introduction to machine component design

machine component intro

1. Course description The objective of this course is to facilitate the students in the development of mechanical design methodology through analysis and application of engineering concepts and enable the students in designing various machine elements Course outcome Know about the types of materials and material properties, Application of materials, Limits , fits, tolerance, and clearances. Understand and Apply Engineering Design process. Apply engineering principles and analytical techniques in the design process . Design the Machine Components like Shafts and Springs Gear Design Flywheels and Bearings. Machine Component Design U15AUT502

2. Machine Component Design Fundamentals of Machine elements by Bernard Hemrock Tata McGraw Hill Publishing Machine Design by Dr. Sadhu Singh Hajra choudry “ Workshop Technology Vol I” U Jindal ,”Machine Design” Tata McGraw Hill Publishing Bhandari,v.B ., "Design of Machine Elements", Tata McGraw Hill Publishing Co. Ltd., New Delhi. T J Prabhu . ”Fundamentals of machine Design “ RS Khurmi and JK Gupta “A Text book of Machine Design “ Eurasia Publishing House NPTEL : Design of Machine Elements – I [ Prof B Maiti ] IIT Khargpur https://www.youtube.com/watch?v=mzWMdZZaHwI&list=PL3D4EECEFAA99D9BE I Introduction II Design of shafts and springs III Gear Design IV Flywheels V Design of Bearings Important Dates CAT I - 10.09.18 CAT II - 22.10.18 Units

3. Introduction Design Classification of Design Morphology of Design Machine Design Machine Element Design

4. Engineering Design

5. Design

6. Modelling/ Design tools are used to communicate/ represent the design How Do We Design ?

7. Definition of Design Iterative process to convince and implement optimum systems to solve society problems and needs – 1965 Finding the right physical components of a physical structure - 1963 Design Simulating what we want to make , before we make , it as many times as may be necessary to feed confident in final result – 1964 booker A creative activity which involves bringing into being something new and useful that has not existed previously -1965 resurch Ref: Machine Design by Dr. Sadhu Singh.

8. Engineering design Concerns with Physical reliability Economic feasibility Financial feasibility High level of sophistication required Manipulation and application of tech High level of understanding physical phenomenon is necessary Design Two methods of design Design by craft evolution Design by drawing ( leads to design engg where much process is shifted from shop floor to design floor ) Level of complexity is way less Routine technology is used to accomplish goals Transforms concepts and ideas into useful machinery

9. Classification of design 1. Adaptive design. The designer only makes minor alternation or modification in the existing designs of the product.

10. 2.Development design. The designer starts from the existing design, but the final product may differ quite markedly from the original product.

11. 3. New design. Needs lot of research, technical ability and creative thinking. (a) Rational design. (b) Empirical design: (c) Industrial design :

12. Rational Design This type of design depends upon mathematical formulae of principle of mechanics.

13. Empirical Design Design using the Empirical formulae. The empirical formulae could be derived on the basis of data obtained from past experience and from the experimental results.

14. Industrial design Production aspects to manufacture any machine component in the industry This design deals with the process of operation inside a industry and about machining of a component.

15. OVER THE WALL AND CONCURRENT ENGINEEIRNG Designer and Concurrent Engineering

16. Designers should listen to ? Over the wall engineering ( monarchy ) Like our schooling { 1-2-3-4-5} Since designs are ideas and to make it real we need a process where lot of members involve,. Material engg Manufacturing engg Some times designs are complicated to manufacture and so the manufacturer returns the product back to designer to accommodate the change in order to machine it And material engineer would suggest a different material for such manufacturing process And so the cost of the product become higher Concurrent Engineering ( democratic ) The draw backs of the OTW are Simply that the designer has to work for all other considering the reality / physical , economical and financial feasibility This could be done only when the designer could get council from his fellow associates regarding the solution to the problem This leads to concurrent engineer thus makes the design engineer to rely on experts for the rest and should be aware of other discipline knowledge

17. Morphology of Design

18. Machine Design Machine design process of achieving/ developing a plan for construction of a machine . A machine is a combination of mechanisms and components that transforms , transmits , uses energy , load motion for a specific task A Machine comprises several different components , elements designed and connected and constrained in away to perform the desired task

19. Design of mechanical System Mechanical system is synergetic collection of machine elements Design of mechanical system comprises thousand and millions of machine elements and so to design a mechanical system a designer should be more sophisticated and experience in machine elements .

20. General Considerations in Machine Design 1. Type of load and stresses caused by the load. 2. Motion of the parts or kinematics of the machine . 3 . Selection of materials. 4 . Frictional resistance and lubrication. 5. Convenient and economical features. 6. Use of standard parts. 7. Safety of operation.

