Design for Manufacture and Assembly DFMA

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Design for Manufacture and Assembly (DFMA)

• ME 183
• September 12, 2005

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What is DFMA?

• Common sense rules can be applied to improve a
  design
• Improve reduce cost, increase reliability,
  increase quality
• Design
• Transformation of concepts and ideas into useful
  machinery
• Multidisciplinary
• Many considerations in the design process
• Safety
• What else?

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What is DFMA?

• Manufacture
• Act of creating designed parts
• Feasible within constraints of tools/skills
• Stable solutions - Tolerances
• Cost
• Durability
• Clarity of design drawings

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What is DFMA?

• Assembly
• Act of taking individually created parts and
  putting them together into a working machine
• Labor money
• Easy access to replaceable (disposable) parts
• idiot proof
• Making small adjustments can improve quality and
  reliability of parts

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Tools of DFMA

• Concurrent Engineering
• Design and manufacturing engineers working
  together!
• 2) Reducing the number of parts
• During operation, does the part move relative to
  all the other parts?
• Different material?
• Isolated from other assembled parts?
• 3) Design efficiency
• Theoretical min of parts min assembly
  time for each part
• estimated actual assembly time

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Tools of DFMA

• 4) Selection of Manufacturing Processes
• Casting
• Molding
• Machining (from stock)
• Sheetmetal stamp/bend
• 5) Selection of Material
• Functionality
• Compatibility between processes and materials

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Tools of DFMA

• 6) Guidelines for Part Handling
• Symmetry
• if asymmetric, the OBVIOUSLY asymmetric
• Non-tangling parts
• Distinguish parts that are shaped similarly
  through non-geometrical means
• Color coding, numbering, etc
• Prevent nesting
• Design parts with orientating geometries

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Tools of DMFA

• Guidelines for insertion and fastening
• Parts need to be easy to insert
• Add chamfers, generous clearances
• Standardize parts
• Provide alignment features
• Pyramid assembly assemble about one axis
• At least reduce reorientation as much as possible
• Make fasteners easy to reach (as few as possible)
• Fasteners in order of cost (least to most
  expensive)
• Snap
• Plastic bending
• Riveting
• Screws

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Quality

• Quality Taguchi philosophy (Robust Design)
• Customer based
• Based on WE Demings observation that 85 of poor
  quality is attributable to manufacturing, 15 to
  the worker
• Should be designed into the product, not
  inspected into it
• Best achieved by minimizing the deviation from a
  target
• Cost should then be the deviation from a target
• Total loss function Quality is the total loss
  imparted to society from the time a product is
  shipped to the customer

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Reliability

• NASA
• Motorolla
• Computer aided analysis (CAE)
• Design for working environment
• Fault tree analysis
• Failure modes of parts

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• What does this mean to us NOW?
• ASME Contest Goals
• design and demonstrate a well-tested,
  cost-effective, and reliable prototype apparatus
  .
• brief description of the device that is suitable
  for posting on the web.  The description should
  allow a moderately skilled mechanic or technician
  to build the device 
• Drill dissection lab
• Analyze a cordless drill, look for examples of
  DFMA

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Drill Dissection

• Groups will disassemble a Sears Drill
• Look for examples of DFMA
• Analyze working components
• Analyze the gear box, clutch assembly
• The organizing committee strongly recommends
  teams consider the use of a battery-powered
  drill.provides a variable speed motor and
  gear-box with lots of torque, a means for
  limiting motor torque output, and a rechargeable
  battery with a charger, all for a reasonable
  cost, and it is easily available to our "skilled
  mechanic or technician

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Gear Box

• Types
• simple gear train
• External or internal mesh
• compound gear trains
• Planetary gear trains
• (also known as epicyclic gear trains)

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Planetary Gear Train
?i angular velocity of body I Ni number of
gear teeth on gear i
Arm (a)
Sun (s)
Ring (r)
Planet (p)
Why negative?
Refer to any machine component text