Using Datums for Economic Process Planning

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Using Datums for Economic Process Planning

• Dr. R. A. Wysk
• IE550
• Fall 2008

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Process Planning

• Single datum planning
• Multiple datum plans

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Process Tolerance Chart

• Process Boundary Matrices

• 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.

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Example 1 - The simplest case single datum,
single feature
A 2 piece or bar stock needs to be faced so
that the required length and surface finish can
be obtained.
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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.
0.005 - 0.0
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Process Plan-Example 1
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Example 2 -- Single datum 2 features.
1.0 ? .005
Sort of like Example 1 but with a 2nd feature
related to the same datum -A-.
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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
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Process Plan for Example 2
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The General Case and Notation.
Cij is part specification or
Constraints Mij is Manufacturing method were i
is the datum feature, and j is the surface
produced
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From the part, you can see that C12 _at_ M12 This
reads, C12 comes directly from process M12 (our
facing operation). Also from the drawing, one
can see that T?C23? T?M12? T?M13? This
reads, the tolerance for feature C23 can be as
large as the sum of the tolerance for producing
M12 and the tolerance for producing M13 ?
Tolerance Stacking
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Notation subscript m implies minimum M
implies maximum C23m -M12M M13m Lets
suppose
Then T?M12? .005 T?C23? T?M12?
T?M13? .010 .005 T?M13? T?M13? .005
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If a negative value results then the process
specification is unfeasible Since C23m - M12M
M13m .995 -4.005 M13m 5.000 M13m ?
Set the process specifications for M13 at
5.000 - 5.005
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.750 ? .010
All hole features are specified with respect to
datums A-B-C and can be treated as intra-feature
entities.
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Process Plan for Example 4
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C12 _at_ M12 T?C12? .01 T?C23? T?M12? T?M13?
C23m -M12M M13m .008 -.51 M13m From
? .518 M13m T?C23? T?M12? T?M13? .008 .01
T?M13? T?M13? lt 0 ? infeasible We need to
position w.r.t -E-