As operators understand how and why spindles can fail, they lessen the chance of poor performance, reduce downtime and keep their machines running.
Over the years, machine tool spindles have advanced into highly technical solutions essential to critical operations on the shop floor. Generally, they are used to rotate grinding wheels and cutting tools and turn parts as they are being machined. Spindle applications include drilling, milling, boring, grinding, routing, cutting, and sawing. Spindles, the heart of a machine, are designed to deliver high levels of precision, speed, accuracy, and repeatability. They represent complex systems that integrate several components that influence machine tool performance.
As with any critical asset, spindles can fail for any number of reasons. Whether due to human error (crash), contaminants, loss or increase of preloads, lubrication issues, improper maintenance, or inappropriate spindle design for an application. Operators can help to minimize these and related issues simply by understanding how and why spindles can fail and, in the process, help keep spindles up and running as intended.
Analyzing Failure
Spindle failures have many contributing factors, including components and systems related to the spindle. Some of the causes of failure can go undiscovered, causing recurring failures which result in lengthy downtimes and costly damage to related equipment. To help determine the root cause of failure, the machine shop should provide a detailed failure analysis report, including the data collected from inspection and testing. For complete failure analysis, the process should include all the equipment that functions along with the spindle.
Common causes of spindle failure
· Normal wear and tear, or fatigue of spindle components, is a root cause of failure that is expected over time. Parts subject to wear include the bearings, spindle shaft, housings (front, rear, and main), rotor, stator, drawbar springs, shaft nuts and cap, encoder, and spacer. If any of these items present signs of wear or damage, the component should be repaired or replaced.
· Contaminants may affect shafts and bearings and include any foreign substances such as water, oil, coolant, condensation, chips, debris, and grinding swarf from the material being machined. Proper installation of seals along with routine maintenance can help reduce risks of contamination.
· Improper lubrication may increase wear, generate excessive heat, and result in higher-than-required operating temperatures, limiting speed and power while reducing energy efficiency. The proper lubricant supplied in the right amount at the right time is a must. Lubricants should be of high quality, correctly specified, and stored for the application and free from moisture or other contaminants. Care should be taken, so neither too much nor too little lubricant be applied. Lubricant containers and all transmission lines should be thoroughly inspected to rule out pre-existing contaminants. In air/oil lubrication systems, clean and dry air must be used for prolonged spindle life. Lubricants are subject to breakdown in service and should be monitored regularly to confirm integrity.
· Mishandling is another commonly encountered cause of spindle breakdown. An impact, radial or axial, to a spindle shaft may cause permanent indentations, resulting in rapid deterioration of a spindle’s precision bearings. Spindles should be handled appropriately and be protected from vibration and other potentially damaging influences to help keep the equipment performing as designed.
Other failures include equipment overloads or improper preload on bearings, imbalance, tool-change errors, improper repair, faulty lubrication lines, encoder issues, control issues that would actuate the drawbar, and many more. In essence, there is no shortage of potential causes that can result in spindle failures.
Do you need quality spindle rebuild services? Get in touch with the spindle rebuilding specialists at MZI Precision at (714) 379-6505.