Engineering design is the process of devising a system,
component, or process to meet desired needs. It is a decision making process in which basic sciences, mathematics, and engineering sciences are applied to convert resources optimally to meet stated objective
Identification of need generally starts the design
process. Recognition of the need and phrasing the need often constitute a highly creative act, because the need may be only a vague discontent, a feeling of uneasiness, or a sensing that something is not right. The need is often not evident at all; recognition is usually triggered by a particular adverse circumstance or a set of random circumstances that arises almost simultaneously
The definition of problem is more specific and must
include all the specifications for the object that is to be designed. The specifications are the input and output quantities, the characteristics and dimensions of the space the object must occupy, and all the limitations on these quantities. We can regard the object to be designed as something in a black box. In this case we must specify the inputs and outputs of the box, together with their characteristics and limitations.
The synthesis of a scheme connecting possible system
elements is sometimes called the invention of the concept or concept design. This is the first and most important step in the synthesis task. Various schemes must be proposed, investigated, and quantified in terms of established metrics.
As the fleshing out of the scheme progresses, analyses
must be performed to assess whether the system performance is satisfactory or better, and, if satisfactory, just how well it will perform. System schemes that do not survive analysis are revised, improved, or discarded. Those with potential are optimized to determine the best performance of which the scheme is capable. Competing schemes are compared so that the path leading to the most competitive product can be chosen.
Evaluation is a significant phase of the total design
process. Evaluation is the final proof of a successful design and usually involves the testing of a prototype in the laboratory. Here we wish to discover if the design really satisfies the needs.
Communicating the design to others is the final, vital
presentation step in the design process. Undoubtedly, many great designs, inventions, and creative works have been lost t0 posterity simply because the originators were unable or unwilling to explain their accomplishments to others.
characteristic that influences the design of the
element or, perhaps, the entire system.
1 Functionality 2 Strength/stress 3 Distortion/deflection/stiffness 4 Wear 5 Corrosion 6 Safety 7 Reliability 8 Manufacturability 9 Utility 10 Cost 11 Friction 12 Weight 13 Life
14 Noise 15 Styling 16 Shape 17 Size 18 Control 19 Thermal properties 20 Surface 21 Lubrication 22 Marketability 23 Maintenance 24 Volume 25 Liability
The consideration of cost plays such an important role
in the design decision process that we could easily spend as much time in studying the cost factor as in the study of the entire subject of design. The cost of manufacturing a single product will vary from city to city and from one plant to another because of overhead, labour, taxes, and freight differentials and the inevitable slight manufacturing variations.
A code is a set of specifications for the 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. It is important to observe that safety codes do not imply absolute safety
A standard is a set of specifications for parts,
materials, or processes intended to achieve uniformity, efficiency, and a specified quality. One of the important purposes of a standard is to place a limit on the number of items in the specifications so as to provide a reasonable inventory of tooling, sizes, shapes, and varieties.
The organizations of interest to mechanical engineers are: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Aluminium Association (AA) American Gear Manufacturers Association (AGMA) American Institute of Steel Construction (AISC) American Iron and Steel Institute (AISI) American National Standards Institute (ANSI)5 ASM International6 American Society of Mechanical Engineers (ASME) American Society of Testing and Materials (ASTM) American Welding Society (AWS) American Bearing Manufacturers Association (ABMA)7 British Standards Institution (BSI) Industrial Fasteners Institute (IFI) Institution of Mechanical Engineers (I. Mech. E.) International Bureau of Weights and Measures (BIPM) International Standards Organization (ISO) National Institute for Standards and Technology (NIST)8 Society of Automotive Engineers (SAE)
The strict liability concept of product liability generally
prevails in the United States. This concept states that the manufacturer of an article is liable for any damage or harm that results because of a defect. And it doesn’t matter whether the manufacturer knew about the defect, or even could have known about it. The best approaches to the prevention of product liability are good engineering in analysis and design, quality control, and comprehensive testing procedures.
“The word ergonomics implies the study of man at
work while the word human factors implies the study of ma n in relation to equipment and environment.”
Design
and performance parameter that contribute to achieving customer requirements
can
Refer to detail description of the completed design,
including all dimensions, material properties and fabrication instructions
Power to be delivered: 20 hp Input speed: 1750 rev/min Output speed: 85 rev/min Targeted for uniformly loaded applications, such as conveyor belts, blowers, and generators Output shaft and input shaft in-line Base mounted with 4 bolts Continuous operation 6-year life, with 8 hours/day, 5 days/wk Low maintenance Competitive cost Nominal operating conditions of industrialized locations Input and output shafts standard size for typical couplings
Power to be delivered: 20 hp Power efficiency: >95% Steady state input speed: 1750 rev/min Maximum input speed: 2400 rev/min Steady-state output speed: 82–88 rev/min Usually low shock levels, occasional moderate shock Input and output shaft diameter tolerance: ±0.001 in Output shaft and input shaft in-line: concentricity ±0.005 in, alignment ±0.001 rad Maximum allowable loads on input shaft: axial, 50 lbf; transverse, 100 lbf Maximum allowable loads on output shaft: axial, 50 lbf; transverse, 500 lbf Base mounted with 4 bolts Mounting orientation only with base on bottom 100% duty cycle Maintenance schedule: lubrication check every 2000 hours; change of lubrication every 8000 hours of operation; gears and bearing life >12,000 hours; infinite shaft life; gears, bearings, and shafts replaceable Access to check, drain, and refill lubrication without disassembly or opening of gasketed joints.
Materials Selection The designer of any product, other than software must
get involved with material selection. Only occasionally will the exact grade of material be specified by the customer. Even then the designer must understand the material to be able to design the product.
So many materials, so much information.
How do we decide? How do we begin to choose?
First we need to look at the function of the product –
Product Analysis Just what it says – analyse the product! What does it do? How does it do it? Where does it do it?
Who uses it? What should it cost?
What is the function of a bike – obvious?
How does the function depend on the type of bike? Racing Touring Mountain bike Commuter Childs
How is it made to be easily maintained?
What should it look like (colours etc.)? What should it cost? How has it been made comfortable to ride?
How do the mechanical parts work and interact?
Textbooks
Manufacturer’s literature Internet Sites
Modulus spans 5 orders of magnitude 0.01 GPa for
foams to 1000 GPa for diamond The charts therefore use logarithmic scales, where twice the distance means ten times. This makes it possible to show the full range on one chart
Allow easy visualisation of properties
Show lots of different materials Can be ‘drilled down’ to specifics Show balances of properties e.g. strength v cost
Ideal for a first ‘rough cut’ selection
1. Think about the design from ergonomic and
functional viewpoint. 2. Decide on the materials to be used. 3. Choose a suitable process that is also economic 4. Is the product performance driven or cost driven? This makes a huge difference when choosing materials
Although we usually choose materials first sometimes
it is the shape and process which is the limiting factor
Drink Container
What are the requirements
Provide leak free environment for storing liquid.
Comply with food standards & protect liquid from
health hazards. For fizzy drinks, withstand pressure. Brand image & identity Easy to open Easy to store & transport Cheap for high volumes
Steel
Aluminium Glass Plastic
