Friday, July 2, 2010
Lean Manufacturing Requires Responsive and Reliable Maintenance
Lean operations require maintenance that is responsive and reliable. When we have isolated operations that are adding value to pieces in a batch that eventually gets passed on to another operation, one machine going down does not present itself as a critical event.
If we have many operations organized in a cell and one piece of equipment breaks down, the entire cell goes down. We require equipment that does not go down very often – ideally not at all – and when it does go down we need to get it up and running as quickly as possible. This imposes requirements on the maintenance system. The maintenance system is not limited to the maintenance function. The system includes standard procedures that are followed by the operators and equipment that does not breakdown and/or can be repaired quickly.
A good way to begin to improve the maintenance system starts with a workshop focused on a single piece of equipment that is or will be critical to a lean, one-piece-at-a-time operation. The workshop team goes through a process of detailing the machine.
The equipment is shut down and (this is very important) locked and tagged out so that no one will be injured in the process. The first tools are rags, brushes of various sizes, detergent, cleaning solutions, and sometimes solvents. The team swarms over the equipment cleaning it from top to bottom. Sometimes there is a temptation to bring out a steam cleaner to get through the gunk. This is best discouraged, because we are using cleaning as a way of inspecting it to identify problems that require attention, not just to get the machine clean. Cleaning by hand allows us to catch problems large and small.
The team members have tags that can be easily wired or tied to the machine close to where a problem is detected. The problems include every loose or missing screw, cracked glass including lenses on dial gauges, and leaks of every kind. In short, any condition of the machine that is not optimal is tagged. The tag includes the date and time it is fastened, the condition to be corrected, and it’s precise location. The information is also recorded on a list. In some cases a two-part tag is used so that a copy can be retained, instead of writing up a list. Tags are numbered to help track the actions taken to resolve the conditions.
In addition to problems, we may see opportunities for improvement. Any gauge that provides information to the operator should be easily visible. This sometimes requires re-locating or re-orienting it. Gauges should show operating ranges, so the operator can easily see when pressure, temperature, or other variables are outside the range. Usually the range is indicated by painting markings on the dial face or on the lens itself. Digital readouts have the operating ranges affixed near the gauge.
We label controls better and placed them within easier reach. Shadow boards are made to hold hand tools, or their standard locations are otherwise be indicated. Adjustments are often made easier by reducing the number of turns required, putting a 90 degree handle on the wheel to be turned so that it can be cranked, standardizing fasteners so that fewer different size wrenches are required, improving signage to remind operators of required steps and precautions. We make lubrication points more accessible, and install lights to indicate that certain actions are required.
Often simple modifications can be made so that the machine will stop automatically before running out of material or jamming, preventing a crash. We modify conditions that make the equipment difficult to clean, such as piping that makes it hard to sweep or nooks and crannies of the equipment where dirt or chips or debris get caught.
One or more members of the team are maintenance personnel who can start making repairs and fixes and removing the tags. Once the correction is made, the tag is removed and tacked or taped to an easel board to keep track of progress.
Including maintenance personnel also allows us to use their experience with the machine and knowledge of what breaks down frequently. If a history of the machine and its maintenance has been kept, this will be data for the team to study.
The team will use their experience and knowledge of the history of the machine to design a standard procedure for preventive maintenance for this equipment. A good procedure will specify the continued use of tags to identify any item that needs attention. It will also detail the preventive maintenance of the equipment that can be done by the machine operator. This is known as autonomous maintenance. Problems that jeopardize safety or quality requires immediate attention. All operators of this equipment will need to be trained on the standard procedure and its importance.
The Maintenance Department will be expected to stay on top of all pending tags. Since the tags have the time and date that they were placed, it will be easy to see what items are taking a long time and may need follow-up, special attention, or additional resources.
Operators and maintenance personnel become a team to keep the machine in optimum condition, which support from management and supervision to overcome any obstacles. These workshops lead to a different way of operating for several people. The team or a portion of it will need to keep a close watch on the new procedures to make sure they are being followed. The team periodically reviews the standard procedures discovering their shortcomings and making adjustments to improve the standards.
Over time other machines will undergo a similar process. They will have standard procedures created, including for autonomous maintenance. The new teamwork between maintenance personnel and value-adding operators will expand to include more equipment. The Maintenance Department will usually find that their operating procedures will have to be modified to meet the new approach. It is vital that the on-going process be followed and evaluated, or there is a real danger that the equipment and the behavior of maintenance personnel and operators will revert to what they were before.
These approaches become Total Productive Maintenance (TPM), as they are integrated into all of the operations and the operators, maintenance personnel, management and supervision all settle into their new roles.