Unit 1

MAINTENANCE

Maintenance • Maintenance is the activity carried out on an

asset in order to ensure that the asset continuously perform its intended function.

• Or to repair an equipment that has failed, or to keep the equipment running , or to restore to its favorable operating condition.

• It improves system’s overall reliability, availability, and consequently higher production efficiency.

Two Basic categories

• Machine & equipment maintenance

• Building maintenance

Goal of Maintenance• To keep production systems in good working order

at minimal cost• Reasons for maintenance

•To avoid production or service disruptions•To avoid missed delivery dates

• To keep resource in good working condition• To maximize useful life of equipment • To minimize operating cost• To minimize breakdowns• To enhance safety of manpower

Benefits of Maintenance

• Increased safety• Reduce downtime• Trouble free service and output at rated

capacity• Reduced cost of operations• Real time product delivery

Evolution of maintenance philosophy

• First generation(1930-40): fix it when broke (Breakdown maintenance)

• Second generation (1950-70): scheduled overhauls (Preventive maintenance)

• Third generation -after1980- condition based, failure data analysis, reliability centered maintenance, Total Productive Maintenance

How Machines/equipment fails?• There is a definite pattern of life span of a

machine/equipment 1. Infant mortality: due to presence of weak or

substandard components, design inadequacy, 2. Second stage –more useful ,less failure if there

then they are unpredictable3. Might fail: reasons are abrupt changes in stress

distribution in the components, fatigue due to flaws in the molecular structure of the metals or plastics involved, sheer quality deficiency

Maintenance cost

• Breakdown of machine makes the workers and machine idle resulting in loss of production, delay in schedules and expensive emergency repairs.

• Down time (idle time)• Cost of spares• Cost of maintenance labor• Losses due to inefficient operation of machine• Capital requirements required for replacement

Maintenance policy

• Reactive maintenance• Proactive maintenance• Predictive maintenance• Total Productive Maintenance

Reactive vs Proactive

Reactive Maintenance:• Breakdown maintenance

• Reactive approach; dealing with breakdowns or problems when they occur

Proactive Maintenance:• Preventive maintenance

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

Breakdown maintenance

• It is emergency based policy in which plant operates until it fails.

• The maintenance staff locate any mechanical, electrical and any other fault to correct it immediately

Preventive maintenance

• It prevents the probable breakdown and it ensures smooth and uninterrupted production by anticipating breakdowns and taking corrective actions

• Preventive maintenance policy has four forms

(1) Time based (2) Work based (3) Opportunity based (4) Condition based

Two aspects of preventive maintenance

• Inspection

• Servicing

Preventive V/S Breakdown Maintenance

• PM is a routine inspection designed to detect potential failure condition and make minor adjustments and repairs that will help prevent major operating problem

• BM is the emergency repair and it involves higher cost of facilities and equipment that have been used until they fail to operate

Continue……

• An effective PM requires properly trained personnel, regular inspection and have to maintain regular records

• PM is planned in such a way that it will not disturb the normal operation

• BM stops normal activities and the machine and the operators are rendered idle till equipment is brought back to normal condition of working

15S-16

Total Maintenance Cost

Breakdown andrepair cost

Optimum Amount of preventive maintenance

Cos

t

Total Cost

Preventivemaintenance cost

Table 15S.1

Total Productive Maintenance • Now a days manufacturing has become

automated and in such situation quality depends on reliability of equipment

• Though operation have been automated, maintenance still depends on human input

• TPM is a company wide equipment maintenance system that organizes all employees from top management to production line worker and can support highly sophisticated and advance equipment.

TPM continue……

• TPM has two objectives• Zero Breakdowns• Zero Defects

• When breakdown and defects are eliminated the equipment utilization will improve

• “TPM is defined as productive maintenance involving total participation.”

• The word total in TPM refers to • Total effectiveness • Total maintenance including maintenance

prevention and corrective maintenance• Total participation of employees

TPM tries to eliminate three big losses that are obstacles to equipment effectiveness:

(1)Downtime: equipment failure from breakdown and set up & adjustment

(2)Speed losses: minor stoppages, reduced speed

(3)Defect: process defects (due to scrap), reduced yields

TPM development program• Basically there are 3 stages and 12 steps of

TPM development program• Preparation stage: a suitable environment

is created by establishing a plan for introduction

• Preliminary Implementation stage: here goals are set and also a time frame is mapped in order to boost the morale of employee

• Implementation stage: company measures the actual result achieved against TPM targets

Predictive Maintenance

• Predictive maintenance• An attempt to determine when best to perform

preventive maintenance activities

Maintenance performance

• Productivity of Maintenance= Output/Maintenance cost

• Downtime index= downtime hoursX100/Production hours

• Maintenance cost index= maintenance costX100/Capital cost

Life Cycle Costing

• Cost effectiveness of a system can be simply defined as the measure of a system in terms of mission fulfillment (system effectiveness) and total life cycle costs'. 

• Cost effectiveness, (which is similar to the standard cost benefit analysis in industrial and business parlance) can be expressed in various terms, depending upon the specific mission or system parameters, that one wishes to measure.

