Lecture # 1-2- Introduction and basic information.pptx

intro to the machine design by R.S KHURMI

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2. Machine Design – I Code: ME - 216 Credit Hours: 2 Lecture INTRODUCTION TO MACHINE DESIGN Dr. Muhammad Imran Mechanical Engineering Program University of Engineering & Technology Taxila

3. 25-Feb-23 Outcome Based Education (OBE) is an educational system focusing on what is learned and not what is taught. What is OBE System

4. What is OBE System 25-Feb-23 An education philosophy that focuses on the Graduate Attributes or Outcomes after completing an academic programme. Focuses on Empirically measuring student performance. Does not specify or require any particular style of teaching or learning. Requires that students demonstrate that they have learned the required skills and content.

5. OBE Questions 25-Feb-23 What do you want the students to learn? Why do you want them to learn? How can you best make students learn it? How will you know what they have learnt?

6. 6 Program educational objectives (PEOs) Program learning outcomes (PLOs) Course learning outcomes (CLOs) Bloom Taxonomy Psychomotor Cognitive Affective What is OBE System

7. Bloom’ Taxonomy Provides a way to organise thinking skills into six levels, from the most basic to the more complex levels of thinking 7 Bloom’s Taxonomy Learning Outcomes

8. Course Contents in OBE System 25-Feb-23 Dr. Muhammad Imran MED, UET, Taxila CLO CLO Statement PLO Bloom Taxonomy CLO-1 Understand the principles and the process for design of machine elements like keys, couplings, brakes, clutches, and fly wheels. PLO-1 Engineering Knowledge C2, Comprehension CLO-2 Analyze the machine design problems which is interrelated to fastening techniques and power transmitting shafts. PLO-2 Problem Analysis C4 Analysis CLO-3 Present the design aspects effectively through oral presentation. PLO-10 Communication A2 Responding

9. Evaluation Criteria Under OBE System Machine Design-I 25-Feb-23 Through Assignments Quizzes 10% Semester Project/Presentation 15% Mid Semester Paper 25% End Semester Paper 50%

10. M achine Design By: R. S. K hurmi Mechanical Design an Integrated Approach By: Robert L. Norton Mechanical Engineering Design By: Joseph Edward Shigley Machine Design By: Robert L. Mott Design of Machine Elements, By M. F. Spotts Books 25-Feb-23 Machine Design By: Dr. Anbdullah Machine Design By: Mubeen CAD/CAM/CIM by P . Radhakrishnan Automation, Production System & CIM by Mikell P. Groover Text Book: Reference Books:

11. Introduction to Machine Design, Overview about basics of Mechanical Engineering, Criteria of the performance & Designing of Machine Parts . Mechanical Properties of Metals. Heat Treatment Processes. Analysis of Load ~ force diagram for Brittle & Ductile materials, Metals Fits, Tolerances & Surface Finish. Codes and Standards. Factor of Safety, its Criteria, Determination of F.O.S for different cases, Role of Economics in Machining. Designing of Pin, Cotter Joints, Riveted Joints, Welded Joints & Flywheel. Designing of Couplings Designing of Keys and Screws. Designing of Clutches and Brakes. Course Contents 25-Feb-23

12. What is the importance of Machine Design for Engineers? What is Machine Design? Creation of new and better machines AND Improving existing ones So that it is economical in the cost of production and operation. Machine Design 25-Feb-23

13. The subject Machine Deisgn is the creation of new and better machines and improving the existing ones . A new or better machine is one which is more economical in the overall cost of production and operation . The process of design is a long and time consuming one . From the study of existing ideas, a new idea has to be conceived . The idea is then studied keeping in mind its commercial success and given shape and form in the form of drawings . In the preparation of these drawings , care must be taken of the availability of resources in money , in men and in materials required for the successful completion of the new idea into an actual reality. In designing a machine component , it is necessary to have a good knowledge of many subjects such as Mathematics, Engineering mechanics, Strength of Materials, Theory of Machines, Workshop Processes and Engineering Drawing. Machine Design

14. Engineering Design: Engineering design is a process of applying various scientific principles and techniques for purpose of defining in detail a product (or) a process (or) a system to its realization. In simpler words design is formulation of a plan , for execution towards satisfying a needs. Machine Design is defined as to fix dimension for machine components. INTRODUCTION

15. General procedure in Machine Design… Detailed drawing Need or aim Synthesis Analysis of the FORCES Material selection Design of elements Modification Recognize and specify the problem Select the mechanism that would give the desired motion and form the basic model with a sketch etc Determine the stresses and thereby the sizes of components, failure or deformation does not occur Modify sizes to ease construction & reduce overall cost Production 25-Feb-23

16. VARIOUS STEPS IN DESIGN PROCESS Recognition of a need: Identifying the customer needs through market research. Definition of the problem: Preparation of complete list of technical specifications. Synthesis: Collection of new ideas (or) modifying the existing Ideas. Analysis: The forces acting on the component are determined. The material for the component is selected. The geometric dimensions of the component are determined.

