Engineering Standards and Realistic Design Constraints

1
Engineering Standards and Realistic Design
Constraints

• 11 January 2005
• GE 498 Senior Design II

2
Engineering Standards

• Each of your design projects must incorporate
  engineering standards.
• Standards are developed by technical specialists
  in each field.
• In this class, you must comply with the standards
  to be described in this lecture along with any
  other applicable standards specific to your
  project.

3
A Short List of Electrical and Mechanical
Standards for GE 497/8

1. All devices using 120-V AC power shall use copper
   wire of at least 14AWG to carry up to 20A, 12AWG
   to carry up to 25A, and 10AWG to carry up to 30A.
   (National Electrical Code Table 310.16)
2. All devices using 120-V AC power shall be
   grounded and shall use a grounded plug. (National
   Electrical Code 250.20(B))
3. All grounding connections shall be made using
   wire sized to match the over-current protection
   device of the outlet 15A protection uses 14AWG,
   20A uses 12AWG, and 30 A uses 10 AWG. (National
   Electrical Code Table 250.122)

4
A Short List of Electrical and Mechanical
Standards for GE 497/8

1. Standard 22 AWG hook-up wire can carry a maximum
   of 7A in unbundled applications and 0.92A in
   bundled applications. 30AWG Wire-wrap wire can
   carry 0.86A in unbundled applications and 0.142A
   in bundled applications. (Handbook of Electronic
   Tables and Formulas)
2. No exposed conductors shall be at more than 14V
   DC above ground or above any other exposed
   conductors. (Underwriters laboratory standard
   1446)

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A Short List of Electrical and Mechanical
Standards for GE 497/8

1. All systems containing compressed gases or
   liquids shall comply with the ASME Boiler and
   Pressure Vessel Code (BPVC).
2. All devices with exposed surfaces exceeding 140F
   shall be clearly marked with warning labels.
   (Occupational Safety and Health Administration)
3. All lasers used in this class shall be limited to
   less than 5mW, and appropriate signage must be
   used. (ANSI standard Z136.1)

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Realistic Design Constraints

• You must also consider the following realistic
  design constraints, as appropriate
• Health and safety
• Ethical
• Sustainability
• (Includes Economic, Environmental, and
  Social/Political factors)
• Manufacturability

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Health and Safety Considerations

• The engineering standards presented earlier all
  promote the design of safe electrical and
  mechanical engineering systems.
• Last semester, you also learned how a Preliminary
  Hazard Analysis can be used to identify and
  eliminate potentially hazardous design features.
• Consider not just accidental injuries but the
  logical conclusions of the devices intended
  operation.
• Remember, your primary consideration must be the
  safety, health and welfare of the public!

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Ethical Considerations

• In GE 301 and GE 497, you studied the ethical
  implications of engineering work.
• Now, carefully consider your device, how it might
  be manufactured, marketed, and used.
• Are there potentially unethical uses of your
  project?
• Does your project promote the safety, health, and
  welfare of the public?

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Sustainability

• A sustainable design is one that balances three
  considerations
• Environmental Stewardship
• Social Impact
• Economic Feasibility
• A design that focuses on one or two of these
  factors at the expense of the others is not
  sustainable.

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Environmental Impact

• Questions to consider while completing your
  design
• What is the environmental impact of the
  production of this device?
• Environmentally sensitive materials used?
• Toxic waste or hazardous emissions generated?
• What is the environmental impact of the operation
  of this device?
• Is this device energy efficient?
• Does it generate greenhouse gases when operated?
• What is the environmental impact of the end of
  this devices life cycle?
• Can components be easily separated and recycled?

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Social/Political Impact

• Questions to consider while completing your
  design
• What is the social impact of the production of
  this device?
• Will its production expose workers to hazardous
  conditions?
• Will its production provide workers with an
  opportunity to earn a living wage?
• What is the social impact of the operation of
  this device?
• Is this device likely to be used for purposes
  that will benefit (or harm) society?
• Will your design be broadly accepted (or at least
  tolerated) by society and the political
  leadership representing it?

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Economic Impact

• Questions to consider while completing your
  design
• What are the economic considerations of the
  production of this device?
• Will your company have to purchase and use
  expensive and specialized equipment?
• Will its production be extremely labor-intensive?
• Is your project as inexpensive as possible to
  produce?
• What is the economic impact of the sale and
  operation of this device?
• Will your project be popular enough to make a
  profit for your company? How many people will
  want one?
• Will your project be durable and maintainable
  enough that your company will not have a large
  amount of warranty work?
• What is the economic impact of the end of this
  devices life cycle?
• Will the company be responsible for accepting and
  recycling the project at the end of its life
  cycle?

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Manufacturability

• The traditional way of doing things was to throw
  it over the wall
• This lead to products that were technologically
  impossible or impractical, and designs that were
  impossible or uneconomical to manufacture
• ISO 9000 now requires cross-functional product
  development to integrate these business functions

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Design for Manufacturability

• Simplify design, reduce number of parts
• Reduces product cost opportunity for error
• Cuts purchasing, mfg, handling costs
• Reduces lead times
• Standardize use common partsreduces
  inventories, stocking costs
• Design for ease of fabrication
• Near net shape (investment casting)
• More cast features, instead of machining
• Design parallel clamping surfaces for machining
• Design to use standard cutting tools
• Eliminate transfer of datum Use retained datum
• Single setup machining

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Design for Manufacturability (contd)

• Mistake-proof the process
• Assembly unambiguous
• Assembles one-way
• Use notches, asymmetric holes
• Apply to consumer use also
• Design in verifiability
• Electronic components w/self tests and/or
  diagnostics
• Design for ease of assembly
• Simple movement patterns automation
• Parts w/tapers chamfers

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Design for Manufacturability (contd)

• Design for Orientation
• Design parts so that they feed consistently into
  a process with the same orientation
• Design parts w/guides to facilitate insertion
  assembly
• Design parts that are easily grasped handled
• Avoid extremely large heavy parts, as well as
  very small and/or fragile parts
• Minimize
• Minimize flexible parts interconnections
• Use plug-in boards back planes to minimize wire
  harnesses
• Efficient Joining Fastening
• Threaded fasteners (screws, bolts) are time
  consuming to assemble and disassemble
• Minimize standardize threaded fasteners, and
  use self tapping screws captured washers, when
  possible
• Consider snap-fit fastening

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Design for Manufacturability (contd)

• Modular Products
• Makes assembly easier, sub assemblies can be
  stored.
• A variety of finished goods can be made quickly
• Modules can be manufactured and tested before
  final assembly
• Automation
• Robotic assembly Design parts to utilize 1
  standard gripper.
• Automated assembly Use a minimum of parts or
  standard parts.
• PCBs
• Minimizing component variety,
• Using auto-insertable or placeable components
• Standardizing component packaging