Preventive Maintenance Schedule

Preventive Maintenance Schedule

Preventive Maintenance Schedule - Many of the maintenance requirements present in vintage machines are not applicable to their modern equivalents, and no doubt the requirements of present day machines will not be the same as for machines of the future.

The problem of effective maintenance and its influence on machine reliability is becoming increasingly recognized as a major aspect of design, and slowly but surely the need for routine maintenance operations is being designed out of the machine. In machine tool design there have been many changes in recent years which have reduced the need for or cost of preventive maintenance.

In the past, the lubrication of large capital cost machines necessitated each moving part being manually lubricated through separate oil or grease nipples, whereas such machines are now arranged with automatic lubrication from a central reservoir, with a control arrangement included so that the power sources to the machine are automatically broken or disconnected should the level of oil drop below the permissible amount.

Similarly in the design of slideways, particularly in the case of planers and floor borers, the introduction of hydrostatic lubrication means that metal to metal contact is eliminated and, with the oil applied through the moving member, the risk of foreign bodies getting between the surfaces is very considerably reduced.

Another example is in the field of high speed spindle design, where the development of the air bearing makes possible the elimination of Lubrication altogether; the application of air bearings to grinding heads has not only avoided metal to metal contact, but the use of compressed air running to exhaust ensures the control and removal of the heat generated.

Maintenance schedules and the cost of maintenance should therefore be kept under constant review, not only with the objective of eliminating unnecessary preventive maintenance, but also to ensure that the financial value of such developments is known and acted upon.

In those industries engaged in high volume production there are two basic methods of manufacture: line production with individual machines fed and linked by highly sophisticated, mechanized handling systems; and individual machines which in themselves perform a sequence of operations resulting in the production of a finished piece part or product, the former often includes the use of the latter. In these industries, preventive maintenance is effectively planned and carried out.

In the jobbing and batch production industries, such manufacturing methods have generally been little used because, it is argued, the wide variety of work produced, both in type and volume, makes it very difficult to plan, and similarly many aspects of preventive maintenance cannot be effectively applied.

In recent years a term 'machining centre' has been coined and it can be defined as an automatic machine capable of carrying out a multiplicity of operations, using different types of cutting tools and working on several faces of a component without the necessity for resetting.

The following schedule for a typical machining centre will, however, give the reader an indication of most of the aspects which have to be covered by preventive maintenance, for the general run of machine tools.

It is assumed in this schedule that the machine is employed on a 3-shift 5-day week basis, with preventive maintenance and adjustment carried out at weekends by the maintenance department, and that, in addition to the normal mechanical movements and electrics, electronic, hydraulic and pneumatic systems are involved.

(i) Daily checks (responsibility of the operator):

(a) Check lubrication levels and oil flow in sight glasses (record if low, report immediately if empty or restricted).

(b) Check coolant level, top up if necessary (record amount).

(c) Keep machine clean and free from chips.

(d) Note and report any leakage from power packs.

(e) Note conditions of the machine s1ides and report any signs of scoring immediately.

(f) Wipe down machine.

(ii) Weekly schedule (responsibility of maintenance department):

(a) Check all filters, clean or replace as required.

(b) Check all lubrication levels. Top up with correct grade as required (record amount).

(c) Check coolant. Top up or clean out and refill as required. The frequency of replacing the coolant will depend upon domestic conditions and type of material, but the rules of cleanliness must be observed.

(d) Check exhaust baffles, etc., for restrictions.

(e) Check hydraulic unit. Is the sound normal?

(f) Record pressures in hydraulic and pneumatic lines.

(g) Examine all exposed hydraulic and pneumatic lines. Repair where necessary.

(h) Check all flexible lines. (i) Where automatic tool changer is fitted, check all tools using test tape for correct action.

(j) Perform tape reader maintenance procedure as outlined in electronic equipment supplier's manual.

(iii) Monthly schedule (responsibility of maintenance department):

(a) Check spindle drive belts for wear; adjust or replace if necessary.

(b) Check all clamps.

(c) Remove and clean air intake filters in hydraulic power supply.

(d) Check hydraulic pump, timing belt and drive coupling.

(e) Check running temperature of hydraulic oil.

(f) Check movement of all axis under manual dial in control.

(iv)Six monthly schedule (responsibility of maintenance department):

(a) Repeat all 120-hour checks.

(b) Repeat all 480-hour checks.

(c) Change all oils.

(d) Replace all filters.

(e) Check and record machine alignment.

(f) Check all axis reference positions and positional accuracy.

(g) Service electronic tape equipment in line with manufacturer's hand book.