Hernan Joglar 2.875 Mechanical Assembly

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2.875 Mechanical Assembly and its Role in Product
Development
Pencil Sharpener Project Report No 3 November 14,
2001
Hernan Joglar John Sharkey
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Part list
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(No Transcript)
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Figure 2. Details of contacts and features in
gearbox cover
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Figure 3. Details of contacts and features in
battery compartment housing
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Pencil Sharpener Indentured Parts List
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Product Structure of Pencil Sharpener
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Part Liaisons and Mates in Pencil Sharpener
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Part Liaisons and Mates in Pencil Sharpener
(cont.)
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Pencil Sharpener Liaison Diagram and Fasteners
Classification
c24
p12
c26
p14
c6
p11
p13
c25
C37
p6
c15
c22
c3
c23
c1
p4
p7
p5
p10
p20
c5
c2
p9
p8
c13
c18
c31
c4
p2
p27
c20
c17
c14
p29
c21
p28
c12
c7
c10
p21
c16
c34
p24
c19
p26
c32
p23
p25
c8
c35
p15
c11
c9
p18
c33
Liaisons Using Threaded Features Screws
Nut Bolt Other mates

c29
Permanent Liaisons Rivets
Adhesive Soldering
c27
c30
p17
p16
c28
C36
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Assembly Choreography (Gross and fine motions,
features where parts are gripped and mated,
lead-ins, and auxiliary operations)

• Create the Gearbox Cover Subassembly (sa6)
• Solder the red wire (part 24) to the input
  contact.
• Solder the blue wire (part 25) to the output
  contact.
• Rivet gearbox cover contacts to the gearbox cover
  (parts 23 and 26)
•  
• Create the Cutter Unit Subassembly (sa7)
• Place the blade holder on a flat surface.
• Put the blade on the blade holder with the cutter
  edge facing the slot. The blade should fit into
  the space provided between the prongs so that the
  hole in the blade gets aligned with the one in
  the blade holder.
• Insert the bolt through the aligned holes. The
  bolt must be held with one finger while the nut
  is grabbed with a tool and screwed from the other
  side.
• For final tightening, hold the bolt with a
  Phillips head screwdriver while the nut is
  tightened on the other side.

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• 3. Create the Battery Compartment Subassembly
  (sa4)
• Rivet the contacts (part 12) to the battery
  compartment housing (part 11).
• Install the battery installation paper guide
  inside the battery compartment. The drawings must
  face the interior the blank face should be at
  the side where the in/out contacts are and the
  tabs must be folded to each side on top of the
  battery compartment so that they are pressed
  between the battery compartment housing and the
  sharpener base (part 5)once the latter is
  installed.
• 4. Create Motor/Gearbox Subassembly (sa5)
• Place the gearbox housing (part 15) on a flat
  surface with the gear compartment facing up.
• Grab the output gear (part 16) from end of its
  shaft where the peg is not squared. Insert the
  other end of the shaft in its hole in the gearbox
  housing so that the squared peg goes into the
  hole.
• Take the intermediate gear (part 17) by the input
  pinion teeth and insert it in the intermediate
  gear pin that is attached to the gearbox so that
  the output pinion faces down. Rotate the
  intermediate gear to ensure proper gear mesh.
• Repeat this last operation with the driven gear
  (part 18).
• Place lubrication (part 22) on all parts inside
  the gearbox.

