Introduction to Industrial Engineering
By Jane M. Fraser
Design or improve a production system
Return to the Table of Contents.
The goal of maintenance is that all required equipment performs flawlessly during all planned production time. Here are some examples:
Total Productive Maintenance (TPM) aims for three zeros:
- "Zero unplanned equipment downtime,
- Zero equipment-caused defects, [and]
- Zero loss of equipment speed.”(IE Handbook 16.65)
Another important Zero is Zero equipment related injuries.
Unplanned or unscheduled downtime occurs when a machine breaks down or works poorly enough that production is halted for repair or adjustment, called remedial or emergency maintenance. Unplanned downtime, unless balanced by overtime production, usually leads to lost production time, idle workers, and failure to meet promised delivery dates to customers. You can see why an organization wants to avoid unplanned downtime.
Obviously, planned or scheduled maintenance helps keep equipment operating properly. It can also prolong the life of the machine and reduce the life cycle cost of the equipment. For example, regular oil changes greatly enhance the performance of a car and greatly increase the life of the engine.
When purchasing equipment the IE should consider maintainability as one criterion.
In the article CNC Alarm Messages Over The Internet from MMS Online, Zelinski describes how CNC machines can be connected to the Internet and can be set up to send email to a technician when there is a failure. The technician, using a laptop computer, can remotely access the machine, again via Internet, and perhaps fix the problem quickly and easily.
The IE has to make a number of decisions in creating a planned maintenance or preventive maintenance program:
Predictive maintenance is a step beyond preventive maintenance. Historical data on a machine and data from sensors or analysis of machine use can help schedule maintenance better. For example, the number of copies made on a copier can be used to schedule types of maintenance. On other machines, sensors can product tool failure and lab analysis of lubricants can detect metal wear. The noise or vibration from a machine and temperature measurements can also indicate its condition.
Total Productive Maintenance (TPM) carries these ideas further, in three phases. First, each machine is brought up to its highest level of performance and availability by identifying and remedying any problems. Improvement may be needed in changing a machine from product to product since such time is lost to production.
Second, each machine is maintained at that level through a carefully designed preventive maintenance schedule, perhaps involving predictive maintenance. Regular clearing by the production worker can be used to uncover problems before they affect production.
Third, through the analysis of data collected in earlier phases, consideration can be given to purchasing new equipment that will reduce the life cycle cost of providing the function needed.
This article describes how a manufacturing plant trained workers to do first line maintenance.
Jobs that had traditionally been done by skilled technicians were routinely being done by machine operators. These included tasks such as lubrication, basic machine programming, machine set up and change-over. One of the major benefits we derived came from the fact that machines were being attended to on the majority of occasions straight away rather than having to wait for the next available maintenance technician to address the problem.
The T in TPM stands for Total and indicates a total focus on maintaining equipment at its highest level in performance and availability. All an IE’s skills and knowledge can be applied here to gain improvements in equipment availability but also to reduce defects, to produce at desired rates, and to improve safety.
TPM uses Overall Equipment Effectiveness (OEE) as one measure:
OEE = availability x performance efficiency x rate of quality.
Monitoring these three components can lead to better understanding of where productivity is being lost, as explained in this article.