Session 11
Multi-Level Bill of Material
Explosion
http://www.pom.edu/mpc/lectures_in_manufacturing_planning.htm
lecture session 11
• Product Structure Diagrams
• Multi-Level Bill of Material Explosion:
Linking MRP Records
• Front and Back Loaded Schedules
• Lead Time Offsetting
• Technical Issues
1
Product Structure Example: P301
Computer
Memory board (M)
Assemble 4 RAM chips and
1 switch (S) onto a board
type (X).
Arithmetic board (A)
Assemble 1 integrated
microprocessor (Z) with 2
ROM chips and 1 switch
(S) onto a board type (Y).
M
A
2
Product Structure Example: P301
Computer (Continued)
Processor unit (P)
Working from back to front of the
box casing (B), assemble one
switch (S) to the inside of each
of the 4 plug connections at the
back of the box. Then fit 4
memory boards (M) into the 4
identical rows of connectors.
Finally, fit the arithmetic board
(A) into the front connector
row.
3
Product Structure Example: P301
Computer (Continued)
Final Assembly
The video unit (V) and the
keyboard unit (K) have been
preassembled (with connecting
cables). Simply connect the
sockets on the end of their
cables to the corresponding
plugs at the rear of the
processor unit (P). The
computer is now ready to use.
P
V
K
4
Product Structure Example: P301
Computer (Continued)
a.
b.
c.
Draw the product structure tree according to the assembly
directions.
Determine low-level codes for each product.
Assume no inventory of any item. How many of each part
should be available to assemble one completed unit?
5
Product Structure Diagram
P301 Computer
a.
6
Product Structure Diagram
P301 Computer (Continued)
b., c.
Item
Low-Level Code
Quantity Required for One Unit*
A – Arithmetic Board
2
1
B – Box Casing
2
1
C – Ram Chip
3
16
K – Keyboard Unit
1
1
M – Memory Board
2
4
P – Processor Unit
1
1
R – ROM Chip
3
2
S – Switch
3
9
V – Video Unit
1
1
X – Board Type X
3
4
Y – Board Type Y
3
1
Z - Microprocessor
3
1
*Assuming no inventory for any item
7
Product Structure Diagram
P301 Computer
a.
8
Linking MRP Records: Examples
The Big B Bike and Trike Shop produces two basic bikes
called A and B. Each period, Paul, the owner. plans to
assemble 10 A bikes and 5 B bikes. Given this information
and the following product structure diagrams for A and B,
fill out the MRP records for component parts G and Y for
the next seven periods.
9
Linking MRP Records: Examples
(Continued)
10
Linking MRP Records: Examples
(Continued)
MPS
Part G
Gross Requirements
Scheduled receipts
Projected available balance 0
Planned Order Release
Q = lot for lot; LT = 1; SS = 0
Part Y
Gross Requirements
Scheduled receipts
Projected available balance 28
Planned Order Release
Q = lot for lot; LT = 2; SS = 0
1
5
7
1
10
10
2
5
Period
3
4
5
5
5
5
2
10
Period
3
4
5
10 10 10
Bike B: 5 u/period
6
5
7
5
Bike A: 10 u/period
6
10
7
10
11
Linking MRP Records: Problem 8 Part a
Part G
Gross Requirements
Scheduled receipts
Projected available balance
Planned Order Release
Q = LFL; LT = 1; SS = 0
0
Part Y
Gross Requirements
Scheduled receipts
Projected available balance 28
Planned Order Release
Q = LFL; LT = 2; SS = 0
1
5
7
2
3
1
16
10
22
18
2
5
Period
3
4
5
5
5
5
6
5
7
5
0
5
0
5
0
5
0
5
0
2
20
Period
3
4
5
20 20 20
6
20
7
10
2
20
0
20
0
0
0
5
0
20
0
10
12
Linking MRP Records: Problem 8 Part b
Suppose 10 units of safety stock are required for part Y. What
changes would result in the records? Would the MRP
system produce any exception messages?
Part Y
Period
PD
Gross Requirements
Scheduled receipts
Projected available balance 28
Planned Order Release
Q = LFL; LT = 2; SS = 10
1
16
10
22
28
2
20
3
20
4
20
5
20
6
20
7
20
2
20
10
20
10
20
10
10
10
10
• Exception message: period 2 below safety stock.
• There will be an increase in the order in period 1 from 18
to 28 units.
13
Front and Back Scheduling Example
Peter’s Power Tools (PPT) has
just received an order for 50
PPT band saws, to be shipped at
the beginning of period 9.
Information concerning the saw
assembly is given in this table.
a.
Draw the product structure diagram
PPT band saw
Item
Lead time (periods)
Components
Saw
2
A(2*), B, C(3)
A
1
E(3), D
B
2
D(2), F(3)
C
2
E(2), D(2)
D
1
E
1
F
3
*Number of parts required to make one parent.
14
PPT Product Structure Diagram
a. Draw the product structure diagram
Saw
A
(2 required)
E
(3 required)
D
B
C
(3 required)
D
F
(2 required) (3 required)
E
D
(2 required) (2 required)
15
PPT Front Loaded Schedule
b. Construct a Gantt chart for the new order using front
scheduling logic.
E
D
F
A
C
B
SAW
1
2
3
4
5
6
7
8
9
Period Number
16
PPT Back Loaded Schedule
c. Construct a Gantt chart for the new order using back
scheduling logic.
F
D
E
B
C
A
SAW
1
2
3
4
5
6
Period Number
7
8
9
17
Scheduling Explanation
The front scheduling logic causes all the work
to be done ahead of schedule which creates
additional inventory and occupies resources
that could be used on other orders. MRP
applies back scheduling logic so that parts
and components are completed when they
are needed to fill customer orders.
18
Lead Time Offsetting
• Precedent Relationship
• Components of Lead Time
–
–
–
–
–
Set-up Time
Run Time
Material Handling Time
Queue Time
Staging Time
• Cumulative Lead Time
• Advantage of Back Loaded Schedules
19
Technical Issues
•
•
•
•
•
•
Low Level Coding
Indented Bill of Materials
Pegging
Cumulative Lead Time
Planning Horizon
Processing Frequency
– Regeneration
– Net Change
20