With the continuous improvement of requirements for crankshaft processing accuracy and efficiency in the automotive industry, crankshaft following grinding technology, as the third-generation grinding process, is gradually replacing traditional manual grinding solutions.
This article systematically elaborates on the technical principles, process solutions, and CBN (Cubic Boron Nitride) wheel applications of following grinding, providing technical reference for precision crankshaft manufacturing through comparative analysis of the technical differences between traditional processes and following grinding.
Introduction
In the field of crankshaft finishing, efficient grinding processes are key core manufacturing technologies that directly affect crankshaft accuracy, connecting rod assembly reliability, engine smoothness, and vehicle service life. Crankshaft grinding technology abroad has developed to the third generation, and domestic equipment manufacturers are also keeping pace with technological frontiers. Crankshaft following grinding machines are being applied in increasingly widespread production.
Limitations of Traditional Crankshaft Grinding Processes
Traditional Process Flow
Traditional crankshaft finishing mostly adopted the process flow of rough grinding – semi-finishing – finishing – polishing on ordinary crankshaft grinders, typically relying on manual operation, highly dependent on worker skills, with unstable processing quality and poor dimensional consistency.
Main Technical Limitations
When grinding connecting rod journals, it was necessary to repeatedly adjust the crankshaft rotation center through eccentric fixtures or indexing heads to make the connecting rod journal concentric with the grinder spindle, then complete grinding through workpiece rotation and wheel feed.
Operators needed to manually measure journal dimensions, adjust wheel positions relying on experience to control grinding amounts, and use dial indicators or templates to correct crankshaft positions to ensure accurate phase angles of connecting rod journals. The ordinary aluminum oxide wheels used relied on manual diamond dressers, with high dressing frequency and poor precision stability.
Efficiency and Precision Bottlenecks
Early crankshaft grinding processes were inefficient, with single-piece processing taking **several hours**. Multi-cylinder crankshafts were particularly time-consuming due to complex phase calibration requirements.
Comparison: Traditional vs Following Grinding
| Comparison Dimension | Traditional Grinding Process | Follow-Up Grinding Process |
|---|---|---|
| Clamping Times | Multiple clamping and adjustments | Completed in one clamping |
| Machining Accuracy | Dependent on worker experience, unstable | Roundness accuracy ≤ 2 μm |
| Machining Efficiency | Several hours per piece | Significantly shortened |
| Automation Level | Manual operation mainly | CNC automation |
| Grinding Wheel Dressing | Manual, high frequency | Automatic, low frequency |
| Flexibility | Poor, difficult model changeover | Excellent, model changeover time reduced by 70% |
| Process Capability | Unstable | PPK ≥ 1.33 |
| Grinding Wheel Type | Aluminum oxide grinding wheel | CBN grinding wheel |
| Grinding Speed | Relatively low | 120–140 m/s |
Current Status of Following Grinding Technology Development
Technology Development History
Currently, integrated crankshaft grinding solutions have formed a complete technical system. The typical representative is CNC following grinders equipped with CBN (Cubic Boron Nitride) wheels, which can complete processing of all main journals and connecting rod journals through one-time positioning and clamping.
Leading Equipment Manufacturers
Multi-wheel linkage grinding systems developed by leading international equipment manufacturers have achieved technological industrialization, mainly including:
- JUNKER (Germany): Multi-wheel linkage grinding systems
- LANDIS (UK): High-precision following grinding technology
- TOYADA (Japan): Flexible grinding solutions
- EMAG NAXOS-UNION (Germany): CBN wheel application technology
Technical Indicator Requirements
- The design of such machine tools must simultaneously meet four major characteristics:
- Multi-model compatibility(flexible production)
- Unit cost control
- Micron-level processing accuracy
- Mass production stability
The core technical indicator requires a process capability coefficient of **Cp ≥ 1.67**, meaning the actual processing tolerance zone is only 50% of the design tolerance zone. This stringent standard places extremely high requirements on machine tool dynamic stiffness and thermal stability.
Following Grinding Technology Principles and Key Parameters
Servo Synchronization Control Principle
By applying servo synchronization control technology for workpiece rotation and wheel feed, all journals can be ground in a single setup without changing the crankshaft rotation center, including following tracking grinding of connecting rod journals. During grinding, real-time trajectory tracking algorithms control wheel swing feed, tracking the eccentrically rotating connecting rod journal for grinding.
Key Parameters and Precision Control
To achieve following grinding, the X-axis must not only have high dynamic performance but also sufficient tracking accuracy to ensure the required shape tolerance of connecting rod journals. Using hydrostatic spindles, hydrostatic guides, hydrostatic lead screws to drive the wheel head, linear grating closed-loop control, and automatic centering three-point steady rest, grinding journal roundness accuracy can reach 2 μm.
Following Grinding Key Parameters
| Parameter Type | Technical Indicator | Description |
|---|---|---|
| Roundness Accuracy | ≤ 2 μm | Adopting hydrostatic technology |
| Grinding Speed | 120–140 m/s | Equipped with CBN wheel |
| Dressing Life | 600–800 pieces/time | Number of crankshafts processable per dressing |
| Process Capability | Cp ≥ 1.67 | Process capability index |
| Process Stability | PPK ≥ 1.33 | Stability during mass production |
| Tracking Accuracy | Micron level | Dynamic performance of the X-axis |
Technical Advantages of CBN Wheels
The application of CBN wheels is an important condition for achieving following grinding of connecting rod journals. Due to the high wear resistance of CBN wheels, the wheel diameter remains almost unchanged during grinding. One dressing can grind 600–800 crankshafts. CBN wheels can use very high grinding speeds, achieving up to 120–140 m/s on crankshaft grinders. With dual wheel heads, grinding efficiency is extremely high.
