Mayuresh Unde

18th Jan, 2011

Equipment Maintenance(PM, TPM)

Origins of Maintenance…

1. Breakdown Maintenance or Repairs

Consequences of equipment problems:

Machine problems Possible / Immediateeffects

Ultimate Cost / Consequences

Malfunction Machine deteriorationMachine InefficiencyOutput Variability

Shortened machine lifeHigh repair cost

Breakdown Safety Hazards Idle workersIdle facilities

Scrap and reworkInjuriesHigh production costSchedule delaysCustomer satisfaction

Preventive Maintenance

1. Preventive Maintenance:1. Maintain normal operating requirements: Run your equipments at

recommended operating conditions to avoid deterioration and extend equipment’s useful life.

2. Maintain equipment requirements: Equipments may require lubrication, greasing, oiling; some may require frequent tightening of bolts and fasteners; some others may require specific tooling and fixtures. Make checklist, standardize setup procedures, operator training to handle these requirements.

3. Keep equipment and facilities clean and organized: Noise, leaks, wobbling fixtures, cracks, discoloration and other sources of problems might be concealed by dirt while they show up immediately on a clean machine. Apply 5 S principles and moreover cluster impedes efficient response to breakdowns, thus increasing the time to repair.

Preventive Maintenance

1. Preventive Maintenance:4. Monitor equipment daily: Operators should monitor equipment daily so that

early signs of problems are promptly detected and fixed.

5. Schedule preventive maintenance Clock or Calendar time intervals – After every shift, every week, month etc Cycles of usages – After every 500 units produced, or 100 working hours, or

50 setups etc Periodic inspection based on failure patterns

6. Manage Maintenance information: PM requires a keeping good records about performance and breakdown history of equipment and the related actions/repairs and costs around it. Need a comprehensive Maintenance Management System to : process work

orders, track repairs, maintain schedules, procedures, trends, reports, root cause analysis etc.

Needs equipment registry comprising of: Type of machine, date in service, upgrades, changes, locations, spare parts required, Serial # etc

MMS complies data and statistics to compute OEE, MTTR, MTBF etc

Preventive Maintenance

1. Preventive Maintenance:7. Predictive Maintenance :

It help determine the condition of in-service equipment in order to predict when maintenance should be performed. This approach offers cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted.

Also called as Condition – based monitoring and maintenance (since equipment remains in service on the condition that potential failure is not detected

Often involves monitoring physical phenomena of the machinery, viz. vibration, speed, temperature, sound etc.

Many-a-times output of the machine is monitored for detecting potential problems – Ex. SPC control charts could show a trend of a potential failure.

Reliability & Maintainability

Reliability is the probability that equipment will perform properly under normal operating conditions, while Maintainability is the effort and cost of performing maintenance.

1. Mean Time Between Failure (MTBF) – A measure of reliability, and represents the average time between failures. Greater the MTBF for a piece of equipment, greater is its reliability.

MTBF = Total Running Time / Number of Failures

The MTBF can be used to estimate the reliability of an item. In this case, the reliability R(T) is defined as the probability that the item will not fail before time T:

R(T) = e - λT

Where: 0 <= R(T) < 1.0e = natural logarithm base ( about 2.718)T = specified timeλ = is the failure rate = 1

MTBF

Problem

Problem: Twenty machines are operated for 100 hours. One machine fails in 60 hrs and another fails in 70 hours. What is the MTBF? Also, calculate the reliability of the same machines at 500 hrs and 900 hrs?

Answer: Eighteen machines ran for 100 hrs, while the other two ran at 60 and 70 hrs respectively. Thus, total running time: 18(100) + 60 + 70 = 1930 hrs

MTBF = 1930 / 2{failures} = 965 hours / failure

Part II - λ = 1/ MTBF = 1/ 965 = 0.0010362 failure /hour

R(500) = e -0.0010362(500) = 0.596R(900) = e -0.0010362(900) = 0.394

Thus there is nearly a 60% probability that the machine will run 500 hrs without failure, and nearly 40% probability that it will run for 900 hrs

Problem

Problem: Suppose the machine’s performance is entirely dependant on one particular component. Each time the component is replaced, the machine’s reliability returns to 100%. How often should the component be replaced so that the machine’s reliability is never less than 90%?

Answer: R(T) = e – λT

0.90 = e -0.0010362(T)

Transposing the formula, T = - ln (0.90) = 101.60.0010362

So, the component should be replaced approximately every 102 hrs.

