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Potential Failure Mode Analysis

1. Heat‑treatment process control items: impact on downstream processes and corresponding FMEA severity—tempering hardness. A. Insufficient hardness: obvious sand‑blasting or shot‑peening grit marks; surface scratches during groove grinding, inner‑diameter machining, and superfinishing; whitening of the raceway and absence of lapping marks during superfinishing (beginning to appear when hardness is ≤58 HRC).

1. Heat Treatment Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Tempering hardness	A. Insufficient hardness: Obvious sand‑blasting or shot‑peening marks are visible; surface scratches occur during grooving, inner‑diameter finishing, and superfinishing; during superfinishing, the raceway turns whitish and loses its luster (this begins to appear when the hardness is ≤58 HRC). B. Excessive hardness: During ultra‑finishing, the raceway appears dark and shiny with no lapping marks; trailing may occur (this begins to appear when the hardness reaches ≥63.5 HRC).	8 A
Decarburized layer	A. Excessive decarburized layer: Sandblasting or shot peening leaves distinct grit marks; during superfinishing, the raceway appears whitish with no lapping marks, and metallographic examination can measure the thickness of the decarburized layer.	8
Golden Appearance	A. The impact on downstream processes is not yet evident, but it significantly affects the service life of the finished bearings.	7 A
Deformation amount	A. Significant ovality deformation: poor ovality in the centerless grinding process, and blocky black scale on the groove edges in the grooving process. B. Large taper deformation: The centerless grinding process exhibits a significant taper variation; if the ovality is also substantial, a tetragonal shape may result.	5

2. Sandblasting and shot blasting processes

Control Project

Impact and Performance of Subsequent Processes

FMEA Severity

Appearance

A. Chamfering, dust‑proof grooves, and blackened channels, with significant amounts of quenching oil present;

B. Affects product cleanliness and customer complaints.

Cleanliness

A. When abrasive grit becomes lodged in the dust‑proof grooves of the 6200/02 inner ring, the bearing may seize during operation.

B. During shot blasting, if the steel shots are not thoroughly cleaned, magnetic attraction may cause them to adhere to the groove‑grinding equipment, resulting in collisions during the groove‑grinding process.

3. Technical Requirements for the End-Milling Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Size	A. Oversized or undersized dimensions and dimensional variability: affect the groove position in grinding and the ultra-precision threading process.	4
Parallel difference	A. Large parallelism error: affects the inner diameter perpendicularity (sd) and the ultra‑precision lapping path on the groove side, including sia and sea.	5
Symmetry	A. Excessive symmetry: black skin in the grinding groove (especially on large circles); decarburized layer cannot be removed (if greater than 8 mils and present on two or more areas, the item may be deemed nonconforming).	5
Appearance	Appearance is an indicator of parallelism and symmetry defects. A. If one side of the end face is bright while the other is white, it will inevitably result in poor concentricity. During end-face grinding, the excess material on the whitish side is removed, whereas the bright side is only subjected to a finishing pass. If the blank’s end face was turned roughly, this condition may leave traces of the turning tool near the bright end of the raceway. B. Visible uneven surface patterns at the end faces may result in double‑sided parallelism deviations. Additionally, slight impact marks at the end‑face chamfers—caused by improper handling during loading/unloading and inadequate packaging in metal crates—can lead to single‑sided parallelism deviations.	/

4. Outer Cylindrical Precision Grinding Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Size	A. Oversized: The outer groove grinding dimension is scrapped; B. Underdimensioning: The outer groove is ground too shallow; C. Dimensional Dispersion: Groove‑grinding dimensions are unstable. When conducting sampling inspections, please account for the influence of temperature variations on dimensional accuracy.	4
Roundness	A. High roundness: adversely affects external groove grinding and ultra‑precision roundness; makes repair in the fine‑grinding stage difficult; impacts the fit clearance during assembly and causes low‑frequency vibration.	4
Taper degree	A. Fine grinding makes repair difficult.	3
Appearance	A. Cutting edge: Fine grinding makes repair difficult; outer groove grinding and excessive roundness lead to scrap. B. Impact Damage: Non‑compliant handling during loading and unloading can cause impact damage to the end faces and outer diameters, potentially resulting in excessive parallelism deviation on one end face, abnormal roundness of the outer diameter, and defects that cannot be corrected by fine grinding.	/

