Exercise 6: The assembly of a product consists of eight tasks as given below. Th

Question

Exercise 6: The assembly of a product consists of eight tasks as given below. The company works 5 days per week in two shifts every day. Each shift is 9 hours and workers have 30 minute meal-break and two 15-minute tea breaks. The desired production rate is 1500 units/week. TaskTime (seconds)Immediate Predecessors 90 90 30 50 20 25 30 70 4 5,6 a) Calculate the maximum cycle time to achieve the desired production rate b) Draw the precedence diagram. c) Assign tasks to stations using the Ranked Positional Weight (RPW) technique assuming a cycle time of 150 seconds. d) Calculate the balance delay

Explanation / Answer

Total available time per shift

= 9 hours – 30 minutes meal break – 2 x 15 minutes = 9 hours – 60 minutes = 8 hours

Thus total available time per day with 2 shifts = 8 x 2 = 16 hours

Total available time in 5 days = 16 x 5 = 80 hours = 80 x 3600 seconds

Desired production rate = 1500 units/ week

Thus Maximum cycle time = 80 x 3600 / 1500 = 192 seconds

MAXIMUM CYCLE TIME TO ACHIEVE DESIRED PRODUCTION RATE = 192 SECONDS

The Precedence diagram as follows :

                                                                                          1

                                   2

                                     3

                                              4

                                  5

                                                                  6

                                                                                                                                            7

                                                                                                                                            8

Following Steps are involved in Ranked Positional Weight (RPW ) method.

Step 1: Draw the precedence diagram

Step 2: For each work element, determine the positional weight. It is the total time on the longest path from the beginning of operation to the last operation of the network.

Step 3: Rank the work elements in descending order of ranked positional weight (R.P.W)

Step 4: Assign the work element to a station. Choose the highest RPW element. Then, select the next one. Continue till cycle time is not violated. Follow the precedence constraints also. Since cycle time is 150 seconds , total duration of any workstation shall not exceed 150 seconds

Step 5: Repeat step 4 till all operations are allotted to one station.

Accordingly , total duration of each path as per following :

Path 1-3-6-7-8 = 90 + 30 + 25 + 30 + 70 = 245 seconds

Path 1-4-6-7-8 = 90 + 50 + 25 + 30 + 70 = 265 seconds

Path 2 – 5- 7 -8 = 90 + 20 + 30 + 70 = 210 seconds

From above, since activity 1 has higher RPW than 2 , we will start with 1. After starting with activity 1, we should choose activity 4 ( over activity 3 ) since 4-6-7-8 will have higher RPW over 3-6-7-8

Workstation

Activity

Total duration ( seconds)

Balance delay = 150 seconds – Total duration

1

1, 4

90 + 50 = 140

150 – 140 = 10

2

2, 5 , 7

90 + 20 + 30 = 140

150 – 140 = 10

3

3,6

30 + 25 = 55

150 – 55 = 95

8

70

150 – 70 = 80

Thus , Cumulative balance delay for all workstations = 10 + 10 + 95 + 80 seconds = 195 seconds

MAXIMUM CYCLE TIME TO ACHIEVE DESIRED PRODUCTION RATE = 192 SECONDS

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.