Principles of Joining

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					Sequencing and Fixturing

        32 MFTN 214
        Winter 2011
         Session 03
Fixture or Jig?
   Fixture supports workpiece during
    manufacturing operation
   Jig supports workpiece during
    manufacturing operation and guides
    cutting tool during the same
    manufacturing operation
Like a Game of Chess
   Chess is about a sequence of moves
    that eventually strangles your opponent
   Meanwhile, you must maintain
    defensive strength
   Gotta think ahead, and the further, the
    better
   That‟s why a human can beat Big Blue
Like Sudoku
   Your next play often depends on what
    you already know
   Play n generally requires that you make
    play n-1 first
   Trying to make play n before play n-1
    typically doesn‟t work
Your Opponent Is Mother Nature
   She‟s a tough opponent
   She‟ll exploit every mistake you make
   She has help
       Murphy‟s Law – if something can go wrong, it will
       O‟Toole‟s Corollary – at the most inconvenient
        time and place
   Outsmarting Mother Nature, Murphy, O‟Toole
       Is easier said than done, but you MUST do it
Objectives of Sequencing
   Ensure product quality
   Utilize available equipment/personnel
   Minimize manufacturing time and cost
   Minimize scrap
   Minimize tooling cost
   Maintain safe working conditions
   Optimize usage of raw materials
“What If?” Thinking
   Spreadsheet programs permit user to
    change input values to a series of data
    and calculations, to examine “What if?”
    scenarios
   First spreadsheet was Visicalc, vintage
    about 1980
“What If?” Thinking
   Consider “What if?” you change
    sequence of manufacturing processes
   Don‟t forget about impossible
    combinations – avoid like the plague
   Try to avoid undesirable combinations
Check List of Considerations
   Better than working from first principles
    (This is not a Physics class)
   Maybe I won‟t forget my name today
   Objective is optimum sequence
   Who knows what “optimum” is?
   Acceptable sequence is practical
    alternative
The Sound of Music
Do Re Mi (Rodgers & Hammerstein)
 Let's start at the very beginning
 A very good place to start
 When you read you begin with A-B-C
 When you sing you begin with do-re-mi
 Do-re-mi Do-re-mi
 The first three notes just happen to be
 Do-re-mi Do-re-mi
 Do-re-mi-fa-so-la-ti
An 8-Step Check List
   Do            So (or Sol)
   Re            La
   Mi            Ti
   Fa            Back to Do
Do (a deer, a female deer)
   Understand article to be made
       Intended use
       Drawings
       Quantity to be made
Re (a drop of golden sun)
   Identify each feature of article
   Identify dimensions and properties
    relating to each feature
   Consider candidate manufacturing
    processes for each feature
   Don‟t forget cleaning, finishing, etc.
Mi (a name I call myself)
   Form of raw material
   Forging? Casting? Bar stock? Sheet?
   What will we do with raw material
   Locating part within raw material
Fa (a long, long way to run)
   Fixtures/jigs to support workpieces
   Fixtures must hold workpieces securely
   Select process and fixture for each
    feature
   Select tool(s) for cutting, forming,
    joining, etc.
So (a needle pulling thread)
   Consider various sequences of
    manufacturing processes
   OK to use computer program
   “Show me” that computer produces
    workable sequence
   Don‟t abdicate your responsibility
La (a note to follow sew)
   Don‟t get trapped by impossible
    combinations
   Try to avoid difficult combinations
   Avoid using finished feature to support
    workpiece in subsequent operation
   Common sense is critical in sequencing
   Stay away from La La Land
Ti (I drink with jam and bread)
   Documentation is critical – called
    Operation Sheet
   Hard copy or electronic – whatever
    works
   Get corporate culture to embrace Op
    Sheet 100% of time
