Tangram Technology Ltd. - Manufacturing for Window Fabricators

Total Productive Maintenance

Small machines do not remove the fact that when a component is required it must be produced. When WIP levels are low there is little slack in the system to work on should a machine fail to be capable of operation. This demands high machine reliability for all machines and fast repair in the event of failure. Another reason for the use of simple, low functionality machines over the use of complex multi-function machines?

A planned maintenance programme is a vital requirement to remove unscheduled stoppages and increase the dependability of machine availability. The Total Productive Maintenance (TPM) approach is used to ensure that unscheduled stoppages do not occur.

Any unscheduled stoppage causes problems in many ways:

Bottleneck machines may run short of product and create a loss of production to the whole system.
Bottleneck machines become more overloaded and time is lost.
Production planning is difficult, if not impossible.
Lead times increase.
Scrap and re-work is increased.

The TPM strategy is developed to reduce these problems and the costs associated with them. TPM ensures that machines are available when required and should include the following points:

Maintenance is planned into the production schedule.
Machines are designed for fast repair.
Maintenance is decentralised to the operators.
Tool kits are provided close to machines.
Stocks are carried of trouble prone items or better still the trouble prone item is designed out of the system.
Predictions are made for machine breakdown via a written history and performance measurements. Most machines suffer the same breakdowns repeatedly, a history will let you diagnose the problem quickly and predict what is going to go wrong. To star in this process, go for those faults that occur most often at the bottleneck.
Maintenance problems are designed out of the machines.

Note: TPM can also be applied to tooling and other critical production items.

This idea of planned maintenance and stoppages for maintenance does not fit well with the old concept of trying to increase machine utilisation - another one of those traditional accounting measures. Machine utilisation obviously falls if the machine is undergoing routine maintenance but the machine reliability almost inevitably increases. Plan for it to control it and reduce the ultimate costs.

TPM is an investment to protect future production capability. Look at the factory. Which pieces of equipment would stop the factory if they failed? How long would it take to get them fixed and how much would it cost? Don't just look at the production equipment but also at the support equipment. If you lost the compressor right now then what happens to your output, and when was the last time that the compressor was serviced?

Five easy steps to starting the Total Productive Maintenance process in the factory

Owner-operators

One of the basics of using TPM in a work cell environment is to use the cell team to carry out basic preventative maintenance on the machines in the cell. This is sometimes termed 'autonomous maintenance' or 'cell-based maintenance'. Maintenance at the cell level brings many benefits:

Cell members are ideally suited to carry out first response maintenance. They can lubricate, clean and inspect to prevent minor concerns developing into major problems.
Cell members know more about their machines than almost anybody else. They know the special quirks of each machine and how to get good production out of the machines.
Cell members have a good idea of the history of the machine, what has gone wrong with the machine in the past and what is likely to fix it now.
The cell members become owner-operators of the machines and take more interest in maintaining them. The cell members become more responsible for their activities and their involvement increases.

An outline process to implement cell based maintenance with owner-operators is:

Step 1: Operator cleans, inspects and checks machine with maintenance staff in attendance. Note: Pay particular attention to Health and Safety issues.

Step 2: Machine is serviced to eliminate oil or air leaks and to bring up to good condition. Any defects noted by operator are repaired and machine is 'delivered' to owner-operator in good condition.

Step 3: Checklists, instructions and standards are developed by owner-operators for use by owner-operators.

Step 4: Maintenance carried out to checklists by owner-operators. Maintenance staff only involved for exceptional projects and service identified by owner-operator.

Step 5: Maintenance work with owner-operator to extend knowledge and skills base. This allows owner-operator to carry out a greater range of maintenance and service tasks.

Cell based maintenance can keep machines operating when they are needed but the important point is to only use them when they are needed -setting the right level of machine utilisation is also critical to operating effectively.

Machine utilisation

It is recommended that the maximum machine utilisation sought is around 80%. This might seem low to those people used to seeking high machine utilisation (generally just to keep the numbers up) but it is the optimum figure to allow enough time for the total productive (planned) maintenance activities and the basic philosophy says that you do not operate a machine if the output is not immediately required. This is in contrast to the concern with super-machines where optimising machine utilisation is considered critical.

Accountants have had a fascination with machine utilisation and this has been one of their key measures of factory efficiency. This is despite the fact that the production area largely does not determine the machine utilisation, this is determined by the demand generated by sales. Production Managers generally have little control over this! Seeking high machine utilisation without matching sales is one sure way to cripple a company (see box below).

Where standard products are being produced, seeking high machine utilisation can result in the production of products that are not needed - simply to get the numbers up - this leads to over production, high inventory values and wasted time in the long run.

OPT says that 'Utilisation and activation of a resource are not the same thing. Activation is when a resource is working and utilisation is when it is working and doing useful work. Producing stock for inventory is not useful work.' What we have previously termed utilisation has often been simple activation without utilisation. Unless the product is going to be used immediately after being processed then the process is simply costing time and effort before it needs to - it is locking capital up in the business that could be used to produce goods for sale.

Remove the current idea of machine utilisation (the machine is working) from your ideas and replace it with true utilisation (the machine is working and doing useful work). Accept that over-capacity (as generally defined) is necessary to cope with the need for maintenance and the flexibility to respond to customer demands.

Machine utilisation kills.

Whilst working with an aluminium window fabricator some years ago there was a fascination by the management with ‘hearing the saws work’. Sawing was the first production step and the management thought that as long as they could hear the saws working then everything else was OK. It didn’t matter that the rest of the factory wasn’t doing anything with the sawn profile - the saws were working. The concept of machine utilisation was so prevalent that immediately on receipt of any order the Production Manager gave it to the sawing area irrespective of the delivery date. One look at the production area showed a different and sadder story.
The saws generated so much work-in progress (WIP) at the front end of the process that the whole production line was totally clogged up. Sawn profile was lost’ in the stacks of WIP for weeks on end and every piece of product was moved, stacked, moved again, stacked again about 5 times before it even got to the next step of the production process. The production process was so chaotic (because the saws had to be kept running) that it actually took 16 weeks to produce an order that could be run through the factory in 3 hours.
The company had a turnover of around Ł5 million and the WIP on the factory floor was worth nearly Ł1.5 million - the company was running out of cash fast. Despite this, the idea of stopping the saws running was so alien to the company that they could not see that this was the main cause of their problems. They refused to stop the saws and machine utilisation claimed another victim within 3 months.

Manufacturing Strategy for Window Fabricators 7 - Machines (2)

Selecting the right machines is only the first step. Keeping them operating (but only at the right time) is just as important.

Download Adobe Acrobat file of complete series to date

Total Productive Maintenance

Five easy steps to starting the Total Productive Maintenance process in the factory

Owner-operators

Machine utilisation

'Manufacturing Strategy' Series.

The 'Manufacturing Strategy' series is designed to give window fabricators a set of ideas for managing production. The series is being published in Fenestra on a monthly basis and published here after the Fenestra publication. The series is:

Last edited: 17/05/05

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