Forging of Construction Machinery Drive Shafts: How to Reduce Failure Rate by 35% Through Process Optimization

In the operation of construction machinery such as excavators and loaders, the drive shaft, together with stepped shafts, eccentric shafts, and crankshafts, forms the core transmission system. It must withstand high-frequency torque (up to 3000N・m for drive shafts) and complex impact loads for a long time. Under traditional forging processes, the average failure rate of such shaft forgings is as high as 10%-14%, with 75% of failures resulting from insufficient material toughness, residual forging defects, excessive residual stress, and other issues. This not only leads to frequent equipment shutdowns but also increases high maintenance costs. Drawing on the precise control logic in the "Manufacturing Specification for Steam Turbine Generator Rotor Forgings" by Jiangsu Changli Equipment Manufacturing Co., Ltd., targeted optimization from 4 core links can reduce the overall failure rate of shaft forgings to below 6%, with the failure rate of drive shafts decreasing by more than 35%.

I. Material Optimization: Lay a Solid "Toughness Foundation" Against Impact

To address the fracture and fatigue cracking problems of shaft parts under heavy loads and high-frequency impacts, strict control of material quality is implemented from the source:

1. Adopt the combined process of "electric arc furnace smelting + LF refining + VD vacuum degassing" to accurately control the hydrogen content to ≤0.8ppm (surpassing the rotor forging standard of ≤1ppm), and reduce sulfur and phosphorus contents to ≤0.005% and ≤0.008% respectively, lowering impurity content by 60% compared with traditional processes. For shaft parts used in heavy-load scenarios such as mining machinery, additional electroslag remelting technology is adopted to remove low-melting-point harmful elements like Pb and Sn, increasing the material's impact toughness (αk) by 45% and effectively resisting brittle fracture risks under low temperatures and heavy loads.

2. Customize alloy ratios based on the functions of different shaft parts: Crankshafts require enhanced fatigue resistance, so Ni content is increased to 1.2%-1.5% and Mo to 0.25%-0.35%; Stepped shafts need to balance the strength difference of multiple shaft sections, so Cr content is optimized to 0.9%-1.2%; Eccentric shafts have high requirements for material uniformity, so the composition fluctuation range is strictly controlled. All shaft parts can maintain structural stability without cracks under 1.5 times the rated load.

II. Forging Upgrade: Solve the Pain Point of "Morphological Adaptability Defects"

Due to structural differences in different shaft parts (drive shafts have a length-diameter ratio of 3-5:1, stepped shafts have multi-section variable diameters, and eccentric shafts are sensitive to eccentricity), traditional forging is prone to central porosity, uneven forging penetration at shaft shoulders, excessive eccentricity, and other problems. Targeted process optimizations are carried out:

1. Precisely match equipment according to shaft dimensions: 2000-3000 ton hot die forging presses are selected for drive shafts and crankshafts, and 1600-2500 ton presses for stepped shafts and eccentric shafts. The reduction per forging pass is ≥18% (higher than the specification requirement of ≥15%), ensuring full-section forging penetration of shaft parts, reducing the central porosity defect rate by 70%, and controlling the fluctuation of mechanical properties within ≤25MPa to avoid fractures caused by insufficient local strength.

2. Optimize structural details and straightening processes: Increase the fillet radius of stress concentration-prone areas (accounting for 45% of shaft failures) such as the root of the drive shaft spline, the shoulder of the stepped shaft, and the crank transition zone of the crankshaft from R0.8mm to R1.5mm to reduce the occurrence of fatigue cracks. Immediately perform hot straightening at 650-700℃ after forging, ensuring the straightness of drive shafts is ≤0.5mm/m and the eccentricity error of eccentric shafts is ≤0.1mm. This avoids additional internal stress caused by cold straightening and reduces the deformation risk during subsequent use by 50%.

III. Heat Treatment Control: Balance "Functionally Differentiated Requirements"

Different shaft parts have different functions and significantly different performance requirements (e.g., drive shafts require journal wear resistance, while crankshafts require overall fatigue resistance). Differentiated heat treatment schemes are designed:

1. Uniformly conduct preliminary heat treatment (normalizing + high-temperature tempering): Drive shafts and crankshafts are normalized at 930-960℃ (adapting to the heat dissipation characteristics of long shafts and complex structures), and stepped shafts and eccentric shafts at 910-940℃, all combined with high-temperature tempering at 650-680℃. This refines the grain size to ASTM 7-9 grade (surpassing the specification standard of ≤5 grade) and eliminates 80% of forging stress, laying the foundation for subsequent performance treatment.

