TPM, Total Productive Maintenance

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Last update: May 25th, 2004

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What is TPM?

Total Productive Maintenance (TPM) is a global approach which brings operations around the machines into focus, in order to minimize downtimes and maximize machines and equipment capacity. Maintenance through TPM is no longer regarded as a non-profit activity. The goal of TPM is to avoid emergency repairs and keep unscheduled maintenance to a minimum.

Picture: Automatic Insertion head moving over PC Board 

Foreword; about Machines Performances

There is a common belief that machine performance is steady, except its slow declining in time. Performance like takt time, machining speed, capability remain generally unquestioned. Yet, thorough follow-ups will reveal reality is far from that ideal.

Analysis of machine yield often relays on achieved production compared to nominal capacity.
Is it low, one will look at operators first, as machines cannot be blamed for lack of motivation...

Reliability, real yield, real processing time or maker's specs are scarcely questioned and believed to be true. Features will always be highlighted by optimistic makers, talking about a perfect world without disruptions nor impact of human factor...
In productivity improvement projects, focus is frequently on the operator. It's true, operator's work deserves some attention, but as soon as his share is optimized (or machines are full automatic), focus must be on the machines themselves.

Bad chosen monitoring indicators may lead to optimistic illusions, far from reality...

A workshop is open 8 hours a day, the machine is scheduled for operating 7 hours
(one hour is spent for various non-productive operations) .

Work rate is: 7 / 8 x 100 = 87.5%
 

Looks good, but what is the real yield of that machine?

Company owns its machines!

As the company owns the machines and equipment, why not try to improve them?
Better access for cleaning or maintenance, improved ergonomics, enhancing performances... There are numerous improvement points.

Besides, if makers of a specific type of machines are few, there is an important risk to become a kind of hostage, for deliveries of spare parts, technical support and of their marketing policy.

If the number of makers is really few, our competitors may have same equipments! How to get significant competitive advantage then?

Some equipments, machines, can control the total performance of the whole company. Theses peculiar resources must have constant focus.
See my theory of constraints pages.

The goal: be a perfect company

In old, middle age Japan starvation periods were current. The islands never offered much usable ground and no natural resources. Being careful with commodities management have always been a necessity. Dramatically in postwar Japan, at the time its industry was reborn, all kind of waste was a sin, as the country was down and any piece of material very valuable. This basic (both historical and cultural) background made it natural to Japanese to consider eliminating waste as a way to yield gains. A perfect company achieves to eliminate all types of waste and succeed having:

Zero accident, zero defects, zero stops!

No incidents nor accidents means no production stops, no "human losses", and no extra expenses. No defects means 100% of processing time is wisely used to generate value, without scrap and waste.

Zero defects = zero control!

In order to minimize machines stops, improve actual machines and to maximize their usage, to decrease operation expenses; postpone or even cancel new investments, as well as introducing newer technologies without repeating former mistakes, it is necessary to:

  • Increase machine productivity
  • Postpone investments for additional equipments
  • Increase machine reliability = find and prevent micro-stops
  • Increase payoff by getting Added Value faster

  • Improve actual methods:

    • Make efficient maintenance, reconsider operator's place (he has 5 wonderful sensors!)
    • Highlight operators' function
    • Improve work conditions
    • Reduce "firemen syndrome" (sudden panic reaction to surprising breakdown)
    • Insure consistency of company development by involving " specialists " (which must have available time) for new investment projects and internal modifications.

Zero default = zero check!

No quality defects mean:

  • Time used 100% for manufacturing goods able to be sold,
  • no scrap,
  • no rework
  • no waste

Work = capacity + wastes

Many investments for additional capacity could be postponed or even canceled by eliminating wastes, nagging on capacity.

To read more about fighting waste in TOYOTA style, click here

Do not mismatch "creating Added Value faster" and "maximizing machine time!"

Action Plan

Before rushing into TPM, targets should be defined with great care. As for SMED or KAIZEN, improvements in an industrial environment are nearly infinite and therefore, prior careful analysis is necessary. The share of Added Value (A.V) in machining time is a key point, because maximizing does not mean endless activating the resource.
An interesting way is to seek guidance by reading about theory of constraints.

When A.V share is known, machine must be used smartly in order to maximize A.V production. Precise standards must be set, as well as tough targets, so that seeking maximum becomes constant action like kaizen is an ongoing effort to improve.

