1_INTRODUCTION - Mechanical Engineering Design& Workshop...

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Unformatted text preview: Mechanical Engineering Design & Workshop Course coordinator: Prof Marek Wiśniewski DSc PhD MSc Mech Eng Institute for Vehicles, Machine Design and Operation Room Phone Fax E-mail 406/A1 042 6312236 042 6312262 [email protected] Mechanical Engineering Design & Workshop Study areas: Business and Technology Mechatronics Prerequisites: Mathematics, Physics, Mechanics, Strength of Materials, Technical Drawings, Materials Science, Fabrication Technologies Literature B.J. Hamrock, B.O. Jacobson, S.R. Schmid: Fundamentals of Machine Elements. Boston: WCB/McGraw Hill 1999. W. Beitz, K.-H. Küttner (Eds.): DUBBEL Handbook of Mechanical Engineering. London: Springer-Verlag. Bonfiglioli Riduttori (Eds.): Gear Motor Handbook. Berlin: Springer-Verlag. R.C. Juvinall, K.M. Marshek: Fundamentals of Machine Component Design. London: John Wiley & Sons, 2006. W. Horwatt, J. Bartoszewicz: Podstawy konstrukcji maszyn dla elektryków. Warszawa: WNT 1978. Literature http://www.mech.uwa.edu.au/DANotes/intro/contents.html http://www.ecs.umass.edu/mie/labs/mda/dlib/machine/machine.html http://www.utm.edu/departments/engin/lemaster/machine_design.htm http://www.co-design.co.uk/dpg/guides.htm http://www.tribology-abc.com/ Objectives 1. Gaining the terminology and key design issues for specific machine elements including springs, bearings, fasteners, gears, etc. 2. Applying mechanics and strength of materials to machine element design 3. Predicting the operation life of machine elements 4. Learning current analytical and computational tools in mechanical design 5. Gaining experience in formulating and solving basic mechanical design problems Outcomes 1. Ability to design machine elements for various applications 3. Ability to solve and optimize open ended design problems 4. Skills in using material/vendor data and computer tools for mechanical design 5. Interest in learning and implementing new machine design materials and methodologies. 6. Ability to effectively use the different analytical, computational and graphical tools Contents • Introduction. Prerequisites. Literature. Objectives. Outcomes. Contents of lecture. Role of machine design. Calculations of machine elements. Safety factors. Outline of designing. Unification and standardisation. Threaded fasteners. Geometry and mechanics of screw threads. Design of the power screws. Threaded fasteners: types, nomenclature and strength classes of bolts and screws, types of threads. Calculation of the threaded joints. Elastic machine elements: characteristics and calculations for metallic and non-metallic springs, spring systems and arrangements. • • • Contents • • Welded joints: types and methods of welding and brazing. Calculation methods for welded joints. Dimension and shape tolerances. Standardised shafts and holes tolerances. Fits of machine elements. Interference fits: stress and deformation, load carrying capacity. Design of shafts. Elements mounted on the shafts: keys and splines; spline, involute and polygone shafts. Toothed gears: spur, bevel, helical, hypoid, worm gearings. Gear systems. Calculations for toothed gears: geometry and load capacity. • • • Contents • • Couplings and brakes: types of couplings, basic calculations, criteria of application. Drive systems: flat and V-belt transmissions, chain drives. Geometry and load capacity of belt and chain drives. Bearing systems: rolling element bearings, areas of application, calculations for steady-state and dynamic loads. Hydrodynamically lubricated bearings: calculations, dimensionless characteristics for load carrying capacity and friction losses. Fabrication technologies: machining, forging, casting – machines and tools. Design and technology: single and serial production. • • • Machine A nineteen's century lathe Machine General definition: A machine is any device that transmits or modifies material, energy and/or information to perform or assist in the performance of tasks. Examples: car, lathe, refrigerator, computer memory (RAM, ROM, EPROM), computer program (word processor, search engine). Specialised definition: machine is an assembly of linked parts or components, at least one of which moves, with the appropriate actuators, control and power circuits, etc., joined together for a specific application, in particular for the processing, treatment, moving or packaging of a material (European Commission Directive 98/37/EC ). Design Design is a mental plan, a scheme of attack, end in view, adaptation of means to ends, preliminary sketch for picture, invention (The Concise Oxford Dictionary). Some physical object should result from the design. This object is to be communicated to others through its visualisation (sketch, engineering drawing, computer simulations etc.). Engineering is concerned with the design of a solution to a practical problem. (A scientist may ask "why?" and proceed to research the answer to the question. By contrast, engineers want to know how to solve a problem, and how to implement that solution.) Design: