Power dropping with no alarm: where the loss actually is

A machine that loses cutting power slowly, without a single alarm, is the most common call I get that turns out not to be a source problem at all. The source reports what it is producing. It does not report what arrives at the workpiece. Everything in between is unmonitored, and that is where the energy goes.

Split the loss before you blame anything

Two measurements, five minutes apart, settle most of these calls.

• Read the set power and the reported output on the screen. Write both down.
• Measure what actually reaches the work: a burn test on tape at a fixed standoff and a fixed time, or a power meter at the nozzle if you have one. Same test as last month, on the same material, so the comparison means something.

If reported output is normal and the delivered energy is down, the source is doing its job and the loss is downstream. If reported output has also dropped, now you are looking at the source, the chiller, or the supply.

The four places energy disappears

• Protective window. Burnt coating, misting, spatter, or a film of oil. This is the single most common cause and the cheapest to fix.
• Focus lens. Contamination heats the coating, the coating degrades, transmission falls further, and the lens fails properly a few weeks later.
• Fibre connector. A connector that has been disconnected and reconnected without cleaning loses a measurable amount every time. It never alarms.
• Collimator and head interior windows. Checked last, blamed last, and occasionally the actual answer.

The beam shape is the cheapest test you own

Fire the red guide beam onto tape at the nozzle and look at the shape, not just the position: round, crescent, blob, or two dots. A crescent means the beam is being clipped somewhere in the path. A soft blob means it is not being focused at that distance. Either one explains a power loss that no screen will show you.

Environment, and the seasonal version of this fault

Power that falls on hot, humid afternoons and recovers overnight is not a source fault, it is water.

• Water pipes sweating at the source inlet on a humid day is the warning sign. Moisture inside the module drops output and does not always raise a fault.
• Chiller temperature set below the dew point of the shop air will condense on cold surfaces. If the shop is at 30 degrees, do not run the laser water at 20 and expect nothing to happen.
• A failed air dryer on a shop-air supply puts water directly into the beam path, where it absorbs energy before the metal ever sees it.

Gradual or step change

• Gradual decline over weeks, with the same material and the same recipe: consumables and optics, in that order.
• Step change overnight, everything else unchanged: something was touched. A lens replaced, a connector reconnected, a mirror swapped, a gas supplier changed, a new material batch.
• Step change after a service visit: start with whatever was assembled during that visit. Alignment errors are almost always introduced, not developed.

What an alarm-free log actually means

It means the source believes it is fine. On older units, some modules will quietly run at reduced output without raising a fault, and derating for temperature is not always logged.

So keep a number. Once a week, same material, same thickness, same recipe, write down the cut speed that still gives a clean edge. When that number starts walking, you will see it in the log before you see it in the scrap bin. A slow decline is invisible day to day and obvious in a table.

FAQ

How do I know if my fiber laser module is degraded?

Compare real output against the rated value with a power meter — a source can report normal while delivering less at the window. Before assuming the source, rule out the cheaper causes first: contaminated optics, a drifting focus and condensation on the source water lines on humid days.