   Op Sheet for one-of-a-kind tooling
Do (same note, an octave higher)
   Completed Op Sheet
   Reality check
   Be sure that every attribute of
    completed article is covered by Op
    Sheet
   Experience is the best teacher
Here‟s a Frinstance
   Mistakes in drawing
   More mistakes in Op Sheet
   “Damn the torpedoes! Full speed
    ahead!”
       (Admiral David Farragut, Battle of Mobile
        Bay, 1864)
Part “a”
   (a) Saw cut to length, 3.875 inches
   (b) Mill both ends to 3.75 inches
    length
   (c) Mill 0.75 inch x 45° bevel
   (d) Drill 0.98 hole
Part “a” (cont)
   (e) Debur
   (f) Clean off cutting fluids (hot caustic
    cleaner)
   (g) Vibratory polish
   (h) Clean off polishing media
   (i) Inspect part
Part “b”
   (a)   Shear beveled corner
   (b)   Shear to length, 1.75 inches
   (c)   Vibratory polish
   (d)   Clean off polishing media
   (e)   Inspect part
Part “c”
   (a) Saw cut to length, 4.125 inches
   (b) Mill both ends to 4 inches length
   (c) Drill 4 holes, 0.4 x 0.4 inch from
    each corner
   (d) Drill 2 holes for each plug weld
   (e) Mill slot for each plug weld
Part “c” (cont)
   (f) Debur
   (g) Clean off cutting fluids (hot caustic
    cleaner)
   (h) Vibratory polish
   (i) Clean off polishing media
   (j) Inspect part
Assembly
   (a) Place two parts “a” in welding fixture,
    which contains a feature to ensure that
    beveled corner of each part “a” is properly
    located; place part “c” in welding fixture.
    Note that the welding process is conducted
    upside down, so that plug weld is made from
    bottom of part “c”. Clamp parts into fixture.
   (b) Make SMAW welds to join parts together
   (c) Inspect weldment
Assembly (cont)
   (d) Place welded assembly and two parts “b”
    in fixture. Conduct this welding process right
    side up. Clamp parts into fixture.
   (e) Make SMAW welds to join parts together
   (f) Chip slag from weldment
   (g) Stress relief heat treatment (800°F for 30
    minutes)
Assembly (cont)
   (h) Glass bead blast to remove any
    residual slag and oxide from heat
    treatment; clean beads & slag
   (i) Inspect part
   (j) Horizontal mill bottom of assembly
   (k) Turn part over and horizontal mill
    0.800 inch slot
   (l) Inspect assembly
Assembly (cont)
   (m) Using fixture that aligns part
    relative to datum “A”, ream and debur
    1.0 inch hole
   (n) Clean off cutting fluids (hot caustic
    cleaner)
   (o) Vibratory polish
   (p) Clean off polishing media
   (q) Inspect part
Assembly (cont)
   (r) Apply rust preventative oil to part
   (s) Pack for shipping

   Who said that life is simple and
    beautiful?
   Sequencing is a tough, but absolutely
    necessary job
Assembly (cont)
   Murphy and Mother Nature are lurking
    in the weeds at every step in the
    process
   They will happily mess you up
   Don‟t let „em
Homework Assignment 03
Homework Assignment 03
There are several errors and omissions in this drawing, as follows:
(1)   The principal (upper) view is not to scale, with respect to length; there should
      have been a “cut” symbol indicating that a portion of the center section of the
      part was omitted in drawing;
(2)   The diameter of most of the length of the part (shown in View B-B) cannot be
      the same as the diameter of the shoulder; assume that the correct diameter is
      1.180 inch;
(3)   The depth of the groove shown in View A-A is probably greater than 0.030
      inch; assume that the correct depth is 0.300 inch;
(4)   There is no angular dimension indicating the position of the features shown in
      View A-A relative to the flat shown in View B-B and the principal view; assume
      that the slot is located at a 45° angle to the vertical and horizontal axes of
      View A-A; also assume that the four tapped holes are located on the vertical
      and horizontal axes, on a circle having a diameter of 0.950 inch; and
(5)   No dimensional tolerances are given.