17. CONTINUE… Evaluation: The possible success of the proposal should be verified from technical and economical stand points. Detailed Design: It’s the actual sizing and dimensioning all individual components in the part. Proto-type & Testing: Proto-type testing may lead to some modification . Production: Actual component manufactured at shop floor.

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19. Adaptive design: The designer only makes minor alteration (or) modifications in the existing designs of the product. Development design: Modifying existing designs into a new idea by adopting a new material or different method of manufacture. New design: This type of design needs lot of research , technical ability and creative thinking . TYPES OF MACHINE DESIGN

20. Further classification of design Rational design: This type of design depends upon mathematical formulae of principle of mechanics. Empirical design: This type of design based on empirical formula based on practice and past experience . Industrial design: Depends upon the production aspects to manufacture. Optimum design: It’s the best design for the given objective function under the specified constraints.

21. Continue… System design: To develop a system that will meet expected needs within realistic constraints such as economical environmental, social, political, ethical, safety and sustainability Element design: Design of machine elements such as piston, crank shaft, gear,etc . Computer aided design: Use of computer systems to assist in the creation, modification, analysis and optimization of a design.

22. 22 Stages of Design Preliminary design, Intermediate design, Detail design, and Development and field service Mechanical design activity in an industrial setting embodies a continuum effort from initial concept to development and field service.

23. 1.Preliminary Design , or conceptual design, is primarily concerned with synthesis , evaluation , and comparison of proposed machines or system concepts. A “black-box” approach is often used, in which reasonable experience based performance characteristics are assigned to components or elements of the machine or system. 25-Feb-23 Overall system analyses, including force analyses , deflection analysis , thermodynamic analysis , fluid mechanic analysis , heat transfer analysis , electro- mechanic analysis , or control system analysis may be required at the preliminary design stage. The result of the preliminary design stage is the proposal of a likely-successful concept to be designed in depth to meet specified criteria of performance , life , weight , cost , safety , or others.

24. 2. Intermediate Design embraces the spectrum of in-depth engineering design of individual components and subsystems for the already preselected machine or system. Intermediate design is vitally concerned with the internal workings of the black boxes, and must make them work as well or better than assumed in the preliminary design proposal. Material selection , geometry determination , and component arrangement are important elements of the intermediate design. Effort, and appropriate consideration must be given to fabrication , assembly , inspection , maintenance , safety , and cost factors , as well. 25-Feb-23 The result of the intermediate design stage is establishment of all critical specifications relating to function , manufacturing , inspection , maintenance , and safety .

25. Detail Design is concerned mainly with configuration , arrangement , form , dimensional compatibility and completeness , fits and tolerances , standardization , meeting specifications , joints , attachment and retention details , fabrication methods , assimilability , producibility , inspectability , maintainability , safety , and establishing bills of material and purchased parts. 25-Feb-23 The result of the detail design stage is a complete set of drawings and specifications , including detail drawings of all parts, or an electronic CAD file, approved by engineering design , production , marketing , and any other interacting departments , ready for production of a prototype machine or system.

26. 4. Development and Field Service activities follow in sequence after the production of a prototype machine or system. Development of the prototype from a first model to an approved production article may involve many iterations to achieve a product suitable for marketing. 25-Feb-23 Field service information, especially warranty service data on failure rates , maintenance problems , safety problem , or other user-experience performance data, should be channeled back to the product design team for future use in product improvement and enhancement of life cycle performance.

27. Safety Reliability Quality Productivity Cost Ecological consideration Availability of men, material & machines Working environment Energy conservation Space constraints Factor influencing machine design

28. 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. Form and size of the parts 5. Frictional resistance and lubrication 6. Convenient and economical features 7. Use of standard parts 8. Safety of operation 9. Workshop facilities 10. Number of machines to be manufactured 11. Cost of construction General considerations in machine design

29. Design should aim at the best with the least expenditure The component should have adequate strength, wear resistance and corrosion resistance The assembly should be backlash free Resonance is to be avoided The design should be simple, fool proof, easy to operate and should reduce operator’s fatigue . The design should need only a minimum maintenance Whenever possible, dimensions of the components should be rounded off to standard values. Design rules

