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Analysis of Typical Failure Cases

Bearing Failure Analysis

I. Background

Accessory: Reducer input shaft

Quantity: Three groups

Note: Recently, our customer reported that two enclosures on a certain platform failed to meet NVH requirements. Upon disassembly, we found that the bearing on the input shaft side of the reducer felt abnormal. Additionally, similar failures occurred on other platforms earlier this year—initially attributed by us to electrical corrosion. Based on preliminary findings, we have determined that the failures across both platforms stem from the same underlying issue. Accordingly, we have consolidated the failed components from both platforms and conducted a thorough re‑analysis. The following presents our analysis conclusions and verification results.

II. Analysis of Test Specimens

1. Exterior Analysis

Note: The entire input shaft and bearings are included. On the motor side, it is a TM 6006; on the reducer side, it is a TM 62/28. Based solely on tactile feedback, both the 6006 and the 62/28 are in good condition, but the 62/28 exhibits a noticeable rattling sensation. Even after cleaning and re‑lubrication, the issue persists; preliminary assessment indicates damage to the internal running surfaces. The following analysis focuses primarily on the TM 62/28.

2. Parameter Analysis

Regarding bearing clearance: after installation, the TM 6006 measures approximately 12 µm, and the TM 62/28 measures approximately 10 µm; thus, the possibility of excessive interference due to insufficient clearance can be ruled out.

Noise performance: TM 6006 ≤ 39 dB, with no noticeable extraneous sounds; TM 62/28 ≤ 52 dB, with more pronounced extraneous sounds.

Dimensions: All data meet national standard requirements.

3. Microscopic Analysis

Platform 1

The inner and outer raceways exhibit a small number of pits or protrusions.

The rolling elements exhibit a high density of crushing pits along the raceway, with fewer pits scattered around the periphery of the raceway.

Platform 2-A

Platform 2-B

On Platform 2, Group A exhibits a small number of pits or protrusions on both the inner and outer raceways; in Group B, numerous pits are distributed predominantly on one side of the raceway.

Platform 2—On the rolling elements of Group A, a greater number of crushing pits are distributed along the running trajectory, with fewer pits scattered around the periphery; in Group B, the pit distribution is more diffuse.

Microscopic Analysis – Pits

Since the above analysis did not further magnify the pit, its shape and depth could not be determined in detail; it was only classified as circular or approximately irregularly circular. To verify the origin of the aforementioned pit, we magnified it to 100×–200×, yielding the following results.

Platform 1

Phenomenon: As shown in the figure above, the pits all exhibit a regular hexagonal morphology, with dimensions ranging from 40 to 60 μm and exhibiting nearly uniform size.

Left: Platform 2-A Right: Platform 2-B

Phenomenon: Consistent with Platform 1, the rolling-element pits on Platform 2-A are irregular rhomboid in shape, with dimensions ranging from 50 to 60 μm and generally uniform in size. On Platform 2-B, the rolling-element pits are triangular, with side lengths averaging around 50 μm and exhibiting relatively uniform dimensions.

Analysis and Conclusion

Based on the aforementioned tests and microscopic images, the pits exhibit a relatively regular shape and uniformly consistent dimensions; therefore, they can be attributed to impurity‑induced crushing.

Based on our company’s past failure‑analysis experience, the aforementioned impurity is a hard particulate; judging from its shape and size, it can be confidently identified as silicon carbide abrasive. Considering the manufacturing and service processes in which silicon carbide may be involved, we conclude that its sources are primarily two: (1) residual silicon carbide abrasive detached from the diamond‑coated rollers during bearing machining, which was not thoroughly removed from the raceways; and (2) minor amounts of abrasive that fell into the bearing raceways during assembly after the customer used a diamond file to deburr the gears prior to installation. To verify these hypotheses, we conducted a morphological analysis of the silicon carbide particles, with results largely consistent with the above findings.

Based on the size (60–80 µm) and shape of the corundum abrasive, it generally corresponds well to the pit morphology.

Its failure mechanism: hard particulate matter enters the bearing interior—particles become embedded in the raceway, creating localized protrusions—during operation, the ball‑bearing surface develops scoring and pitting—resulting in abnormal bearing noise.

Definition of Servo Motors and Their Bearing Requirements

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