Ceramic Cutting Tools and Additive Manufacturing

Posted on May 1, 2024 in Technology

Tutorial 7: Ceramic Cutting Tools

Why Negative Rake Angles?

Ceramic cutting tools typically have negative rake angles due to their material properties. Ceramics exhibit low shear and tensile strength but excel in compressive strength. By employing a negative rake angle, the cutting forces primarily act in compression, effectively utilizing the material’s strength.

Desirable Cutting Tool Properties

Three key properties of an effective cutting tool material are:

  1. Toughness: Resistance to fracture failure.
  2. Hot Hardness: Resistance to temperature-induced failure.
  3. Wear Resistance: Prolonged tool life through gradual wear resistance.

Cutting Tool Wear Mechanisms

Several mechanisms contribute to cutting tool wear:

  1. Abrasion: Mechanical wear caused by hard particles in the workpiece.
  2. Adhesion: Material transfer between the tool and workpiece.
  3. Diffusion: Atomic exchange at the tool-chip interface.
  4. Chemical Reaction: Chemical interactions between the tool and workpiece or environment.
  5. Plastic Deformation: Permanent deformation of the cutting edge.

Locations of Tool Wear

Tool wear primarily occurs in two locations:

  1. Crater Wear: On the rake face of the tool.
  2. Flank Wear: On the side of the tool, including notch wear (at the workpiece surface) and nose radius wear (at the tool point).

Factors Affecting Tool Wear

Among cutting conditions, cutting speed has the most significant impact on tool wear.

WC-Co Cemented Carbides

Increasing cobalt content in WC-Co cemented carbides enhances both hardness and toughness.

Taylor Tool-Life Equation

In the Taylor tool-life equation (VT^n=C):

  • A high n value is desirable as it allows for higher cutting speeds and longer tool life.
  • A high C value is desirable as it indicates higher cutting speeds for a given tool life.

Temperature and Crater Wear

Temperature significantly influences crater wear, primarily driven by diffusion and chemical affinity between the tool and chip. Higher temperatures generally lead to increased crater wear.

Temperature’s Impact on Tool Life

Temperature affects tool life through several mechanisms:

  • Reduced strength and hardness of tool material at higher temperatures.
  • Increased chemical reactivity and diffusion.
  • Compromised effectiveness of cutting fluids.
  • Potential for thermal shock in interrupted cutting.

Types of Wear and Mechanisms

Two common types of wear are:

  1. Flank Wear: Primarily caused by abrasion.
  2. Crater Wear: Primarily caused by diffusion.

Tutorial 8: Additive Manufacturing

Advantages of Additive Manufacturing

Additive manufacturing offers advantages over conventional machining, particularly for parts with high complexity and low production quantities. Its layer-by-layer approach allows for complex geometries without the need for specialized tooling, resulting in shorter lead times and cost-effectiveness for small production runs.

Generic Additive Manufacturing Processes

  1. STL File Generation: Converting a CAD model into a format suitable for additive manufacturing.
  2. STL File Manipulation: Repositioning, reorienting, scaling, and adding supports to the model.
  3. Slicing: Dividing the model into thin layers for fabrication.

STL File Format

STL files represent the surface of a 3D model using triangular facets, each defined by the coordinates of its vertices and a normal vector.

Machine Axes

Additive manufacturing machines typically have 2.5 axes, controlling movement in the X and Y directions, with the Z-axis orientation adjustable.

Building Orientation

Building orientation affects support generation, build time, energy consumption, surface roughness, and internal stress within the part.

Feedstock Forms

Additive manufacturing utilizes feedstock in various forms, including liquids, solids (wire or sheet), and powders.

Purpose of Slicing

Slicing generates the 2D layer geometry of a 3D part at different heights for fabrication.

Functions of Support Structures

Support structures serve several purposes:

  • Supporting overhanging features.
  • Maintaining part stability during fabrication.
  • Preventing distortion of thin features.
  • Conducting heat away from the part.