Student: Cycle Time

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IE 472 – Operations of Manufacturing Systems
Midterm, Fall 08/09
1) State true or false for each of the following statements

( T ) In the EOQ model, the sum of holding and setup costs is fairly insensitive to the order quantity.
(

F ) The Wagner-Whitin algorithm is based on the property that the inventory carried to period t + 1 will always be less than that of period t

( F ) Zero cycle time is one of the main targets of JIT.
( T ) With cross-training and autonomation, it becomes possible for a single worker to operate several machines at once.
(

F ) The classical Kanban system made use of three types of cards: a production card, a move card and a sequencing card.

(

F ) In MRP, pegging is the reverse action of netting.

( T ) Nervousness in MRP occurs when a small change in the master production schedule results in a large change in planned order releases. (

F ) The JIT’s target of zero-inventory can not be achieved in systems that utilize MRP.

( T ) Practically, increasing throughput must be accompanied with increasing the level of WIP as long as the bottleneck rate is not reached. ( F ) The bottleneck station is identified as the one that has the lowest utilization.

(

F ) Increasing the number of parallel machines in a non-bottleneck workstation reduces the cycle time.

( F ) In a balanced production line, cycle time becomes the inverse of the throughput at WIP levels greater than the critical WIP.
( F ) The higher the practical worst case cycle time is, the better the production line will be.
(

F ) In the lean philosophy, “muda” can be achieved by performing “kaizen” events.

2) The product structure trees for products A and F are shown below. Part of the master production schedule showing when the company will complete production operations for quantities of these products is shown in the table below. Find the gross requirements for item B throughout the first 12 weeks of the master schedule.

Week
Product A
Product F

1

2

3
4
5
6
7
8
9
10 11 12 13
200 150 250 160 250 300 325 300 225 180 150
80 180 125 200 210 100 180 150 250 200 260
A LT = 1 wk

2B
LT = 3 wks

3C
LT = 2 wks

F

LT = 2 wks

3B

2X

LT = 3 wks

LT = 4 wks

1Y
LT = 2 wks

Solution:
Assuming that the lot-for-lot lot sizing rule is used for all items, we get the following planned order releases for products A and F:
Week
Product A
Product F

1

2
3
4
5
6
7
8
9
10 11 12
200 150 250 160 250 300 325 300 225 180 150
80 180 125 200 210 100 180 150 250 200 260

13

From the information provided in the product structure trees, The gross requirements for item B = 2×Planned order release amount of product A + 3×Planned order release amount of product F

Accordingly, the gross requirements for item B are given below. Week
Item B

1
2
3
4
5
6
7
8
9
10
11
12
240 940 675 1100 950 800 1140 1100 1350 1050 1140 300

3) In problem 2, if the ordering cost for item B is SR50, the inventory holding cost per unit is SR 0.15/unit/year, use part-period-balancing lot sizing rule to determine the lot sizes of item B.

Solution:
First, we have to adjust the units of the holding cost, h = SR 0.15/unit/year h=

0.15
= SR 0.003 /unit/week assuming that there are 50 weeks per year. 50

Quantity for

Ordering cost

Part-periods

period 1

Inventory
carrying cost

240

50

0

0

1180

50

940 × 1 = 940

2.82

1855

50

940 + 675 × 2 = 2290

6.87

2955

50

2290 + 1100 × 3 = 5590

16.77

3905

50

5590 + 950 × 4 = 9390

28.17

4705

50

9390 + 800 × 5 = 13390

40.17

5845

50

13390 + 1140 × 6 = 20230

60.69

Then, the quantity to be ordered in period 1 is 4705 which covers the demand requirement up to week 6.

Quantity for

Ordering cost

Part-periods

period 7

Inventory
carrying cost

1140

50

0

0

2240

50

1100...
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