运营管理复习题

Operations Management Homework 1

Please print your work Question 1 (15 points):

Use the assembly line balancing data shown in

the figure (task times are in seconds).

The production requirement is at least

350 units per shift (operating 7.5 hours

per shift).

(a) Calculate the cycle time in seconds.

Round off the cycle time to nearest

multiple of 10 seconds such that at

least 350 units will be produced. (2

points)

(b) Perform line balancing using the RPW* method and calculate line efficiency. (8 points)

(c) Can you improve the balancing by trial and error （试错法）? (5 points)

Question 2 （10 points ）: Find the cycle time for the following. Solution: CT1 = 6, CT2 = 60/(1+2+2+2) = 60/7 = 8.57 CT3 = 36/(2+3) = 36/5 = 7.2, CT4 = 7 Overall cycle time = 8.57 Question 3 (20 points): Left Angels Inc. fabricates garages with the following process steps. Roofs are punched in a roof punching press (6 minutes per roof) and then formed in a roof forming press (8 minutes per roof).

Bases are first punched in base punching press (9 minutes per base), then formed in base forming press (10 minutes per base), and finally the formed base is welded in a base-welding machine (5 minutes per base).

The base sub-assembly and the roof then go to final assembly where they are welded together (8 minutes per garage) on the assembly welding machine to complete the garage. Assume one operator at each station .

Solution: (a) Draw a process flow diagram . (buffer storage locations omitted) Roof

Base

(b)What is the minimum MLT for a garage to be completed? Along the base unit

production line: time = 9 + 10 + 5 + 8 = 32 min. This is minimum MLT .

(c)What is the capacity of the factory in terms of garages per hour?

Bottleneck operation is base forming with time = 10 min. This will determine the cycle time and the capacity = 6 per hour.

(d)If the factory were producing at capacity, what would then utilization of each resource be? Utilization: Roof punching: 6/10 = 0.6, Roof forming: 8/10 = 0.8, Base punching: 9/10 =0.9, Base forming: 10/10 = 1, Base welding: 5/10=0.5

Final welding: 8/10 = 0.8

Question 4 (20points)

Day Joining Leaving

Mon 35 35

Tue 35 35

Wed 35 0

Thu 35 35

Fri 35 35

Sat 35 35

Sun 0 35

Mon 35 35

Tue 35 35

Wed 35 0

Thu 35 35

Fri 35 35

Sat 35 35

Sun 0 35

Mon 35 35

Tue 35 35

Wed 35 0

Thu 35 35

Fri 35 35

Sat 35 35

Sun 0 35

Question 5 : (15 points)

Sharp Discount Wholesale Club had two service desks, one at each entrance of the store. Customers arrive at each service at an average of one every six minutes. The service rate at each service desk is four minutes per customer.

(a)How often (what percentage of time) is each service desk idle?

(b)What is the probability that both service clerks are busy?

(c)What is the probability that both service clerks are idle?

(d)How many customers, on average, are waiting in line in front of each service desk?

(e)How much time does a customer spend at the service desk (waiting plus service time)?

Solution: This is a single channel (server) system: model 1

Priority Rules:

1.Select the task with the smallest task time (SPT rule).

2.Select the task with the largest task time (LPT rule).

3.Determine Rank Positional Weights (RPW) for tasks; select the task with

the largest RPW. This is also called weighted LPT rule.

RPW=当前工序及其所有后续工序时间的总和。