Parting and grooving
Parting and grooving are common CNC machining processes used to separate workpieces from blanks or create grooves of specific width and depth, such as undercuts, sealing grooves, and locating slots. Parting involves completely severing a workpiece radially, separating it into two separate parts; grooving involves creating a non-through groove on or within the workpiece. Parting and grooving operations are characterized by poor tool rigidity, harsh cutting conditions, and the tendency to generate vibration. Therefore, optimal tool selection, cutting parameters, and operating methods are crucial to ensure both quality and efficiency.
The structural design of parting and grooving cutters is crucial for ensuring parting and grooving quality. Their geometric parameters must be optimized based on the CNC machining requirements and workpiece material. Parting cutters have a narrow, long blade head, resulting in poor rigidity. Therefore, a larger lead angle (typically 90°) and a smaller rake angle (0°-5°) are required to enhance blade strength. The width of the main cutting edge of a parting cutter should be determined based on the workpiece diameter, generally ranging from 2-6mm. Wider main cutting edges are used for larger diameter workpieces to improve efficiency, while narrower main cutting edges are used for smaller diameter workpieces to minimize material waste. Grooving cutters have a similar structure to parting cutters, but the main cutting edge width is determined by the groove width. The blade length should be greater than the groove depth to ensure the desired CNC machining depth. Parting and grooving cutters are typically made of high-speed steel or carbide. High-speed steel tools are suitable for low-speed cutting and complex groove formations, while carbide tools are suitable for high-speed cutting and CNC machining high-strength materials such as 45 steel and stainless steel.
The installation of cutting and grooving tools requires strict requirements, which directly affects processing accuracy and tool life. When installing the tool, it is necessary to ensure that the main cutting edge is at the same height as the workpiece axis. If the main cutting edge is higher than the workpiece axis, the tool back angle will decrease, and the friction between the back tool face and the workpiece will increase. If it is lower than the workpiece axis, the tool rake angle will decrease, the cutting force will increase, and vibration will be easily generated. The centerline of the tool should be perpendicular to the workpiece axis to ensure a smooth cut surface and symmetrical groove shape. Large deviations will cause the cut surface to tilt or the bottom of the groove to be non-perpendicular to the axis. In addition, the length of the tool extending from the tool holder should be as short as possible, generally 1.5-2 times the length of the cutter head, to increase tool rigidity and reduce vibration. For high-speed cutting, a tool bar with good rigidity, such as a square tool bar or a thick-walled round tool bar, is required to prevent the tool bar from bending and deformation under the action of cutting forces.
When selecting cutting parameters for parting and grooving, consider tool rigidity and workpiece material to avoid vibration and tool damage. The cutting speed should be determined based on the tool and workpiece materials. When using high-speed steel tools for parting or grooving steel, a cutting speed of 20-40 m/min is recommended; carbide tools can use a speed of 50-100 m/min. Excessively high cutting speeds can accelerate tool wear and even cause chipping; too low a cutting speed can reduce efficiency and easily produce built-up edge. The feed rate is generally 0.05-0.2 mm/min, with a higher value for roughing to improve efficiency and a lower value for finishing to ensure groove quality. The depth of cut is equal to the workpiece radius for parting and the groove depth for grooving. Cut to the desired depth in a single pass to avoid uneven tool wear caused by multiple cuts. The use of cutting fluid is crucial for parting and grooving operations. Use extreme pressure emulsions or sulfurized cutting oils, delivered directly into the cutting zone via high-pressure jetting, to lower cutting temperatures, minimize tool wear, and improve surface quality.
Standardized parting and grooving procedures are required to ensure process safety and quality. The workpiece should be clamped during parting. Workpieces with a large aspect ratio should be supported with a steady rest or steady rest to prevent bending and deformation under the cutting forces. During the parting process, the cutting process should be monitored at all times to ensure unobstructed chip flow. If chip blockage occurs, the machine should be stopped and cleared immediately to prevent chips from entanglement in the tool or workpiece and causing an accident. As the workpiece is about to be parted, the cutting force suddenly decreases, potentially causing vibration. At this point, the feed rate should be reduced, or manual feed should be used, and the parting process should be slowed down to prevent the workpiece from flying and injuring personnel if it breaks. For deep grooving, a layered cutting method can be used: cutting to a certain depth first and then gradually deepening the depth, with each layer cutting 0.5-1mm to reduce cutting forces and vibration. For closed or stepped grooves, the tool feed distance must be precisely controlled. This can be achieved using the lathe’s dial or CNC system.
Common problems and solutions in parting and grooving operations are crucial for ensuring smooth processing. If tool chipping occurs during processing, it may be due to excessive feed rate, high cutting speed, insufficient tool rigidity, or excessive workpiece hardness. This can be resolved by reducing the feed rate, cutting speed, replacing a more rigid tool, or annealing the workpiece. If the cut surface is uneven or the groove bottom is rippled, it may be due to improper tool installation, excessive vibration, or severe tool wear. Reinstall the tool, adjust the cutting parameters, or replace the tool. If the workpiece deforms during parting, it may be due to insufficient clamping force or poor workpiece rigidity. Increase the clamping force or use auxiliary supports. For parting and grooving difficult-to-machine materials such as stainless steel and high-temperature alloys, use specialized carbide tools (such as WC-Co alloys), lower cutting speeds, higher feeds, and increased cooling and lubrication to improve tool life and process quality.
With the development of CNC technology, parting and grooving processes have become automated and intelligent. Through programming, CNC lathes can precisely control the tool’s motion trajectory and cutting parameters, enabling the automatic processing of complex groove shapes, such as circular and spiral grooves. The constant linear velocity cutting function in the CNC system ensures a stable cutting speed during the parting process, improving the quality of the cut surface; the tool tip radius compensation function corrects the effects of tool wear on the groove width, ensuring groove accuracy. In mass production, CNC lathes equipped with automatic feeding devices and automatic tool changing systems can achieve continuous parting and grooving processing, significantly improving production efficiency. In the future, with advances in tool materials and manufacturing technologies, parting and grooving processes will develop towards higher precision, higher efficiency, and more environmentally friendly processes, providing better processing services for the machinery manufacturing industry.
