CNC Machining of high manganese steel rolling wheels
High-manganese steel rollers are key components used for crushing and crushing materials in industries such as mining, metallurgy, and construction. Typically made of ZGMn13 high-manganese steel, they possess high toughness and wear resistance. When subjected to intense impact and compression, their surface rapidly undergoes work-hardening, forming a tough, wear-resistant layer while the core retains excellent toughness. CNC Machining high-manganese steel rollers is challenging due to the severe work-hardening, high cutting forces, and tendency to stick to the tool. Therefore, specialized turning processes and tooling are required to ensure both quality and efficiency.
The material properties of high-manganese steel rolling wheels determine the unique characteristics of turning. ZGMn13 high-manganese steel has a manganese content of 11%-14% and a carbon content of 1.0%-1.4%. It has a single-phase austenitic structure and a low hardness (around HB200) when unimpacted. However, during cutting, due to intense plastic deformation, the surface rapidly undergoes work hardening, increasing the hardness to HB400-500 and the work-hardened layer depth to 0.1-0.3mm. This work hardening phenomenon makes subsequent cutting more difficult, increases cutting forces, and intensifies tool wear. Furthermore, high-manganese steel has extremely high toughness, with an elongation of 50%-80%. During cutting, chips are difficult to break, and long, tough ribbons of chips are easily formed, which entangle the tool and workpiece, affecting process continuity and surface quality. Furthermore, high-manganese steel has poor thermal conductivity, only about one-third that of 45 steel. The large amount of cutting heat generated during cutting cannot be dissipated promptly, concentrating in the cutting area. This causes a sharp increase in tool temperature, accelerating tool wear and failure.
The selection of turning tools for high-manganese steel rolling wheels is crucial for successful machining. Tool materials with high hardness, high wear resistance, and good heat resistance must be selected. Commonly used tool materials include carbide and high-speed steel, with carbide tools being the preferred choice for machining high-manganese steel. YG-type carbides (such as YG8 and YG15) offer high toughness and impact resistance, making them suitable for rough turning of high-manganese steel rolling wheels. YG8 has a hardness of HRA89-90 and a flexural strength of 1400-1600 MPa, capable of withstanding high cutting forces and impact loads. YW-type carbides (such as YW1 and YW2) offer high hardness and wear resistance, while also offering a certain degree of toughness. They are suitable for semi-finishing and finishing turning of high-manganese steel rolling wheels. YW1 has a hardness of HRA91-92 and a flexural strength of 1200-1400 MPa, ensuring surface quality. High-speed steel tools (such as W18Cr4V) have poor heat resistance and are only suitable for low-speed finishing or finishing operations, with cutting speeds generally not exceeding 10 m/min. Tool geometry also requires special design: a small rake angle (0°-5°) is recommended to increase tool strength and resist work hardening; a large relief angle (8°-12°) is recommended to reduce friction between the tool and the workpiece; and a lead angle of 45°-60° is recommended to reduce radial cutting forces and prevent workpiece deformation and vibration.
When selecting cutting parameters for high-manganese steel rolling wheels, it’s important to fully consider their material properties to minimize work hardening and tool wear. Cutting speed is a crucial parameter influencing machining results. Excessively high cutting speeds exacerbate work hardening and tool wear, while excessively low cutting speeds reduce machining efficiency. The cutting speed is generally 5-10 m/min for rough turning, and 10-15 m/min for finish turning. When using carbide tools, the cutting speed can be increased appropriately, but should not exceed 20 m/min. The feed rate should be determined based on the machining stage and surface quality requirements. For rough turning, the feed rate is 0.2-0.3 mm/r to quickly remove excess stock; for finish turning, the feed rate is 0.1-0.15 mm/r to ensure surface quality. The back-cut should be as large as possible: 3-5 mm for rough turning to penetrate the work-hardened layer and avoid cutting on it; for finish turning, the back-cut is 0.5-1 mm to ensure machining accuracy. When selecting cutting parameters, the principle of “low speed, high feed, and large cutting depth” should be followed to reduce the impact of work hardening and improve processing efficiency.
The turning process and operating techniques of high-manganese steel rolling wheels significantly impact machining quality and efficiency. The general machining process is: rough turning the outer diameter → semi-finish turning the outer diameter → finish turning the outer diameter → machining the end face and step. The primary purpose of rough turning is to remove the majority of the stock. A large back-cut should be used to cut through the as-cast surface oxide scale and loose structure, preventing the accumulation of a work-hardened layer. During semi-finish turning, a 1-2mm stock should be left for finishing, and any shape errors after rough turning should be corrected. Final dimensional accuracy and surface quality should be ensured during finish turning, with a surface roughness of Ra 3.2-6.3μm. During operation, chips should be promptly removed to prevent them from entanglement between the tool and workpiece. Compressed air or a cooling lubricant can be used to flush away chips. The choice of cooling lubricant is also crucial. An emulsion with good cooling properties should be used to reduce cutting temperature and tool wear. The cooling lubricant should be sprayed thoroughly into the cutting area to ensure effective cooling. In addition, the quality of tool sharpening cannot be ignored. The cutting edge of the tool after sharpening should be sharp and the surface roughness should be low to reduce cutting force and work hardening. During the turning process, if the tool is found to be severely worn, the tool should be replaced in time to avoid the degradation of processing quality due to tool passivation.
The quality inspection of high manganese steel rolling wheels after turning is the final step to ensure the performance of parts. The inspection items include dimensional accuracy, form and position tolerances, surface quality and hardness. Dimensional accuracy mainly tests the outer diameter and length of the rolling wheel, which can be measured with tools such as micrometers and vernier calipers; form and position tolerances mainly test the roundness and cylindricity of the outer circle and the verticality of the end face, which can be measured with instruments such as dial indicators and roundness meters; surface quality mainly tests the surface roughness and the presence of defects such as cracks and scratches. The surface roughness can be measured by a roughness meter or a sample comparison; the hardness test mainly tests the hardness of the surface work-hardened layer, which can be measured with a Rockwell hardness tester or a Brinell hardness tester to ensure that the surface hardness meets the design requirements. For unqualified parts, the reasons should be analyzed and appropriate rework measures should be taken, such as re-turning or adjusting cutting parameters. Through strict quality inspections, it can be ensured that the performance of the high manganese steel rolling wheel meets the use requirements and its service life and reliability are improved.
