What is the impact of different R angles of carbide inserts?
During machining, the R-angle of a carbide insert affects tool durability, cutting forces and vibration, chip breaking performance, and workpiece surface finish.
Tool Durability
Advantages of a Large Radius: A large Radius provides more carbide support at the insert tip, significantly improving the tool tip’s ability to withstand the significant mechanical shock, pressure, and thermal stresses of heavy cutting. It is one of the most effective ways to prevent tool tip chipping or micro-chipping during heavy loads, intermittent cutting, or machining hard or uneven materials. Furthermore, the larger contact area helps distribute the high heat generated by cutting more evenly throughout the insert volume and removes more heat through the chips, reducing the likelihood of localized overheating at the tool tip, thermal cracking, and crater wear, thereby improving tool durability.
Disadvantages of a Small Radius: Tools with a small Radius have poor impact resistance. During cutting, especially when machining hard or uneven materials, the tool tip is susceptible to significant impact, resulting in increased tool wear and reduced tool durability.
Cutting Force and Vibration
Issues with Large Radius Angles: Large radius angles cause cutting forces to be directed more radially (perpendicular to the workpiece axis) than in the ideal axial direction. For workpieces with insufficient rigidity (such as slender shafts or thin-walled parts), excessive radial forces can cause workpiece bending, vibration, and even tool breakage, severely impacting dimensional and shape accuracy and potentially stimulating vibration in the process system (machine tool-fixture-tool-workpiece system). Deformation of the workpiece/tool caused by radial forces directly affects the workpiece’s size (diameter) and shape (roundness and cylindricity).
Advantages of Small Radius Angles: Tools with small radius angles are relatively sharp, resulting in relatively low cutting forces and vibration during cutting, which helps maintain process stability. For vibration-sensitive machining scenarios, such as precision machining and thin-walled workpiece machining, small radius tools may be more advantageous.
Chip breaking Performance
Large Radius (R) angles facilitate chip breaking: Large radius angles facilitate thicker chips with a larger curl radius. Thick, curled chips are more easily broken into safe “C” or “9”-shaped chips upon impact with the workpiece or tool surface, rather than forming unmanageable, long ribbons. This facilitates chip removal and handling, minimizing adverse effects such as scratches on the machined surface.
Chip breaking Performance with Small R Angles: Small R angle tools produce relatively thinner chips during cutting, and their curl may not be as high as those produced by tools with large R angles. In some cases, they may be more prone to forming long ribbons, requiring other methods (such as changing cutting parameters or using chip breakers) to improve chip breaking performance.
Surface Accuracy
Large R angles are suitable for rough machining of workpieces with large diameters and thicknesses. Small R angles are suitable for fine machining of thin plates and workpieces.