5. Outer Cylindrical Superfinishing Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Ultra-high precision depth	A. Insufficient ultra-precision depth: Roundness and surface roughness cannot be corrected; B. Excessive super‑finishing depth: outer diameter out of tolerance; C. Ultra‑fine depth of dispersion: It affects the concentration of outer‑diameter dimensions, leading to dimensional dispersion in groove grinding.	5
Roundness	A. High roundness: adversely affects external groove grinding and ultra‑precision roundness; makes repair in the fine‑grinding stage difficult; impacts the fit clearance during assembly and causes low‑frequency vibration.	2
Taper degree	A. Fine grinding makes repair difficult.	2
Appearance	/	/

6. Outer Groove Grinding Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Size	A. Affects the assembly fit rate.	3
Roundness	A. It affects the rotational accuracy of the product, the fit clearance during assembly, and low-frequency vibration. B. When the roundness exhibits five or more distinct facets, it is generally caused by vibration marks.	5
Trench position	A. Affects the consistency of ultra-precision machining.	3
Side swing	A. It affects the quality of ultra-precision machining and the rotational accuracy of bearings.	5
Curvature	A. Large or small curvature: affects the correspondence between axial clearance and radial clearance, potentially impacting bearing safety; B. Curvature thread retention: Affects ultra-precision machining quality and bearing noise.	4
Roughness	A. Abrasive‑induced scratching: Due to the detachment of abrasive grains, inadequate chip evacuation, or the presence of exceptionally sharp single abrasive grains on the grinding wheel, these grains are pressed into the workpiece surface by the high‑speed rotation of the wheel. During superfinishing, this may manifest as trailing marks, invisible single points, or white spots (detectable via vibration measurement). At present, it is known that the indentation depth typically ranges from 3 to 5 µm, with maximum depths reaching up to 8 µm. B. Roughness too coarse: During ultra‑finishing, it may not be fully corrected, leaving white spots. C. Excessive surface smoothness: the ultra‑finishing depth cannot be further reduced.	2
Residual magnetism	A. It can cause collisions during ultra‑precision machining; raceways with residual magnetism will attract large amounts of metal chips, reducing product cleanliness; and residual magnetism in the finished product will increase the starting torque.	/
Ripple degree	Ripple, also known as chatter marks, arises from insufficient system rigidity—such as inadequate machine‑tool bed stiffness, excessive runout of the electric spindle, weak cutting performance of the grinding wheel, out‑of‑round wear of the wheel, cracks in the wheel, or poor lubrication and cooling—and from self‑excited vibrations and resonance. In our company, the most common cause is that, during grinding, uneven sulfur impregnation leads to varying bond strengths across the wheel; consequently, abrasive grains detach at different rates. Areas with higher bond strength resist grain shedding, resulting in localized dulling. This uneven wear naturally induces a wavy surface on the wheel, which, during machining, triggers vibration and produces chatter marks. A. Impact on super‑finishing quality: If the raceway with vibration marks is not repaired after super‑finishing, it will retain regular, blocky grinding‑wheel marks. These vibration marks are typically visible to the naked eye under lighting, and during color scraping, distinct bands of varying color intensity can be observed. On a roundness tester, they become apparent upon filtering.	/
Burn injury	A. Burns are generally difficult to detect with the naked eye and must be inspected using an acid‑etching method.	6
Color-scraping oil	Due to the mixing of color‑scraping oil with normal materials, or inadequate cleaning of the color‑scraping oil, residual color‑scraping oil may remain after ultra‑finishing. If the semi‑finished and finished products are not thoroughly cleaned, this will directly compromise bearing cleanliness.	/
Appearance	A. Outer‑circle scratches: Once present, outer‑circle scratches—regardless of whether they can be repaired by fine grinding—already cause significant or irregular roundness errors during the groove‑grinding process. B. End-face Scratches: End-face scratches may result from excessive surface roughness in the end‑face machining process, excessive magnetic force, or an improperly dressed backing block, and can carry over to subsequent operations, potentially leading to customer complaints.	/

