7-1
Design of Work Systems
WORK MEASUREMENT TIME STUDY (Direct Time Study & Activity Sampling)
7-2
Design of Work Systems
Work Measurement TIME STUDY •
Standard time
•
Stopwatch time study
•
Historical times
•
Predetermined data
•
Work Sampling
7-3
Design of Work Systems
Historical Experience • •
Relatively easy, convenient, and inexpensive Not objective, unknown accuracy
Not recommended
7-4
Design of Work Systems
Time Studies
•
Labor processing standards are based on observing worker doing task • •
•
Observe only a sample of work Use average time & pace to set standard
Disadvantages • •
Requires a trained & experienced analyst Standard cannot be set before task is performed
7-5
Design of Work Systems
The Eight Steps to Conducting a Time Study 1.
Define the task to be studied (after a methods analysis)
2.
Break down the task into precise elements
3.
Decide how many times each element of the task must be measured
4.
Record the times and ratings of performance for the task elements [Rating = (Observed rating / standard rating)] (*Rating = assessment of a worker relative work rate based on observer’s observation compared with standard pace.)
7-6
The Eight Steps to Conducting a Time Study - continued Design of Work Systems
5.
Compute the average observed cycle time (element times adjusted for unusual influences)
6.
Compute the normal time for each task element Normal time = (Average actual cycle time) x (Rating factor)
7-7
Design of Work Systems
The Eight Steps to Conducting a Time Study - continued 7. Sum the normal times for each element to develop a total normal time for the task 8. Compute the standard time: Standard time =
Total normal time (1- Allowance factor)
7-8
Design of Work Systems
Allowances •
•
•
Personal time allowance - 4% - 7% of total time - use of restroom, water fountain, etc. Delay allowance - based upon actual delays that occur Fatigue allowance - to compensate for physical or mental strain, noise level, tediousness, heat and humidity, assumption of an abnormal position, etc.
7-9
Design of Work Systems
(Example 1) - Direct Time Study Work Element
Cycle 1
Cycle 2
Cycle 3 Cycle 4 Cycle 5
1
Take glass
8
9
8
10
8
2
Place on jig and turn on the machine
10
12
10
11
12
3
Milling Operations (fully automatic)
25
25
25
25
25
4
Lift glass and put it on conveyor
8
8
6
8
6
Time study data using snap back stop watch. Time in seconds. Total allowance is 15% of the normal time. Workers rating is 110%. Compute the total standard time. Calculate the labor cost per product if the worker’s wage is RM 3 per-hour.
7-10
Design of Work Systems
Direct Time Study (Example) Element
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5 Average Normal time
1
8
9
8
10
8
8.6
9.46
11.129
2
10
12
10
11
12
11
12.1
14.235
3
25
25
25
25
25
25
25
25
4
8
8
6
8
6
7.2
7.92
9.318
Element 1: Average time = (8+9+8+10+8)/5 = 8.6 sec Normal time = Average time x Rating = 8.6 x 1.1 = 9.46 sec Standard time = Normal time /(1-allowance) = 9.46 / (1-0.15) = 11.129 sec Total Standard Time = 11.129+14.235+25+9.318 = 59.682 sec/product
Std time
7-11
Design of Work Systems
Direct Time Study (Example)
Calculate the labor cost for each product if the worker’s wage is RM 3 per-hour. RM 3 / hr −4 Worker' s wage = = 8.33(10) RM / sec 3600 sec/ hr Labor Cost per product = 59.682 sec x 8.33(10) − 4 RM / sec = RM 0.0497 / product
7-12
Design of Work Systems
- Example 2 Work Elements
Cycle 1
Cycle 2
Cycle 3
Cycle 4
1
0.22
0.26
0.25
0.23
2
0.15
0.18
0.15
0.16
3
0.90
1.10
1.04
1.00
4
0.72
0.80
0.76
0.68
Data from snap back stop watch in minutes of a manual assembly process time study. The worker is rated at 108%. The allowances are 5% for fatigue, 6% for delay, and 6% for personal relief. The worker’s salary is RM1000 per month. a) Compute the total assembly standard time for the assembly process. b) If the demand is 100,000 unit per month, estimate the number of operators required for the assembly process. The company is operating 24 days per month and a single 8 hour shift per day. c) If the company can only manage to employ 18 workers, compute the over time cost per day for each worker for the production of 100,000 units per month. Assume only 15 workers are available for over time and the over time pay rate is 1.5 times of the normal wage.
7-13
Design of Work Systems
Solved Problem Element
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Average
Normal Time
Std Time
1
0.22
0.26
0.25
0.23
0.24
0.259
0.312
2
0.15
0.18
0.15
0.16
0.16
0.173
0.208
3
0.90
1.10
1.04
1.00
1.01
1.091
1.314
4
0.72
0.80
0.76
0.68
0.74
0.799
0.963
(a) Element 1 Average Time =
0.22 + 0.26 + 0.25 + 0.23 = 0.24 min 4
Normal Time = Average Time x Rating = 0.24 x 1.08 = 0.259 min Standard Time = Normal Time x
1 1 = 0.259 × = 0.312 min 1 - Allowance 1 − 0.17
Total Assembly Standard Time = 0.312 + 0.208 + 1.314 + 0.963 = 2.797 min/unit
7-14
Design of Work Systems
Solved Problem b) If the demand is 100,000 unit per month, estimate the number of operators required for the assembly process. The company is operating 24 days per month and a single 8 hour shift per day.
