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Design%20for%20Manufacturing%20and%20Assembly

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Design for Manufacturing and Assembly Design for manufacturing (DFM) is design based on minimizing the cost of production and/or time to market for a product, while ... – PowerPoint PPT presentation

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Title: Design%20for%20Manufacturing%20and%20Assembly


1
Design for Manufacturing and Assembly
  • Design for manufacturing (DFM) is design based on
    minimizing the cost of production and/or time to
    market for a product, while maintaining an
    appropriate level of quality. The strategy in DFM
    involves minimizing the number of parts in a
    product and selecting the appropriate
    manufacturing process.
  • Design For Assembly (DFA) involves making
    attachment directions and methods simpler.

2
DFM and DFA Benefits
  • It reduces part count thereby reducing cost. If a
    design is easier to produce and assemble, it can
    be done in less time, so it is less expensive.
    Design for manufacturing and assembly should be
    used for that reason if no other.

It increases reliability, because if the
production process is simplified, then there is
less opportunity for errors.
It generally increases the quality of the product
for the same reason as why it increases the
reliability.
3
DFM and DFA
  • DFM and DFA starts with the formation of the
    design team which tends to be multi-disciplinary,
    including engineers, manufacturing managers, cost
    accountants, and marketing and sales
    professionals.
  • The most basic approach to design for
    manufacturing and assembly is to apply design
    guidelines.
  • You should use design guidelines with an
    understanding of design goals. Make sure that the
    application of a guideline improves the design
    concept on those goal.

4
DFM and DFA Design Guidelines
  • Minimize part count by incorporating multiple
    functions into single parts. Several parts could
    be fabricated by using different manufacturing
    processes (sheet metal forming, injection
    molding). Ask yourself if a part function can be
    performed by a neighboring part.

5
DFM and DFA Design Guidelines
  • Modularize multiple parts into single
    sub-assemblies.

6
DFM and DFA Design Guidelines
  • Design to allow assembly in open spaces, not
    confined spaces. Do not bury important components.

7
DFM and DFA Design Guidelines
  • Parts should easily indicate orientation for
    insertion. Parts should have self-locking
    features so that the precise alignment during
    assembly is not required. Or, provide marks
    (indentation) to make orientation easier.

8
DFM and DFA Design Guidelines
  • Standardize parts to reduce variety.

9
DFM and DFA Design Guidelines
  • Design parts so they do not tangle or stick to
    each other.

10
DFM and DFA Design Guidelines
  • Distinguish different parts that are shaped
    similarly by non-geometric means, such as color
    coding.

11
DFM and DFA Design Guidelines
  • Design parts to prevent nesting. Nesting is when
    parts are stacked on top of one another clamp to
    one another, for example, cups and coffee lids

12
DFM and DFA Design Guidelines
  • Design parts with orienting features to make
    alignment easier.

13
DFM and DFA Design Guidelines
  • Provide alignment features on the assembly so
    parts are easily oriented.

14
DFM and DFA Design Guidelines
  • Design the mating parts for easy insertion.
    Provide allowance on each part to compensate for
    variation in part dimensions.

15
DFM and DFA Design Guidelines
  • Design the first part large and wide to be stable
    and then assemble the smaller parts on top of it
    sequentially.

16
DFM and DFA Design Guidelines
  • If you cannot assemble parts from the top down
    exclusively, then minimize the number of
    insertion direction. Never require the assembly
    to be turned over.

17
DFM and DFA Design Guidelines
  • Joining parts can be done with fasteners (screws,
    nuts and bolts, rivets), snap fits, welds or
    adhesives.

18
DFM and DFA Design Guidelines
19
Minimizing the Number of Parts
To determine whether it is possible to combine
neighboring parts, ask yourself the following
questions
  • Must the parts move relative to each other?
  • Must the parts be electrically or thermally
    insulated?
  • Must the parts be made of different material?
  • Does combing the parts interfere with assembly of
    other parts?
  • Will servicing be adversely affected?

If the answer to all questions is NO, you
should find a way to combine the parts.
20
Minimizing the Number of Parts
  • The concept of the theoretical minimum number of
    parts was originally proposed by Boothroyd
    (1982). During the assembly of the product,
    generally a part is required only when
  • A kinematic motion of the part is required.
  • A different material is required.
  • Assembly of other parts would otherwise be
    prevented.
  • If non of these statements are true, then the
    part is not needed to be a separate entity.

