Using Work Sampling To Improve Maintenance Efficiency And Inventory Management

What is Work Sampling and How is it Used?

As a maintenance manager, you arrange a preliminary study with activity (work) sampling of a group of your maintenance people (after proper briefing, of course).

Explain what work sampling is and how it is used/ might be used in workplace.

Work sampling is a statistical method that is used predicting the total time that is used up in an activity by a worker in various categories which define an activity (Meisels et al., 2001).

Write down steps in collection and analysis of work sampling data.

The first step is defining the problem by stating the main objectives or purpose of the problem and by describing the details of each element to be measured.

The second step is obtaining the necessary approvals of the personnel in charge of the department in which the study is to be made.

The third step is determining the anticipated precision of the final results in percentage or standard error.

The fourth step is stating the confidence level.

The fifth step is making preliminary estimates of the occurrence of the activity or delay in percentage. The preliminary estimates are to be measured for one or two days.

The sixth step involves designing the study, making plans to be used in taking the observations and designing the observations form. Designing the study involves determining the number of observations to be made, observations needed and the days or shifts needed for the study (Pelletier & Duffield, 2003).

The seventh step involves making observations and data recording.

The eighth step is summarizing the data at the end of each day.

The ninth step involves checking the precision or accuracy of the data at the end of the study.

The tenth and final step is preparing the report, stating the results and making recommendations where necessary.

Observations were taken at random intervals of time, resulting in the following numbers of observations for the people who are involved:

	John	Kate	Paul	Eva
Repairing machine (“Wrench time”)	241	251	271	201
Waiting for Access Permit	29	49	39	49
Finding plant drawings and information	8	11	5	8
Not at the job site	12	9	5	17
Awaiting supporting trades	15	5	16	15
Not occupied	71	57	36	68
Travelling	28	22	32	46

Think on the data provided. The total number of samples is relevant only for a person – each person’s data stands alone. Figures to one decimal place are enough.

2A.1 For each person, find the percentage value for each activity.

	John	Kate	Paul	Eva
Repairing machine (“Wrench time”)	59.7%	62.1%	67.1%	49.8%
Waiting for Access Permit	7.2%	12.1%	9.7%	12.1%
Finding plant drawings and information	2.0%	2.7%	1.2%	2.0%
Not at the job site	3.0%	2.2%	1.2%	4.2%
Awaiting supporting trades	3.7%	1.2%	4.0%	3.7%
Not occupied	17.6%	14.1%	8.9%	16.8%
Travelling	6.9%	5.4%	7.9%	11.4%

2A.2 Find the limit of accuracy achieved for each of the activities of each person, to a 95% confidence level.

Formula:

S =(2*SQRT(p*(1-p)/N))/p

	John	Kate	Paul	Eva
Repairing machine (“Wrench time”)	8.2%	7.8%	7.0%	10.0%
Waiting for Access Permit	35.8%	26.8%	30.4%	26.8%
Finding plant drawings and information	70.0%	59.5%	88.9%	70.0%
Not at the job site	56.9%	65.9%	88.9%	47.5%
Awaiting supporting trades	50.7%	88.9%	49.0%	50.7%
Not occupied	21.5%	24.6%	31.8%	22.1%
Travelling	36.5%	41.5%	33.9%	27.8%

2A.3 If an accuracy of 3% is required, to a 95% confidence level, how many readings are needed for each of the activities performed by John?

Steps in Collecting and Analyzing Work Sampling Data

Formula:

N = (p(1-p)*4)/((s^2)*(p^2))

	John
Repairing machine (“Wrench time”)	3,006.0
Waiting for Access Permit	57,471.3
Finding plant drawings and information	220,000.0
Not at the job site	145,185.2
Awaiting supporting trades	115,259.3
Not occupied	20,845.1
Traveling	59,682.5

2A.4 Draw conclusions from the data and your calculations. What actions could you take as a manager?

It is evident that the number of more observations is needed to be made for John to ascertain that he is not productive compared to observations that need to be made to ascertain that he is productive.

Your plant uses on average 96 bearings each year. They cost $60 each, and your storeroom carrying cost is about 25% of the value of inventory per year. The cost of issuing each order is $50.

What is the Economic Order Quantity?

Economic Order Quantity (EOQ) is the number of units in which a company should add to its inventory with each order so as to minimize the inventory total costs (Eroglu & Ozdemir, 2007). The costs include holding costs, order costs, and shortage costs (Salameh & Jaber, 2000).

The vendor can supply at 10% discount for bulk packs. If ordered in a standard bulk pack of 100 items. What do you recommend to minimize total costs to your company? [Compare the total annual costs of each option, considering purchase cost, order cost, and holding cost (based on average inventory – assume a linear usage rate through the year)]

Holding cost = order quantity * holding cost * price/2

Holding cost = 350*0.25*60/2 = 2,625

Discounted holding cost = 350*0.25*54/2 = 2,362.5

Unit cost = 96* 60 = 5,760

Discounted unit cost = 96 *54 = 5,184

Order cost = order cost * demand/order quantity

Order cost = 50*96/350 = 13.71

Total cost = 8,398.71

Discounted total cost = 7,560.21

Thus, in order to minimize the total cost of the company, then the company should buy at the 10% discount for bulk packs.