(b) Working time of 1 operator = 1 × 8
hr day min min × 24 × 60 = 11,520 day mth hr mth
min mth = 4,118.70 unit Monthly quantity produced by 1 operator = min mth 2.797 unit 11,520
unit Monthly Demand mth = 24.28 ≈ 25 Number of operators required = = Capacity per operator 4118.70 unit mth 100,000
7-15
Design of Work Systems
Solved Problem c) If the company can only manage to employ 18 workers, compute the over time cost per day for each worker for the production of 100,000 units per month. Assume only 15 workers are available for over time and the over time pay rate is 1.5 times of the normal wage. (c) Monthly
quantity
produced
Monthly
quantity
shortage
by 18 operators
= 100,000
= 4,118.70
- 74,137
unit mth day 24 mth
= 25,863
25,863 Daily
quantity
shortage
=
Time
required
to produced
1077.6
unit day
= 1077 . 6
= 1077 . 6
= 3 , 014
unit × 18 = 74 ,137 units mth unit mth
(monthly shortage, need OT)
unit day
unit min × 2 . 797 day unit
min day
= 50 . 234
hr day
7-16
Design of Work Systems
Solved Problem Due to only 15 operators are available for over time work, therefore over time hours for each operator per day hr hr day = = 3.349 15 operator operator − day 50.234
RM mth = 5.208 RM Normal wage = day hr hr 24 ×8 mth day RM RM Over time wage = 1.5 x 5.208 = 7.812 hr hr 1,000
Over time cost per operator per day = 3.349
hr RM RM × 7.812 = 26.162 operator − day hr operator − day
7-17
Design of Work Systems
Work Sampling • • •
Labor standard is set using output and % of time worker spends on tasks Involves observing worker at random times over a long period Advantages • •
•
Less expensive than time studies Observer requires little training
Disadvantages •
Ineffective with short cycles
7-18
Design of Work Systems
Work Sampling •
Used for • • •
Ratio delay studies Setting labor standards Measuring worker performance
7-19
Design of Work Systems
The Five Step Work Sampling Procedure
1.
2. 3.
4.
5.
Take a preliminary sample to obtain an estimate of the parameter value Compute the sample size required Prepare a schedule for observing the worker at appropriate times Observe and record worker activities; rate worker performance Determine how workers spend their time (usually as a percent)
7-20
Design of Work Systems
Work Sampling Equations
Normal Time =
Standard Time =
(Total Observation Time) x (Productive %) x (Rating)
Total Output Normal Time (1 – Allowance)
7-21
Design of Work Systems
Work Sampling (Example) Status Productive Idle
Tally
Sum
Percentage
IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII I
41
41/45 = 91%
IIII
4
4/45 = 9%
Work sampling studies were conducted for 6 consecutive days at a factory. A total of 45 observations were made during the 8 hours working period for each day. The number of units managed to be produced are 3000 units for 1 week. The factory is operating 6 days a week. The data above are included with rating and allowance of 97% and 15%. Compute the process standard time.
7-22
Design of Work Systems
Work Sampling (Example) Status
Tally
Sum
Percentage
Productive
IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII I
41
41/45 = 91%
Idle
IIII
4
4/45 = 9%
Total observation time = 8
hr min × 60 × 6 day = 2880 min day hr
Standard Time, ST =[
Total observation time 1 × Productive % × Rating] × Total output 1 − allowance 2880 min 1 × 0.91× 0.97 × 3000 unit 1 − 0.15 min = 0.997 unit
Standard Time, ST =
7-23
Design of Work Systems
Tutorial 1 Proses
Description
Average Time (min)
1
Manual
23
2
Manual
32
3
Automatic machine
9
4
Manual
8
Rating : 110% Allowance: 20% (a) Compute the standard time for each process. (b) If the company has no problem with the availability of manpower, recommend the maximum capacity for the factory for a 8 hour shift work.
7-24
Design of Work Systems
Tutorial 1 (a) Proses
Description
1
Manual
2
Manual
3
Automatic machine
4
Manual
(b)
Average Time (min)
Normal time
Std Time
7-25
Design of Work Systems
Tutorial 2 Emirates Consultant conducted a work sampling studies for 5 consecutive days at an assembly factory. A total of 48 observations were made during the 8 hour working period for each day. The data collected during the 5 day studies is illustrated in Table 1. The whole assembly process is operating on 5 working days per week, 95% rating and the company’s allowable allowances is 20%. (i) Compute the standard time (min/unit) for the assembly process. (ii) At peak demand period, the factory is normally required to produce 3,100 units per week. If only 60% of the employee is willing to work over time, compute the average overtime per day must be arranged in order to meet the peak demand. Item
Data
Total output over 5 days studies
2,500 unit
Assembly process at fast speed
35% of observations
Assembly process at moderate speed
45% of observations
Assembly process at slow speed
5% of observations
Production is stopped due to no operator
5% of observations
Production is stopped due to no material
10% of observations
7-26
Design of Work Systems
Tutorial 2 (i) Total observation time = Std Time = (ii) unit Peak Demand = wk unit Capacity during normal 8 hours = day
7-27
Design of Work Systems
Tutorial 2 Capacity shortage = unit/day If all employees are forced to do over time, the over time hours min = day
Considering only 60% of employees are available for over time, then total overtime =
hour day
7-28
Design of Work Systems
END OF CLASS