tools Computer Aided Design (CAD) software is a basic tool to create drawings and/or mathematical models of designs. Computer models of designs can be checked for flaws without having to make expensive and time-consuming prototypes. The computer can automatically translate some models to instructions suitable for CNC (Computer Numeric Control) machinery. The computer also allows increased reuse of previously developed designs, by presenting an engineer with a library of predefined parts ready to be used in designs. Physical models of designs (usually more expensive than mathematical ones) include among others: scale models, non-destructive testing, destructive tests. Engineering calculations Problems covered by the Strength of Materials (PREREQUISITE): 1. Stress and deformation analysis: • Tension and compression • Direct shear stress • Torsional shear stress • Bending stress 2. Combined stresses (analysis of the complex loading conditions) 3. Static indeterminacy (deflections, energetic methods) 4. Stability of structures (buckling of columns) Engineering calculations Problems that shall be introduced in the Mechanical Engineering Design: 1. Applying methods of the Strength of Materials to machine elements 2. Vibration analysis of mechanical systems 3. Tribology (friction and wear) considerations: • Friction losses and efficiency of machine • Lifetime of rubbing couples in respect to their abrasive wear • Lifetime of rubbing elements in respect to their surface fatigue • Limiting thermal operating conditions of sliding contacts Engineering materials Engineering materials Factor of safety Safety factor X is a multiplier applied to the calculated maximum load (force, torque, bending moment or a combination) to which a component or assembly will be subjected. The factor of safety of a structure under static loads can be expressed in terms of normal stresses as σ ult X= σ des or for tangential stresses as τ ult X= τ des Index ult denotes the ultimate stress and des is the design one. Factor of safety Strength test: a) stress vs. deformation, b) tested specimen a) Stress σ b) Deformation ε Note Polish symbols: Rm for ultimate stress σult, Re for yield stress σy Factor of safety Safety criterion for fluctuating stress Factor of safety Fluctuating stress 1.21 Factor of safety Factor of safety (also called design factor) is a measure of the relative safety (or redundancy, or „overengineering”) of the load-carrying component or assembly. A factor of safety of 1 implies no safety at all. An appropriate factor of safety is chosen based on a number of considerations: •the accuracy of load and wear estimates •the quality of materials chosen •the consequences of failure •the cost of redundancy Factor of safety Typical figures for factor of safety: • Components whose failure could result in substantial financial loss, serious injury or death: X = 4 - 16 • Normal case for structures or machine elements: X = 2 - 4 (lower figures for ductile materials, higher for brittle ones; lower figures for high confidence in the knowledge of operating conditions; lower figures for high certainty about material properties) • Elements of aircrafts: X = 1.15 – 1.25 • Space exploration: X = 1.01 – 1.05 Role of machine design Conception (need) Feasibility study Operations research Detail design Reserarch and development (R&D) Industrial design Ergonomics Industrial relations ..... DESIGN Manufacturing Distribution (sale) Operation Maintenance Note the feedback from all stages of machine life to DESIGN! Removal Occupations of engineers German Society of Engineers (VDI) reported 1998 the following activities: •Design •Research and development •Fabrication and control •Sales and marketing •Maintenance and transport •Management 28% 10% 24% 10% 16% 12% Outline of designing Problem statement: defining the machine inputs and outputs, describing the functional and economic (materials and fabrication) limitations Identifying the state of the art: generating and evaluating the bank of existing solutions (inventions could be added) Drafting a number of solutions, evaluating them and choosing the (probably) best variant according to specified criteria Outline of designing Flowchart of the design process Outline of designing Criteria (weights) for evaluation of solutions Outline of designing all criteria uniformly applied across all candidates when selecting the most suitable solution verification of design: practicalisation remembering Murphy’s law („if anything can go wrong, it will”) the optimum (?) solution Drawings A variety of line styles are used to graphically represent physical objects. Types of lines include the following: •visible - are continuous lines used to depict edges directly visible from a particular angle •hidden - are short-dashed lines that may be used to represent edges that are not directly visible •center - are alternately long- and short-dashed lines that may be used to represent the axes of circular features •section - are thin lines in a parallel pattern used to indicate surfaces in section views resulting from "cutting." Section lines are commonly