 

 

TPM Total Productive Maintenance

TPM came up when machine productivity was to be improved. Japanese engineers spend a lot of time on shop floor (the "gemba", or "where it happens") watching and taking data.

A machine's day

No machine can run during total available shop time. There are necessities like changeovers, feedings, preheating or daily maintenance requesting the machine to stop, or at least suffer non productive time. Compared to shop opening time, the machine productive time is called Gross (or raw) machining time.

In this gross machining time, one expects production achievements to be equal to time divided by standard pace or machine takt. Yet production data show results are much lower! Random disruptions cause performance to drop; failures, drifts, micro-stops...
As a matter of fact, real takt is always lower than standard takt.

Gross machining time minus lost time equals real or net machining time. Losses occur further on when we realize time used to produce parts was spent to produce good parts as well as defective ones... Some of the defective ones may be reworked, with additional expenses, others may just end as scrap.

Machine's day breakdown

 
Available Time = shop opening
Gross machining TimePlaned non-productive actions
Net machining Time breakdown, performance loss
Usable time non quality

Several events and random problems will reduce the share of productive time. You cannot sell what you can't produce.
A competitor can.

TPM Monitoring - Loss Measurement.

The figure above shows well all kind of losses causing machine productivity to drop. Choosing non acurate monitoring system may not reflect the real situation. To insure a good monitoring and drive improvement projects, a far more detailed system is requested.
TPM proposes an all-in-one rate combining all machine productivity factors;

OEE Overall Equipment Efficiency. OEE is also called "demonstrated capacity".

Let's see how to calculate OEE and what it components are:

A = available time: workshop opening time or possible operating time.

Available Time = shop opening

B = gross machining time
B = A - total of machine stops (failures, changeovers, feedings..)

Gross machining TimePlaned non-productive actions

C = net machining time
C = B - performance loss = difference between theoretical and actual takt due to minor stops

Net machining Timebreakdown, performance loss

During C good parts as well as defective are processed

D = usable time => time producing good parts
D = C - quality loss: non quality, settings, trials, starting...

Usable timenon quality

With above definitions, we can define three rates:

Availability rate = B/A = (Workshop opening time-stops) / Workshop opening time

Performance rate = C/B = net running rate x speed yield with: Net running rate = (quantity processed x cycle time) / (Workshop opening time - stops)
And
speed yield = theoretical cycle time/ real cycle time

Quality rate = D/C = (Total processed quantity - No good quantity) / total processed quantity

And finally a super rate: Overall Equipment Efficiency, OEE.

OEE = availability x performance x quality

 

 

Graphic chart courtesy of Hans Peter Staber

 

 

 

OEE

OEE is the sole indicator encompassing all parameters which affect productivity of a machine.

While computing OEE, if one of the three rates declines, OEE declines as well.

 

 

OEE

Read more about OEE

How follow-up of OEE allows a global view, and close examination of its components helps finding out next improvement action.

Reminders

  • Only sold parts or products will bring profit. Discarded production may be recovered by rework but with additional expense. Sometimes it's just a total loss.

  • In a just-in-time production context, every exceeding production is a waste, because the units have to be sold at discount prices or disposed. The wasted time cannot be used to produce useful other production.

  • Real takt is always lower than spec.

  • Time spent for production is also used to produce defective units!
    		•

    Before starting TPM, few companies are aware of such wastes.

     

     

    Waste definitions & quantification

    TPM indicators and metrics seem simple, yet their details and related data can be difficult to gather.
    Formal and clear definitions of waste types and metrics is necessary prior of starting.

    Once defined and accepted, these categories will be the database to feed, manually or automatically. For each event affecting the machine, its duration is to be fed into the database, according to category breakdown. This data collection job can quickly become a chore, so it is wise to think and design a system ahead.

    The proportion of micro-stops is generally totally unknown (unaware) until the first analysis reveals its importance.

    This example is taken from an Automatic Insertion workshop where electronic component are shot through PCB holes. It is suitable to any other activity.

    Proposed definitions:

    Machine stop:
      • machine breakdown > 5 mn
      • Energy shutdown ( air / electricity / hydraulics )
      • changeover: according to normal scheduling or unexpected
      • parts shortage
      • spare parts shortage
      • lack of manpower
    Performance loss:
      • reloading / feeding of components < 5 mn
      • minor stops < 5 mn
      • speed / takt drift
      • optimization of insertion programs
    non-quality losses:
      • components broken
      • false insertion (value error or polarity)

    Example of calculation

    A workshop is working daily 8 hours (480 minutes). Machine available time is typically 440 minutes. Machine stops accumulate a total of 50 minutes, which can be broken down in:

    • Changeovers = 20 minutes
    • Machine breakdown = 20 minutes
    • Adjustments = 10 minutes

    Cycle time according to specs is 120 pieces / hour, but actual measurement reveals 100 pieces / hour only.
    Quantity manufactured : 600 pieces / day
    Quantity rejected : 18 pieces, 12  recoverable, 6 to be disposed.

