Lean Maintenance Calculators
A collection of our most popular calculators in Excel format for off-line use
Lean Maintenance
Lean Maintenance is a key ingredient to a successful Lean Manufacturing environment.
Lean Manufacturing Needs Reliable Machines
Lean Manufacturing seeks to cut out three types of waste:
- Processes that do not add value for the customer
- Inefficiencies in processes
- Variations in the pace of production.
The latter concept is “mura” or “unevenness”. If an employee’s work day is divided between being idle for five minutes and working frantically for ten, then her workload should be smoothed out so she can work steadily all day.
In a Lean Manufacturing factory:
- Production is scheduled as it is ordered, rather than to build inventory
- Batch sizes are kept small
- Work-in-process moves smoothly from one operation to the next, rather than being stored as intermediate inventory
Therefore unscheduled downtime is a serious problem in a Lean Manufacturing facility. Unscheduled repairs interrupt the flow of work-in-process, thereby adversely affecting delivery time. There might not be a place for work-in-process to be stored even if the preceding operations can continue. The costs of unscheduled downtime are enormous in such a factory.
Lean Maintenance supports a Lean Manufacturing approach by preventing unscheduled downtime. The method is to reduce or eliminate the factors that cause machine breakdowns.
Why Machines Break Down
The four most common root causes for machines to break down are: operator error; programming error (for computer-controlled tools); inadequate maintenance; and environmental causes.
Operator errors can be as simple as improperly placing material or using too much force on a tool.
Numeric-control or computer-guided machines may have program bugs. A simple example would be trying to drill too quickly for the type of material.
Regular maintenance operations might be neglected, especially in a busy factory. An operator could forget to add lubricants. The operator might not be trained to perform all the necessary steps.
Many environmental conditions can take their toll on equipment: heat, humidity, vibration, or airborne chemicals.
Of course, some of these conditions may combine. An operator might neglect to clean away dust, and unusually humid weather could change that dust into a sticky clog over a cooling fan.
How “Lean Maintenance” Differs from “Lean Manufacturing”
Lean Manufacturing uses customer orders to pull production from raw materials. It is most successful when the company has a fairly reliable mix of orders coming in at a steady pace.
It is, indeed, possible to set a maintenance schedule so that the schedule pulls the maintenance activity. However, by itself, a schedule cannot prevent unexpected breakdowns.
Such breakdowns are equivalent to casting the manufacturing schedule aside because the most important customer has placed a rush order that pre-empts all others.
On the production side, a new customer order may trigger purchasing new raw material. This lead time should be built into the customer’s delivery schedule. However, a machine breakdown that requires an expensive, out-of-stock replacement part immediately harms the schedule. It is uneconomical to stock every possible replacement part to avoid this situation.
The performance parameters of the machines are more readily available than the likelihood of breakdowns for those machines. This type of analysis requires research into the maintenance and repair histories. See the article about Preventive Maintenance] for more background.
To conclude: Lean Maintenance differs from Lean Manufacturing because the maintenance must be planned, where the manufacturing can be “pulled” by customer orders:
- Machine breakdowns cannot be fitted into a schedule; instead they pre-empt the schedule
- Breakdowns may require ordering replacement parts on a “rush” basis
- Simply scheduling maintenance does not guarantee the absence of breakdowns
There is one similarity: both require careful planning based on the actual capabilities of the machines, whether to produce or to require preventive maintenance.
Overview of an Approach to “Lean Maintenance”
Recall that the primary concept for Lean Manufacturing is to reduce several types of waste. For Lean Maintenance, the equivalent “waste” concepts to be avoided are:
- Wasted Maintenance: maintenance or repair that does not add value…that does not improve the availability of the machine
- Inefficient Maintenance, even if it does add value
- Sporadic Maintenance, with cycles of low versus frantic activity…it is better to smooth out the schedule
Wasted Maintenance
Many of the gurus advocating Lean Maintenance point to blindly scheduled maintenance as a waste, especially if it involves replacing expensive components or incurring high labour costs or lengthy downtime.