KISS Keep It Simple Stupid
21
DFM Design Guidelines
Another aspect of design for manufacturing is to
make each part easy to produce. The up to date
DFM guidelines for different processes should be
obtained from production engineer knowledgeable
about the process. The manufacturing processes
are constantly refined.
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DFM Design GuidelinesInjection Molding
Fabrication of Plastics
Injection Molding
43
DFM Design GuidelinesInjection Molding
Provide adequate draft angle for easier mold
removal.
Minimize section thickness, cooling time is
proportional to the square of the thickness,
reduce cost by reducing the cooling time.
44
DFM Design GuidelinesInjection Molding
Keep rib thickness less than 60 of the part
thickness in order to prevent voids and sinks.
45
DFM Design GuidelinesInjection Molding
Provide smooth transition, avoid changes in
thickness when possible.
46
DFM Design GuidelinesInjection Molding
  • Use standard general tolerances, do not
    tolerance
  • Dimension Tolerance Dimension Tolerance
  • 0 d 25 0.5 mm 0 d 1.0 0.02
    inch
  • 25 d 125 0.8 mm 1 d 5.0 0.03
    inch
  • 125 d 300 1.0 mm 5 d 12.0 0.04
    inch
  • 300 1.5 mm 12.0
    0.05 inch
  • Minimum thickness recommended
  • .025 inch or .65 mm, up to .125 for large
    parts.
  • Round interior and exterior corners to .01-.015
    in radius (min.), prevents an edge from chipping.

47
DFM Design GuidelinesRotational Molding
Rotational molding process consists of six steps
  • A predetermined amount of plastic, powder or
    liquid form, is deposited in one half of a mold.
  • The mold is closed.
  • The mold is rotated biaxially inside an oven.
  • The plastics melts and forms a coating over the
    inside surface of the mold.
  • The mold is removed from the oven and cooled.
  • The part is removed from the mold.

48
Rotational Molding Machines
Vertical wheel machine
49
Rotational Molding
Advantages
  • Molds are relatively inexpensive.
  • Rotational molding machines are much less
    expensive than other type of plastic processing
    equipment.
  • Different parts can be molded at the same time.
  • Very large hollow parts can be made.
  • Parts are stress free.
  • Very little scrap is produced

50
Rotational Molding
Limitations
  • Can not make parts with tight tolerance.
  • Large flat surfaces are difficult to achieve.
  • Molding cycles are long (10-20 min.)

51
Rotational Molding
Nominal wall thickness
  • Polycarbonate wall thickness is typically between
    .06 to .375 inches, .125 inch being an ideal
    thickness.
  • Polyethylene wall thickness is in the range of
    .125 to .25 inch, up to 1 inch thick wall is
    possible.
  • Nylon wall thickness is in the range of .06 to
    .75 inch.

52
Rotational Molding Examples
53
Rotational Molding Examples
54
DFM Design GuidelinesSheet-metal Forming
55
DFM Design GuidelinesSheet-metal Forming
56
DFM Design GuidelinesSheet-metal Forming
57
DFM Design Guidelines - Casting
Casting, one of the oldest manufacturing
processes, dates back to 4000 B.C. when copper
arrowheads were made.
Casting processes basically involve the
introduction of a molten metal into a mold
cavity, where upon solidification, the metal
takes on the shape of the mold cavity.
  • Simple and complicated shapes can be made from
    any metal that can be melted.
  • Example of cast parts frames, structural parts,
    machine components, engine blocks, valves, pipes,
    statues, ornamental artifacts..
  • Casting sizes range form few mm (teeth of a
    zipper) to 10 m (propellers of ocean liners).

58
Casting Processes
  1. Preparing a mold cavity of the desired shape with
    proper allowance for shrinkage.
  2. Melting the metal with acceptable quality and
    temp.
  3. Pouring the metal into the cavity and providing
    means for the escape of air or gases.
  4. Solidification process, must be properly designed
    and controlled to avoid defects.
  5. Mold removal.
  6. Finishing, cleaning and inspection operations.

59
Sand Casting Terminology
60
Casting Defects
Hot spots thick sections cool slower than other
sections causing abnormal shrinkage. Defects such
as voids, cracks and porosity are created.
61
Casting Defects and Design Consideration
62
DFM Design Guidelines - Casting
Recommended minimum section thickness
63
DFM Design Guidelines - Casting
64
DFM Design Guidelines Machining
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