ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 1 ENT 253 MECHANICAL DESIGN Lecture 1 Material Dr. HAFTIRMAN ASRUL SAAD SCHOOL OF MECHATRONIC MECHANICAL PROGRAM UniMAP

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 2 CHAPTER OUTLINE  Mechanical Engineering Design  Mechanical Design  Material  Stress and Strength  Uncertainty  Units  Standards and Codes  Design Factor and Factor Safety  Reliability  Dimensions and Tolerances

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 3 DESIGN  To design is either to formulate a plan for the satisfaction of a specified need or to solve a problem. If the plan results in the creation of something having a physical reality, then the product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable.  Design is an innovative and highly iterative process. It is also a decision-making process. The engineering designer has to be personally comfortable with a decision-making, problem-solving role.  Design is a communication-intensive activity in which both words and pictures are used, and written and oral forms are employed. Engineers have to communicate effectively and work with people of many disciplines. These are important skills, and an engineer’s success depends on them.  A designer’s personal resources of creativeness, communicative ability, and problem-solving skill are intertwined with knowledge of technology and first principles. Engineering tools such as mathematics, statistics, computers, graphics, and languages are combined to produce a plane that, when carried out, produces a product that is functional, safe, reliable, competitive, usable, manufacturable, and marketable, regardless of who builds it or who uses it.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 4 Mechanical Engineering Design  Mechanical engineers are associated with the production and processing of energy and with providing the means of production, the tools of transportation, and the techniques of automation.  The disciplinary base are mechanic of solids and fluids, mass and momentum transport, manufacturing process, and electrical and information theory.  Mechanical engineering design involves all the disciplines of mechanical engineering.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 5 MECHANICAL DESIGN  Material  Load and Stress Analysis  Deflection and stiffness  Design of Mechanical Elements

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 6 MATERIAL Ferrous Metal Nonferrous Material Organic Non metal I norganic

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 7 MATERIAL  Ferrous Gray Cast Iron Nodular Cast Iron White Cast Iron Malleable Cast Iron Alloy Cast Iron Cast Steel

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 8 MATERIAL  Nonferrous Aluminum Magnesium Bronze Titanium Brass Zinc

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 9 MATERIAL  Organic Rubber Plastic Petroleum Leather Wood Paper  Inorganic Cement Graphite Cement Glass Ceramics

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 10 STRESS AND STRENGTH  Stress is a state property at a specific point within a body, which is a function of load, geometry, temperature, and manufacturing processing.  Strength is a property of a material of a mechanical element. The strength of an element depends on the choice, the treatment, and the processing of the material.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 11 STRESS AND STRENGTH  The capital letter S to denote strength.  S s is a shear strength.  S y is a yield strength.  S u is an ultimate strength.  σ (sigma) to designate normal stress.  τ (tau) to designate shear stress.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 12 UNCERTAINTY  Examples of uncertainties concerning stress and strength include:  Composition of material and the effect of variation on properties.  Variations in properties from place to place within a bar of stock.  Effect of processing locally, or nearby, on properties.  Effect of nearby assemblies such as weldments and shrink fits on stress conditions.  Effect of thermomechanical treatment on properties.  Intensity and distribution of loading.  Validity of mathematical models used to represent reality.  Intensity of stress concentrations.  Influence of time on strength and geometry.  Effect of corrosion.  Effect of wear.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 13 UNITS  In the symbolic units equation for Newton’s second law, F = ma, F=MLT -2 where, F=force, M=mass, L=length, T= time  The International System of Units (SI)  F=ML/T 2 => (kilogram)(meter)/(second) 2 => kg.m/s 2 W=mg=>(1kg)(9.81m/s 2 )=9.81N

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 14 STANDARDS AND CODES  A standard is a set of specifications for perts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality.  One of the important purposes of a standard is a place limit on the number of items in the specifications so as to provide a reasonable inventory of tooling, size, shape, and varieties.  A code is a set of specifications for analysis, design, manufacture, and construction of something.  The purpose of a code is to achieve a specified degree of safety, efficiency, and performance or quality.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 15 STANDARDS AND CODES  All of the organizations and societies listed below have established specifications for standards and safety or design codes.  AAAluminum Association  AGMAAmerican Gear Manufacturers Association  AISCAmerican Institute of Steel Construction  AISI American Iron and Steel Institute  ANSIAmerican National Standards Institute  ASM American Society for Metals  ASMEAmerican Society of Mechanical Engineers  ASTMAmerican Society of Testing and Materials  AWSAmerican Welding Society  ABMAAmerican Bearing Manufactures Association  BSIBritish Standards Institution  IFIIndustrial Fasteners Institute  ISOInternational Standards Organization  SAESociety of Automotive Engineers  NISTNational Institute for Standards and Technology

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 16 DESIGN FACTOR AND FACTOR OF SAFETY  n d = loss-of-function strength/allowable stress  n d = S/σ(or τ)  “n d “ is called the design factor  The factor of safety has the same definition as the design factor. The factor safety is called “n”

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 17 RELIABILITY  Reliability of element is the statistical measure of the the probability that a mechanical element will not fail in use.  The reliability R can be expressed by a number having the range 0≤R≤1  A reliability of R=0.90 means that there is a 90 percent chance that the part will perform its proper function without failure.  In the reliability method of design, the designe’s task is to make a judicious selection of materials, processes, and geometry (size) so as to achieve a specific reliability goal.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 18 DIMENSIONS AND TOLERANCES The terms are used in dimensioning;  Nominal size=>The size we use in speaking of an element. Nominal size  Limits=> The stated maximum and minimum dimensions.  Tolerance=> The difference between the two limits.  Bilateral tolerance=>The variation in both directions from the basic dimension. The basic size is between two limits. Bilateral tolerance  Unilateral tolerance=>The basic dimension is taken as one of the limits, and variations is permitted in only one direction. Unilateral tolerance  Clearance=> A general term that refers to the mating of cylindrical parts such as a bolt and a hole. The word clearance is used only when internal member is smaller than the external member. The diametral clearance is the measured difference in the two diameters.  Allowance=>The minimum stated clearance or the maximum stated interference for mating parts.

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 19 PROBLEMS

ENT 253 MECHANICAL DESIGN SEM /2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 20 SOLUTION