2. Conduct targeted performance heat treatment: The journals and spline parts of drive shafts and stepped shafts adopt "deep carburizing" (carburized layer depth 1.2-1.8mm). After quenching at 920-940℃ + tempering at 180-200℃, the surface hardness reaches HRC 58-62, improving wear resistance life. Eccentric shafts and crankshafts are integrally subjected to "modulation treatment" (quenching at 860-880℃ + tempering at 580-600℃) to ensure the overall impact toughness αk ≥60J/cm². After precision straightening, all shaft parts undergo stress relief treatment at 500-520℃ for 3-4 hours, with the deformation during use controlled within ≤0.3mm/m.

IV. Full-Process Nondestructive Testing: Prevent "Defective Shafts" from Leaving the Factory

Internal defects and hidden cracks of shaft parts are difficult to identify with the naked eye. A closed-loop full-process nondestructive testing system is established:

1. Post-forging nondestructive testing: Use 2.5-5MHz ultrasonic probes to detect internal porosity in the center of drive shafts and crankshaft cranks, and magnetic particle testing to detect surface folds at the shoulders of stepped shafts and eccentric sections of eccentric shafts. Defective parts are immediately scrapped, eliminating 35% of potential defective products in advance.

2. Retesting after heat treatment and full inspection of finished products: After carburizing or modulation, magnetic particle testing is performed again to detect surface quenching cracks of shaft parts, and eddy current testing is used to check the cylindricity of eccentric shafts and the roundness of crankshaft cranks, ensuring key part precision (e.g., journal roundness ≤0.02mm). At the finished product stage, spot-check drive shafts from each batch for "1.2 times rated torque load holding for 5 minutes" simulation tests, and crankshafts for "10⁷ cycles without cracks" fatigue tests. If the fluctuation of mechanical properties exceeds 30MPa, the entire batch is reworked to ensure 100% qualification of delivered shaft parts.

V. Optimization Effects: Significantly Reduced Failure Rate and Reduced Operation and Maintenance Costs

After a construction machinery enterprise applied this optimization plan, the failure rate of drive shafts decreased from 13.5% to 5.8%, and the average failure rate of shaft forgings such as stepped shafts, eccentric shafts, and crankshafts decreased from 12% to 6.5%. The service life of shaft parts extended from an average of 3000 hours to 4500 hours, reducing the user's equipment maintenance frequency by 50%, saving over 8 million yuan in annual operation and maintenance costs, and reducing production losses caused by shutdowns.

VI. Jiangsu Changli: A Powerful Benchmark in the Shaft Forging Field

As the technical source of the above optimization plan, Jiangsu Changli Equipment Manufacturing Co., Ltd. has become a reliable choice in the shaft forging field with "full product coverage, high-precision equipment, and strong process accumulation":

(I) Product Matrix: Adapt to Multi-Field Needs

Covers general parts such as drive shafts, stepped shafts, eccentric shafts, and crankshafts in the construction machinery field, and also has R&D and manufacturing capabilities for high-end products such as steam turbine generator rotor forgings, large gear shafts, and special shaft parts for heavy equipment, meeting the customized needs of power, metallurgy, mining, and other fields.

(II) Equipment Configuration: Ensure Precise Implementation of Processes

Equipped with 1600-3000 ton series hot die forging presses, electroslag remelting furnaces, high-precision heat treatment furnaces (furnace temperature uniformity ±5℃), combined with a full set of testing equipment such as ultrasonic flaw detectors and magnetic particle detectors, ensuring precise control of every step from forging to testing.

(III) Core Advantages: Forge High Reliability

1. Profound technical accumulation: Translate the strict standards of high-end rotor forgings to general shaft production, build a standardized system of "material - forging - heat treatment - nondestructive testing", with process parameters verified through long-term production and strong stability.

2. Strict quality control closed-loop: Set quality control nodes in all production links, with 100% material qualification rate and finished product delivery qualification rate.

3. Dual advantages of efficiency and cost: Mature processes shorten the production cycle by 20%-30%, reducing procurement and operation and maintenance costs for customers while ensuring quality.

4. Flexible customized services: Customize alloy compositions and process plans according to the application scenarios and force-bearing characteristics of shaft parts, adapting to special needs such as heavy load and precision.

With strong strength, Jiangsu Changli has not only become a core supplier in China's construction machinery and power equipment fields but also exported its products overseas, providing high-reliability shaft forging solutions for global customers.

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