Variant Process Planning Pla nning •
Uses similarity among components to retrieve existing process plans – Standard process plan
•
A process plan that can be used by a family of components is called standard process plan
•
Certain degree of editing of standard plan is usually required to use it for a new component
•
Two Operational Stages Preparatory stage and Production Stage
Part Drawing xxx –xx xxx—xx xxx--xx Coding Family one 1 1 1
1
1
1 1
Family formation ---------------- ------------------------------------------------------ ------------- --------
1 1
Standard plan File (indexed by Family Matrix)
Process plan Fig. 5 The preparatory stage
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xxxxx
Family one Family one 1 1 1 1
Coding
Part Drawing
Family Search Standard plan File
Process Plan ------ ------------- --------
-----xxx------ ---ccc----
Editing
Standard Plan Retrieval Fig. 6 The production Stage
Preparatory Stage •
Involves coding of existing components, part family formation and formation of family matrix, preparation of standard process plan, etc
•
Standard plan is written in terms of OP codes and OP plans (Operation plan) as given in fig. 7.
•
An operation plan contains a sequence of manufacturing operations that are normally performed together in a workstation Operation Code 01 SAW 01 02 LATHE 02
Operation Plan Cut to size Face end Center drill Drill Ream Bore Turn straight Turn groove Chamfer Cutoff Face Chamfer Grind Inspect dimension Inspect finish
03 04
GRIND 05 INSP 06
(a) Operation-plans with OP codes
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01 02 03 04
SAW 01 LATHE 02 GRIND 05 INSP 06
(b) OP-Code Sequence
Fig.7 (a) Operation-plans with OP codes (b) OP-Code Sequence Production Stage •
System is ready for preparation of process plan for new items
•
Involves coding of incoming component, inputting the codes to search routine to find the family to which the item belongs, the retrieval of standard process plan, etc.
•
For a frequently produced part, it might be desirable to perform the search by direct code matching
•
In this case, a process plan for an existing part is retrieved
An example of a variant planning system •
A simplified coding system shown in Table 1 is used
•
The construction sequence of variant planning system is
Ø Family formation Ø Database structure Ø Search algorithm Ø Plan editing Ø Process-parameter selection
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Table 1 - A simplified code system names as S-CODE
0
L D
1 2 3
Digit 1
Digit 2
Digit 3
Digit 4
Primary shape
Secondary shape
Auxiliary shape
No shape element
No shape element
Initial form Round bar
≤
L 0.05< ≤ 3 D L ≥3 D L ≤ 2 with deviation D
l a n o i t a t o R
4
L
5
D Flat
6
7
0.05
l a n o i t a t o r n o N
>
2 with deviation
d n u o r h t i w s p e t S
No shape element
No shape element
Hexagonal bar
With screw thread
With screw thread
Square bar
With functional groove Drill with pattern
Sheet
Two or more from 2-4
Cast or forged
With functional groove Rotational cross section Rectangular cross section
s e l o H
Plate and slabs
Long
Rectangular with chamfer
Stepped plane surface
Welded assembly
Cubic
Hexagonal bar
Curved surface
Square bar
Family Formation •
Component requiring similar processes are grouped into t he same family
•
Coding and classification is used
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Then part-family matrix is created
•
Part-family matrix is a binary matrix similar to the machine part matrix
Construction of Family Matrix •
P ijl - represent a part-family matrix for family l , i = 1, 2… I , where I is the number of attributes in each code position j = 1, 2… J , where J is number of digits (code length)
•
For the S-code, I = 8, and J = 4
•
P ijl
= 1 implies
that, for part family l , code position j is allowed to have a value i
Construction procedure
Let
C jkl be the value of code position j for component k in family l National Institute of Technology Calicut
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k = 1, 2… K , where K is the number of components For k = 1 to K For j = 1 to J
i
= l
P ij
C jkl =1
End do End do An example
Consider the following part family k 1 Part A123 Code 2010
2 3 4 5 6 A120 A131 A432 A451 A112 2110 2110 2120 2130 1110
Construct the part-family matrix. Solution
1 2 3 4 0 1 1 1 1 1 1 2 1 1 3 1 4 5 6 7 The Part-family Matrix Database Structure •
A database is a cross-referenced data files
•
Contains all the necessary information for an application and can be accessed to by different programs for specific application
•
Three approaches to construct a database are Hierarchical, network and relational
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Some of the available database management systems are ORACLE, ACCESS, CODASYL, d BASE, etc
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These systems are high-level language for database construction and manipulation
•
The data hierarchy in the hierarchical approach used for the construction of database for the design of variant system is shown in figure 8
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Family Matrix Name
Family matrix
Standard plan ID
OP Code Sequence
Name Name Name OP Code
Family matrix Family matrix Family matrix OP Plan
OP Plan
Fig. 8 A data hierarchy Search Procedure •
Basic idea of a variant system is to retrieve process plans for similar components
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Search for a process plan is based on the search of a part family to which the component belongs
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A given code may be matched with a family matrix in a family-matrix search
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Let C j be a value of code position j for the given component
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P nl is a pointer for family matrix l , which links to the next family matrix
•
l P s is a pointer for family matrix l , which links to the directory of the standard plan
file •
P ijl is the content of family matrix l ; when it equals 1, code position j is allowed to have a value of i
Algorithm
Step 1. For all l (part family), do step 2. End step. Step 2. For j = 1 to J , do step 3, end, go to step 5. l Step 3. i = C j , if P ij = 1 end step; otherwise,
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l
Step 4. l = P n ; go to step 2. l
Step 5. Standard plan found; P s is the pointer to the standard plan. Terminate process. An Example •
Consider a variant processing planning system shown in figure 9.