6. Internal Groove Grinding Process

The inner groove grinding process is essentially the same as the outer groove grinding process, but with the following differences:

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
(Roundness of the edge)	A. It affects the rotational accuracy of the product, the fit clearance during assembly, and low-frequency vibration. B. When the roundness exhibits a predominantly diamond‑shaped profile, in addition to roundness‑instrument measurement, it must be inspected on 120‑degree and 90‑degree gauges as appropriate for the specific conditions.	5
Ripple degree	Because the inner‑race grinding wheel spindle has greater rigidity than the outer‑race spindle, waviness is unlikely to occur under normal conditions. However, when factors such as machine‑tool collisions, grinding wheel cracks, poor wheel balancing, or insufficient spindle accuracy—any of which compromise rotational accuracy and the spindle’s secondary dynamic balance—multi‑diamond‑shaped waviness may arise. A. Note: Due to the influence of angular measurement errors in instrumentation, multi‑diamond‑shaped waviness may be detected with reduced sensitivity on certain instruments, or even remain undetectable.	/
Appearance	A. Groove: Outer‑circle scoring—so long as it is present, regardless of whether it can be repaired by fine grinding, it has already caused significant or irregular roundness errors during the groove‑grinding process. B. End-face Scratches: End-face scratches may result from excessive surface roughness in the end‑face machining process, excessive magnetic force, or an improperly dressed backing block, and can carry over to subsequent operations, potentially leading to customer complaints.	/

7. Inner Diameter Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Size	Impact on product installation and the fit between the bearing and the shaft	6
(Roundness of the edge)	Slightly affects product installation performance and rotational accuracy.	5
Taper degree	Affecting product installation performance	4
Vertical difference	Impact on product rotational accuracy	4
Roughness	Impact on product installation	2
Appearance	Primarily caused by impact damage to the raceway and scratches on the inner-diameter measuring jaws.	/

8. Ultra-Precision Machining Process

Control Project	Impact and Performance of Subsequent Processes	FMEA Severity
Ultra-high precision depth	Impact on product vibration levels, noise, and service life Measures to enhance ultra-precision depth: A. Increase the pressure and extend the cutting time; B, Increase the swing speed and reduce the workpiece rotational speed. C, Reduce the viscosity of cutting fluid; D. Switch to a coarse-grit oilstone; E, The hardness of the ring and the depth of superfinishing also exhibit an inverse relationship.	4
Roundness	Impact on the low-frequency value of the product’s vibration velocity rating	5
Channel curvature	It affects the correspondence between the product’s axial clearance and radial clearance.	4
Roughness	The measures to influence the high-frequency values of the product’s vibration velocity level are the opposite of those used for the ultra‑precision depth project.	/
Silk Road	It affects product noise (specifically, resulting in a harsh sound). The Silk Road’s shortcomings are primarily attributable to the following factors: A. It is caused by poor accuracy of the support, centering axis, or bearing. B, Head bearing wear; C, Poor cooling; D. The oilstone groove is incorrectly positioned; E, Improper positioning of the oilstone, either at the front or rear, can lead to chipping, deformation, and other defects.	6
Appearance	Mainly: end-face scratches, end-face abrasions, and large-circle raceway damage.	/
Contusion	Ultra‑fine front‑impact damage: primarily manifests as trailing, with the Taylor instrument indicating an uneven, bumpy surface. Post‑super‑resolution smearing: No trailing artifacts present.	/
Ultra-distillation	The cause of super‑distillation: During ultra‑precision cutting, the metal chips generated do not have sufficient time to detach; coupled with inadequate cooling, these chips melt and form metallic distillates, commonly referred to as “super‑distillation.” Conventional machining processes typically do not give rise to super‑distillation.	/

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