Metal Cutting and CNC machines(1)

Overview of Machining Operations

  • Machining operations create various shapes and surfaces through the removal of material.

  • Generated Surfaces include:

    • Cylinder

    • Cone

    • Plane

    • Formed surfaces using tools like Broach.

Material Removal Processes

  • A family of shaping operations characterized by material removal from a starting workpart to achieve the desired geometry.

    • Machining: Involves material removal using a sharp cutting tool (e.g., turning, milling, drilling).

    • Abrasive Processes: Utilizes hard, abrasive particles for material removal (e.g., grinding).

    • Nontraditional Processes: Employ various energy forms other than sharp cutting tools for material removal.

Importance of Machining

  • Versatility: Can machine a wide variety of work materials, chiefly metals.

  • Geometric Capabilities: Capable of producing:

    • Screw threads

    • Accurate round holes

    • Straight edges and surfaces

    • Good dimensional accuracy and surface finish.

Disadvantages of Machining

  • Material Waste: Chips generated are often wasted material.

  • Time-Consuming: Machining operations generally take longer than other shaping processes.

Role in Manufacturing Sequence

  • Machining typically occurs after other processes like casting and forging which provide the basic shape.

  • It refines the shape, dimensions, finish, and special geometric details not achievable by other methods.

Key Machining Operations

  • Turning: A single point cutting tool removes material from a rotating workpiece, forming a cylindrical shape.

  • Drilling: Creates round holes using a rotating drill bit with cutting edges.

  • Milling: Involves a rotating multiple-cutting-edge tool to create flat or straight surfaces, with forms including peripheral milling and face milling.

Cutting Tool Classification

  • Single-Point Tools: One dominant cutting edge, commonly found in turning operations.

  • Multiple Cutting Edge Tools: Have more than one edge; used in milling and drilling.

Cutting Conditions in Machining

  • Defined by three dimensions:

    • Cutting Speed (v): The primary motion during machining.

    • Feed (f): Secondary motion.

    • Depth of Cut (d): How deep the tool penetrates the work surface.

  • Material Removal Rate (RMR) Calculation: RMR = v * f * d.

Roughing vs. Finishing Cuts

  • Roughing: Removes large amounts of material quickly; medium to high feeds and depths, low speeds.

  • Finishing: Finalizes part dimensions and finish; low feeds and depths, high cutting speeds.

Machine Tools and Functions

  • Machine Tools: Power-driven machines performing machining operations include grinding, turning, and milling.

    • They hold workparts, position tools, and provide necessary power.

Chip Formation

  • Describes the mechanics of machining accurately with a focus on the shear zone.

  • Types of chips formed in machining include:

    • Discontinuous chips

    • Continuous chips

    • Continuous chips with built-up edge (BUE)

    • Serrated chips.

Forces in Machining

  • Forces acting on chips include frictional force, normal force, and shear force.

  • Cutting Force (Fc) and Thrust Force (Ft) can be measured and related to unmeasured forces.

Importance of Cutting Temperatures

  • High temperatures can reduce tool life and affect part accuracy due to thermal expansion.

  • Approximately 98% of energy in machining converts to heat at the tool-chip interface.

CNC Machines

  • CNC (Computer Numerical Control) machines automate the machining process using coded instructions.

    • They can perform complex part manufacturing with high precision and repeatability.

  • CNC systems consist of controllers that monitor and adjust machining parameters continuously.

Advantages of CNC Over Conventional Machining

  • Offers increased accuracy, reduced operational time, and lower labor costs as fewer operators are needed.

  • CNC machines enhance reliability and can produce complex designs with less possibility of human error.

Types of Programming Codes for CNC

  • G-code: Commands for geometric movements (e.g., rapid movement, linear feed move).

  • M-code: Controls miscellaneous machine functions (e.g., spindle rotation, coolant control).

Summary of Operations Related to Turning and Drilling

  • Turning includes variations like facing, taper turning, contour turning, and threading.

  • Drilling operations can include reaming, tapping, and countersinking.

Work Holding and Cutting Tools

  • For lathes, options include holding work between centers, chucks, collets, and face plates.

  • Drilling operations allow workparts to be clamped in vises or custom fixtures.