•
The coding system in this process planning system is the S-CODE. Consider a new item – mounting bracket shown in figure 10.
•
Its GT code, as per the S-CODE, is 6514.
•
Identify standard plan (OP code) for the component
One
1 1 1 1 1 1 1 1
Two
1 1 1 1 1 1 1 2 0
1 2 1
2
1
2
1
SAW01
LATHE01
2
MILL02
MILL05
3
INSP06
1 1
LATHE02
GRIND05
INSP06
0
DRILL06
GRIND06
INSP06
3
0 Fig. 9 Variant Process Planning System data
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Fig. 10 Component to be planned
Step 1. l = 1 2. j = 1 3. 4. 2. 3.
i = C 1 = 6, P 61,1 = 0
l = P n1
2 , go to 2
=
6, P 6,1
j = 1
i
=
C 1
2
j = 2
3
i = C 2
2
j = 3
3
=
i
=
C 3
=
2
2
5, P 5, 2
= 1 end step = 1 end step
2
= 1, P 1, 3 = 1 end step
2
j = 4
3
i = C 4
2
j = 5 go to step 5
5
next
=
4, P 42,4 2
Plan found P s =
= 1 end step
2
OP Code 1 Mill 02 2 Mill 05 3 Drill 01 4 Grind 06 5 Insp 03 6 Insp 06
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Plan Editing and Parameter Selection •
Before process plan can be released to the shop, some modification of the standard plan is necessary, and process parameters must be added to the plan
Two type plan editing
Ø Editing the standard plan itself in the database Ø Editing of the plan for the component Editing the Standard Plan •
Implies that permanent change in the stored plan be made
•
Affects the process plan generated for the entire family of components
•
The structure of the database must be flexible enough for expansion, and addition and deletion of data records
Editing of the Plan for the Component •
Temporary change and therefore, does not affect any other component in the family
•
Standard plan has to be modified to suit the specific needs of the given component
•
Some operations or entire OP record have to be removed and others must be changed
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Additional operations also may be required to satisfy the design
Selection of Process-parameter •
A complete process plan includes not only operations, but also process parameters
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Process parameters can be found in machining data handbook or can be calculated using optimizing techniques
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First approach is easier and more appropriate for the variant plan system
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The structure of the parameter file is shown in fig. 11
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Consider a mounting bracket shown in figure 10, which requires face-milling operation – MILL02
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Work piece material is cast iron (BHN = 180)
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Depth of cut for roughing is 0.25 and a 0.5-in.-diameter cutter is used
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The velocity and feed parameter of the process can be found out from the figure 11 as 55 and 0.001 respectively
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Such parameter file can be integrated with the variant planning system
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Information such as depth of cut and cutter diameter can be retrieved directly from the OP plan for each operation
•
Same approach can be used for standard time selection also
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Face mill
Steel
s
1 Level Material
Cast iron
Broze
Other n
2 Level Material BHN <200
BHN <150
BHN <220 r
3 Level depth of cut d = 0.25”
d = 0.05” 4t Level Cutter diameter
V = 55
D=1 f = 0.003
D = 0.75 f = 0.002
D = 0.5 f = 0.001
Fig. 11 A process parameter file
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