Maintenance Management

Introduction

Maintenance ◦ All activities that maintain facilities and equipment in good working order so that a system can perform as intended

Breakdown maintenance ◦ Reactive approach; dealing with breakdowns or problems when they occur

Preventive maintenance ◦ Proactive approach; reducing breakdowns through a program of lubrication, adjustment, cleaning, inspection, and replacement of worn parts

Maintenance Reasons

Reasons for keeping equipment running

◦ Avoid production disruptions

◦ Not add to production costs

◦ Maintain high quality

◦ Avoid missed delivery dates

Breakdown Consequences

Production capacity is reduced ◦ Orders are delayed

No production ◦ Overhead continues ◦ Cost per unit increases

Quality issues ◦ Product may be damaged

Safety issues ◦ Injury to employees ◦ Injury to customers

Total Maintenance Cost

Breakdown and

repair cost

Optimum Amount of

preventive maintenance

Dem

an

d

Total Cost

Preventive

maintenance cost

Preventive Maintenance

Preventive maintenance: goal is to reduce the incidence of breakdowns or failures in the plant or equipment to avoid the associated costs

Preventive maintenance is periodic ◦ Result of planned inspections

◦ According to calendar

◦ After predetermined number of hours

Frequency of breakdown

If the average cost of a breakdown is $1,000, and the cost of preventative maintenance is $1,250 per month, should use preventive maintenance?

Number of breakdowns 0 1 2 3

Frequency of occurrence .20 .30 .40 .10

Number of

Breakdowns

Frequency of

Occurrence

Expected number of

Breakdowns

0

1

2

3

.20

.30

.40

.10

1.00

0

.30

.80

.30

1.40

Expected cost to repair = 1.4 breakdowns per month X $1000 = $1400

Preventive maintenance = $1250

PM results in savings of $150 per month

Predictive Maintenance

Predictive maintenance ◦ An attempt to determine when best to perform preventive maintenance activities

Total productive maintenance ◦ JIT approach where workers perform preventive maintenance on the machines they operate

Breakdown Programs

Standby or backup equipment that can be quickly pressed into service

Inventories of spare parts that can be installed as needed

Operators who are able to perform minor repairs

Repair people who are well trained and readily available to diagnose and correct problems with equipment

Replacement

Trade-off decisions ◦ Cost of replacement vs cost of continued

maintenance

◦ New equipment with new features vs maintenance

◦ Installation of new equipment may cause disruptions

◦ Training costs of employees on new equipment

◦ Forecasts for demand on equipment may require new equipment capacity

When is it time for replacement?

Calculating OEE

OEE

The OEE calculation is based on the three OEE Factors: Availability, Performance, and Quality. Here's how each of these factors is calculated.

Availability Availability takes into account Down Time Loss, and is calculated as:

Availability = Operating Time / Planned Production Time

Performance Performance takes into account Speed Loss, and is calculated as:

Performance = Total Pieces / Operating Time) / Ideal Run Rate

Quality Quality takes into account Quality Loss, and is calculated as:

Quality = Good Pieces / Total Pieces

OEE OEE takes into account all three OEE Factors, and is calculated as:

OEE = Availability x Performance x Quality

It is very important to recognize that improving OEE is not the only objective. Take a look at the following data for two production shifts.

Superficially, it may appear that the second shift is performing better than the first, since its OEE is higher. Very few companies, however, would want to trade a 5.0% increase in Availability for a 3.5% decline in Quality

Example OEE Calculation The table below contains hypothetical

shift data, to be used for a complete OEE calculation, starting with the calculation of

the OEE Factors of Availability, Performance, and Quality. Note that the same units of measurement (in this case minutes and pieces) are consistently used throughout the calculations

OEE

Shift Length 8 hours = 480 min.

Short Breaks 2 @ 15 min. = 30 min.

Meal Break 1 @ 30 min. = 30 min.

Down Time 47 minutes

Ideal Run Rate 60 pieces per minute

Total Pieces 19,271 pieces

Reject Pieces 423 pieces

Planned Production Time = [Shift Length - Breaks] = [480 - 60] = 420 minutes Operating Time = [Planned Production Time - Down Time] = [420 - 47] = 373 minutes Good Pieces = [Total Pieces - Reject Pieces] = [19,271 - 423] = 18,848 pieces

Availability=Operating Time / Planned Production Time

373 minutes / 420 minutes=0.8881 (88.81%)

Performance=(Total Pieces / Operating Time) / Ideal Run Rate

(19,271 pieces / 373 minutes) / 60 pieces per minute=0.8611 (86.11%)

Quality=Good Pieces / Total Pieces

0.8881 x 0.8611 x 0.9780=0.7479 (74.79%)

OEE=Availability x Performance x Quality

0.8881 x 0.8611 x 0.9780=0.7479 (74.79%)