfully constrained.

32. MECHANISMS • Mechanism is a part of a machine which has moving parts that performs some function. • Ex: Threading mechanism in a lathe machine, steering gear mechanism in a car, etc. The study of mechanism involves its analysis as well as synthesis. Analysis includes the study of motion and forces concerning different parts of the existing mechanism, while Synthesis includes the design of different components of the mechanism.

33. TERMINOLOGIES RELATED TO STUDY OF MECHANISMS: • Machine and mechanisms: • Machines are mechanical devices used to accomplish work. • A mechanism is a heart of a machine. It is the mechanical portion of the machine that has the function of transferring motion and forces from a power source to an output. • Mechanism is a system of rigid elements (linkages) arranged and connected to transmit motion in a predetermined fashion. • Mechanism consists of linkages and joints.

34. FOUR BAR MECHANISM ( FOUR BAR CHAIN) Mechanism: If one of the links or elements of a kinematic chain is fixed, the arrangement can be used for transmitting or transforming motion. It is then termed as a mechanism. In short, a mechanism is a kinematic chain with one link fixed. Ex: clockwork, typewriter, lock etc. The above diagram shows a simple mechanism.

35. A four bar chain is the simplest kinematic chain. It consists of four links, forming four turning pairs 1,2, 3, 4 as shown in the fig. above. • If one of the links in a four bar chain is fixed, then the arrangement is known as a four bar mechanism. In four bar mechanism, the remaining three links move relative to each other. • In most of the applications, the input motion to the mechanism is given by the prime mover. As the motion of the prime mover is rotary, in designing the mechanism, it is necessary to ensure that the input link can make complete rotation. • In a four bar chain, one of the links can make complete rotation if it satisfies GRASHOFF's LAW, which states that: • In a four bar chain, the sum of the shortest and largest link lengths cannot • be greater than the sum of the remaining two link lengths, if there is to be • continuous relative rotation of one of the links with respect to other link.

36. Slider crank mechanism: • A four-bar linkage with output crank and ground member of infinite length. A slider crank (see illustration) is most widely used to convert reciprocating to rotary motion (as in an engine) or to convert rotary to reciprocating motion (as in pumps), but it has numerous other applications. • Positions at which slider motion reverses are called dead centers. When crank and connecting rod are extended in a straight line and the slider is at its maximum distance from the axis of the crankshaft, the position is top dead center (TDC); when the slider is at its minimum distance from the axis of the crankshaft, the position is bottom dead center (BDC).

37. The conventional internal combustion engine employs a piston arrangement in which the piston becomes the slider of the slider-crank mechanism. • To convert rotary motion into reciprocating motion, the slider crank is part of a wide range of machines, typically pumps and compressors. • Application of slider crank mechanism: • Reciprocating engine • Rotary engine • Oscillating cylinder engine • Hand Pump • Scotch Yoke • Oldham's coupling • Elliptical Trammel