The advantages of the application of PM in machine tools are considerable, the number of downtime hours is reduced by 95% and unplanned repair hours by 65% during an installation period of less than 4 years.
The average availability of production hours fell below 80%, to more than 86%. The annual investment plan is drastically reduced, while increasing the quality of the product and decreasing the percentage of waste.
A complete MP program for machine tools affects all plant personnel, and not just maintenance personnel. It is a mistake to think that PM is the sole responsibility of maintenance.
Cleaning: A good maintenance plan begins with good cleaning. This work is often assigned to the operator and no special attention is paid to the instructions, it is obviously a mistake, because all work needs instructions: how, when, and with what to do it. Sometimes the machines are complicated to the point that it would be impossible for the operator to clean them without a considerable loss of time, in this case maintenance is in charge of this task. Very often combining these operations with lubrication and inspection before and after the ordinary day, or during lunch breaks.
Lubrication: Any tool works better if it is properly lubricated. The choice of lubricants, their storage, distribution and use in production, the establishment of suitable intervals for lubrication operations, and the recording and checking of lubrication are the responsibility of the maintenance engineer. A complete, reliable and effective lubrication program is essential in the PM program. Even so, we must point out that a lubrication program is not enough, but must be combined with other predictive maintenance techniques (Analysis of lubricants, Thermography).
Responsibility for lubrication can be centralized or decentralized. The daily lubrication is the responsibility of the operator and therefore the verification is in charge of the production. Weekly lubrication is in charge of the operator as well. When it comes to special or very complex machines, the operation requires specialized personnel. In these cases, the responsibility falls on the maintenance section.
Instructions for lubrication usually come with the machine. In their most suitable form they contain a drawing or photograph of the machine and a brief description of the different points, the type and quantity of lubricant necessary for each operation and the interval between them.
Inspections: The most important part of any PM program is the inspection. The inspection activity not only reveals the condition of the machine tool, but also involves an adjustment, repair or replacement of worn parts; that is, the correction elimination of circumstances that may be the cause of breakdowns or deterioration of the machine.
It has been seen that a combination of observations, tests and measurements can result in a method applicable to most circumstances in the industry.
The system consists of 5 different inspection levels, each with its own particular objective.
Level 1: Daily observation.
It is carried out by the operator. It involves observing the operation of the machine tool in its normal work cycle, checking all its functions.
Level 2: Weekly observation.
It is carried out by the lubricator during the weekly operation. It includes level 1 activities, with additional observations of oil pressure, the operation of lubrication devices, and oil leaks.
Level 3: Minor inspection.
In charge of a specially trained maintenance employee with good knowledge of machine tools and electrical and hydraulic control systems. The inspections are such that it is not necessary to stop the machine. Includes levels 1 and 2.
Level 4: general inspection. Includes levels 1,2 and 3, and requires machine stop.
They are checked. The level of the machine, the play of the main shaft bearing, the parallelism of the guides with respect to the center line. It also includes the adjustment of clutches and brakes, keys and bearings, replacement of worn parts, replacement of belts, etc. A general inspection is usually carried out every two years, or every year or every 6 months in two shifts, depending on the type of machine. The stoppage of the machine must be planned with production.
When starting the PM program, the production department is often not accepting of the idea. The success of the project depends on this.
Level 4 gives a good idea of the current quality of the machine and its reliability. If any of the tests indicate incorrect conditions, it is recommended that the quality control inspection (Level 5) be done to give detailed information about the machine tool conditions.
Level 5: Quality control inspection. It is usually every three years, when installing a new or rebuilt machine, or by request. Sometimes the production department requests it for special precision machines or there may be complaints or returns due to product quality control.