21. Machine elements A Machine is Made up of numerous Machine elements . A Machine parts which would have motion with respect to the neighbouring parts are called as machine elements A Machine element can also have several parts assembled together to perform the intended task Ex: Roller Bearing

22. Steps involved in Design of Machine Elements Function of Elements Determination of forces Construction of free diagram of forces acting on element Selection of material Availability Cost Properties Manufacturing process Possible type of failure Determination of dimension

23. Procedure In Designing Machine Elements Selecting a Suitable type of machine elements from consideration of its function Estimating the size of the machine element that is to be satisfactory Evaluating machine element performance against requirement Modifying the design and dimension until performance is neared to whoever is consider most important.

24. Failure and Factor of safety Ref: Fundamentals of Machine Design by Bernard Hamrock Failure FMEA [ Failure mode Effect Analysis ] FTA [fault tree analysis] Benefit of FMEA and FTA Factor of Safety Problems on Factor of safety

25. Failure Failure of machine elements in service completely inoperable operable but unable to perform intended fn unreliable and unsafe for continuous usage The Design analysis attempts to predict the strength of a machine elements so that it could exercise its d uty under safe condition for the provided load as long as required

26. Theories Of Failure Maximum Principle Stress theory Failure occurs when the maximum normal stress equals the tensile yield strength Maximum Shear Stress Theory Failure occurs when maximum shear stress in the machine element equals the maximum shear stress at yielding due to tension Maximum strain Theory Failure occurs when the maximum strain in the member equals the tensile yield strain Distortion energy theory Failure occurs when strain energy of distortion per unit volume becomes equal to the strain energy of distortion per unit volume at the yield point.

27. Failure Mode and Effects Analysis and Fault trees FMEA make designers To possibly think and reason the foreseeable and reasonable failure mode for every component and Provide its alternative solution . In FTA is statistical hard data are considered to identify failure. Ref: Fundamentals of Machine Design by Bernard Hamrock

28. Benefits of FMEA and Fault T ree Analysis It makes the designer to think of minimizing the catastrophic event due to failure of single component. Redundancy in design Active Passive Fail safe Feature Doctrine of Manifest danger Ref: Fundamentals of Machine Design by Bernard Hamrock

29. Redundancy in Design Active Two are more component is used though one is sufficient All the employed components will actively take part in functioning Passive Two are more component is used though one is sufficient The second / alternative component will function only at the failure of the component that is in function Hudson cactus 1549 Ref: Fundamentals of Machine Design by Bernard Hamrock

30. Doctrine of Manifest Danger It’s a powerful method used by the designer to detect the single component failure before its leads to a catastrophic event Where the failure of the single component could be detected earlier by means of sound or vibration. Generally in Drum braking , the braking shoe is riveted with long rivet such that after a period of time , nearer to the failure, the long rivet would produce a squeaking sound while braking Ref: Fundamentals of Machine Design by Bernard Hamrock

31. Fundamental considerations in Design of machine elements – Safety

32. Safety factor / factor of safety The Factor of Safety is defined as the ratio of yield stress to the working stress / permissible stress = in case of ductile Material = in case of Brittle Material [Failure ]Max stress based on material = * Stress at the component works possible maximum stress developed under load Where represents A B C where A = quality of material , workmanship and maintenance inspection B = Control over load applied to part C = accuracy of stress analysis experimented data and experience with similar devices is given by D and E D – Danger to personnel E – Economic impact Ref: Fundamentals of Machine Design by Bernard Hamrock  

33. Ref: Fundamentals of Machine Design by Bernard Hamrock

34. Material Selection in Design Ref: Material Selection in Mechanical Design by Michael F Ashby Engineering Materials Selection of Materials Properties Single Parameter Chart Two Parameter Chart

35. Engineering materials Metals Ceramics and glasses Polymers and elastomers Composites

36. Metals Large no of free electrons Good conductors of electricity and heat Non transparent to visible light Well deformable and ductile It can be made stronger by alloying and also by treating Since metals are usually ductile and so employed in cyclic load environment and they can fail from fatigue Resistant to corrosion

37. Elasticity range and Plastic deformation

38. Ceramics and glasses Compound of metallic and non-metallic elements Good insulators More resistant to high temperature Brittle in nature ( material that fractures below 5% of strain ) 15 time stronger in compression than in tension Highly stiff, hard and abrasive resistant The stress strain diagram is not determined by the tensile test

39. Polymers and Elastomers Polymers- thermoplastic and thermosets Thermoplastic are more ductile than thermosets and they soften at high temp Thermosets are britle Elastomer – large elastic deformation but brittle fracture Polymer and elastomer property greatly vary with temperature and five times less dense than metals Challenger Space shuttle Disaster – rubber O ring – temperature

40. Selection of materials 1. Availability of the materials, 2 . Properties 3. Suitability of the materials for the working conditions in service, and 4 . The cost of the materials.

