Lec 4:CUTTING TOOLS

Cutting Tools and Turning Process Overview

Introduction to Turning Process

• The turning process involves a single point cutting tool, generating surfaces through rotary motion. The two key components are the generatrix (the surface generated) and the directrix (the direction of feed).

• Typically, the generatrix is circular while the directrix is linear, resulting in a cylindrical surface. This foundational understanding sets the stage for deeper exploration into cutting tools.

Tool Geometry Basics

• Key phases of a cutting tool include the rake face and flank face, which play crucial roles in machining operations. Understanding these faces is essential before delving into input conditions for turning processes.

• Basic input parameters for single-point machining are:

• Cutting speed

• Feed rate

• Depth of cut

These parameters significantly influence machining efficiency and outcomes.

Tool Angles and Their Importance

• Tool geometry encompasses various angles critical to performance:

• Rake angles (back rake angle, side rake angle)

• Flank angles (clearance or relief angles)

Understanding these angles helps optimize cutting efficiency and tool longevity.

Rake Surface Functionality

• The rake surface directs chip flow during material removal; its angle can be positive, negative, or zero based on design requirements.

• Increasing the rake angle sharpens the tool but may reduce strength due to less material at the cutting edge, leading to potential thermal softening under high temperatures. Thus, there’s a trade-off between sharpness and durability.

Types of Rake Angles

• Three types of rake angles are discussed:

• Positive rake angle: Facilitates easy chip flow.

• Zero rake angle: Parallel to shank; used in specific applications.

• Negative rake angle: Commonly employed with hard materials to enhance tool strength despite increased forces during machining operations.

Flank Angles and Their Role

Flank Angle Significance

• Flank angles minimize rubbing action against workpieces during machining, enhancing surface finish quality.

• A balance must be struck as increasing flank angles can also decrease tool strength; thus optimal values are selected based on material properties being machined. Typical ranges for HSS tools are between five to twelve degrees depending on application needs.

Cutting Edge Dynamics

• The cutting edges play a pivotal role in material shearing; their design influences overall effectiveness.

• Two primary types of cutting edge angles exist:

• Side cutting edge angle

• End cutting edge angle

These determine how effectively materials can be removed from workpieces during operation.

Tool Signatures Explained

Systems for Tool Signature Representation

• Four systems exist for representing tool signatures:

• AAC system (American System)

• Orthogonal/Continental system

Each system has unique advantages in defining tool geometry but focuses primarily on back rake, side rake, flank angles, and nose radius representation methods. Understanding these systems aids in selecting appropriate tools for specific tasks based on their geometrical characteristics.

Conclusion on Tool Design Considerations

• Effective tool design requires careful consideration of all mentioned factors—angles, geometry, materials—to ensure optimal performance across various machining scenarios.

This comprehensive understanding allows engineers to tailor tools specifically suited for their intended applications while balancing performance with durability concerns throughout manufacturing processes.