referred to as "cross-hatching" Drawings The objects can be represented with different views (front, rear, top, bottom, left and right side). There are two ways to place the different views on the drawing: • the ISO standard considers a projection on the opposite direction, like an X-ray radiography; the top view is under the front view, the right view is at the left of the front view... This is called First Angle Projection. • the American standard (called Third Angle Projection) places the left view on the left and the top view on the top... Drawings The standard in use is represented by a truncated cone that shows the projection used: a) First angle projection b) Third angle projection a) b) Drawings In most cases, a single projection is not sufficient to show all necessary features, and several views are used. Types of views include the following: • orthographic projection - show the object as it looks from the front, right, left, top, bottom, or back, and are typically positioned relative to each other according to the rules of either first-angle or third-angle projection. Not all views are necessarily used (orthographic comes from the Greek for straight drawing). • section - depict what the object would look like if it were cut perfectly along cutting plane lines defined in a particular view, and rotated 90° to directly view the resulting surface(s) • detail - show portions of other views, magnified for clarity • auxiliary projection - similar to orthographic projections, however the directions of viewing are other than those for orthographic projections. Drawings Dimensioning The required sizes of features are conveyed through use of dimensions. Distances may be indicated with either of two standardized forms of dimension: linear and ordinate. • With linear dimensions, two parallel lines, called extension lines, spaced at the distance between two features, are shown at each of the features. A line perpendicular to the extension lines, called a dimension line, with arrows at its endpoints, is shown between, and terminating at, the extension lines. The distance is indicated numerically at the midpoint of the dimension line, either adjacent to it, or in a gap provided for it. • With ordinate dimensions, one horizontal and one vertical extension line establish an origin for the entire view. The origin is identified with zeroes placed at the ends of these extension lines. Distances along the x- and y-axes to other features are specified using other extension lines, with the distances indicated numerically at their ends. Drawings Sizes of circular features are indicated using either diametral or radial dimensions. Radial dimensions use an R followed by the value for the radius. Diametral dimensions use a Greek character Φ (circle with forward-leaning diagonal line through it) called the diameter symbol, followed by the value for the diameter. A radially-aligned line with arrowhead pointing to the circular feature, called a leader, is used in conjunction with both diametral and radial dimensions. All types of dimensions are typically composed of two parts: the nominal value, which is the "ideal" size of the feature, and the tolerance, which specifies the amount that the value may vary above and below the nominal. Tolerancing of dimensions and roughness requirements will be given in following chapters. Drawings NOTES Notes – textual information – are also typically included in drawings, specifying details not otherwise conveyed. Notes are almost always in completely uppercase characters, for uniformity and maximal legibility after duplication of the drawing, which may involve substantial reduction in size. Leaders may be used in conjunction with notes in order to point to a particular feature or object that the note concerns. Drawings Hydraulic piston Drawings Pulley Drawings Third-angle projection! 39 Drawings Drawings Drawings Drawings Industrial design rights Industrial design rights are intellectual property rights that protect the visual design of objects that are not purely utilitarian. An industrial design consists of the creation of a shape, configuration or composition of pattern or color, or combination of pattern and color in three dimensional form containing aesthetic value. An industrial design can be a two- or threedimensional pattern used to produce a product, industrial commodity or handicraft. Under the Hague Agreement Concerning the International Deposit of Industrial Designs, a World Intellectual Property Organization (WIPO) administered treaty, a procedure for an international registration exists. An applicant can file for a single international deposit with WIPO or with the national office in a country party to the treaty. The design will then be protected in as many member countries of the treaty as desired. (THEORY) Industrial design rights PRACTICE ...
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This note was uploaded on 11/09/2010 for the course AEROSPACE AE 1202 taught by Professor Dr.adib during the Spring '10 term at Sharif University of Technology.

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