41. Properties of solid Material Strength Elasticity Stiffness Ductility Malleability Toughness Thermal conductivity Specific heat capacity

42. Strength . It is the ability of a material to resist the externally applied forces without breaking or yielding. The internal resistance offered by a part to an externally applied force is called stress. Stiffness . It is the ability of a material to resist deformation under stress. The modulus of elasticity is the measure of stiffness. Elasticity . Ability to regain its original shape after deformation when the external forces are removed. This property is desirable for materials used in tools and machines. It may be noted that steel is more elastic than rubber.

43. Plasticity. Deformation produced under load permanently . This property of the material is necessary for forgings, in stamping images on coins and in ornamental work. Ductility . It is the property of a material enabling it to be drawn into wire with the application of a tensile force. A ductile material must be both strong and plastic. Ability of the material to undergo greater deformation under axial load Brittleness . It is the property of breaking of a material with little permanent distortion. Brittle materials when subjected to tensile loads snap off without giving any sensible elongation. Cast iron is a brittle material.

44. Malleability. A malleable material has ability of deforming greater under action of compressive load . The malleable materials commonly used in engineering practice (in order of diminishing malleability) are lead, soft steel, wrought iron, copper and aluminum .

45. Toughness It is the property of a material to resist fracture due to high impact loads like hammer blows. The toughness of the material decreases when it is heated. This property is desirable in parts subjected to shock and impact loads.

46. Machinability. It is the property of a material which refers to a relative case with which a material can be cut. The machinability of a material can be measured by the energy required to remove a unit volume of the material. It may be noted that brass can be easily machined than steel.

47. Resilience . the capacity to recover quickly from difficulties Property of a material to absorb energy and to resist shock and impact loads. It is measured by the amount of energy absorbed per unit volume within elastic limit. Creep When a part is subjected to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called creep. Polymer products ( plastic water bottle , water bucket ) Fatigue. When a material is subjected to repeated stresses, it fails at stresses below the yield point stresses. Such type of failure of a material is known as *fatigue. The failure is caused by means of a progressive crack formation which are usually fine and of microscopic size.

48. Archard wear constant When solids slide , the volume of the material lost from one surface per unit distance slid The wear resistance of material is characterized by Archard wear constant A= Area of the surface p=normal pressure pressing together  

49. Hardness. The ability of a metal to cut another metal. The hardness of a metal may be determined by the following tests: Brinell hardness test, Rockwell hardness test, Vickers hardness (also called Diamond Pyramid) test, and Shore scleroscope .

50. Single parameter chart Ref: Material Selection in Mechanical Design by Michael F Ashby

51. DENSITY

52. MODULUS OF ELASTICITY     Covalent bond = 20 to 200 Metallic and ionic bond = 15 to 100 Possion ratio Max 0.5 for rubber Minimum could not be less than zero For steel 0.30 For Al 0.33 For Mg 0.33 Cast iron 0.26

53. THERMAL CONDUCTIVITY

54. Thermal Expansion

55. Specific Heat Capacity Heat capacity of the material @ 1 g of mass at 1 degree Celsius Qty of heat energy taken or given up by a material, when there is change in temperature , is proportional to the mass of the object, difference in temp and the characteristic constant specific heat capacity Different material at same temperature range on cooling would likely to give up different amount of heat

56. Two parameter chart Ref: Material Selection in Mechanical Design by Michael F Ashby

57. Primary consideration for material selection in designing machine elements Stiffness versus density Strength versus density Stiffness versus strength Wear rate versus limiting pressure

58. Modulus of Elasticity (stiffness ) vs Density

59. Ceramics Metals polymers

60. Strength vs Density

61. Stiffness ( modulus of elasticity ) Vs Strength

62. Wear Constant vs Limiting pressure

63. Stiffness vs Relative cost

64. Fits , Tolerance and allowances Need for Tolerance Types of Tolerance Terminologies in tolerance and allowances Types of Fit Tolerance Designation system Methods for Calculating Tolerance , allowance and identifying Fits Ref: Workshop Technology by Hajra Choudhry

65. Fits , Tolerance and allowances Design and Manufacturing relied and one another , there are two most important facts No component can be manufactured for accurate Dimension Even though the component can be manufactured for such accurate dimension no system is to measure it. And also if machined for such accuracy the cost of the product would be very high.

66. Method of Assigning Tolerance Unilateral The tolerance value would be unidirectional, i.e the size would have limits in positive or negative Bilateral The tolerance value would be in bidirectional, i.e the size would have limits in both positive and negative

67. Terminologies in limits, fits and tolerance

68. Types of Fit Clearance fit Allowance would be Positive The component can be assembled easily Interference Fit Allowance would be in Neagtive The Component could be assembled by force / pressuring Transition Fit Could be in between of both clearance and interference fit

69. Designation system for Tolerance

70. Two Types of System for calculating Limits Hole Basis system In hole basis system the size of hole is kept constant and size of the shaft is varied Shaft Basis System In shaft Basis System the Size of the Shaft is kept constant and size of the hole is varied Generally the hole basis system is followed as the shaft size could be altered easier than that of hole.