Note the word “blindly”, however. Their advice is to measure, say, the wear of a part or the viscosity of the lubricant. This is “condition-based maintenance”, which defers maintenance until there truly is a need. Two requirements for condition-based maintenance are: measure the critical indicators that will change before the machine fails; and measure with enough lead time to schedule the maintenance and procure any required parts.
Refer to the repair history as a guide for how long a machine actually did run before a breakdown. This can provide a rough plan for scheduling maintenance. Also use that repair history as a guide to what should be tested in order to implement condition-based maintenance.
Inefficient Maintenance
To borrow a phrase from automotive maintenance, “While you’ve got the hood open, you should also…”. Scheduling several maintenance tasks for the same time can be much more efficient than arranging for repeated shutdowns.
Good planning also ensures that the right parts and tools are available, along with people who have the appropriate skills.
Of course, a “Lean” approach would also examine how efficiently the actual work is performed. Are there extra trips back to a storeroom for supplies? Would it help to invest in a maintenance trolley? Would better tools help the employees do a better job? What about training session from the manufacturer?
Sporadic Maintenance
Clearly the “frantic hurry” phase of maintenance comes during an unscheduled breakdown. In this situation, the repair person is most likely to make mistakes due to time pressures. This has the least likelihood of having all the necessary tools and parts.
Many maintenance managers aim to keep their maintenance crew scheduled to about an 80% load. This leaves some time for emergency repairs but the crew still is busy throughout the shift.
Another example of sporadic maintenance is a maintenance blitz. Beyond the obvious problems of overloading the maintenance team’s schedule, this blitz also means that skills may have become rusty in the intervening time.
The Guiding Precepts for “Lean Maintenance”
You should pause here and take the Lean Maintenance / TPM Assessment quiz.
The following precepts help guide the planning for Lean Maintenance:
Each machine, or at least each model of machine, has its own maintenance needs. Do not assume that each needs the same schedule.
Each operator should perform regular inspections and maintenance on their machines. These people should know the machines well, and can certainly take part in minor maintenance. Invest in training them for these tasks. Add instruction sheets and find other ways to make it simple.
One example of making maintenance easy is an automobile’s dipstick: bright yellow handle like the other two things the driver is encouraged to check; only one place to put it in; has markings for “too low”, “in range” and “overfull”.
Post a schedule for the maintenance activities, with boxes for the employee to initial and date, beside the instruction sheet.
Train the operators how to write work orders or how to report trouble verbally. This helps the repair people, and their schedulers, know what is wrong or where to start looking.
If less than 10% of maintenance activity is “repairs”, you might ease back on the preventive measures. If it is more than 20%, put more work into preventing the worst breakdown and repair situations. If your maintenance people can get everything done in the regular day shift, you’re doing well.
Without a computerized maintenance management system (CMMS), how do you log, track, and report on patterns of maintenance and repair activity? What do you use to determine the right frequency for preventive maintenance? How do you determine how many spare parts you need to keep a machine going without making emergency orders to your supplier?
In the best maintenance environments, a significant portion of the work schedule involves training and mentoring the operators to take on regular maintenance work.
None of this comes together without management support and commitment.
Next Steps for “Lean Maintenance”
Many gurus of Lean Maintenance suggest integrating that program into your existing factory’s production methodology. The next article deals with the essentials of Lean Maintenance , which apply to any situation. A third article discusses how to evaluate the success of a Lean Maintenance program. The fourth article discusses how Lean Maintenance is integrated with different production disciplines, such as Six Sigma or 5S.
Oskar Olofsson, 2011
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I am a Swedish-based Lean consultant, and the owner of the World-Class-Manufacturing.com web site.
Contact Oskar Olofsson© WCM Consulting AB, Vaxholm, Sweden