The development of wind power technology has brought significant changes to the wind turbine bearing industry. Domestic manufacturers increasingly replace imported bearings, particularly planetary carrier bearings for wind turbine gearboxes.
These bearings typically feature extra-large, lightweight, thin-walled tapered roller bearing rings. Growing customer demands and market competition require more advanced machining processes and tighter quality control.
Extra-large bearings generally have outer diameters exceeding 600 mm. Lightweight, thin-walled rings have wall thickness-to-outer diameter ratios below 1:20.
Their limited rigidity makes them vulnerable to deformation during grinding. Consequently, manufacturers often experience poor machining accuracy, low production efficiency, and reduced product acceptance rates.
Developing suitable machining processes is therefore essential. Effective process optimization must control dimensional accuracy, geometric tolerances, and machining stability.
Research on Bearing Ring Machining Processes
The rapid localization of planetary carrier bearings has increased demand for extra-large thin-walled tapered roller bearings. Conventional machining processes cannot adequately accommodate their large dimensions and low structural rigidity.
Traditional methods often produce low machining efficiency and inconsistent product quality. These limitations make it difficult to meet customer delivery requirements.
Therefore, manufacturers urgently need optimized machining processes for these specialized bearing rings.
Post-Heat-Treatment Machining Process Routes
Machining routes must reflect the structural characteristics of extra-large thin-walled single-row tapered roller bearing rings. Different rigidity ratios also require different processing strategies.
Engineers should develop separate machining routes for inner and outer rings. This approach helps control deformation and maintain machining accuracy.
> Inner Ring Machining Process Route
Single-row tapered roller bearing inner rings contain two ribs on opposite sides. These features help limit deformation during heat treatment and subsequent machining.
The conventional inner ring machining route follows this sequence:
Post-heat-treatment hard turning → Additional tempering → Fine grinding of both end faces, bore, and raceway → Final grinding of both end faces, bore, raceway, and large rib → Superfinishing of the raceway and rib.
> Outer Ring Machining Process Route
Lightweight single-row tapered roller bearing outer rings generally follow machining routes similar to those of inner rings. However, their bowl-shaped geometry makes them more vulnerable to deformation.
During heat treatment and subsequent machining, different rigidity ratios produce different deformation levels. The bearing ring rigidity ratio follows the equations below.
γ = Be / D
Be = (D − De) / 2 − (1 / 3) × B × tan α
Where:
- D = Outer ring outside diameter (mm)
- De = Outer ring raceway diameter (mm)
- α = Outer ring raceway angle (degrees)
- B = Outer ring width (mm)
Extensive machining trials established different processing routes for outer rings with different rigidity ratios. The following methods address three rigidity categories.
> Outer Ring Rigidity Ratio ≥ 0.05
Post-heat-treatment hard turning → Additional tempering → Fine grinding of both end faces, outside diameter, and raceway → Final grinding of both end faces, outside diameter, and raceway → Raceway superfinishing.
> Outer Ring Rigidity Ratio Between 0.03 and 0.05
For rings with 0.03 < γ < 0.05, the machining route includes additional rough grinding.
Post-heat-treatment hard turning → Additional tempering → Rough grinding of both end faces, outside diameter, and raceway → Fine grinding of both end faces, outside diameter, and raceway → Final grinding of both end faces, outside diameter, and raceway → Raceway superfinishing.
> Outer Ring Rigidity Ratio ≤ 0.03
Rings with rigidity ratios of 0.03 or below require more grinding stages. Their extremely low rigidity makes deformation control particularly challenging.
Post-heat-treatment hard turning → Additional tempering → Rough grinding of both end faces, outside diameter, and raceway → First fine grinding → Second fine grinding → Final grinding → Raceway superfinishing.
Both fine grinding stages and final grinding cover the two end faces, outside diameter, and raceway.
Lower rigidity ratios generally indicate thinner bearing ring walls. Such rings deform easily under external forces and temperature changes.
These characteristics significantly increase machining difficulty and precision requirements. Multiple grinding stages gradually remove machining allowances and correct deformation.
This approach helps achieve the required raceway accuracy and overall geometric precision.
Optimization of Bearing Ring Turning Processes
Clamping methods strongly influence the quality of hard turning for extra-large tapered roller bearing rings. Conventional machining uses four-jaw chucks and pressure plates to secure workpieces.
However, concentrated clamping forces can cause three-lobed deformation in thin-walled rings. Lightweight rings are especially vulnerable to this problem.
After finish turning, excessive ovality and end-face warpage can complicate subsequent machining. Severe deformation may even cause component rejection.
To address these problems, the optimized process replaces conventional four-jaw clamping with magnetic chuck fixation. Magnetic holding reduces localized deformation caused by mechanical jaws.
