The Explosion Calculus
n
MRP processing at one level:
Gross requirements at one level of product
structure are translated into production schedule
(planned order release) at that level.
n
Explosion into lower levels:
Planned Order Release (POR) quantities at one
level of product structure are translated into
gross requirements at lower levels.
1
MRP – Example
n
You are producing skateboards, and each
consists of one unit of board, and two units
of subassembly of roller-set. Roller-sets
are produced inside the plant, and consist
of two components rollers and axles.
Prepare the MRP tables of all items.
2
1
Skateboard assembly
Material
Inventory
3
Product Structure /
Bill-of-matreial (BOM)
Item A: Skateboard
Material
Inventory
Item B: Board
Item C: Roller-set
Item D: Roller
Item E: Axle
4
2
Bill of Material (BOM)
Parent of B and C
A
Level 0
Components of A
B[1]
C[2]
Level 1
D[2]
2 units of C, and 1
unit of B to make 1
unit of A
E[1]
Level 2
2 units of D, and 1
unit of E to make 1
unit of C
5
Master Production Schedule
Week
A
D
1
2
3
Item
Lead time (weeks)
4
5
6
50
7
40
A
1
8
9
10
80
60
B
2
C
1
D
3
E
2
6
3
Inventory Master Parts File
Item
A
Current inventory levels 10
Lot size
L4L
Material
Inventory
B
C
20 50
100 L4L
Work-in-process
Inventory
D
30
200
E
20
150
Finished good
Inventory
7
Open Orders Data
Scheduled Receipts (Due Dates)
ITEM / WEEKS 1 2 3 4 5 6 7
A
B
20
C
90
D
40
E
8
9
8
4
MRP table for item A
WEEKS 1 2 3 4 5
GR
SR
PIB
10 10 10 10 10
NR
PR
POR
40
6 7
50
8 9 10
80
0 0
40
40
0 0
0
80
80
80
9
MRP table for item B
WEEKS 1 2
GR
SR
PIB
NR
3
4 5 6
40
20
20 20 40 40 0 0
7
8
9
80
0
0
20
80
100
PR
POR
100
10
5
MRP table for item C
WEEKS 1 2
3
4 5
GR
80
SR
90
PIB
50 140 140 140 60
NR
PR
POR
6
7
8
9
160
60 60
60
0
100
100
100
11
MRP table for item D
WEEKS 1
GR
SR
PIB
NR
PR
POR
2
3
4
40
5
6
7
8 9
260
40
30 30 70 30 30 30 30 170 170
230
400
400
12
6
MRP table for item E
WEEKS 1
2
3
4 5
6
7
GR
SR
PIB
NR
PR
POR
8 9
100
20 20 20 20 20 20 20 70 70
80
150
150
13
MRP Outputs
Planned Orders (Release Dates)
ITEM / WEEKS 1 2 3 4
5
6
7
A
40
B
100
C
D
E
8
9
80
100
400
150
14
7
Capacity Requirement Planning to
validate MRP
Planned Order Quantity Released at a
given period may exceed the available
capacity at that period.
n Therefore POR quantities must be valid for
shop capacity.
n
15
Example for CRP
Item :
Week
POR
C
1
0
2 3 4
5
60 20 150 0
Processing
time = 0.3 hours /unit
Item: D
Week 1 2 3 4
5
POR 70 30 50 100 120
Processing
time = 0.25 hours /unit
They are produced in the same workstation:
runs 8 hours /day and 5 days /week.
16
8
Capacity Requirements
Week
POR (C)
Process time
POR (D)
Process time
Capacity Req.
Capacity
Excess capacity
Capacity shortage
1
0
0.3
70
0.25
17.5
40
22.5
0
40 – 17.5 = 22.5 hours
2
60
0.3
30
0.25
25.5
40
14.5
0
3
20
0.3
50
0.25
18.5
40
21.5
0
4
150
0.3
100
0.25
70
40
0
30
5
0
0.3
120
0.25
30
40
10
0
6
0
0.3
0
0.25
0
40
40
0
0 x 0.3 + 70 x 0.3 = 17.5 hours
17
CRP
Capacity Req.
Capacity
17.5
40
25.5
40
18.5
40
70
40
30
40
0
40
18
9
Shifting lot to previous periods with excess
capacity
19
Splitting lot into two or more periods
20
10