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Using Datums for Economic Process Planning. Dr. R. A. Wysk ISE789 Spring 2011. Process Planning . Single datum planning Multiple datum plans. Process Boundary Matrices. Process Tolerance Chart.

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using datums for economic process planning
Using Datums for Economic Process Planning

Dr. R. A. Wysk

ISE789

Spring 2011

process planning
Process Planning
  • Single datum planning
  • Multiple datum plans
process tolerance chart

Process Boundary Matrices

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.

slide4

+ .005

- .0

4.0

+ .005

- .005

2.0

128

A

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.

slide7

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

slide8

Oper.

Description

Machine

Tool

10

Retrieve 2’’ Bar

Warehouse

--

20

Cut to 4.25’’ length

Cut-off saw

--

30

Face backside (remove

Lathe

Facing tool

1/8 ‘’ stock)

40

Flip and face front-side

Lathe

Facing tool

50

Remove and inspect

--

--

Process Plan-Example #1

slide9

5  .005

+ .005

- 0

4

+ 0.01

- 0

2.0

A

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-.

slide10

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

slide12

C23

C12

C4

M12

M13

A

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

slide13

From the part, you can see that

C12 @ 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

slide14

Notation: subscript m implies minimum

M implies maximum

C23m = -M12M+ M13m

Let’s suppose

Then

TM12 = .005

TC23 = TM12 + TM13

.010 = .005 + TM13

TM13 = .005

slide15

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 M13at 5.000 - 5.005

slide16

Example #4

4 .008

2 holes

.250  .010

 Ø .008 C A B

M

+

+

+

2.0  .01

1

B

1

1

1

Raw Material 4’’ x 2’’ x .5’’

A

M

 Ø .01  C A B

.5  .01

C

.750  .010

All hole features are specified with respect to datums A-B-C and can be treated as intra-feature entities.

slide18

Example #5

.750  .010

.250  .010

B

  .008 C D E

  .01  C D E

M

M

.5

1

1

.25  MAX

+

.75

D

.25± .01

A

.5 ± .01

2 holes

E

.25±.01

.50 ±.01

C

C23

M12

Raw Material 4’’ x 2’’ x .5’’

M13

M14

M15

slide19

C12@ 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 < 0  infeasible

We need to position w.r.t -E-

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