This approach improves machining accuracy and prevents excessive geometric deviations after finish turning.
The magnetic chuck surface contains evenly distributed radial T-slots. Operators can install magnetic conducting blocks to support machining multiple features in one setup.
Some electromagnetic chucks also feature stepped magnetic grooves. These grooves simplify the positioning of tapered roller bearing outer rings.
Operators can adjust the magnetic holding force according to machining requirements. The chuck distributes magnetic force uniformly around points on the same circular diameter.
Uniform magnetic holding helps maintain consistent accuracy around the bearing ring. Different workpiece weights and contact areas require appropriate magnetic force settings.
After adopting magnetic clamping, manufacturers observed clear improvements in diameter variation and end-face warpage. Table 1 compares geometric tolerances before and after the change.
| Geometric Tolerance Inspection Item | Four-Jaw Chuck (mm) | Magnetic Clamping (mm) |
|---|---|---|
| Bore Diameter Variation in a Single Radial Plane (Vdsp) | 0.1–0.2 | 0.05–0.1 |
| Outside Diameter Variation in a Single Radial Plane (VDsp) | 0.15–0.3 | 0.07–0.15 |
| Inner Raceway Diameter Variation (VDip) | 0.1–0.2 | 0.05–0.1 |
| Outer Raceway Diameter Variation (VDep) | 0.15–0.3 | 0.07–0.15 |
| Inner Raceway-to-Bore Wall Thickness Variation (Ki) | 0.05–0.1 | 0.03–0.06 |
| Outer Raceway-to-Outside Diameter Wall Thickness Variation (Ke) | 0.05–0.15 | 0.03–0.06 |
| Warpage of Both End Faces | 0.15–0.3 | 0.1–0.2 |
Table 1. Comparison of Geometric Tolerances Before and After Changing the Clamping Method
Optimization of Bearing Ring Grinding Processes
Grinding allowances and process parameters strongly influence machining quality and efficiency. Appropriate settings help control deformation while maintaining dimensional accuracy.
The optimization focuses on distributing machining allowances and adjusting critical grinding parameters. Both aspects are essential for stable production.
> Grinding Allowances for Bearing Rings
Grinding allowance optimization aims to establish minimal, stable material removal while maintaining product accuracy and performance. This approach improves efficiency, reduces costs, and prevents deformation.
For lightweight single-row tapered roller bearing inner rings, fine grinding allowances range from 0.1 to 0.15 mm per side. Final grinding allowances decrease to 0.05–0.08 mm per side.
Outer rings experience more persistent deformation during machining. Therefore, their processing difficulty generally exceeds that of inner rings.
Engineers must consider outer ring rigidity ratios when determining machining allowances. Comparing different allowance strategies helps improve efficiency without sacrificing precision.
Table 2 provides recommended grinding allowances for different rigidity ratios.
| Rigidity Ratio (γ) | Grinding Process | Machining Allowance per Side (mm) |
|---|---|---|
| ≥ 0.05 | Fine Grinding | 0.1–0.15 |
| Final Grinding | 0.05–0.08 | |
| 0.03 < γ < 0.05 | Rough Grinding | 0.1–0.15 |
| Fine Grinding | 0.05–0.08 | |
| Final Grinding | 0.03–0.05 | |
| ≤ 0.03 | Rough Grinding | 0.1–0.15 |
| First Fine Grinding | 0.05–0.08 | |
| Second Fine Grinding | 0.05–0.08 | |
| Final Grinding | 0.03–0.05 |
Table 2. Recommended Machining Allowances for Bearing Rings
> Bearing Ring Grinding Parameters
Grinding parameter optimization for thin-walled single-row tapered roller bearing rings focuses on several critical factors. These factors determine material removal, surface quality, dimensional accuracy, and process stability.
Grinding Wheel Speed
Grinding wheel speed changes the number of abrasive grains participating in cutting per unit time. Higher speeds increase cutting frequency and can reduce surface roughness.
This improvement may also increase machining efficiency. However, excessive speed intensifies friction and compression between abrasive grains and the workpiece.
As grinding forces and temperatures rise, thermal stresses can accumulate in thin-walled rings. These stresses may cause plastic deformation and reduce machining accuracy.
Workpiece Rotational Speed
Workpiece rotational speed directly determines the effective feed rate across the grinding surface. Manufacturers must balance machining efficiency against dimensional precision.
At excessively low speeds, the grinding zone receives insufficient feed per unit time. Repeated abrasive cutting paths reduce efficiency and may increase surface roughness.
