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Session 11Multi-Level Bill of Material

Explosionhttp://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

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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

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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.

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Product Structure Example: P301 Computer (Continued)

Final AssemblyThe 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.

PV

K

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Product Structure Example: P301 Computer (Continued)

a. Draw the product structure tree according to the assembly directions.

b. Determine low-level codes for each product.c. Assume no inventory of any item. How many of each part

should be available to assemble one completed unit?

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Product Structure DiagramP301 Computer

a.

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Product Structure DiagramP301 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

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Product Structure DiagramP301 Computer

a.

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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.

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Linking MRP Records: Examples (Continued)

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Linking MRP Records: Examples (Continued)

1 2 3 4 5 6 75 5 5 5 5 5 57

Projected available balance 0

1 2 3 4 5 6 710 10 10 10 10 10 1010

Projected available balance 28

PeriodPart GGross RequirementsScheduled receipts

Planned Order ReleaseQ = lot for lot; LT = 1; SS = 0

Period

Q = lot for lot; LT = 2; SS = 0

Part YGross RequirementsScheduled receipts

Planned Order Release

MPSBike B: 5 u/period

Bike A: 10 u/period

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Linking MRP Records: Problem 8 Part a

1 2 3 4 5 6 75 5 5 5 5 5 57

Projected available balance 0 2 0 0 0 0 0 03 5 5 5 5 5

1 2 3 4 5 6 716 20 20 20 20 20 1010

Projected available balance 28 22 2 0 0 0 0 018 20 20 20 10

PeriodPart GGross RequirementsScheduled receipts

Planned Order ReleaseQ = LFL; LT = 1; SS = 0

Period

Q = LFL; LT = 2; SS = 0

Part YGross RequirementsScheduled receipts

Planned Order Release

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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?

• Exception message: period 2 below safety stock.• There will be an increase in the order in period 1 from 18 to

28 units.

Part YPeriod PD 1 2 3 4 5 6 7Gross Requirements 16 20 20 20 20 20 20Scheduled receipts 10Projected available balance 28 22 2 10 10 10 10 10Planned Order Release 28 20 20 20 10Q = LFL; LT = 2; SS = 10

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Front and Back Scheduling Example

Peter’s Power Tools (PPT) hasjust received an order for 50PPT band saws, to be shipped atthe beginning of period 9.Information concerning the sawassembly 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.

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PPT Product Structure Diagram

Saw

A(2 required) B C

(3 required)

E(3 required) D D

(2 required)F

(3 required)E

(2 required)D

(2 required)

a. Draw the product structure diagram

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PPT Front Loaded Schedule

ED

FA

CB

SAW

1 2 3 4 5 6 7 8 9Period Number

b. Construct a Gantt chart for the new order using front scheduling logic.

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PPT Back Loaded Schedule

FDE

BC

ASAW

1 2 3 4 5 6 7 8 9Period Number

c. Construct a Gantt chart for the new order using back scheduling logic.

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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.

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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

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Technical Issues

• Low Level Coding• Indented Bill of Materials• Pegging• Cumulative Lead Time• Planning Horizon• Processing Frequency

– Regeneration– Net Change