Process Selection / Process planning and solved problem
Process planning / Process selection / Process modification
Process planning is a systematic determination of the methods by which a product is to be manufactured economically and competitively.
While planning for a new component, a sequence of operations with the minimum cost of processing is to be considered. The process sequence is always subject to modification with a view to minimize the cost of manufacturing of that component. So, the objective of process planning is to identify the most economical sequence of operations to produce a component.
The steps in process planning are as follows:
1. Analyze the part drawing to get an overall picture of what is required.
2. Make recommendations to or consult with product engineers on product design changes.
3. List the basic operations required to produce the part to the drawing or specifications.
4. Determine the most practical and economical manufacturing method and the form or tooling required for each operation.
5. Devise the best way to combine the operations and put them in sequence.
6. Specify the gauging required for the process.
Steps 3-5 aim to determine the most practical and economical sequence of operations to produce a component.
Example Problem for process planning
The process planning engineer of a firm listed the sequences of operations as shown in Table to produce a component.
Sequence
Number
|
Process
sequence
|
1
|
Turning - Milling -
Shaping - Drilling
|
2
|
Turning - Milling -
Drilling
|
3
|
All operations are
performed with CNC machine
|
The details of processing times of the component for various operations and their machine hour rates are summarized in the following Table.
Operation
|
Machine hour rate in Rupees
|
Process sequence
|
||
1
|
2
|
3
|
||
Turning
|
200
|
5
|
5
|
-
|
Milling
|
400
|
8
|
14
|
-
|
Shaping
|
350
|
10
|
-
|
-
|
Drilling
|
300
|
3
|
3
|
-
|
CNC
operations
|
1000
|
-
|
-
|
8
|
Find the most economical sequence of operations to manufacture the component.
Solution
(a) Cost of component using process sequence: 1.
The process sequence 1: Turning - Milling - Shaping – Drilling.
The calculations for the cost of the above process sequence are,
Operation
No.
|
Operation
|
Time
|
Machine
hour rate in Rs.
|
Cost
in Rs.
|
|
in
minutes
|
in
hours
|
||||
1
|
Turning
|
5
|
(5/60)
= 0.083
|
200
|
(0.083*200)
=16.60
|
2
|
Milling
|
8
|
(8/60)
= 0.133
|
400
|
(0.133*400)
=53.20
|
3
|
Shaping
|
10
|
(10/60)
= 0.167
|
350
|
(0.167*350)
=58.45
|
4
|
Drilling
|
3
|
(3/60)
= 0.050
|
300
|
(0.050*300)
=15.00
|
Total
Cost
|
143.25
|
||||
(b) Cost of component using process sequence: 2.
The process sequence 2: Turning - Milling - Drilling.
The calculations for the cost of the above process sequence are,
Operation
No.
|
Operation
|
Time
|
Machine
hour rate in Rs.
|
Cost
in Rs.
|
|
in
minutes
|
in
hours
|
||||
1
|
Turning
|
5
|
(5/60)
= 0.083
|
200
|
(0.083*200)
=16.60
|
2
|
Milling
|
14
|
(14/60)
= 0.233
|
400
|
(0.233*400)
=93.20
|
3
|
Drilling
|
3
|
(3/60)
= 0.050
|
300
|
(0.050*300)
=15.00
|
Total
Cost
|
124.80
|
||||
(c) Cost of component using process sequence: 3.
The process sequence 3: All operations are performed with CNC machine
The calculations for the cost of the above process sequence are,
Operation
No.
|
Operation
|
Time
|
Machine
hour rate in Rs.
|
Cost
in Rs.
|
|
in
minutes
|
in
hours
|
||||
1
|
CNC
operations
|
8
|
(8/60)
= 0.133
|
1000
|
(0.133*1000)
= 133
|
Total
Cost
|
133
|
||||
Decision
The process sequence 2 has the least cost. Therefore, it should be selected for manufacturing the component.
