Tooling for Machining 42CrMo Alloy Steel Forgings (Quenched and Tempered Steel, Quenching Material, 42CrMo Alloy Steel Forgings) and Cubic Boron Nitride (CBN) Inserts - Grades BN-S20 and BN-H20, used for rough and finish machining respectively. These two grades of cutting tools can significantly improve machining efficiency, reduce production time, and decrease production costs. The tools can also be used for turning, milling, and boring operations on quenched and tempered steel, nitrided steel, nitrided components, carburized 42CrMo alloy steel forgings, post-heat treated high-hardness 42CrMo alloy steel forgings, mold steels (quenched or tempered), 20CrMnTi, SUJ2 high-carbon chromium bearing steel, Cr12MoV, and 42CrMo alloy steel forgings with hardness values above HRC45 (HRC58, HRC62, HRC60, HRC65, etc.).
The machining of 42CrMo alloy steel forgings has the following characteristics:
1. High hardness and high strength with minimal plasticity: This is the main processing characteristic of 42CrMo alloy steel forgings. When the hardness of 42CrMo alloy steel forgings reaches HRC50-60, it becomes one of the most difficult materials to machine.
2. High cutting forces and temperatures: To improve cutting conditions and increase heat dissipation area, smaller main and secondary rake angles are selected for the tools. However, this may cause vibration, so a rigid process system is required.
3. Less tendency to produce built-up edges: Due to the high hardness and brittleness of 42CrMo alloy steel forgings, machining can easily produce built-up edges, resulting in a lower surface roughness on the machined surface.
4. Prone to tool edge chipping and wear: The brittleness of 42CrMo alloy steel forgings leads to short contact between the cutting chips and the tool edge during turning, concentrating cutting forces and heat near the cutting edge, which can cause tool edge chipping and wear.
5. Low thermal conductivity: The thermal conductivity of 42CrMo alloy steel forgings is generally around 7.12 W/(m·K), approximately 1/7 of that of No. 45 steel. Due to the low thermal conductivity, it is difficult for cutting heat to be carried away by the chips, which accelerates tool wear.
Cutting Parameters for PCBN Tools in Machining 42CrMo Alloy Steel Forgings:
1) For precision machining of 42CrMo alloy steel forgings using PCBN tools: When the hardness of the hardened workpiece is higher than 45HRC, the best results are obtained. The higher the workpiece hardness, the lower the cutting speed should be. For example, when machining a workpiece with a hardness of 70HRC, a cutting speed of 60-80m/min is recommended. Generally, when machining materials with a hardness of HRC55-65, the cutting speed of CBN tools should be between 50-120m/min. For milling, Vc = 100-160m/min, and the feed rate Vf = 70-160mm/min. For reaming, Vc = 60-130m/min, ap = 0.1-0.2mm, and f = 0.07-0.2mm/r.
2) When machining with large allowances on hardened workpieces: Due to factors such as quenching deformation, when the machining allowance on hardened workpieces exceeds 1mm, the cutting resistance of the tool is 6-9 times higher than that in finish machining. In this case, using smaller feed rates to reduce cutting resistance is the most effective method. If intermittent cutting is performed on 42CrMo alloy steel forgings, it is recommended to set the cutting speed to 2/3 of the finish machining speed. BN-S20 by Hualing can withstand intermittent cutting while achieving deep longitudinal machining.
3) For precision turning of 42CrMo alloy steel forgings with a cutting depth of 0.1-0.3mm and a feed rate of 0.05-0.025mm/r, the surface roughness of the machined workpiece is Ra 0.3-0.6μm, and the dimensional accuracy can reach 0.013mm. If a rigid standard CNC lathe with good tool rigidity and sharp cutting edges is used, the surface roughness can reach Ra 0.3μm and the dimensional accuracy can reach 0.01mm, comparable to the level achieved by CNC grinding.