Reliability & Maintainability

1. Mean Time To Repair: (MTTR) is a measure of maintainability. High MTTR is an indication of low maintainability

MTTR = Ʃ (Downtime for Repair ) Number of Repairs

2. Downtime for repair includes time waiting for repairs, time spent doing repairs, and time spent testing and getting equipment ready to resume operation.

Availability

Availability is the proportion of time equipment is actually available to perform work out of the total time it should be available

A = Actual Running Time / Planned Running Time

Where, Planned running time = (Total plant time – Planned downtime)Actual running time = ( Planned running time – all other downtime)

Suppose a plant runs two 8 hr shifts, and during each shift there is a 2 hrs of planned downtime. Thus the planned running time = 16 – 2(2) = 12 hrs

If the machine is stopped each day an average of 110 mins for setups and 75 minsfor breakdowns and repairs, then actual running time =

12(60) – (110 + 75) = 535 minutes

Thus Availability of the equipment is = 535 / 12(60) = 0.7431

Efficiency

Efficiency is the measure of how well a machine performs while running

Rate Efficiency = (Actual production volume X Actual Cycle Time)Actual Running Time

Suppose the same machine as in the previous example, runs for 535 mins a day. Also, suppose the average daily throughput of the machine is 830 units, and the actual cycle time is observed to be 0.6 min/part. Calculate Rate efficiency.

RE = (830 X 0.6) / 535 = 498 / 535 = 0.9308

Thus, the machine is processing parts only 93.08 % of the time it is running. Parts jamming, breaking the queues and other interruptions are consuming 6.92% of the machine running time.

Quality Rate

The Quality rate Q is an index of the equipment’s ability to produce output that is non-defective or conforms to requirements

Quality Rate (Q) = (Actual production volume – Defect Output)Actual production volume

Suppose the machine in the example produces an average of 30 defective units out of 830 units / day. The Quality Rate is Q = 800 / 830 = 0.9639

A measure of equipment effectiveness that incorporates availability, performance efficiency and quality rate is the Overall Equipment effectiveness

(OEE)OEE = Availability X Performance X Quality

OEE = A X E X Q

OVERALL EQUIPMENT EFFECTIVENESS (OEE)

Thus for our example, OEE = A X E X Q = 0.7431 X 0.9308 X 0.9639 = 0.667 (66.70 %)

Total Productive Maintenance (TPM)

TPM is a company-wide system developed to maintain, monitor, and improve all capital assets of a company. For production it is a system that maximizes equipment effectiveness and maintains product flow.

– TPM is not just about “maintenance”. It is about getting the most overall benefit from your equipment over the life of the equipment.

– TPM will not be an overnight success. Implementing it throughout a plant correctly will take several years.

Operator Maintenance Operator Maintenance

Conventional TPM

I useI maintain &

I fix We maintain

5 Pillars of TPM

Training & Skill Development

Early Equipment Management

Maintenance Process Improvement

MPI Tools and Activities:

1. Improving Maintenance Procedures – Organize and optimize maintenance procedures, like SMED techniques

2. Lubrication management3. Document Management – Standard Operating

Procedures, Work Instructions, Equipment Manuals4. Preventive Maintenance Schedule5. Comprehensive Maintenance management system (MMS)6. Predictive technologies7. Spare parts management

Systematic Equipment Improvement

A systematic approach to eliminate waste through analysis of the “6” major losses utilizing cross functional teams to continuously investigate, test and implement improvements with a goal of maximizing equipment effectiveness (OEE)

Autonomous Maintenance

Autonomous Maintenance:-1. A collaborative team activity involving

production, maintenance and engineering2. An approach thatDevelops operating and maintenance skillsStrengthens communication and cooperation

3. A series of activities implemented in well defined developmental steps

4. Maintenance OrganizationDecentralizationCentral Maintenance

Implementing TPM

5 Step approach for implementing TPM:

1. Program Feasibility2. Program Objectives and Master Plan3. Target Areas / Target area committees4. Plant wide roll-out5. Management Support

TPM Goals:

Zero defects Zero accidents Zero unplanned downtime Zero speed losses Zero Waste

Benefits of TPM: Increased skills through additional training Better job satisfaction

Operators – More involvement in solving annoying equipment problemsMaintenance – More challenging work

Improved plant productivity and capacity Lower operating costs Improved equipment lifespan Better ability to satisfy customers