30. Requirement Model (Rough idea) Creation How a design is born marketability Availability of FUNDS Available material Manufacturing resources Analysis Market survey Aesthetic Ease of handling Safety Economical Recyclability Force/stress Material/s used Sizes 25-Feb-23

31. Mechanical engineering design involves all the disciplines of mechanical engineering Example: Fluid Flow , Heat Transfer , Friction (Tribology), Energy , Transport , Material Selection , Thermo Mechanical Treatments , Statistical Descriptions … Phases- Machine design, machine-element design, machine-component design, systems design, and fluid-power design Mechanical Engineering Design 25-Feb-23

32. What is Machine Design? Core of mechanical engineering Stress and strain Designing for safety Static failure theories Fatigue failure theories Machine elements Mechanical material properties Stress Concentrations Fracture Mechanics Optimization Composite Materials Manufacturing Processes Computer Aided Machine Design and Analysis Measuring Stress and Strain 25-Feb-23

33. What is the basic knowledge required for Machine Design? Mathematics Engineering Mechanics Strength of Materials Mathematics Engineering Mechanics Strength of Materials Workshop Processes Engineering Drawing Mathematics Engineering Mechanics Strength of Materials Workshop Processes Engineering Drawing Computing Finite Element Analysis, Computational Fluid Dynamics etc Mechanics of Machines Mechanics of Materials Fluid Mechanics & Thermodynamics 25-Feb-23

34. Important considerations in Machine Design 1. Type of LOAD and STRESS caused by the load Steady loads Dead loads Live loads Variable loads Shock loads (suddenly) Impact loads (applied with some velocity) Stress and strain (Tensile, compressive, shear) Thermal stresses Torsional stresses Bending stress 25-Feb-23

35. Loads M echanical  forces, moments… T hermal C hemical changing in place/ time … static cyclic dynamic 25-Feb-23

36. Effect of V arying L oad cycle assymetry ratio cycle mean stress ratio σ v σ r Fatique limits 25-Feb-23

37. Loads & S tresses 25-Feb-23

38. Direct Stress Load: Any external force acting upon a machine member Types of load: Dead (or) Steady (or) Static load: The load which does not change in magnitude and direction. Ex. Self weight (ii) Live (or) Varying load: The load which is continuously changing. Ex. Vehicle pass over a bridge

39. Continue… (iii) Suddenly applied load (or) shock load: The load which is applied suddenly Ex: Blows of a hammer (iv) Impact load: The load which is applied with some initial velocity (or) The load which is dropped from certain height. Ex: forging

40. Continue… Stress: The internal resistance of force per unit area is called stress. σ =P/A Where P = Load or force acting on the body A = Cross- sectional area of the body Strain: The rate of change of deformation (or) It’s the ratio of change in dimension to the original dimension. e = δ l/l Relationship between σ , e,E , δ l Deformation, ( δ l ) =pl/AE

41. TYPES OF STRESSES AND STRAINS Tensile Stress: The stress induced in a body , when subjected to two equal and opposite pulls as result of which there is an increase in length , is known as tensile stress . The ratio of increase in length to the original length is known as tensile strain . Tensile stress σ = Resisting force = Cross sectional area and tensile strain, ε = Increase length = Original length

42. Compressive Stress The stress induced in a body, when subjected to two equal and opposite pushes as a result of which there is a decrease in length of the body , is known as compressive stress . The ratio of decrease in length to the original length is known as compressive strain . Compressive stress, σ = Resisting force = Cross sectional area Compressive strain, ε = Decrease in length = Original length

43. Shear Stress : The stress induced in a body, when subjected to two equal and opposite forces which are acting tangentially across the resisting section as a result of which the body tends to shear off across the section , is known as shear stress . The corresponding strain is known as shear strain . Shear stress, q = Shear resistance = Shear area Shear strain Φ = Transverse displacement = Distance

44. FACTOR OF SAFETY AND LATERAL STRAIN FACTOR OF SAFETY: It is defined as the ratio of the ultimate stress to the working stress of the material. Factor of Safety = Ultimate Stress Working Stress LATERAL STRAIN: The strain at right angles to the direction of applied load is known as lateral strain . Lateral Strain = Increase or Decrease in Lateral Dimension Original Lateral Dimension

45. Modulus of Elasticity (Young’s Modulus (E): According to Hooke’s law, the stress in a material is proportional to the strain upto the elastic limit . Therefore within the elastic limit, the ratio of the axial stress to the corresponding axial strain is found to be a constant . This constant is called Modulus of Elasticity or Young’s Modulus . It is denoted by E. Modulus of Elasticity or Young’s Modulus = Axial Stress Axial Strain E = Modulus of Rigidity or Shear Modulus (G): The ratio of shear stress to the corresponding shear strain is found to be a constant upto the elastic limit of the material . This constant is called Modulus of Rigidity or Shear Modulus of the material. It is denoted by G. Modulus of Rigidity or Shear Modulus = Shear Stress = G = Shear Strain

