Avoiding Disastrous Situations

The saying, "an ounce of prevention is worth a pound of cure" truly applies to CNC machine tool usage. Maintenance tasks fall into two categories: Preventive maintenance and corrective maintenance.

Columns From: 12/1/2004 Modern Machine Shop,

The saying, "an ounce of prevention is worth a pound of cure" truly applies to CNC machine tool usage.

Maintenance tasks fall into two categories: Preventive maintenance and corrective maintenance. Preventive maintenance can be done at just about any time. On the other hand, corrective maintenance is seldom predictable. The machine goes down and won't run again until it's repaired. In almost all cases, corrective maintenance is an online task and will adversely affect the machine's productivity.

Three things most commonly cause the need for corrective maintenance. The first is improper machine usage. This includes overtaxing machine components and mistakes that lead to crashes.

The second cause of corrective maintenance is component failure. Eventually, almost every component on the machine will wear out and fail. Of course, certain machine components are more likely to wear out faster than others.

The third cause is lack of preventive maintenance. Most machine tool builders can provide you with a list of those machine components that are most prone to failure.

Certain parts are considered perishable, having a relatively short life expectancy. Light bulbs, air and oil filters, and coolant are examples of highly perishable items. Other items may not be so perishable, but they're not very expensive, and when they fail, they render the machine useless.

Yet other items that are prone to failure may be too expensive to keep backups for. Ballscrews, linear ways and spindle bearings fall into this category. Fortunately, most machine tool builders keep a supply of these items in stock for immediate delivery.

Most machine tool builders provide a recommended schedule for preventive maintenance. Don't ignore these inspections. If an inspection exposes a machine component that is about to fail (such as the spindle bearings), the machine can still be used until parts are ordered and the service engineer is scheduled to come in. On the other hand, if you run the machine until the component fails, the machine will sit idle until it is repaired.

Certain preventive maintenance procedures are related to keeping the machine components in proper alignment. If you don't maintain them on a regular basis, the machine's general performance will suffer. Consider the headstock alignment of a turning center. Improper alignment will lead to a taper in all turned workpieces.

Almost all companies have a DNC system that allows them to transfer CNC programs to and from the machine. Most DNC systems allow you to back up this data in the same way you back up CNC programs. Control parameters and programmable controller parameters are examples of data you should back up. Make sure you keep a hard copy of them.

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