Faculty of Engineering
Second Semester 1433/1434,
Final Exam / Subject: Work Study IE341
Date: 5/7/1434, Time allowed: 2 Hrs
Total Marks: 40 Points
Instructors: Dr. Mohamed Mostafa
Answer the Following Questions
1. Future production requirements in the turret lathe department must be satisfied through the acquisition of several new machines and the hiring of new operators, the exact number to be determined. There are three new parts that will be produced. Part A has annual quantities of 20,000 units; part B, 32,000 units; and part C, 47,000 units. Corresponding standard times for these parts are 7.3 min, 4.9 min, and 8.4 min, respectively. The department will operate one 8-hour shift for 250 days/yr. The machines are expected to be 98% reliable, and the anticipated scrap rate is 4%. Worker efficiency is expected to be 100%. How many new turret lathes and operators are required to meet these production requirements?
2. The production rate for a certain assembled product is 45 units/hr. The total assembly work content time is 33 min of direct manual labor. The line operates at 95% uptime. Ten workstations have two workers on opposite sides of the line so that both sides of the product can be worked on simultaneously. The remaining stations have one worker. Repositioning time lost by each worker is 10 sec/cycle. It is known that the number of workers on the line is three more than the number required for perfect balance. Determine (a) number of workers, (b) number of workstations, (c) the balance delay, and (d) manning level.
3. The snapback timing method in direct time study was used to obtain the times for a worker-machine task. The recorded times are listed in the table below. Element d is a machinecontrolled element and the time is constant. Elements a, b, c, e, and f are operatorcontrolled and were performance rated at 90%. Element f is an irregular element, performed every five cycles. The operator-controlled elements are all external to machine -controlled element d. The machine allowance is zero, and the PFD allowance is 13%. Determine (a) the normalized time for the cycle and (b) the standard time for the cycle. The worker’s actual time spent working during an 8-hour shift was 7.08 hours, and he produced 400 units of output during this time. Determine (c) the worker’s performance during the operator-controlled portions of the cycle and (d) the worker’s efficiency during this shift.
Element / a / b / c / d / e / fObserved time (min) / 0.14 / 0.25 / 0.18 / 0.45 / 0.20 / 0.62
2-14 Future production requirements in the turret lathe department must be satisfied through the acquisition of several new machines and the hiring of new operators, the exact number to be determined. There are three new parts that will be produced. Part A has annual quantities of 20,000 units; part B, 32,000 units; and part C, 47,000 units. Corresponding standard times for these parts are 7.3 min, 4.9 min, and 8.4 min, respectively. The department will operate one 8-hour shift for 250 days/yr. The machines are expected to be 98% reliable, and the anticipated scrap rate is 4%. Worker efficiency is expected to be 100%. How many new turret lathes and operators are required to meet these production requirements?
Solution: WL = (20,000 x 7.3 + 32,000 x 4.9 + 47,000 x 8.4)/(1 – 0.04)
WL = (146,000 + 156,800 + 394,800)/0.96 = 726,667 min = 12,111 hr
AT = 8(250)(0.98) = 1960 hr/yr
n = w = 12,111/1960 = 6.16 rounded up to 7 workers and 7 lathes
4-10 The production rate for a certain assembled product is 45 units/hr. The total assembly work content time is 33 min of direct manual labor. The line operates at 95% uptime. Ten workstations have two workers on opposite sides of the line so that both sides of the product can be worked on simultaneously. The remaining stations have one worker. Repositioning time lost by each worker is 10 sec/cycle. It is known that the number of workers on the line is three more than the number required for perfect balance. Determine (a) number of workers, (b) number of workstations, (c) the balance delay, and (d) manning level.
Solution: (a) = 60(0.95)/45 = 1.2667 min
Ts = Tc – Tr = 1.2667 – 10/60 = 1.10 min
For perfect balance, Eb = 1.0
w = Twc /Ts Eb = 33.0/1.1(1.0) = 30 workers if line is perfectly balanced. Actual number of workers is three more than for perfect balance. Therefore, w = 30 + 3 = 33 workers
(b) Given that 10 stations have 2 workers (total 20 workers), so the remaining 13 stations have 1 worker each.
n = 10 + 13 = 23 stations
(c) Eb = = 33.0/33(1.1) = 0.909
Balance delay d = 1- Eb = 1 – 0. 909= 0.091 = 9.1%
(d) = 33/23 = 1.435
13-18 The snapback timing method in direct time study was used to obtain the times for a worker-machine task. The recorded times are listed in the table below. Element d is a machinecontrolled element and the time is constant. Elements a, b, c, e, and f are operatorcontrolled and were performance rated at 90%. Element f is an irregular element, performed every five cycles. The operator-controlled elements are all external to machine -controlled element d. The machine allowance is zero, and the PFD allowance is 13%. Determine (a) the normalized time for the cycle and (b) the standard time for the cycle. The worker’s actual time spent working during an 8-hour shift was 7.08 hours, and he produced 400 units of output during this time. Determine (c) the worker’s performance during the operator-controlled portions of the cycle and (d) the worker’s efficiency during this shift.
Element / a / b / c / d / e / fObserved time (min) / 0.14 / 0.25 / 0.18 / 0.45 / 0.20 / 0.62
Solution: (a) Tn = (0.14 + 0.25 + 0.18 + 0.20 + 0.62/5)(0.90) + 0.45
Tn = = 0.805 + 0.45 = 1.255 min
(b) Tstd = 0.805(1 + 0.13) + 0.45(1 + 0) = 0.91 + 0.45 = 1.36 min
(c) Given Q = 400 pc during 7.08 hr of an 8-hour shift
Machine time during shift = 400(0.45) = 180 min
Worker time during shift = 7.08(60) – 180 = 244.8 min
Cycle time for worker portion of cycle Tc = 244.8/400 = 0.612 min
Pw = 0.805/0.612 = 1.315 = 131.5%
(d) Worker efficiency Ew = 400(1.36/60)/8.0 = 1.133 = 113.3%