Using Datums for Economic Process Planning Dr. R. A. Wysk IE550 Fall 2008

Process Planning Single datum planning Multiple datum plans

Process Tolerance Chart Values in Process Tolerance Charts typically represent the BEST attainable values. They also represent single-feature relationships. We refer to these intra- feature process planning. Process Boundary MatricesProcess Boundary Matrices

A 2” piece or bar stock needs to be “faced” so that the required length and surface finish can be obtained A 128 Example #1 - The simplest case; single datum, single feature

Solution: In checking the work piece, datum -A- becomes the reference plan for the length, 4.0. The OD accuracy is obtained at the rolling mill, and no OD turning is required. The length needs to be faced to final dimension

Oper.DescriptionMachineTool 10Retrieve 2’’ BarWarehouse-- 20Cut to 4.25’’ lengthCut-off saw-- 30Face backside (remove 1/8 ‘’ stock) LatheFacing tool 40Flip and face front-sideLatheFacing tool 50Remove and inspect-- Process Plan-Example #1

1.0  A 5 .005 Sort of like Example #1 but with a 2nd feature related to the same datum -A-. Example #2 -- Single datum; 2 features.

Solution: - 4” segment is the same as in Example #1 -Addition segment requires that: -OD is reduced to 1” -Length needs to be reduced to 5 .005

Process Plan for Example #2

A C 12 C 23 C4C4 M 12 M 13 C ij is part specification or Constraints M ij is Manufacturing method were i is the datum feature, and j is the surface produced j is the surface produced The General Case and Notation.

From the part, you can see that C 12  M 12 This reads, “C 12 comes directly from process M 12 (our facing operation).” Also from the drawing, one can see that T  C 23  = T  M 12  + T  M 13  This reads, “the tolerance for feature C 23 can be as large as the sum of the tolerance for producing M 12 and the tolerance for producing M 13 ”  Tolerance Stacking

Notation: subscript m implies minimum M implies maximum C 23m = -M 12M + M 13m Let’s suppose Then T  M 12  =.005 T  C 23  = T  M 12  + T  M 13  T  C 23  = T  M 12  + T  M 13 .010 = T  M 13  T  M 13  =.005

If a negative value results then the process specification is unfeasible Since C 23m = - M 12M + M 13m.995 = M 13m = M 13m  Set the process specifications for M 13 at

.750 .010 All hole features are specified with respect to datums A-B-C and can be treated as intra-feature entities.  Ø.01  C A B M Example #  holes.250 .010  Ø.008  C A B M 2.0 .01 A 111 B 1.5 .01 C Raw Material 4’’ x 2’’ x.5’’

Process Plan for Example #4

Example #5   B .010  .01  C D E M +.25  MAX. 75 D.25±.01A. 5 ±.01 E 2 holes.250 .010  .008  C D E M.50 ±.01 C M 12 M 13 C 23 M 14 M 15.25±.01 Raw Material 4’’ x 2’’ x.5’’

C 12  M 12 T  C 12  = ±.01 T  C 23  = T  M 12  + T  M 13  C 23m = -M 12M + M 13m.008 = M 13m From .518 = M 13m T  C 23  = T  M 12  + T  M 13 .008 =.01 + T  M 13  T  M 13  < 0  infeasible We need to position w.r.t -E-