Preventive maintenance is critical activity for realizing the maximum efficiency and output from the equipment. Equipment productivity is impacted by various losses such as breakdowns, changeover times, reduced speeds and rejections. Most of these losses are result poorly maintained equipment. Traditionally concept of breakdown maintenance was used, which means maintenance will be done only when equipment will breakdown. With Preventive maintenance approach equipment losses can be minimized and productivity can be improved.
The planned approach to preventative maintenance was introduced to Japan from the US in the 1950s. Seiichi Nakajima, of the Japan Institute of Plant Maintenance (JIPM), is credited with pioneering the development of the approach through the stages of Preventative (Time-based) Maintenance and Productive (Predictive/Condition-based) Maintenance and then into Total Productive Maintenance (TPM). Today, TPM is best Preventive maintenance approach to improve equipment efficiency and productivity.
Following are five critical success factors for delivering benefits from TPM:
Maximise equipment effectiveness;
Develop a system of productive maintenance for the life of the equipment;
Involve all departments that plan, design, use or maintain equipment in implementing TPM;
Actively involve all employees from top management to shop floor workers;
Promote TPM through motivation management: autonomous small group activities.
There are Major six categories of equipment loss addressed through TPM:
Breakdowns due to equipment failures: Equipment failure loss is the the largest factor Which-obstructs efficiency is the equipment failure loss. The failure can be classified into two types; one is the function-stoppage type ad the other is the function-deterioration type. The function-stoppage type failure is the one which occurs unexpectedly, while the function-deterioration type. failure is the one in which the equipment function decreases.
Set up and unnecessary adjustments:This loss is caused by machine stopping due to change of the product on the machine. Most of time in changeover is generally lost in the adjustments.
Idling and minor stops:The minor stoppage loss differs from failure and is the one in which temporary trouble causes the equipment to stop or idle. It might be called a “minor trouble.”
Running at reduced speed:The speed loss is the: loss caused by the difference between the designed speed and the actual working speed. For example, where the line was operated at the designed speed, it was found that the line caused poor quality or mechanical trouble in the line. In that case, the. line had to be run at a slower speed than the designed one. This loss from this situation is called Speed loss.
Start-up losses:The start-up loss is the one that occurs until the start-up, running-in and machining conditions of the equipment have been stabilized.
Rework and scrap:This is the loss caused when defects are found and have to be reworked. In general, the defects are likely to be considered as waste which should be disposed of. But since even the reworked products need wasted manpower to repair them, this must be considered as the loss.
As basic steps for achieving Equipment Efficiency, it is important to perform the elimination of slight defects, restoration of equipment deterioration, the pursuit of “what the equipment must be” conditions, as well as complete understanding of abnormal equipment conditions. Achievement of equipment efficiency based on these basic steps can contribute to the elimination of chronic losses.
Objective of Preventive maintenance known as Planned maintenance in TPM is to focus on preventive actions to eliminate equipment failures/ breakdowns in order to ensure availability and reliability of equipment and to minimize cost of maintenance.
Planned maintenance starts by identifying minimizing slight defects on the equipment by using powerful approach of Autonomous Maintenance. Every small defect on the machines must be identified and rectified. As a second step in planned maintenance all repeated causes of defects must be identified and eliminate using Root cause analysis process.
Main role of maintenance team in implementing planned maintenance or preventive maintenance is as follows:
Participate with Production and help operators with technical support in finding deterioration on equipment during Initial Cleaning.
Remove Abnormality tags put by operators during Autonomous Maintenance after analyzing causes and implementing corrective action.
Detection of deterioration by inspection using optimal condition check sheet and correct as above.
Abolish causes of forced deterioration with the help of Production.
Using breakdown analysis sheet of equipment, find whether the breakdown is natural or forced and implement measures to prevent breakdowns. If the breakdown is natural, and analysis reveals weak design, improve the design by kaizen.
Follow TBM and CBM for vital and essential parts of equipment
• TBM – Time Based Maintenance: The maintenance activity to be carried out based on the schedule prepared based on the manufactures’ recommendation and past experience. For example, if a part is to be changed after a period of two months, carry out as per schedule. Time based Maintenance activities are selected on the basis of equipment supplier’s recommendation and past performance of the equipment. Periodic inspection, cleaning, servicing, part replacement, lubrication, and oil replacement activities are carried at predetermined intervals to restore equipment deterioration.
• CBM – Condition Based Maintenance: Based on the condition of part, decide whether to change or not. For example, bearing replacement in a Spindle arrangement is based on abnormality symptom i.e based on the condition of part and not by time limit.
Defects, deterioration and weak points of design are arrived at by using why-why analysis. Countermeasures are implemented for the removal of defects and restoration of condition of parts.
Improvements are made to strengthen the weak points of design, design change of parts. These are Kaizens. Create MP (Maintenance Prevention) sheet.
Development of Kaizens for reliability and maintainability improvements
Improvement of Maintenance skills
In Advanced stages of Planned or Preventive maintenance, Predictive maintenance techniques such as vibration analysis, oil analysis, infrared analysis, Ultrasound analysis etc are used to predict and prevent the failure.
Using Planned maintenance approach of preventive maintenance in TPM can help improve machine efficiency significantly, thus improving productivity and reducing costs.