    Raw machining rate = (440-50) / 440 x 100 = 88.6%

    Net machining time(0.6minute/piece x 600 pieces) / (440-50) x 100 =92.3%
    Speed rate = 0.5/0.6 x 100 = 83.3%
     Performance rate 76.9% (0.833 x 0.923 x 100)

    Quality rate = (600-18) / 600 x 100 =     97%

    OEE = 0.886 x 0.769 x 0.97 x 100 = 66.1%

    TPM, how to?

    Until now, our explanation about TPM was maintenance focused, but what is it to daily operation?
    The acronym TPM, Total Productive Maintenance stands for:

    • Maintenance: keep in good shape, repair when necessary, cleanse, lubricate and accept to spend required time.
    • Productive: Try to perform these operations while production is going on or with fewest disturbance.
    • Total: consider all aspects (even painting the machine) and associate everybody.

    Basically:

    • Cleanliness and order: first requirement, as no time saving nor performance can be achieved in a messy dirty place. Early warning by leaks detection isn't possible when everything's just greasy and dirty. These pre requisites are 5S housekeeping principles.
    • Know the machines: how does it work, what performances, what weak points.
    • Follow-up daily machines / workshop performance, set a target and strive to reach it.
    • Associate everybody: collect data, follow-up, monitor, suggest improvements, increase knowledge and know how, keep motivation.

    Operators know their machines well. They usually develop a special relation toward their work tools and are precious 5 sense intelligent sensors able to forecast problems by odor, noise, color or vibrations...

    Maintenance, MTBF, MTTR and availability

    In order to cope with stops and failures that nag on available time, it is mandatory to analyze the downtime and get to know each machine's reliability and maintenance-ability.

    Reliability index: MTBF

    (Mean Time Between Failure)

    • MTBF = Total machining time / number of stops

    Maintenance-ability index: MTTR

    (Mean Time To Repair)

    • MTTR = Total downtime / number of stops

    Availability rate

    • Availability = MTBF / ( MTTR + MTBF )

    Example: available time
     

     

    Event

    duration (hours)

    1

    Normal work

    4

    2

    Stop

    2

    3

    Normal work

    2

    4

    Changeover

    0.5

    5

    Normal work

    3

    6

    Failure

    1

    7

    Normal work

    1

    8

    Breakdown

    0.5

    9

    		 Normal work

    1

    10

    Stop

    1

    A From the example:

    MTBF = (4+2+3+1+1) / 4 = 2,75h

    MTTR = (2+1+1+0,5) / 4 = 1,125h

    Availability = MTBF / ( MTTR + MTBF ) = 2,75/(2,75+1,125) = 70,96%

    Analysis: on this machine, mean breakdown duration is 1h 6mn, and mean time between failures is 2h 3/4. Globally this machine is available for value creation only 71% of its time. 29% is lost in stops and repairs. This machine cannot be let without overview as it stops frequently. Repairs are long, but is it a matter complexity, accessibility, lack of organization or lack of know how?
     NOTE: Changeover is considered "normal work" as it was planed. It does not affect the calculations.

    Machine stoppage analysis

     

    Often, when a machine comes to stop, the typical sequence of events from moment of stop to restart at normal speed is:

    • Ta = moment machine stops,

      • Dwelling until operator takes notice, reacts, comes to have a look at control panel or work area. If he's unable to restart, he'll call for help, tech for instance.

      • Dwelling during the time of message transmission, tech reaction time, comprising the time to go from his location to the machine.

      • Diagnostic: technician take some time to establish the stoppage cause.

      • He has no relevant tools, as he didn't know the stoppage cause. he'll return to get spare parts, tools, etc.

      • Repair: repair time is related to failure nature and grade of complexity, as well as tech's know-how.

      • Adjustment and trials: depending the repair, heating, tests and adjustments may be necessary.

      • Speed-up: some machines will take some restart and a speed-up sequence to recover normal speed.