46. Poisson’s Ratio ( μ ) or (1/m): It has been experimentally found, that if a body is stressed within its elastic limit , the lateral strain bears a constant ratio to the linear strain . Mathematically, Lateral strain = A constant Linear strain This constant is known as poisson’s ratio and is denoted by 1/m or μ . Strain Energy (or) Resilence: When a body is loaded with in the elastic limit the work done on the body is stored in the form of energy . The strained body is now capable of doing some external work on removal of the load . The energy stored in the body due to internal strain is called strain energy or resilience. Strain energy = ( σ 2 /2E) ×A×l------------- N.mm

47. Hooke’s Law It states that, “ Within elastic limit the stress induced in the material is directly proportional to strain”. σ α e σ = E e . E = σ e Where, σ – Stress; e – Strain; E – Young’s Modulus

48. Stress Strain Diagram STRESS/LOAD EXTENSION/STRAIN P roportional Limit E lastic Limit Y ield Point U ltimate Strength B reaking Limit

49. Stress Strain Diagram Point P: Proportional Limit: Within Proportional Limit stress is directly proportional to strain. Hence the material will regain its original shape after unloading. The stress corresponding to the load is known as Limit of Proportionality . Point E represents the elastic limit . In the region PE, the stress is not proportional to strain. It means the stress strain diagram is not a straight line. Any loading beyond point E, will cause permanent deformation. The stress corresponding to the load at E is called at Elastic Limit. Yield Stress (Point Y) : The loading beyond E causes extension much larger than the extensions observed earlier. The material yields to a greater extent and the stress corresponding to the load at Y is termed as Yield Stress Beyond Y, a much smaller increase in the load causes considerable extension and the materials is said to be semi plastic mode.

50. At U, the material yields at a particular point and a neck is formed there. The stress corresponding to that load at U is called maximum stress (Ultimate stress) Beyond U, the extension governed by the time of loading. The load required to cause extension is smaller than the load at M. The area of cross section is considerable reduced. The elongation continues till the material breaks at B. The stress corresponding to the load at B is called Breaking stress.

51. Continue… Percentage reduction in area: % reduction in area = (A-A 1 )/A ×100 A – Original area of cross-section.m 2 A 1 – Cross- sectional area after fructure at the neck,m 2 Percentage elongation: % elongation in length= (l 1 -l/l × 100 l 1 – Length of specimen after fracture, mm l – original length, mm

52. Torsional shear stress When a machine member is subjected to the action of two equal and opposite couples acting in parallel planes, then the machine member is said to be subjected to torsion. The stress set up by torsion is known as torsional shear stress. Consider a shaft fixed at one end and subjected to a torque (T) at the other end. As a result of this torque every cross-section of the shaft is subjected to torsional shear stress.

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55. 55 Bending Stresses in Straight Beams Bending Stress: In engineering practice, the machine parts of structural members may be subjected to static or dynamic loads which cause bending stress in the sections besides other types of stresses such as tensile, compressive and shearing stresses.

56. 56 A little consideration will show that when a beam is subjected to the bending moment, the fibers on the upper side of the beam will be shortened due to compression and those on the lower side will be elongated due to tension. It may be seen that somewhere between the top and bottom fibers there is a surface at which the fibers are neither shortened nor lengthened. Such a surface is called neutral surface. The intersection of the neutral surface with any normal cross-section of the beam is known as neutral axis. The stress distribution of a beam is shown in previous Fig. The bending equation is given by

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58. Impact and shock loading The load acting on any machine component can be of either of these two types 1. Gradual load 2. Suddenly applied (or) Impact (or) Shock load. Gradual load: Gradual load is one which, goes on increasing over a period of time till the maximum value is reached. Suddenly applied (or) Impact (or) Shock load: Impact (or) shock load which is applied suddenly (or) with some initial velocity. Ex: Punching presses, Hammer

59. Principal Stress Principal plane is a plane in which the shear stress is zero, and the direct stresses acting along these planes are known as principal stress. When shear stress is also acting in addition we have to find out maximum and minimum principal stresses.

60. Eccentric loading An external load, whose line of action is parallel but does not coinside with the centroidal axis of the machine component, is known as an eccentric load (P). The distance between the centroidal axis of the machine component and the eccentric load is called eccentricity. It is generally denoted by e.