[Image 3: Following grinding principle diagram]
Following Grinding Process Solutions
Single-Process Machining
Five-wheel grinding for main journals of four-throw crankshafts and dual-wheel grinding for connecting rod journals of four-throw crankshafts. This process is highly efficient, with easily controlled journal runout after grinding. After one wheel dressing, dimensional consistency of all journals can be guaranteed. The disadvantage is poor flexibility, only capable of processing one product series.
Composite Machining Process
Composite machining refers to grinding all main journals and connecting rod journals in one setup, with following grinding technology used for connecting rod journals. The biggest advantage of this grinding method is good flexibility, with production changeover time reduced by 70%. Composite machining has two process options:
- Sequential Grinding: Sequential processing of main journals and connecting rod journals
- Synchronous Grinding: Simultaneous processing of main journals and connecting rod journals
[Image 5: Synchronous grinding of main journals and connecting rod journals diagram]
Process Selection Recommendations
According to product type and production requirements, select appropriate process solutions:
- Mass production of single product: Recommend single-process machining
- Multi-variety small batch: Recommend composite machining process
- High precision requirements: Prioritize synchronous grinding solution
CBN Wheels: The Key to Efficient Grinding
CBN Material Characteristics
The continuous improvement of cutting tool performance has laid an important foundation for the advancement of efficient high-speed crankshaft processing technology. In addition to traditional high-speed steel and carbide materials, breakthrough developments in superhard materials have brought revolutionary changes to modern processing technology. The application of superhard tool materials such as PCD (Polycrystalline Diamond) and PCBN (Polycrystalline Cubic Boron Nitride) provides key solutions for advanced processes such as difficult-to-machine material cutting, dry cutting, and hard state processing.
In the field of crankshaft finishing, the application of CBN (Cubic Boron Nitride) wheels shows rapid growth. Although CBN wheels have higher initial investment, their excellent processing efficiency and ultra-long service life make the per-piece processing cost lower than traditional wheels.
Process Performance Advantages
CBN wheels have unparalleled technical advantages in precision crankshaft grinding:
Material Characteristic Advantages:
- Ultra-high hardness second only to diamond, microhardness up to 8000–9000 HV
- Excellent thermal stability capable of withstanding temperatures above 1400℃
- Good chemical inertness, low reactivity with ferrous materials
Process Performance:
- Grinding ratio (G value) can reach 100 times that of traditional corundum wheels
- Surface roughness can achieve 0.5 μm or below
- Dimensional accuracy can be controlled within ±2 μm
- Grinding force reduced by 30%–50%, reducing workpiece deformation
CBN Wheel vs Traditional Wheel Comparison
| Comparison Item | CBN Wheel | Traditional Aluminum Oxide Wheel |
|---|---|---|
| Hardness | 8000–9000 HV | 2000–2500 HV |
| Grinding Ratio (G Value) | 100+ times that of traditional wheel | Baseline |
| Surface Roughness | ≤ 0.5 μm | 1.6–3.2 μm |
| Dimensional Accuracy | ±2 μm | ±5–10 μm |
| Grinding Force | Reduced by 30%–50% | Baseline |
| Grinding Speed | 120–140 m/s | 30–60 m/s |
| Dressing Life | 600–800 pieces/time | 50–100 pieces/time |
| Processing Time | Reduced by 50% | Baseline |
| Comprehensive Cost | Reduced by 50%+ | Baseline |
Economic Benefit Analysis
According to research data from German NAXOS-UNION, using CBN wheels can reduce processing time by **50%** while reducing comprehensive processing costs by **more than 50%**.
[Image 6: CBN wheel structure and application diagram]
Summary and Outlook
Technical Advantages Summary
Following grinders have been successfully applied to crankshaft finishing. During processing, they can detect and correct journal roundness and dimensions. Theoretically, the practical deviation of plunge grinding for main journals and following grinding for connecting rod journals is zero. The application of this technology in passenger car and commercial vehicle crankshaft production lines, with stable performance of process capability index PPK ≥ 1.33, fully demonstrates its reliability in mass production.
Core Advantages:
– **Single Setup**: Complete processing of all main journals and connecting rod journals
– **Micron-Level Precision**: Roundness accuracy ≤ 2 μm
– **High Flexibility**: Production changeover time reduced by 70%
– **Stable and Reliable**: Process capability index PPK ≥ 1.33
Application Prospects
With the in-depth development of intelligent manufacturing and digital technology, crankshaft following grinding technology will continue to optimize in the following aspects:
– **Intelligent Integration**: Online measurement, adaptive compensation, digital twin verification
– **Process Optimization**: Higher grinding speeds, longer wheel life, lower processing costs
– **Multi-Domain Applications**: Expansion from passenger cars and commercial vehicles to construction machinery, marine power, compressors, and other fields
– **Green Manufacturing**: Dry grinding, low energy consumption, less waste
Just as gears hold an eternal position in mechanical transmission, crankshafts and their processing technology will continue to drive technological progress in the power machinery field.