The preventive maintenance team at American Axle and Manufacturing (AAM) addressed an issue found during a routine preventive maintenance work order. Relying on their skills and field experience, they corrected the issue with minimal effect on productive time. Catching the issue in a timely manner saved the company an estimated $50,000.
A routine preventive maintenance work order was placed to change a hydraulic filter on one of the Plant 6, front-axle assembly line hydraulic systems; BT 33608, station 17b. While completing the work order, the hydraulic repairman believed the system did not sound like it was operating at 100 percent. He sensed that the pump was generating irregular vibration and submitted a corrective work order for a vibration analysis test.
After reviewing vibration analysis data, maintenance personnel found accelerated harmonics of turning speed and high axial and radial readings. Based on the findings, it was suspected that the unit had a loose condition with misalignment. This information was reported back to maintenance and production.
Due to production demands on this line, maintenance personnel were allowed only 30 minutes to make the correction. In an effort to save valuable time, they utilized a strobe light during production to read the exact make and model of the Steelflex coupling.
Figure 1. Original coupling shows a failed
Steelflex spring and red residue
remaining from the grease separation.
They found a red residue on the outside of the coupling (Figure 1), which according to reference materials, is failed grease or separated grease. Because of the coupling style, maintenance did not have a replacement coupling on-site. They ordered the current version of the same coupling and received it during that same shift. The coupling had to be altered in-house because the manufacturer did not produce the required size. During this time, maintenance personnel were able to research and acquire a replacement grease that would not separate under centrifugal forces (Texaco Coupling Grease) and schedule the 30-minute window for completing the repair.
American Axle and Manufacturing Production released the unit for 30 minutes to complete the work order. Based on time constraints, they broke the old coupling free, leaving the coupling halves/hubs installed on the shaft. They installed the new spring and casing, then refilled the coupling with the appropriate grease. The unit was returned to production within the 30-minute window and new readings were taken.
The high axial and radial readings were returned to a more tolerable level, but the elevated harmonic readings showed that the unit was still misaligned. Knowing that the misalignment could potentially damage the installed coupling, maintenance personnel ordered a coupling and scheduled a laser alignment during a scheduled downtime. Afterward, the vibration analysis readings were returned to original GM/Delphi readings (Figure 2).
Figure 2. The graph on top is the “before” reading that clearly shows
the multiple harmonics of turning speed with the 1X predominant. The
graph on bottom shows the final readings after all repairs, illustrating
that the peak velocities have returned to within GM/Delphi specifications.
Thermography to the Rescue
Upon service of the coupling, maintenance noticed and reported the adjacent hydraulic reservoir was operating substantially hotter than the other units. Thermography was used to determine the source point of the increased heat generation. Through thermal imaging, it was determined that the heat was being generated at the pump. Specifically, the image supports severe internal leakage and case drain leakage through the case drain (Figure 3).
Figure 3. Thermography image shows
internal leakage and case drain leakage.
Maintenance personnel scheduled additional vibration analysis and oil analysis tests to pinpoint the root cause and further component damage while they located a suitable pump replacement. The pump manufacturer had upgraded the pump style from the original design, and the two styles were not compatible. To avoid making adjustments to the new-style pump and incurring several daytime delays, maintenance personnel placed a special 24-hour order for a pump replacement. Vibration analysis readings generated no abnormal readings and detected no metal-on-metal wear. Oil analysis completed sampling and testing to determine that the oil chemistry had deteriorated well beyond acceptable levels and the particulate levels were high. Personnel scheduled the unit for repair during routinely scheduled downtime. They changed the pump and filter and then drained, flushed and refilled the system. Vibration analysis, thermography and oil analysis readings were completed after repairs, and all returned to normal operating levels, well within AAM standards.
The correct hydraulic operation prevented a catastrophic failure on the front-axle assembly line station 17b. This hydraulic system feeds the component conveyor that positions the component for torque testing. If this system fails, the parts cannot get tested for torque and hence would stop the final assembly line. Based on the length of time required to properly complete any one of the above maintenance procedures, a catastrophic failure would have caused a minimum of four hours of downtime with costs of approximately $96,000. The cost of this downtime could have easily exceeded $576,000 if the parts were not readily available or obtainable.