Excessively high speeds can disrupt the dynamic stability of the grinding system. Resulting vibrations and centrifugal deformation may affect dimensional accuracy and roundness.
Feed Rate
Grinding feed includes transverse feed in the radial cutting-depth direction and longitudinal feed along the axial direction. Together, these parameters determine material removal during each grinding pass.
Excessive feed increases material removal rates, grinding forces, and heat generation. These effects can cause thermal deformation and surface burns, reducing surface quality.
Insufficient feed extends machining cycles and lowers productivity. Longer processing times also increase manufacturing costs.
> Optimization of Multi-Stage Grinding Parameters
Thin-walled bearing rings require a three-stage grinding strategy: rough grinding, fine grinding, and final grinding. Each stage uses parameters suited to its machining objectives.
Rough Grinding Stage
Rough grinding primarily removes most of the machining allowance while maintaining uniform stock for subsequent operations. A 60-grit grinding wheel supports efficient material removal.
The grinding wheel operates at 1,200–1,500 r/min. This stage removes approximately 65%–70% of the total grinding allowance.
Fine Grinding Stage
Fine grinding improves dimensional accuracy and surface quality before final grinding. The process continues using a 60-grit wheel to maintain machining consistency.
Grinding wheel speed increases to 1,300–1,600 r/min. This stage removes approximately 20%–28% of the total grinding allowance.
Final Grinding Stage
Final grinding achieves the required dimensional and geometric accuracy, including roundness and cylindricity. An 80-grit wheel improves the final surface finish.
Grinding wheel speed increases to 1,500–1,800 r/min. The remaining machining allowance represents approximately 7%–10% of the total grinding stock.
Process Verification
The study evaluated an extra-large, lightweight tapered roller bearing outer ring for a wind turbine planetary carrier bearing. The test component had the following dimensions.
Outside diameter: 890 mm
Width: 55 mm
Effective ring wall thickness: 24.27 mm
Raceway angle: 14°30′
The calculated outer ring rigidity ratio was 0.027. Therefore, engineers selected the machining route and allowances for rigidity ratios of 0.03 or below.
The optimized process incorporated three major improvements.
Additional Tempering Treatment
The process adds an additional tempering treatment before hard turning. This treatment improves material stability and supports subsequent precision machining.
Improved Magnetic Clamping
The hard turning process uses an improved magnetic chuck instead of conventional mechanical clamping. This method enhances clamping accuracy and reduces deformation.
Optimized Grinding Parameters
Each grinding stage uses parameters suited to its specific machining requirements. This approach maintains machining quality while controlling deformation and surface damage.
After machining, inspectors evaluated the bearing ring against the required quality standards. Table 3 presents the specified tolerances and measured results.
| Inspection Item | Required Standard (mm) | Measured Result (mm) |
|---|---|---|
| Outside Diameter Variation in a Single Radial Plane (VDsp) | ≤ 0.045 | 0.02 |
| Outer Ring Width Variation (VCs) | ≤ 0.02 | 0.008 |
| Raceway Roundness (DCir) | ≤ 0.024 | 0.011 |
| Outer Raceway Diameter Variation (VDep) | ≤ 0.024 | 0.012 |
| Mean Outside Diameter Variation (VDmp) | ≤ 0.029 | 0.009 |
| Outer Raceway-to-Outside Diameter Wall Thickness Variation (Ke) | ≤ 0.025 | 0.011 |
| Outer Raceway Generatrix Inclination Variation Relative to Reference End Face (SDe) | ≤ 0.005 | 0.003 |
| Warpage of Both End Faces | ≤ 0.02 | 0.013 |
| Finished Bearing Outer Ring Radial Runout (Kea) | ≤ 0.05 | 0.03 |
| Finished Bearing Outer Ring Axial Runout (Sea) | ≤ 0.075 | 0.05 |
Table 3. Bearing Ring Precision Requirements and Inspection Results
All measured dimensional and geometric characteristics met the specified process requirements. Continuous production of 150 bearing rings also produced inspection results that satisfied every applicable standard.
Conclusion
This study investigated the main machining challenges associated with extra-large thin-walled tapered roller bearing rings. It systematically analyzed the factors affecting ring deformation.
Based on inner and outer ring characteristics, engineers developed machining routes for different rigidity ratios. These routes address the specific deformation risks of lightweight bearing rings.
The results demonstrate the effectiveness of combining optimized machining routes, appropriate allowances, and precise grinding parameter control. These measures improve dimensional accuracy and reduce machining defects.
Process optimization also reduces scrap rates and improves product quality consistency. The proposed methods provide a practical technical approach for efficient manufacturing of extra-large thin-walled bearings.
These findings can support manufacturing process upgrades and production capacity improvements across the bearing industry.