Turning-Centre Programming Study Notes

Turning-Centre Programming

Objectives

  • Understand the key differences between turning centres and machining centres that impact part-program preparation.

  • Familiarity with tape formats and word addresses utilized in turning-centre part programs.

  • Identify various axes systems in turning centres applicable to part programming.

  • Grasp the basic formats of word addresses used in part programs for turning centres.

  • Comprehend the utilization of G-codes and M-codes specific to part programs.

  • Effectively apply tool-nose radius compensation to minimize machining errors.

  • Develop part programs incorporating complex contours.

  • Acknowledge the various techniques for thread cutting using turning centres.

  • Grasp the function of special canned cycles in turning centres.

14.1 Comparison Between Machining Centres and Turning Centres

  • Although the programming approaches for machining centres and turning centres are largely similar, specific differences must be addressed during programming:

    • Axes System: Predominantly X and Z axes in turning centres, with potential additional axes like C and W depending on the machine design.

    • Tools Used: Mainly single-point cutting tools such as turning and boring tools. C-axis machines may incorporate milling tools in the turret, enabling minor milling tasks like keyway or PCD drilling.

    • Multiple Cuts: Turning often requires extensive roughing cuts to eliminate larger material quantities, as opposed to machining centres requiring fewer precise cuts.

    • Internal and External Features: Similar programming for internal and external features, though careful positioning is crucial for internal cutting.

    • Tool Post Complexity: Some older machines had dual tool posts; however, modern centres often have a single tool turret, simplifying programming.

    • Different G and M Codes: Similarity in many codes, but differences exist due to the machine structure.

    • Tool-nose Radius Compensation: Essential in turning centres since the programming is done with respect to the tool nose, which varies from machining centres.

    • Work Rotation: Turning centres simplify programming by transforming 3D profiles into 2D profiles via work rotation. Usually, only two axes operate simultaneously.

    • Tool Indexing: Generally through turret indexing; some machines may have magazines enabling close tool change positioning.

    • Diameter Programming: Most turning components dimension in diameters; the X-axis movements are often doubled for diameter representation rather than radial direction.

14.2 Tape Formats

  • A typical tape format for turning centres (e.g., GE FANUC 18T) follows a similar structure as machining centres:

    • Block Number: N04 - four digits with leading-zero suppression.

    • Preparatory Function: G03 allows up to four preparatory functions in one block, but only one from that block takes effect.

    • X and Z Axis Addresses:

      • X(U): Absolute values specified by X; incremental by U.

      • Z(W): Similar structure for the Z axis with absolute and incremental specifications.

    • Miscellaneous Addresses: Several addresses for radius values (R), centre coordinates (I, K), feed specifications (F), spindle speed (S), tool functions (T), and miscellaneous functions (M).

    • End Of Block (EOB) character is crucial; omissions can lead to erroneous programming behavior.

    • Comments can be included in parentheses. Block Skip (/) at the start of a block ignores the data if activated.

    • General recommended sequence for data within a block: /, N, G, X, Z, U, W, etc.

14.3 Axes System

  • The arrangement of a turning centre is fundamentally established with:

    • Z Axis: Spindle axis.

    • X Axis: Radial axis perpendicular to Z, extends towards the principal tool post.

    • Meaning of Datums:

    • Machine Datum: Predefined fixed position; usually at the intersection of spindle axis and clamping surface.

    • Component Datum: Programmers fix a position on the component for convenience in programming.

    • Tool Datum: The point serves as the reference for turret indexing and axes movement.

    • Tool offsets must be entered for each tool used in the turret for precise programming and measurements.

14.4 General Programming Functions

14.4.1 Tool Function

  • Tools selected in programs via the T word, which activates the turret station and tool offset register number. The register includes:

    1. X and Z axis tool offsets

    2. Tool nose radius value

    3. Tool nose orientation number

  • The format is T4 for turret station indexing.

14.4.2 Speed Function

  • Spindle speeds can be set directly in RPM or in constant surface speed (m/min). Use G96 (constant surface speed) and G97 (constant RPM).

  • G50 command can set upper limits to the spindle speed.

14.4.3 Feed Specification

  • Feed rates can be defined as mm/min (G98) or mm/rev (G99), with G98 being the default post power-on. Ensure correct formatting (e.g., decimals).

14.4.4 Units

  • G20 specifies inch input and G21 for metric input, modal until canceled by the opposite command.

14.4.5 Miscellaneous Functions

  • M codes provide machine actions. Examples include:

    • M00: Program Stop

    • M01: Optional Stop

    • M02: End of Program

    • M03: Spindle Clockwise Start

    • M08: Coolant ON

    • M09: Coolant OFF

  • M codes must be singular in each block; only the last entered is effective.

14.4.6 Program Number

  • Every program requires an identification via the O word with a max of four digits, typically placed at the program’s start.

14.4.7 Block Number

  • N word indicates block numbers; customary to be the first entry unless a Block Delete is triggered.

14.5 Motion Commands

General Motion Commands

  • G00: Rapid Positioning. Overrides specified feed rate with maximum allowed feed rates.

  • G01: Linear Interpolation at a set feed rate—uses absolute, incremental, or mixed addressing modes.

  • G02/G03: Circular Interpole for clockwise (G02) or counter-clockwise (G03) movements; requires either radius or center coordinates.

  • Other commands include G04 for dwell time, and chamfer/corner radius specifics may follow G01.

14.6 Cut Planning

  • Essential for roughing and finishing in turning, optimizing total tool movement to enhance efficiency and minimize air cutting. Examples illustrate ideal material removal strategies.

14.7 Thread Cutting

  • Various thread types can be cut; G33 code synchronizes spindle and feed for proper threading actions. Examples provided.

14.8 Canned Cycles

14.8.1 Turning Canned Cycle

  • Streamlines programming for repetitive tasks, optimizing program length. Illustrations support understanding.

14.8.2 Facing Canned Cycle

  • Defined for face operations, useful for multiple facing cuts.

14.8.3 Thread Cutting Canned Cycle

  • Similar to rough turning; G33 will be active for synchronization during threading operations, further reducing programming length.

Summary

  • Fundamental differences exist in programming turning centres vs machining centres.

  • Tape formats and axes systems are interconnected; unique programming aspects for motion commands and special features like nose radius compensation impact overall programming efficacy.

  • Cut planning crucially reduces machining times, especially in scenarios where unwanted material must be removed.

  • Thread and canned cycles offer efficiencies relative to traditional programming lengths.