Lubrication is at the heart of any industrial robot's mechanical maintenance. Yet in many plants it remains the task most easily postponed: it generates no immediate alarm, it is invisible to the naked eye, and its effects—positive or negative—take time to surface. Until a gearbox fails and the line comes to a halt.
Why lubrication matters so much
A robot's gearboxes—cycloidal, harmonic or planetary, depending on the axis and manufacturer—are high-precision components operating within very tight tolerances. The lubricant performs three simultaneous functions: reducing friction between metal surfaces, dissipating heat and protecting against corrosion. When the lubricant degrades, all three functions deteriorate at the same time.
The most common consequence is accelerated wear of the rolling elements and ring gears, creating backlash that the robot cannot compensate for. This leads to loss of repeatability, vibration and, ultimately, mechanical failure. A failed gearbox is one of the costliest repairs and generates some of the longest downtime events in any industrial robot.
Oil or grease: they are not interchangeable
One of the most frequent mistakes in production environments is assuming that all axes on the same robot use the same type of lubricant. In practice, manufacturers such as ABB, KUKA and FANUC specify different products for different axes—and even for different robot models within the same range. As a general rule:
- Oil: typically used in wrist-axis gearboxes and some body-axis gearboxes. It enables better circulation and heat dissipation.
- Grease: common in bearings and harmonic-drive gearboxes. Its consistency makes it suitable for sealed cavities that do not require fluid circulation.
Using the wrong product—even a high-quality one—can cause seal incompatibility, foam formation or insufficient adhesion in vertical positions. Always consult the robot's technical documentation or seek specialist advice before substituting one lubricant for another.
Warning signs that the lubricant is degraded
Laboratory analysis of the lubricant is not always feasible on the shop floor, but there are observable indicators that point to a developing problem:
- Unusual noise (clicking, squealing or a continuous hum) during movement of a specific axis.
- Elevated temperature on the gearbox housing, detected by touch or an infrared thermometer.
- Visible oil leaks around drain plugs or axis seals.
- Dark discolouration or metallic particles in the lubricant when drained.
- Rising servo-motor current readings logged by the controller.
If you notice any of these signs, do not wait for the scheduled interval: act before the wear becomes irreversible. Our guide on diagnosing a stopped industrial robot offers a systematic approach to assessing the equipment before calling a technician.
Indicative intervals and the factors that shorten them
Manufacturers set lubricant-change intervals based on operating hours. These intervals are starting points, not absolute rules. The following factors can significantly reduce them:
- Heavy duty cycles: robots operating close to their payload limit or running very fast cycles generate more heat and degrade the lubricant sooner.
- Extreme ambient temperatures: both cold and excessive heat affect viscosity and service life.
- Contaminated environments: dust, metal swarf or cutting-fluid mist can penetrate seals and contaminate the lubricant.
- High-hour robots: in older generations, worn seals accelerate contamination.
In plants running two or three shifts a day, a robot may reach its manufacturer-recommended lubrication interval in under a year of actual operation. Scheduling the change alongside other preventive maintenance tasks allows downtime to be grouped and minimises the impact on production.
How to plan the change without stopping production
A robot lubricant change does not necessarily require a lengthy line stoppage if it is well planned:
- Use planned stoppages: shift changes, holidays or maintenance windows on other equipment are ideal opportunities.
- Warm the robot up before draining: running the robot for a few minutes beforehand reduces oil viscosity and ensures a complete drain.
- Record the volume drained and its colour: comparing these with historical data gives valuable insight into the gearbox's internal condition.
- Do not mix lubricants of different specifications: if you are switching products, flush the gearbox with the new lubricant before the final fill.
- Verify the final level and check for leaks: after filling, run the robot at low speed for a few minutes and confirm there are no leaks from plugs or gaskets.
If you manage multiple robots from different manufacturers, a preventive maintenance contract with an independent service provider lets you centralise interval tracking and ensure full traceability for every intervention.
Lubrication and calibration: a critical combination
One often-overlooked aspect is that work on gearboxes can affect the robot's reference position if not carried out carefully. When handling fill and drain plugs—especially on robots with absolute encoders—an unintended axis movement can cause the robot to lose its mastering. It is best practice to mechanically lock the axes before any lubrication work and to verify calibration once the job is complete.
To understand what this verification involves, explore our ABB robot maintenance, KUKA and FANUC services, where this procedure is included in every preventive intervention.