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f. Insert the safety lever (part 21) on its
pin in the gearbox housing. The safety lever must
be placed with its prong facing up. This prong
must stay outside the gearbox cover when that
part is installed therefore it is important at
this point to observe that lever positioning
allows the right location of the prong. g.
Place the gearbox cover (sa 6) on top of the
gearbox housing. This is a difficult mate for two
reasons                          i. The safety
lever must be held so that it doesnt rotate
about its pin. ii.  The ends of the blue
and red wires must stay outside the gearbox.
In order to circumvent the above difficulties,
the gearbox housing must be held with one hand
with the thumb finger holding the safety lever so
that it doesnt rotate. Then, the gearbox cover
must be grabbed with the other hand while
pressing the wires against the edges at the
corresponding sides of the cover. It is very
important for appropriate electrical connection
that the wires come out the gearbox at the same
side where their corresponding contacts are.
Subsequently, the cover should be installed on
the gearbox by first making coincide the edges of
both parts located at the end opposite to where
the motor is. Once the cover is installed, the
wires must be slid around the edges until they
reach the squared holes that will be left for
them to come out at both sides of the Motor/Gear
Subassembly.
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• h. Press the gearbox cover against the gearbox to
  make both parts fit and to enable the
  intermediate electrical contact to store the
  tension that will let it keep pressing the output
  gear.
• Install the self threaded screw that attaches the
  gearbox cover to the gearbox (part 19).
• j. Turn the gear housing upside down so that the
  cover is at the bottom and in contact with a flat
  surface.
• Take the Cutter Unit Subassembly and insert the
  square hole in the blade holder on the square peg
  in the output gear shaft.
• l. Test the circuit inside the gearbox by
  connecting the blue and red wires to a circuit
  tester while pressing the safety lever and the
  cutter unit. The instrument should indicate that
  the circuit is closed.
• m. Solder the black wire (part 14) to the
  electric motor () terminal (part 20).
• Solder the blue wire (part 25) to the electric
  motor (-) terminal.
• Insert the electric motor in its compartment in
  the gearbox housing. Rotate the motor until it
  fits the motor location pegs. The negative
  terminal must be placed at the same side where
  the blue cable is coming out the gearbox housing.
  When that is accomplished, the motor will not
  rotate any more. Its rim will then be inserted in
  the motor location hole and the motor gear will
  engage the driven gear inside the gearbox.
• p. Test the gear engagement by rotating the
  cutter unit and listening to the noise of the
  motor rotating.
• Note the motor fixture described in DFC Project
  Report 2 has been deleted in the above
  sequence.

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• 5. Create the Battery Compartment Cover
  Subassembly (sa3)
• Rivet the contacts (Part 8) on the battery
  compartment cover (part 9).
• Using an adhesive, place the rubber foot (part
  10) on the battery compartment cover.
• 6. Create the Base Subassembly (sa2)
• Using an adhesive, place the rubber foot (part 6)
  on the sharpener base (part 5).
• Attach the battery compartment cover subassembly
  to the sharpener base. First insert the rims on
  the battery compartment cover in the
  corresponding slot on the sharpener base. Then
  press both parts against each other on the
  opposite end until the snap fit attaches both
  parts together.
• 7. Complete assembly (sa1)
• Grab the battery compartment housing, turn it
  upside down and place it on the gear/motor
  subassembly. The rims on the battery compartment
  housing must be slid inside the slots provided at
  both sides of the gearbox housing. When in its
  correct position, the circular rim in the battery
  compartment housing is inserted in the circular
  slot in the bottom of the electric motor.
• Solder the black wire to the in/out contact in
  the battery compartment housing that is located
  at the same side as the safety lever.
• Solder the red wire to the remaining in/out
  contact in the battery compartment.

 

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d. Grab the sharpener case (part 7) in one hand
and, with the other one, place inside it the
Battery Compartment Subassembly (sa 4) and the
Motor/Gearbox Subassembly (sa 5), so that the
rims in the sharpener case fit the slots in the
battery compartment housing and the holes in both
parts become aligned. To perform this action
prongs are provided in the interior of the
sharpener case and the outside of the gearbox
housing. These prongs must slide against each
other as the insertion is performed in order for
the assembly to be accomplished. e. Using a
magnetic Phillips head screwdriver insert the
battery compartment self threaded screw (part 3)
in the aligned hole and tighten it. f. Install
the Base Subassembly so that both of its
cylindrical screw guides are inserted in the
spaces provided on both sides of the gearbox
housing. Once these guides reach their position
they act as holes and mate with pegs at the
opposite side of the sharpener case. This mate
allows for the holes in the interior of both of
the above features to become aligned. Similarly,
the above mate allows the insertion of the rim on
the edges of the in the slot on the edges of the
sharpener case.
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• g. Place and tighten the two self threaded screws
  that attach the base to the sharpener case.
• h. Place and tighten the two self threaded screws
  that attach the base to the battery compartment
  housing using a Phillips head screwdriver.
• i. Grab the pencil guide (part 2) with the
  chamfered rim for pencil guidance facing up.
  Press the cutter unit down to allow room for the
  pencil guide to be inserted in the slot between
  the sharpener case and the gearbox housing. The
  slot in the interior of the sharpener case must
  fit the rim in the upper surface of the pencil
  guide. Release the cutter unit to allow for its
  circular rim to fit in the hole at the bottom
  surface of the pencil guide.
• j. Place the Shavings receptacle by inserting one
  of the lateral slots on the sharpener case in one
  of the lateral slots in the receptacle and press
  on the opposite side to make the snap fit attach
  both parts together.