Your plant uses spare parts on an average one each 2 years. They cost $2000 each, and the stockholding cost is 25% of that. The cost of lost production after a failure while a repair is made (i.e. cost of stock-out) is estimated as $20,000. The lead time to obtain a spare part is 6 months. How many parts, if any, should be held in store?

There is no need to hold the parts in the store due to the period of time that is taken for one spare part to be worn out. Consequently, doing a mathematical calculation, it is revealed that the safety stock for the spare part is 0.00.

Analysis of Maintenance Staff Work Sampling Data

Responsibilities of maintenance and reliability section include ensuring that the reorder quantities of the various items have been correctly established. From your stores records, you find the data related to filters:

1000 are used per year, at a cost of $75 each

Holding cost is 25% of filter cost per year

Ordering cost is $25 per order (through your automatic ordering system)

Delivery lead time is 5 days

Standard deviation of daily demand is 2 tyres.

What should be the quantity per order?

EOQ = sqrt(2*annual demand rate*order cost/holding cost)

EOQ = SQRT(2*1000*25/18.75)

EOQ = 51.64

Service availability is a priority, so you have set the probability of not running out of filters in store at 97%. At which stock level should a batch of filters be re-ordered to meet the requirement?

 Safety stock = normsinv(service level) * standard deviation of lead time

Safety stock = 8.41

Average demand during lead time = average daily demand * lead time days = 2.74 * 5 = 13.7

Reorder point = safety stock + average demand during lead time = 8.41 + 13.7 = 22.11

You are requested to set up a time log system, run it for 2 weeks, and then report your findings to senior management on your time utilization and productivity in a one-page memo with findings of the analysis.

Develop tables for the data collection, recording and analysis. Show each working day for two weeks, at hourly time blocks for taking snapshots of activities or not doing anything using a list of categories that apply to your work area: e.g. Travelling, Emails, Drawing, Machining, Cleaning, Inspecting, Operating, Programming, Waiting for material, Administration meetings, planning, etc. Allot a symbol letter to each, e.g. “M” for Meetings.

For two weeks, record in log on how you spend your time. Do not analyse it as the period proceeds: just enter the symbol in each hour block (note time you record, if taken using random tables for data collection) that relates to whatever you did for the most part of that hour.

At the end of the 2 weeks period, analyse what you have collected and report your conclusions in the requested one-page memo/submit to the Manager (for the purpose of this assignment, it is me! And submit in Moodle) (Hint: such memos do not have the courteous tags such as “Dear boss” or “Sincerely” that you might use in a letter. Prepare in an easy to understand tabular form to present the findings and any suggestion for further enhancing your time utilisation/ productivity and required support, if any)

Time log

	9:00 AM	10:00 AM	11:00 AM	12 NOON	1:00 PM	2:00 PM	3:00 PM	4:00 PM	Glossary T – Travelling E – Emails M- Machining C – Cleaning I – Inspecting P -Programming W – Waiting for material A – Administration meetings N – Nothing (Idle)
27/8/2018	E	E	M	M	M	I	C	P
28/8/2018	T	T	T	W	O	O	O	E
29/8/2018	I	I	C	C	C	C	P	P
30/8/2018	A	A	P	P	P	O	O	E
31/8/2018	T	T	T	E	E	A	A	A
3/9/2018	A	A	P	P	P	P	I	I
4/9/2018	P	W	W	I	C	C	P	P
5/9/2018	P	P	P	I	I	N	N	N
6/9/2018	A	A	E	E	P	P	T	T
7/9/2018	W	P	P	I	I	E	T	T

INTERNAL MEMO

FROM: John Doe, Senior Programming Officer  

TO: Tom Harry, Manager

DATE: September 10, 2018

SUBJECT: Performance Management

Mr. Harry,

I have attached my daily performance report for the two week period between 27^th August and 7^th September.

The two week period has been very busy in the Programming department. Majority of the working time was spent on programming (19 hours), and Inspecting (10 hours). The programming activities were also carried out in the two other subsidiary companies (Telco Limited and Safcom Limited). Traveling time to the two subsidiaries consumed 11 hours of the working hours. Delivery of reports through the e-mail and replying to other job-related emails took a total of 10 hours. Other aspects of programming which entails cleaning, machining and inspecting had 7 hours, 3 hours and 10 hours respectively.

A lot of valuable time is being wasted in waiting for materials and being idle, 4 hours and 3 hours respectively. Administration meetings also take a significant time for the department which can be used to ensure a smooth flow of activities in achieving the set KPIs.

Please let me know if you have any questions,

Best,

John Doe

Programming Officer

Fibre Technologies

References

Eroglu, A., & Ozdemir, G. (2007). An economic order quantity model with defective items and shortages. International journal of production economics, 106(2), 544-549.

Meisels, S. J., Dichtelmiller, M. L., Jablon, J. R., Dorfman, A. B., & Marsden, D. B. (2001). The work sampling system (Vol. 3). Pearson Education/Pearson Early Learning.

Pelletier, D., & Duffield, C. (2003). Work sampling: valuable methodology to define nursing practice patterns. Nursing & health sciences, 5(1), 31-38.

Salameh, M. K., & Jaber, M. Y. (2000). Economic production quantity model for items with imperfect quality. International journal of production economics, 64(1-3), 59-64.