    • Tf = Stop is over

    This process repeats itself more or less each time the machine stops, regardless to stoppage cause, with variable duration. Responsiveness at each step can be improved:

  • Quick reaction in formula 1 pit spirit
  • Parts and material at hand, nearby (inventories, maintenance kits...)
  • Know-how and accuracy (through training, autonomous organization...)
  • Suppress or reduction of adjustments and trials

     

    		•

    Each time operator lacks the knowledge to make a minimum diagnostic and fix the simplest problems, he'll have to call for help. This assistance can be:

    • remote location from the spot,
    • not available (absent),
    • at home but on duty
    • not available because fixing another problem

    The risk is than important for stoppage to last, even the cause is simple and could be fixed easily and quickly.

    Such phenomenon fosters more know-how and more autonomy for production operators.

    Five steps to zero failures

    Five simple steps to achieve no failures:

    1. Respect basic requirements: cleansing, lubrication, tightening, torques...
    2. Respect conditions for use
    3. Repair any defect
    4. Improve poor design
    5. Prevent human failures, during normal operation and during repairs

    Respect basic requirements means to stick to maker's instructions. Neglecting cleansing, lubrication or other basic maintenance operations is a risk factor for fast equipment decay. Saving those operations to increase production time is a no-good, short term choice, ending most likely with an extended repair afterwards. Current maintenance must be thorough fully planed, but cannot be neglected.

    It is sometimes tempting to modify machine cycle times and speed, timings and other adjustments. Here also there is a risk of accelerated decay and problems in operations, as all equipment components were designed for a specific range.

    Repairing and mending is a warranty for keeping machine operational. Painting blisters or worn out parts is not only improving cleaner work conditions but is also contribution to 5S housekeeping principles and helps making leakage visible before they turn into serious problem.

    Improving poor design can take various, more or less technical ways. Machine makers have to solve problems and find solutions suitable for their purpose. Ergonomics and access are often considered secondary compared to design-to-cost constraints.

    Users and owners should therefore feel free to modify in a more operation-suitable way.

    Who's in charge?

    between production operators and maintenance techs, how to share the tasks?

    First, look at the table on the right. Once operators prooved a real autonomy and basic know-how, their share can be enriched..

    Maintenance techs workload can be lightened by empowering operators to take over simple, routine tasks. This in turn frees valuable time for more complex, technical matter, allows to concentrate on preventive maintenance and improvements.

    What?

    Operator

    Maintenance

    Respect basic conditions

    Mandatory

    Mandatory

    Respect conditions for use

    Mandatory

    Mandatory

    Repair any defect

    Do or ask to be done

    Do and record/feedback

    Improve poor design

    Feedback about difficulties, poor design and suggest improvements

    Study improvements, do or propose

    Prevent human failures

    Respect work guides and procedures

    Improve work techniques and maintenance

    Cleaning = preventive maintenance!

    Preventive maintenance is made of:

    1. Daily maintenance: cleaning, lubrication, tightening...
    2. Inspection = diagnostic
    3. Repair: early replacement = early treatment

    Daily systematic dust and dirt elimination allows early problem detection such as leaks, abnormal worn outs, scrap...

    Regular tightening check, associated with lubrication extends machine's life, and prevent breakdowns.

    With maker's documents and recommendations, set the shop standards for cleaning and lubrication.

    		  

    Conclusion

    Machine theoretical performances are far from actual, daily measured achievements. A lot of disturbing factors cause the performance to drop. Simple follow-up, like "machine work time/shop open time" ratio might therefore be misleading.

    OEE give a complete, yet synthetic, all encompassing view of the machine efficiency. Further analysis on OEE components highlight where improvement efforts must be focused.

    TPM does not interfere with "classic" maintenance on fundamentals, but proposes to empower the people in steady contact with machines to take over a part of the job. For them, it is an opportunity to enrich their routine. Well done, TPM improves machine yield, favors team spirit and value operator's contribution to value creation.

    TPM is a good opportunity to raise operator's skills and know-how, to foster improvement suggestions.

    TPM should be started in a pilot process or workshop and later extended.

    Beware not to turn actors into "accountants" as data capture for OEE requires often a huge effort! Don't forget production is about sellable goods, not data!

    Author, Chris HOHMANN, is consultant and trainer.

    Former production and engineering manager, he practiced TPM and other lean manufacturing tools and techniques.

    Contact author

     

    URL : http://chohmann.free.fr/
    © Chris HOHMANN