Rolling process parameters
As an important surface strengthening and precision machining method, the proper selection of rolling parameters directly determines the surface quality, dimensional accuracy, and mechanical properties of the workpiece. The rolling process utilizes a rolling tool to apply a certain amount of pressure to the workpiece surface, causing plastic deformation of the surface metal, thereby reducing surface roughness and increasing surface hardness and fatigue strength. During this process, parameters such as rolling pressure, rolling speed, feed rate, and number of rolling passes interact and collectively affect the workpiece’s machining results. Therefore, precise control is required based on the workpiece material, original surface condition, and machining requirements.
Rolling pressure is one of the most core parameters in the rolling process, which directly affects the degree of plastic deformation of the surface metal of the workpiece. When the pressure is too small, the plastic deformation of the workpiece surface is insufficient, the roughness of the original surface cannot be effectively eliminated, and the improvement of the surface hardness and fatigue strength is not obvious; while too much pressure will cause excessive deformation of the surface metal of the workpiece, which may cause defects such as cracks and peeling, and even cause the workpiece to have dimensional tolerances or shape distortion. For example, for materials with good plasticity such as low carbon steel, the rolling pressure can be appropriately increased to obtain a more ideal surface quality; while for higher strength materials such as high carbon steel and alloy steel, due to their poor plasticity, a smaller rolling pressure should be selected to prevent surface cracking. In actual operation, the rolling pressure usually needs to be determined through trial rolling, and is generally controlled between 50% and 80% of the yield strength of the material.
The coordination of rolling speed and feed rate has a significant impact on machining efficiency and surface quality. The rolling speed refers to the rotational speed of the workpiece (for shaft parts) or the moving speed of the rolling tool (for flat parts), while the feed rate refers to the distance the rolling tool moves axially per revolution. Within a certain range, increasing the rolling speed can improve machining efficiency, but too high a speed will shorten the contact time between the rolling tool and the workpiece surface, resulting in insufficient plastic deformation. It will also affect the surface quality of the workpiece due to increased frictional heat generation. When the feed rate is too large, the number of rolling passes per unit length is reduced, the surface plastic deformation is uneven, and ripples are easily generated; if the feed rate is too small, the machining time will be increased and production efficiency will be reduced. Therefore, it is necessary to reasonably match the rolling speed and feed rate according to the diameter and length of the workpiece. For example, for shaft parts with smaller diameters, a higher rolling speed and a smaller feed rate can be used to ensure uniform surface quality.
The number of rolling passes is also a key parameter that affects the rolling effect. It is closely related to the original surface roughness of the workpiece and the processing requirements. For workpieces with a large original surface roughness, multiple rolling passes are usually required to eliminate surface defects by gradually increasing the amount of plastic deformation, and ultimately achieve the ideal surface accuracy. The first rolling pass is mainly to eliminate the macroscopic unevenness of the surface, and subsequent rolling passes are used to refine the surface structure and increase the surface hardness. However, the more rolling passes, the better. Too many rolling passes will cause excessive work hardening of the surface metal of the workpiece, which will reduce the plasticity and toughness of the material and increase the processing cost. In general, for ordinary parts, 1-2 rolling passes can meet the requirements; for precision parts with extremely high surface quality requirements, the number of rolling passes can be appropriately increased to 3-4 times, but the pressure of each rolling pass must be strictly controlled to avoid adverse effects.
The parameters of the rolling tool, such as roller diameter, fillet radius, and surface hardness, also play an important role in the effectiveness of the rolling process. When the roller diameter is larger, the contact area with the workpiece surface increases, and the pressure per unit area decreases, which is suitable for rolling materials with good plasticity; when the roller diameter is smaller, the contact area is small and the unit pressure is large, which is suitable for materials with higher hardness. The fillet radius of the roller should match the curvature of the workpiece surface. A fillet radius that is too small will cause stress concentration on the workpiece surface, while a fillet radius that is too large will reduce the rolling effect. In addition, the surface hardness of the rolling tool must be higher than the surface hardness of the workpiece. It is generally made of high-speed steel or cemented carbide to ensure the wear resistance and service life of the tool and avoid affecting the stability of the rolling quality due to tool wear.
