Facility Maintenance

Typical Job Categories for Maintenance Plant Maintenance Electricians Tinsmiths Welders Pipe fitters Fire/emergency People Steam fitters

Bricklayers Painters Glaziers Concrete Workers Carpenters Millwrights

Heavy Movers Window Washers Janitors Gardeners

Machine Maintenance

General Mechanics Machinists Sheet Metal Workers Welders Electronic Technician Computer Technicians

MAINTENANCE PROCEDURES        Emergency Maintenance        Preventative Maintenance

CLASS EXERCISE - EMERGENCY STAND-BY CAPACITY A production line has 20 electric resistance welders It costs $40 per day to won each welder If one or two welders are down, replacement spares can be rented at $50 per day per

machine If 3,4, or 5 welders are out, they can be rented but production slow downs result and

the total cost is $100 per day per extra machine (rental + slow down) If 6 or more machines are out, the total cost (rental + slow down) is $500 per day per

extra machine

Objective: Calculate how many spare welders need to be purchased by your company to minimize the total operating costs.

Cost to Rent Number of Machines Out of OrderProbability that Number of Machines will be broken: Total =100%

Emergency – Standby Capacity

We have a line with 50 robot GMA weldersThe cost to do a preventative maintenance overhaul

on each machine is $200/machineAverage breakdown repair costs are $700/machine

Objective: Calculate the cost if we elect to repair only when a machine breaks down. How much must we set

aside each month?

Probability of Breakdown as a function of months after overhaul of all machines.

1.00

The months time the probability results in the partial expected time for failure.

Since the partial probabilities add to 100%, the partial times add to the expect time for a failure = 8.42 months

They Add to 100%

The cost of repair-on-breakdown then = ($700/machine) /(8.42 months) * 50 machines

= $4157/month Thus, we better place $4157 in a fund every month if we decide to do repair-on-breakdown policy.

We have a line with 50 robot GMA weldersThe cost to do a preventative maintenance overhaul

on each machine is $200/machineAverage breakdown repair costs are $700/machine

Objective: Calculate if preventative maintenance should be done and if so what the schedule should be.

Calculate Cost for Preventative Maintenance

For every preventative maintenance overhaul we do it will cost:

= $200/machine * 50 machines = $10,000

If we do a preventative maintenance every month, it will cost $10,000/month

If we do a preventative maintenance every 2 months, it will cost $5,000/month, etc.

Even though we do preventative maintenance, we can expect some breakdowns to occur anyway. We can calculate the number of expected breakdowns each month using the following equation. 

Where:Bn = expected number of breakdowns

N = number of machinesPn = probability of machine

breakdown in period n

1n122n11n

n

1nn PB......PBPBPNB

50.2)05.0(50NPB 11     That is, 2.5 breakdowns in the first month

63.3)05(.50.2)02.05(.50PB)PP(NB 11212     That is, 3.63 breakdown in first 2 months

Expected Cost = Ave. Number * $700/machine = 2.5 * $700 = $1750

Total Cost = Expected Cost + Prev. Maint. Cost = 1750 + 10000 = 11750

PL

OT

$4157