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Potential Problems and Risk Areas

• Description Probability Impact
• Reversed motor polarity wiring (black on )
  High High
• Reversed battery compartment wiring
  High High
• Solder joint or wire breakage during gearbox
  insertion Low High
• Solder joint or wire breakage during motor
  insertion Low High
• Motor pinion clearance thru gearbox hole
  High Med
• Loss of motor location during final assembly
  High Med
• Improper location of battery compartment on
  gearbox Med Med
• Part damage from shaver receptacle insertion
  (snap fit) Med Med

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Suggested Design Improvements

• Description Impact
• Reversed motor polarity wiring (black on )
• - Use wire connector instead of solder
  joint Med
• Reversed battery compartment wiring (red on
  right)
• - Imprint wiring polarity on battery compartment
  injection mold High
• Solder joint or wire breakage during gearbox
  insertion
• - Use wire connector instead of solder joint
  Med
• Solder joint or wire breakage during motor
  insertion
• - Use wire connector instead of solder joint
  Med
• Motor pinion clearance thru gearbox hole
• - Reduce and control gearbox manufacturing
  variance Med
• Loss of motor location during final assembly
• - Include snap/fit feature between battery
  compartment and gearbox High
• Improper location of battery compartment on
  gearbox
• - Use wire connectors instead of solder joint
  Med
• Part damage during shaver receptacle insertion
  (snap fit)
• - Training, coupled with control of manufacturing
  variations Low

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Fixtures and Special Tooling

• Fixtures
• Riveting fixture. or special tooling, for battery
  compartment
• Riveting fixture, or special tooling, for gearbox
  cover
• Bending fixture for gearbox cover electrical
  contacts
• Bending fixture for battery cover electrical
  contacts
• Bending fixture for battery compartment
  electrical contacts (nice to have)
• Soldering station and fixture for electric motor
  (black and blue leads)
• Soldering station and fixture for battery
  compartment (black and red leads)
• Standard Tools and Special Tooling
• Heat stake tooling for battery compartment
  electrical contacts
• Magnetic Phillips head screwdriver (4 length)
  for battery compartment screw
• Small wrench, or pliers, for blade screw and nut
• Wire strippers (22 gage)
• Wire tinning and pre-form bending
• Soldering station for gearbox cover
• Electrical test station for operation of
  motor/gearbox sub-assembly
• Lubrication dispenser gun

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Assembly Time Analysis

• Throughput requirement based on production volume
• 250,000 units/year _at_ 250 workdays/year 1000
  units/day
• 1000 units/day _at_ 8 hours/day 125 units/hour
  2.08 mins/unit
• Assembly time per Boothroyd Handling and
  Insertion Times
• Handling Time per unit 105.48 (sec/unit)
• Location Time per unit 47.50 (sec/unit)
• Reversible Fastening Time per unit 54.20
  (sec/unit)
• Irreversible Fastening Time per unit 121.00
  (sec/unit)
• Total predicted assembly time 328.18 (sec/unit)
• Note does not include inspection and test time
• Measured Handling, Location and Reversible
  Fastening Times
• Test1 309 sec
• Test2 222 sec
• Assembly Efficiency
• Three un-necessary parts Sharpener case, paper
  guide, and pencil guide

207.18 (sec)
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Example Assembly Process
Note Test, inspection and packaging times are
SWAGS
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Part Handling Gross Motion
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Part Handling Gross Motion (cont)
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Part Insertion Fine Motion
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Part Insertion Fine Motion (cont)