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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.
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