EML 3004 C CHAPTER 5 Engineering Design Tools

EML 3004 C CHAPTER 5 Engineering Design Tools Namas Chandra Introduction to Mechanical engineering Chapter 4 -1

EML 3004 C Objectives Examine the role of computer in engineering design Learn when and when not to use the computer. Examples of computer use for analysis, data collection and real-time control Sections 5. 1 Estimation 5. 5 Computer Analyses 5. 2 5. 7 Spreadsheets Significant Figures, Dimensioning, and Tolerance 5. 3 Prototyping 5. 4 Reverse Engineering Namas Chandra Introduction to Mechanical engineering 5. 8 Solid Modeling and CAD (in conjunction with ME Tools) Chapter 4 -2

EML 3004 C 5. 1 Estimation § A simple ‘back of the envelope’ calculation is importance to validate the soundness of design ideas. § Anytime you change design, you need to do this-of course full calculations are needed at later stages. Namas Chandra Introduction to Mechanical engineering Chapter 4 -3

EML 3004 C 5. 1 Estimation-2 Namas Chandra Introduction to Mechanical engineering Chapter 4 -4

EML 3004 C 5. 2 Significant Figures, Dimensioning and Tolerance § § Accuracy of a number is specified by significant figures. Definition of significant digits 1. All non-zero digits (1 -9) are significant 2. Zeroes that have ANY non-zero digit to the LEFT are significant zeroes 3. All other zeroes not covered by rule 2 are NOT significant. Example: 22. 302 has 5 significant figures 0. 004000 has 4 significant figures (zeroes to the left of 4 are not significant 1. 0000 E 06 has 5 significant figures. (use scientific notations) § Product of a sequence of numbers will have the same significant figures as the least of the factors. Example: 1. 23*22. 45*0. 1375= not 3. 79685625 =3. 80 Namas Chandra Introduction to Mechanical engineering Chapter 4 -5

EML 3004 C 5. 2 Adding and Subtracting -2 § Precision of a number is given by the number of significant digits after the decimal. § The rule expresses that the answer should have so many digits to the RIGHT of the decimal instead of focusing in on the number of significant digits as the other rule did. § The focus is upon the number of positions to the RIGHT of the decimal § THE SUM OR DIFFERENCE CAN BE NO MORE PRECISE THAN THE LEAST PRECISE NUMBER INVOLVED IN THE MATHEMATICAL OPERATION. Example: 160. 45 + 6. 732 =167. 18 (2 positions to the right of decimal) 45. 621 + 4. 3 - 6. 41=43. 5 Namas Chandra Introduction to Mechanical engineering Chapter 4 -6

EML 3004 C 5. 2 Accuracy § Accuracy depends on the number of digits beyond the decimal point. § Namas Chandra Introduction to Mechanical engineering Tolerance shown in the figure indicates to the machinist the accuracy to which the various dimensions need to be maintained. Chapter 4 -7

EML 3004 C 5. 3 Prototyping § § § After many initial revisions and computer simulations, you arrive at a final configuration. At this stage, you are ready to construct a prototype. Prototype is a mock-up of the final product § that contains all the salient features § that omits all the non-essential elements A model of a foot for analysis Namas Chandra Introduction to Mechanical engineering Rapid Prototyping for testing/verification Chapter 4 -8

EML 3004 C 5. 4 Reverse Engineering § § In reverse engineering, engineer dissects a working product to examine the details. Allows to study the functions of each of the component as built and used. Very useful in failure analysis of products The detailed study is used § to replicate a competitor’s product with modification § understand the working for improvement § to analyze and avoid patent violation § Documentation greatly helps reverse engineering Namas Chandra Introduction to Mechanical engineering Chapter 4 -9

EML 3004 C 5. 4 Computer analysis § § At this stage, you do detailed analysis of the prototype and simulate the system You can use general engineering programs like § § Pro-Engineer Abaqus Solid Works Ansys Or mathematical programs like § Matlab § Mathcad Or, use direct programming using C, C++, JAVA or Fortran to build models. Namas Chandra Introduction to Mechanical engineering Chapter 4 -10

EML 3004 C 5. 7 Spreadsheets in Design 1. Excel and Lotus are examples of spreadsheets useful in design. 2. If the system is complex (as most of them are!!) spreadsheets can be used to study the effect of one variable on another. 3. For example if we are interested in locating the center of gravity of our vehicle very close to the center, when we are still choosing the various components, we can use spreadsheets. Namas Chandra Introduction to Mechanical engineering Chapter 4 -11

EML 3004 C 5. 7 Spreadsheets in Design § Since the weights and locations are known then we can use simple formulae to locate the C. G. § With this table now, you can alter the location or/and add/delete parts still to suit your goal of C. G. Namas Chandra Introduction to Mechanical engineering Chapter 4 -12

EML 3004 C CHAPTER 5…concludes Engineering Design Tools Namas Chandra Introduction to Mechanical engineering Chapter 4 -13