• Thus, Cost Effectiveness figure of Merit= System Effectiveness / Life Cycle Cost (LCC)

• It therefore flows out that, while evaluating any equipment, life cycle costs have to be considered to arrive at the cost effectiveness, else we will be evaluating the equipment only on 'System Effectiveness' parameter.

Life Cycle- Womb to tomb approach• Any equipment which is in use in the armed

forces, had been introduced at a particular time after the need had been felt, operated and used by the concerned agencies and discarded when it no more fulfilled the mission assigned to it. 

• This in effect is the Life Cycle Concept of an equipment and can be defined as the period since an equipment is conceived, developed, produced or procured, operated and maintained and finally discarded. 

Phases of Life Cycle.•  Need or Requirement Phase.  In this phase, based on the threat

perception, operational plans, technological development necessities, the need for a particular equipment is established.  After the feasibility study, the equipment is undertaken by R&D wing for development.

• “     Design and Development Phase. In this phase, R&D wing designs the equipment as per the norms laid down.  After the prototypes have been developed, technical trials are conducted.

• “     Evaluation and Trials.  After the technical trials, the equipment is subjected to extensive user and environmental trials to validate the performance  In case of imported equipment, study teams may visit foreign countries to identify and evaluate an equipment before it is imported for trials.

• “     Manufacture or Procurement After the decision to introduce an equipment is taken, it is either manufactured or procured from trusted vendors.

• “     Operation and Maintenance.  Equipment is issued to units for training, equipping and usage.  It is operated and maintained.  Periodic repairs and overhauls are carried out and modification and modernisation programmes are implemented as applicable.

• “     Disposal.  Once the equipment has outlived its physical/ operational/economic life, or has technologically become obsolete, it is discarded and disposed off.

Economic life of an Equipment• Useful economic life of an equipment can be defined as the

period for which the equipment fulfils its mission as per the laid down qualitative requirements at the desired costs.  Besides the physical life, this period is affected by operational, economic, environmental and other conditions.  Factors affecting the useful economic life of an equipment are as under:

• “     Operational Obsolescence.  The equipment must fulfil the task in the contemporary operational environment Operational obsolescence will set in, due to its non-effectiveness in the present operational scenario.  This will curtail the fife of equipment.

• “     Technological Obsolescence.  In the present environment of rapid technological advancement, equipment may become technologically obsolescent and lose its effectiveness thus curtailing its life.

• “     Economic Factor.  Operation and maintenance of the equipment must remain within the Emits of cost effectiveness.  If the cost of operation and maintenance becomes very heavy, the equipment may be phased out earlier thus reducing its life.

• “     Obsolescence of Support System.  If the support requirements like spares needed for functioning of equipment are not available, the equipment ceases to function and is hence discarded.

• “     Stretch Potential. Life of equipment can be enhanced by way of modifications and modernisation to maintain its reliability and functioning at the desired level.  Greater the amenability to modernisation and modification greater the stretch potential and longer is the life of the equipment

Assessment of Life of an Equipment• It is of utmost importance that life of equipment be

accurately assessed by scientific methods.  • This is to avoid gaps in planning and to forecast the

replacements, modernisation and formulate realistic acquisition policies. 

• In the past, when equipment and weapons systems were not as sophisticated and complex as they are today, life of equipment was assessed mainly by past performances in an empirical manner.  This was not a reliable method.  However, with introduction of the state-of-the-art equipment various tests have been - evolved to assess the Time between Overhauls (TBO) and total useful life more realistically- various methods for predicting life of equipment are in vogue today.  Some of the important ones are:

• Technological Forecasting.  At the time of introduction, it is necessary that anticipated technological advancement and future operational environment be predicted.

• Accelerated Life Testing.  The present day technology has made it Possible to test the equipment scientifically and predict the life.  For example, by firing limited number of shells from a gun and measuring the wear and tear, scientific estimate of the life of the barrel is made.  Even if the absolute cost is high, the overall savings could be phenomenal.

• Destructive Trials.  The equipment is operated till it ceases to function.  Though this is a costly method, it not only helps in assessment of in service life period but also in evaluation of its maintenance, repairs and overhauls requirements.

• Fatigue Life Testing.  This method of testing is used extensively for components that are subjected to continuous vibrations or undergo continuous reversal of stresses like main rotor blades of a helicopter.  Components are subjected to this test for a specific duration after which computerised analysis of inter-crystalline molecular structure is made to determine the TBO and useful life.

• Calendar Life Testing.  The life of some components is limited to a calendar life instead of the actual usage in turns of Kms or hours.  Usually such components are rubber parts or other similar items that deteriorate with age or environmental conditions like humidity, temperature, salinity etc.  Methods like Simulated Environment Chamber tests are used to determine life of such components.

LCC

• Cost Breakdown Structure• Description of all the categories.

Life Cycle Costing

• Packing charges.• Insurance charges.• Exchange rates.• Payment schedule - payment and delivery -

penalties and interests.• Any advance payments.• Credit facilities.• Transportation charges.