Consider the following four-step process. Assume demand arrives at a rate of 6 j

Question

Consider the following four-step process. Assume demand arrives at a rate of 6 jobs per hour.

Station

Processing Time (minutes)

Number of Workers

A

2.5

1

B

5.0

1

C

3.0

1

D

4.0

1

a. At which station should the additional worker be placed? Clearly explain your answer.
b. With the additional worker placed where you suggest in part a, answer the following questions
with “paper-and-pencil” calculations,
i. What is the utilization of each station? What is the bottleneck?
ii. What is the average flow time?
iii. With sufficient demand, what is the maximum throughput rate achievable by the process?
iv. What is the average throughput rate?
v. What is the average time between items?
vi. What is the average work-in-process?

Station

Processing Time (minutes)

Number of Workers

A

2.5

1

B

5.0

1

C

3.0

1

D

4.0

1

Explanation / Answer

a. process output

A= 60/ 2.5 =24

B = 60/5 =12

C = 60/3 =20

D = 60/4 =15

Station B is bottleneck as it has lowest output rate an additional woker needs to be placed here.

b. With additional woker placed at B, the output of this station also becomes double i.e.24.

(i) The process capacity is now 15 which is equal to the capacity of D the slowest station now ( bottleneck)

Utilisation of workstations with unlimited supply of work

A - 15/ 24 = 62.5%

B- 15/24 = 62.5%

C- 15/20 = 75%

D =15/15 =100%

Utilisation with given demand /supply

A = 6/24 =25%

B= 6/24 =25%

C- 6/20 =30%

D- 6/15 =40%

(ii) Flow time - Avg processing time = 2.5+2.5+3+4 = 12min.

(iii) Throughput rate = 6 per hour

(iv) Max throughput = 15 per hour

(v) Avg time between the items = 10 min

(vi) Avg WIP = 2 units

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