61. 2. KINEMATICS of the machine (Motion of the parts) Find the simplest arrangement that would give the most efficient motion that is required. 3. Selection of MATERIAL s Knowledge of the properties of the materials and their behaviour under working conditions is required. Strength, hardness, durability, flexibility, weight, resistance to heat and corrosion, electrical conductivity, machinability, etc. Important considerations in Machine Design 25-Feb-23

62. Engineering materials Metals Non-metals Metals: Ferrous – Which contains iron as the major constituent Ex. Steel, Cast Iron Non-ferrous – materials don't contains Iron. Ex. Copper, Aluminium Non-Metals: Ceramic materials – oxides, carbides and nitrides of various metals. Ex. Glass, Brick, Concrete, Cement etc. Organic materials – Polymeric materials composed of carbon compounds. Ex: Paper, fuel, rubber, paints, etc.

63. Factors to be considered for the selection of materials Availability Cost Physical properties Mechanical Properties Manufacturing process Physical properties: Colour Electical conductivity Shape Thermal conductivity Size Density

64. Strength  ability to resist external forces Stiffness  ability to resist deformation under stress Elasticity  property to regain its original shape Plasticity  property which retains the deformation produced under load Ductility  property of a material to be drawn into wire form with using tensile force Brittleness  property of breaking a material without any deformation Malleability  property of a material to be rolled or hammered into thin sheets Toughness  property to resist fracture under impact load Machinability  property of a material to be cut Resilience  property of a material to absorb energy Creep  material undergoes slow and permanent deformation when subjected to constant stress with high temperature Fatigue  failure of material due to cyclic loading Hardness  resistant to indentation, scratch Material selection based on Mechanical properties

65. 4. Form and size of the parts Use I-beam or Angle-iron? The size will be determined by the forces/torques applied (stresses on the object) and the material used such that failure (fracture or deformation) would not occur Important considerations in Machine Design 65 25-Feb-23

66. Understand the problem Identify the known Identify the unknown and formulate State all assumptions and decisions Analyze the problem Evaluate solution Present solution Designer Responsibilities 25-Feb-23

67. Fail Safe and Safe Life Design Concepts Catastrophic failures of machines or system that result in loss of life , destruction of property , or serious environmental degradation are simply unacceptable to the human community , and, in particular, unacceptable to the designers of such failed machines or systems. A designer can never provide a design of 100 percent reliability, that is, she or he can never provide a design absolutely guaranteed not to fail. There is always a finite probability of failure. 25-Feb-23

68. The Fail Safe Design technique provides unnecessary load paths in the structure so that if failure of a primary structural member occurs, a secondary member is capable of carrying the load on an emergency basis until failure of the primary structure is detected and repair can be made. The Safe Life Design technique is to carefully select a large enough safety factor and establish inspection intervals to assure that the stress levels, the potential flaw sizes, and the governing failure strength levels of the material combine to give such a slow crack growth rate that the growing crack will be detected before reaching a critical size for failure. Both fail safe life design depend upon inspectability . Fail Safe and Safe Life Design Concepts 68 25-Feb-23

69. Failure Criteria Any change in the size , shape , or material properties of a machine or machine part that renders it incapable of performing its intended function must be regarded as a mechanical failure . 69 25-Feb-23

70. Modes of Mechanical Failure Force- and/or temperature-induced elastic deformation Yielding Brinnelling Ductile rupture Brittle fracture Fatigue: High cycle fatigue Low-cycle fatigue Thermal fatigue Surface fatigue Impact fatigue Corrosion fatigue Fretting fatigue 70 25-Feb-23

71. Corrosion: Direct chemical attack Galvanic corrosion Pitting corrosion Intergranular corrosion Selective leaching Erosion corrosion Cavitation corrosion Hydrogen damage Biological corrosion Stress corrosion Modes of Mechanical Failure 71 25-Feb-23

72. Wear: Adhesive wear Abrasive wear Corrosive wear Surface fatigue wear Deformation wear Impact wear Fretting wear Impact: Impact fracture Impact deformation Impact fretting Impact fatigue Modes of Mechanical Failure 72 25-Feb-23

73. Fretting: Fretting fatigue Fretting wear Fretting corrosion Creep Thermal relaxation Stress rupture Thermal shock Galling and seizure spalling Modes of Mechanical Failure 73 25-Feb-23

74. Radiation damage Buckling Creep bucking Stress corrosion Corrosion wear Corrosion fatigue Combined creep and fatigue Modes of Mechanical Failure 74 25-Feb-23

75. Machine E lements 75 75 25-Feb-23