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 BT 33608, Station 17b, one of the front-axle assembly line hydraulic systems in Plant 6. While completing the work order, the hydraulic repairman felt 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.

VIBRATION ANALYSIS

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 was reported 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. They found a red residue on the outside of the coupling (Figure 1), which, according to reference materials, is failed or separated grease. Because of the coupling style, maintenance didn’t have a replacement coupling on hand. 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 didn’t produce the required size. During this time, maintenance personnel were able to research and acquire a replacement grease that wouldn’t separate under centrifugal forces (Texaco coupling grease) and scheduled the 30-minute window for completing the repair.


Figure 1. Coupling shows failed Steelflex spring and
red residue left from grease separation.

AAM production released the unit for 30 minutes to complete the work order. Based on time constraints, maintenance personnel 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. They returned the unit to production within the 30-minute window and took new readings. The high axial and radial readings returned to a more tolerable level, but the elevated harmonic readings showed that the unit was still misaligned. Knowing that misalignment could possibly damage the installed coupling, maintenance personnel ordered a coupling and scheduled a laser alignment during a scheduled downtime. Afterward, the vibration readings returned to proper levels (Figure 2).


Figure 2. Top graph (‘before’ reading) clearly shows
the multiple harmonics of turning speed with the 1x
predominant. Bottom graph (final readings) shows
that the peak velocities have returned to within
GM/Delphi specifications.

THERMOGRAPHY

Upon service of the coupling, maintenance noticed and reported the adjacent hydraulic reservoir operated substantially hotter than the other units. It used thermography to determine the source point of the increased heat generation. Through thermal imaging, technicians determined that the pump generated the heat. Specifically, Figure 3 supports severe internal leakage and case drain leakage.


Figure 3. Thermography image shows internal leakage
and case drain leakage.

OIL ANALYSIS

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 weren’t compatible. To avoid making adjustments to the new-style pump and incurring several daytime delays, maintenance personnel ordered a special 24-hour pump replacement. Vibration analysis readings generated no abnormal readings and detected no metal-on-metal wear. Oil analysis technicians completed sampling and testing to determine that the oil chemistry had deteriorated well beyond acceptable levels and the particulate levels were high. Personnel slated 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 Station 17b. This hydraulic system feeds the component conveyor that positions the component for torque testing. If this system fails, the parts can’t get tested for torque and, hence, stops the final assembly line. Based on the length of time required to properly complete any one of the described 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 weren’t readily available or obtainable.

Rick Kus, Dave Giacobozzi, Julius O’Steen, Jim Panoff, Ron Radford and Max Segar are PM team members at American Axle and Manufacturing in Detroit.