Chapter 1: Introduction

Transcription

1 Chapter 1: Introduction The i8 concept car, a hybrid sports car requiring three liters per 100 km (94 mpg) and acceleration from 0 to 100 km/hr in under five seconds. Source: Courtesy of BMW. The invention all admir'ʹd, and each, how he To be th'ʹ inventor miss'ʹd; so easy it seem'ʹd, Once found, which yet unfound most would have thought Impossible John Milton rd Fundamentals of Machine Elements, 3 ed.

2 Definition of product need Original concept Conceptual design Design analysis Physical and analytical models Prototype testing Evaluation Revised design Final evaluation Production drawings Material specification, Process and equipment selection, Tool and die design and construction Manufacturing (a) Market analysis Specification Concept design Main design flow Detail design Manufacture Sell (b) Product Development Approaches Figure 1.1: Approaches to product development. (a) Classic approach, with large design iterations typical of the over- the- wall engineering approach. Source: Adapted from Kalpakjian and Schmid [2003]. (b) A more modern approach, showing a main design flow with minor iterations representing concurrent engineering inputs. Source: Adapted from Pugh [1996].

3 The Safety Hierarchy Design Procedure 1.1: The Safety Hierarchy A designer should a_empt the following, in order, in a_empting to achieve reasonable levels of safety: 1. Eliminate hazards through design. 2. Reduce the risk or eliminate the hazard through safeguarding technology. 3. Provide warnings. 4. Train and instruct. 5. Provide personal protective equipment.

4 Design for Manufacture Bearing Cover Connecting rod Pin Cover Seating Piston Rivet Blade clamp Seating Bush Needle bearing Roll pin Pin Counterweight Gear Bearing Housing Seal Washer Washer Pin Piston Bush Blade clamp Plug Seating Connecting rod Pin Gear Bearing Housing Guard Guard Washer Set screw Set screw (a) Figure 1.2: Effect of manufacturing and assembly considerations on the design of a reciprocating power saw. (a) Original design, with 41 parts and min assembly time; (b) modified design, with 29 parts and min assembly time. Source: Adapted from Boothroyd [1992]. (b)

5 Pugsley Safety Factor Characteristic a B A C vg g f p vg vg g f p g vg g f p f vg g f p p vg g f p vg = very good, g=good, f=fair, and p=poor. A = quality of materials, workmanship, maintenance, and inspection. B = control over load applied to part. C = accuracy of stress analysis, experimental data or experience with similar parts. Characteristic E a D ns s vs ns s vs a vs = very serious, s = serious, and ns = not serious D = danger to personnel E = economic impact Table 1.2: Safety factor characteristics D and E. Pugsley safety factor: n s = n sx n sy Table 1.1: Safety factor characteristics A, B, and C.

6 Unit Checks Design Procedure 1.2: Procedure for Unit Checks It is generally advisable to carry units throughout calculations. However, an expression can generally be evaluated by: 1. Establish units of specific terms of an equation while making use of Table 1.3a. 2. Place units of terms into both sides of an equation and reduce. 3. The unit check is complete if both sides of an equation have the same units.

7 Invisalign (a) (b) Figure 1.3: The Invisalign product. (a) An example of an Aligner; (b) a comparison of conventional orthodontic braces and a transparent Aligner. Source: Courtesy of Align Technology, Inc.

8 Invisalign Production Figure 1.4: The process used in application of Invisalign orthodontic treatment. (a) Impressions are made of the patient'ʹs teeth by the orthodontist and shipped to Align Technology, Inc. These are used to make plaster models of the patient'ʹs teeth. (b) High- resolution, three- dimensional representations of the teeth are produced from the plaster models. The correction plan is then developed using computer tools. (c) Rapid- prototyped molds of the teeth at incremental positions are produced through stereolithography. (d) An aligner is produced by molding a transparent plastic over the stereolithography part. Each Aligner is used for approximately two weeks. The patient is left with a healthy bite and beautiful smile. Source: Courtesy of Align Technology, Inc. Fundamentals of Machine Elements, 3rd ed. (a) (b) (c) (d)

9 (a) SI units Quantity Unit SI symbol Formula SI base units Length meter m - Mass kilogram kg - Time second s - Temperature kelvin K - SI supplementary unit Plane angle radian rad - SI derived units Energy joule J N-m Force newton N kg-m/s 2 Power watt W J/s Pressure pascal Pa N/m 2 Work joule J N-m SI Units and Prefixes (b) SI SI symbol Multiplication factor for 1,000,000,000,000 = tera T 1,000,000,000 = 10 9 giga G 1,000,000 = 10 6 mega M 1000 = 10 3 kilo k 100 = 10 2 hecto h 10 = 10 1 deka da 0.1 = 10 1 deci d 0.01 = 10 2 centi c = 10 3 milli m = 10 6 micro µ = 10 9 nano n = pico p Table 1.3: SI units and Prefixes.

10 Acceleration of gravity 1 g= m/s 2 ( ft/s 2 ) Energy Btu (British thermal unit) = amount of energy required to raise 1 lbm of water 1 F (1 Btu = ft- lb) kilocalorie =amount of energy required to raise 1 kg of water 1K (1 kcal =4187 J) Length 1 mile =5280 ft 1 nautical mile = ft Power 1 horsepower =550 ft- lb/s Pressure 1 bar =10 5 Pa Temperature Fahrenheit: t F = 9 5 t C + 32 Rankine: t R = t F Kelvin: t K = t C (exact) Kinematic viscosity 1 poise =0.1 kg/m- s 1 stoke = m 2 /s Volume 1 cubic foot =7.48 gal l 1 in =0.254m= 25.4 mm 1 lbm = kg 1 R = 5 9 K 1 ft = m 1 lb =4.448 N 1 lb =386.1 lbm- in./s 2 1 ton =2000 lb (shor or 2240 lb (long ton) 1 tonne =1000 kg (metric ton) 1 kgf = N 1 lb/in. 2 = 6895 Pa 1 ksi =6.895 MPa 1 Btu = 1055 J 1 ft- lb = J 1 hp = 746W= 2545 Btu/hr a 1 kw =3413 Btu/hr 1 quart = m 3 = liter 1 kcal =3.968 Btu a Note that in countries using the metric system,ahorsepower is d as 75 kpm/s, or 736 W. Conversion Factors Table 1.4: Conversion factors and definitions.