23) Over the past three months, a line has averaged 315 parts per day, where one

ID: 366309 • Letter: 2

Question

23) Over the past three months, a line has averaged 315 parts per day, where one day consists of one eight-hour shift, and has had an average WIP level of 400 parts. Management has been dissatisfied with the performance of the line because it is achieving lower throughput with higher WIP than another line. Your job is to evaluate this line to the extent possible with the data below by addressing the following questions. a. (12 points) Compute ro, To, and Wo for the line. b. (4 points) Compare the performance of the line to the practical worst case. berTime Rate per Process (parts/hour) per Station (minutes) Punching Braking Assembly Finishing 30 12 20 50 2.0 5.0 3.0 1.2

Explanation / Answer

The Capacities per process are calculated as follows:

Process

Rate per machine (Parts/Hour)

# of m/c per station

Rate per station

time (minutes per job)

Time (hour per job)

Punching

2.0

2/60

= 0.0333

Braking

5.0

5/60

= 0.0833

Assembly

3.0

60/3

= 0.05

Finishing

1.2

1.2/60

= 0.02

As the lowest capacity is 40 parts per hour for Assembly process, the Assembly process is bottleneck for the line.

Bottleneck rate = rb = 40 parts/hour

Raw process time = To = sum of process time = (0.0333 + 0.0833 + 0.05 + 0.02) = 0.1866 hour

Critical Inventory, W0 = rb x To = 40 x 0.1866 = 7.5 ~ 8 parts

Actual throughput is 315 units per day, a day consists of single 8-hour shift.

Actual Throughput (units per hour) = 315/8 = 39.375 units per hour

Actual TH = 39.375 units per hour

Current inventory level = w = 400 parts

Then, the flow rate for the Practical Worst Case (PWC) is given as follows:

THPWC = (w x rb) / (W0 + w – 1)

THPWC = (400 x 40) / (8 + 400 – 1)

THPWC = 39.31

Since Actual TH > THPWC, the line is efficient than practical worst case.